Thursday, October 13, 2011

Why It's Cool: Asteroid Vesta rocked by mighty impacts

Asteroid Vesta rocked by mighty impacts

A little bit of history, first:

Ceres was the first asteroid ever discovered.  It was found in 1801 by Giuseppe Piazzi, and was actually predicted by an earlier astronomer and mathematician, Johann Daniel Titius in 1766.  This prediction was reinforced by Johann Elert Bode in 1772, and the mathematical formula used has become known as Bode's Law.  (This was discredited when Neptune was discovered and didn't fit the model.)

Uranus was discovered in 1781, and it happened to fit Bode's Law, so the idea gained credibility, and the search for the "missing planet" in between Mars and Jupiter was on.  When Guiseppe discovered Ceres, he first took it as the missing planet, but conservatively announced it to be a comet.  However, its observed motions differed from all known comets up to that time, and soon even more objects like it were discovered, all in similar orbits between Mars and Jupiter.

In 1802, William Herschel first used the term asteroid (star-like) to describe Ceres and its kin, since the bodies could only be seen as points of light, even through a telescope.  A century later, almost 500 more had been discovered.  Today, 540,000 are catalogued with known orbits, and the list is always growing.  This video shows the discoveries of asteroids from 1980 to 2010.  You can see around the time computers were beginning to see use in astronomy when the screen explodes with pixels, each one a newly discovered object.

I'd like to make an important point here, one that flies in the face of that video, and a particular scene in Star Wars:  The Empire Strikes Back.  Despite Han Solo's amazing display of starship navigational skills, asteroid belts are mostly empty space, and in reality it would be difficult to find an asteroid within one.

In the asteroid discovery video, each pixel would be an object about 2 million miles across, which is about the size of the sun, far, far larger than any asteroid.  To show the asteroid belt in true scale, you'd need either microscopic vision to see the asteroids, or telescopic vision to be able to see objects at great distances.

During our own space program, 9 space probes have been sent through the asteroid belt with no complications from asteroids or debris.  Some have gone out of their way to find an asteroid to photograph.

On to the story at hand:

Vesta is the second-largest asteroid in the asteroid belt, after Ceres.  Ceres is so big it retains a roughly spherical shape and is now known as a dwarf planet, just like Pluto.  Vesta was first seen in 1807, the fourth asteroid discovered, and like other asteroids, it was only seen as a point of light by the best telescopes on Earth.  When Hubble was launched, it took a look at Vesta to get a better view.  Even Hubble could only capture a grainy, pixellated image, but it showed a mysterious flattened edge, possible evidence of a big impact.

Now that we have a satellite orbiting Vesta, a topographical map, which shows the different elevations on the surface, has been developed, and that shows us where the asteroid got hit and how badly.  It seems that Vesta has been struck twice in the same spot in its past by other large objects, leaving deep impact basins, one on top of the other.  It is thought that debris from these impacts make up 5% of the meteors that fall to Earth, a significant proportion.

And yes, I did say that the asteroid belt is actually rather empty, but that doesn't mean collisions don't happen.  They are very rare, to be sure, but the belt and the rest of the solar system have been around for a few billion years now, plenty of time for objects to crash into each other.

Studying asteroids can have a huge effect on life here on Earth, especially if one is discovered that could hit us.  If we continue to look for, map, and track asteroids in our neighborhood, we could spot the next dino-killer with enough time to react and push it out of our way, preventing global catastrophe.  The odds of this happening any particular year are infinitesimal, but the odds of it happening eventually are about 100%.  And if we spot that asteroid, I think we'll all be happy we were looking for it.

No comments:

Post a Comment