Iron and titanium in the atmosphere of an exoplanet

August 15, 2018, University of Geneva
Artist's view of a sunset over KELT-9b. The nearby warm blue star covers 35° in the planet's sky, about 70 times the apparent size of the sun in the Earth's sky. Under this scorching sun, the planet's atmosphere is warm enough to shine in reddish-orange tones and vaporize heavy metals such as iron and titanium. Credit: Denis Bajram

Exoplanets, planets in other solar systems, can orbit very close to their host stars. When the host star is much hotter than the sun, the exoplanet becomes as hot as a star. The hottest "ultra-hot" planet was discovered last year by American astronomers. Today, an international team led by researchers from the University of Geneva (UNIGE), who collaborated with theoreticians from the University of Bern (UNIBE), Switzerland, discovered the presence of iron and titanium vapours in the atmosphere of this planet. The detection of these heavy metals was made possible by the surface temperature of the planet, which reaches more than 4000 degrees. This discovery is published in the journal Nature.

KELT-9 is a star located 650 light years from Earth in the constellation Cygnus (the Swan). With a temperature of over 10,000 degrees, it is almost twice as hot as the sun. This star is orbited by a giant gas planet KELT-9b, which is 30 times closer than the Earth's distance from the sun. Because of this proximity, the planet circles its star in 36 hours and is heated to a temperature of over 4,000 degrees. It's not as hot as the sun, but hotter than many . At present, we do not yet know what such a planetary looks like, or how it can evolve under such conditions.

The NCCR PlanetS researchers performed a theoretical study on the atmosphere of the planet KELT-9b. "The results of these simulations show that most of the molecules found there should be in atomic form, because the bonds that hold them together are broken by collisions between particles that occur at these extremely high temperatures," explains Kevin Heng, professor at the UNIBE. This is a direct consequence of the extreme temperature. Their study also predicts that it should be possible to observe gaseous atomic iron in the planet's atmosphere using current telescopes.

Light reveals the chemical components of the atmosphere

The research team had observed this planet precisely as it was moving in front of its (i.e. during a transit). During 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. This is achieved with a spectrograph, which separates white light into its component spectrum. Iron vapour, if present, would leave a recognisable fingerprint in the spectrum of the planet.

Using the HARPS-North spectrograph, built in Geneva and installed on the Telescopio Nazionale Galileo in La Palma, astronomers discovered a strong signal corresponding to iron vapour in the planet's spectrum. "With the theoretical predictions in hand, it was like following a treasure map," says Jens Hoeijmakers, a researcher at the Universities of Geneva and Bern and lead author of the study. "And when we dug deeper into the data, we found even more," he adds. The team also detected the signature of titanium in vapour form.

This discovery reveals the atmospheric properties of a new class of so-called "ultra-hot Jupiter." However, scientists believe that many exoplanets have completely evaporated in environments similar to KELT-9b. Although this planet is probably massive enough to withstand total evaporation, this new study demonstrates the strong impact of stellar radiation on the composition of the atmosphere. Indeed, these observations confirm that the on this planet break apart most molecules, including those containing iron or titanium. 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. "This planet is a unique laboratory to analyze how atmospheres can evolve under intense stellar radiation," concludes David Ehrenreich, principal investigator with the UNIGE's FOUR ACES team.

Explore further: Hunting molecules to find new planets

More information: H. Jens Hoeijmakers et al, Atomic iron and titanium in the atmosphere of the exoplanet KELT-9b, Nature (2018). DOI: 10.1038/s41586-018-0401-y

Related Stories

Hunting molecules to find new planets

June 19, 2018

It's impossible to obtain direct images of exoplanets as they are masked by the high luminous intensity of their stars. However, astronomers led by UNIGE propose detecting molecules present in the exoplanet's atmosphere in ...

The longest period transiting planet candidate from K2

July 17, 2018

To discover and confirm the presence of a planet around stars other than the sun, astronomers wait until it has completed three orbits. However, this very effective technique has its drawbacks since it cannot confirm the ...

Hot Jupiter KELT-16b offers unique opportunity for research

March 21, 2017

(Phys.org)—A large international team of researchers has found that a hot Jupiter called KELT-16b is likely to offer a unique opportunity for research for many years to come. In their paper published in The Astronomical ...

Recommended for you

The epoch of planet formation, times twenty

December 12, 2018

Astronomers have cataloged nearly 4,000 exoplanets in orbit around distant stars. Though the discovery of these newfound worlds has taught us much, there is still a great deal we do not know about the birth of planets and ...

Periodic radio signal detected from the blazar J1043+2408

December 12, 2018

Using Owens Valley Radio Observatory (OVRO), astronomers have detected a periodic signal in the radio light curve of the blazar J1043+2408, which could be helpful in improving our understanding about the nature of blazars ...

Rosetta witnesses birth of baby bow shock around comet

December 12, 2018

A new study reveals that, contrary to first impressions, Rosetta did detect signs of an infant bow shock at the comet it explored for two years – the first ever seen forming anywhere in the solar system.

Juno mission halfway to Jupiter science

December 12, 2018

On Dec. 21, at 8:49:48 a.m. PST (11:49:48 a.m. EST) NASA's Juno spacecraft will be 3,140 miles (5,053 kilometers) above Jupiter's cloud tops and hurtling by at a healthy clip of 128,802 mph (207,287 kilometers per hour). ...

5 comments

Adjust slider to filter visible comments by rank

Display comments: newest first

Surveillance_Egg_Unit
5 / 5 (2) Aug 16, 2018
"Because of this proximity, the planet circles its star in 36 hours and is heated to a temperature of over 4,000 degrees. It's not as hot as the sun, but hotter than many stars. At present, we do not yet know what such a planetary atmosphere looks like, or how it can evolve under such conditions."

It is doubtful that the planet KELT-9b originated in such an orbit around its Star at such close proximity. The dust and gas from which it formed also would have had to be at a larger distance from its Star, otherwise Mass would not have been able to clump together as infalling Matter through Gravity to compress said Matter into the structure of a planet. At a distance far enough away from its Star, the planet's Mass would been cool enough to attract more gas and dust from its surrounding disk. Therefore, KELT-9b had to have evolved elsewhere and then somehow wandered into its present orbit where it has become too hot and molten to evolve further.
Andy Lloyd
not rated yet Aug 16, 2018
Or, could hot Jupiters like this have spooled out of the parent star directly, perhaps as the result of interactions with a binary companion in the primordial dense core? This planet, at 3 Jupiter masses, is shedding massive amounts of hydrogen due to this heat and proximity to the stellar wind (Yan & Henning 2018). Its composition is evolving rapidly.
Gigel
not rated yet Aug 16, 2018
I think the planet and its star are pretty young. Some tens of millions of years or so.
rossim22
5 / 5 (1) Aug 16, 2018
It is doubtful that the planet KELT-9b originated in such an orbit around its Star at such close proximity. The dust and gas from which it formed also would have had to be at a larger distance from its Star, otherwise Mass would not have been able to clump together as infalling Matter through Gravity to compress said Matter into the structure of a planet. At a distance far enough away from its Star, the planet's Mass would been cool enough to attract more gas and dust from its surrounding disk. Therefore, KELT-9b had to have evolved elsewhere and then somehow wandered into its present orbit where it has become too hot and molten to evolve further.


Or maybe in the past this was a binary star system and KELT-9b is no longer a star.
rrwillsj
not rated yet Aug 16, 2018
Or, perhaps, just another example of my Theory of Stupid Design, driven by drunkenly chaotic deities.

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.