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Why Hasn't This Asteroid Disintegrated?
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.
Give me a nuke, Bruce Willis, Steve Buscemi, and Sad Batman, and I'll make sure that asteroid is good and proper disintegrated!
how do they work?
Maybe it doesn't know any better. Rocks aren't exactly known for their keen intelligence.
TFS says that vdW interactions are interactions between polar molecules... that's absolutely false! The reason water has a high surface tension is due to hydrogen bonding, which is a combination of polar interactions and charge transfer. The reason that polar molecules attract is entirely due to electrostatic reasons... electric dipoles aligning causing favorable interactions. Van der Waals interactions are when NON-polar molecules spontaneously polarize one another to form instantaneous dipoles, which attract electrostatically. The key here is that vdW attractions occur even in molecules that do not have any static dipole... the dipole-dipole interactions are dynamic and fluctuating. One of the hallmarks of vdW interactions are their asymptotic behavior. Charge-charge interactions die off as r^-1. Dipole-dipole interactions die off as r^-3. vdW interactions die off as r^-6.
Results of a new study (Busch et al.) combining the 2001 Goldstone and Arecibo radar data with optical lightcurves are presented in the journal Icarus. Shape, spin state and surface structure of 1950 DA are estimated. New observations intended to resolve the prograde/retrograde spin issue were inconclusive, therefore two distinct shape models are presented. One rotates in a prograde sense and is roughly spheroidal with a mean diameter of 1.16 +/- 0.12 km. The other rotates in a retrograde sense, is oblate, and about 30% larger. Both models suggest a nickel-iron or enstatite chondritic composition.
So, since it has been established that the asteroid in question is pretty much a chunk of metal, and the rate of rotation would be fast enough to dislodge independent pieces of material, the obvious answer is "the rubble already flew off, this is a big hunk of nickel-iron." After doing that bit of research, I don't care what is in the summary or the article behind this story, they'd better show up with a good argument that this piece of metal has any rubble clinging to it before I will waste the effort considering other explanations.