Astronomers
have discovered possibly the smallest extrasolar planet yet, a rocky world
that's orbiting a star in the constellation Leo.
"After
final confirmation, the new exoplanet will be the smallest found to date,"
said lead researcher Ignasi Ribas of the Spanish Research Council (CSIC).
"The study opens a new path that should lead to the discovery of even
smaller planets in the near future, with the goal of eventually finding worlds
more and more similar to the Earth."
The newly
discovered planet weighs about five Earth masses and is located 30 light-years
from Earth. A planet of this mass is expected to be rocky
rather than gaseous, but there are no actual pictures of it. (A light-year
is the distance light travels in one year, or about 5.88 trillion miles — 9.46
trillion kilometers.)
That mass
means the planet is a "super-Earth," a category that includes planets
with masses of between one and 10 times the Earth. Astronomers estimate its
radius to be about 50 percent greater than that of Earth's radius of 4,000
miles (6,400 kilometers).
Dubbed GJ
436c, the planet orbits its host star (GJ 436) in just 5.2 Earth days, and is
thought to complete a revolution about its axis in 4.2 Earth days. A complete
revolution of Earth takes 24 hours and a full orbit around the sun takes 365
days.
The
astronomers predicted the existence of the small exoplanet due to its
gravitational effects on the orbit of an inner planet — a "hot ice
planet" discovered in 2004. In the new study, detailed this week in Astrophysical
Journal, the researchers found that for every two orbits of the hot ice planet, the new
planet completes one.
Most of the
280 or so planets discovered to date outside of our solar system are much
larger gas giants called "hot-Jupiters."
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