Look down into a pit on Mars. The caved-in roof of a lava tube could be a good place to explore on the Red Planet

Want to look inside a deep, dark pit on Mars? Scientists and engineers using the HiRISE Camera on board NASA’s Mars Reconnaissance Orbiter have done just that.

From its orbit about 260 km (160 miles) above the surface, HiRISE can spot something as small as a dinner table, about a meter in size. But can it look inside a cave-like feature on the Red Planet and actually resolve any details inside this pit?

Continue reading “Look down into a pit on Mars. The caved-in roof of a lava tube could be a good place to explore on the Red Planet”

It Hasn’t Rained on Mars for a Long Time, but These Sand Dunes Look Like Raindrops, and They’re Filled with Chemicals Made in Water

Mars is well-known for being a dry and arid place, where dusty red sand dunes are prevalent and water exists almost entirely in the form of ice and permafrost. An upside to this, however, is the fact that these conditions are the reason why Mars’ many surface features are so well preserved. And as missions like the Mars Reconnaissance Orbiter (MRO) have shown, this allows for some pretty interesting finds.

Consider the picture recently taken by Curiosity’s High Resolution Imaging Science Experiment (HiRISE) instrument while orbiting above the Copernicus Crater on Mars. This image showed raindrop-like features that are actually signs of sand dunes that are rich in olivine. These same types of dunes exist on Earth but are very rare since this mineral weathers quickly and turns to clay in wet environments.

Continue reading “It Hasn’t Rained on Mars for a Long Time, but These Sand Dunes Look Like Raindrops, and They’re Filled with Chemicals Made in Water”

A Meteoroid Smashed Into the Side of a Crater on Mars and Then Started a Landslide

In 2006, NASA’s Mars Reconnaissance Orbiter (MRO) established orbit around the Red Planet. Using an advanced suite of scientific instruments – which include cameras, spectrometers, and radar – this spacecraft has been analyzing landforms, geology, minerals and ice on Mars for years and assisting with other missions. While the mission was only meant to last two years, the orbiter has remained in operation for the past twelve.

In that time, the MRO has acted as a relay for other missions to send information back to Earth and provided a wealth of information of its own on the Red Planet. Most recently, it captured an image of an impact crater that caused a landslide, which left a long, dark streak along the crater wall. Such streaks are created when dry dust collapses down the edge of a Martian hill, leaving behind dark swaths.

Close up of the crater captured by the MRO’s HiRISE instrument. Credit: NASA/JPL/University of Arizona

In this respect, these avalanches are not unlike Recurring Slope Lineae (RSL), where seasonal dark streaks appear along slopes during warmer days on Mars. These are believed to be caused by either salt water flows or dry dust grains falling naturally. In this case, however, the dry dust on the slope was destabilized by the meteor’s impact, which exposed darker material beneath.

The impact that created the crater is believed to have happened about ten years ago. And while the crater itself (shown above) is only 5 meters (16.4 feet) across, the streak it resulted in is 1 kilometer (0.62 mi) long! The image also captured the faded scar of an old avalanche, which is visible to the side of the new dark streak.

The image was captured by the MRO’s High Resolution Imaging Science Experiment (HiRISE), which is operated by researchers at the Planetary Image Research Laboratory (PIRL), part of the Lunar and Planetary Laboratory (LPL) at the University of Arizona, Tucson.

Wider-angle view of the impact crater captured by the MRO’s HiRISE instrument and the resulting dark streak. Credit: NASA/JPL/University of Arizona

This is just the latest in a long-line of images and data packages sent back by the MRO. By providing daily reports on Mars’ weather and surface conditions, and studying potential landing sites, the MRO also paves the way for future spacecraft and surface missions. In the future, the orbiter will serve as a highly capable relay satellite for missions like NASA’s Mars 2020 rover, which will continue in the hunt for signs of past life on Mars.

At present, the MRO has enough propellant to keep functioning into the 2030s, and given its intrinsic value to the study of Mars, it is likely to remain in operation right up until it exhausts its fuel. Perhaps it will even be working when astronauts arrived on the Red Planet?

Did the Milky Way Steal These Stars or Kick Them Out of the Galaxy?

Despite thousands of years of research and observation, there is much that astronomers still don’t know about the Milky Way Galaxy. At present, astronomers estimate that it spans 100,000 to 180,000 light-years and consists of 100 to 400 billion stars. In addition, for decades, there have been unresolved questions about how the structure of our galaxy evolved over the course of billions of years.

For example, astronomers have long suspected that galactic halo came from – giant structures of stars that orbit above and below the flat disk of the Milky Way – were formed from debris left behind by smaller galaxies that merged with the Milky Way. But according to a new study by an international team of astronomers, it appears that these stars may have originated within the Milky Way but were then kicked out.

The study recently appeared in the journal Nature under the title “Two chemically similar stellar overdensities on opposite sides of the plane of the Galactic disk“. The study was led by Margia Bergmann, a researcher from the Max Planck Institute for Astronomy, and included members from the Australian National University, the California Institute of Technology, and multiple universities.

Artist’s impression of the Milky Way Galaxy. Credit: NASA/JPL-Caltech/R. Hurt (SSC-Caltech)

For the sake of their study, the team relied on data from the W.M. Keck Observatory to determine the chemical abundance patterns from 14 stars located in the galactic halo. These stars were located in two different halo structures – the Triangulum-Andromeda (Tri-And) and the A13 stellar overdensities – which are bout 14,000 light years above and below the Milky Way disc.

As Bergemann explained in a Keck Observatory press release:

“The analysis of chemical abundances is a very powerful test, which allows, in a way similar to the DNA matching, to identify the parent population of the star. Different parent populations, such as the Milky Way disk or halo, dwarf satellite galaxies or globular clusters, are known to have radically different chemical compositions. So once we know what the stars are made of, we can immediately link them to their parent populations.”

The team also obtained spectra from one additional using the European Southern Observatory’s Very Large Telescope (VLT) in Chile. By comparing the chemical compositions of these stars with the ones found in other cosmic structures, the scientists noticed that the chemical compositions were almost identical. Not only were they similar within and between the groups being studies, they closely matched the abundance patterns of stars found within the Milky Way’s outer disk.

Computer model of the Milky Way and its smaller neighbor, the Sagittarius dwarf galaxy. Credit: Tollerud, Purcell and Bullock/UC Irvine

From this, they concluded that these stellar population in the Galactic Halo were formed in the Milky Way, but then relocated to locations above and below the Galactic Disk. This phenomena is known as “galactic eviction”, where structures are pushed off the plane of the Milky Way when a massive dwarf galaxy passes through the galactic disk. This process causes oscillations that eject stars from the disk, in whichever the dwarf galaxy is moving.

“The oscillations can be compared to sound waves in a musical instrument,” added Bergemann. “We call this ‘ringing’ in the Milky Way galaxy ‘galactoseismology,’ which has been predicted theoretically decades ago. We now have the clearest evidence for these oscillations in our galaxy’s disk obtained so far!”

These observations were made possible thanks to the High-Resolution Echelle Spectrometer (HiRES) on the Keck Telescope. As Judy Cohen, the Kate Van Nuys Page Professor of Astronomy at Caltech and a co-author on the study, explained:

“The high throughput and high spectral resolution of HIRES were crucial to the success of the observations of the stars in the outer part of the Milky Way. Another key factor was the smooth operation of Keck Observatory; good pointing and smooth operation allows one to get spectra of more stars in only a few nights of observation. The spectra in this study were obtained in only one night of Keck time, which shows how valuable even a single night can be.”

360-degree panorama view of the Milky Way (an assembled mosaic of photographs) by ESO. Credit: ESO/S. Brunier

These findings are very exciting for two reasons. On the one hand, it demonstrates that halo stars likely originated in the Galactic think disk – a younger part of the Milky Way. On the other hand, it demonstrates that the Milky Way’s disk and its dynamics are much more complex than previously thought. As Allyson Sheffield of LaGuardia Community College/CUNY, and a co-author on the paper, said:

“We showed that it may be fairly common for groups of stars in the disk to be relocated to more distant realms within the Milky Way – having been ‘kicked out’ by an invading satellite galaxy. Similar chemical patterns may also be found in other galaxies, indicating a potential galactic universality of this dynamic process.”

As a next step, the astronomers plan to analyze the spectra of additional stars in the Tri-And and A13 overdensities, as well as stars in other stellar structures further away from the disk. They also plan to determine masses and ages of these stars so they can constrain the time limits of when this galactic eviction took place.

In the end, it appears that another long-held assumption on galactic evolution has been updated. Combined with ongoing efforts to probe the nuclei of galaxies – to see how their Supermassive Black Holes and star formation are related – we appear to be getting closer to understanding just how our Universe evolved over time.

Further Reading: W.M. Keck Observatory, Nature

Huge Sheets of Ice Found Hidden Just Beneath the Surface of Mars

Its an established fact that Mars was once a warmer and wetter place, with liquid water covering much of its surface. But between 4.2 and 3.7 billion years ago, the planet lost its atmosphere, which caused most of its surface water to disappear. Today, much of that water remains hidden beneath the surface in the form of water ice, which is largely restricted to the polar regions.

In recent years, scientists have also learned of ice deposits that exist in the equatorial regions of Mars, though it was unlcear how deep they ran. But according to a new study led by the U.S. Geological Survey, erosion on the surface of Mars has revealed abundant deposits of water ice. In addition to representing a major research opportunity, these deposits could serve as a source of water for Martian settlements, should they ever be built.

The study, titled “Exposed subsurface ice sheets in the Martian mid-latitudes“, recently appeared in Science. The study was led by Colin M. Dundas, a researcher with the U.S. Geological Survey, and included members from the Lunar and Planetary Laboratory (LPL) at the University of Arizona, Johns Hopkins University, the Georgia Institute of Technology, the Planetary Science Institute, and the Institute for Geophysics at the University of Texas at Austin.

Artists concept of the Mars Reconnaisance Orbiter (MRO). Credit: NASA/JPL

For the sake of their study, the team consulted data obtained by the High Resolution Imaging Science Experiment (HiRISE) aboard the Mars Reconnaissance Orbiter (MRO). This data revealed eight locations in the mid-latitude region of Mars where steep slopes created by erosion exposed substantial quantities of sub-surface ice. These deposits could extend as deep as 100 meters (328 feet) or more.

The fractures and steep angles indicate that the ice is cohesive and strong. As Dundas explained in a recent NASA press statement:

“There is shallow ground ice under roughly a third of the Martian surface, which records the recent history of Mars. What we’ve seen here are cross-sections through the ice that give us a 3-D view with more detail than ever before.”

These ice deposits, which are exposed in cross-section as relatively pure water ice, were likely deposited as snow long ago. They have since become capped by a layer of ice-cemented rock and dust that is between one to two meters (3.28 to 6.56 ft) thick. The eight sites they observed were found in both the northern and southern hemispheres of Mars, at latitudes from about 55° to 58°, which accounts for the majority of the surface.

It would be no exaggeration to say that this is a huge find, and presents major opportunities for scientific research on Mars. In addition to affecting modern geomorphology, this ice is also a preserved record of Mars’ climate history. Much like how the Curiosity rover is currently delving into Mars’ past by examining sedimentary deposits in the Gale Crater, future missions could drill into this ice to obtain other geological records for comparison.

At this pit on Mars, the steep slope at the northern edge (toward the top of the image) exposes a cross-section of a thick sheet of underground water ice. Credits: NASA/JPL-Caltech/UA/USGS

These ice deposits were previously detected by the Mars Odyssey orbiter (using spectrometers) and ground-penetrated radar aboard the MRO and the ESA’s Mars Express orbiter. NASA also sent the Phoenix lander to Mars in 2008 to confirm the findings made by the Mars Odyssey orbiter, which resulted in it finding and analyzing buried water ice located at 68° north latitude.

However, the eight scarps that were detected in the MRO data directly exposed this subsurface ice for the first time. As Shane Byrne, the University of Arizona Lunar and Planetary Laboratory and a co-author on the study, indicated:

“The discovery reported today gives us surprising windows where we can see right into these thick underground sheets of ice. It’s like having one of those ant farms where you can see through the glass on the side to learn about what’s usually hidden beneath the ground.”

These studies would also help resolve a mystery about how Mars’ climate changes over time. Today, Earth and Mars have similarly-tiled axes, with Mars’ axis tilted at 25.19° compared to Earth’s 23.439°. However, this has changed considerably over the course of eons, and scientists have wondered how increases and decreases could result in seasonal changes.

Artist’s impression of glaciers that may have existed on the surface of Mars in the past. Credit: NASA/Caltech/JPL/UTA/UA/MSSS/ESA/DLR Eric M. De Jong, Ali Safaeinili, Jason Craig, Mike Stetson, Koji Kuramura, John W. Holt

Basically, during periods where Mars’ tilt was greater, climate conditions may have favored a buildup of ice in the middle-latitudes. Based on banding and color variations, Dundas and his colleagues have suggested that layers in the eight observed regions were deposited in different proportions and with varying amounts of dust based on varying climate conditions.

As Leslie Tamppari, the MRO Deputy Project Scientist at NASA’s Jet Propulsion Laboratory, said:

“If you had a mission at one of these sites, sampling the layers going down the scarp, you could get a detailed climate history of Mars. It’s part of the whole story of what happens to water on Mars over time: Where does it go? When does ice accumulate? When does it recede?”

The presence of water ice in multiple locations throughout the mid-latitudes on Mars is also tremendous news for those who want to see permanent bases constructed on Mars someday. With abundant water ice just a few meters below the surface, and which is periodically exposed by erosion, it would be easily accessible. It would also mean bases need not be built in polar areas in order to have access to a source of water.

This research was made possible thanks to the coordinated use of multiple instruments on multiple Mars orbiters. It also benefited from the fact that these missions have been studying Mars for extended periods of time. The MRO has been observing Mars for 11 years now, while the Mars Odyssey probe has been doing so for 16. What they have managed to reveal in that time has provided all kinds of opportunities for future missions to the surface.

Further Reading: NASA, Science

These Streaks on Mars Could be Flowing Sand, not Water

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.

The study, titled “Granular Flows at Recurring Slope Lineae on Mars Indicate a Limited Role for Liquid Water“, recently appeared in the scientific journal Nature Geoscience. Led by Dr. Colin Dundas, of the US Geological Survey’s Astrogeology Science Center, the team also included members from the Lunar and Planetary Laboratory (LPL) at the University of Arizona and Durham University.

This inner slope of a Martian crater has several of the seasonal dark streaks called “recurrent slope lineae,” or RSL, which were caputred by the HiRISE camera on NASA’s Mars Reconnaissance Orbiter. Credits: NASA/JPL-Caltech/UA/USGS

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.

As Dundas explained in a recent NASA press release:

“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.

Dark, narrow streaks flowing downhill on Mars at sites like the Horowitz Crater are inferred to be due to seasonal flows of water. Credit: NASA/JPL-Caltech/Univ. of Arizona

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.

NASA’s Mars Reconnaissance Orbiter investigating Martian water cycle. Credit: NASA/JPL/Corby Waste

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!

Further Reading: NASA

What Made this Mysterious Pit on Mars? Impact Crater or Natural Collapse?

The HiRISE camera on NASA's Mars Reconnaissance Orbiter captured this unusual crater or pit on the surface of Mars. Frozen carbon dioxide gives the region its unique "Swiss cheese" like appearance. Image:NASA/JPL/University of Arizona

The HiRISE camera on NASA's Mars Reconnaissance Orbiter captured this unusual crater or pit on the surface of Mars. Frozen carbon dioxide gives the region its unique "Swiss cheese" like appearance. Image:NASA/JPL/University of Arizona
The HiRISE camera on NASA’s Mars Reconnaissance Orbiter captured this unusual crater or pit on the surface of Mars. Frozen carbon dioxide gives the region its unique “Swiss cheese” like appearance. Image:NASA/JPL/University of Arizona

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.

More Reading:

Get Away From It All with these Amazing DTM Views of Mars

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.

Gasa Crater on Mars. Rendered using Autodesk Maya and Adobe Photoshop. HiRISE data processed using HiView and gdal. Credit: NASA/JPL/University of Arizona/USGS/image editing by Kevin Gill.

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:

DTM image of the Central Peak of Elorza Crater on Mars. Credit: NASA/JPL/University of Arizona/USGS

To this amazing image?

Martian sunrise over the Central Peak of Elorza Crater. Rendered using Autodesk Maya and Adobe Photoshop. HiRISE data processed using HiView and gdal. Credit: NASA/JPL/University of Arizona/USGS/image editing by Kevin Gill

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.

Fissure in the Cerberus region. This false color view of a volcanic fissure in the Cerberus region of Mars was created using a digital terrain model (DTM) from the High Resolution Imaging Science Experiment (HiRISE) camera aboard NASA’s Mars Reconnaissance Orbiter. The horizon was taken from Curiosity Mastcam imagery. Credit: NASA/JPL-Caltech/University of Arizona/ image editing by Kevin Gill.

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:

Doin’ Science with Curiosity. Created using HiRIST DTM and Ortho data and NASA model of Curiosity. Rendered using Autodesk Maya and Adobe Photoshop. Curiosity Model: Brian Kumanchik, NASA/JPL-Caltech. Image editing by Kevin Gill.

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:

You can see more of Sean’s work on his Flickr page

And you can see all of Kevin’s Mars DTM images at his Flick page here. Kevin also recently wrote up a great explanation of his image editing for The Planetary Society, which you can read here.

Thanks to Kevin Gill for sharing his images and expertise!