A giant planet
about 2.8 times the mass of Jupiter, called KELT-9b, has been detected around
an incredibly hot star. It is both the hottest planet ever discovered and the
only planet found to orbit a star that hot.
In KELT-9b's
daytime, its temperature reaches 4,327 C (7,820 F) – just 1,200 C cooler than
our Sun. It is about 2.8
times the mass of Jupiter but overall
it appears much larger as it has only half its density.
"It's a
planet by any of the typical definitions based on mass, but its atmosphere is
almost certainly unlike any other planet we've ever seen just because of the
temperature of its day side," said study author Scott Gaudi of Ohio State
University in a statement.
The star that the
planet orbits is called KELT-9. It is found about 650 light years away from
Earth in the Cygnus constellation. The star is almost 9,900 C, straddling the
temperature boundary between two types of hot star. A-type stars are between
about 7,000 and 9,700C and B-type stars are even hotter, with KELT-9 roughly in
between.
It's
extremely rare to find planets orbiting either A-type or B-type stars. Only 6
have been found around A-types and none have been found around B-types before.
The
intense radiation from KELT-9 on its orbiting star is thought to be blasting
away the planet's atmosphere,
leaving a trail of gas behind the planet.
"KELT-9
radiates so much ultraviolet radiation that it may completely evaporate the
planet," said Keivan Stassun of Vanderbilt University, also a study
author.
"Or,
if gas giant planets like KELT-9b possess solid rocky cores as some theories
suggest, the planet may be boiled down to a barren rock, like Mercury."
As
well as the sheer amount of radiation that its star emits, the planet KELT-9b
also orbits extremely close to its star, intensifying the dose it receives.
There
is no chance of finding life on KELT-9b, researchers say, as the maximum known
temperature that life can exist on Earth is 122 C. But studying outlier planets
like KELT-9b can help us understand how planetary systems form even in the most
extreme circumstances.
"As
we seek to develop a complete picture of the variety of other worlds out there,
it's important to know not only how planets form and evolve, but also when and
under what conditions they are destroyed," Stassun concluded.
The discovery is
detailed in a paper published in the journal Nature.
No comments:
Post a Comment