The Dawn spacecraft is now in orbit around the main belt asteroid Vesta! Yay!
The spacecraft entered orbit around the main belt asteroid on Saturday, July 15. Two days later — today — it snapped this spectacular high-res image:
[Click to enprotoplanetate.]
Wow, what a mess! As expected, it’s littered with craters, but there are some interesting things to note. Some craters appear to be very deep, while others are shallow — that indicates a different type of terrain (asteroidain?) where the impactors hit (although in some cases it might be a lighting effect; a more direct sunlight angle makes craters look shallow). The grooves I mentioned in a previous post are everywhere, some looking more like scarps (cliffs) now. And look at that huge cliff on the upper right! I’ll be very curious to see that area at different angles. Is it part of a big basin, a collapse feature? Or is it a cliff caused by cracking in the surface? By the way, that lump in the center casting a shadow to the left is actually a mountain or mound of some kind well over 100 kilometers across.
The resolution is stunning; each pixel in the high-res version is about 1.4 km (0.9 miles) across — the asteroid itself is 530 km (330 miles) wide. Dawn is orbiting at a distance of 16,000 km (9900 miles; a bit more than the diameter of the Earth) and will slowly lower its orbit over time. Vesta’s mass is uncertain, so engineers played it safe and put it into a high orbit. This will allow an accurate mass to be determined, and then scientists and engineers can calculate how much thrust is needed to safely close in. That will take some time, about three weeks. During that time Dawn scientists will search the region around Vesta for tiny moons. None has ever been seen from Earth, but there’s nothing like being there.
… and I’ll add, we almost didn’t go. Back in 2005/6, this mission was actually canceled by NASA, causing quite the stir in the astronomy community. However, a strong voice was raised against this cutback, and Dawn was back on. After a long, long journey, it’s now where it belongs: in deep space, exploring, doing science, and expanding our frontiers.
I can hope the same will be true for JWST.
The Moon is shrinking!
Well, a little: new results from the Lunar Reconnaissance Orbiter indicate that over recent geological time, the Moon has shrunk by approximately 100 meters in diameter!
Here’s the evidence, or at least one piece of it:
[Click to unshrinkenate.]
That image shows the Gregory scarp, a cliff across the surface of the Moon. Scarps like these have been known for centuries — I’ve observed many myself using a backyard telescope — but it was always thought they were big and restricted to just some areas on the Moon. LRO, though has found many smaller scarps, and also importantly that these scarps are distributed globally, all across the surface of our nearest neighbor in space.
What does this have to do with shrinkage?