By Amy Mainzer

With WISE, I roamed the skies — seeing everything from the closest asteroids to the most distant galaxies. When I was a kid, maybe 6 or 7, I remember reading the encyclopedia about Andromeda, Mars and Jupiter. After that, I spent a lot of my free time (and a fair amount of gym class) wishing that I could be “out there” exploring the stars, imagining what it must be like to get close to a black hole or the lonely, cold surface of a moon. Fast-forwarding several decades, I’ve just spent a tremendously satisfying and delightful year using some of our most sophisticated technology to see “out there” for real. It’s pretty cool when your childhood dreams come true!

Today, the operations team sent the command to kill the survey sequence and put WISE into a deep sleep. While I’m sad to see the survey stop, the real voyage of discovery is just getting started as we unpack the treasures that our spacecraft beamed back to us. Although I’m going to miss waking up to see a new slew of pictures fresh from outer space, what I’ve looked at so far is only a tiny fraction of the millions of images we’ve garnered. My colleagues and I are working nonstop now to begin the decades-long process of interpreting the data. But I can already say for certain that we’re learning that the universe is a weirder, more wonderful place than any science fiction I’ve ever read. If I could go back in time to when I was kid, I’d tell myself not to worry and to hang in there through the tough parts — it was all worth it.

A cast of hundreds, maybe thousands, of people have worked on WISE and deserve far more credit than they get. The scientists will swoop in and write papers, but all those results are squarely due to the brilliance, stubborn persistence and imagination of the technicians, managers, engineers of all stripes (experts in everything from the optical properties of strange materials to the orbital perturbations of the planets), and administrative staff who make sure we get home safely from our travels. Although we may not be able to fly people around the galaxy yet, one thing Star Trek got right is the spirit of camaraderie and teamwork that makes projects like WISE go. For the opportunity to explore the universe with such fine friends and teammates, I am truly grateful.

by Sue Smrekar
Deputy Project Scientist - Mars Reconnaissance Orbiter

A theme of Mars exploration is “Follow the Water,” since understanding the history of water on our planetary neighbor will help us understand if there were environments favorable for life to occur and how climate has changed over time. This is because all life on Earth requires water and we assume the same applies elsewhere in the universe. The Mars Reconnaissance Orbiter has made numerous discoveries that have provided new insights into past wet environments on Mars, water vapor in the planet’s current atmosphere and ice in the subsurface. However, so far, liquid water remains elusive.

The Shallow Radar, or “SHARAD” instrument is the only one on the Mars orbiter that was designed with a goal of discovering liquid water below Mars’ surface. This ground-penetrating radar instrument, which was supplied by the Italian Space Agency, transmits a radar signal at approximately 20 megahertz, and receives any radar waves that bounce off the surface or subsurface layers. The radar instrument has sufficient strength to see layers to a depth of about one kilometer (a little more than one-half mile), and even deeper in the polar caps. Layers in the subsurface reflect the radar wave if there is sufficient contrast in their dielectric properties (their bulk electrical properties), as for example between dry sand and ice-filled sand. Water is a much better conductor than other geologic materials, and thus should be readily detected if present.

This image from NASA’s Mars Reconnaissance Orbiter shows gully channels in a crater in the southern highlands of Mars.The gullies emanating from the rocky cliffs near the crater’s rim (upper left) show meandering and braided patterns typical of water-carved channels. Image credit: NASA/JPL/University of Arizona

Of all the features believed to be formed by water on Mars, we have found only two gullies known to have recent flows – within the last 5-10 years. Gullies are narrow channels that emanate from cliff walls, starting well below the local ground surface. Dr. Michael Malin used the Mars Orbital Camera on Mars Global Surveyor to repeatedly image these features because of their fresh, unweathered appearance. These efforts led to the discovery of the two relatively new gullies.

To date, the Shallow Radar instrument’s observations of dozens of regions containing gullies show no evidence of liquid water. Since slopes of the cliffs where the two new gullies occur are extremely steep, some scientists put forth an alternate hypothesis in which dry debris tumbling downhill could have formed the latest channels. Yet many of the features observed at these and other gullies strongly suggest that liquid water had at least some role in carving the channels. These channels may have formed when a past climate change caused subsurface ice to melt. Or perhaps liquid water was trapped in a past aquifer. But for now, liquid water, if it exists today on Mars, remains out of reach of the Mars Reconnaissance Orbiter.