exist — terrestrial worlds around Sun-
like stars, preferably at the right distance
from the star that the temperature would
allow for liquid water. What it found was
much more interesting.
It turns out that the most common
WWW.ASTRONOMY.COM 29
Beta Pictoris is a well-known example of a star with
a surrounding debris disk. This star was the first
to have an exoplanet imaged directly. Infrared
observations made from the European Southern
Observatory in Chile revealed a planet orbiting the
star (whose bright presence has been artificially
removed by the large disk to increase the contrast
needed to reveal the planet). ESO/A.-M. LAGRANGE ET AL.Rocky planets larger than Earth, dubbed super-Earths, are becoming increasingly common among exoplanet finds. No such planet exists in our solar system, of
course. These super-Earths — all artist’s renditions, except for Earth at the far right for comparison — all sit within their stars’ habitable zones, meaning they could
potentially support life. NASA AMES/JPL-CALTECH
The planet 51 Pegasi b, imagined in
this artist’s rendition, was the first
extrasolar planet discovered circling
a Sun-like star. It is a hot Jupiter that
orbits its star once every four days,
from a distance some seven times
closer than Mercury orbits the Sun.
ESO/M. KORNMESSER/NICK RISINGER (SKYSURVEY.ORG)type of planet in the Milky Way is one
that does not exist in our own solar sys-
tem, with a radius between that of Earth
and that of a planet like Neptune, four
times larger than Earth. Members of
this new class of planets are known assuper-Earths, if their density suggests that
they are rocky, or mini-Neptunes, if a
lower density indicates a gaseous nature.
Ideally, we’d know not only the radius,
which can be determined by the transit
method, but also the mass, for which we
need a detection via radial velocity.
Unfortunately, most of the stars stud-
ied by Kepler are too far away or too faint
to enable useful radial velocity measure-
ments to be made. A new NASA satellite,
TESS (short for Transiting Exoplanet
Survey Satellite), is searching for planetsKEPLER-22 b
KEPLER-69 c
KEPLER-62 eKEPLER-62 f
EARTH