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! ☺

We’re in the midst of the last cycle in MRO’s Primary Science Phase (PSP). Conjunction is coming up, when Mars is behind the Sun, so we won’t be able to communicate with the spacecraft for a few weeks. We’ll get a welcome break during that time – Uplink will have two whole planning cycles off, and Downlink will get a chance to catch up with their processing.

I can’t believe it’s been two years since the last conjunction and the start of PSP! A lot has changed since we started out with those first images. (more…)

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.

This past summer the IAU met in Prague to decide the fate of Pluto, and also to give names to several craters on Mars. After more than two years after I submitted the request, a fresh and rayed Martian crater now officially bears the name Gratteri. Gratteri is the birthplace of my Father, my Grandfather and their forefathers going back as far as back as any Tornabene can remember. Gratteri is a small medieval town of only 1100 people, but once was a more heavily populated duchy that ruled the Madonie region from the coast to the mountain tops. Unbenownst to me at the time I submitted my suggestion to the IAU, was the etymology of the name. By a staggering coincidence, the name Gratteri is derived from the Greek word ‘krater‘ meaning a basin or bowl to mix wine and water (see http://en.wikipedia.org/wiki/Krater), which in the English language has come to signify a quasi-circular pit formed by an explosion (volcanic or hypervelocity impact). I was floored to say the least! Not only did I come to study these features on Earth, Mars and other bodies as my lifelong passion, but it was also the name of the town of my ancestral origins!

Well, soon I will be in Italy for the MRO PSG in Rome and then for the Terrestrial Analogues meeting in Trento. After these two meetings, I will be taking three days off to go down to Sicily for a long overdue break. My parents await me in Gratteri, and it will be so nice to meet them there for my second visit. I am particularly excited as I will be bringing a HiRISE image of the Martian Gratteri crater to present to the Mayor and townsfolk. In addition to a poster print out of the HiRISE image taken during our first cycle, I will be bringing an annotated version that I made and would like to share with you here. I used Google Earth to find Gratteri and acquired the satellite image along with the proper scale so that I could superimpose it on the HiRISE image. Gratteri is the cluster of buildings on the right with the cutout being approximately 2.5 km in width. The Martian crater Gratteri is almost 7 km in diameter. I was once again reminded, and immediately humbled, by the shear scale of this crater that I claim to know so much about! I’m amazed how big this rather small Martian crater is in relation to our terrestrial stomping grounds.

Well, I best be off. I still have so much packing to do! Not to mention, I haven’t even finished my talk yet…

Ciao miei Amici! Ci vediamo dopo!

Over at NASA Ames, the HiRISE Clickworkers program is in beta-testing. Anyone (this means you!) with a browser and a net connection can participate in the cataloging, or more precisely, keywording of HiRISE images.

This is an ambitious effort. Originally (years before HiRISE), Clickworkers was used to tag craters on Mars, helping pin down the relative ages of various regions. This time around, you identify a dozen or so possible feature types, then move on to the next image. So you have to be a little more discerning, though examples are provided.

I was just looking at the sizes of our images to date. We’re coming up on one thousand images that have been map projected. And it looks like we just recently passed the one million megapixel mark (one thousand gigapixels, or one terapixel!) in the geometrically projected ones (when rotated so that North is up, there tends to be a lot of empty pixels framing the images).

Assuming a standard screen size of 1.25 megapixels (1280×1024), that is 800,000 screenfuls. If you looked at one per second, it would take you almost ten days to view it all! But one thousand volunteers could get through it in a day, and spend 100 seconds per image, which seems reasonable. [Though of course they'll need time for sleep, etc!]

The idea of using human brain power as a sort of massively distributed computation engine (shades of The Matrix) has come a long way. Amazon’s Mechanical Turk pays volunteers for tasks such as identifying features, translating documents or answering questions. It was recently used in the search for a person (computer scientist Jim Gray) missing at sea. Volunteers viewed over a half million images, covering 3,500 square miles of ocean, though unfortunately his sailboat did not turn up.

Still, ‘crowdsourcing‘ (as Wired called it) seems like it will continue to be an efficient way to perform tasks that computers are currently very poor at. Here at the Lunar and Planetary Lab, it has also been used by Spacewatch to find Earth-approaching asteroids. So, essentially, you could help save the planet in a real-life version of the classic game Asteroids! Clickworkers also has a program where you can tag Mars Global Surveyor images, scouting interesting locations for HiRISE to target.

We can’t let the machines have all the fun!

We’ve been looking at the first images for the last several minutes, they are incredible. We have identified many boulders, craters, channels, and other incredible features. Everything is looking as well as we have dreamed. Stay tuned for more!