Massive Cave Found on Mars

mrcgran writes "Space.com is reporting a very deep hole found on Mars: 'The geological oddity measures some 330 feet (100 meters) across and is located on an otherwise bright dusty lava plain to the northeast of Arsia Mons, one of the four giant Tharsis volcanoes on the red planet. The Mars Reconnaissance Orbiter (MRO) used its High Resolution Imaging Science Experiment (HiRISE) instrument to draw a bead on the apparent deep hole — a feature that may cause more scientists to ponder about potential subsurface biology on Mars. Because the spot lacks a raised rim or tossed out material called ejecta, researchers have ruled out the pit being an impact crater. No walls or other details can be seen inside the hole, and so any possible walls might be perfectly vertical and extremely dark or — more likely — overhanging.' The original image and its cutout at full resolution can be found in the HiRISE site."

Comments

Floor seen on one image

[dwarmstr]

If you read the preprint (PDF), you'd note that luckily, one of the caves actually was imaged with the floor sunlit, giving the authors the ability to calculate the depth of that particular cave. This was covered on May 23rd on the Planetary Society blog.

Re:Floor seen on one image

[FiloEleven]

And for those interested in the depth of that cave, it is estimated to be ~130 meters. Additionally, temperatures inside these openings (of which there are seven) appear to be more stable than on the surface.

Re:Oh man

[PFI_Optix]

Y'know, if the UAC would follow a few simply rules of planetary colonization, they wouldn't have such problems.

1) When your life depends on the structural integrity of your base/space station, keep it well lit. Dark corners and unlit passageways invite unobserved problems and make excellent hiding places for demonic hordes.

2) Emergency lighting is your friend. Self-contained lights that can run off batteries for days have existed since the 20th century. USE THEM.

3) Teach your space marines how to use a pistol and flashlight at the same time. Television actors pretending to be cops can do it, so can they.

4) Keep hidden compartments, passageways, and crawlspaces to a minimum. This will drastically reduce construction and maintenance costs by keeping the design simple, and make it far easier for a lone marine to save all of humanity.

5) Develop lockdown procedures. They're useful in the event of a sudden loss of pressure to prevent your entire base from leaking air out a single fracture. They can also come in handy when your absurd experiments fail and you find yourself surrounded by blood-thirsty monsters. Seal all the doors. Combine this with #4 so that they can't simply bypass the doors by crawling through unnecessarily large ventilation shafts or open ceilings.

Lava Tube

[jnaujok]

Given the fact that it's on the side of a volcano, and the fact that it's in the middle of a lava field, the most likely answer is that it opens into a lava tube. Most likely a small meteorite hit the center of the circle and caused a circular fracture that fell into the underlying tube.

Re:Lava Tube

[jnaujok]

1. the opening would be elongated along the axis of the tube

Possibly, but only if the size of the hole is similar to the size of the tube. If this is a shot through the "ceiling" and doesn't come close to the walls, (and if the Dena guess of 130m for the diameter of the cave is close) then this could easily be just a punched "skylight". If the tube is, in fact, even larger, then it might very well be possible to see no difference in the edges. Lava tubes, at least from the data I've seen, tend to have mostly flat ceilings and are not purely cylindrical.

2. it should be more cracked and irregular since there would be little surface erosion to smooth things out

Actually, I'd expect that with only gravity to do it's work, and if it was caused by a meteor impact, that the shape would be almost perfectly circular, with any further cracks being either covered by the pervasive Martian dust (see the Spirit and Opportunity data.) Also, impacts in stone tend not to make many cracks (see this image for an example of how cement breaks. Admittedly volcanic basalt is not concrete, but the idea is similar. Also, how long has this cave been here? A thousand years, a million, a billion? It could be just about any of the above.

3. lava tubes tend to be fairly shallow so the bottom should be visible

Lava tubes tend to be shallow on Earth. However the Ape Cave lava tube in Washington is clearly at least as deep as it is wide [See here], and since we can't see walls on a 100m wide image, we can assume (and I know all about that word) that it might easily be 100m deep. Also, seeing the bottom depends on lots of factors. What is the angle of the sun (hard to tell from the lack of shadows) and the resulting angle to the spacecraft. There's a lot of ways to get near zero light, even given a cave only 50 meters deep.

4. lava tubes tend to be curved and smooth inside, so you'd expect more reflection

Lava tubes on Earth. Which are a few thousand years old. Look at Ape Cave in the above image and show me "smooth and shiny." I see bumpy and cracked. What happens when you expose basalt to ionizing radiation? Mars, lacking in a major magnetic field, allows a lot of radiation to impact the surface. What does that do to basalt? On the moon it makes it dark and bumpy. (see regolith)

5. the walls would be visible on two sides and at least one of them should be getting sunlight

Again, only if this hole spanned the width of the tube because of natural collapse. Lower gravity on Mars means you can have much larger air-supported structures. Lack of water or an erosion cycle means that the tube is less likely to collapse on its own. As some one else stated, these structures could act totally differently on Mars than on Earth. Perhaps on Mars, the thin, cold atmosphere leads to near immediate radiative cooling of the surface and almost all lava flows were under the surface. Once you form an insulating skin that prevents outgassing to proceed to the surface, it could be possible that a large gap would form between the ceiling of the flow and the current lava flow even without a noticable down-slope flow pool. Maybe the entire lava field is just the surface of one big bubble.

It's always dangerous to extrapolate Earth features to other planets and expect there to be no difference. This is a fascinating feature that deserves further study.

Either that, or the Martians are cloaking their secret base. One of the two...

Re:Weird

[SpaceLifeForm]

No. Sinkholes exhibit that feature, for example, in Florida.