Astronomers have detected atomic iron and titanium in the atmosphere of KELT-9b, a gas giant exoplanet orbiting a star in the constellation Cygnus, about 650 light-years from Earth.
Artist’s impression of a sunset on the ultrahot Jupiter KELT-9b. Image credit: Denis Bajram.
KELT-9b belongs to a family called ultrahot Jupiters, incredibly hot giant exoplanets that orbit very close to their parent stars.
The planet is approximately 2.8 times more massive than Jupiter but only half as dense.
It whips around its host star, KELT-9 (also known as HD 195689), in 36 hours at a distance only 1/30th that from Earth to the Sun.
KELT-9b is tidally locked to the star and its day side is perpetually bombarded by stellar radiation.
With a day-side temperature peaking at 7,820 degrees Fahrenheit (4,327 degrees Celsius), the planet is hotter than most stars.
“This planet is a unique laboratory to analyze how atmospheres can evolve under intense stellar radiation,” said Dr. David Ehrenreich, an astronomer at the Observatoire Astronomique de l’Université de Genève, Switzerland.
Dr. Ehrenreich and colleagues observed KELT-9b as it traveled in front of its parent star, an event known as a transit.
“During a transit, a tiny fraction of the light from the star filters through the planet’s atmosphere and analysis of this filtered light can reveal the chemical composition of the atmosphere,” they explained.
“This is achieved with a spectrograph, an instrument that spreads white light into its component colors, called a spectrum.”
“If present among the components of the atmosphere, iron vapor would leave a well-recognizable ‘fingerprint’ in the spectrum of the planet.”
Using the HARPS-North spectrograph on the Telescopio Nazionale Galileo in La Palma, the team discovered a strong signal corresponding to iron vapor in the spectrum of KELT-9b.
“With the theoretical predictions in hand, it was like following a treasure map. And when we dug deeper into the data, we found even more,” said Dr. Jens Hoeijmakers, an astronomer at the Universities of Geneva and Bern.
“We also detected the signature of another metal in vapor form — titanium.”
Although KELT-9b is probably massive enough to withstand total evaporation, this study demonstrates the strong impact of stellar radiation on the composition of the planetary atmosphere.
“These observations confirm that the high temperatures reigning on this planet break apart most molecules, including those containing iron or titanium,” the astronomers said.
“In cooler giant exoplanets, these atomic species are thought to be hidden within gaseous oxides or in the form of dust particles, making them hard to detect. This is not the case on KELT-9b.”
The study was published online this week in the journal Nature.
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H. Jens Hoeijmakers et al. Atomic iron and titanium in the atmosphere of the exoplanet KELT-9b. Nature, published online August 15, 2018; doi: 10.1038/s41586-018-0401-y
