Three ‘super-Earth’ exoplanets orbiting nearby star discovered

(Top) The full K2 light curve of GJ 9827 from Campaign
12, corrected for systematics using the technique described in
Vanderburg & Johnson (2014) and Vanderburg et al. (2016b).
(Middle) The corrected K2 lightcurve with best-fit low
frequency variability removed. (Bottom) Phase folded K2 light
curves of GJ 9827 b, c. and d. The observations are plotted in
open black circles, and the best fit models are plotted in red.
Credit: Rodriguez et al., 2017.

(Phys.org)—NASA’s prolonged Kepler mission, known as K2, has
made another significant discovery, revealing the existence
of three new exoplanets. The newly found alien worlds circle
the nearby star GJ 9827 and were classified as
“super-Earths.” The finding is presented in a paper published
Sept. 6 on arXiv.org.

Kepler is the most prolific planet-hunting telescope. The
spacecraft has discovered more than 2,300 exoplanets to date.
After the failure of its two reaction wheels in 2013, the
mission was repurposed as K2 to perform high-precision
photometry of selected fields in the ecliptic. Since then, the
revived Kepler spacecraft has detected nearly 160 extrasolar
worlds.

Now, a team of astronomers led by Joseph Rodriguez of the
Harvard-Smithsonian Center for Astrophysics (CfA) in Cambridge,
Massachusetts, reports the finding of three new exoplanets from
the data provided by K2. The Kepler spacecraft observed GJ 9827
from December 2016 to March 2017, during its Campaign 12. These
observations allowed the team to discover that this nearby late
K-type dwarf star is orbited by three . The newly found planets were
classified as “super-Earths” as they have masses higher than
Earth’s but lower than that of Solar System’s gas giants.

“In this paper, we present the discovery of three transiting
planets orbiting the nearby star GJ 9827 using data from the K2
mission,” the researchers wrote in the paper.

Located some 100 light years away from the Earth, GJ 9827 is a
bright star of spectral type K6V. It has a radius of about 0.63
solar radii and is approximately 15 percent less massive than
our Sun. The scientists found that the star is circled by three
planets, designated GJ 9827 b, c and d, located about 0.02,
0.04 and 0.06 AU from the host respectively.

According to the paper, GJ 9827 b has a radius of 1.64 Earth
radii but its precise mass remains uncertain. The researchers
estimate that its mass should be between 3.5 and 4.26 Earth
masses. The planet orbits its parent star in approximately 1.21
days and has an equilibrium temperature of 1,119 K.

With a radius of 1.29 Earth radii and an estimated mass of
about 2.5 Earth masses, GJ 9827 c is smallest and less massive
planets of the newly discovered trio. The exoplanet has an
equilibrium temperature of 774 K and an orbital period of 3.65
days.

GJ 9827 d is about two times larger than the Earth and at least
five times as massive as our planet. This alien world has an
equilibrium temperature of 648 K and it takes it 6.2 days to
fully orbit its host star.

The new discovery reported by Rodriguez’s team makes GJ 9827
the closest exoplanet host discovered by K2 mission to date.
The star’s proximity and brightness as well as similarity in
the size of make the system an excellent target
for further atmospheric studies. The scientists hope that
future space observatories like the James Webb Space Telescope
(JWST) could provide important insights about atmospheric
properties of the three newly discovered extrasolar worlds.

Explore further:

Astronomers discover two ‘warm Jupiter’ exoplanets orbiting
distant stars

More information: A System of Three Super Earths
Transiting the Late K-Dwarf GJ 9827 at Thirty Parsecs,
arXiv:1709.01957 [astro-ph.EP] arxiv.org/abs/1709.01957

Abstract
We report the discovery of three small transiting planets
orbiting GJ 9827, a bright (K = 7.2) nearby late K-type dwarf
star. GJ 9827 hosts a 1.64+0.22−0.20
R super Earth on a 1.2 day period, a
1.29+0.17−0.16 R super Earth
on a 3.6 day period, and a 2.08+0.28−0.26
R super Earth on a 6.2 day period. The radii of the
planets transiting GJ 9827 span the transition between
predominantly rocky and gaseous planets, and GJ 9827 b and c
fall in or close to the known gap in the radius distribution of
small planets between these populations. At a distance of ∼30
parsecs, GJ 9827 is the closest exoplanet host discovered by K2
to date, making these planets well-suited for atmospheric
studies with the upcoming James Webb Space Telescope. The GJ
9827 system provides a valuable opportunity to characterize
interior structure and atmospheric properties of coeval planets
spanning the rocky to gaseous transition.

© 2017 Phys.org

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