Cool Planets #3: New Asteroids

Centaurs and Trojans are zooming around the sun. (No joke!)

There are a whole lot of other blobs racing around the same orbit as Jupiter and traveling just as fast as it does. (I'm serious!)

The asteroids have been sprung loose from their old location in the gap between the orbits of Mars and Jupiter. (Well...kinda.)

Allow me to explain. Maybe you were taught that there are lots of asteroids--rocky, irregularly shaped objects--and these mostly reside in a band between the orbits of Mars and Jupiter. And that these asteroids are presumably debris that never coalesced into a planet or the result of a planet that fell apart.

Well it turns out that there are lots of asteroids and things like them all over the solar system and not just in the Mars-Jupiter gap. The ones that orbit beyond Jupiter (but inside of Neptune) are called Centaurs. They tend to be balls of frozen gas rather than rocks. Just as Jupiter and the planets beyond it are mostly made of liquid and frozen gases, while the planets inward from Jupiter are rocky.

Now a bunch of these Centaurs go around in the same orbit as Jupiter, and they are all either one-sixth of an orbit ahead of Jupiter or one-sixth of an orbit behind it. These are called Trojan Centaurs or Jupiter Trojans. Pretty darn strange if you ask me!

Why do they go around exactly 60 degrees (one-sixth of of an orbit) ahead of or behind Jupiter? Well that's called a Lagrangian Point and there are mathematics that make Lagrangian points special and help keep Trojans from getting absorbed by gravity into the main object in the orbit. Look it up if you want to know more.

These Trojans go around in a kind a swarm, where they stay generally in the same position relative to Jupiter, but move around in the swarm under continual "nudges" from the gravity of the individual Trojans and the planets.

Neptune is the other planet with known Trojans. Just six of them have been spotted. All are "ahead of" Neptune, none are in the trailing Langrangian point. But astronomers think Neptune may turn out to have ten times as many Trojans as Jupiter.

Some of Saturn's major moons have smaller Trojan moons that orbit with them. They cluster in the Lagrangian points of the major moon's orbit around Saturn (not the Lagrangian points in Saturn's orbit around the Sun).

Are there any Earth Trojans keeping us company in the Lagrangian points of our orbit around the Sun? Astronomers have looked but so far all they've found is some "Lagrangian dust".

I found all this cool new stuff out when I helped my daughter with her astronomy homework. The Solar System has "gotten" a lot more complex and mysterious since I studied it in elementary school.

It is "so last century" to think of of asteroids as an orderly procession of rocks that dutifully parade around the Sun in the gap between Mars and Jupiter. Now we know that there are lots of small rocky or icy objects orbiting everywhere from Mercury to way beyond Pluto.

And some of them do amazing stunts like "racing" Jupiter around its own orbit--all the while keeping a precise "mathematically safe distance" behind or ahead of their huge competitor. A competitor whose powerful gravity wants to suck them in and devour them in its thick soupy atmosphere.

Actually, the Jupiter Trojans are only temporarily safe, but that's another story.