An international team of researchers from the Kiepenheuer Institute for Solar Physics and the University of Texas at Arlington has spotted signs of an additional exoplanet in the Gliese 832 planetary system.
A three-planet system. Image credit: NASA.
Gliese 832 is a red dwarf star located in the constellation Grus, about 16 light-years from Earth.
Also known as GJ 832, HD 204961 or LHS 3685, the star has about half the mass and radius of the Sun.
Astronomers had previously detected two massive exoplanets – the Jupiter-like gas giant Gliese 832b and the super-Earth Gliese 832c — around this star.
Gliese 832b has a mass of 0.64 times that of Jupiter and orbits the star 3.53 AU out.
Gliese 832c resides very close its star — about 0.16 AU. It has an orbital period of 35.68 days, a mass 5.4 times that of Earth’s and receives about the same average energy as Earth does from the Sun.
In the new study, University of Texas researcher Suman Satyal and co-authors analyzed the simulated data with an injected Earth-mass planet on this nearby planetary system hoping to find a stable orbital configuration for the planet that may be located in a vast space between Gliese 832b and c.
The two known planets were discovered by the radial velocity technique, which detects variations in the velocity of the central star, due to the changing direction of the gravitational pull from an unseen exoplanet as it orbits the star.
By regularly looking at the spectrum of a star — and so, measuring its velocity — one can see if it moves periodically due to the influence of a companion.
“We also used the integrated data from the time evolution of orbital parameters to generate the synthetic radial velocity curves of the known and the Earth-like planets in the system,” Dr. Satyal explained.
“We obtained several radial velocity curves for varying masses and distances indicating a possible new middle planet.”
The Gliese 832 planetary system. Image credit: Suman Satyal.
According to the team’s analysis, the additional planet — Gliese 832d — has a mass between 1 to 15 Earth’s masses and resides at a distance of 0.25-2 AU.
“The existence of this possible planet is supported by long-term orbital stability of the system, orbital dynamics and the synthetic radial velocity signal analysis,” Dr. Satyal noted.
“At the same time, a significantly large number of radial velocity observations, transit method studies, as well as direct imaging are still needed to confirm the presence of possible new planets in the Gliese 832 system.”
The team’s findings are published in the Astrophysical Journal.
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S. Satyal et al. 2017. Dynamics of a Probable Earth-mass Planet in the GJ 832 System. ApJ 845, 106; doi: 10.3847/1538-4357/aa80e2
