At the start of this week three different major news organizations posted articles about a so-called “discovery” of a cave on the Moon that could sustain a human colony.

What all three articles [now updated with a fourth] demonstrated however was how little research was done by the journalists who wrote the articles, as well as the lack of any editorial supervision to make sure the news organization publishing the stories didn’t look stupid.

Here are the articles in question:

• The Guardian: Underground cave found on moon could be ideal base for explorers
• BBC: Cave discovered on Moon could be home for humans
• New Scientist: Scientists have confirmed a cave on the moon that could be used to shelter future explorers
• Space.com: Newly discovered cave on the moon could house future lunar astronauts [Added July 18]

The original paper that these stories are based on can be read here. It didn’t take me more than five seconds to immediately recognize that the pit in question, dubbed the Mare Tranquillitatis pit, has been known about for years. I in fact wrote about it as long ago as 2011, when researchers used Lunar Reconnaissance Orbiter (LRO) to take oblique images of it. One such image is to the right, cropped and enhanced to post here.

The new research has simply used the radar instrument on LRO to take oblique radar data to see if there are any cave passages at its base, and found that there could be voids leading off from the pit as much as “tens of meters” long, or about 100 feet or so.

This is good research, but the finding is hardly significant. Numerous other studies have suggested the same results, all tantalizing but entirely unconfirmed until we can send some probe (manned or manned) into these pits. In addition, hundreds of similar lunar pits have been documented for more than a decade.

Yet the first two articles above treated this cave as God’s gift to humanity, as if it was the first such pit found on the Moon that could hold a human base, while the third provided so little information about the background of this work that the article was essentially worthless.

I write this as a warning to my readers. Mainstream news sources no longer do the proper due diligence that should be expected from writers and editors. If you want good information, you need to go to sources that specialize in the subject (such this website), and you must go to more than one in order to understand the subject entirely.

Hat tip Cotour.

Click for full image.

Though the number of new pictures showing pits and possible caves from the high resolution camera on Mars Reconnaissance Orbiter (MRO) has significantly tailed off in the past year, as I noted in my previous post on Martian pits in September, the pictures are still rolling in. This post will highlight five new photos and the pits therein.

The first two, on the right, are both located on the southern flanks of the giant volcano Arsia Mons, where many such pits are found. They were taken respectively on August 16, 2020 and August 27, 2020. The first was a captioned image from MRO’s science team:

In this image, the ceiling of the lava tube collapsed in one spot and made this pit crater. The pit is about 50 meters (150 feet) across, so it’s likely that the underground tube is also at least this big (much bigger than similar caves on the Earth). HiRISE can’t see inside these steep pits because it’s always late afternoon when we pass overhead and the inside is shadowed at that time of day.

What I find most interesting about both images is that the skylights do not occur where you’d expect. In image #1, the meandering rill that suggests an underground lava tube is about 1,000 feet south of the pit. The pit itself seems unrelated to that rill. In image #2, the surface shows no obvious evidence of an underground tube matching the three aligned pits. There is the hint of a narrow depression along the alignment of the three pits, but this could just as easily be evidence of wind-blown dust along that alignment.

In the full image all three pits appear to sit inside a very wide and very shallow northwest-to-southwest depression, but this is hardly certain, and regardless the three pits align in a different direction.

The overview map below provides some context.

The white boxes show the location of these two images. The black boxes show the locations of the many other pits that scientists have identified in the past few years, and have been highlighted in earlier posts since 2018 on Behind the Black. (The full list of previous posts is at the bottom of this article.)

The scatter of pits around Arsia Mons suggests that the pits do not form in connection to any major structural fault or formation, such as the giant major northeast-to-southwest fault that cuts through Arsia Mons and also aligns with the two giant volcanoes to the north, Arcreaus and Pavonis.

Instead, the scatter on the volcanoes slopes suggest they all formed during one of the many eruption events about a billion years ago that formed this volcano, the lava flowing down its flanks with some of that flow going through lava tubes.

No conclusions at this time however are reliable. We have a very poor map of these tubes and the flows that caused them. And that there are so few on the slopes of Pavonis Mons means nothing. The scientists could simply have not yet had time to document or find them.

Click for full image.

In a sense, the next image to the right, taken on August 20, 2020 by MRO, illustrates the level of incompleteness of our knowledge. Like the first two pits, this pit is found on the flanks of a different giant volcano, Elysium Mons, located about two thousand miles to the west

Though it appears to be a very typical skylight pit into a lava tube, as is suspected for most of the pits found at Arsia Mons, as far as I can tell this might be the first such pit photographed on the slopes of Elysium Mons by MRO’s high resolution camera. Even if it isn’t, it appears that either lava tube skylights are not found surrounding Elysium Mons (which would be very surprising), or researchers have simply not yet begun to document them.

Or to put it more simply, the data is very incomplete.

The last two images, taken on August 25, 2020 and August 31, 2020 respectively, show pits and sinkholes into voids below, but in both cases the voids are not caused by flowing lava, but by the bulging upward of the ground due to pressure from underground magma, which causes the ground to crack. That cracking causes the voids.

The overview map to the right makes this obvious. The two white boxes, numbered four and five, show the locations of today’s last two images, both found in the cracked region south of the relatively low-relief giant shield volcano Alba Mons, and almost due north of the chain of three giant volcanoes, Arsia, Pavonis, and Arcreaus Mons.

Scientists call these cracks graben. Unlike a rill or lava flow, grabens start and stop suddenly, and were formed here as the magma pushed up, causing the cracks along fault lines, with some sections then slipping downward into those cracks.

To see the full images click here and here.

MRO photos #4 and #5 to the right show this, though more obviously in #5. Here the pits align with a long relatively straight depression.

With #4 the long depression is barely visible, but at the same time it appears strongly that the south end of the bigger pit connects underground with the smaller pit to the south.

The depressions in #5 on Earth would not be called pits, but sinkholes, as the ground appears to be sinking into a larger void below.

One more detail which illustrates why things are never simple. If you click on the full image for #5 you will see that just to the south, off the edge of my cropped section, is another graben, but instead of being angled north/south it lies perpendicular, in a east/west orientation. For some reason there are graben in this area that cross-cut the main north-south trend. Why only here however is a mystery I wouldn’t dare to explain.

All previous pit posts since 2018:

• November 12, 2018
• January 30, 2019
• February 22, 2019
• April 2, 2019
• May 7, 2019
• July 1, 2019
• August 12, 2019
• September 20, 2019
• November 19, 2019
• November 26, 2019
• February 20, 2020
• February 28, 2020
• May 22, 2020
• September 8, 2020

It has been several months since my last Martian pit update, mostly caused by the lack of new pit images coming down from the high resolution camera on Mars Reconnaissance Orbiter (MRO). I think this lack is not because of a lack of additional pits or caves but instead signals the completion of a first high resolution survey of the known pits so far found on Mars. A full list of all past pit updates can be found at the bottom of this post.

Regardless, the image to the right, cropped to post here, is the only such image in months, taken on April 14, 2020, and shows a small isolated pit in the lava slopes between the giant volcanoes Arsia and Pavonis Mons. In the full photograph you can see how isolated is this pit. To the limits of the image there are no other such features, the terrain a relatively smooth plain with only some small ridges and and a scattering of what seem to be partly obscured or eroded small craters.

The overview below map shows this pit’s relationship to the volcanoes as well as to all other known nearby pits.

The white box indicates this pit’s location. The black boxes are all the other pits documented in earlier posts on Behind the Black. The nearest other pit to the north, highlighted in a post in February 2019, is very similar, a single sudden pit in the middle of a relatively featureless plain.

In fact, most of the pits in this area are alike, isolated pits with no other related features. If they are skylights into lava tubes, those tubes show no expression on the surface, which suggests they are either deep underground or simply don’t exist. The assumption that these pits are skylights into larger cave systems is based on Earth experience. On Mars however volcanic lava flow might express itself in different ways.

To better understand this geology we simply have to enter these pits and explore them.

All Martian pit posts since 2018:

• November 12, 2018
• January 30, 2019
• February 22, 2019
• April 2, 2019
• May 7, 2019
• July 1, 2019
• August 12, 2019
• September 20, 2019
• November 19, 2019
• November 26, 2019
• February 20, 2020
• February 28, 2020
• May 22, 2020

Researchers found that Martian and lunar tubes are respectively 100 and 1,000 times wider than those on Earth, which typically have a diameter of 10 to 30 meters. Lower gravity and its effect on volcanism explain these outstanding dimensions (with total volumes exceeding 1 billion of cubic meters on the Moon).

Riccardo Pozzobon adds: “Tubes as wide as these can be longer than 40 kilometres, making the Moon an extraordinary target for subsurface exploration and potential settlement in the wide protected and stable environments of lava tubes. The latter are so big they can contain Padua’s entire city centre”.

Moreover, the data suggests their roofs, even at this size, will be very stable because of the lower gravity, making them excellent locations for large human colonies.

The researchers also suggest that there are many intact such lava tubes under the mare regions on the Moon, their existence only hinted at by the rare skylights created due to asteroid impact.

Since 2018 I have made it a point to document every new pit image taken on Mars by the high resolution camera on Mars Reconnaissance Orbiter (MRO). The list of can be found at the bottom of this post.

In the most recent release from MRO, a number of new pits were photographed. All continue to suggest that Mars has a lot of underground voids, some caused by lava flow, some by tectonic activity, some by water ice erosion, and some almost certainly caused by processes we don’t yet know. The images also suggest that we have only identified a small fraction of those underground voids.

The first image to the right, cropped to post here, shows the one new pit in the northern lowlands of Utopia Planitia, near a series of meandering channels and canyons dubbed Hephaestus Fossae and Hebrus Valles.

This appears to be the fifth such pit found in this region. Previously I had documented the first four. The overview map to the right adds this fifth pit. Note how the pit is much closer to the head of Hephaestus. In the full image you can see fissures both to the north and south, as well as many nearby aligned depressions, suggesting the existence of more underground passages, some possibly linked to voids under this very pit.

The pit itself seems filled, with no apparent side passages, though to the southwest there might be something leading off in the shadows.

The overall terrain in this region, including these pits, the fissures, and the many aligned depressions, strongly suggests a lot of underground voids. As I noted in 2019:

Scientists are not sure what caused these channels. Several have proposed that they could have been caused by catastrophic floods of water, melting because of heating from the volcano. Others suspect these rills are indications of lava flows coming down from Elysium Mons, forming lava tubes. In either case there appears no consensus.

I would add that newer research might replace catastrophic floods of water with some form of massive glacial activity across large vast areas of these plains. This new possibility is very preliminary, and I mention it only because I have gotten a sense from scientists that this is now being considered, though no one as far as I know has yet articulated it in depth in any published paper.

Two of other newly photographed pits are located, like almost all known pits on Mars, near the large volcanoes of the Tharsis Bulge. The context map to the right shows all the imaged pits I’ve documented so far, with the two new ones indicated by the white boxes labeled “skylight” and “lava tube.” Both are northwest of the volcano Arsia Mons, and both have features that suggest they are related to past lava flows coming down from that volcano.

The next image below and to the right, cropped to post here, shows the skylight. Though it is all alone on a relatively featureless plain, on the full image directly to the south about a mile away is a string of depressions.

Click for full image.

Click for full image.

Click for full image.

Next is actually not one pit but a string of pits aligned to strongly suggest the existence of an underground lava tube, very similar and near to another string of pits previously shown in a 2019 post and located by the nearest black box just to the northwest.

If you click on the full image, you will see that this meandering depression extends off the image both to the north and south. Though it might be documented more completely in wider lower resolution images, the high resolution camera on MRO has not yet covered it entirely. For all we know, it might even connect with the lava tube to the northwest. Or it could be a second parallel tube. In looking at most of the other high resolution images taken by MRO in this area, it appears there are a lot of similar lava tube features.

Altogether, the pit and depressions for both images point uphill to the volcano Arsia Mons.

The last pit image released is shown below and to the right. It shows another pit aligned with another string of depressions. In this case the pit is found on the northwest flank of the giant volcano Elysium Mons, located far to the west of the Tharsis Bulge, on the other side of Mars’ volcano country.

Once again, the string suggests a existence of a passage below. And since this is on the flanks of a volcano, the first assumption is that the voids were created by a lava tube flow. A review of all nearby MRO high resolution images shows many similar pits and depression strings, but also suggests that the voids were created not by lava flows but by cracking caused as the ground bulged upwards from the pressure of the magma chamber below.

We would need a planetary geologist to help settle this. It would also help if that planetary geologist could spend some time at the location, with a rock hammer, doing some in situ geology research.

All previous pit posts since 2018:

• November 12, 2018
• January 30, 2019
• February 22, 2019
• April 2, 2019
• May 7, 2019
• July 1, 2019
• August 12, 2019
• September 20, 2019
• November 19, 2019
• November 26, 2019
• February 20, 2020
• February 28, 2020

I could call this my monthly Martian Pit update. Since November 2018 I have each month found from two to five new and interesting cave pits in the monthly download of new images from the high resolution camera on Mars Reconnaissance Orbiter (MRO). My previous posts:

• November 12, 2018
• January 30, 2019
• February 22, 2019
• April 2, 2019
• May 7, 2019
• July 1, 2019
• August 12, 2019

All except the last August 12 post were for pits on the flanks of Arsia Mons, the southernmost in the line of three giant volcanoes to the southeast of Olympus Mons, and were thus almost certainly resulting from lava flows.

The August 12 post instead showed pits found in Utopia Planitia, one of the large plains that comprise the Martian northern lowlands where scientists think an intermittent ocean might have once existed. All of these pits are found in a region of meandering canyons dubbed Hephaestus Fossae.

In the most recent MRO release scientists once again focused on the pits in or near Hephaetus, imaging four pits, two of which have been imaged previously, as shown in my August post and labeled #2 and #4 in this article, and two (here and here) that appear new. The image on the right, cropped to post here, shows the two new pits, dubbed #1 and #3. In the full image of #1, it is clear that this pit lines up nicely with some other less prominent depressions, suggesting an underground cave. Pit #3 however is more puzzling. In the full image, this pit actually runs perpendicular to a long depression to the west. There are also no other related features around it.

What makes all four of these pits intriguing is their relationship to Hephaestus Fossae and a neighboring rill-like canyon dubbed Hebrus Valles, as shown in the overview map below.

All the pits are found in the downstream end of both Hephaestus Fossae and Hebrus Valles. Note also that to the east of this overview is the giant volcano Elysium Mons, which means these canyons are flowing down from that volcano.

Scientists are not sure what caused these channels. Several have proposed that they could have been caused by catastrophic floods of water, melting because of heating from the volcano. Others suspect these rills are indications of lava flows coming down from Elysium Mons, forming lava tubes. In either case there appears no consensus.

Click for full image.

Click for full image.

I could not help wondering what the southeastern sources of both these two rills looked like. Not surprisingly, the scientists were interested long before me, and have taken a bunch of high resolution MRO images of both.

To the right are sections of the most prominent sources of the two canyons, cropped and reduced to post here. As you can see, there are no obvious outlets coming from the uphill direction to the east. Then again, a lot of time has passed since any liquid water could have flowed here. In that time a lot of Martian dust has been deposited. Furthermore, you can see with both sources that a considerable amount of what looks like alluvial fill debris has fallen from the cliff walls, creating the long slopes down to the bottom. Any openings that might have once been here have certainly been long buried by these processes.

Because of the likelihood of water in this region, some scientists have proposed [pdf] this region as a prime exploration target, especially because of the possibility of caves.

One last interesting factoid. I could not help noticing that all four pits are at the same latitude, 21-21 degrees north. This places them south of the northern glacial band that exists from 30 to 60 degrees latitude. Thus, these pits could provide the answer to one of the fundamental questions scientists have about Mars: How far south does the ice table below the surface extend? It appears, based on the buried glaciers that have been identified, that this ice table gets as far south as 30 degrees. Whether it exists at 20 degrees north latitude however remains unknown.

My guess is that elevation would be a factor. At higher elevations, such as the flanks of the volcanoes, buried ice table would have more chance of existing at lower latitudes. In Utopia Planitia, however, the low elevation plus the low latitude would suggest that buried ice is unlikely.

We do not yet know this, however. These pits however might someday tell us.

While a cave-exploring drone on Earth may use propellers, free-flying spacecraft exploring caves on the Moon, where there is practically no atmosphere, or in the thin air of high altitude lava tubes on Mars’ giant volcanoes, would have to use small thrusters. The mission of the terrestrial drone deployed at the Lofthellir Ice Cave focused on validating the idea of using a drone-equipped LiDAR to safely navigate and accurately map rock and ice inside a dark lava tube in the absence of GPS or any prior map.

Under a research contract with NASA, Astrobotic has developed a custom navigation software product, known as AstroNav, to give drones and small free-flying spacecraft the ability to autonomously explore and map subterranean environments. AstroNav employs both stereo vision and LiDAR, works without GPS or previously stored maps, and can operate in real-time while a novel environment is explored at a high rate of speed.

…”The Astrobotic drone and LiDAR performed exactly as we had hoped, and was able to help us map the Lofthellir Lava Tube in 3D within minutes” says Lee. “We now have a highly accurate model of the shape and dimensions of the cave, and of the configuration of its many rocky and icy features, such as rock falls, ice columns, and micro-glaciers.”

The concept is an excellent one, especially for exploring the caves and pits of Mars. This test however only checked out the lidar. A drone that could do this on either Mars or the Moon does not yet exist.

I have posted their video of the flight below the fold.

Note: Thanks to reader Eddie Willers for noting that I mistakenly located this research in Greenland, not Iceland. Post now corrected.

Regular readers of this webpage will know that I am a caver, and am fascinated with the pits and caves that have so far been identified on Mars, as illustrated by an essay I wrote only last week.

Some of the cave research I have cited has being led by planetary scientist Glen Cushing of the U.S. Geological Survey. Two weeks ago Dr. Cushing sent me a slew of pictures of caves/pits that he has accumulated over the years, many of which he has not yet been able to highlight in a paper. At least two were images that I had already featured on Behind the Black, here and here.

One pit image however I had never seen. A cropped and reduced close-up is shown on the right, with the full photograph viewable by clicking on the image. In many ways this pit is reminiscent of many pits on Mars. Its northern rim appears to be an overhang several hundred feet deep that might have an underground passage continuing to the north. The southern lip is inviting in that its slope appears to be very accessible for vehicles, meaning this pit/cave might be a good location to build a first colony.

Because of that accessible southern lip, I decided to do more digging about this particular pit. I was quickly able to find the uncaptioned release of the complete image by doing a quick search through the image catalog of Mars Reconnaissance Orbiter’s (MRO) high resolution camera. That image, reduced and cropped to post here, is shown below, on the right.

As always, if you click on the image you can see the full resolution and complete image.

My first reaction was, “Whoa! That tiny pit is at the head of an increasingly growing canyon!” To a caver on Earth, this instantly implies that water has flowed out of that pit and down the canyon, carving it out as it flowed. It also implied that the possible underground passage under the pit’s north rim might conceivably be extensive.

Reinforcing this first impression were the numerous dark streaks flowing down the canyon’s cliff walls to the south. They all seemed to originate at about the same elevation as the pit itself, suggesting they all come from the same contact between two geological layers, a contact where water tends to gather. On Earth, when water seeps downward through water-soluble limestone and then gets blocked at a contact of more resistant material, it then starts to flow horizontally, creating a cave at that contact. The Martian dark streaks and pit in the image to the right suggest a similar process is occurring here.

I was now very intrigued, and decided I needed to see if MRO’s high resolution camera had taken any more images in this area. I also wanted to know where that canyon went to the south, and how far it went. At the MRO image archive I did a search by location, zooming in on the pit’s latitude (North 28.787°) and longitude (East 284.591°).

The image to the left shows this image’s general location, indicated by the black cross at the northwest edge of Kasei Valles, one of the many gigantic canyon systems draining downward from Mars’s biggest volcanoes. Though far smaller than the more famous Marineris Valles to the south, Kasei Valles is still incredibly long and large, about 1500 miles long and 300 miles wide in places. In comparison the Grand Canyon is only 18 miles wide at its widest, with a length of less than 300 miles.

This story gets better. As I zoomed in I discovered that the high resolution MRO image of that pit above, only about 160 feet wide, was located at the end of one of the major canyons draining into Kasei Valles, as now indicated by the red cross in the image to the left. While the pit might be small, whatever drained from it was, over time, able to carve a truly substantial channel, as part of the one or more one or more catastrophic floods that formed both Kasei and Marineris Valles..

The image to the left also shows that MRO has taken no other images of this canyon or its surrounding terrain, so we do not really know whether there are more cliff seeps along the canyon walls to the south. The lack of images also leaves open the question whether there are any other entrances to the north of this pit, on the plains above.

I leave you with one last image on the right, cropped from a Mars Odyssey image and showing the entire canyon south of this tiny pit. Though I don’t have a scale for this photograph, the white box shows the approximate size of the MRO image above, with the location of the pit indicated. By extrapolating the scale on that image, I estimate that the distance from the pit to the canyon outlet is about 40 miles, with the canyon outlet about ten miles wide.

In other words, this tiny pit is one of the major sources of a canyon that is in many ways comparable to parts of the Grand Canyon. How spectacular is that?

The Mars Odyssey image to the right makes its clear that this pit is not the only source for this canyon. Drainage from the side tributaries certainly contributed, as did the many seeps that I suspect line the walls of this canyon. Moreover, the canyon itself appears to have been formed along faults, so that water from that single tiny pit did not do all the work to form the canyon. The geological structure itself contributed.

Nonetheless, the data illustrated by these images makes that tiny pit most enticing. It not only appears to be relatively easy to access its interior, there is visual evidence that suggests the presence of water.

If I was a future settler of Mars, I would give this pit a very high priority for exploration. In fact, I think someone (maybe Elon Musk?) should already be considering a probe to delve its depths.

Time for many cool images! Over the years I have written frequently about the pits/caves on Mars, in both magazine articles and the many posts here at Behind the Black. The following posts are the most significant, with the June 9, 2015 providing the best geological background to many of these pits, especially the many located near the giant volcanoes of Mars.

• November 12, 2010: Sinkholes on Mars
• December 2, 2010: More caves on Mars
• June 9, 2015: Finding caves on Mars
• June 5, 2018: Another intriguing pit on Mars
• July 24, 2018: Another skylight entrance pit found on Mars
• November 12, 2018: More Pits on Mars!

As I wrote in that June 9, 2015 post:

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.

Today’s selection of cool images, all found in the January image release from the high resolution camera of Mars Reconnaissance Orbiter (MRO), include a handful of new pits near Arsia Mons in the volcanic Tharsis Montes bulge, such as a lonely and very distinctive pit to the northeast of the volcano, a second lonely and very distinctive pit to the north of the volcano, and finally the line of three shown in the image to the right, cropped and reduced to post here, with the original viewable by clicking on the image.

That these pits are all in a line, and that they also in line with a shallow straight depression, strongly suggests that they are skylights into a lava tube below. Located to the northwest of Arsia Mons, the southeast-to-northwest trend of the line reinforces this conclusion, suggesting that we are looking at surface evidence of an underground lava tube that flowed down from Arsia Mons, when that giant volcano was active, eons ago.

It is hard to say if any of these pits would provide access into that lava tube. Even a close look at each does not provide enough detail to see whether any passages continue under their rims. If I had to guess, from the image, I would say that access is blocked.

However, there is another detail in the image that suggests otherwise. Note the dark trails to the west of all three pits. These suggest that the prevailing wind is blowing material from the pits in this direction. The problem is that it should be difficult to get the material at the bottom of the pits up to the surface, unless these pits provide open access to a larger interior underground volume. The temperature and pressure differences between the surface and the interior would sometimes cause the atmosphere in the lava tube to expand, causing air to blow upward out of the pits and bringing with it fine particles from below that the surface winds could then catch and deposit to the west.

Not all interesting Martian pits, however, are found near the volcanoes. The pit shown at the top of this post is instead located in the middle of Amazonis Planitia, one of the largest regions of Mars’s northern lowland plains where once an intermittent ocean might have once existed, and is only one of about a dozen located close together at 22 degrees north latitude and 202 degrees east longitude. (Go here and click on the map at this location and you can view the many other similar pits in this small area.)

Whether these pits are volcanic in origin I do not know. Their trend points directly away from Olympus Mons, which suggests they might be evidence of an underground lava tube. Olympus Mons is quite a distance away, however, which makes it unlikely that the pits are related directly to the volcano.

The MRO January image release also includes another similar line of sinkholes in another area of the northern lowlands, this time in Utopia Planitia, at 22 degrees north latitude and 118 degrees east longitude. In this area are many similar fissures and linear sinks that appear more likely caused by faults and fissures in the ground than lava tube flows. The area has not been photographed as thoroughly as the pits in Amazonis Planitia, so it is hard to get a full sense of the geology there.

What makes this Amazonis Planitia pit especially interesting is the large very distinctive dark streak running down its northern wall but originating just below the rim. Such dark streaks are strongly believed to be evidence of melting ice seeping out of the wall which, as it flows down, changes the color of the surface material. (See this BtB post for another very dramatic example.)

While this pit might not be volcanic, it quite possibly could be a good access point to undergound water. It also, to my mind, reinforces the hypothesis put forth in the paper I highlighted yesterday, that a water ice table probably exists below the surface almost everywhere on Mars. And if it doesn’t, it is still likely from the building evidence that there are many places where it does exist and be accessible.

For general reference, the global Mars map below shows the general locations of all these regions, and how they relate to each other as well as to the locations of all past and planned landers/rovers.

Cool image time! In my routine monthly review of the hundreds of new images released from the high resolution camera on Mars Reconnaissance Orbiter (MRO), I came across another most intriguing geological feature, the image of which is posted to the right, after cropping.

As the scale shows, the pit is about 300 feet across. Calculating the pit’s depth would require someone with better math skills than I. The website provides information about the sun angle, which can be used to extrapolate the shadows and then roughly calculate the depth.

The most fascinating aspect of this pit is the impression of incredible thinness for the pit’s overhung edges. All of the pit’s edges appear significantly overhung, and the thickness of the overhang seems incredibly paper-thin. This thinness is likely only an illusion, though in Mars’s light gravity it is perfectly possible for the overhang to be far thinner and more extended than anything you would find on Earth.

The image itself is in color, though the only color visible is within the pit itself. In that blueness at the base it seems to me that there is a pile of dust/debris, but once again, that conclusion should not be taken very seriously.

If you take a look at the full image, what is impressive is the bland flatness of the surrounding terrain. There is no hint that there might be underground passages hidden here. While most of the scattered craters are probably impact craters, many (especially those with unsymmetrical shapes) could be collapse features indicating the presence of underground voids. None however is very deep. Nor is there any other pits visible.

Below is a global map of Mars with the location of this pit indicated by a black cross. It is just on the edge of the transition zone between the lower northern plains and the southern highlands, where the shoreline of an intermittent sea is thought by some scientists to have once existed. This is also an area where not a lot of high resolution images have been taken, mostly because of its apparent blandness as seen in previous imagery.

This image demonstrates however that Mars is going to have interesting geology everywhere, and that we won’t really know it well until we have explored it all.

Cool image time! In the June release of images from the high resolution camera on Mars Reconnaissance Orbiter, I came across the image on the right, cropped slightly to post here, of a pit in a region dubbed Hephaestus Fossae that is located just at the margin of Mars’s vast northern plains.

Below and to the right is an annotated second image showing the area around this pit. If you click on it you can see the full resolution image, uncropped, and unannotated.

The scale bar is based on the 25 centimeter per pixel scale provided at the image link. Based on this, this pit is only about ten to fifteen meters across, or 30 to 50 feet wide. The image webpage says the sun was 39 degrees above the horizon, with what they call a sun angle of 51 degrees. Based on these angles, the shadow on the floor of the pit suggests it is about the same depth, 30 to 50 feet.

The shadows suggest overhung walls. This, plus the presence of nearby aligned sinks, strongly suggests that there are extensive underground passages leading away from this pit.

For a caver on Earth to drop into a pit 30 to 50 feet deep is nowadays a trivial thing. You rig a rope (properly), put on your vertical system, and rappel in. When you want to leave you use that same vertical system to climb the rope, using mechanical cams that slide up the rope but will not slide down.

On Mars such a climb would be both easier and harder. The gravity is only one third that of Earth, but the lack of atmosphere means you must wear some form of spacesuit. Moreover, this system is not great for getting large amounts of gear up and down. Usually, people only bring what they can carry in a pack. To use this Martian pit as a habitat will require easier access, preferable by a wheeled vehicle that can drive in.

The pit’s location however is intriguing. The map below shows its location on a global map of Mars. This region is part of the Utopia Basin, the place with the second lowest elevation on Mars.

If you go to the Mars Reconnaissance Orbiter image archive and zoom into this area (latitude 21.5; longitude 122) you can find a variety of images of similar nearby northern plains features, many of which I have highlighted previously, lines of mesas and especially cones, craters, and pits. This second link shows a line of sinks very similar to sinks above, located in the same general region as today’s pit.

The geology here suggests that the northern plains, at least here, have a lot of underlying passages. From a caver’s perspective, this makes great sense, especially if that northern plain was once an intermittent ocean. When the water table was high, it would not be surprising if that water acted to erode voids in fissures and cracks, producing caves below that table. When the water table dropped, these voids would lose the water that was helping to hold their ceilings up. There would be collapses, resulting in sinkholes on the surface. This is exactly what we see here.

On Earth, sinkholes only occur in a few places above the cave. Most of the cave below remains invisible to the surface. I would not be surprised if this was the situation on Mars as well. The pits and sinkholes only provide a glimpse to the underlying cave system, which I suspect is somewhat vast.

It will also provide crucial information, once we can fully explore it, for understanding the geological and environmental history of Mars.

Why? This explains it:

A cottage industry has popped up in which the cave dwellers earn extra money by renting out rooms in their homes, which over time have clustered within Zhong cave, a limestone cavern big enough to hold four American football fields. The hangar-like cave is so large that their wooden or bamboo-made residences form a small, subterranean village built along its undulating walls.

…Officials say that residents have not taken care of the cave, leaving it unsuitable for inhabitation, and that the government should oversee the village as it is listed as a protected community by the Getu River Tourism Administration, a local agency. They have offered each resident 60,000 renminbi, or approximately $9,500, to leave.

Only five families have agreed to move. The remaining 18 families have held on stubbornly to their homes inside the cave. They say that the new homes are too small, that they fear losing access to their land, and that they alone, because of their historical connection to the cave, should have the right to independently control its small tourism economy.

The Chinese government is simply not offering them enough to leave. And should they leave, I would expect the villagers to come out on the raw end of the deal, while the cave itself, no longer protected by their presence and financial self-interest to preserve it, will also suffer.

Hat tip Willi Kusche.

In 2009, the Kaguya probe found a large shaft with an opening about 50 meters in diameter in the Marius Hills area. The shaft descends about 50 meters beneath the surface.

The JAXA team analyzed data obtained from a lunar radar sounder on the probe that indicated an underground structure extended west from the shaft. The study confirmed that the cavern, likely created by volcanic activity, has not collapsed, and there is the possibility of ice or water existing in rocks within the cave, the team said.

Do a search on Behind the Black using the search terms “cave” and “moon” and you will see many images of this pit, taken by Lunar Reconnaissance Orbiter as a follow-up to the Kaguya mission.

One doesn’t have to go to Belize to get these benefits. I could have traveled to England, Mexico, Hawaii, or any one of several dozen other countries to see the exotic, the new, and the unexplored. In fact, I have already done so in Russia, Ukraine, Germany, and Czechia (the new official name of the Czech Republic). Belize however was relatively close, the local population spoke English, I had never been there before, and most important, someone else was organizing things! When David and Eleanor Larson invited me to join their Belize project I decided this was a great opportunity to visit a strange and new place with a minimum of aggravation or planning. They had already done it, and I merely had to sign up and agree to do whatever their project needed doing. So, off I went.

Upon arrival, I soon discovered several very important additional reasons why this cave project exists. First there are the caves. They are grand and beautiful things, with very vast chambers filled with delicate and rare formations. The picture below, taken by fellow caver Laura Sangiala, shows one wall of the gigantic entrance room of one cave.

Caver Larry Zimmer can be seen on the left. The entrance itself, out of view on the right, is an opening up a 100 foot slope probably 200 feet across. To the left the cave disappears into darkness in a meandering passage about 100 feet wide with a 60-foot-wide river flowing through it

Mapping these caves makes it possible to know what is there, and thus easier to protect. The Larsons’ project has been doing this now for Belize’s Institute of Archaeology for more than a decade.

Then there are the things one finds in these caves. Belize as well as Guatemala next door were part of the great Mayan empire, and during its height a thousand years ago caves were an important part of that civilization’s religious beliefs. Thus, the caves routinely have many important archaeological artifacts that must be protected and preserved, such as the almost intact pot shown in the photo on the right, with pottery shards behind it (photo by Laura Sangiala), found in one of the caves I was surveying this past week. Mapping these artifacts provides scientists a detailed baseline of data for future research, while also providing the Institute the information it needs to better manage these resources.

Protecting and documenting the caves and their archaeology is the most obvious reason to doing this work, but there is another reason that is actually far more fundamental. Belize is a somewhat poor country whose most important resource is tourism. Without its interesting historical, geological, and archaeological sites, the people of Belize would lose a significant source of income, and so, it is in their own self-interest to protect these caves.

The photo on the right is of tour guide Marcus Cucul (photo by caver Don Smith), who accompanied us on almost every cave trip. Marcus, however, was not there to survey. Instead, he and several other tour guides came each time to lay down flagging tape and carefully mark trails so that travel by future tour guides would be better controlled, thereby better protecting each cave’s formations and archaeology. Marcus, like the other tour guides, runs a tour company, Maya Guide Adventures, and for that company to prosper he and his fellow guides have to manage the caves responsibly so that they will remain beautiful and interesting to see for many years into the future.

In fact, my experience in Belize once again reaffirmed my belief that private property and profit are the best ways to protect the environment. Because the caves have a financial value to these tour guides, there is a practical financial reason for the guides to protect them. If these guides were forbidden to lead cave tours, they would have no incentive to protect them, and the resulting random and uncontrolled visits would result in the caves’ destruction.

Because Belize’s law puts the ownership of all caves under the jurisdiction of the Institute of Archaeology, which generally lacks the resources to protect them all, this work by the tour guides is essential. For example, Barton Creek Cave is a major tourist river cave that requires a canoe to see. Though the property surrounding the entrance is privately owned, the landowner, Mike Bogart, cannot prevent access to the cave to others. He offers tours, using the canoes he provides, but others can do the same and access the cave by canoeing up the river past his property. They need only get a government permit.

Thus, under this socialized system, with no single owner responsible for each cave, the only way the caves can be protected is for the tour guides and operators to band together to protect the caves themselves. In fact, their effort to flag the trails these past few weeks was begun expressly because they all saw the damage that uncontrolled visitation was causing, and wanted to stop it

Hopefully, their effort will bear fruit, and the caves and their guides’ livelihoods will prosper for years to come. And if the cave maps we Americans produce can help contribute to that success, then my short trip to Belize will have accomplished a lot more than provide me a few days of vacation pleasure.

Hat tip Danae.

In the end, the work of more than 60 researchers yielded a picture of “a relatively tall, skinny hominid with long legs, humanlike feet, with a core and shoulder that is primitive,” Berger says. Some body parts have come into sharper focus than others. In an analysis of the remarkably complete hands, paleoanthropologist Tracy Kivell of the University of Kent in the United Kingdom found that bones in the wrist were shaped like those in modern humans, suggesting that the palm at the base of the thumb was quite stiff. That would allow forces to dissipate over a larger area of the hand than in more primitive humans—a trait associated with tool use. At the same time, H. naledi had a weird thumb and long, curving fingers, as if it still spent a lot of time climbing.

The story of the discovery is interesting in that the fossils were found in a cave in a room that is very difficult to access, so difficult that the scientists themselves have never seen the site. Instead, they have sent very small cavers inside to do the fossil gathering.

There are many caveats to this story. The 15 skeletons appear different than humans, but to then create a whole human species from this single location is a bit risky.

I think the biggest mystery about this find involves its location. How the heck did these 15 individuals get trapped in this room at the back of a cave that requires you to squeeze down a vertical 100-foot chute only about 8 inches wide to enter?

There is a local cave here in the Tucson area that is a maternity colony for one species of bats. During the summer the females gather here to gossip and then give birth to their babies, after which they move on until next year. Because of a desire to help these bats, a few years ago the managers of the cave decided to close it during the summer months. This way humans wouldn’t be there to disturb the mothers during their labor.

The managers also decided to do regular bat counts of the bats leaving the cave each evening to feed, in order to get an estimate of the population size. To everyone’s delight they found the numbers rising year-to-year, following the summer closure. The total population of bats isn’t actually going up, but it appears that bats are finding this cave to be a good place to give birth, so more and more of them are making it their summer residence.

In the end the situation will contribute to an actual rise in population, as providing the maternity colony a safe haven will allow for more successful births and more babies.

In the past three years the bat count numbers over each summer would exhibit a typical bell curve, going up and then declining as the summer progressed, with the largest numbers ranging between 75 to 150 each night. However, last year there was one evening in which no bats left the cave. The bat biologist leading the bat count, Sandy Wolf, has theorized that this might be because the mothers are synchronizing their labor so that everyone gives birth at the same time and, because of that, on that night no one exits for feeding.. She knows that some species do this, but for this particular species such behavior has never been documented.

Anyway, she decided to find out. This has required that someone be at the entrance counting the bats at least every other evening. (In past years the counts were only done about once a week.) This has required more help, and thus Sandy has called for volunteers to do the work.

And that is how I and fellow caver Jerry Isaman ended up hiking up the hill to the cave with digital camera, infrared lights, and monitor this past Saturday.

The camera and infrared lights were aimed at the entrance, with the monitor set up about thirty feet away, hidden from the entrance. We could watch the monitor and easily see bats entering and leaving, with me counting those going out and Jerry counting those going in. The camera meanwhile taped everything, so that our counts could later be confirmed and checked for accuracy.

I had expected this would be both boring and difficult to do. You start staring at the monitor unceasingly at around sunset, and nothing usually happens for the first fifteen minutes or so. Then the first bat flies out. I think “Whoopie!” as I click my clicker counter.

I found. however, that spotting the bats was far easier than expected, and that the work was not really boring at all. Once the first bat left things got busy for about a half hour, with bats flying out about 2 to 4 per minute. Then things quieted down, and after 90 minutes, when nothing flew out for 10 full minutes, we shut down and packed up.

The most challenging part of the count was when a bat decided to go back into the cave. It appeared that many of them had to plan their entrance and couldn’t do it on the first attempt. They would circle around several times, dive toward the entrance and then change their mind the last second, repeatedly faking Jerry out, who was about to count them for re-entering the cave and now could not. I meanwhile had to make sure I didn’t count them as exiting the cave.

The coolest thing about Saturday was the count itself: We counted 218 bats leaving, the highest count of the year. Though we were not there on the night no bats came out, confirming Sandy’s theory, our count once again indicated that the population using the cave is increasing.

I hope to do this again later this summer. It might not be the traditional way to spend an evening, with dinner and a movie, but it certainly is more interesting.

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.

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.

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.

David Blair, a graduate student in Purdue’s Department of Earth, Atmospheric and Planetary Sciences, led the study that examined whether empty lava tubes more than 1 kilometer wide could remain structurally stable on the moon. “We found that if lunar lava tubes existed with a strong arched shape like those on Earth, they would be stable at sizes up to 5,000 meters, or several miles wide, on the moon,” Blair said. “This wouldn’t be possible on Earth, but gravity is much lower on the moon and lunar rock doesn’t have to withstand the same weathering and erosion. In theory, huge lava tubes – big enough to easily house a city – could be structurally sound on the moon.”

You can read their paper here. If this is so, then the possibility of huge colonies on the Moon increases significantly, as it will be much easier to build these colonies inside these giant lava tubes.

Indian scientists have released a new set of color images taken by their Mars orbiter, Mangalyaan.

The image on the right is of Arsia Mons, one of the three giant volcanoes to the east of Mars’ biggest volcano, Olympus Mons. Arsia Mons is important for future manned colonization, as there are known caves on its western flanks. In addition, those western flanks show solid evidence of past glaciers, which means that it is very likely that those caves will harbor significant quantities of water-ice, making settlement much easier.

The pits range in size from about 5 meters (~5 yards) across to more than 900 meters (~984 yards) in diameter, and three of them were first identified using images from the Japanese Kaguya spacecraft. Hundreds more were found using a new computer algorithm that automatically scanned thousands of high-resolution images of the lunar surface from LRO’s Narrow Angle Camera (NAC).

This work is essentially the same as that done by James Fincannon and I back in 2011 (see links here, here, here, and here) but with much greater thoroughness.

I have only visited Nevada twice before, and those visits had been limited to the area around Las Vegas. Thus, my impression of the state had been similar to what most other people assume: a big ostentatious urban city surrounded by boring flat deserts.

Instead what I found is that Nevada is probably one of the most beautiful states in the nation. It has many mountain ranges, interspersed with wide flat valleys, a number of which have lakes or swampy areas because the water is trapped there, draining neither to the Pacific or Atlantic.

Yet, it is desert country. The limited amount of water means that the state is lightly populated, and the few farms or ranches that you pass actually act to amplify the feeling of emptiness. This is further enhanced by the frequent mountain ranges. Every time you cross over a range, you find yourself high in the air with a spectacular view of the vast valleys below.

The Forest Service job that I was part of this past week was focused on inventorying and surveying a number of known caves covering a large area in northeastern Nevada. The work had actually started several years earlier, so that this particular week was the final wrap up, mapping the last few known caves on the list while also ridge-walking several different canyons in an effort to find some new discoveries.

None of this work was easy to reach. Unlike the east, where you can usually park relatively close to the cave and spend most of your trip exploring the cave itself, in the west the caves are smaller and the country is vaster and more remote, so that most of the experience involves a great deal of hiking just to get to the cave entrance.

Moreover, the methods of finding new caves is very different. In the east new cave passages are usually found by digging either inside a known cave or following the surface water drainages and digging either where water sinks into limestone bedrock or reappears at a spring. And you generally have to dig, because most of the easy-to-find entrances have long-ago been discovered.

In the west, there rarely is enough water to produce a flowing stream. Caves are formed differently. Moreover, there is rarely a need to dig into a cave, as the majority of easy-to-enter caves have simply not yet been found.

Instead, you literally need to walk the entire mountainside, looking continuously for holes that might be a cave entrance. And because of the vastness of the land as well as its remoteness, there are giant swathes of territory that have never been checked. To check them out, however, requires a determination and single-mindedness that most people do not have.

For example, when we weren’t surveying a known cave this past week, we were tramping up the sides of mountains — with elevation gains of anywhere between 300 and 1,800 feet — and poking our heads into the various holes that we had spotted by binoculars from below.

Discovery is never easy. For every hundred small holes you look at, you might find one new cave of note or significance — and only if you are lucky. For example, on Monday I and three other cavers, Anthony Smith, Jim Rolf, and Bruce Lynn, worked our way along the base of a cliff high on a mountainside, surveying a string of spectacular holes that had been identified during a previous work week. As you can see from the picture below, all the holes seemed very tempting, any one of which might have been the entrance to a significant cave.

Bruce is the white speck in front of one of the smaller holes a bit left of center.

Unfortunately, none were. All ended up to be shelters, the deepest extending into the mountainside only about seventy feet. And instead of beautiful cave formations, we found a lot of animal bones and pack rat poop. (This poop is interesting, however. The rats will urinate repeatedly in the same spots, and when the urine dries it leaves behind a thin deposit. Over time these deposits will pile up and form something called amber rat, a dark reddish material that will often flow down the sides of walls and produce formations resembling cave flowstone and stalactites.)

This is the reality of exploration. Most of the work will produce nothing. The one discovery I mentioned earlier in the week turned out to be far less interesting when we went back to survey it. Oh well.

You keep pushing, however, because eventually there will be a pay-off, and when it happens, you will have the joy of seeing something no human has ever seen before.

And in the case of Nevada, as well as much of the west, the potential is gigantic. There is just so much unexplored territory, and too few people to check it all out. Hidden in those mountains are certainly many undiscovered caves, waiting only for the person with the determination and patience to do the work to find them.

The image on the left will give you a good idea of what my day was like: Twelve hours of driving across Arizona and Nevada. Tomorrow the cave work begins.

For the next seven days my daytime posting is going to be spotty, as I will be in some remote areas of Nevada working on an on-going Forest Service project to inventory and survey caves in an area in the northeastern area of the state. The project is mostly over, but as I have surveyed, sketched, and done the cartography for many eastern U.S. caves, the guy running the project asked if I would be interested in participating. Interested? I was thrilled.

Though we will be in a somewhat remote area, I still hope to post periodically during the week, not only about the usual topics but also about some of the caves we will have surveyed, some of which are rarely visited. I will also try to post some pictures of the spectacular country we expect to visit. (The photo on the right was provided to me by Tom Gilleland, who is running the project.) Stay tuned.