We opened a new show  in the Willard Smith Planetarium at Pacific Science Center. It’s all about NASA’s current missions in the inner solar system: MESSENGER to Mercury and Dawn to Vesta and Ceres.
As part of that show we’re updating the images we show from MESSENGER and Dawn on a weekly basis. I’ll try to show them to you the week after we use the in the planetarium.
NASA Caption 
Released October 12, 2011
PASADENA, Calif. — This detail of a Dawn FC (framing camera) image shows a fresh scarp rimmed crater with many boulders on the crater floor. These boulders have diameters of 100-200m, which is roughly the size of many asteroids! Also evident in this image are linear mass movement features, which originate from the rim of the crater (bottom of image) and are due to material slumping towards the center of the crater. There are also many smaller, and presumably younger, impact craters on the walls of this crater.
NASA’s Dawn spacecraft obtained this image with its framing camera on September 20th 2011.
Let me unpack what NASA said for you:
- “Fresh scarp rimmed crater “ – This crater is new, and it has a sharp edge, like a cliff (a scarp).
- “Boulders on the crater floor. These boulders have diameters of 100-200m,” – That’s those tiny black dots in the middle there.
- “Linear mass movement features” – Dirt moved. It moved in a straight line. The lines you see that go from the edge of the crater in towards the middle are these “linear features.” And technically I shouldn’t call it dirt. Regolith is better, but dirt gives you the right idea.
- “Due to material slumping towards the center of the crater.” – slumping is like sliding. Imagine yourself sitting against a wall. You sit straight at first and then get tired so you scootch down a little, and maybe lean over on your elbow. Slumping is dirt doing the same thing, it’s just … slumped. It’s different that sliding because when you slide you end up all in a completely different place. Slumping you just compact in place, maybe spreading out a little at the bottom.
- “Presumably younger” – when one crater is on top of another you can assume the crater on top is younger.
The boulders (dots) are my favorite part of this image.
NASA Caption 
Date acquired: September 19, 2011
Instrument: Wide Angle Camera (WAC) of the Mercury Dual Imaging System (MDIS)
Of Interest: This image provides us with a beautiful view of a portion of Mercury’s southern hemisphere. The bright rayed crater near the limb is Debussy .. Also visible, near the center of the image, is Matabei , a small crater distinguishable by its unique dark rays.
These limb images provide information about Mercury’s shape.
I love bright craters – they’re bright because they’re new, not because their composition is different. So rocks are made of minerals, and minerals are usually crystals: they have a lattice of atoms very perfectly aligned. If you just leave a crystal out on a planet it gets scratched up, banged around and the surface gets marred or weathered. If you crack that crystal open, it cracks (cleaves) along those perfect lattice boundaries, between atoms, exposing a new surface. This surface is perfectly flat –flat at the molecular level!! – and therefore reflective like a mirror. This is a cleavage plane. When you smack a meteorite into a planet, you kick up a bunch of rocks and minerals, cracking them all open along those cleavage planes. These fall back down to the planet, reflective, pretty, and unmarred – which looks from space like a bright white crater and rays.
~ A l i c e !