The "Yeti" figure in the photo from Gusev Crater.

One of the hottest topics circulating around the blogosphere over the
past 12 hours or so has been the discovery of a human-like figure found
in a photo taken by the Mars Exploration Rover Spirit at its current location
at Gusev Crater.

Some have been saying that the figure, which has been dubbed a Yeti by
enthusiasts, could point to the existence of life on Mars. NASA itself
hasn't said anything about all this yet, but most internet analysts are
confident that the Yeti is merely a rock that has been shaped by

Now I don't want to spoil anybody's fun. But let's look at the evidence.
First, take a look at the figure itself, which I have cropped from the
original high-res NASA photo. In the NASA photo the figure occurs right
around the 860 pixel X 2200 pixel point.

Notice the position of the blue cross-hairs, which are my addition.

Now look at the same area of the photo zoomed back one step.

And now zoomed back another step.

Notice the size of the small rocks in front of the rover in comparison to the
position of the so-called Yeti.

Perspective, of course, will make things in the distance look smaller.
If you were to stand on the lip of the Ballinger meteor crater in Arizona,
for example, things would appear very tiny at the bottom of the crater
to your eyes. And I know, because I've been there and have done that.
The question is whether that is operating in the Mars photo.

The MERs use a camera with a 43 mm lens. Thus the perspective distortion
common to wide-angle lenses (which make objects close to the lens look
larger) or to telephoto lenses (which shorten the apparent distance) does
not come into play. A 43 mm lens is a very "naturalistic" lens when
compared with what we normally see with our human eye.

If we were standing where the MER is sitting using our neked eye, the
distance from the Yeti to the rover does not appear to be very great.
The fall-off in front of the rover would have to be very severe indeed
to make anything like a human-sized figure look that tiny. And, assuming
that there isn't that severe of a terrain fall-off, and it doesn't appear
that there is when compared to the solar panel or the rocks in the photo,
that would mean that the Yeti (I actually think it looks more like a Fremen
in Frank Herbert's Dune wearing a stilsuit) is very tiny indeed. We're
probably talking Tom Thumb or Fairy size for the thing, maybe even smaller.

Okay. So what are the odds of ancient fairies on Mars who wear stilsuits?
Uh, I leave that one to you.

As if we didn't have bigger things to worry about.

In related news, I did a post here recently about the incredibly hardy
Mars rovers Spirit and Opportunity, who have gone long past their
expected life-spans. Now it seems that NASA is joining in the celebration
of their 4th anniversary by issuing a special patch. Pretty cool, huh.

Happy Birthday to the rovers!