Note the special time! In this week's Planetary Society hangout at 5pm PDT / midnight UTC, I'll talk with MESSENGER deputy principal investigator Larry Nittler about what MESSENGER has accomplished in its prime and extended missions at Mercury, and what it stands to do if awarded a mission extension.
The case for water ice hidden in permanently shadowed regions at the north pole of the planet Mercury received another boost recently. On Wednesday March 20, 2013 at the Lunar and Planetary Science Conference, Nancy Chabot presented the very first visible-light images of what is in the shadows of these polar craters.
Last week the GRAIL mission published their first scientific results, and what they have found will send many geophysicists back to the drawing board to explain how the Moon formed and why it looks the way it does now. To explain how, I'm going to have to back way up, and explain the basic science behind gravity data.
Water ice at Mercury's poles? That's crazy, right? The MESSENGER team has made a very good case that radar-bright material seen by the Arecibo telescope is, in fact, water ice, covered in most places by a veneer of dark organic material.
Water ice at Mercury's poles? That's crazy, right? Mercury is so close to the Sun that it seems inconceivable that you could have water ice there. But Mercury's rotational axis has virtually no tilt (MESSENGER has measured its tilt to be less than 1 degree), so there are areas at Mercury's poles, most often (but not always) within polar craters, where the Sun never rises above the horizon to heat the surface.
I'm preparing a talk for the Pacific Astronomy and Telescope Show here in Pasadena on Sunday afternoon at 1:45. I have spent the morning putting together a slide that I have long wanted to have for presentations.
When Mariner 10 flew past Mercury, it caught an immense impact basin lying half in and half out of sunlight, which they named Caloris. Even with only half the basin visible, scientists knew it was one of the largest in the solar system. Geologists had to wait more than 25 years to see the rest of Caloris, and when they did it turned out to be even bigger than they had thought. But the fact that Caloris was only half in sunlight was fortuitous in one sense, because it meant that the spot on Mercury that was exactly opposite the area of the Caloris impact was also partially in sunlight. That spot looks weird.