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! ☺

At this point, the storm is considered a “hemispherical event,” meaning it’s mainly affecting “only” half of the planet (the southern hemisphere, in this case). We have our fingers crossed that this will not expand and become a global event like the 2001 dust storm.

These storms, like weather on Earth, are difficult to predict, especially because they are relatively rare and we have much less information about them than we do about terrestrial weather. This is an opportunity to learn more about how the storms start and spread by gathering more data on the Martian dust and atmosphere. The CRISM instrument can measure the composition of the dust, for example, so we’ve helped them acquire extra images by canceling a number of our own images that would have been obstructed by the dust anyway. MARCI continues to take daily images of the globe, monitoring the storm’s activity.

While we wait to see what the dust does, our Targeting Specialists are scrambling to cancel observations and figure out where to take a chance and try imaging. Some areas are still relatively clear. We also have to deal with additional complications in our camera settings: even in areas where we can see the surface, the atmosphere is still dusty, so more light is reflected into the camera. We are learning how to adjust our instrument parameters to accommodate this, but without being able to predict where the dust will be, it’s very difficult!

Hopefully out of the chaos we’ll still get some good images. We will certainly learn more about operating our camera, and about Mars itself.

(Title is a quotation from Louisa May Alcott)

A couple of weeks a go, we started the planning process by defining scientifically interesting areas on Mars to image. At this point, we didn’t know exactly where the MRO spacecraft would be in its orbit around Mars when the imaging sequence would begin (two weeks later). Consequently, we chose large regions of interest, rather than pinpointing the exact locations of each image that we wanted to acquire. Once MRO’s orbit pattern during the imaging sequence was predicted, we then carefully decided where within each region of interest HiRISE should acquire image. With this preliminary plan in hand, we then discussed our imaging desires with the teams for the other MRO science instruments, such as CTX (the context imager) and CRISM (the multispectral imager).

After a week of iterations and teleconferences, we had a working schedule of observations that incorporated the imaging desires of all the MRO science instruments. We then undertook the process of carefully designing each scheduled HiRISE observation (image). Planning a HiRISE image involves setting the proper camera parameters so that we take a good image. We need to set parameters such as exposure duration, the aerial extent of the image, the image resolution and data compression. Each parameter needs to be carefully weighed against factors such as the brightness of the surface of Mars, the clarity of the Martian atmosphere, the scientific objective of the image and the amount of data storage space available on the spacecraft.

After an intense week of designing our HiRISE observations, we sent these camera commands to JPL. At JPL, the commands were tested on a computer simulator (the OTB or ‘Orbiter Test Bed’). The purpose of this test was to ensure that each command would execute flawlessly on the spacecraft (and they did). These commands were transmitted to MRO earlier this morning (Thursday 9/28/06). Mars is currently about 309 million kilometers (about 192 million miles) from the Earth. At this distance, it took about 22 minutes for our commands to travel from Earth to Mars. These commands will automatically run on the spacecraft tomorrow and begin returning fantastic images of Mars. Tomorrow should be an exciting day!