Astronomers discover an exoplanet that is hotter than most stars

One side of the planet is in perpetual daylight, and the other side has a never ending night. The dayside temperature is about 4,326 degrees Celsius.

Around 650 light years away is a 300 million year old star that is twice as large as the Sun and twice as hot. Astronomers observing the star, known as KELT-9 noticed a tiny dip in the brightness of the star, around 0.5 percent. This was the indication that a planet was in orbit around the star. The planet was designated as KELT-9b. There was a regular dip in the brightness every 1.5 days, which indicated that the planet had a "year" as long as one and a half Earth days.

The percentage of the brightness drop also indicated the size of the planet. It was about 2.8 times the size of Jupiter, and a class of planets known as hot Jupiter. The planet is tidally locked to its host star, in the same way that the Moon is tidally locked to the Earth. One side of the planet is in perpetual daylight, and the other side has a never ending night. The dayside of the planet is hot — hotter than most stars. Temperatures on the dayside of the planet reach 4,326 degrees Celsius.

The unusual planet is described by researchers from Vanderbilt University and Ohio State University in the journal Nature. Astronomers further hope to study the planet with the Spitzer space telescope, the Hubble space telescope and the James Webb Space Telescope which is yet to be launched.

Scott Gaudi, professor of astronomy at The Ohio State University, and lead author of the study said, "As has been highlighted by the recent discoveries from the MEarth collaboration, the planet around Proxima Centauri, and the astonishing system discovered around TRAPPIST-1, the astronomical community is clearly focused on finding Earthlike planets around small, cooler stars like our sun. They are easy targets and there’s a lot that can be learned about potentially habitable planets orbiting very low-mass stars in general. On the other hand, because KELT-9b’s host star is bigger and hotter than the sun, it complements those efforts and provides a kind of touchstone for understanding how planetary systems form around hot, massive stars"

KELT-9b is being slowly evaporated by the extreme ultraviolet radiation from the host star. The planet may have a tail, similar to a comet, but further observations are required to confirm this. The eventual fate of the planet is also in question. If gas giants have a rocky core, then after all the matter is evaporated by a star, then KETL-9b will be reduced to a tiny rocky planet similar to Mercury. However, it is also possible that the star will expand beyond the orbit of the planet, and engulf it. Keivan Stassun, a professor of Physics and Astronomy at Venderbilt University says, "The long-term prospects for life, or real estate for that matter, on KELT-9b are not looking good."


also see