PH3c: Astronomers Discover Low-Mass Exoplanet Orbiting Sun-like Star

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Professional astronomers and volunteers from the Planet Hunters citizens science program have discovered a low-mass, low-density exoplanet circling a Sun-like star known as PH3.

PH3, also known as Kepler-289, KOI-1353 or KIC 7303287, is a young star located about 2,300 light-years from the Sun.

Two planets in the system – Kepler-289b (PH3b) and Kepler-289c (PH3d) – had been previously validated statistically.

Kepler-289c is a gas giant – a warm version of our Saturn, while Kepler-289b’s mass is poorly known. It could be mostly rocky, watery, or gassy. The planets have orbital periods of 126 and 35 days, respectively.

Now, the astronomers and Planet Hunters volunteers have discovered a third alien world, dubbed PH3c, between these two planets with a period of 66 days.

According to the team, PH3c nearly avoided detection. “This is because it has a highly inconsistent orbit time around the star, due to the gravitational influence of other planets in the system.”

“PH3c’s orbital period changed by 10.5 hours in just 10 orbits,” explained Joseph Schmitt, a graduate student at Yale University and the first author of a paper published in the Astrophysical Journal (arXiv.org preprint).

“If Earth experienced such large changes, then if 2014 were 365 days long, 2024 would be 367.4 days long, almost two and a half days longer than 2014,” the astronomers said.

PH3c is about 2.7 times the radius of Earth and 4 times as massive.

Its low density means that, despite its low mass, a large chunk of the planet must be composed of hydrogen and helium: 2 percent by mass and 50 percent by radius.

“There’s also a quirky aspect of the planetary trio. The outer planet’s year is 1.91 times longer than the middle planet’s year, and the middle planet’s year is 1.91 times longer than the inner planet’s year. We’re not sure if this is just a coincidence or whether this might tell us something about how the planets were formed,” Mr Schmitt said.

Source : sci news