Why Hasn't This Asteroid Disintegrated? 74
sciencehabit writes: Planetary scientists have found an asteroid spinning too fast for its own good. The object, known as 1950 DA, whips around every 2.1 hours, which means that rocks on its surface should fly off into space. What's keeping the remaining small rocks and dust on the surface? The researchers suggest van der Waals forces, weak forces caused by the attraction of polar molecules, which have slightly different charges on different sides of the molecule. For example, water molecules exhibit surface tension because of van der Waals forces, because the negative charge of one water molecule's oxygen atom is attracted to nearby water molecules' hydrogen atoms, which have a positive charge at their surfaces. Similar attractions could be occurring between molecules on the surfaces of different pieces of dust and rock. Such forces would be comparable to those that caused lunar dust to stick to astronauts' space suits.
Why can't it just be one mass? (Score:5, Interesting)
The article doesn't explain why the idea of this particular body being one mass instead of a rubble pile has been dismissed. Is there a good one?
Molten piece of crystalline rock with ionic bonds (Score:3, Interesting)
What's keeping a piece of rock that used to be molten lava together? Crystalline ionic attractive forces. Van der Waals forces would not be strong enough to keep such an asteroid together, and that's proof that the whole thing flew off as one piece from some supernova explosion. Maybe that's the idea of catching these asteroids with spacecraft - see what stuff looks like coming straight out of a supernova, as opposed to stuff that has been impact pounded into the Moon's surface, or glowing-hot shooting star thermally remelted on the Earth's surface. The stuff that lands on Earth is mostly remnants of shooting stars that did not completely combust, but there might be some meteorite rocks that were traveling with speed close to that of Earth on rendezvous, and only attained terminal velocity in the atmosphere that's not fast enough to melt them. So some meteorites that land on the Earth could be very similar to a captured asteroid out there, and a lot cheaper. Another aspect of capturing an asteroid is practice: for when we have to capture stuff in space to build space stations out of them. Space is very very empty, huge distances of vacuum with very little stuff sprinkled here and there. Any stuff, any matter, is worth gold in outer space, especially away from a gravity well like Earth or Jupiter, but the Moon is better.