快猫短视频

SNAPSHOTS of Eros continue to baffle astronomers months after a spacecraft
crash-landed on the rocky asteroid. The latest surprise is curious 鈥減onds鈥� of
dust on the asteroid鈥檚 surface.

NASA鈥檚 Near Earth Asteroid Rendezvous spacecraft sent back close-up images of
Eros just before crashing into it in February
(快猫短视频, 17 February, p 13).
They revealed a world strewn with boulders the size of large
buildings. These were probably created when a collision with another asteroid
punched a huge crater in Eros鈥檚 side, says Joseph Veverka of Cornell University
in New York.

But the images also show smooth 鈥減onds鈥� of dust in some of the smaller
craters, whose origin is a mystery. 鈥淚t鈥檚 a unique and puzzling phenomenon,鈥�
says Veverka. 鈥淲hat we鈥檇 like to understand is why we haven鈥檛 seen this on other
objects, such as the Moon.鈥�

One clue to how the ponds formed may be their location. They cluster in a
region of Eros that spends a lot of time in twilight, hovering between night and
day. Veverka says that when sunlight hits the asteroid, electrons are ejected
from the rocky surface, leading to charge differences between dark and sunlit
patches. He speculates that these charge differences could levitate fine dust,
which might then flow into craters and settle out in the shade.

Erik Asphaug of the University of California in Santa Cruz warns that this
dust, if it鈥檚 common, could hinder future attempts to land spacecraft on
asteroids: 鈥淚t will be a real problem to human and robot explorers.鈥� He says
even a slight disturbance could send dust clouds wafting into the sky, clogging
equipment. Before any landing, scientists may need to do some homework on the
behaviour of charged dust in microgravity.