Chris Clark wrote:

While perusing one of the big (eleven-thousand-pixel-wide) panoramic images assembled from the individual images sent back by Spirit ( http://photojournal.jpl.nasa.gov/catalog/pia05049 ), I'm wondering why I don't see "tracks" left in the surface by the airbag-encased lander as it bounced and rolled to a halt. Are "tracks" there and I'm just failing to notice them? Is the surface so hard that no tracks would have been left? Have any such tracks been erased by wind? Other ideas?

They are there but "bounce marks" might be a more descriptive term than tracks as they look more like splotches instead of tracks. The most obvious ones are in the depression called Sleepy Hollow. See http://marsrovers.jpl.nasa.gov/gallery/press/spirit/20040105a/PIA04991.jpg . Sleepy Hollow is the light colored area at the far right side of the image. The bounce marks are the two irregular shaped dark spots, one in the center of the Hollow and one near the Hollow's edge, nearest the lander. The marks show up much better in the more recent high resolution color images (see below). I used the above image as an example since it's small and downloads quickly. BTW, in one of the press conferences it was announced that the airbag cocoon bounced 28 times over 57", moving (bouncing) from NW to SE. They also mentioned that during the parachute descent it was descending about 50 km/hr faster than a skydiver on Earth while still in freefall (again, this was when the parachute was *open*).

On a slightly different topic, when looking at the Mars images, is there a method one can use to orient the images (i.e. how do we tell which way is, say, "north")? Yes.

Browse image http://marsrovers.jpl.nasa.gov/gallery/press/spirit/20040113a/Horizon_hills_... Medium Image (687 kB) http://marsrovers.jpl.nasa.gov/gallery/press/spirit/20040113a/Horizon_hills_... Large Image (6.8 MB) http://marsrovers.jpl.nasa.gov/gallery/press/spirit/20040113a/Horizon_hills_... Patrick