KELT-9 and its planet, KELT-9b

Discovery of hottest exoplanet so far is a “testament to the discovery power of small telescopes”

Image credit: NASA/JPL-Caltech/Robert Hurt

An international research team has announced the discovery of an unusual planet – a ‘hot Jupiter‘ with surface temperature similar to that of the Sun – which was first observed by a small, low-cost telescope.

The discovery of the planet, KELT-9b, was announced at the spring meeting of the American Astronomical Society, and published in Nature.

“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 Professor Scott Gaudi, an Ohio State University astronomer and a lead author of the study.

The gas giant, 2.8 times more massive than Jupiter, is tidally locked to its star, like the Moon is to Earth. This has resulted in the planet having a ‘day side’ permanently being bombarded by stellar UV radiation. This extreme radiation has caused its atmosphere to expand.

On the day side of KELT-9b, researchers record a surface temperature of 4600K, just 1200K hotter than our own sun. The heat is so intense that molecules such as water and carbon dioxide are unable to form. The still-mysterious night side” may be cool enough for molecules to temporarily form.

According to the researchers, KELT-9b’s star emits such intense radiation that it “may completely evaporate the planet, causing the gas of the planet to boil off.

A clue of the planet’s existence was first detected by astronomers using the KELT-North telescope in 2014; a tiny drop in the star’s brightness, suggesting that a planet may have passed across its face. Following observations confirmed this was a hot Jupiter. Hot Jupiters are large, gaseous, swiftly-orbiting exoplanets with high surface temperatures.

While most major astronomical telescopes are designed to observe faint stars in small patches of sky, the kilodegree extremely little telescopes (KELTs) skim over millions of bright stars at low resolution. This allows astronomers to search for planets at low cost, using mostly off-the-shelf technology.

The hardware for a KELT costs approximately $75,000 while most astronomical telescopes cost millions of dollars to build.

There are two KELTs in operation, one in the Northern and one in the Southern hemisphere. They were designed to fill a gap in the available technologies for hunting exoplanets. Since beginning operations in 2005 (KELT-North) and 2009 (KELT-South), the robotic telescopes have observed several new exoplanets.

“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 Professor Joshua Pepper, a Lehigh University astronomer who built the KELT telescopes.

The astronomers next hope to take a closer look at the extraordinary planet using other telescopes, including the Hubble Space Telescope, and, in the future, the James Webb Space Telescope. This could allow them to view KELT-9b in higher resolution, and determine whether the heat of its sun is causing planetary matter to boil off in a comet-like tail.

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