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12 March 2004

Editorial: Chasing rabbits on Mars

Forrest M. Mims III

Images of Mars made by telescopes and by visiting spacecraft have long stimulated the imagination of professional and amateur observers alike.

The images sent from Mars by the rovers Spirit and Opportunity are no exception, especially since they reveal some very unusual features and objects. For example, the numerous small spheres photographed by Opportunity created quite a stir. The preliminary consensus seems to be that the spheres have a watery origin.

A news item in the 5 March 2004 issue of the E-Bulletin included imagery of unidentified, tiny tubes in a section of rock ground by the rapid abrasion tool on the Opportunity. The news item also included an image of a strange, semicircular pattern in martian soil or rock. It required a full day of inquiries and more than a dozen e-mails before we traced the curious pattern to an imprint that was left behind after the Mossbauer instrument's faceplate was pressed into martian soil.

These Mars features have had an insignificant impact on the public compared to the Mars "bunny" photographed by Opportunity.

This mysterious little object featured a pair of ear-like projections. The bunny even moved between photographs. Because of its strange appearance and its obvious movements, the Mars bunny created quite a stir on the web.

There was so much interest in the bunny that NASA studied it in some detail. They measured the size of the bunny and how fast it moved between various photographs. They measured its spectral reflectance. When the bunny disappeared, NASA found that it was apparently hiding under Opportunity's landing platform.

All this is perfect material for those who thrive on stories about extraterrestrials and flying saucers. Depending on your point of view, fortunately or unfortunately there seems to be a simple explanation for the Mars bunny that does not involve life on Mars or a NASA cover up to hide the bunny after it was first observed. Instead, the bunny appears to be a piece of debris that fell or blew away from Opportunity's lander during or after its arrival.

So how does the bunny move? It is so light that it is easily blown about by martian breezes.

A NASA web report concludes that the rabbit's yellow color suggests it might be a fragment of one of the air bags. There are many other possibilities.

According to Rob Manning, lead engineer for entry, descent and landing, "We cannot say exactly where [the bunny] came from, but we can say that there are several possibilities: cotton insulation, Vectran covers and wraps from the airbag, Zylon bridle tensioning ties, or felt insulation from the gas generators."

Manning ruled out parachute fabric, explaining that the bunny does not appear to be blue enough to be the undyed nylon or red enough to be the dyed nylon of the parachute.

The real puzzle of the Mars bunny is how it attracted much more attention from some Mars enthusiasts than the astonishing rock ledge that rims the shallow crater in which Opportunity came to rest. Those rocks have proved to be a completely unexpected bonus for the scientists studying martian geology.

You can read NASA's report about the Mars bunny at http://marsrovers.jpl.nasa.gov/spotlight/opportunity/b19_20040304.html.

If you visit this site, be sure to click around until you find the raw image files sent back by both of the Mars rovers. Many of those amazing images are much more intriguing than the fluff of space debris dubbed the Mars bunny.