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artist’s conception depicts an Earth-like planet orbiting an evolved
star that has formed a stunning "planetary nebula." Earlier in its life,
this planet may have been like one of the eight newly discovered worlds
orbiting in the habitable zones of their stars. Credit: David A. Aguilar (CfA).High Resolution (jpg)-Low Resolution (jpg)
Cambridge, MA -Astronomers
announced today that they have found eight new planets in the
"Goldilocks" zone of their stars, orbiting at a distance where liquid
water can exist on the planet's surface. This doubles the number of
small planets (less than twice the diameter of Earth) believed to be in
the habitable zone of their parent stars. Among these eight, the team
identified two that are the most similar to Earth of any known
exoplanets to date.
"Most of these planets have a good chance of being rocky, like
Earth," says lead author Guillermo Torres of the Harvard-Smithsonian
Center for Astrophysics (CfA).
These findings were announced today in a press conference at a meeting of the American Astronomical Society.
The two most Earth-like planets of the group are Kepler-438b and
Kepler-442b. Both orbit red dwarf stars that are smaller and cooler than
our Sun. Kepler-438b circles its star every 35 days, while Kepler-442b
completes one orbit every 112 days.
With a diameter just 12 percent bigger than Earth, Kepler-438b has a
70-percent chance of being rocky, according to the team's calculations.
Kepler-442b is about one-third larger than Earth, but still has a
60-percent chance of being rocky.
To be in the habitable zone, an exoplanet must receive about as much
sunlight as Earth. Too much, and any water would boil away as steam. Too
little, and water will freeze solid.
"For our calculations we chose to adopt the broadest possible limits
that can plausibly lead to suitable conditions for life," says Torres.
Kepler-438b receives about 40 percent more light than Earth. (In
comparison, Venus gets twice as much solar radiation as Earth.) As a
result, the team calculates it has a 70 percent likelihood of being in
the habitable zone of its star.
Kepler-442b get about two-thirds as much light as Earth. The
scientists give it a 97 percent chance of being in the habitable zone.
"We don't know for sure whether any of the planets in our sample are
truly habitable," explains second author David Kipping of the CfA. "All
we can say is that they're promising candidates."
Prior to this, the two most Earth-like planets known were
Kepler-186f, which is 1.1 times the size of Earth and receives 32
percent as much light, and Kepler-62f, which is 1.4 times the size of
Earth and gets 41 percent as much light.
The team studied planetary candidates first identified by NASA's
Kepler mission. All of the planets were too small to confirm by
measuring their masses. Instead, the team validated them by using a
computer program called BLENDER to determine that they are statistically
likely to be planets. BLENDER was developed by Torres and colleague
Francois Fressin, and runs on the Pleaides supercomputer at NASA Ames.
This is the same method that has been used previously to validate some
of Kepler's most iconic finds, including the first two Earth-size
planets around a Sun-like star and the first exoplanet smaller than
After the BLENDER analysis, the team spent another year gathering
follow-up observations in the form of high-resolution spectroscopy,
adaptive optics imaging, and speckle interferometry to thoroughly
characterize the systems.
Those follow-up observations also revealed that four of the newly
validated planets are in multiple-star systems. However, the companion
stars are distant and don't significantly influence the planets.
As with many Kepler discoveries, the newly found planets are distant
enough to make additional observations challenging. Kepler-438b is
located 470 light-years from Earth while the more distant Kepler-442b is
1,100 light-years away.
The paper reporting these results has been accepted for publication in The Astrophysical Journal and is available online.
in Cambridge, Mass., the Harvard-Smithsonian Center for Astrophysics
(CfA) is a joint collaboration between the Smithsonian Astrophysical
Observatory and the Harvard College Observatory. CfA scientists,
organized into six research divisions, study the origin, evolution and
ultimate fate of the universe.
For more information, contact:
David A. Aguilar
Director of Public Affairs
Harvard-Smithsonian Center for Astrophysics
Public Affairs Specialist
Harvard-Smithsonian Center for Astrophysics