New
discovery is likely to be a rocky world in the ‘Goldilocks’ zone of its parent
star where the temperature is just right for liquid water to flow
The Guardian, Ian Sample, science editor, 7 January 2015
An alien world that orbits a distant star in the constellation of Lyra may be the most Earth-like planet ever found outside the solar system.
The Guardian, Ian Sample, science editor, 7 January 2015
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| An Earth-like planet orbiting a star that has formed a planetary nebula. Earlier in its life, this planet may have resembled the newly discovered Kepler 438b. Illustration: David A Aguilar/CfA |
An alien world that orbits a distant star in the constellation of Lyra may be the most Earth-like planet ever found outside the solar system.
The planet,
named Kepler 438b, is slightly larger than Earth and circles an orange dwarf
star that bathes it in 40% more heat than our home planet receives from the
sun.
The small
size of Kepler 438b makes it likely to be a rocky world, while its proximity to
its star puts it in the “Goldilocks” or habitable zone where the temperature is
just right for liquid water to flow.
A rocky
surface and flowing water are two of the most important factors scientists look
for when assessing a planet’s chances of being hospitable to life.
Kepler
438b, which is 470 light years away, completes an orbit around its star every
35 days, making a year on the planet pass 10 times as fast as on Earth. Small
planets are more likely to be rocky than huge ones, and at only 12% larger than
our home planet, the odds of Kepler 438b being rocky are about 70%, researchers
said.
Scientists at the Harvard-Smithsonian Center for Astrophysics announced the discovery at a meeting of the American Astronomical Society in Seattle on Tuesday, along with seven other planets that also lie in the habitable zones of their stars. The haul doubles the number of small planets – those less than twice the size of Earth – believed to be orbiting in their parent stars’ habitable zones.
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| Kepler-186f is part of five-planet system 795 lights years away. The find is described in the journal Science as ‘a landmark on the road to discovering habitable planets’. Photograph: Nasa Ames/SETI Institute/JPL-Cal/PA |
Scientists at the Harvard-Smithsonian Center for Astrophysics announced the discovery at a meeting of the American Astronomical Society in Seattle on Tuesday, along with seven other planets that also lie in the habitable zones of their stars. The haul doubles the number of small planets – those less than twice the size of Earth – believed to be orbiting in their parent stars’ habitable zones.
All were
spotted with Nasa’s Kepler space telescope which detects planets as they move
across the faces of their stars, causing the light picked up by the telescope
to dim periodically by a minuscule amount.
One of the
other planets, Kepler 442b, lies in the same constellation 1,100 light years
away. It is about a third larger than Earth, receives about two thirds as much
starlight, and has a 60% chance of being rocky, according to a report to be
published in The Astrophysical Journal.
Guillermo Torres, lead author on the study, said the size and amount of light falling on
the planets made them the most Earth-like planets yet found beyond our solar
system. Before their discovery, the exoplanets most similar to our own were
Kepler 186f, which is 10% larger than Earth and receives a third as much light,
and Kepler 62f, which is 40% larger and gets about 41% as much light.
The
scientists do not know if the planets have atmospheres, but if they are cloaked
in insulating layers of gas, the mean temperatures of Kepler 438b and 442b are
expected to be about 60 and zero degrees Celsius respectively.
The
Harvard-Smithsonian team used a computer program called Blender to confirm that
the planets originally spotted by the Kepler space telescope were real. False
sightings can happen when pairs of stars that lie behind the one being studied
eclipse each other, causing the background light to dim slightly. In some
cases, this can be mistaken for a planet moving in front of its star.
“The pair
of stars can be way behind the target star, but if they are in the same line of
sight, the result is a very tiny dimming that can look like a planet,” said
Torres.
The Blender
program gives a statistical probability that the planet is real and not an
effect of background stars eclipsing one another. Of 12 suspected planets
Torres and his colleagues assessed with the program, 11 came out at more than
99.7% likely to be real.
David Kipping, a co-author on the study, said that Kepler 438b and 442b were “as
close to Earth analogues as we’re going to find in the Kepler data”.
Astronomers
are keenly waiting on the next generation of telescopes, including Hubble’s
replacement, the James Webb Space Telescope, and the European Extremely Large Telescope, which is being built in the Atacama desert in Chile, to help them
examine the atmospheres of distant planets for signs of life.
In the
meantime, scientists plan to look for other, indirect signs, that a planet may
be well-suited for life. Kipping is searching through the Kepler data for hints
that some planets have moons, which can improve their odds of being habitable.
Our own moon stabilises Earth’s tilt, making the temperatures far less erratic
than they would be otherwise. Alien planets that share a solar system with a
gas giant like Jupiter are also interesting, because the vast size of the
planet acts as a shield against devastating asteroid and comet impacts.
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