Low Flyovers Will Give the Best Close-up Views

Does this image prove water ice near the poles of Mercury? Here’s how a Mercury MESSENGER scientist sees it. The top left view shows the crater rim outlined in pink and the edge of the 24-meter/pixel, low-altitude broadband MDIS instrument image in green. The large bottom image (with processing) reveals details of the shadowed surface inside the crater. The yellow arrows in the top right image indicate a region inside the crater that has a lower reflectance. The edge of the low-reflectance region has a sharp and well-defined boundary. The sharp boundary suggests that the low-reflectance material is sufficiently young to have preserved a sharp boundary against lateral mixing by impact craters. The sharp boundary matches the location predicted by temperature models for the stability of a surface layer of volatile, organic-rich material tens of centimeters thick on top of a thicker layer of water ice. Courtesy: NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington

Sometime in the next few months, the long-running MESSENGER mission at Mercury is going to take its last swoop over the planet, and then angle into Mercury’s surface. The long-planned Hover Campaign, uses orbit-correction maneuvers to delay the spacecraft’s final plunge for a few weeks so that they can send it on some low-pass runs and get some last good birds-eye views of the cratered terrain. They’ll also be using the spacecraft’s magnetometer (which senses the magnetic fields and magnetic anomalies in the surface), and the neutron spectrometer, which will let them get more data on the crustal composition.

In particular, the mission scientists want to zero in on those mysterious shadowed craters at Mercury’s poles, to study the water ice that exists within their chilly dark areas. If it does, then they’ll have some proof that water can exist in this region, and try to figure out just how the water got there. One idea is that comet bombardments could have deposited ice in these regions. Since the walls of the craters do not get sunlight, the ice could have been safely locked away there for a while.

How long? It’s a good question. The images and data returned about Mercury ice so far indicate that it is relatively young, meaning it was delivered (or uncovered) in recent geological time.  Mercury ice is a mystery, and although it sounds crazy that ice could exist so close to the Sun, the MESSENGER images and data have shown that it’s there and sitting there quite happily NOT getting melted by sunlight. It’s yet another dazzling result delivered from a very successful mission.

Why the rush to get MESSENGER in low swooping and controlled orbits? Well, the spacecraft is running out of propellant, and its subject to the gravitational pull of the Sun, both of which will combine to send it to its final resting place on Mercury. Mission controllers are taking advantage now of the spacecraft’s continuing good health to plan the final views and studies, and giving it the best altitude to do so. Once the propellant is gone, that’s the end of the road for a mission that has lasted since its 2004 launch, and has been orbiting Mercury since March 18, 2011. I remember the evening it went into orbit; we went down to the University of Colorado’s Laboratory for Atmospheric and Space Physics (my old employer) to sit with friends who are on the spacecraft team and watch as the mission slipped into orbit around the planet after a nearly five-year trip to get there.

The MESSENGER spacecraft is the first ever to orbit the planet Mercury, and the spacecraft’s seven scientific instruments and radio science investigation have done a spectacular job of studying this world, and helping us to understand its history and evolution. MESSENGER has acquired over 250,000 images and extensive other data sets. I suspect that there will be many incredible papers written about this treasure trove of information about the solar system’s smallest rocky planet. Stay tuned as MESSENGER spends her final weeks cranking out some spectacular science!

Less Than 1 AU and Counting…

Dear Pluto,

A few days ago the New Horizons spacecraft passed an important milestone: it was 1 A.U. from its major target: Pluto. that means YOU!  That also means it was as far away from you as Earth is from the Sun. By now, it’s even closer.  A lot of us here on Earth are keeping track of the spacecraft’s whereabouts by checking the New Horizons web site counter that lets us know where things stand for the mission.

A few days before THAT, New Horizons did a little mid-course correction to get it lined up even more precisely for its trip past you on July 14, 2015. At that point, the spacecraft was nearly 3 billion miles (4.77 billion kilometers) from the Sun, and that’s a record for a trajectory correction burn!

Images of Nix and Hydra. Courtesy New Horizons mission.

The excitement is building as the spacecraft gets closer and closer. The cameras are studying the Pluto system and just a month ago were able to spot the two tiny Plutonian moons Nyx and Hydra. As things progress, there will be more images and data, showing us an increasingly larger-looking Pluto and its worlds.

This is really a huge milestone project. One of my friends is the principal investigator for the mission—Alan Stern. He has boundless enthusiasm for this mission, which stretches back as long as I’ve known him. We were in graduate school at the same time at the University of Colorado, and had the same advisor. I remember going to his thesis defense, and hearing him give talks about Pluto and comets, and I’ve always learned a lot from him. I’m proud to continue our friendship many years later.

As you might expect for the PI of a mission to an outer world, Alan embraces all things Pluto—and I do mean ALL! Just today he sent me a link to a page called “Janet’s Planet”, which contains a cute Youtube video about how kids can connect with Pluto. The title of the vid is #DearPluto and it challenges kids to write a letter to Pluto. Alan has recorded his OWN video letter for Janet’s page, which you can see on HER Youtube page. Anybody can record or write a letter to you, Pluto. I think it’s really jazzy way to get kids hooked (even more) on Pluto! Even better, getting Plutophiles everywhere to get with their inner kid and send a note to their favorite world.

The next few months will be pretty exciting for Plutophiles, and we’re keeping an eye out on you, Pluto. It won’t be long before we are there and checking you out!

With great excitement,

Your friends on Earth.