Astronomers Find Three Smallest
Planets Outside Solar System
ScienceDaily (Jan. 11, 2012)
— A team of astronomers led by scientists at the
California Institute of Technology (Caltech) has
discovered the three smallest confirmed planets
ever detected outside our solar system. The three
planets, which all orbit a single star, are
smaller than Earth and appear to be rocky with a
solid surface. Until now, astronomers have found
at most only four other rocky planets, also
called terrestrial planets, around other stars.
of new planets is too close to the central star to
be in its habitable zone -- the ring-shaped
region around a star where the temperature is mild
enough for liquid water, and possibly life, to
exist. But the planets are the first rocky ones to
be found orbiting a type of dim, small star called
a red dwarf, the most common kind in the Milky
Way. Their existence suggests that the galaxy
could be teeming with similarly rocky planets --
and that there's a good chance that many are in
the habitable zone.
The red dwarf, called KOI-961, was first flagged
as a potential planetary system by the Kepler
mission, a space telescope that looks for planets
around sunlike stars by scanning the sky for stars
that periodically dip in brightness -- the result
of one or more planets passing in front of them. Although Kepler
reported 900 potential planetary systems in
February, only about 85 of those were red-dwarf
systems. The fact that a relatively small sample
of red dwarfs produced three terrestrial planets
means that either the Caltech-led team was really
lucky or, more likely, that these planets are
commonly found around red dwarfs.
"When you combine that with the fact that these
are some of the most numerous stars in the galaxy,
you realize this type of system could be common,"
says Philip Muirhead, a postdoctoral scholar at
Caltech. "There's no question that it's exciting."
Muirhead is the lead author on the paper
describing the discovery, which has been accepted
by the Astrophysical Journal. The team
will also present their results in two talks on
January 11 at the meeting of the American
Astronomical Society in Austin, Texas.
dwarfs make up eight out of every ten stars in the
galaxy," adds John Johnson, assistant professor of
astronomy and one of the paper's coauthors. "That
boosts the chances of other life being in the
universe -- that's the ultimate result
here. If these planets are as common as they
appear -- and because red dwarfs themselves are so
common -- then the whole galaxy must be just
swarming with little habitable planets around
faint red dwarfs."