Comet-Chasing Spacecraft Encounters Rare Asteroid

Riding with Robots writes "Yesterday the robotic spacecraft Rosetta, on its way to a distant encounter with Comet Churyumov-Gerasimenko, flew by the asteroid 'Steins,' which is roughly 4.6 kilometers wide. Steins is one of the relatively rare E-type asteroids. The mission team live-blogged throughout the day, and a press conference with the first pictures will be available soon." Rosetta's flyby took it to within 800 kilometers of Steins while both objects were roughly 360 million kilometers from Earth. According to Rosetta's fact sheet (PDF), the craft will next swing by Earth in 2009 and take a look at another asteroid in 2010 on its way to the rendezvous with the comet in 2014.

Comments

Relatively rare?

[bigtallmofo]

Steins is one of the relatively rare E-type asteroids.

The summary says they're rare, but the Wikipedia article indirectly linked says they form a majority of the asteroids "inward of the main belt". I'm very confused!

http://en.wikipedia.org/wiki/E-type_asteroid

E-type?

[cheebie]

From the linked Wikipedia entry:

# X-group

        * M-type (16 Psyche) metallic objects, the third most populous group.
        * E-type (44 Nysa, 55 Pandora) differ from M-type mostly by high albedo
        * P-type (259 Aletheia, 190 Ismene; CP: 324 Bamberga) differ from M-type mostly by low albedo

So, the probe has encountered a shiny metal asteroid. Has anyone informed Bender?

Re:E-type?

[knutkracker]

So, the probe has encountered a shiny metal asteroid. Has anyone informed Bender?

Fron Wikipedia:

M-type asteroids are asteroids of unknown composition

E-type (44 Nysa, 55 Pandora) differ from M-type mostly by high albedo (0.3 or better)

"Bite my moderatley-reflective mystery-material ass-teroid"?

Some Nice pictures

[mbone]

Here are the first results. The asteroid has a nice crater chain on it and looks roughly like a cut diamond.

Re:Some Nice pictures

[meringuoid]

This series of craters really looks strange. What's the probability of this?

A lot of asteroids are fairly loosely built, more like heaps of rubble than large boulders. So: let such an asteroid have a close encounter with a planet on its travels, let us say Jupiter. Let it pass close to the planet, and be torn apart by tidal forces, and then escape on the other side. It's now a strung-out row of smaller bodies - remember Shoemaker-Levy 9? Then passing through the main asteroid belt, let it collide with a more solid asteroid. Result: a chain of impact craters.

You see similar things on larger bodies - there are impact chains on the Moon, for instance - but these are attributed to debris ejected from a larger impact falling back to the surface further along from the impact site. On an asteroid I doubt gravity would pull anything back, so we'd need a third party to have arranged for a series of impacts instead.