Strange New Planet Discovered --"Hotter Than Most Stars"
"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 Scott Gaudi, professor of astronomy at The Ohio State University and
a leader of the study.
A newly discovered Jupiter-like world is so hot that it's stretching the definition of
the word "planet."
With a day-side temperature of 4,600 Kelvin (more than 7,800 degrees Fahrenheit), planet
KELT-9b is hotter than most stars, and only 1,200 Kelvin (about 2,000 degrees Fahrenheit)
cooler than our own sun.
For instance, it's a gas giant 2.8 times more massive than Jupiter but only half as dense,
because the extreme radiation from its host star has caused its atmosphere to puff up
like a balloon.
And because it is tidally locked to its star--as the Moon is to Earth--the day side of the
planet is perpetually bombarded by stellar radiation, and as a result is so hot that
molecules such as water, carbon dioxide, and methane can't form there.
The properties of the night side are still mysterious--molecules may be able to form
there, but probably only temporarily.
KELT-9b orbits a star, dubbed KELT-9, which is more than twice as large and nearly twice
as hot as our sun.
Keivan Stassun, a professor of physics and astronomy at Vanderbilt who directed the study
with Gaudi said, "KELT-9 radiates so much ultraviolet radiation that it may completely
evaporate the planet.
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."
That is, if the star doesn't grow to engulf it first.
"KELT-9 will swell to become a red giant star in about a billion years," said Stassun.
"The long-term prospects for life, or real estate for that matter, on KELT-9b are not
looking good."
Given that its atmosphere is constantly blasted with high levels of ultraviolet radiation,
the planet may even be shedding a tail of evaporated planetary material like a comet,
Gaudi added.
While Gaudi and Stassun spend a lot of time developing missions designed to find habitable
planets in other solar systems, the scientists said there's a good reason to study worlds
that are unlivable in the extreme.
"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," Gaudi said.
Stassun added, "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.
In 2014, astronomers using the KELT-North telescope at Winer Observatory in Arizona
noticed a tiny drop in the star's brightness--only about half of one percent-- that indicated
that a planet may have passed in front of the star.
The brightness dipped once every 1.5 days, which means the planet completes a "yearly"
circuit around its star every 1.5 days.
Subsequent observations confirmed the signal to be due to a planet, and revealed it to
be what astronomers call a "hot Jupiter"--the ideal kind of planet for the KELT telescopes
to spot.
KELT is short for "Kilodegree Extremely Little Telescope."
Astronomers at Ohio State, Vanderbilt University, and Lehigh University jointly operate two
KELTs (one each in the Northern and Southern Hemispheres) in order to fill a large gap
in the available technologies for finding extrasolar planets.
Other telescopes are designed to look at very faint stars in much small sections of the
sky, and at very high resolution.
The KELTs, in contrast, look at millions of very bright stars at once, over broad sections
of sky, and at low resolution.
It's a low-cost means of planet hunting, using mostly off-the-shelf technology: whereas a
traditional astronomical telescope costs millions of dollars to build, the hardware for a KELT
telescope runs less than $75,000.
"This discovery is a testament to the discovery power of small telescopes, and the ability
of citizen scientists to directly contribute to cutting-edge scientific research," said
Joshua Pepper, astronomer and assistant professor of physics at Lehigh University, who built
the two KELT telescopes.
The astronomers hope to take a closer look at KELT-9b with other telescopes--including
Spitzer, the Hubble Space Telescope (HST), and eventually the James Webb Space Telescope.
Observations with HST would enable them to see if the planet really does have a cometary
tail, and allow them to determine how much longer that planet will survive
its current hellish condition.
The Daily Galaxy via The Ohio State University
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