Exoplanet Three Times More Massive Than Jupiter Discovered 1,200 Light-years Away

Astronomers have discovered a planet three times more massive than Jupiter in a star system located around 1,250 light-years away from our own.

The distant world, known as Kepler-88 d, is the most massive in the star system, which contains two other planets, according to a study published in The Astronomical Journal. It orbits its star every four years in an elliptical, or egg-shaped, path.

A team of scientists led by the University of Hawaii Institute for Astronomy discovered the planet after six years of observations with the W. M. Keck Observatory, located on the dormant volcano Mauna Kea in Hawaii.

Their latest discovery sheds new light on the Kepler-88 system, which was already well-known among astronomers for its intriguing characteristics. The two planets that orbit closer to the star, known as Kepler-88 b and c, have a peculiar orbital relationship known as "motion resonance."

For example, Kepler-88 b—the sub-Neptune-sized innermost planet—orbits the star in just 11 days, while the orbital period of the second planet Kepler-88 c, which has about the same mass as Jupiter, is almost exactly double at 22 days.

This means that for every two orbits that Kepler-88 b completes, Kepler-88 c—which is twenty times more massive—will complete one. This motion resonance greatly increases the gravitational influence that each of the worlds has on the other.

The rhythmic symmetry is energetically efficient, with planet b getting a "push" for every two orbits it completes, much like a child being pushed on a swing. Because 88 is so much larger, its gravity has a significant influence on the orbital timing of 88 b.

"We say that such synchronized pairs of orbits are orbital resonances," Richard Pogge, an astronomer from Ohio State University, who was not involved in the study, wrote in an educational fact sheet. "The analogy is to consider a child on a swing being pushed another person."

Kepler-88 planetary system
An artist’s illustration of the Kepler-88 planetary system. W. M. Keck Observatory/Adam Makarenko

"If the pushes of the child come at random times, sometimes pushing with their swing and boosting them, other times pushing against their swing and slowing them down, they average out and the swing doesn't change much. However, if the pushes are all timed just right so that you push the child with their swing each time, the in-phase pushes build up and the child's swing gets amplified," he said.

In our own solar system, Jupiter has large influence on the other other planets and objects due its large mass. For example, the gas giant's gravitational influence is thought to be responsible for the small size of Mars, the presence of the asteroid belt and other characteristics of our solar system.

The Hawaii astronomers believe that Kepler-88 d may have had a similar influence on its own star system.

"At three times the mass of Jupiter, Kepler-88 d has likely been even more influential in the history of the Kepler-88 system than the so-called King, Kepler-88 c, which is only one Jupiter mass," Lauren Weiss, lead author of the latest study from UH IfA said in a statement. "So maybe Kepler-88 d is the new supreme monarch of this planetary empire—the empress."

Earlier this month, another team of researchers announced the discovery of a remarkable six-planet system containing planets in almost perfect rhythm that also display motion resonance.

According to a study published in the journal Astronomy & Astrophysics, the six planets are close to a so-called "3:2 resonance." This means that as the innermost planet completes three orbits, the second one completes roughly two, with this pattern repeated for all the subsequent planets.

Correction 4/30/20, 10:14 a.m. ET: This article was updated to remove incorrect information indicating that the mass of Kepler-88 d is 300 times that of the Earth. We regret the error.