TY - JOUR
T1 - The mass of the Mars-sized exoplanet Kepler-138 b from transit timing
AU - Jontof-Hutter, Daniel
AU - Rowe, Jason F.
AU - Lissauer, Jack J.
AU - Fabrycky, Daniel C.
AU - Ford, Eric B.
N1 - Funding Information:
Acknowledgements D.J-H. acknowledges support through the NASA Postdoctoral Program and funding from the Center for Exoplanets and Habitable Worlds. The Center for Exoplanets and Habitable Worlds is supported by the Pennsylvania State University, the Eberly College of Science and the Pennsylvania Space Grant Consortium. J.F.R. acknowledges NASA grant NNX14AB92G issued through the Kepler Participating Scientist Program. D.C.F. is an Alfred P. Sloane Fellow and was supported by the Kepler Participating Scientist Program award NNX14AB87G. E.B.F. was supported in part by NASA Kepler Participating Scientist Program award NNX14AN76G and NASA ExoplanetResearchProgramaward NNX15AE21G,aswellasthe Centerfor Exoplanets and Habitable Worlds.
Publisher Copyright:
© 2015 Macmillan Publishers Limited. All rights reserved.
PY - 2015/6/17
Y1 - 2015/6/17
N2 - Extrasolar planets that pass in front of their host star (transit) cause a temporary decrease in the apparent brightness of the star, providing a direct measure of the planet's size and orbital period. In some systems with multiple transiting planets, the times of the transits are measurably affected by the gravitational interactions between neighbouring planets. In favourable cases, the departures from Keplerian orbits (that is, unaffected by gravitational effects) implied by the observed transit times permit the planetary masses to be measured, which is key to determining their bulk densities. Characterizing rocky planets is particularly difficult, because they are generally smaller and less massive than gaseous planets. Therefore, few exoplanets near the size of Earth have had their masses measured. Here we report the sizes and masses of three planets orbiting Kepler-138, a star much fainter and cooler than the Sun. We determine that the mass of the Mars-sized inner planet, Kepler-138 b, is 0.066-0.037+0.059 Earth masses. Its density is 2.6-1.5+2.4 grams per cubic centimetre. The middle and outer planets are both slightly larger than Earth. The middle planet's density (6.2-3.4+5.8 grams per cubic centimetre) is similar to that of Earth, and the outer planet is less than half as dense at 2.1-1.2+2.2 grams per cubic centimetre, implying that it contains a greater portion of low-density components such as water and hydrogen.
AB - Extrasolar planets that pass in front of their host star (transit) cause a temporary decrease in the apparent brightness of the star, providing a direct measure of the planet's size and orbital period. In some systems with multiple transiting planets, the times of the transits are measurably affected by the gravitational interactions between neighbouring planets. In favourable cases, the departures from Keplerian orbits (that is, unaffected by gravitational effects) implied by the observed transit times permit the planetary masses to be measured, which is key to determining their bulk densities. Characterizing rocky planets is particularly difficult, because they are generally smaller and less massive than gaseous planets. Therefore, few exoplanets near the size of Earth have had their masses measured. Here we report the sizes and masses of three planets orbiting Kepler-138, a star much fainter and cooler than the Sun. We determine that the mass of the Mars-sized inner planet, Kepler-138 b, is 0.066-0.037+0.059 Earth masses. Its density is 2.6-1.5+2.4 grams per cubic centimetre. The middle and outer planets are both slightly larger than Earth. The middle planet's density (6.2-3.4+5.8 grams per cubic centimetre) is similar to that of Earth, and the outer planet is less than half as dense at 2.1-1.2+2.2 grams per cubic centimetre, implying that it contains a greater portion of low-density components such as water and hydrogen.
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U2 - 10.1038/nature14494
DO - 10.1038/nature14494
M3 - Article
AN - SCOPUS:84934936722
SN - 0028-0836
VL - 522
SP - 321
EP - 323
JO - Nature
JF - Nature
IS - 7556
ER -