Finding caves on Mars

A quick holiday fund-raising campaign for Behind the Black!
Scroll down to read this post.
In past years I have managed to avoid asking for donations for Behind the Black during the holiday season. My finances however now compel me to do a short one-week fund-raiser, from November 11 to November 17.
I do not use Twitter for ethical reasons, which I have been told cuts down on traffic to the website. So be it. Furthermore, Facebook has clearly acted in the past two years to limit traffic to Behind the Black, almost certainly for political reasons. So be this as well. Finally, I do not post outside ads, as I have found them annoying to my readers and not that profitable to me.


Therefore, I need to ask for the direct support from my readers. If you like what I do here, please consider contributing, either by making a one-time donation or a monthly subscription, as indicated in the tip jar below.


Regular readers can support Behind The Black with a contribution via paypal:

Or with a subscription with regular donations from your Paypal or credit card account:

If Paypal doesn't work for you, you can support Behind The Black directly by sending your donation by check, payable to Robert Zimmerman, to
Behind The Black
c/o Robert Zimmerman
P.O.Box 1262
Cortaro, AZ 85652


Or you could consider purchasing one of my books, as indicated in the boxes scattered throughout the website. My histories of space exploration are award-winning and are aimed for the general public. All are page-turners, and all not only tell the story of the beginning of the human exploration of space, they also help explain why we are where we are today. And I also have a science fiction book available, Pioneer, which tells its own exciting story while trying to predict what life in space will be like two hundred years in the future.


Note that for this week only I am also having a sale on the purchase of the last 20 hardbacks of Leaving Earth. (Click on the link for more information about the book, which was endorsed by Arthur C. Clarke himself!) This award-winning out-of-print book is now only available as an ebook, but I still have a handful of hardbacks available, normally for sale for $70 plus $5 shipping. For this week only you can buy them, personally autographed by me, for $50 plus $5 shipping! Just send me a check, payable to Robert Zimmerman, to the address above, with a note saying that the money is for the Leaving Earth hardback.


Please consider donating. Your help will make it possible for me to continue to be an independent reporter in the field of space, science, technology, and culture.

A new study of pits on Mars has isolated one particular type of pit that has all the features of an Earth-like cave entrance, with a large number located in the regions around the giant volcanoes where evidence of past glacier activity has been found. From the abstract:

These Atypical Pit Craters (APCs) generally have sharp and distinct rims, vertical or overhanging walls that extend down to their floors, surface diameters of ~50–350 m, and high depth to diameter (d/D) ratios that are usually greater than 0.3 (which is an upper range value for impacts and bowl-shaped pit craters) and can exceed values of 1.8. Observations by the Mars Odyssey Thermal Emission Imaging System (THEMIS) show that APC floor temperatures are warmer at night and fluctuate with much lower diurnal amplitudes than nearby surfaces or adjacent bowl-shaped pit craters.

In other words, these pits are deeper with steeper and overhanging walls that suggest underlying passages. They also maintain warmer temperatures at night with their day/night temperatures changing far less than the surface, similar to caves on Earth where the cave temperature remains the same year-round.

The study’s most important finding, from my perspective, was the location of these pit craters.

Distribution of cave pits around Arsia Mons

More than 100 were located along the line of the three giant volcanoes to the east of Olympus Mons, the solar system’s largest volcano, as shown on the map to the right. The majority were clustered around Arsia Mons, the southernmost of the three volcanoes, and a place where scientists believe there were active glaciers in the past, a belief that is strengthened by the routine occurrence of water vapor clouds above Arsia Mons’ slopes, suggesting a lot of still present underground water.

Put the two together, available water plus underground caves, and you have an ideal place to establish the first human colonies on Mars. The water provides oxygen and energy, while the cave provides a convenient and easy place to build those first habitats. Not only does the natural roof provide radiation shielding without the need for major construction, you can seal it more easily to create an artificial atmosphere. And because the temperature ranges are more reasonable the environment will be more benign for both equipment and humans.

Martian cave formation processes

The geology that forms these caves is in itself fascinating, as Mars’ lighter one-third gravity field changes how things happen. As shown on the left, the paper proposes two main theories for the formation of these pit craters, which are believed to be part of the lava tube flows coming down the volcanoe’s slopes. In both cases a lava tube forms. In the top example the flow ceases before the roof collapses, so that the roof debris accumulates on the bottom of the pit and can often block access to the additional cave passages on either side. With the bottom example, the roof collapse occurs while the lava is still flowing, which transports the material away and thus prevents it from blocking the entrances to the side passages.

There are only a handful of Earth equivalents to these deep lava tube formed pits. On Earth the high walls and significant overhangs do not last long in the stronger gravity. With Mars’ lighter gravity, however, it is possible for much more delicate underground structures to survive. Thus, it is very possible that the lava tubes on Mars are larger in volume at any one point. The lighter gravity however is going change how the lava flows, so estimating their length is at this point more difficult.

The bottom line: Locating these pits also helps locate Mars’ prime real estate for human colonization. They not only provide quick and easy havens for construction, their location in the same area where glaciers and underground ice is expected to exist makes surviving there far easier.



  • J Fincannon

    Great news on the finding of more caves on Mars! With all the likely water, reduced radiation impact, better temperatures, these will be great spots to look for extant Martian life. Lets hope we can get a fleet of nicely de-contaminated robotic explorers to investigate these spots prior to the cave in-habitation by Earthlings.

  • davidjden

    This is fascinating, Bob. I agree with your perspective on the study’s most important finding (fwiw). I wonder, what is the trade between latitude and altitude, when it comes to human habitation? Perhaps water and shelter win the day, regardless. Thanks also for linking to that Brown paper and the cloud photos — I had no idea.

  • Do a search on Behind the Black for caves and you’ll come up with a lot of neat stuff I’ve posted over the years, some of which is actually original research poking through data from the moon.

Leave a Reply

Your email address will not be published. Required fields are marked *