Ice excavated from the subsurface, by a crater 6m (20 feet) in diameter, sublimates away over the course of the martian summer. Each of these HiRISE images are 35m (115 feet) across and were taken in October 2008 and January 2009.
Image credit: NASA/JPL-Caltech/University of Arizona

An exciting new paper came out in yesterday’s issue of Science magazine, with HiRISE team member Shane Byrne as the lead author. Water ice has been discovered being exposed by fresh Martian craters!

This is exciting for several reasons: first, these are very tiny craters – only a few meters (yards) across. This means they’re not excavating very deep into the crust of Mars. So the ice has to be really shallow – less than a few feet below the surface! Secondly, the location of these craters is surprising – they’re between 40-55 degrees north latitude. This is far from the polar regions, where we’d expect to find ice (for example, where the Phoenix mission landed at 68 degrees north, ice was found by digging down into the dirt).

The third exciting aspect of this ice is its purity. We’d expect this ice to be mixed in with dirt and dust and rock. Instead, we found that it’s 99% pure ice! (Only 1% is dirt mixed in.) This can be measured because we watched the ice disappear over time. By taking repeated images of the same spot, HiRISE got a time sequence as the ice slowly faded. It faded so slowly that it has to be almost all ice – a dirtier mixture would have faded much faster as it sublimated (went directly from a solid to a gas) in Mars’s extremely dry atmosphere.

Speaking of dry atmospheres, this also has interesting implications about the history of the Martian climate – there had to have been more water vapor in the atmosphere in the recent past than we previously thought. We still have lots of questions about how this ice formed, how much of it there is, and how many more of these craters we’ll find. Luckily, we’ve got a long mission ahead of us to explore these issues!

This discovery is also a great example of how the instruments on MRO work together. CTX initially detected these new craters as “dark spots,” and HiRISE followed up to confirm that they’re really impact craters. Some of those HiRISE images revealed some very bright white material, and then CRISM confirmed that material really is water ice. The instruments worked together to accomplish the best combined science. Go team! ☺

Here are some more detailed stories, images, and multi-media:

• Really nice movie with Shane Byrne talking about the discovery and excellent animations showing the locations of the craters and the time-evolution of the ice disappearing: NASA multimedia – then go to “Video Gallery” on the right, and click on “Mars – Exposed”.

• NASA press release, and all of the images and materials from the press conference

• UA news story

We’ve seen many more news stories & blogs – thanks for the interest, everyone! It’s great that everyone thinks this is as exciting as we do! ☺

A number of our science team members are at LPSC, the annual Lunar and Planetary Science Conference, this week. This is a big gathering in Houston, Texas, where members of the planetary science community share their work from over the last year. Unfortunately, we don’t have an active blogger there, but I wanted to point out some other people sending out excellent reports about HiRISE science.

The Martian Chronicles has two great articles about presentations given by HiRISE Team Members: Spiders on Mars, from our Deputy PI Candice Hansen (more about this topic here, under “Spring at the South Pole of Mars”); and Layers and Swiss Cheese, which mentions two HiRISE people, Kathryn Fishbaugh and Shane Byrne. The polar group has been very active in helping to plan and target images, and their results are really cool (ha, ha!).

Star Stryder has also been at LPSC, with lots of stories through the week. The post Pingos, Polygons and other Puzzles mentions two types of Martian landforms I know members of our team are studying in HiRISE images, although there aren’t many specifics about their LPSC presentations. For some visuals to go along with the story, here are some HiRISE images of possible pingos and plentiful polygons.

I also thought their reports on speeches by the NASA bigwigs were very interesting: NASA Administrator Mike Griffin telling young scientists not to specialize in the face of changing funding priorities, and Alan Stern discussing possible MSL delays.

So, check out these reports, and if you see any other good ones, add a link below in the comments! Hopefully we’ll get more as the week progresses.

Today a press release went out about a forthcoming paper in the journal Geology (click here for full text online or here to download a PDF). John Grant, a Co-Investigator on the HiRISE science team, is the lead author, and most of the co-authors are also on our science team.

What is a megabreccia? A breccia is a jumbled-up mixture of broken rocks, cemented together by a finer-grained material. We see them in impact craters and volcanoes on the Earth, places where there was a lot of violent energy to break up rocks. A megabreccia is just a larger version of that – something we can see with HiRISE resolution, as opposed to something you’d have to pick up in your hand to identify. The megabreccia in Holden formed when the explosion that opened the crater shattered rocks, mixed them up, and then the fragmented ejecta collapsed back down into the crater. Before HiRISE, we didn’t have the resolution to detect these textures.

This is a cutout of an image taken in Holden Crater, showing the megabreccia texture, in false color as usual. A context map is shown to the right, showing where in the crater rim this image is located (click these images to enlarge). The blocks here are mostly darker, and they’re embedded in a lighter-toned material. The dark chunks are kind of “scooped out,” which means they’re more easily eroded than the surrounding light-colored rock. Scientists think this may be because they’re sedimentary rocks, formed at the bottom of a lake or river. The stripey dark blobs on top are sand dunes that are slowly covering up the area again.

This megabreccia is located in an area scientists find fascinating for other reasons, too: there are clays that were laid down over a long period of time when it had to be wet. This implies there was once a lake in this crater – perhaps more than once over its history. At one point, the lake broke through the rim of the crater, releasing a huge flood of liquid water. You can see the channel this formed in the context map above. This flood eroded away material that was covering the megabreccia, exposing it for HiRISE to see.

The HiRISE image PSP_003077_1530 shows another part of Holden Crater, and the caption includes more information about the geologic history of the area.

Hi. I’m a grad student who is co-author on a paper that just came out in Geology last week. It was very exciting to be a part of such an important project! The Mars Orbiter Camera found two locations on Mars where gullies had formed new bright deposits between images! Since gullies are thought to form with liquid water (either from the subsurface or surface), these new deposits were thought to be evidence of very recent (within the past 10 Earth years), liquid water on the martian surface.

A team of scientists at the United States Geological Survey used two HiRISE stereo images to create a very high-resolution topography model of the crater that contains one of the bright deposits. Our team at UA used this model to examine whether the bright deposit in the Centauri region is more likely formed by a water-rich or a completely dry flow. Our results show that a completely dry flow could explain the deposit’s location and shape. Since it is very difficult to produce liquid water on the surface of Mars today, our work suggests that this bright deposit was formed without water. This does not mean that the gully that the deposit is in formed without water or that water never existed on the martian surface. Our work is just relevant to the recent bright deposit we studied.

HiRISE images show similar bright deposits around Mars. I am studying these deposits to look for one that cannot be explained by a dry flow alone. Finding one would mean that liquid water might be reaching the surface today, which could help NASA figure out where to look for past and present life on Mars!

Three HiRISE papers are coming out in a special issue of the journal Science today. Our science team has been working hard on analyzing the images we take, and they’ve discovered some interesting things.

One paper talks about a few aspects of the history of water on Mars: HiRISE images of “rock glaciers” and bright deposits in gullies that might be extremely recent. HiRISE observations of an area called Athabasca Valles were used to show that it is actually covered with a thin veneer of lava. A third paper discusses thin layers in the North Polar cap. HiRISE is able to discern very fine layering (seen in an excerpt of image PSP_001636_2760 at left), as well as the color and thickness of each layer. Since these layers were laid down over hundreds of thousands of years of Martian history, they provide a record of climate change on the planet.

You can find a lot of things on the HiRISE website that are impossible to include in a print journal – like full-resolution color versions of the images from the papers, and (my favorite) cool 3-D flyover movies of the stereo observations. Our webmaster designed this lovely page for accessing these special products. Have fun flying over Mars!