Close Encounter with a Comet

For all its spectral magnificence, the tail of a comet is about as close as you can get to nothing at all, a banner of dust so tenuous that a cubic mile's worth wouldn't fill a shoebox. Yet that near nothingness holds many secrets. Comets are leftovers from the creation of the solar system 4.5 billion years ago; they also delivered organic chemicals and water--the crucial building blocks of life--to the young Earth. Scientists would love, therefore, to get a bit of comet into the lab for analysis.

Now it looks as though they will. On Feb. 6 a remarkable space...