Search Results for: Arsia Mons

Sinkholes galore!

Sinkholes galore south of Olympus Mons
Click for full image.

Cool image time! The photograph to the left, cropped to post here, was part of the November image dump from the high resolution camera on Mars Reconnaissance Orbiter (MRO). It shows a wind-swept dusty plain trending downhill to the west that is filled with more than a hundred depressions or sinkholes.

Unlike other pit images I have posted previously, this one is not focused on one particular pit or a string of pits. Instead, what makes it interesting is the large number of pits, scattered across the terrain in a random pattern. Their random distribution suggests that they are unrelated to any specific underground feature, such as a lava tube. Instead, some aspect of the underground geology here is causing the ground to sink at random points.

Below is an overview map showing where this dusty pit-strewn plain is located, indicated by the blue cross.
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Skylights into Martian lava tube?

Possibly connected skylights into lava tube
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Close-up of skylights
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Cool image time! In the archive of images from the high resolution camera on Mars Reconnaissance Orbiter (MRO) I came across the uncaptioned image on the right, dubbed “Possibly Connected Lava Tube Skylight Pair in Tharsis Region.”

The top image, cropped and reduced to post here, is a wide view, showing a narrow depression oriented in a north-south direction. Downhill is to the north, with the caldera of the giant volcano Arsia Mons to the south. The white box indicates the area covered by the bottom image, cropped and expanded to post here. Within this close-up are two dark spots, each about 150 feet across.

The two dark spots surely look like small pit openings. Their alignment with the north-south depression strongly suggests that an underground lava tube is below. That this depression is also aligned with the downhill slope further reinforces this supposition.

The depression itself also aligns with the gigantic fault that runs from the northeast to the southwest through all three of the giant Tharsis Bulge volcanoes. Arsia Mons is the southernmost of the three. It is also where that fault is most clearly expressed by two dramatic breaks in the volcano’s rim in the northeast and southwest, as seen in the overview image below. Scientists have taken of lot of images of these breaks in an effort to better understand the geology and how it fits in with the formation of the volcanoes.

Overview of Arsia Mons

However, a review of the entire image archive of MRO’s high resolution camera shows that scientists have taken very few close-up images in this region. The black box in the overview map on the right is the location of this image. As of now, only three other high resolution images, as indicated by the white boxes, have been taken by MRO of this part of the volcano’s north slope.

That the skylights and depression align with this giant fault is not evidence that this supposed lava tube is linked to that fault. Lava will flow down the mountain’s slopes, fault or no fault. At the same time, the fault’s existence is also going to encourage north-south cracks and fissures, which in turn could have served as a convenient flow route for the lava. Without a closer look, on site, it is hard to know one way or the other..

I’ve located a few more lava related cool images in the MRO archive, so I’m going to make this week lava week on Behind the Black. Stay tuned!

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Cave pits in the Martian northern lowlands

New pits in Hephaestus Planitia

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:

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.
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Monitoring Martian pits not near Arsia Mons

Second look at Hephaestus Fossae pit
Click for full image.

In reviewing the August image release from the high resolution camera on Mars Reconnaissance Orbiter (MRO), I came upon two different new pit images, the more interesting of which is highlighted on the right, cropped to post here..

Finding new pit images from MRO isn’t surprising, since the spacecraft has been photographing pits almost monthly since November (see: November 12, 2018, January 30, 2019, February 22, 2019, April 2, 2019, May 7, 2019, and July 1, 2019).

What makes these two new pit images more intriguing are their location, and the fact that both pits were previously photographed by MRO and posted on Behind the Black on June 5, 2018 and July 24, 2018. Both are located in Hephaestus Fossae, a region of fissures on the edge of the great Martian northern lowlands to the west of the great volcano Elysium Mons.

Almost all the pits from past MRO images have been found on the slopes of Arsia Mons, the southernmost of the three giant volcanoes southeast of Olympus Mons. In fact, last month I even asked the question, “Why so many pits there, and so few pits elsewhere?” The explanation from Chris Okubo of the U.S. Geological Survey, who is requesting these images, was that maybe it was due to geology, or maybe it was because we simply do not yet have enough information and might not have identified the many caves/pits elsewhere.

It appears that this same question had already been on the minds of Okubo and his partner, Glen Cushing, also of the USGS. As Okubo wrote me when I asked him about these new images:
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Where are the caves on Mars?

Overview map of pits near Arsia Mons

Each month I go through the monthly download of new images from the high resolution camera on Mars Reconnaissance Orbiter (MRO). And each month since November I have found a bunch of newly discovered pits photographed in the region around the volcano Arsia Mons (see: November 12, 2018, January 30, 2019, February 22, 2019, April 2, 2019, and May 7, 2019). The map on the right has been updated to include all those previous pits, indicated by the black boxes, with the new pits from June shown by the numbered white boxes.

To the right are the first three pits in the June archive, with the link to each image site found here (#1), here (#2), and here (#3).

Pits 1 through 3
For full images: Number 1, Number 2, Number 3.

All three are what the scientists doing this research call Atypical Pit Craters:

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.

The fourth pit, shown in the reduced and cropped image below, might actually be the most interesting of the June lot.
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The many pits of Arsia Mons

The many pits of Arsia Mons

When it comes to Mars, it appears that if you want to find a pit that might be the entrance to an underground system, the place to look is on the slopes of Arsia Mons, the southernmost volcano in the chain of three giant volcanoes between Olympus Mons to the west and the vast canyon Marineris Valles to the east.

To the right is an overview map showing the pits that have been imaged since November by the high resolution camera of Mars Reconnaissance Orbiter (MRO). The black squares show the pits that I highlighted in previous posts on November 12, 2018, February 22, 2019, and April 2, 2019. The numbered white squares are the new pits found in March photograph release from MRO.

And this is only a tiny sampling. Scientists have identified more than a hundred such pits in this region. Dubbed atypical pit craters by scientists, they “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 much greater than impact craters, facts that all suggest that these are skylights into more extensive lava tubes.

Below are the images of today’s four new pits.
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More Martian Pits!

More pits on Mars!

As I said in my last post in February showing recent pit discoveries on Mars, I could almost make this a monthly series. In the March image download from the high resolution camera of Mars Reconnaissance Orbiter (MRO) were three (maybe four) more pits, all likely skylights above lava tubes and all located near the giant volcano Arsia Mons in the region dubbed the Tharsis Bulge. The image to the right shows all three, with a possible fourth just northwest of pit #2 and visible in its full image. For the full images of the other two pits go here (#1) and here (#3). In all three cases, click on the “black & white map projected” link to see the full image with scale.

Overview map

The overview map on right shows where these three pits are located. If you compare this map with my previous overview maps from November 12, 2018 and February 22, 2019 you can see that while these pits are all found on the volcanic slopes surrounding Arsia Mons, they are all different pits. Moreover, the ten pits listed in these three posts are only a small sampling of the more than hundred already found.

Whether these pits are deadend sinks or skylights into underground lava tubes that connect is at this point unknown. It would be a reasonable speculation to assume that some are deadends, and some link to extensive tubes of varying lengths. It would also be dangerous. Mars is alien. While the geology will be based on the same physical laws found on Earth, the lighter gravity is going to produce things differently.

The three images above however do show some intriguing details.
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Another batch of caves/pits found on Mars

Four new pits on Mars

Overview of February 2019 pits

In the past year the monthly image releases from the high resolution camera on Mars Reconnaissance Orbiter (MRO) archive have frequently included newly discovered pit entrances. Each time I have written posts highlighting these new pits, in June, July, November 2018 and January 2019. In fact, this is happening so frequently I could almost label it a monthly update!

The November release imaged three pits found on the southern flanks of Arsia Mons. The January 2019 release found several north of the volcano, two of which are very close to the two middle new pits highlighted above. The February release, which is the focus of this post, included four more pits, shown above, all located north and west of Arsia Mons, as shown in the overview map to the right.

Pits 2 and 3 above appear to belong to a cluster of pits all located in the general area between Arsia and Pavonis Mons. (You can see their uncaptioned releases here and here.) Most sit alone on a flat somewhat featureless plain. Sometimes there are flow features nearby, but each pit usually seems to sit unique and unrelated to these other faint features.

Pit 1 is very intriguing in that it sits amid a very long chain of pits and canyons, all aligned, as shown in the image below and to the right.
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The many pits/caves of Mars

Sinkhole in Martian northern lowlands with dark seep

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.

As I wrote in that June 9, 2015 post:
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Volcanic vent between Arsia and Pavonis Monsa

volcanic vent on Mars

Cool image time. The photo on the right, rotated, cropped, and reduced to post here, was taken in September by the high resolution camera of Mars Reconnaissance Orbiter (MRO) and was part of the November image release. Click on the image to see the entire photograph at full resolution.

The uncaptioned release dubs this feature as “Small Eruptive Vents South of Pavonis Mons.” In truth, these vent pits are located almost exactly the same distance from both Pavonis Mons, the middle volcano in the line of three giant Martian volcanoes, and Arsia Mons, the southernmost of the three.

The image is interesting for several reasons. First, note the bulge surrounding the vent, making this look almost like a miniature volcano all its own. In fact, that is probably what it is. When it was active that bulge was likely caused by that activity, though it is hard to say whether the bulge was caused by flow coming from out of the vent, or by pressure from below pushing upward to cause the ground to rise. It could even have been a combination of both.

To my eye, most of the bulge was probably caused from pressure from below pushing upward. The edge of the bulge does not look like the leading edge of a lava flow. Still, this probably happened so long ago that Martian wind erosion and dust could have obscured that leading edge.

That this is old is indicated by the dunelike ripples inside the large pit, and the pond of trapped dust in the smaller pit. Because of the thinness of the Martian atmosphere it takes time to gather that much dust, during which time no eruptions have occurred.

One more interesting detail: If you look at the pits in full resolution, you will see that, based on the asymmetrical wind patterns between the west and east rims, the prevailing winds here are from the west. Located as it is just to the east of the gigantic saddle between Arsia and Pavonis Mons, this wind orientation makes sense, as a saddle between mountains tends to concentrate the wind, much like a narrowed section in a river produces faster water flow and rapids. As for why the wind blows mostly from the west, my guess (which should not be taken very seriously) is that it is probably caused by the same meteorological phenomenon that causes this generally on Earth, the planet’s rotation.

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Dust devil tracks on the Martian southern highlands

Dust devil tracks

Today’s cool image is cool because of how little is there. The image to the right, cropped to post here, was part of the December image release from the high resolution camera on Mars Reconnaissance Orbiter (MRO). The uncaptioned release labeled this image simply as “Southern Intercrater Plains.” Located in the Martian southern highlands, this location is located almost due south of Arsia Mons, the southernmost in the chain of three giant volcanoes to the west of Marineris Valles (as indicated by the white dot on the overview image below).

If you click on the image you can see the entire photograph, though in this case it won’t show you much else than in the excerpt to the right. The terrain here appears flat. The only features of note are some small knobs and the random dark lines that are almost certainly accumulated dust devil tracks. There are also many dark spots, which might also be the shadows of even smaller knobs, but could also be instrument artifacts. I am not sure.

Location of dust devil image

The southern highlands are mostly cratered, with few signs that water ever flowed there. This image for example gives the impression of a vast lonely terrain that has changed little since the very earliest days of Mars’ history.

I expect that scientists could possibly assign some age to this terrain, merely by studying the dust devil tracks. If we calculate how often dust devils might traverse this place, and then count the tracks, assigning their order by faintness, with the faintest being the oldest, it could be possible to obtain a rough age of the oldest tracks.

Still, all that would do would tell us the approximate length of time in which a dust devil track can remain visible. And even if this is a long time, it doesn’t constrain the age of the surface very much, as the weather on Mars has certainly changed with time, especially because we think the atmosphere was once thicker.

What formed this flat terrain? My first guess would be a lava flow, caused when the numerous nearby craters were formed by impact. These craters were likely created during the great bombardment between 3 and 4 billion years ago, and while they have certainly been modified more than lunar craters because of the presence of an atmosphere on Mars, they are likely to have not changed much during that time. Similarly, this flat terrain is likely much like it was, several billion years ago. Dust devils have deposited dust and their tracks, but the hard bedrock remains as it was soon after it solidified.

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Present and future landing sites on Mars

With InSight’s landing on Mars set for 11:54 am (Pacific) this coming Monday, November 26, 2018, I decided to put together a map of Mars showing the location of all the successful landers/rovers, adding the landing sites for the planned landers/rovers through 2020. This will give some context to InSight’s landing site.

Landing sites on Mars

The map does not show the landing sites for the failed Soviet, American, and British landers.

As I noted in describing the Mars2020 landing site, the location of the bulk of these landing sites, along the transition zone from the southern highlands and the northern lowlands, demonstrates the areas of the planet that interest geologists the most. It is here that we find many shoreline features, suggestive of the ocean that many scientists theorize existed intermittently in the northern lowlands. It is here that planetary scientists can quickly gather the most information about Martian geological history. And it is here that they have the opportunity to study the widest range of rock types.

From an explorer’s perspective, however, this approach has its limits. It does not provide us a look at a wide variety of locations. It is not directly aimed at finding lower latitude locations where ice might actually exist. And it is decidedly not focused in studying the planet from the perspective of future colonists. I am sometimes frustrated that we have as yet no plans to send any rovers into Marineris Valles, or to the western slopes of Arsia Mons, the southern most volcano in the chain of three giant volcanoes where there are indications that ice might exist underground, or to any of the places where caves are known to exist where a colony could be built more easily. In fact, the caves on the slopes of Arsia Mons seems a prime exploration target.

Eventually these locations will be explored, likely by private landers aimed at scouting out locations for future private settlements. I am just impatient.

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Volcanic rivers on Mars

Granicus Valles

Cool image time! The photo on the right, cropped and reduced to post here, was part of the November image release from the high resolution camera on Mars Reconnaissance Orbiter (MRO). If you click on the image you can see the full resolution picture.

The uncaptioned release webpage is dubbed “Faults in Granicus Valles.” The image itself only shows a small part of Granicus Valles, named after a river in Turkey, that flows down from the estern slopes of the giant volcano Elysium Mons. While far smaller than the four big Martian volcanoes in the Tharsis region to the east and near Marines Valles (which I highlight often), Elysium Mons still outshines anything on Earth at a height of almost 30,000 feet and a width of 150 miles. It sits at about the same northern latitude of Olympus Mons, but all by itself, rising up at the very northern edge of the transition zone between the southern highlands and the northern plains, with the vast Utopia Basin, the second deepest basin on Mars, to the west.

Overview of Elysium Mons and Granicus Valles

Granicus Valles itself is almost five hundred miles long. At its beginning it flows in a single straight fault, but once it enters the northern plains of Utopia Basin it begins to meander and break up into multiple tributaries. The MRO image above shows only a tiny portion in the northern plains, as illustrated by the white box in the overview map to the left.
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More Pits on Mars!

Pits near Arsia Mons

Cool image time! In the November image release from the high resolution camera on Mars Reconnaissance Orbiter (MRO) were three images, dubbed by me in the collage above as number one, number two, and number three, showing pits south of Arsia Mons, the southernmost volcano in the chain of three giant volcanoes to the east of Mars’s largest volcano, Olympus Mons, and to the west of the Marineris Valles valley.

Mars overview showing pit locations

The image on the right provides the geographical context of the three pits. They are all south of the volcano on the vast lava flow plains that surround it. The location of pits #1 and #2 is especially intriguing, on the east and west edges of what appears to be a large lava flow that had burst out from the volcano, leaving a large lava field covering a vast area several hundred miles across just to the south. You can also see a similar large lava field to the north of the volcano. Both fields appear to have been formed when lava poured through the breaks created by the fault that cuts through the volcano from the northeast to the southwest.
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Intriguing water-ice cloud on Mars

Water-ice cloud over Arsia Mons

An extended water-ice cloud has formed recently on the downwind side of the large Martian volcano Arsia Mons. The image above, cropped to post here, was taken by Europe’s Mars Express orbiter, and shows the cloud extending westward from the volcano.

In spite of its location, this atmospheric feature is not linked to volcanic activity but is rather a water ice cloud driven by the influence of the volcano’s leeward slope on the air flow – something that scientists call an orographic or lee cloud – and a regular phenomenon in this region.

The cloud can be seen in this view taken on 10 October by the Visual Monitoring Camera (VMC) on Mars Express – which has imaged it hundreds of times over the past few weeks – as the white, elongated feature extending 1500 km westward of Arsia Mons. As a comparison, the cone-shaped volcano has a diameter of about 250 km.

… Mars just experienced its northern hemisphere winter solstice on 16 October. In the months leading up to the solstice, most cloud activity disappears over big volcanoes like Arsia Mons; its summit is covered with clouds throughout the rest of the martian year.

However, a seasonally recurrent water ice cloud, like the one shown in this image, is known to form along the southwest flank of this volcano – it was previously observed by Mars Express and other missions in 2009, 2012 and 2015.

What the article does not mention about these seasonal water ice clouds is that they are thought to be related to the evidence of past glaciers on the volcano’s western slopes. Some scientists believe that significant underground ice, left over from those glaciers, is what causes the clouds.

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Zooming in on a Martian surprise

Global map of Mars

Let’s take a journey. Above is a global map of Mars, showing its largest and well known geological features. While far smaller than Earth, its lack of oceans means that Mars’ actual dry surface has about the same square footage as the continents of Earth. It is a vast place. Getting a close look at every spot is going to take many decades of work, and probably won’t be finished until humans are actually walking its surface.

Let’s pick a spot, zoom in and find out what’s there.
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Martian craters go splat!

Overview of the volcanic Tharsis Bulge on Mars

Cool image time! In continuing my exploration of this month’s Mars Reconnaissance Orbiter (MRO) image release, I found two interesting images of small craters, one as part of that image release, the other found completely by accident.

The map on the right, taken from the MRO HiRISE archive page, shows the locations of these two images. Both are located in the lava plains that surround the giant volcano Pavonis Mons, the central volcano of the three volcanoes to the east of Olympus Mons. Previously, I have done posts focusing specifically on both Pavonis Mons and Arsia Mons. Not only is the geology of these gigantic volcanoes fascinating, there is evidence that ancient glacial ice lurks in lava tubes on their slopes, making them potentially prime real estate for future explorers.

The first image, labeled #1 on the image above, was taken in January 2018 to get a better look at a small crater on the surrounding lava plains, and was part of the MRO March image release. I have cropped it to post here, focusing on the crater itself.

My first reaction on seeing the image was, “Did this impact not go splat when it hit?”
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Massive flow on Mars

Massive flow on Mars

Cool image time! The image on the right, cropped to post here, comes from a Mars Reconnaissance Orbiter image that shows a massive relatively recent and dark slope streak that emanates out from a single point on the surface. (Note that the release at this link rotates the image so that north points down. I have rotated back so that north points up.)

Streaks form on slopes when dust cascades downhill. The dark streak is an area of less dust compared to the brighter and reddish surroundings. What triggers these avalanches is not known, but might be related to sudden warming of the surface.

These streaks are often diverted by the terrain they flow down. This one has split into many smaller streaks where it encountered minor obstacles. These streaks fade away over decades as more dust slowly settles out of the Martian sky.

Point of origin for flow

Location of flow, west of Olympus Mons

The MRO release focuses on the fingerlike breakup of the flow as it descends into sand-dune filled plain. What is more interesting to me is the terrain where this flow originated. A close-up of that area from the full image, shown on the right, reveals a feature that could be a wash running in line with the flow’s origin, and leading uphill to a dark feature that is a likely a cliff face. (The light in this image is coming from the southeast.)

This location, at 15.2N latitude, 214.9E longitude and shown by the small cross in the image on the right and captured from this page, is west of Olympus Mons, the largest volcano on Mars. This suggests to me that the originating feature might be an outlet from a lava tube, from which water suddenly seeped out to produce this massive slope streak. A look at the mesa from which this flow came, cropped from the full image and posted below the fold, shows numerous similar slope streaks of varying ages flowing out of this mesa, with some very faint because they occurred farther in the past. Some are even within the bowl at the top of the mesa.

Whether these come from lava tubes is definitely unclear, and I suspect I will be told by geologists not likely. The seeps however do suggest strongly that this mesa might be a very good location for future colonists to look for underground water ice. Since clouds form on the western slopes of Arsia Mons, the southernmost of the three giant volcanoes to the east of Olympus Mons, and that past glacial activity has been documented there, I wonder if some of these same conditions might also exist here, on the nearby terrain west of Olympus Mons.
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A spectacular collapse feature at Arsia Mons

Collapse at Arsia Mons

Cool image time! This post could be called an update to my January 8th post, Exploring Arsia Mons. In that post I had compiled together the ten images of Arsia Mons, the southernmost volcano in the line of three giant volcanoes on Mars, that JPL had highlighted over several weeks in early January.

Today, I decided to do some of my own exploration of some of the many images taken of Arsia Mons by all of the Martian orbiters. My goal had been to explore the volcano’s western slopes (an area that had not been featured in the JPL releases) because that is the area where research has found evidence of past glacial activity as well as seasonal water clouds. I haven’t finished that survey, but in the process I came across a spectacular image of a collapse that had been visible in image nine of the January 8th post, but did not stand out there because of the lighting. The image on the right is that better image, cropped to focus in on the collapse itself.

The material at the base of the wall resembles piled up mud, which suggests this collapse is a Martian version of a mud slide. If so, it also suggests the presence of liquid. At the same time, the muddy look might not be from liquid but because of the lighter Martian gravity causing avalanches to be appear different there. The light gravity means material is not as dense, so when it collapses it might break apart more easily into a sandy type flow.

I am only an amateur geologist, so my theories here should not be taken very seriously. Nonetheless, I am sure there are planetary geologists who have looked at this closely because of the information about Martian geology that they can glean from it. I’d be curious to hear their thoughts.

Meanwhile, my exploration of the western slopes of Arsia Mons will continue. In Pioneer the science fiction book I wrote in the early 1980s (now available), I placed my Martian colony in Mangala Valles, a meandering canyon to the west of Olympus Mons that feeds out from the higher southern regions into the lower northern flat plains where even then some scientists thought an ocean might have once existed. My thinking then was that this might be a good location to find underground water. It now appears, with our greater knowledge, that the slopes of the volcanoes themselves might be more promising, and I am curious to find the most likely places in this region where a future colony might end up.

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Exploring Arsia Mons

Master index

In November over a period of two weeks the Mars Odyssey team posted ten images of Pavonis Mons, the smallest of the aligned three giant volcanoes just to the east of Olympus Mons, the largest known volcano in the solar system. I then made all of those images available in a single link, with some analysis.

They have now done the same thing for the southernmost (and possibly the most interesting) of those three aligned volcanoes, Arsia Mons. From the first image below:

Arsia Mons is the southernmost of the Tharsis volcanoes. It is 270 miles (450km) in diameter, almost 12 miles (20km) high, and the summit caldera is 72 miles (120km) wide. For comparison, the largest volcano on Earth is Mauna Loa. From its base on the sea floor, Mauna Loa measures only 6.3 miles high and 75 miles in diameter. A large volcanic crater known as a caldera is located at the summit of all of the Tharsis volcanoes. These calderas are produced by massive volcanic explosions and collapse. The Arsia Mons summit caldera is larger than many volcanoes on Earth.

In other words, you could fit almost all of Mauna Loa entirely within the caldera of Arsia Mons.

The image on the right above is the master index, annotated by me to show the area covered by each image. The images can accessed individually below.
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Exploring one of Mars’ giant volcanoes

Master index

For the past two weeks JPL’s image site has been releasing a string of images taken by Mars Odyssey of the smallest of Mars’ four giant volcanoes.

Pavonis Mons is one of the three aligned Tharsis Volcanoes. The four Tharsis volcanoes are Ascreaus Mons, Pavonis Mons, Arsia Mons, and Olympus Mars. All four are shield type volcanoes. Shield volcanoes are formed by lava flows originating near or at the summit, building up layers upon layers of lava. The Hawaiian islands on Earth are shield volcanoes. The three aligned volcanoes are located along a topographic rise in the Tharsis region. Along this trend there are increased tectonic features and additional lava flows. Pavonis Mons is the smallest of the four volcanoes, rising 14km above the mean Mars surface level with a width of 375km. It has a complex summit caldera, with the smallest caldera deeper than the larger caldera. Like most shield volcanoes the surface has a low profile. In the case of Pavonis Mons the average slope is only 4 degrees.

The image on the right is the context image, annotated by me to show where all these images were taken. The images can accessed individually below.

Each of these images has some interesting geological features, such as collapses, lava tubes, faults, and flow features. Meanwhile, the central calderas are remarkable smooth, with only a few craters indicating their relatively young age.

The most fascinating geological fact gleaned from these images is that they reveal a larger geological trend that runs through all of the three aligned giant volcanoes to the east of Olympus Mons.

The linear and sinuous features mark the locations of lava tubes and graben that occur on both sides of the volcano along a regional trend that passes thru Pavonis Mons, Ascreaus Mons (to the north), and Arsia Mons (to the south).

This trend probably also indicates the fundamental geology that caused all three volcanoes to align as they have.

Arsia Mons is of particular interest in that water clouds form periodically above its western slope, where there is also evidence of past glaciation. Scientists strongly suspect that there is a lot of water ice trapped underground here, possibly inside the many lava tubes that meander down its slopes. These facts also suggest that this might be one of the first places humans go to live, when they finally go to live on Mars.

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Europe’s Trace Gas Orbiter detects clouds over Martian volcano

Europe’s Trace Gas Orbiter (TGO) has detected clouds over the western slopes of the giant Martian volcano Arsia Mons.

This is not a new discovery, merely a confirmation of many past observations, all of which suggest that water-ice glaciers once flowed down those western slopes, and that some of that ice remains trapped in underground caves and lava tubes there. Undeniably this region appears at present to be the most valuable real estate on Mars. It has caves where the first colonies can be more easily built. Those caves likely have water in them. And the location is near the equator, which is easier to reach and also makes the environment somewhat less hostile.

TGO is presently slowly aerobraking itself down to its planned science orbit, which it is expected to reach in 2018.

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Scientists narrow the next Mars rover candidate landing sites to 8

Jezero Crater

For the next Mars rover, scheduled to launch in 2020, scientists have now narrowed their candidate landing sites to eight, with Jezero Crater (pictured on the right) the favorite choice.

The top vote getter was Jezero crater, which contains a relic river delta that could have concentrated and preserved organic molecules. “The appeal is twofold,” says Bethany Ehlmann, a planetary scientist at the California Institute of Technology (Caltech) in Pasadena. “Not only is there a delta, but the rocks upstream are varied and diverse.”

The image clearly shows the scientific attraction of Jezero Crater, with an obvious meandering river canyon opening out into an obvious river delta. The crater in the delta will also give them an opportunity to do some dating research, since that crater had to have been put there after the delta was formed.

The choice however illustrates the difference in goals between scientists and future colonists. Scientists are looking for the most interesting locations for understanding the geological history of Mars. Future colonists want to find the best places to establish a home. Jezero Crater, as well as the other eight candidate sites, do not necessarily fit that settlement need. For a colonist it might be better to put a rover down on the flanks of Arsia Mons, one of Mars’ giant craters where scientists have evidence of both water-ice and caves. None of the candidate sites, however, are aimed anywhere close to this volcanic region, because scientifically it is not as interesting.

This is not to say that the candidate sites might not be good settlement sites. It is only to note that the focus of these scientists is research only. Furthermore, it is probably premature anyway to look for settlement sites. We need to know more about Mars itself.

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Finding caves on Mars

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.
» Read more

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India extends Mangalyaan’s mission by six months

Western slopes of Arsia Mons

Having successfully completed its nominal six month mission and continuing to operate perfectly, ISRO has extended the mission of India’s Mangalyaan Mars orbiter for another six months.

Take a gander at the images the orbiter has been sending down. Quite impressive. The cropped image on the right shows the western slopes of the giant volcano Arsia Mons, with white water vapor hovering above those slopes. (Click on the image for the full resolution version.) The water vapor is significant because scientists believe that this region once had many glaciers, and that much of that water is still present and trapped below the surface as ice, possibly in many of the caves that are there. The vapor’s presence, a routine occurance here, strengthens this theory.

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New images from Mangalyaan

Arsia Mons

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.

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Glaciers on Mars!

A geological study of orbital images of Gale Crater has led scientists to conclude that the crater was once covered in glaciers.

To carry out the study, the team has used images captured with the HiRISE and CTX cameras from NASA’s Mars Reconnaissance Orbiter, together with the HRSC onboard the Mars Express probe managed by the European Space Agency (ESA).

Analyses of the photographs have revealed the presence of concave basins, lobated structures, remains of moraines and fan-shaped deposits which point to the existence of ancient glaciers on Gale. In fact they seem to be very similar to some glacial systems observed on present-day Earth. “For example, there is a glacier on Iceland –known as Breiðamerkurjökull– which shows evident resemblances to what we see on Gale crater, and we suppose that is very similar to those which covered Gale’s central mound in the past,” says Fairén.

This is not the first place on Mars where scientists believe glaciers once flowed. The northwestern slopes of Arsia Mons, one of Mars’s giant volcanoes in the Tharsis Bulge, is also believed to have once harbored glaciers.

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A place on Mars that was possibly habitable only 200 million years ago.

A place on Mars that was possibly habitable only 200 million years ago.

This article discusses the possibility of liquid water from the melting of the glaciers that scientists think once covered the western slopes of the giant volcano Arsia Mons. I have also written about this area in an article I wrote for Sky & Telescope last year on exploring caves in space. It is thought that there might be caves here in which some of that water from those glaciers might still be found.

As one scientist is quoted as saying in this article, “Arsia Mons would be the next place I would want to go.” Like the south pole of the Moon, it likely has all the ingredients for establishing a habitable colony.

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