A hole in Mars

<blockquote id="quote"><font size="2" face="Verdana, Arial, Helvetica" id="quote">quote:<hr height="1" noshade id="quote"><i>Originally posted by PheoniX_VII</i>
<br />Quite possibly, the spots are entrances to deep underground caves capable of protecting Martian life, were it to exist.<hr height="1" noshade id="quote"></blockquote id="quote"></font id="quote">If they really were that dark, the more likely explanation is that these spots are the surfaces of pools of liquid hydrocarbons such as oil.

<blockquote id="quote"><font size="2" face="Verdana, Arial, Helvetica" id="quote">quote:<hr height="1" noshade id="quote">The above hole is about the size of a football field and is so deep that it is completely unilluminated by the Sun.<hr height="1" noshade id="quote"></blockquote id="quote"></font id="quote">There is no definite evidence for that claim in the HIRISE image. The contrast can be set for each individual photo. The terrain in that image has very little contrast, so the contrast settings for the image were probably stretched around a relatively small range. That means things that are normally various shades of gray can be rendered all black. (In the limiting case for contrast-stretching, all pixels become either all-white or all-black.)

Without examining the imaging details, it remains possible that the darkest pixels in this image are brighter than the avrage pixels in other images. Have any of our experts learned enough about image documentation to determine what the exposure range was for this image? -|Tom|-

The HiRISE project conveniently did the crop of the full resolution image of the hole for us. Here’s what they say about the object:

“The HiRISE camera is very sensitive and we can see details in almost any shadow on Mars, but not here. We also cannot see the deep walls of the pit. The best interpretation is that this is a collapse pit into a cavern or at least a pit with overhanging walls. We cannot see the walls because they are either perfectly vertical and extremely dark or, more likely, overhanging.

The pit must be very deep to prevent detection of the floor from skylight, which is quite bright on Mars.”

I did a little rough calculation myself and got ~200 m wide for the hole. And if you notice around the edges you can see the visible part of the Martian crust; one side is in the shade and the other side is in the sun. If you assume that the visible part of the crust is foreshortened in our view of it, and assume that it slopes downward at a 45° angle, then the crust around the hole is ~4.5 m, or ~14 ft thick.

One is reminded of a hole cut in ice—like the kind you make when you go ice fishing. What’s underneath? Maybe a large cavern left over from ancient volcanic activity.



[Edited]

The data for the map-projected image also states that it is 3:27 PM on Mars, which is consistent with the right side of the crust-cut around the edge of the hole producing a bright glare, and the left side crust being in shadow. But we can see the shaded part as a dark grey—not black. Therefore I agree with HiRISE that the walls must be overhanging. If the walls were vertical or sloped toward the hole center, we would be able to see good evidence of it in the form of reflected light.

If this were a large pool of hydrocarbons, say a tar pit, coming to the surface we would expect to see some reflection of light. I can’t look this up now but I seem to recall that there are instruments on board the MRO capable of measuring the depth of the cavern bottom. It seems to me that this would be a great avenue of research that the public would be very interested in.

This is more than a little interesting. I agree with Neil's objection to the liquid pool idea. But none of the other proposed explanations is very satisfying either. For example the overhanging walls idea runs into material strength issues:

*) How much bigger than the hole must the cavern be to prevent us fron seeing the recessed walls or the bottom?
*) Them, compare that to how much overhang can exist in Martian crust material (or in solid rock, or in solid steel) before its weight causes it to break?

I have not tried to run any of the numbers, but I'm going to guess that the first question requires a cavern that is at least 2X larger than the hole, and the second question requires a cavern that is no more than 1 or 2 percent larger than the hole.

Dang. Where's a rover when you REALLY need one?

www.lpi.usra.edu/meetings/lpsc2007/pdf/1371.pdf
www.planetary.org/blog/article/00000984/

Above are links to two articles/papers on this object and other similar holes in the Martian landscape, which were imaged previously by THEMIS.

“Analyses of the candidates suggest that they are not of impact origin, not patches of dark surface material, and are likely skylight openings into subsurface cavernous openings…Thermal inferred data suggests temperatures inside these features that remain constant throughout each diurnal cycle (i.e., each day and night—parenthesis added).” The temperatures inside these caverns are warmer at night and cooler during the day than surface temperatures, properties consistent with subterranean caverns, especially on Mars where surface temperatures would fluctuate widely due to the thin atmosphere.

I would think that the explanation is obvious:

"Just after Dr. McCoy is diagnosed with a fatal illness, the ship encounters a spaceship disguised as an asteroid, on course with a populated planet. When the command team beams over to try to stop a collision, they must contend with the computer oracle which controls the inhabitants of the ship, of whom McCoy becomes one when he elects to remain there after falling in love with the high priestess." From <i>'For the World Is Hollow and I Have Touched the Sky</i>' The Original Star Trek Series.

Obviously Mars is a spaceship.

rd

I have read both of the posted articles, good literature research Neil. Does anyone know if any Mars orbiting probes have X-band or Ku-band ground penetrating radar aboard? Also, just a comment, any discussion of structural intergrity must integrate several facts when talking about overhang: a) lower gravity than earth, so adjust calculations. b) These caves are part of shield volcanoes, the crust in a shield volcano on earth is basaltic (magma low in silica). c) these could be side vents blasted from gaseous escape (are there debris fields that suggest this?)

Please comment on these ideas.

Mark