10 Things You Probably Didn't Know About Asteroids, Comets & Other Near Earth Objects

Many of you have probably heard about asteroid 2005 YU55, the massive rocky body that tomorrow night will collide with Earth in a ball of flames pass the planet safely, albeit closer than any asteroid in the last 35 years.

And while astronomers are certain we'll be spared this time, the brush with such a massive rock raises important questions about so-called near-Earth objects like asteroids, comets, and meteoroids. So without further ado, here are ten things you probably didn't know about our solar system's more minor bodies.


10. The difference between asteroids, comets, meteoroids, meteors and meteorites
Let's just get this out of the way, shall we? According to NASA's Near Earth Object (NEO) Program, a large, rocky body in orbit around the Sun is referred to as either an asteroid or a minor planet. Asteroids are thought to have been created in the "warmer" solar system, i.e. within Jupiter's orbit. Comets, on the other hand, are believed to have formed in the cold, outer solar system — beyond the orbit of our solar system's outermost planets.

Comets and asteroids also differ in composition, the most notable difference being the comet's possession of an icy nucleus, which, when subjected to the relatively warmer temperatures of the inner solar system, begins to vaporize, creating a distinctive glow called a "coma," and a long, bright tail of dust and debris. There are other features that distinguish asteroids and comets, but recent findings continue to blur the lines between the two.

Smaller Sun-orbiting particles, thought to originate from comets and asteroids, are known as meteoroids. When a meteoroid enters Earth's atmosphere, it usually vaporizes, becoming a meteor in the process (aka a "shooting star"). If a meteoroid is large enough to make it through Earth's atmo and make landfall without vaporizing completely, it's no longer a meteor, but a meteorite. The same goes for asteroids. (For more info, see NASA's NEO FAQ page, which is also the source of the handy chart featured here.)


9. Meteoroids: there's a lot of them
Seeing as a meteoroid can be classified as pretty much anything bigger than a speck of dust and smaller than an asteroid, it makes sense that there would be quite a few of them orbiting the Sun and burning up in Earth's atmo at any given moment. The International Space Station, for example is the most heavily shielded spacecraft ever to occupy Earth's orbit. Why? To keep its astronauts and equipment safe from meteoroids. It's estimated that 100,000 of the buggers will make contact with the ISS over the course of its 20-year stint in space, and while the majority of these wont measure larger than a centimeter across, medium size particles (between 1cm and 10cm across) still pose a grave threat to the space station and its crew, and call for impressive sounding defensive measures like "multi-layered hypervelocity Whipple shields." (For more info on the safety measures employed on the International Space Station, see this informational sheet prepared by NASA's Micrometeoroid and Orbital Debris (MMOD) Protection program.)


8. Your odds of getting smacked by a meteorite
They're slim, even if Earth is constantly being bombarded by meteoroids. The fact is that most of them simply don't survive long enough once breaking atmo to attain meteorite status, and those that do have barely any chance of actually hitting anybody. Such an event is only confirmed to have happened once, when Annie Hodges of Sylacauga, Alabama (pictured here) was struck in the hip by an eight pound meteorite after it crashed through her roof and bounced off a radio. Several studies have attempted to calculate the likelihood of a meteorite actually hitting a human target, taking into consideration everything from the average time a person spends outside to the amount of Earth's surface that the average person takes up. One of the most commonly cited figures is from a paper published in Nature in 1985, that calculates the rate of impacts to humans as .005 per year, or once every 180 years.

7. Why you need a telescope to spot 2005 YU55
YU55 is what's known as a C-type — or "carbonaceous" — asteroid, meaning it is especially rich in carbon. The composition of C-type asteroids makes them extremely dark (think darker than charcoal), and therefore difficult to spot with anything weaker than a telescope with at least a 6" mirror. (For those of you with scopes with this much imaging power, be sure to check our instructional on how to spot 2005 YU55 tomorrow night.)


6. 2005 YU55 could help us learn more about Panspermia
Panspermia is the hypothesis that the building blocks for life are found throughout the universe, and are carried around on asteroids, comets and the like. If you've ever heard someone say that life on Earth may have come from space, they were probably talking about Panspermia (or the related astrobiological hypothesis of exogenesis).

According to Dan Yeomans, manager of NASA's Near-Earth Object Program, the 2005 YU55 flyby presents a unique opportunity to learn about C-type asteroids, without which, Yeoman speculates, humans probably wouldn't exist. Since we rarely get an opportunity to see an asteroid so close (the last time we saw an asteroid like this so close to home was over 30 years ago), astronomers and astrophysicists the world over will be observing the asteroid to learn as much as possible about its composition. Objects like 2005 YU55 play an important part in the Panspermia hypothesis for their role in bringing carbon-based materials to a young Earth. If astronomers were to observe evidence that 2005 YU55 also harbors other organic materials (or even frozen water — see the note above about blurring the lines between asteroids and comets), it would go a long way in supporting the Panspermia hypothesis.


5. Getting hit by 2005 YU55 would suck
Ok, so you almost definitely knew this, but just how much would it suck, exactly? After all, Yoemans says that the NASA's Near-Earth Object program is "extremely confident, 100 percent confident" that 2005 YU55 will not make contact with Earth, but that doesn't mean we can't speculate over how catastrophic it would be were the asteroid actually to hit us.

Well, according to Jay Melosh, professor of Earth and atmospheric sciences at Purdue University, if 2005 YU55 were to hit the planet, it would likely produce a crater about 4 miles wide and 1700 feet deep, generating 7+ magnitude earthquakes and, depending on where it struck, devastating tsunami waves (for more info see Impact: Earth! which is based on Melosh's calculations).


Again, will this actually happen? No. But observing the asteroid will help us be better prepared for when one does plot a course for Earth. As Yoeman says, "this [asteroid] is not a threat... But it is an opportunity."


4. Speaking of catastrophic Earth-asteroid impacts, aren't we about due for one of those?
Maybe, but it's not likely. Some of you may have heard about an asteroid named Apophis. Astronomers believe Apophis to be 885 feet across, and estimate that on April 13, 2029, the asteroid will fly within 20,000 miles of Earth's surface — that's closer than the orbit of many of the planet's satellites.

Astronomers are confident that Apophis will spare us on its 2029 flyby, but say that there is a 1/250,000 chance that it will pass through a "gravitational keyhole" that would set the asteroid on course for a future planetary impact exactly 7 years later. Could it happen? Yes. Is it likely? No.


...But it could totally happen.

3. But Michael Bay told me we could deflect an incoming asteroid with nuclear weapons... we can do that, right?
Actually, yes. Back in 2007, NASA issued a report claiming that the best way to deflect asteroids and other near Earth objects away from Earth was with the use of nuclear devices... in space. Except NASA wouldn't do it by planting it in the asteroid's core, ala Armageddon, they'd do it by triggering the explosion in the vicinity of the asteroid. The power of the explosion would amounts to a nuclear-bomb-sized "nudge" capable of throwing the Asteroid off-course and preventing a collision with Earth.


2. We can even "finesse" an asteroid off a collision course with Earth. That is to say, WITHOUT the use of nuclear explosions...
...because some people think the idea of "weaponizing" space isn't such a good idea, chief among them being the group of astronauts and scientists comprising The B612 Foundation (The Little Prince, anyone?).


One of the methods of deflection proposed by The B612 Foundation is to launch a probe of significant mass (weighing 1—2 tons, but depending upon the size of the asteroid) and "parking" it in space — not on the asteroid, but near it. The gravity of the asteroid would pull on the probe, but the mass of the probe would be just enough to pull ever so slightly on the asteroid, as well.

If we were to move the probe very slowly with jet propulsion, we could, in theory, gently tug on the asteroid, "finessing" it into a safe orbit. (For more details on this approach, check out this brilliant TED talk on asteroids and the technologies we can use to deflect them away from Earth, delivered earlier this year by Bad Astronomy's Phil Plait at TEDxBoulder.


1. We have found almost all of the asteroids that pose a threat to Earth. We think.
Recent findings from NASA's WISE satellite indicate that there are actually far fewer asteroids and near-Earth objects threatening life on Earth than we once thought. What's more, the so called "Near-Earth Asteroid Census" found that 90 percent of NEOs have now been mapped, which should allow us to keep an eye on them in the event one decides to make a bee-line for Earth.

Top image by bulliver
Image of Annie Hodges via
Le Petit Prince cover art by Antoine de Saint Exupéry via
Artist's impression of Chicxulub impact by Donald E. Davis via
"DNA Toolkit" image via NASA


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