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Why 3I_ATLAS Moves Faster Than 200 000 km_h. Space Documentary · Night Science Stories

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Speaker 1: Hi guys, the measured speed is a clue. It is
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Speaker 1: not a number pulled from thin air. It is a
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Speaker 1: fingerprint of an origin story that began around another star
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Speaker 1: and played out across our entire galaxy. When astronomers first
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Speaker 1: tracked the path of the object now called 3I slash ATLAS,
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Speaker 1: they found that it was already moving at roughly 61
0:27
Speaker 1: km per second with respect to the Sun, which is
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Speaker 1: a little more than 220,000 km per hour. That velocity
0:37
Speaker 1: is not a brief burst from jets or an engine.
0:41
Speaker 1: It is the natural consequence of how gravity shapes the
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Speaker 1: motion of a body that fell into our neighbourhood from
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Speaker 1: interstellar space on an unbound path. As it plunges deeper
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Speaker 1: into the solar gravitational well, it accelerates. As it climbs out,
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Speaker 1: it will decelerate, keeping the same excess speed far from
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Speaker 1: the Sun that it had before it arrived. That is
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Speaker 1: what a hyperbolic trajectory means. It is the signature of
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Speaker 1: an object that does not belong here. This is only
1:17
Speaker 1: the third confirmed interstellar visitor ever seen crossing our planetary system.
1:24
Speaker 1: It was discovered in the first days of July of
1:27
Speaker 1: the year 2025 by the Asteroid Terrestrial Impact Last Alert
1:34
Speaker 1: System at the Rio Hurtado site in Chile. From the start,
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Speaker 1: its path showed that it came from beyond the sphere
1:43
Speaker 1: of the planets. The National Aeronautics and Space Administration emphasizes
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Speaker 1: two practical facts right away. First, there is no danger.
1:54
Speaker 1: The minimum distance to Earth will be about 1.8 astronomical units,
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Speaker 1: which is on the order of 270 million kilometers. Second,
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Speaker 1: the comet will reach its closest point to the Sun
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Speaker 1: around late October of the year 2025 at about 1.4
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Speaker 1: astronomical units, just inside the orbit of Mars. Those numbers
2:21
Speaker 1: fix both the safety question and the observing calendar. To
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Speaker 1: understand why the speed exceeds 200,000 km per hour, we
2:31
Speaker 1: need a clean mental model. Think of three linked pieces.
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Speaker 1: One is the energy story. The second is the frame
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Speaker 1: of reference. The third is the origin of the object's
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Speaker 1: inbound motion before the sun took over. Energy first. Far
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Speaker 1: from the Sun, where solar gravity is weak, the interstellar
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Speaker 1: object travelled through the local galactic neighbourhood at essentially constant
3:01
Speaker 1: speed as it fell inward toward the Sun, gravitational potential
3:05
Speaker 1: energy converted into kinetic energy. energy. That is why its
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Speaker 1: heliocentric speed rose from tens of kilometers per second to
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Speaker 1: more than 200,000 kilometers per hour as it moved inward.
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Speaker 1: At the Sun's closest approach the speed peaks. Thereafter, it
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Speaker 1: gives back the borrowed energy and slows, asymptotically returning to
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Speaker 1: the same interstellar cruising speed it had before arriving. In
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Speaker 1: orbital mechanics, this constant is called the hyperbolic excess velocity.
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Speaker 1: For 3I slash ATLAS, early solutions based on the growing
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Speaker 1: data arc found that excess to be around 58 km
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Speaker 1: per second. With nothing but solar gravity acting, that number
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Speaker 1: barely changes. It is the interstellar pedigree, written in units
4:02
Speaker 1: of motion. Now, the frame of reference. You can measure
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Speaker 1: the speed relative to Earth, relative to the Sun, or
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Speaker 1: relative to a conceptual frame called the local standard of rest.
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Speaker 1: The commonly quoted value here is relative to the Sun.
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Speaker 1: That is the measurement that matters for a path through
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Speaker 1: our system. and it is why the speed is more
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Speaker 1: than 200,000 km per hour at discovery and higher still
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Speaker 1: near perihelion. In everyday terms, it is moving faster than
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Speaker 1: any natural object bound to the Sun at Earth's distance.
4:45
Speaker 1: Only a specialised spacecraft skimming the solar atmosphere has gone faster.
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Speaker 1: The Parker Solar Probe during a record perihelion in late
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Speaker 1: December of the year 2024, reached roughly 690,000 km per
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Speaker 1: hour relative to the Sun. That dramatic comparison shows the
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Speaker 1: scale of the numbers we are talking about. The comet
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Speaker 1: is not a spacecraft, but its speed is in the
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Speaker 1: same league as the fastest human-made object when gravity is
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Speaker 1: doing all the work. Where did that excess speed come
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Speaker 1: from in the first place? For that, we have to
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Speaker 1: leave the solar system entirely and look at how small
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Speaker 1: icy bodies are launched into the galaxy. The current consensus,
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Speaker 1: shaped by observations of planetary systems and by dynamical models,
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Speaker 1: is that most interstellar objects begin as planetesimals in their
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Speaker 1: home systems. When giant planets form, they scatter enormous numbers
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Speaker 1: of these building blocks. Some are thrown inward and destroyed.
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Speaker 1: Some are slung outward and escape. In a young system
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Speaker 1: with multiple massive planets or within a crowded stellar nursery,
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Speaker 1: ejection becomes efficient. Those bodies drift into the galactic population
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Speaker 1: of wanderers that every so often pass near the sun.
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Speaker 1: Reviews over the past few years outline the mechanisms clearly
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Speaker 1: and predict that the galaxy should team with such fugitives
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Speaker 1: from planet formation. 3. I slash A-T-L-A-S is the newest
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Speaker 1: direct sample. What makes 3 I slash A-T-L-A-S especially interesting
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Speaker 1: is that its motion carries a clue to the kind
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Speaker 1: of stellar neighborhood it came from. A modeling analysis published
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Speaker 1: in July of the year 2025 set the object in
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Speaker 1: the context of a galactic population model built from Gaia
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Speaker 1: star data. The kinematics of the comet as it approached
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Speaker 1: the sun match expectations for objects that come from the
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Speaker 1: Milky Way's thick disk, a galactic component rich in ancient stars,
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Speaker 1: that tend to have larger random velocities relative to the Sun.
7:19
Speaker 1: The same study used that connection to infer a likely
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Speaker 1: age greater than seven and a half billion years, with
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Speaker 1: the possibility that the material in this comet predates our
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Speaker 1: solar system by billions of years. If that inference holds,
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Speaker 1: the high speed we see today is partly a fossil
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Speaker 1: of the hotter, more dynamic early Milky Way, as well
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Speaker 1: as the exuberant scattering inside the comet's birth system. Motion
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Speaker 1: and history are bound together. New work tracks the comet
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Speaker 1: back through our region of the galaxy and finds a
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Speaker 1: busy history by numerically integrating the orbit of three I-slash-Atlas
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Speaker 1: together with the motions of tens of millions of nearby
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Speaker 1: stars from the Gaia catalogue. One team identified on the
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Speaker 1: order of two dozen close stellar passages within roughly one
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Speaker 1: parsec over the last 10 million years. That result does
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Speaker 1: not point to a single parent star. Instead, it shows
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Speaker 1: how an interstellar body can pick up small nudges over
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Speaker 1: vast times as it threads the labyrinth of local stellar gravity.
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Speaker 1: The speed we measure now is the vector remnant of
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Speaker 1: ejection long ago plus the cumulative whispers of the galaxy since.
8:51
Speaker 1: While dynamics tell us about past motion, composition hints at
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Speaker 1: where in a planetary system 3I-ATLAS formed. Spectroscopy with the
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Speaker 1: James Webb Space Telescope in early August of the year
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Speaker 1: 2025 captured the object's spectrum. with the near-infrared spectrograph instrument.
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Speaker 1: The first reported results show a coma dominated by carbon
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Speaker 1: dioxide relative to water, with a carbon dioxide to water
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Speaker 1: ratio around 8 to 1, among the highest ratios ever
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Speaker 1: measured in a comet. That ratio can be produced if
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Speaker 1: the nucleus formed far from its star near the carbon
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Speaker 1: dioxide ice line. or if the outer layers were processed
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Speaker 1: by radiation over a long time in interstellar space. Either way,
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Speaker 1: the extreme chemistry adds to the case that the object
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Speaker 1: is old and that its present swift passage carries material
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Speaker 1: records from a different stellar nursery. The cloud of facts
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Speaker 1: about this object is expanding quickly because many eyes are
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Speaker 1: on it. The Hubble Space Telescope imaged the comet in
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Speaker 1: late July of the year 2025 and revealed a tear-shaped
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Speaker 1: envelope of dust surrounding the nucleus. Those data gave the
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Speaker 1: first firm size constraints, placing the nucleus somewhere between roughly
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Speaker 1: 440 metres and about five and six tenths kilometres across.
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Speaker 1: That range matters when we ask whether outgassing could meaningfully
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Speaker 1: alter the object's path or speed. For a nucleus that large,
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Speaker 1: the non-gravitational push from jets of gas and dust can
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Speaker 1: curve the trajectory slightly, but it cannot supply the tens
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Speaker 1: of thousands of kilometres per hour needed to create the
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Speaker 1: measured hyperbolic excess. Gravity set the baseline speed. Comet jets
11:05
Speaker 1: only fine-tune the track. Even before discovery, telescopes had captured
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Speaker 1: the traveller by chance. The transiting Exoplanet Survey satellite recorded
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Speaker 1: the comet in May and June of the year 2025,
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Speaker 1: more than seven weeks before the alert. Researchers stacked those
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Speaker 1: images to tease out a faint signal and reported a
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Speaker 1: gradual brightening as the comet crept inward. That paper is
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Speaker 1: valuable for speed, because it added early astrometry to the
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Speaker 1: orbit fit and sighted a hyperbolic excess velocity around 58
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Speaker 1: km per second. It also gave a rare first. This
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Speaker 1: is the first time that the Exoplanet Hunting Telescope caught
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Speaker 1: an interstellar object in pre-discovery data. The National Aeronautics and
12:01
Speaker 1: Space Administration has assembled a long list of observers across
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Speaker 1: the fleet. Hubble continues to monitor. The James Webb Space
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Speaker 1: Telescope has already observed the object. The new spectrophotometer for
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Speaker 1: the history of the universe, Epic of Ryanization and ICES Explorer,
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Speaker 1: observed it in August of the year 2025. Mars orbiters
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Speaker 1: and rovers will try to capture it near the Mars
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Speaker 1: encounter window. Even spacecraft nearer to the Sun, such as
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Speaker 1: the Parker Solar Probe and heliospheric images, may add unique
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Speaker 1: vantage points when geometry permits. The result is a coordinated
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Speaker 1: experiment in how to extract the maximum science from a
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Speaker 1: fast and fleeting visitor. The speed also sets the rhythm
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Speaker 1: of observation. Because of the geometry of the encounter, the
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Speaker 1: comet passes behind the Sun from Earth's viewpoint during the
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Speaker 1: weeks around perihelion. For ground-based telescopes, there will be a
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Speaker 1: pause and then a return of visibility in early December
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Speaker 1: of the year 2025. That schedule is not a curiosity.
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Speaker 1: It is a direct consequence of the path and the
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Speaker 1: high inbound speed. On a slower, wider swing, we might
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Speaker 1: have had a longer observing window from Earth. On this
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Speaker 1: faster dive, the best chance to study peak activity falls
13:40
Speaker 1: to eyes elsewhere in the solar system. When you compare
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Speaker 1: three I-slash-A-T-L-A-S to the previous two interstellar objects, the role
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Speaker 1: of speed becomes even clearer. The first one I-slash-Oumuamua whipped
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Speaker 1: around the Sun in September of the year 2017 with
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Speaker 1: a maximum speed near 87 km per second at perihelion,
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Speaker 1: but its excess speed far from the Sun was closer
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Speaker 1: to 26 km per second. The second, 2i slash Borisov,
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Speaker 1: behaved more like a familiar comet and cruised through at
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Speaker 1: about 177,000 km per hour relative to the Sun, with
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Speaker 1: an excess speed around 32 km per second. 3i slash
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Speaker 1: Atlas came in hotter, with a measured excess around 58
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Speaker 1: km per second. and a discovery speed of roughly 221,000
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Speaker 1: km per hour. That ranking reflects different histories. Each object
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Speaker 1: left a different star under different circumstances, and then spent
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Speaker 1: different spans of time being stirred by the galaxy. How
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Speaker 1: does an interstellar object end up with an excess of
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Speaker 1: 50 plus kilometers per second. One part is the kinematic
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Speaker 1: lottery of the galaxy. Our Sun is on a nearly
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Speaker 1: circular path around the Milky Way. Nearby stars and small
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Speaker 1: bodies have their own random motions layered on top of
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Speaker 1: that vast rotation. When a free floating object approaches the
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Speaker 1: solar system, the relative speed depends on how its motion
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Speaker 1: vector lines up with the sun's. If it happens to
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Speaker 1: be moving roughly with the sun, the excess can be modest.
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Speaker 1: If it comes from a direction that subtracts little and
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Speaker 1: adds much, the excess can be large. That is the
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Speaker 1: simplest piece. A second part is the launch from the
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Speaker 1: home system. In a young planetary system, a planet the
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Speaker 1: mass of Jupiter or more can fling a small body
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Speaker 1: outward at several kilometers per second relative to the star.
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Speaker 1: In a binary star system, A close passage can add
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Speaker 1: still more. Those ejections do not need to supply dozens
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Speaker 1: of kilometres per second by themselves. They only need to
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Speaker 1: push the body past the escape speed of the system.
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Speaker 1: The rest of the excess a visiting observer measures later.
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Speaker 1: comes from the difference between the stellar motions. Reviews of
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Speaker 1: interstellar objects and exocomets make this point explicitly. The speeds
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Speaker 1: we see in our sky are the vector sum of
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Speaker 1: two systems' motions, not evidence of engines. A third part
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Speaker 1: is the galactic environment. Over billions of years, a small
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Speaker 1: body wanders in and out of giant molecular clouds, past
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Speaker 1: star-forming regions and through tidal fields that slightly reshape its path.
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Speaker 1: Individual encounters with stars at a distance of a fraction
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Speaker 1: of a parsec add tiny nudges. A recent analysis found
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Speaker 1: roughly two dozen such close passages for 3 I slash
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Speaker 1: A-T-L-A-S over 10 million years. That accumulation does not tend
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Speaker 1: to slow an object in any systematic way, but it
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Speaker 1: does broaden the distribution of speeds and directions that we
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Speaker 1: observe when one eventually passes by the Sun. Seen this way,
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Speaker 1: the more than 200,000 kilometers per hour is a time-averaged
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Speaker 1: monument to its long walk across the galaxy. There is
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Speaker 1: an important limit to keep in mind. Cometary outgassing can
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Speaker 1: add small, non-gravitational forces. It can act like a set
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Speaker 1: of asymmetric thrusters. In the case of Oumuamua, that subtle
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Speaker 1: push explained a puzzling change in motion without invoking exotic materials.
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Speaker 1: For 3 I slash ATLAS, outgassing will surely matter for
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Speaker 1: precision orbit fitting, but the magnitude of those forces is
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Speaker 1: tiny compared to the gravitational energy exchange with the Sun.
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Speaker 1: You can estimate this by comparing the momentum carried by
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Speaker 1: typical gas production rates to the momentum represented by a
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Speaker 1: nucleus that is hundreds of metres to a few kilometres
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Speaker 1: across moving at tens of kilometres per second. The numbers
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Speaker 1: differ by orders of magnitude. The right conclusion is this.
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Speaker 1: Outgassing tweaks the course. Gravity sets the speed. High speed
18:55
Speaker 1: also reshapes the observing problem into a logistical race. The
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Speaker 1: list of space assets matters because the best angles and
19:04
Speaker 1: the best solar elongations do not always happen for Earth observers.
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Speaker 1: The European Space Agency has noted, that its Mars Express
19:15
Speaker 1: and the ExoMars Trace Gas Orbiter will attempt observations near
19:20
Speaker 1: the time when the comet passes closest to Mars in
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Speaker 1: early October of the year 2025 at a separation of
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Speaker 1: roughly 30 million kilometres. Other teams have explored opportunities for
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Speaker 1: spacecraft farther out. Some analyses even consider whether images like
19:42
Speaker 1: those on the Parker Solar Probe and heliophysics missions could
19:47
Speaker 1: capture the comet's tail against the interplanetary background during the
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Speaker 1: critical weeks when Earth cannot. Every successful observation tightens the
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Speaker 1: orbit solution and refines the speed, we quote, Like any
20:04
Speaker 1: fast story, this one develops quickly. The same National Aeronautics
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Speaker 1: and Space Administration page that gave the first public primer
20:14
Speaker 1: has been adding confirmed facts as they arrive. It lists
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Speaker 1: the expected return to Earth visibility in early December of
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Speaker 1: the year 2025. It lists the safe distances. It points
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Speaker 1: to a growing multimedia archive, including a trajectory diagram generated
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Speaker 1: by the Jet Propulsion Laboratory and image galleries. It even
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Speaker 1: highlights the education-ready takeaway that this comet is an opportunity
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Speaker 1: to explain what a hyperbolic orbit really is. The premise
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Speaker 1: is simple and powerful. An object that is moving too
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Speaker 1: quickly to be captured by the Sun's gravity will not
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Speaker 1: loop around. It will pass and go. That is why
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Speaker 1: the target is a once-only opportunity. Composition and speed intertwine
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Speaker 1: again in the Webb results. A coma with carbon dioxide
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Speaker 1: outgassing greater than water by a factor of about 8
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Speaker 1: suggests either formation in an especially cold outer disk region,
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Speaker 1: or a surface that has been altered by radiation and
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Speaker 1: micrometeoroid gardening during a very long interstellar voyage, or both.
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Speaker 1: Either way, Such an ice recipe influences how quickly the
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Speaker 1: coma rises with solar heating and how the dust tail
21:43
Speaker 1: responds to solar radiation pressure. That in turn affects how
21:48
Speaker 1: easily images on spacecraft or from Earth can track the
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Speaker 1: motion of the coma versus the motion of the nucleus.
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Speaker 1: It is not just a chemistry footnote, it is a
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Speaker 1: tactical detail in the observing campaign and a structural clue
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Speaker 1: to the comet's birthplace. The most striking visual so far
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Speaker 1: comes from Hubble, which shows a compact teardrop envelope around
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Speaker 1: the nucleus. In August, mission scientists used those images to
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Speaker 1: bound the nucleus size and to describe the dust cocoon
22:26
Speaker 1: in plain language. That shape is a reminder that what
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Speaker 1: we watch move at extraordinary speed. is a fragile assembly
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Speaker 1: of ices and dust grains that survived ejection from a
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Speaker 1: distant star system and the long trip through the galaxy.
22:45
Speaker 1: The engineering feat here is nature's. A weakly bound rubble
22:50
Speaker 1: of ice has held together long enough to be seen
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Speaker 1: by us and measured. Then it will vanish back into
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Speaker 1: the dark. Why does the speed matter for the story
23:02
Speaker 1: we tell about our own origins? Interstellar comets do not
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Speaker 1: merely pass by as curiosities. Their velocities, directions and chemistry
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Speaker 1: constrain how planetary systems form and clear themselves. When you
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Speaker 1: assemble the statistics of many visits, you learn about how
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Speaker 1: common giant planets are. about how efficiently different kinds of
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Speaker 1: systems eject material, and about how the galaxy stirs those
23:32
Speaker 1: relics over time. The current discovery cadence and recent population
23:37
Speaker 1: modelling even suggest that there is almost always at least
23:42
Speaker 1: one interstellar object somewhere inside the solar system, just usually
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Speaker 1: faint and hard to find. 3I slash A-T-L-A-S, by being
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Speaker 1: bright enough and fast enough at the right time, becomes
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Speaker 1: a touchstone for that larger picture. All of this returns
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Speaker 1: us to the original question. Why does 3I slash Atlas
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Speaker 1: move at more than 200,000 km per hour, and what
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Speaker 1: does that say about its past? It moves that quickly
24:18
Speaker 1: because it came from far outside the Sun's gravitational reach
24:23
Speaker 1: with a substantial interstellar cruising speed, probably inherited from a
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Speaker 1: star in the Milky Way's thick disk. That excess speed,
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Speaker 1: set by its ejection and by the random velocities of
24:37
Speaker 1: stars in our part of the galaxy, was then amplified
24:42
Speaker 1: on approach to the Sun by the straightforward conversion of
24:46
Speaker 1: gravitational potential energy into kinetic energy. The number we recite
24:52
Speaker 1: is not arbitrary. It is the combined product of a
24:56
Speaker 1: launch during a violent phase of planet formation. a long
25:01
Speaker 1: drift through the galaxy with many small stellar encounters, and
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Speaker 1: a final sprint down the solar gravitational slope. The comet's
25:11
Speaker 1: chemistry now argues that it formed far from its star
25:16
Speaker 1: in a cold region rich in carbon dioxide ice. The
25:20
Speaker 1: kinematics argue that the parent system belongs to an older,
25:24
Speaker 1: dynamically hotter stellar population. The end result is a compact
25:30
Speaker 1: body that carries ancient information and travels quickly enough to
25:34
Speaker 1: demand our attention for a short time and then depart forever.
25:41
Speaker 1: There is one more lesson in the numbers. A natural
25:44
Speaker 1: object moving at more than 200,000 kilometers per hour is
25:50
Speaker 1: not surprising in a galaxy where the Sun itself speeds
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Speaker 1: around the center at hundreds of kilometers per second. What
26:00
Speaker 1: is surprising is that we can now spot such a
26:03
Speaker 1: traveler early, triangulate its speed with exquisite precision, and point
26:08
Speaker 1: multiple spacecraft and telescopes to catch it on the fly.
26:13
Speaker 1: That capability turns speed into science. With three, I slash A-T-L-A-S,
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Speaker 1: every kilometre per second that we measure and every spectral
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Speaker 1: line that we trace helps decode a story that began
26:28
Speaker 1: around another star and took a billion-year detour through the
26:32
Speaker 1: Milky Way to reach our cameras. That is why its
26:37
Speaker 1: velocity is a clue and not just a headline. It
26:42
Speaker 1: tells us that the small cold things that seed planets
26:45
Speaker 1: in other systems do not stay put. Some of them
26:49
Speaker 1: cross the void, and once in a while one screams
26:53
Speaker 1: past our sun, reminding us that planet-making is a galactic process,
27:01
Speaker 1: and that even a single number can carry the memory
27:05
Speaker 1: of a very long journey. For night science stories, the
27:10
Speaker 1: takeaway is crisp. The high speed is the proof and
27:14
Speaker 1: the map. It proves the comet is unbound. It maps
27:18
Speaker 1: a likely ancestry in an old, fast-moving stellar population and
27:24
Speaker 1: a birth zone far from a distant star where carbon
27:28
Speaker 1: dioxide ice was abundant. It connects the gravity we can calculate,
27:33
Speaker 1: the chemistry we can observe, and the galactic dynamics we
27:37
Speaker 1: can model into a single narrative we can watch unfold
27:42
Speaker 1: over months. The clock runs quickly on this visitor, but
27:46
Speaker 1: the message is slow and deep. The small bodies that
27:50
Speaker 1: build planets are not confined to one sky. They travel,
27:55
Speaker 1: they carry their histories in their motion, and sometimes their speed.
28:00
Speaker 1: is the simplest way to read their past. What we
28:04
Speaker 1: do not know is a long list and each item
28:08
Speaker 1: maps to a specific observing tactic. The nucleus is still unresolved.
28:14
Speaker 1: The sharpest images from the Hubble Space Telescope constrain its
28:18
Speaker 1: diameter to be no smaller than about 440 metres and
28:21
Speaker 1: no larger than about 445 metres about 5 and 6
28:29
Speaker 1: tenths kilometres, a range that straddles two orders of magnitude
28:35
Speaker 1: in mass, depending on the density you assume. That is
28:39
Speaker 1: not a cosmetic uncertainty. Mass controls how easily sunlight-driven jets
28:46
Speaker 1: can torque the body and alter its path. The only
28:50
Speaker 1: path to narrow this window is continued high-resolution imaging when
28:55
Speaker 1: the geometry improves after the object re-emerges from behind the
29:00
Speaker 1: sun in early December of the year 2025 and careful
29:06
Speaker 1: modelling of how the dustcomber's brightness profile blurs the point
29:11
Speaker 1: like nucleus in those images. That is exactly what the
29:15
Speaker 1: Hubble programme says it will do once the target returns
29:19
Speaker 1: to safe elongations. We do not yet have a secure
29:24
Speaker 1: rotation period or a firm direction for the spin axis.
29:28
Speaker 1: A slow rotation hides under the light of even a
29:32
Speaker 1: faint coma. Early photometry found only low amplitude brightness changes,
29:38
Speaker 1: and in some data set no convincing periodicity at all,
29:43
Speaker 1: which is typical when a dust coma is damps the
29:46
Speaker 1: nucleus signal. One detailed study with the 10-metre class Gran
29:51
Speaker 1: Telescopio Canarius reported a period close to 17 hours with
29:57
Speaker 1: a small brightness amplitude that shrank as activity grew through July,
30:03
Speaker 1: which is exactly what you expect if newly released dust
30:07
Speaker 1: increasingly veils the bare nucleus. As a cross-check, Independent teams
30:14
Speaker 1: using the transiting exoplanet survey satellite pre-discovery stacks reported no
30:21
Speaker 1: statistically strong periodic signal across about 20 days of coverage,
30:26
Speaker 1: again consistent with a weak nucleus modulation washed out by
30:31
Speaker 1: coma light. The way forward is straightforward. Keep building a
30:36
Speaker 1: multi-month light curve from large telescopes and solve for a
30:41
Speaker 1: rotation period that stays stable across filters and instruments. Use
30:47
Speaker 1: structure in the dust fans that point sunward in the
30:50
Speaker 1: Hubble and Very Large Telescope images as traces of active
30:55
Speaker 1: areas to infer pole direction. If the pole solution is real,
31:00
Speaker 1: it will predict a seasonal pattern in jet direction that
31:04
Speaker 1: can be tested on the post-Perihelion leg. The composition story
31:09
Speaker 1: is both exciting and unfinished. The first near-infrared spectra from
31:15
Speaker 1: the James Webb Space Telescope on August 6th of the
31:20
Speaker 1: year 2025 show a coma dominated by carbon dioxide, with
31:26
Speaker 1: water present at much lower abundance, along with detections of
31:31
Speaker 1: carbonyl sulfide, water ice, carbon monoxide, and dust. The carbon
31:37
Speaker 1: dioxide to water mixing ratio sits near 8 to 1,
31:41
Speaker 1: which is among the highest values ever measured in a comet,
31:45
Speaker 1: and stands well above the trend established for long-period comets
31:50
Speaker 1: observed at similar solar distances. That number has real interpretive power.
31:57
Speaker 1: It points either to formation near the carbon dioxide ice
32:01
Speaker 1: line in a very cold outer disk, or to a
32:05
Speaker 1: surface that has been processed in space so that heat
32:09
Speaker 1: penetration is insufficient to liberate much water relative to carbon dioxide.
32:15
Speaker 1: But we have only a first look. We do not
32:18
Speaker 1: yet know if this ratio will hold as the object warms,
32:23
Speaker 1: or whether it will pivot toward a more familiar water-dominated
32:27
Speaker 1: coma closer to the Sun. The plan to answer this
32:31
Speaker 1: is to take repeated spectra with the James Webb Space
32:35
Speaker 1: Telescope and with ground-based instruments after reappearance to map how
32:41
Speaker 1: the volatile mix evolves with heliocentric distance. The spectrophotometer for
32:47
Speaker 1: the history of the universe. Epoch of Ryanization and ICES
32:52
Speaker 1: Explorer has already mapped an extended carbon dioxide envelope hundreds
32:58
Speaker 1: of thousands of kilometers across. So matching those global maps
33:04
Speaker 1: to the point source spectra from the James Webb Space
33:07
Speaker 1: Telescope will be one of the next clean tests. Even
33:12
Speaker 1: the most basic molecule in cometary science, water, arrived with
33:17
Speaker 1: a surprise. Ultraviolet imaging with the Neil Gehrel's Swift Observatory
33:22
Speaker 1: detected hydroxyl emission beyond three astronomical units, implying ongoing water production.
33:30
Speaker 1: at an unusually large distance. That calls for a mechanism
33:34
Speaker 1: beyond pure sun-warmed surface ice. One plausible picture is that
33:40
Speaker 1: larger icy grains lofted from the nucleus sublimate in the
33:44
Speaker 1: coma and act as an extended secondary source of water.
33:49
Speaker 1: To confirm or refute that picture, observers will combine ultraviolet
33:55
Speaker 1: traces of hydroxyl with thermal infrared monitoring of large coma
34:00
Speaker 1: grains and with optical spectroscopy of cyanide and other radicals
34:06
Speaker 1: that rise as water-driven activity strengthens. The balance among hydroxyl,
34:12
Speaker 1: carbon dioxide, Carbon monoxide and cyanide will be one of
34:17
Speaker 1: the crispest diagnostics for what drives the comet now and
34:21
Speaker 1: how that driver changes with time. The visible colour and
34:26
Speaker 1: the dust physics carry their own unknowns. Early very large
34:31
Speaker 1: telescope spectroscopy in the first week of July showed a
34:35
Speaker 1: red and featureless continuum redder than many familiar comets and
34:41
Speaker 1: closer to the colours of some trans-Neptunian objects and the
34:45
Speaker 1: centaur named Pholus. That already hints at a dark, complex
34:51
Speaker 1: organic surface and fine dust grains. But polarimetry, which measures
34:57
Speaker 1: how the scattered light is oriented, delivered the sharper shock.
35:01
Speaker 1: A coordinated campaign with the Very Large Telescope, the Nordic
35:06
Speaker 1: Optical Telescope and the Bulgarian Rojan Telescope found an unusually
35:12
Speaker 1: deep and narrow negative polarisation branch at small phase angles,
35:18
Speaker 1: reaching a minimum near negative 2.7% and switching sign near
35:22
Speaker 1: 17 degrees. That combination has not been seen in other
35:29
Speaker 1: comets and even differs from the previous interstellar comet named 2I-Borisov.
35:37
Speaker 1: Negative polarisation at small angles often signals compact submicron grains
35:43
Speaker 1: with particular surface textures or mixtures of ice and darker organics.
35:49
Speaker 1: But the exact mix that reproduces this deep branch is
35:52
Speaker 1: still unknown. The way to settle it is to build
35:56
Speaker 1: a full polarimetric phase curve across as wide a range
36:00
Speaker 1: of scattering angles as the geometry allows, and to combine
36:05
Speaker 1: that with mid-infrared measurements of the silicate feature shapes that
36:10
Speaker 1: betray grain size and porosity. That program is underway across
36:19
Speaker 1: multiple observatories. The green question is unresolved. Photographers recorded an
36:25
Speaker 1: emerald tint in mid-September images, and cyanide has been spectroscopically detected,
36:32
Speaker 1: which is one known path to green glows in comets,
36:35
Speaker 1: along with the more common dicarbon bands. But other groups
36:40
Speaker 1: report no clear sign of dicarbon yet, and colour imaging
36:44
Speaker 1: can mislead when filters and processing differ. Here, the standard
36:50
Speaker 1: is simple. confirm the presence or absence of the key
36:54
Speaker 1: emissive molecules with spectroscopy. Optical spectra from the Very Large
36:59
Speaker 1: Telescope show cyanide at heliocentric distances as large as just
37:05
Speaker 1: over three astronomical units and do not yet show dicarbon.
37:11
Speaker 1: That argues for a cautious description. If the green persists
37:16
Speaker 1: and dicarbon remains absent, then cyanide and possibly oxygen atoms
37:22
Speaker 1: could be the dominant contributors to the tint. If dicarbon
37:26
Speaker 1: emerges later, the colour story will change. Either way, the
37:31
Speaker 1: fix is to keep taking medium resolution spectra across the
37:36
Speaker 1: relevant bands as the object brightens and as the dust
37:41
Speaker 1: coma grows. Another open issue is the scale and direction
37:47
Speaker 1: of non-gravitational acceleration. Outgassing can act like asymmetric thrusters and
37:53
Speaker 1: nudge the trajectory in the previous interstellar object named 1
37:57
Speaker 1: I slash Oumuamua. This effect was the centre of a
38:03
Speaker 1: long debate because the acceleration was strong and chemically puzzling.
38:08
Speaker 1: For 3 I slash Atlas. The expectation from comet physics
38:14
Speaker 1: is that the effect should be modest for a kilometre-scale nucleus,
38:18
Speaker 1: likely below the threshold that could be robustly identified in
38:24
Speaker 1: early astrometry. The way to know is to wait for
38:27
Speaker 1: a longer arc of precise positions taken before and after perihelion,
38:33
Speaker 1: then fit standard outgassing parameters and see whether the residuals
38:38
Speaker 1: shrink The small-body database at the Jet Propulsion Laboratory will
38:43
Speaker 1: fold in non-gravitational terms only when the data justify them.
38:49
Speaker 1: That is a measurement to watch in December and beyond.
38:53
Speaker 1: We have only a provisional grip on how the comet's
38:57
Speaker 1: chemistry is changing with time. By mid-August, the Very Large
39:03
Speaker 1: Telescope team reported a dramatic rise in neutral nickel line
39:08
Speaker 1: emission and the first solid detections of cyanide, while water
39:13
Speaker 1: and oxygen lines remained faint at large distances from the Sun.
39:18
Speaker 1: The question is whether that early heavy atom signature marks
39:23
Speaker 1: unusual release mechanisms from the dust, or whether it is
39:27
Speaker 1: simply a sensitivity effect that vanishes once water and dicarbon
39:33
Speaker 1: flood the coma at smaller heliocentric distances, repeated high resolution
39:39
Speaker 1: spectroscopy at different distances and solar phase angles will give
39:44
Speaker 1: the answer. The key is to measure how nickel and
39:49
Speaker 1: cyanide production rates scale relative to water and carbon dioxide
39:55
Speaker 1: and compare those scalings to solar system comets. We also
40:00
Speaker 1: do not yet know the internal structure. Is the nucleus
40:05
Speaker 1: a compact monolith with a thin refractory crust or a
40:09
Speaker 1: porous rubble assembly with many small vents? Disentangling that is
40:14
Speaker 1: not photogenic, but it is doable. It requires connecting the
40:19
Speaker 1: time variability of the Comer morphology with thermophysical models that
40:24
Speaker 1: include heat diffusion, sublimation fronts, and changes in tensile strength
40:31
Speaker 1: as the material cyclically warms and cools. In practice, that
40:36
Speaker 1: means measuring the timescale on which jets turn on and
40:40
Speaker 1: off as local sunrise and sunset sweep across the surface.
40:45
Speaker 1: and matching that to model predictions that depend on porosity
40:50
Speaker 1: and thermal inertia. Hubble images from late July show a
40:54
Speaker 1: clear sun-facing plume and the hint of a developing anti-solar
41:00
Speaker 1: dust tail, which gives the first pieces of that timing puzzle.
41:05
Speaker 1: More images after perihelion will sharpen the constraints. No one
41:10
Speaker 1: has yet measured the deuterium to hydrogen ratio in water
41:14
Speaker 1: vapour from this object, which would be a major clue
41:18
Speaker 1: to its formation temperature and heritage. The James Webb Space
41:23
Speaker 1: Telescope instruments can, in principle, detect the deuterated water lines
41:30
Speaker 1: if the coma is bright enough and if the geometry
41:33
Speaker 1: cooperates but the signal is faint and the object will
41:38
Speaker 1: be behind the Sun for Earth observatories right at peak activity.
41:43
Speaker 1: Sub-millimeter facilities that are powerful for isotopic work will face
41:49
Speaker 1: the same geometry problems and the additional challenge of a distant,
41:54
Speaker 1: relatively faint target. The near-term plan is therefore indirect. Measure
42:01
Speaker 1: stable isotopes where they are more accessible such as the
42:05
Speaker 1: ratio of carbon-13 to carbon-12 in cyanide bands, and compare
42:11
Speaker 1: to solar system values. If those come back unusual, they
42:16
Speaker 1: will strengthen the case for a distinct formation environment, even
42:20
Speaker 1: without a definitive water isotope measurement. The dynamical origin remains debated.
42:26
Speaker 1: One analysis that extrapolated the inbound velocity relative to the
42:31
Speaker 1: local standard of rest concluded that the object fits the
42:36
Speaker 1: kinematic profile of the Milky Way thick disk, and could
42:40
Speaker 1: therefore be very old, perhaps older than 7.5 billion years.
42:47
Speaker 1: A separate study that looked at a control sample of
42:50
Speaker 1: stars with similar three-dimensional velocities argued that thin-disk membership is
42:56
Speaker 1: more likely. A third approach integrated the orbit backward against
43:02
Speaker 1: the motions of nearby stars and found some two dozen
43:06
Speaker 1: passages within about one parsec across the last 10 million years,
43:12
Speaker 1: which is enough to scramble any clean trajectory back to
43:16
Speaker 1: a specific parent star. This is not arm-waving. Each claim
43:23
Speaker 1: is testable as the orbit and the chemistry become better constrained.
43:28
Speaker 1: A thick disk heritage would predict an overall older lower
43:32
Speaker 1: metallicity chemical signature. A thin disk origin would fit a
43:37
Speaker 1: wider range of compositions. The plan to make progress is
43:41
Speaker 1: to combine precise post-perihelion astrometry with the growing spectroscopic inventory
43:48
Speaker 1: and ask whether the kinematic and chemical priors point to
43:53
Speaker 1: the same galactic population. There is also the matter of
43:59
Speaker 1: how early activity began. Pre-discovery stacks from the transiting exoplanet
44:05
Speaker 1: survey satellite reveal the object in May, many weeks before
44:10
Speaker 1: the alert, and the brightness evolution suggests it may have
44:15
Speaker 1: been active at a solar distance near six and four
44:19
Speaker 1: tenths astronomical units. A separate team used archival data from
44:25
Speaker 1: the Zwicky Transient Facility to push the activity limit even
44:30
Speaker 1: farther back. If activity truly started beyond six astronomical units,
44:36
Speaker 1: the driver cannot have been water. Carbon dioxide and carbon
44:41
Speaker 1: monoxide are the prime candidates. That is consistent with the
44:45
Speaker 1: James Webb Space Telescope carbon dioxide dominance and with the
44:51
Speaker 1: spectrophotometer for the history of the universe. of Ryanization and
44:57
Speaker 1: ICES Explorer detection of an extended carbon dioxide coma. The
45:02
Speaker 1: observational path forward is to keep pairing wide-field infrared mapping
45:08
Speaker 1: of the global carbon dioxide envelope with point-source spectroscopy that
45:14
Speaker 1: isolates the volatile mix close to the nucleus. That combination
45:19
Speaker 1: will tell us how the activity source terms feed the
45:23
Speaker 1: expanding coma. The observational cadence itself is a scientific constraint.
45:29
Speaker 1: Around late October of the year 2025, the comet is
45:35
Speaker 1: almost behind the Sun as seen from Earth. That blackout
45:39
Speaker 1: for ground-based observers falls tantalisingly close to perihelion. It means
45:46
Speaker 1: the most intense phase of near-solar heating must be covered
45:51
Speaker 1: by spacecraft at other vantage points. The Parker Solar Probe's
45:55
Speaker 1: Wide Field Imager, formerly the Wide Field Imager for Solar Probe,
46:00
Speaker 1: is expected to have a window from late September into
46:04
Speaker 1: early November to catch the dust environment against the inner heliosphere,
46:09
Speaker 1: just when terrestrial telescopes cannot. The European orbiters at Mars
46:15
Speaker 1: aim to observe around the early October closest passage at
46:20
Speaker 1: a distance of roughly 30 million kilometres. Jupiter missions and
46:25
Speaker 1: outer heliophysics images will also attempt rides along. The practical
46:31
Speaker 1: point is clear. A coordinated fleet is the only way
46:36
Speaker 1: to fill the perihelion gap. After that, Earth-based telescopes and
46:42
Speaker 1: the Hubble Space Telescope resume the watch in early December.
46:47
Speaker 1: We do not yet know whether the nucleus will fracture.
46:51
Speaker 1: Many comets fragment under thermal and rotational stresses. The perihelion
46:57
Speaker 1: distance of a little over one and three-tenths astronomical units
47:02
Speaker 1: is not a recipe for catastrophic heating by itself, especially
47:07
Speaker 1: compared to sun grazers. But the torques from asymmetric outgassing
47:12
Speaker 1: can spin up a small body to the point of
47:16
Speaker 1: structural failure. The signs to monitor are abrupt jumps in brightness,
47:22
Speaker 1: followed by a change in the coma morphology and the
47:25
Speaker 1: appearance of condensations in high-resolution stacks. If that happens, the
47:31
Speaker 1: follow-up will be immediate. Spectra will look for freshly exposed
47:36
Speaker 1: ices and astrometry will try to track fragments. If it
47:41
Speaker 1: does not happen, that non-detection is valuable too. It sets
47:46
Speaker 1: a lower bound on cohesion for an interstellar nucleus, a
47:50
Speaker 1: number that can be compared to values inferred for long-period
47:54
Speaker 1: comets born in our own distant cloud. Brightness predictions are
48:00
Speaker 1: another open thread. Through mid-September, the object began to brighten
48:06
Speaker 1: faster than a simple power law would forecast, which could
48:10
Speaker 1: be a pre-perihelion flare-up or simply the point where carbon
48:15
Speaker 1: dioxide-driven activity transitions to a mixed regime. Amateur and professional
48:22
Speaker 1: photometry will keep logging the secular light curve. The specific
48:26
Speaker 1: test is whether the post-perihelion fading follows the usual hysteresis
48:32
Speaker 1: pattern seen in many comets, where the outbound light curve
48:36
Speaker 1: does not simply track the inbound one in reverse. That
48:40
Speaker 1: asymmetry tells you about thermal lag and layering in the nucleus,
48:46
Speaker 1: which in turn links back to how it formed. We
48:50
Speaker 1: also lack a firm dust-to-gas ratio and grain size distribution.
48:56
Speaker 1: The height and shape of the 10-micrometer silicate feature and
49:00
Speaker 1: the slope of the mid-infrared continuum are the classic tools,
49:05
Speaker 1: and observers will try to get them with the James
49:08
Speaker 1: Webb Space Telescope and with large ground-based facilities in the
49:14
Speaker 1: months after reappearance. Those measurements combined with the optical polarisation curve,
49:21
Speaker 1: can pin down whether the dust is dominated by compact
49:25
Speaker 1: submicron particles or by fluffy aggregates, and whether ice-coated grains
49:32
Speaker 1: make up a significant fraction. The answer matters because dust
49:37
Speaker 1: carrying embedded volatiles is a natural way to reconcile distant
49:42
Speaker 1: water detections with a carbon dioxide dominated gas phase close
49:48
Speaker 1: to the nucleus. A crisp statistical question remains open. How
49:54
Speaker 1: common are objects like this in our skies at any
49:58
Speaker 1: given time? Detection of the third interstellar body in less
50:03
Speaker 1: than a decade suggests that at least one such object
50:07
Speaker 1: is usually within the solar system at any moment, yet
50:10
Speaker 1: most are too faint to spot. Population models will be
50:14
Speaker 1: updated with this detection and with the vetted selection function
50:19
Speaker 1: of the surveys that found it. But the most incisive
50:23
Speaker 1: inputs will come not from the discovery itself, but from
50:27
Speaker 1: the measured speed distribution, chemical fingerprints, and the rate of
50:32
Speaker 1: changes near perihelion. Each of those will feed the next
50:37
Speaker 1: generation models of planet formation and ejection in other stars, systems,
50:45
Speaker 1: There is a communications question as well. Claims of exotic
50:49
Speaker 1: behaviour will continue to surface. The antidote is measurement. The
50:54
Speaker 1: deep negative polarisation is a measured optical property that can
50:59
Speaker 1: be compared against a library of solar system bodies. The
51:04
Speaker 1: carbon dioxide to water ratio near 8 to 1 is
51:09
Speaker 1: a measured value from a well-calibrated spectrograph. The early hydroxyl
51:14
Speaker 1: detections are measured in ultraviolet imaging. The cyanide lines are
51:20
Speaker 1: measured in optical spectra. When those numbers are combined with
51:25
Speaker 1: a consistent orbit fit and with post-perihelion non-gravitational parameters, the
51:31
Speaker 1: room for speculation shrinks and the physical picture grows. That
51:37
Speaker 1: is how this field advances. A brief inventory of the
51:43
Speaker 1: key unknowns and the instruments that will address them helps
51:47
Speaker 1: frame the next few months. The range of allowed nucleus
51:51
Speaker 1: diameters will tighten with Hubble imaging and with refined coma
51:56
Speaker 1: modelling in December and January. The spin period and pole
52:01
Speaker 1: direction will be solved by a combination of long baseline
52:06
Speaker 1: light curves and jet morphology fits. with results checked against
52:11
Speaker 1: any seasonally modulated activity. The carbon dioxide dominance versus water
52:17
Speaker 1: rise will be traced by repeat near infrared spectra with
52:21
Speaker 1: the James Webb Space Telescope and by wide-field carbon dioxide
52:26
Speaker 1: maps from the Spectrophotometer for the History of the Universe
52:31
Speaker 1: Epoch of Ryanization and ICES Explorer. The negative polarization curve
52:38
Speaker 1: will be extended and compared to silicate feature shapes in
52:42
Speaker 1: the mid-infrared for grain size and porosity constraints. The cyanide
52:48
Speaker 1: and nickel production rates will be tracked against water and
52:53
Speaker 1: carbon dioxide. to test for unusual heavy atom release. The
52:58
Speaker 1: non-gravitational acceleration will be fitted once the post-perihelion astrometry fills
53:05
Speaker 1: in the long arc. The dynamical origin question will be
53:09
Speaker 1: revisited as the refined orbit is run backward through the
53:13
Speaker 1: field of nearby stars and checked against thick disk and
53:18
Speaker 1: thin disk priors, and the perihelion gap will be partly
53:22
Speaker 1: bridged by the Parker Solar Probe Wide Field Imager and
53:27
Speaker 1: by Mars orbiters, whose observing plans are already public. What
53:33
Speaker 1: we may never know is worth stating plainly. We may
53:37
Speaker 1: never identify the exact star, the cumulative nudges from passing
53:44
Speaker 1: stars and clouds over billions of years erase the precise trail.
53:49
Speaker 1: We may never pin down the deep interior layering without
53:53
Speaker 1: an occultation or a serendipitous split, and we may not
53:57
Speaker 1: get the gold standard water isotope ratios unless the coma
54:03
Speaker 1: becomes much richer in water than it is today. But
54:07
Speaker 1: even with those limitations, The dataset will be exceptional. This
54:13
Speaker 1: is only the second time we can watch an interstellar
54:16
Speaker 1: comet behave like a comet, not an inert shard. The
54:21
Speaker 1: specific chemistry and the specific speed make it a case
54:25
Speaker 1: study in planets forming elsewhere. The tactical timeline is clear
54:31
Speaker 1: enough to plan around. Through late September and October, the
54:36
Speaker 1: object slides into solar conjunction for Earth, and the best
54:40
Speaker 1: hope for continuous coverage lies with images aboard spacecraft, in
54:45
Speaker 1: the inner solar system, and at Mars. Around late October,
54:51
Speaker 1: it reaches perihelion. By early December, it returns to view
54:56
Speaker 1: for ground-based telescopes and for the Hubble Space Telescope. The
55:00
Speaker 1: James Webb Space Telescope can then schedule follow-on spectra to
55:06
Speaker 1: capture the outbound composition. That is when many of the
55:11
Speaker 1: unknowns listed here will begin to shrink. There is value
55:16
Speaker 1: in tests that fail. If the cyanide lines level off
55:20
Speaker 1: while the overall brightness continues to grow, that calls for
55:25
Speaker 1: a change in the chemistry model. If the negative polarisation
55:29
Speaker 1: minimum shifts with time. The dust-grain mix is not static.
55:35
Speaker 1: If the non-gravitational terms never rise above noise, that tells
55:40
Speaker 1: us the outgassing thrusts are weak and probably symmetric. in
55:45
Speaker 1: the aggregate if water stays a secondary player even much
55:49
Speaker 1: nearer to the Sun. The case strengthens for formation in
55:53
Speaker 1: a very cold outer disk far from a parent star
55:58
Speaker 1: or for an insulating crust that redirects heat. And if
56:02
Speaker 1: the postperihelion light curve does not mirror the inbound curve,
56:07
Speaker 1: it will illuminate how layers in the surface respond to
56:12
Speaker 1: the Sun. One lesson of interstellar visitors is that impatient
56:17
Speaker 1: stories age poorly. The numbers you want most arrive last.
56:22
Speaker 1: That is the nature of orbital geometry and of signal-to-noise.
56:27
Speaker 1: For 3 I slash A-T-L-A-S, the mission briefs are already public.
56:33
Speaker 1: The National Aeronautics and Space Administration list of participating assets
56:39
Speaker 1: includes the Hubble Space Telescope, the James Webb Space Telescope,
56:45
Speaker 1: the Transiting Exoplanet Survey Satellite, the Swift Observatory, the Spectrophotometer
56:51
Speaker 1: for the History of the Universe, Epoch of Ryanization, and
56:55
Speaker 1: ISIS Explorer, and a roster of planetary and heliophysics spacecraft
57:01
Speaker 1: from Mars to near the Sun, those eyes will do
57:05
Speaker 1: exactly what you would design for this target. They will
57:09
Speaker 1: gather spectra across the volatile bands, map the global carbon
57:14
Speaker 1: dioxide envelope, trace the dust polarisation with phase angle, and
57:19
Speaker 1: fill the perihelion gap from vantage points Earth cannot reach.
57:25
Speaker 1: They will then hand the target back to Earth-based telescopes
57:29
Speaker 1: for the long outbound watch, when non-gravitational terms can finally
57:35
Speaker 1: be fitted and residuals finally inspected. So the state of
57:41
Speaker 1: knowledge is this. We know the speed is high and interstellar,
57:46
Speaker 1: and we know the orbit will carry the object out
57:49
Speaker 1: for good. We know the coma is anomalously rich in
57:53
Speaker 1: carbon dioxide, that water appears even far beyond three astronomical units.
58:00
Speaker 1: that cyanide and neutral nickel have appeared in the spectra,
58:05
Speaker 1: and that the dust polarisation is unusually negative at small angles.
58:11
Speaker 1: We do not yet know the precise size, the rotation
58:14
Speaker 1: period and pole, the dust grain size distribution, the dust
58:19
Speaker 1: to gas ratio, the deuterium to hydrogen ratio, the level
58:24
Speaker 1: of non-gravitational acceleration, the risk of fragmentation, or the exact
58:30
Speaker 1: galactic population to which the parent system belongs. Each unknown
58:35
Speaker 1: is paired to an imminent measurement. That is why this
58:40
Speaker 1: interstellar comet matters scientifically. It is not a single headline.
58:46
Speaker 1: It is a schedule of tests. Over the next few months,
58:50
Speaker 1: the answers will arrive in the form of repeated spectra,
58:55
Speaker 1: longer light curves. new images from different vantage points and
59:01
Speaker 1: a refined orbit solution. That is how we will turn
59:05
Speaker 1: a fast stranger into a well-constrained data point for how
59:10
Speaker 1: planets form across the Milky Way. Counting visitors is not
59:16
Speaker 1: a matter of collecting souvenirs. It is a matter of
59:19
Speaker 1: rates and biases. We have seen only three confirmed interstellar
59:25
Speaker 1: objects in eight years. That small tally says more about
59:30
Speaker 1: our limited reach than about the galaxy's supply. 3 i
59:34
Speaker 1: slash Atlas was confirmed in early July of the year
59:38
Speaker 1: 2025 as the third such visitor after 1 i slash
59:44
Speaker 1: Umuamua in the year 2017 and 2 i slash Borisov
59:50
Speaker 1: in the year 2019. Each one was found by a
59:55
Speaker 1: wide field survey that happened to be looking in the
59:58
Speaker 1: right direction at the right moment. The pace of confirmed
1:00:03
Speaker 1: discoveries is therefore not the true cadence of flybys. It
1:00:09
Speaker 1: is the cadence of our instruments catching up. A cleaner
1:00:14
Speaker 1: way to think about frequency is to start from the
1:00:18
Speaker 1: physics and the stellar motions around us. When you combine
1:00:23
Speaker 1: the typical space velocities of nearby stars from the Gaia
1:00:28
Speaker 1: catalogue with gravitational focusing by the Sun, you can predict
1:00:33
Speaker 1: how many unbound bodies should sweep through the inner system,
1:00:37
Speaker 1: regardless of whether we notice them. That calculation gives a
1:00:42
Speaker 1: simple headline number. On average, about seven interstellar objects pass
1:00:49
Speaker 1: within one astronomical unit of the Sun every year. The
1:00:53
Speaker 1: velocity distribution is skewed toward moderate speeds. Roughly 92% arrive
1:01:00
Speaker 1: with speeds below 100 km per second at infinity relative
1:01:05
Speaker 1: to the Sun. Only a small fraction form a high-speed tail.
1:01:11
Speaker 1: In addition, that same modelling predicts a demographic mix tied
1:01:16
Speaker 1: to galactic structure. The vast majority should come from the
1:01:20
Speaker 1: Milky Way thin disk, a few per decade from the
1:01:24
Speaker 1: thicker and older disk population, about one per decade from
1:01:28
Speaker 1: the halo, and only a few per century from objects
1:01:32
Speaker 1: unbound to our galaxy. Those numbers give context for 3
1:01:36
Speaker 1: I slash A T L A S. It is statistically
1:01:41
Speaker 1: normal to have one or more interstellar bodies passing through
1:01:45
Speaker 1: the inner solar system every year, even if our telescopes
1:01:51
Speaker 1: do not see them. So why have we seen so few?
1:01:55
Speaker 1: Detection is hard for three practical reasons. First, these bodies
1:02:01
Speaker 1: are small and dark. A typical object the size of
1:02:05
Speaker 1: Oumuamua is far fainter than the survey limits until it
1:02:09
Speaker 1: is already near the sun and moving fast. Second, geometry matters.
1:02:16
Speaker 1: Many pass through at low solar elongation where ground-based telescopes
1:02:21
Speaker 1: cannot look without washing out the signal in scattered sunlight. Third,
1:02:26
Speaker 1: motion itself is a penalty. A long exposure smears a
1:02:31
Speaker 1: fast target into a streak and lowers the detection significance,
1:02:35
Speaker 1: a phenomenon called trailing loss. Survey simulations that include these
1:02:41
Speaker 1: effects predict a very uneven harvest depending on how deep
1:02:46
Speaker 1: and how often a given telescope scans the sky and
1:02:50
Speaker 1: which parts of the sky it emphasizes. The optimal hunting
1:02:55
Speaker 1: grounds cluster around the solar apex and anti-apex directions, where
1:03:00
Speaker 1: relative motions line up to boost discovery odds. The upgrade
1:03:06
Speaker 1: that changes the statistics is the Legacy Survey of Space
1:03:11
Speaker 1: and Time at the Vera Rubin Observatory. Several independent studies
1:03:16
Speaker 1: have quantified what a deeper, faster, wider survey will do.
1:03:21
Speaker 1: One peer reviewed analysis projects roughly 15 interstellar objects in
1:03:27
Speaker 1: 10 survey years under conservative assumptions and notes. that this
1:03:32
Speaker 1: is likely a lower limit because the true size distribution
1:03:37
Speaker 1: is still uncertain. A separate synthetic detection study found that
1:03:42
Speaker 1: the yield could range from essentially zero to roughly 70
1:03:47
Speaker 1: per year depending on the albedos and the slope of
1:03:51
Speaker 1: the size frequency distribution. At the recent joint meeting of
1:03:55
Speaker 1: the Europlanet Science Congress and the Division for Planetary Sciences,
1:04:01
Speaker 1: survey specialists presented updated simulations that bracket the Rubin yield
1:04:07
Speaker 1: between roughly 6 and roughly 50 interstellar objects over the
1:04:13
Speaker 1: core survey, again highlighting the sensitivity to unknown population parameters.
1:04:20
Speaker 1: The spread in those forecasts is not a problem. It
1:04:24
Speaker 1: is a prediction we can test as soon as the
1:04:28
Speaker 1: survey starts operating at scale. Before Oumuamua, the best we
1:04:33
Speaker 1: could say came from null results. A careful analysis of
1:04:38
Speaker 1: years of Pan-STARRS and Allied surveys set an upper limit
1:04:43
Speaker 1: on the space density of kilometre-class unbound objects. That ceiling
1:04:49
Speaker 1: turned into an estimate once Oumuamua appeared, and a widely
1:04:53
Speaker 1: cited calculation inferred a number density on the order of
1:04:57
Speaker 1: a few tenths per cubic astronomical unit for Oumuamua-sized bodies.
1:05:03
Speaker 1: That value implied a surprisingly large total mass in interstellar planetesimals,
1:05:10
Speaker 1: unless most stars contribute substantially, a clue that galactic recycling
1:05:15
Speaker 1: of planet-building leftovers is vigorous. The first limit told us
1:05:21
Speaker 1: only that such bodies are not extremely common at large sizes.
1:05:27
Speaker 1: The first detection told us that smaller ones may be
1:05:30
Speaker 1: common enough that, with better surveys, we should see a
1:05:34
Speaker 1: steady stream. Two I slash Borisov and now three I
1:05:40
Speaker 1: slash Atlas sharpened that picture, but the uncertainties remain large.
1:05:45
Speaker 1: Because three data points do not fix a population. The
1:05:50
Speaker 1: other end of the size spectrum tells a different story
1:05:54
Speaker 1: about frequency. We are bathed in a continuous stream of
1:05:59
Speaker 1: interstellar dust. Spacecraft have measured it in situ for decades.
1:06:05
Speaker 1: Ulysses detected the flow of micrometer scale grains plunging through
1:06:09
Speaker 1: the heliosphere during the 1990s and 2000s. Cassini sampled interstellar
1:06:16
Speaker 1: grains in the inner solar system and even inside the
1:06:21
Speaker 1: orbit of Earth. Those measurements are not the same as
1:06:25
Speaker 1: seeing a discrete comet. but they demonstrate a persistent flux
1:06:30
Speaker 1: of extrasolar material crossing our planetary space at characteristic speeds
1:06:36
Speaker 1: of a few tens of kilometers per second. On that
1:06:40
Speaker 1: microscopic scale, interstellar visitors are not rare at all. They
1:06:46
Speaker 1: are background. What about larger interstellar meteors that burn up
1:06:52
Speaker 1: in our atmosphere. One candidate fireball from early January of
1:06:57
Speaker 1: the year 2014 was later cited by the United States
1:07:01
Speaker 1: Space Command as having sufficiently high speed to imply an
1:07:06
Speaker 1: unbound orbit, based on classified tracking data. At the same time,
1:07:12
Speaker 1: multiple independent reviews of meteor catalogues caution that measurement errors
1:07:18
Speaker 1: can easily push ordinary bound meteoroids into seemingly hyperbolic solutions,
1:07:25
Speaker 1: and that robust, confirmed cases are therefore exceptionally rare. The
1:07:31
Speaker 1: correct takeaway is cautious. There may be occasional interstellar meteors,
1:07:36
Speaker 1: but present radar and optical networks are not yet precise
1:07:41
Speaker 1: enough to quote a reliable rate. This uncertainty does not
1:07:46
Speaker 1: weaken the case for frequent macroscopic visitors within the inner
1:07:50
Speaker 1: solar system, It simply underscores that confirmation thresholds differ between
1:07:56
Speaker 1: a tractable orbit found by many telescopes and a brief
1:08:03
Speaker 1: atmospheric flash measured with large uncertainties. Turn back to the
1:08:11
Speaker 1: practical question for planning observations and missions. If roughly seven
1:08:17
Speaker 1: interstellar bodies pass within one astronomical unit of the Sun
1:08:22
Speaker 1: per year, and if most are small and faint, then
1:08:26
Speaker 1: the job of modern surveys is to raise the fraction
1:08:30
Speaker 1: we detect from a few percent to a sizable piece
1:08:33
Speaker 1: of that flow. The Rubin survey will be the keystone,
1:08:37
Speaker 1: but not the only one. Smaller wide-field facilities can run
1:08:42
Speaker 1: targeted search modes toward the solar apex and anti-apex, where
1:08:48
Speaker 1: the yield is expected to concentrate. Early alerts will let
1:08:52
Speaker 1: large telescopes obtain spectra and high-resolution images and will let
1:08:58
Speaker 1: heliophysics images catch the dust environments for those objects that
1:09:03
Speaker 1: brighten quickly. If a detection occurs soon enough and the
1:09:08
Speaker 1: speed is moderate, mission concepts like the European Comet Interceptor
1:09:13
Speaker 1: or proposed rapid-response spacecraft could attempt a close pass. Population
1:09:19
Speaker 1: studies show that reachable targets exist at a rate of
1:09:24
Speaker 1: about one to a few per decade for a craft
1:09:28
Speaker 1: with aggressive propulsion and a prepositioned flight plan. How often
1:09:34
Speaker 1: will we meet something like 3i slash Atlas specifically, meaning
1:09:39
Speaker 1: an active comet with a nucleus hundreds of meters to
1:09:43
Speaker 1: kilometers across and an interstellar speed comparable to or greater
1:09:49
Speaker 1: than 50 kilometers per second at infinity? On present models,
1:09:55
Speaker 1: the answer is sparse, but not vanishingly so. The same
1:09:59
Speaker 1: Gaia-based arrival rate analysis that yields seven within one astronomical
1:10:05
Speaker 1: unit per year also infers a much lower number density
1:10:09
Speaker 1: for clearly cometary, interstellar bodies, the two I-slash-Borisov class relative
1:10:15
Speaker 1: to Oumuamua-like objects. That points to discovery opportunities roughly once
1:10:22
Speaker 1: per decade as survey sensitivity climbs. In that frame, The
1:10:27
Speaker 1: appearance of 3I slash Atlas within a decade of 2I
1:10:31
Speaker 1: slash Borisov is not an outlier, but a reasonable draw
1:10:36
Speaker 1: from a small sample, boosted by the steady improvement of
1:10:41
Speaker 1: all sky searches. You can also reframe frequency by galactic provenance.
1:10:47
Speaker 1: The Milky Way thin disk supplies the bulk of visitors.
1:10:52
Speaker 1: These are the familiar motions of nearby stars that share
1:10:56
Speaker 1: the Sun's broad rotation around the galaxy. A smaller slice
1:11:01
Speaker 1: arrives from the older, dynamically hotter thick disk. A tiny
1:11:06
Speaker 1: fraction comes from the halo, and an even smaller fraction
1:11:11
Speaker 1: is unbound to the galaxy. Those categories are not just labels,
1:11:16
Speaker 1: they carry testable predictions. Thick disk visitors should, on average,
1:11:21
Speaker 1: move faster and be older. Unbound visitors would be extremely
1:11:26
Speaker 1: fast and extremely rare. 3I slash Atlas, with its high
1:11:32
Speaker 1: interstellar speed and possible thick disk ancestry suggested by population modelling,
1:11:39
Speaker 1: sits exactly where the tail of the distribution says it should.
1:11:44
Speaker 1: The rarity of that tale explains why objects with comparable
1:11:49
Speaker 1: speeds will be uncommon in any single decade of observation,
1:11:54
Speaker 1: but not impossible in a generation. Finally, do not confuse
1:12:00
Speaker 1: the rate of arrivals with the rate of announcements. The
1:12:04
Speaker 1: headline discoveries depend on survey, uptime, weather, moon phase, cadence,
1:12:10
Speaker 1: and community follow-up. A fast object that hugs low elongations
1:12:15
Speaker 1: during a lunar bright time may slip by. The practical
1:12:19
Speaker 1: lesson is that frequency questions have two answers. The physical
1:12:24
Speaker 1: rate in space is set by galactic dynamics and gravitational focusing,
1:12:29
Speaker 1: and it is already high. The observed rate on Earth
1:12:32
Speaker 1: is set by how and when we look, and it
1:12:36
Speaker 1: is poised to climb. If the Legacy Survey of Space
1:12:41
Speaker 1: and Time delivers even the conservative figure of roughly one
1:12:45
Speaker 1: to two interstellar objects per year, the community will accumulate
1:12:50
Speaker 1: a dozen to a few dozen solid cases across the
1:12:55
Speaker 1: next decade. If the population is steeper or brighter than assumed,
1:13:00
Speaker 1: the yield could be far larger, perhaps dozens per year
1:13:05
Speaker 1: in the best case. Either way, the interval between confirmed
1:13:09
Speaker 1: interstellar visitors is shrinking from years to months as the
1:13:13
Speaker 1: instrumentation improves. That is the real answer to how often
1:13:18
Speaker 1: we are visited. Often, already, and soon, measurably often. The
1:13:24
Speaker 1: upshot for night science stories is simple. There is nothing
1:13:29
Speaker 1: exceptional about the arrival of an unbound body. The exceptional
1:13:33
Speaker 1: part is our growing ability to spot them before they
1:13:37
Speaker 1: rush past. A flow on the order of several per
1:13:40
Speaker 1: year within Earth's orbit is already a given from stellar kinematics,
1:13:46
Speaker 1: a detection rate of many per decade. is a reasonable
1:13:50
Speaker 1: near-term expectation. 3. I slash A-T-L-A-S is a bright example
1:13:57
Speaker 1: caught in the Act. With the next generation surveys, it
1:14:01
Speaker 1: will not be alone in our catalogues for long.