Race to the Bottom Planets are like insurance premiums: smaller
is usually better. But better worlds are in short supply. As I
write this, a total of 347 exoplanets worlds orbiting other
stars have been reported in the scientific literature.? This
roster is expanding at roughly one planet a week, and it?s a
decidedly beefy crowd.? Many exoplanets are comparable in mass
to Jupiter, and the biggest is nearly eight thousand times as
hefty as Earth. Such bulky orbs are likely to be wrapped in
thick, malodorous atmospheres: hardly the type of place that ET
would be pleased to call home. But what about those smaller,
better worlds, at the bottom of the heap?? Are there any
lightweights among the exoplanet crowd? Well, there?s Gliese
581e, which weighs in at a mere 1.9 times the tonnage of Earth,
and is the least massive exoplanet known to circle an ordinary
star.? If the density of this planet is similar to that of terra
firma, then its diameter is a mere 24% greater than the world
under your feet. Last month?s dis