"Unusual spires on Comet Wild2" APOD 22nd June 2

[JohnD]

All,
Today's APOD describes 'spires' on this comet, and seems very surprised to find them. One can't reply there, so I must here.

"Spires" in ice are not unusual, in fact they are well known, in glacier ice that has sublimed, in sunlight and in a very cold atmosphere. The same mechanism could account for cometary ice spires.

See a picture of ice spires here: http://www.kfunigraz.ac.at/geowww/geoskript/Seiten/pix/buesserschnee.jpg
JOhn

[Moose]

See a picture of ice spires here: http://www.kfunigraz.ac.at/geowww/geoskript/Seiten/pix/buesserschnee.jpg
JOhn

John, I'd looked at the photo before I fully read/comprehended your description. Imagine my susprise at seeing that fellow standing in the ice spires on Comet Wild2. :o 8-[

I can't speak towards the rarity of ice spires on earth or in space, but that is a pretty cool photo.

[Irishman]

linky linky
http://antwrp.gsfc.nasa.gov/apod/ap040622.html

From here:
http://www.jpl.nasa.gov/news/news.cfm?release=2004-154
The diameter of one large crater, called Left Foot, is one fifth of the surface of the comet. Left Foot is one kilometer (.62 miles) across, while the entire comet is only five kilometers (3.1 miles) across.

But that doesn't match the picture:
http://www.jpl.nasa.gov/images/comet/pia06285-browse.jpg

In the picture, Left Foot is small - Right Foot is bigger. Shoemaker Basin comes closest to the description, with Walker being second. Out of what's visible.

[ToSeek]

It's a bogus comparison anyway: diameter is not linearly related to surface area. Even given the figures, the surface area of the comet would be 78 square kilometers while the area of the crater would be 0.75, a factor closer to 100-to-1 than 5-to-1.

[beskeptical]

There is also a big chunk (http://www.sfgate.com/cgi-bin/object.cgi?paper=chronicle&file=MNGP278BIA1.DTL&di rectory=/c/a/2004/06/18&type=news&object=/chronicle/pictures/2004/06/18/mn_wild2_2vuz.jpg) missing from one side of the comet that is pretty wild. At first it just looks like shadow, but then you see the jet and realize it isn't shadow, there isn't a piece of rock, (or ice), there.