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.)