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Cosmic Collisions: Asteroids, Comets, and the Science of Planetary Defense · Star Trails: From Backyard Astronomy to Cosmic Wonder

• 0:00
  Howdy stargazers and welcome to this episode of Star Trails.
• 0:12
  I'm Drew and I'll be your guide to the night sky for the week starting March the 2nd through
• 0:17
  the 8th.
• 0:19
  This week Mercury makes its presence known on the western horizon.
• 0:23
  We check in with the Blaze Star and with recent talk of a potential asteroid collision with
• 0:29
  Earth, spoiler alert, it's not going to hit us.
• 0:33
  We'll take a detailed look at space rocks, their dangers, and what can be done about them.
• 0:39
  So grab a comfortable spot under the night sky and let's get started.
• 0:45
  We begin the week with a beautiful crescent moon in the western sky, just three days past
• 0:51
  new, glowing at about 10% illumination on the evening of March 2nd.
• 0:57
  By March 7th the moon reaches its first quarter phase making it a perfect target for binoculars
• 1:03
  or a small telescope as its craters and mountain ranges cast dramatic shadows along the terminator line.
• 1:11
  Planets are putting on a show this week too.
• 1:14
  Venus now in retrograde will shine brilliantly in the western evening sky after sunset and on March
• 1:21
  the 2nd it will form a stunning pairing with the crescent moon.
• 1:25
  So be sure to step outside and catch that celestial duo.
• 1:30
  Meanwhile, Mercury is making a rare and fleeting appearance, reaching its greatest eastern elongation
• 1:37
  on March 8th, meaning it will be at its best visibility for this period.
• 1:42
  Look low on the western horizon shortly after sunset and you just might spot this elusive inner planet.
• 1:57
  We still have our eyes on T Corona Borealis, a star system that could erupt into a rare nova
• 2:04
  at any moment.
• 2:05
  This binary star located in the constellation Corona Borealis goes nova roughly once every 80 years,
• 2:14
  meaning it might become visible to the naked eye for the first time since 1946.
• 2:21
  Known as the blaze star, T Corona Borealis is expected to brighten from a dim magnitude of 10
• 2:29
  which isn't visible to the naked eye to magnitude 2 which is as bright as Polaris.
• 2:42
  Today we're talking about space rocks, asteroids, comets, meteors, and everything in between.
• 2:51
  You might have heard the recent buzz about asteroid 2024 YR-4,
• 2:56
  which briefly made headlines when early observations suggested a slim chance it could hit Earth in 2032.
• 3:05
  Of course, more recent calculations ruled that out, reducing the risk to almost zero.
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  But it got me thinking, what else is out there, flying through space, occasionally paying our planet a visit?
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  From the massive asteroid that wiped out the dinosaurs to the Tunguska explosion that flattened a forest in Siberia,
• 3:26
  these space rocks have shaped Earth's history.
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  And speaking of dramatic impacts, we can't forget Comet Shoemaker-Levy-9, which slammed into Jupiter in 1994,
• 3:39
  giving us front-row seats to a cosmic collision of epic proportions.
• 3:44
  So let's break it all down. What are these objects? Where do they come from? And should we be worried about them?
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  First up, asteroids.
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  Asteroids are rocky leftovers from the early solar system, basically the building blocks that never quite became planets.
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  Most of them orbit in the asteroid belt, a vast region between Mars and Jupiter that's home to millions of these space rocks.
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  Ranging from tiny pebbles to giant bodies hundreds of miles wide.
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  Some famous asteroids include Ceres and Vesta, which NASA's Dawn spacecraft studied up close.
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  Ceres is particularly interesting because it's large enough to be classified as a dwarf planet.
• 4:32
  And scientists suspect it may have a subsurface ocean, hinting at the possibility of past or present life.
• 4:39
  To learn more about Ceres, go back and check out Episode 46.
• 4:44
  While most asteroids stay put in the asteroid belt, some venture closer to Earth.
• 4:50
  These are called Near-Earth Objects, or NEOs.
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  This includes asteroids like Apophis, which once sparked fears of a collision in 2029,
• 5:01
  though we now know it will safely pass by.
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  That brings us back to 2024, why are for?
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  When it was first discovered, its orbit was uncertain and there was a slim chance it could impact Earth.
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  But thanks to follow-up observations, astronomers refined its trajectory and ruled out any danger for now.
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  That's exactly why space agencies like NASA and the European Space Agency tracked thousands of NEOs.
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  Ready to sound the alarm if one gets too close.
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  Space rocks hit Earth's atmosphere every day, but most of the time they burn up as meteors, what we call shooting stars.
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  But sometimes they're big enough to cause real damage.
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  The most famous example is the Tunguska event of 1908, when a meteor, probably 60 to 100 meters wide,
• 5:54
  entered Earth's atmosphere over Siberia and exploded 3 to 6 miles above the ground.
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  The blast flattened 800 square miles of forest with an energy release similar to a nuclear bomb.
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  For years, this event was a mystery.
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  No impact crater was ever found because the object exploded in mid-air.
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  A phenomenon called an air burst.
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  If this had happened over a major city, the destruction would have been unimaginable.
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  Now, fast forward to 2013, when something eerily similar happened over Chelyabinsk, Russia.
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  A 20 meter wide meteor entered the atmosphere at more than 40,000 miles per hour.
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  Creating a brilliant fireball that was briefly brighter than the sun.
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  Almost 30 kilometers above the city, it exploded with the force of 30 atomic bombs,
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  shattering windows and damaging buildings across six Russian cities.
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  Unlike Tunguska, this event was caught on thousands of dash cams,
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  giving us an unprecedented look at a real-life meteor explosion.
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  The shock wave injured 1,500 people, mostly from shattered glass,
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  serving as a stark reminder that even small space rocks can pack a serious punch.
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  The most infamous asteroid impact in history that we know of was the one that made the dinosaurs extinct.
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  66 million years ago, an asteroid roughly 6 miles wide slammed into what is now the year of the 19th century.
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  The impact created a crater, an enormous scar over 90 miles across.
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  The explosion released as much energy as 10 billion Hiroshima bombs.
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  It triggered tsunamis, wildfires and a global dust cloud that blocked out the sun, causing temperatures to plummet.
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  In the aftermath, nearly 75% of the earth's surface was destroyed.
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  In the aftermath, nearly 75% of all life on earth, including the dinosaurs, went extinct.
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  This single event reshaped evolution, clearing the way for mammals and eventually us to take over.
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  And here's the wild part.
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  Impacts of this magnitude aren't just ancient history. They could happen again.
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  Scientists estimate that asteroids large enough to cause global devastation hit earth every few million years.
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  Through the years, NASA has studied ways to alter the course of asteroids.
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  The most successful test of this has been the DART mission.
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  DART stands for Double Asteroid Redirection Test.
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  And in 2022, it became the first ever attempt to intentionally alter the trajectory of an asteroid.
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  The target was a small asteroid called Dimorphos, which orbits a larger asteroid named Dytamos.
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  Neither of these were a threat to earth, but they made the perfect test case for an asteroid deflection experiment.
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  NASA launched the DART spacecraft, a small probe about the size of a refrigerator,
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  and sent it crashing into Dimorphos at more than 14,000 miles per hour.
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  The idea was simple. If we could hit the asteroid hard enough, we could change its orbit just slightly.
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  And it worked.
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  Before impact, Dimorphos took 11 hours and 55 minutes to orbit Dytamos.
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  After the collision, that orbit shortened by 32 minutes, a much bigger change than scientists expected.
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  So how do we actually move an asteroid?
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  It comes down to momentum transfer, essentially a cosmic game of billiards.
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  When DART hit Dimorphos, it transferred its momentum into the asteroid.
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  But that's not all. What really made a difference was the ejecta.
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  The impact sent thousands of tons of rock and dust flying off into space,
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  creating a kind of recoil effect that amplified the push on the asteroid.
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  This was a huge breakthrough because it proved that if we ever find a real asteroid on a collision course with Earth,
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  we might be able to nudge it away given enough time.
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  DART was just the beginning.
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  Future missions like ESA's HERA probe will return to Dimorphos in 2026 to study the aftermath and help us redefine asteroid deflection techniques.
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  Another way to potentially move an asteroid is using a so-called gravity tractor.
• 10:54
  This sounds like science fiction, a Star Wars tractor beam, maybe.
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  But it's actually based on the physics of gravity and how the mass of two objects affect one another.
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  Instead of slamming an asteroid at high speed, a gravity tractor spacecraft would hover near the asteroid and slowly pull it off course.
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  Here's how that works.
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  We send a heavy spacecraft to a threatening asteroid, big enough that its gravitational pull can have an effect.
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  The spacecraft parks near the asteroid, but instead of touching it, it hovers at a close distance.
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  Even though the spacecraft is small compared to the asteroid, it still has mass,
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  and its gravitational pull subtly tugs on the asteroid over time.
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  Over years or even decades, this tiny but constant force slowly nudges the asteroid off its collision course with Earth.
• 11:55
  Of course, this method only works if we detect an asteroid threat decades in advance because the gravitational pull is very small and takes a long time to make a difference.
• 12:06
  It also requires a spacecraft with significant mass, which means launching a heavy probe into deep space, something that would take a lot of planning and resources.
• 12:18
  While Hollywood loves the idea of blowing up asteroids with nukes, Armageddon style, in reality, a gentle nudge decades in advance is a much safer and reliable way to protect our planet.
• 12:33
  If asteroids are the rocky leftovers of the solar system, comets are the icy wanderers.
• 12:40
  Comets are made of frozen gases, dust, and rock. They come from the Oort cloud and the Kuiper Belt, regions far beyond Neptune, where billions of these icy bodies orbit.
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  When a comet gets close to the sun, the heat causes its icy surface to sublimate, turning directly from solid to gas.
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  This creates the beautiful glowing coma and dust detail we see from Earth.
• 13:08
  Unlike asteroids, comets don't usually pose a threat to Earth, but every once in a while, a rogue one might swing too close for comfort.
• 13:17
  One of the most dramatic cometary events ever witnessed was the Shoemaker-Levy 9 impact on Jupiter in 1994.
• 13:27
  This comet had been torn apart by Jupiter's gravity and over six days its fragments slammed into the gas giant, creating massive explosions larger than Earth itself.
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  The scars seen in Jupiter's atmosphere lasted for months.
• 13:44
  This was the first time humans had ever witnessed an impact between two solar system objects in real time, and it showed how Jupiter acts as sort of a cosmic vacuum cleaner,
• 13:56
  sucking in potential threats before they reach us.
• 14:00
  Before we wrap up, let's talk about Earth's second moon. Well, sort of.
• 14:06
  Recently, astronomers discovered 2024 PT-5, a small asteroid that's been caught in Earth's gravity, temporarily making it a mini-moon.
• 14:18
  Unlike our actual moon, it won't be here long. It'll likely drift away within a few months.
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  Earth has had several of these temporary moons over the years. They're tiny, often no bigger than a car, and eventually slip away.
• 14:34
  Perhaps one day they could be targets for future space missions.
• 14:39
  I mentioned these mini-moons in more detail back in episode 38, in a discussion of orbital resonances in our solar system, so if you missed it, go back and give it a listen.
• 14:55
  If you found this episode helpful, let me know and feel free to send in your questions and observations.
• 15:01
  The easiest way to do that is by visiting our website, startrails.show.
• 15:07
  This is also a great way to share the show with friends. Until next time, keep looking up and exploring the night sky.
• 15:15
  Clear skies, everyone!