I’ve noticed a few articles on comets and asteroids doing the rounds at the moment, so I’ve gathered them all here rather than do loads of posts.
Asteroid TC3 2008 might not be an evocative name, but the piece of rock was spotted shortly before it entered Earth’s atmosphere, allowing a rare glimpse of an asteroid as it travels through space before hitting the Earth. The thing exploded over the desert in Sudan and 222kg of it were recovered, allowing meteors as they are normally found to be studied knowing how the asteroid appeared in our telescopes. This was the first time a definate link could be established between the results of the laboratory and those of the telescope.
Examination of the pieces has yielded interesting information. Not only is the asteroid of a rare type, but it’s a bit of an oddball even for these rare types. It contains signs of having been blasted off a larger structure by a powerful impact, with the mineral olivine turned to iron and carbon heated to the extent of producing nanodiamonds. Organic materials such as amino acids survived both this and the tumble down to Earth.
And tumble was the word. Looking at how the brightness (magnitude) changed in the telescope eyepiece, the astronomers determined that the asteroid was shaped like ‘a loaf of walnut-raisin bread’, tumbling over and over. As the Sun reflected off the changing apparent size of the thing, the brightness altered.
A movie or two of the asteroid in space as well as further information on the topic can be found in this Astronomy Now article and related links.
Using the same idea as above, astronomers at Lowell Observatory have measured the rate at which the nucleus of comet 10P/Tempel 2 spins. The nucleus is shaped like a rugby ball and if you look at it end on, you see a smaller area than a side view gives, this means less light is reflected in your direction and so the thing dims. Using this to clock the rotation rate, a team led by David Schleicher determined that the comet’s spin has declined by a rate equivalent to ten seconds every five years.
Tempel 2 is described as a fairly anemic old comet, developing a crust of inert materials after many travels round the Sun removed the volatiles in the original article.
One rather more pristine comet was Lulin, travelling in from its home a light year away, this comet visits once in a million years and became naked eye visible in February. Its progress through the solar system was rapid, allowing little time for observations, but a team at Lowell managed it. Unlike the two objects above, Lulin’s rotation rate wasn’t measured by changing brightness. As it was new to this Sun warming it up thing, the comet vented some unusual chemicals, cyanogen, from holes near the poles. These holes could be tracked from their exhaust, not only allowing the rotation rate to be studied, but maybe even allowing a 3D model of the surface to be built up, according to this Discovery News article.