Astronomers reveal discovery of the hottest gas giant exoplanet known yet

Thursday, June 8, 2017

On Monday, astronomers at the Ohio State University, Columbus, revealed the discovery of an exoplanet, named KELT-9b and according to the university's astronomy professor Scott Gaudi, it is "the hottest gas giant planet that has ever been discovered". The discovery was reported online in the Nature journal.

Artist's impression of KELT-9b orbiting its star, KELT-9.
Image: NASA/JPL-Caltech.

The astronomers say the planet's surface temperature is more than 4000°C (7232°F), nearly as hot as the Sun. The planet takes about 36 to 48 hours to orbit around its star, KELT-9. KELT-9 is about two and a half times larger than the Sun and nearly twice its temperature. The star is about 650 light years from the earth, but it is about 300 million years old. KELT-9 is a blue A-type star, which shines brightly but, unlike some other stars such as our own Sun, their life span is on the order of millions rather than billions of years.

About a year ago, NASA reports, at the Winer Observatory in Arizona, observers using the KELT-North telescope noticed a minute drop in KELT-9's brightness — about 0.5%. This pattern was observed once every one and a half days, implying the planet comes in between the line of sight of the star from Earth, meaning the planet completes one revolution in that time period. Observations using the Hubble telescope could reveal whether the planet possesses a comet-like tail, which could help the astronomers estimate how long the planet may live.

Professor Gaudi told the BBC the planet KELT-9b "is about three times the mass of Jupiter and twice as big as Jupiter." He said the team discovered the planet in 2014. He added, "it took us this long to finally convince ourselves that this truly bizarre and unusual world was in fact a planet orbiting another star".

Much like the Moon is to the Earth, KELT-9b is tidally locked to its star; with one side of the planet always exposed to its star. Due to tidal locking, the planet's surface temperature facing the star is roughly 4300°C (7772°F), more than the surface temperature of an average Red Dwarf star. Its close proximity to its parent star exposes it to ultraviolet radiation, and according to the calculations, the planet loses planetary material anywhere between ten billion to ten trillion grams each second. Professor Gaudi said, "It's a planet by any of the typical definitions of mass, but its atmosphere is almost certainly unlike any other planet we've ever seen just because of the temperature of its dayside".

According to Keivan Stassun, a professor of physics and astronomy at Vanderbilt University, Tennessee, "KELT-9 will swell to become a red giant star in a few hundred million years". Professor Stassun directed the study with Gaudi. The discovery was a collaboration between Ohio State University, Vanderbilt University, Lehigh University, and the South African Astronomical Observatory. They operate a dual-location system, one location in each hemisphere, called the Kilodegree Extremely Little Telescope. Professor Gaudi told the BBC that it was named "as a joke".

Scott Gaudi, Professor of Astronomy, Ohio State University‍:"It's a planet by any of the typical definitions of mass"


  • B. Scott Gaudi, Keivan G. Stassun, Karen A. Collins, Thomas G. Beatty, George Zhou, David W. Latham, Allyson Bieryla, Jason D. Eastman, Robert J. Siverd, Justin R. Crepp, Erica J. Gonzales, Daniel J. Stevens, Lars A. Buchhave, Joshua Pepper, Marshall C. Johnson, Knicole D. Colon, Eric L. N. Jensen, Joseph E. Rodriguez, Valerio Bozza, Sebastiano Calchi Novati, Giuseppe D'Ago, Mary T. Dumont, Tyler Ellis, Clement Gaillard, Hannah Jang-Condell. "A giant planet undergoing extreme-ultraviolet irradiation by its hot massive-star host" — Nature (magazine), June 5, 2017