We live in a time when our spacecraft orbiting Mars at an altitude of about 300 km. can snap photos of a dust devil and transmit them back to us so we can share them on the internet. Not only that, but we have rovers wandering around on the surface taking pictures of the dust storms, too. Big deal, you say? So what, you say?
When robotic missions first began to land on the surface of Mars in the 1970s, they revealed a harsh, cold and desiccated landscape. This effectively put an end generations of speculation about “Martian canals” and the possibility of life on Mars. But as our efforts to explore the Red Planet have continued, scientists have found ample evidence that the planet once had flowing water on its surface.
In addition, scientists have been encouraged by the appearance of Recurring Slope Lineae (RSL), which were believed to be signs of seasonal water flows. Unfortunately, a new study by researchers from the U.S. Geological Survey indicates that these features may be the result of dry, granular flows. These findings are another indication that the environment could be too dry for microorganisms to survive.
For the sake of their study, the team consulted data from the High Resolution Image Science Experiment (HiRISE) camera aboard the NASA Mars Reconnaissance Orbiter (MRO). This same instrument was responsible for the 2011 discovery of RSL, which were found in the middle latitudes of Mars’ southern hemisphere. These features were also observed to appear on Martian slopes during late spring through summer and then fade away in winter.
The seasonal nature of these flows was seen as a strong indication that they were the result of flowing salt-water, which was indicated by the detection of hydrated salt at the sites. However, after re-examining the HiRISE data, Dundas and his team concluded that RSLs only occur on slopes that are steep enough for dry grains to descend – in much the same way that they would on the faces of active dunes.
“We’ve thought of RSL as possible liquid water flows, but the slopes are more like what we expect for dry sand. This new understanding of RSL supports other evidence that shows that Mars today is very dry.”
Using pairs of images from HiRISE, Dundas and his colleagues constructed a series of 3-D models of slope steepness. These models incorporated 151 RSL features identified by the MRO at 10 different sites. In almost all cases, they found that the RSL were restricted to slopes that were steeper than 27° and each flow ended on a slope that matched the patterns seen in slumping dry sand dunes on Mars and Earth.
Basically, sand flows end where a steep angle gives way to a less-steep “angle of repose”, whereas liquid water flows are known to extend along less steep slopes. As Alfred McEwen, HiRISE’s Principal Investigator at the University of Arizona and a co-author of the study, indicated, “The RSL don’t flow onto shallower slopes, and the lengths of these are so closely correlated with the dynamic angle of repose, it can’t be a coincidence.”
These observations is something of a letdown, since the presence of liquid water in Mars’ equatorial region was seen as a possible indication of microbial life. However, compared to seasonal brine flows, the present of granular flows is a far better fit with what is known of Mars’ modern environment. Given that Mars’ atmosphere is very thin and cold, it was difficult to ascertain how liquid water could survive on its surface.
Nevertheless, these latest findings do not resolve all of the mystery surrounding RSLs. For example, there remains the question of how exactly these numerous flows begin and gradually grow, not to mention their seasonal appearance and the way they rapidly fade when inactive. On top of that, there is the matter of hydrated salts, which have been confirmed to contain traces of water.
To this, the authors of the study offer some possible explanations. For example, they indicate that salts can become hydrated by pulling water vapor from the atmosphere, which might explain why patches along the slopes experience changes in color. They also suggest that seasonal changes in hydration might result in some trigger mechanism for RSL grainflows, where water is absorbed and release, causing the slope to collapse.
If atmospheric water vapor is a trigger, then it raises another important question – i.e. why do RSLs appear on some slopes and not others? As Alfred McEwen – HiRISE’s Principal Investigator and a co-author on the study – explained, this could indicate that RSLs on Mars and the mechanisms behind their formation may not be entirely similar to what we see here on Earth.
“RSL probably form by some mechanism that is unique to the environment of Mars,” he said, “so they represent an opportunity to learn about how Mars behaves, which is important for future surface exploration.” Rich Zurek, the MRO Project Scientist of NASA’s Jet Propulsion Laboratory, agrees. As he explained,
“Full understanding of RSL is likely to depend upon on-site investigation of these features. While the new report suggests that RSL are not wet enough to favor microbial life, it is likely that on-site investigation of these sites will still require special procedures to guard against introducing microbes from Earth, at least until they are definitively characterized. In particular, a full explanation of how these enigmatic features darken and fade still eludes us. Remote sensing at different times of day could provide important clues.”
In the coming years, NASA plans to carry out the exploration of several sites on the Martian surface using the Mars 2020 rover, which includes a planned sample-return mission. These samples, after being collected and stored by the rover, are expected to be retrieved by a crewed mission mounted sometime in the 2030s, and then returned to Earth for analysis.
The days when we are finally able to study the Mars’ modern environment up close are fast approaching, and is expected to reveal some pretty Earth-shattering things!
Finding a source of Martian water – one that is not confined to Mars’ frozen polar regions – has been an ongoing challenge for space agencies and astronomers alike. Between NASA, SpaceX, and every other public and private space venture hoping to conduct crewed mission to Mars in the future, an accessible source of ice would mean the ability to manufacture rocket fuel on sight and provide drinking water for an outpost.
So far, attempt to locate an equatorial source of water ice have failed. But after consulting old data from the longest-running mission to Mars in history – NASA’s Mars Odyssey spacecraft – a team of researchers from the John Hopkins University Applied Physics Laboratory (JHUAPL) announced that they may have found evidence of a source of water ice in the Medusae Fossae region of Mars.
This region of Mars, which is located in the equatorial region, is situated between the highland-lowland boundary near the Tharsis and Elysium volcanic areas. This area is known for its formation of the same name, which is a soft deposit of easily-erodible material that extends for about 5000 km (3,109 mi) along the equator of Mars. Until now, it was believed to be impossible for water ice to exist there.
However, a team led by Jack Wilson – a post-doctoral researcher at the JHUAPL – recently reprocessed data from the Mars Odyssey spacecraft that showed unexpected signals. This data was collected between 2002 and 2009 by the mission’s neutron spectrometer instrument. After reprocessing the lower-resolution compositional data to bring it into sharper focus, the team found that it contained unexpectedly high signals of hydrogen.
To bring the information into higher-resolution, Wilson and his team applied image-reconstruction techniques that are typically used to reduce blurring and remove noise from medical and spacecraft imaging data. In so doing, the team was able to improve the data’s spatial resolution from about 520 km (320 mi) to 290 km (180 mi). Ordinarily, this kind of improvement could only be achieved by getting the spacecraft much closer to the surface.
“It was as if we’d cut the spacecraft’s orbital altitude in half,” said Wilson, “and it gave us a much better view of what’s happening on the surface.” And while the neutron spectrometer did not detect water directly, the high abundance of neutrons detected by the spectrometer allowed the research team to calculate the abundance of hydrogen. At high latitudes on Mars, this is considered to be a telltale sign of water ice.
The first time the Mars Odyssey spacecraft detected abundant hydrogen was in 2002, which appeared to be coming from subsurface deposits at high latitudes around Mars. These findings were confirmed in 2008, when NASA’s Phoenix Lander confirmed that the hydrogen took the form of water ice. However, scientists have been operating under the assumption that at lower latitudes, temperatures are too high for water ice to exist.
These scans have suggested that there was either low-density volcanic deposits or water ice below the surface, though the results seemed more consistent with their being no water ice to speak of. As Wilson indicated, their results lend themselves to more than one possible explanation, but seem to indicate that water ice could part of the subsurface’s makeup:
“[I]f the detected hydrogen were buried ice within the top meter of the surface. there would be more than would fit into pore space in soil… Perhaps the signature could be explained in terms of extensive deposits of hydrated salts, but how these hydrated salts came to be in the formation is also difficult to explain. So for now, the signature remains a mystery worthy of further study, and Mars continues to surprise us.”
Given Mars’ thin atmosphere and the temperature ranges that are common around the equator – which get as high as 308 K (35 °C; 95 °F) by midday during the summer – it is a mystery how water ice could be preserved there. The leading theory though is that a mixture of ice and dust was deposited from the polar regions in the past. This could have happened back when Mars’ axial tilt was greater than it is today.
However, those conditions have not been present on Mars for hundreds of thousands or even millions of years. As such, any subsurface ice that was deposited there should be long gone by now. There is also the possibility that subsurface ice could be shielded by layers of hardened dust, but this too is insufficient to explain how water ice could have survived on the timescales involved.
In the end, the presence of abundant hydrogen in the Medusae Fossae region is just another mystery that will require further investigation. The same is true for deposits of water ice in general around the equatorial region of Mars. Such deposits mean that future missions would have a source of water for manufacturing rocket fuel.
This would shave billions of dollars of the costs of individual mission since spacecraft would not need to carry enough fuel for a return trip with them. As such, interplanetary spacecraft could be manufactured that would be smaller, lighter and faster. The presence of equatorial water ice could also be used to provide a steady supply of water for a future base on Mars.
Crews could be rotated in and out of this base once every two years – in a way that is similar to what we currently do with the International Space Station. Or – dare I say it? – a local source of water could be used to supply drinking, sanitation and irrigation water to eventual colonists! No matter how you slice it, finding an accessible source of Martian water is critical to the future of space exploration as we know it!
During late summer in the Southern hemisphere on Mars, the angle of the sunlight as it strikes the surface brings out some subtle details on the planet’s surface.
In this image, the HiRISE camera on board NASA’s Mars Reconnaissance Orbiter (MRO) captured an area of frozen carbon dioxide on the surface. Some of the carbon dioxide ice has melted, giving it a swiss-cheese appearance. But there is also an unusual hole or crater on the right side of the image, with some of the carbon dioxide ice clearly visible in the bottom of the pit.
NASA scientists are uncertain what exactly caused the unusual pit. It could be an impact crater, or it could be a collapsed pit caused by melting or sublimation of sub-surface carbon dioxide ice.
MRO has been in orbit around Mars for over 10 years, and has completed over 50,000 orbits. The MRO has two cameras. The CTX camera is lower resolution, and has imaged over 99% of the Martian surface. HiRISE is the high-resolution camera that is used to closely examine areas and objects of interest, like the unusual surface pit in this image.
We’ve posted several ‘flyover’ videos of Mars that use data from spacecraft. But this video might be the most spectacular and realistic. Created by filmmaker Jan Fröjdman from Finland, “A Fictive Flight Above Real Mars” uses actual data from the venerable HiRISE camera on board the Mars Reconnaissance Orbiter, and takes you on a 3-D tour over steep cliffs, high buttes, amazing craters, polygons and other remarkable land forms. But Fröjdman also adds a few features reminiscent of the landing videos taken by the Apollo astronauts. Complete with crosshatches and thruster firings, this video puts you on final approach to land on (and then take off from) Mars’ surface.
(Hit ‘fullscreen’ for the best viewing)
To create the video, Fröjdman used 3-D anaglyph images from HiRISE (High Resolution Science Imaging Experiment), which contain information about the topography of Mars surface and then processed the images into panning video clips.
Fröjdman told Universe Today he worked on this video for about three months.
“The most time consuming was to manually pick the more than 33,000 reference points in the anaglyph images,” he said via email. “Now when I count how many steps there were in total in the process, I come to seven and I needed at least 6 different kinds of software.”
Fröjdman, a landscape photographer and audiovisual expert, said he wanted to create a video that gives you the feeling “that you are flying above Mars looking down watching interesting locations on the planet,” he wrote on Vimeo. “And there are really great places on Mars! I would love to see images taken by a landscape photographer on Mars, especially from the polar regions. But I’m afraid I won’t see that kind of images during my lifetime.”
Between HiRISE and the Curiosity rover images, we have the next best thing to a human on Mars. But maybe one day…
By day, Kevin Gill is a software engineer at the Jet Propulsion Laboratory. But on nights and weekends he takes data from spacecraft and turns them into scenes that can transport you directly to the surface of Mars.
Gill is one of many so-called “amateur” image editing enthusiasts that take real, high-resolution data from spacecraft and create views that can make you feel like you are standing on the surface of Mars, or out flying around the Solar System.
Some of the best data around for these purposes come from the HiRISE camera on board the Mars Reconnaissance Orbiter. Data known as Digital Terrain Model (DTM) files, the HiRISE DTMs are made from two or more images of the same area of a region on Mars, taken from different angles. This data isn’t just for making stunning images or amazing movies. For scientists, DTMs are very powerful research tools, used to take measurements such a elevation information and model geological processes.
So, just how do you go from this DTM image from HiRISE:
To this amazing image?
I’m going to let Kevin explain it:
To prep the data, I use Photoshop (to convert the JP2 file to a TIFF), and then standard GIS tools like gdal (Geospatial Data Abstraction Library) to create textures for 3D modeling. Using Autodesk Maya, I input those into a material as a color texture (orthoimagery) or displacement map (the DTM data).
I connect that material to a NURBS plane (sort of like a polygon mesh) that is scaled similarly to the physical properties of the data. I set up a camera at a nice angle (it takes a number of low-resolution test renders to get an angle I like) and let it render.
Then I just pull that render into Photoshop where I have a series of monochromatic color tints which gives the image it’s Martian feel. For the sky, I use either a sky from a MSL MastCam image or one that I took outside with my cell phone. If I’m using a sky I took with my cell phone, I’ll adjust the colors to make it look more like it would on Mars. If the colors in the image are still boring at this point, I may run a HDR adjustment on it in Photoshop.
What all this means is that you can create all these amazing view, plus incredible flyover videos, like this one Kevin put together of Endeavour Crater:
Or you can have some fun and visualize where the Curiosity rover is sitting:
We’ve written about this type of image editing previously, with the work of the people at UnmannedSpaceflight.com and others. Of course, the image editing software keeps improving, along with all the techniques.
Kevin also wanted to point out the work of other image editing enthusiast, Sean Doran.
“Sean’s work is resulting in views similar to mine,” Kevin said via email. “I know he’s using a process very different from mine, but we are thinking along the same lines in what we want out of the end product. His are quite impressive.”
For example, here is a flyover video of the Opportunity rover sitting along the rim of Endeavour Crater:
NASA’s truly outstanding Opportunity rover continues “making new discoveries about ancient Mars” as she commemorates 13 Years since bouncing to a touchdown on Mars, in a feat that is “truly amazing” – the deputy chief scientist Ray Arvidson told Universe Today exclusively.
“Reaching the 13th year anniversary with a functioning rover making new discoveries about ancient Mars on a continuing basis is truly amazing,” Ray Arvidson, Opportunity Deputy Principal Investigator of Washington University in St. Louis, told Universe Today.
Put another way Opportunity is 13 YEARS into her 3 MONTH mission! And still going strong!
During the past year the world famous rover discovered “more extensive aqueous alteration within fractures and more mild alteration within the bedrock outcrops” at Endeavour crater, Arvidson elaborated.
And now she is headed to her next target – an ancient water carved gully!
The gully is situated about 0. 6 mile (1.6 km) south of the robots current location.
But to get there she first has to heroically ascend steep rocky slopes inclined over 20 degrees along the eroded craters western rim – and it’s no easy task! Slipping and sliding along the way and all alone on difficult alien terrain.
Furthermore she is 51 times beyond her “warrantied” life expectancy of merely 90 Sols promised at the time of landing so long ago – roving the surface of the 4th rock from the Sun during her latest extended mission; EM #10.
How was this incredible accomplishment achieved?
“Simply a well-made and thoroughly tested American vehicle,” Arvidson responded.
The six wheeled rover landed on Mars on January 24, 2004 PST on the alien Martian plains at Meridiani Planum -as the second half of a stupendous sister act.
Her twin sister Spirit, had successfully touched down 3 weeks earlier on January 3, 2004 inside 100-mile-wide Gusev crater and survived more than six years.
Opportunity concluded 2016 and starts 2017 marching relentlessly towards an ancient water carved gully along the eroded rim of vast Endeavour crater – the next science target on her heroic journey traversing across never before seen Red Planet terrains.
Huge Endeavour crater spans some 22 kilometers (14 miles) in diameter.
Throughout 2016 Opportunity was investigating the ancient, weathered slopes around the Marathon Valley location in Endeavour crater. The area became a top priority science destination after the slopes were found to hold a motherlode of ‘smectite’ clay minerals based on data from the CRISM spectrometer circling overhead aboard a NASA Mars orbiter.
The smectites were discovered via extensive, specially targeted Mars orbital measurements gathered by the CRISM (Compact Reconnaissance Imaging Spectrometer for Mars) spectrometer on NASA’s Mars Reconnaissance Orbiter (MRO) – accomplished earlier at the direction of Arvidson.
Opportunity was descending down Marathon Valley the past year to investigate the clay minerals formed in water. They are key to helping determine the habitability of the Red Planet when it was warmer and wetter billions of years ago.
What did Opportunity accomplish scientifically at Marathon Valley during 2016?
“Key here is the more extensive aqueous alteration within fractures and more mild alteration within the bedrock outcrops,” Arvidson explained to me.
“Fractures have red pebbles enhanced in Al and Si (likely by leaching out more soluble elements), hematite, and in the case of our scuffed fracture, enhanced sulfate content with likely Mg sulfates and other phases. Also the bedrock is enriched in Mg and S relative to other Shoemaker rocks and these rocks are the smectite carrier as observed from CRISM ATO data.”
Marathon Valley measures about 300 yards or meters long. It cuts downhill through the west rim of Endeavour crater from west to east – the same direction in which Opportunity drove downhill from a mountain summit area atop the crater rim.
Opportunity has been exploring Endeavour since arriving at the humongous crater in 2011. Endeavour crater was formed when it was carved out of the Red Planet by a huge meteor impact billions of years ago.
“Endeavour crater dates from the earliest Martian geologic history, a time when water was abundant and erosion was relatively rapid and somewhat Earth-like,” explains Larry Crumpler, a science team member from the New Mexico Museum of Natural History & Science.
Opportunity has been climbing up very steep and challenging slopes to reach the top of the crater rim. Then she will drive south to Cape Byron and the gully system.
“We have had some mobility issues climbing steep, rocky slopes. Lots of slipping and skidding, but evaluating the performance of the rover on steep, rocky and soil-covered slopes was one of the approved extended mission objectives,” Arvidson explained.
“We are heading out of Cape Tribulation, driving uphill to the southwest to reach the Meridiani plains and then to drive to the western side of Cape Byron to the head of a gully system.”
What’s ahead for 2017? What’s the importance of exploring the gully?
“Finish up work on Cape Tribulation, traverse to the head of the gully system and head downhill into one or more of the gullies to characterize the morphology and search for evidence of deposits,” Arvidson elaborated.
“Hopefully test among dry mass movements, debris flow, and fluvial processes for gully formation. The importance is that this will be the first time we will acquire ground truth on a gully system that just might be formed by fluvial processes. Will search for cross bedding, gravel beds, fining or coarsening upward sequences, etc., to test among hypotheses.”
How long will it take to reach the gully?
“Months to the gully,” replied Arvidson. After arriving at the top of the crater rim, the rover will actually drive part of the way on the Martian plains again during the southward trek to the gully.
“And we will be driving on the plains to drive relatively long distances with an intent of getting to the gully well before the winter season.”
As of today, Jan 31, 2017, long lived Opportunity has survived 4630 Sols (or Martian days) roving the harsh environment of the Red Planet.
Opportunity has taken over 216,700 images and traversed over 27.26 miles (43.87 kilometers) – more than a marathon.
See our updated route map below. It shows the context of the rovers over 13 year long traverse spanning more than the 26 mile distance of a Marathon runners race.
The rover surpassed the 27 mile mark milestone on November 6, 2016 (Sol 4546).
The power output from solar array energy production is currently 416 watt-hours, before heading into another southern hemisphere Martian winter in 2017. It will count as Opportunities 8th winter on Mars.
Meanwhile Opportunity’s younger sister rover Curiosity traverses and drills into the lower sedimentary layers at the base of Mount Sharp.
Stay tuned here for Ken’s continuing Earth and planetary science and human spaceflight news.
Mars has some impressive geological features across its cold, desiccated surface, many of which are similar to featured found here on Earth. By studying them, scientists are able to learn more about the natural history of the Red Planet, what kinds of meteorological phenomena are responsible for shaping it, and how similar our two planets are. A perfect of example of this are the polygon-ridge networks that have been observed on its surface.
One such network was recently discovered by the Mars Reconnaissance Orbiter (MRO) in the Medusae Fossae region, which straddles the planet’s equator. Measuring some 16 story’s high, this ridge network is similar to others that have been spotted on Mars. But according to a survey produced by researchers from NASA’s Jet Propulsion Laboratory, these ridges likely have different origins.
This survey, which was recently published in the journal Icarus, examined both the network found in the Medusae Fossae region and similar-looking networks in other regions of the Red Planet. These ridges (sometimes called boxwork rides), are essentially blade-like walls that look like multiple adjoining polygons (i.e. rectangles, pentagons, triangles, and similar shapes).
While similar-looking ridges can be found in many places on Mars, they do not appear to be formed by any single process. As Laura Kerber, of NASA’s Jet Propulsion Laboratory and the lead author of the survey report, explained in a NASA press release:
“Finding these ridges in the Medusae Fossae region set me on a quest to find all the types of polygonal ridges on Mars… Polygonal ridges can be formed in several different ways, and some of them are really key to understanding the history of early Mars. Many of these ridges are mineral veins, and mineral veins tell us that water was circulating underground.”
Such ridges have also been found on Earth, and appear to be the result of various processes as well. One of the most common involves lava flowing into preexisting fractures in the ground, which then survived when erosion stripped the surrounding material away. A good example of this is the Shiprock (shown above), a monadrock located in San Juan County, New Mexico.
Examples of polygon ridges on Mars include the feature known as “Garden City“, which was discovered by the Curiosity rover mission. Measuring just a few centimeters in height, these ridges appeared to be the result of mineral-laden groundwater moving through underground fissures, which led to standing mineral veins once the surrounding soil eroded away.
At the other end of the scale, ridges that measure around 2 kilometers (over a mile) high have also been found. A good example of this is “Inca City“, a feature observed by the Mars Global Surveyor near Mars’ south pole. In this case, the feature is believed to be the result of underground faults (which were formed from impacts) filling with lava over time. Here too, erosion gradually stripped away the surrounding rock, exposing the standing lava rock.
In short, these features are evidence of underground water and volcanic activity on Mars. And by finding more examples of these polygon-ridges, scientists will be able to study the geological record of Mars more closely. Hence why Kerber is seeking help from the public through a citizen-science project called Planet Four: Ridges.
Established earlier this month on Zooniverse – a volunteer-powered research platform – this project has made images obtained by the MRO’s Context Camera (CTX) available to the public. Currently, this and other projects using data from CTX and HiRISE have drawn the participation of more than 150,000 volunteers from around the world.
By getting volunteers to sort through the CTX images for ridge formations, Kerber and her team hopes that previously-unidentified ones will be identified and that their relationship with other Martian features will be better understood.
The incredible HiRISE camera on board the Mars Reconnaissance Orbiter turned its eyes away from its usual target – Mars’ surface – and for calibration purposes only, took some amazing images of Earth and our Moon. Combined to create one image, this is a marvelous view of our home from about 127 million miles (205 million kilometers) away.
Alfred McEwen, principal investigator for HiRISE said the image is constructed from the best photo of Earth and the best photo of the Moon from four sets of images. Interestingly, this combined view retains the correct positions and sizes of the two bodies relative to each other. However, Earth and the Moon appear closer than they actually are in this image because the observation was planned for a time at which the Moon was almost directly behind Earth, from Mars’ point of view, to see the Earth-facing side of the Moon.
“Each is separately processed prior to combining (in correct relative positions and sizes), so that the Moon is bright enough to see,” McEwen wrote on the HiRISE website. “The Moon is much darker than Earth and would barely show up at all if shown at the same brightness scale as Earth. Because of this brightness difference, the Earth images are saturated in the best Moon images, and the Moon is very faint in the best (unsaturated) Earth image.”
Earth looks reddish because the HiRISE imaging team used color filters similar to the Landsat images where vegetation appears red.
“The image color bandpasses are infrared, red, and blue-green, displayed as red, green, and blue, respectively,” McEwen explained. “The reddish blob in the middle of the Earth image is Australia, with southeast Asia forming the reddish area (vegetation) near the top; Antarctica is the bright blob at bottom-left. Other bright areas are clouds. We see the western near-side of the Moon.”
HiRISE took these pictures on Nov. 20, 2016, and this is not the first time HiRISE has turned its eyes towards Earth.
Back in 2007, HiRISE took this image, below, from Mars’ orbit when it was just 88 million miles (142 million km) from Earth. This one is more like how future astronauts might see Earth and the Moon through a telescope from Mars’ orbit.
If you look closely, you can make out a few features on our planet. The west coast outline of South America is at lower right on Earth, although the clouds are the dominant features. In fact, the clouds were so bright, compared with the Moon, that they almost completely saturated the filters on the HiRISE camera. The people working on HiRISE say this image required a fair amount of processing to make such a nice-looking picture.
You can see an image from a previous Mars’ orbiter, the Mars Global Surveyor, that took a picture of Earth, the Moon and Jupiter — all in one shot — back in 2003 here.
For years, scientists have understood that in Mars’ polar regions, frozen carbon dioxide (aka. dry ice) covers much of the surface during the winter. During the spring, this ice sublimates in places, causing the ice to crack and jets of CO² to spew forth. This leads to the formation of dark fans and features known as “spiders”, both of which are unique to Mars’ southern polar region.
For the past decade, researchers have failed to see these features changing from year-to-year, where repeated thaws have led to their growth. However, using data from the Mars Reconnaissance Orbiter‘s (MRO) HiRISE camera, a research team from the University of Colorado, Boulder and the Planetary Science Institute in Arizona have managed to catch sight of the cumulative growth of a spider for the first time from one spring to the next.
Spiders are so-named because of their appearance, where multiple channels converge on a central pit. Dark fans, on the other hand, are low-albedo patches that are darker than the surrounding ice sheet. For some time, astronomers have been observed these features in the southern polar region of Mars, and multiple theories were advanced as to their origin.
In 2007, Hugh Kieffer of the Space Science Institute in Boulder, Colorado theorized that the dark fans and spiders were linked, and that both features were the result of spring thaws. In short, during Mars’ spring season – when the southern polar region is exposed to more sunlight – the Sun’s rays penetrates the ice sheets and warm the ground underneath.
This causes gas flows to form beneath the ice that build up pressure, eventually causing the ice to crack and triggering geysers. These geysers deposit mineral dust and sand across the surface downwind from the eruption, while the cracks in the ice grow and become visible from orbit. While this explanation has been widely-accepted, scientists have been unable to observe this process in action.
By using data from the MRO’s High Resolution Imaging Science Experiment (HiRISE), the research team was able to spot a small-channeled troughs in the southern region which persisted and grew over a three year period. In addition to closely resembling spidery terrain, it was in proximity to dark fan sites. From this, they determined that they were witnessing a spider that was in the process of formation.
As Dr. Ganna Portyankina – a researcher from the Laboratory for Atmospheric and Space Physics at the University of Colorado, Boulder, and the lead author on the team’s research paper – explained to Universe Today via email,
“We have observed different changes in the surface caused by CO² jets before. However, they all were either seasonal changes in surface albedo, like dark fans, or they were only short-lived and were gone the next year, like furrows. This time, the troughs have stayed over several years and they develop dendritic-type of extension – right the way we expect the large spiders to develop.”
Furrows that were similar to the spidery terrain have been spotted at Mars’ north pole in the past, which coincided with a Martian spring. On these occasions, scientists using data from HiRISE instrument reported seeing small furrows on sand dunes, where eruptions had deposited dark fans. However, in what is typical of northern furrows, these were non-persisting annual occurrences, disappearing when summer winds deposited sand in them.
In contrast, the troughs Dr. Portyankina and her team observed in the southern polar region were persistent over a three-year period. During this time, these features extended and developed new “tributaries”, forming a dendritic pattern that resembled a Martian spider. From this, they concluded that the previously-observed northern furrows have the same cause – i.e. sublimation causing outgassing.
However, they also concluded that the northern furrows do not develop over time because of the high-mobility of dune material in the northern polar region. The difference, it seems, comes down to the presence of erosive sand material in the north and south, which creates (or starts) the erosive process that leads to the formation of spider-like troughs – which both kick-stars the process but can also erase it.
“Many locations in the south polar regions with seasonal dark fans show no visible sand deposits,” said Dr. Portyankina. “Dark fans in those locations might be only a mix of regolith and dust, or even just dust on its own – as it is really everywhere on Mars… [T]hose locations that have sand will experience higher erosion simply because there is granular material in the gas flow. Basically, it is old simple sandblasting. This means, it must be easier and faster to carve spiders in those locations.”
In other words, where sand exists beneath the ice sheet, the ground beneath that is likely to be rockier (i.e. harder)> The formation of spider terrain may thereofre require that the ground beneath the ice be soft enough to be carved, but not so loose that it will refill the channels during a single seasonal cycle. In short, the formation of spidery terrain appears to be dependent upon the difference in surface composition between the poles.
In addition, from the many year’s of HiRISE data that has been accumulated, Dr. Portyankina and her team were also able to gauge the current rate of erosion in Mars’ southern polar region. Ultimately, they estimated that smaller spider-like furrows would require a thousand Martian years (about 1,900 Earth years) in order to become a full-scale spider.
This study is certainly significant, since understanding how seasonal changes and present-day erosion lead to the creation of new topographical features is important when it comes to understanding the processes that shape Mars’ polar regions. As we get closer and closer to the day when crewed missions and even settlement become a reality, knowing how these processes shape the planet will be fundamental to making a go of things on Mars.