Wild 2

Paolo Ulivi writes:

I can't say I am very much into cometary geology, but this is my
interpretation of the Stardust pictures of Wild 2: no one would have
expected such an heavily cratered body.

It's premature to call the features you see "craters". At the press
conference yesterday, it was noted that they could be erosion features.
The highest resolution images should help to distinguish the cases.

Paolo Ulivi wrote:

I can't say I am very much into cometary geology, but this is my
interpretation of the Stardust pictures of Wild 2: no one would
have expected such an heavily cratered body. Remember that until
1974 Wild 2 was orbiting between Jupiter and Uranus and this is
only its fifth perihelium at a distance from the sun small enough
to "activate" the nucleus. It seems to me that it will turn out to
be difficult to explain the number of craters since the comet spent
so much time beyond Jupiter, in a region of the Solar System where
impacts should be rarer and less energetic than in the inner Solar
System.

I don't see anything surprising or difficult to explain at all.
If Wild 2 was never closer to the Sun than Jupiter before 1974,
and was in 1974 in essentially the same condition it was in four
or five billion years ago, then most of the craters could be be
four or five billion years old. I would expect *every* solid
body to be 100% covered with craters unless and until something
obliterates them.

What strikes me also is that Halley and Borrelly were far less
cratered than Wild 2.

Is it possible to tell that from the pictures of Halley and
Borrelly? If so, apparently those comets have lost a lot more
surface material to evaporation by solar heating, obliterating
the primordial craters.

-- Jeff, in Minneapolis

..