Hydroxyl (OH) Seen for the First Time in an Exoplanet Atmosphere

Artist's concept of a hot Jupiter exoplanet orbiting a star similar to tau Boötes (Image used with permission of David Aguilar, Harvard-Smithsonian Center for Astrophysics)

The molecule hydroxyl (HO) is common on Earth, but astronomers have not yet determined how abundant it is on other worlds. For the first time, astronomers have conclusively detected it in the atmosphere of an ultra-hot Jupiter, WASP-33b.

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An Exoplanet So Hot There Are 7 Different Kinds of Gaseous Metals in its Atmosphere

This artist's illustration shows an alien world that is losing magnesium and iron gas from its atmosphere. The observations represent the first time that so-called "heavy metals"—elements more massive than hydrogen and helium—have been detected escaping from a hot Jupiter, a large gaseous exoplanet orbiting very close to its star. The planet, known as WASP-121b, orbits a star brighter and hotter than the Sun. Image Credit: NASA, ESA, and J. Olmsted (STScI)

The search for exoplanets has revealed types of planets that are nothing like the worlds in our own Solar System. One such type is the hot-Jupiter. They’re gas giants like Jupiter that orbit their host star very closely. That proximity raises their temperatures to extreme heights.

Hot-Jupiters can be hot enough to vaporize metals, making their atmospheres un-Earthlike. A team of astronomers examining one exoplanet has found 7 different gaseous metals in its atmosphere.

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Do Hot Jupiters Form Close in, or Do They Migrate? A Newly-Discovered Planet Might Help Answer This

Credit: NASA/JPL

The discovery of over 4000 planets (4,171 confirmed and counting!) beyond our Solar System has revolutionized the field of astronomy. Unfortunately, one of the downsides of all these discoveries is how it has shaken up theories about how our Solar System formed. In the past, astronomers thought that the eight planets (or nine, or over one hundred, depending on your point of view) formed where they are currently located.

However, the discovery of gas giants that orbit close to their stars (aka. “Hot Jupiters”) has confounded this thinking. But according to a recent NASA-supported study, the recent discovery of a young gas giant could offer clues as to how Jupiter-like planets form and whether or not they migrate. This discovery was made possible thanks to the Spitzer Space Telescope, which continues to reveal things about our Universe even in retirement.

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Extremely Hot Exoplanets Can Have Extreme Weather, Like Clouds of Aluminum Oxide and Titanium Rain

An illustration of a Hot Jupiter orbiting close to its star. Image Credit: ESA/ATG medialab, CC BY-SA 3.0 IGO

Thanks to the success of the Kepler mission, we know that there are multitudes of exoplanets of a type called “Hot Jupiters.” These are gas giants that orbit so close to their stars that they reach extremely high temperatures. They also have exotic atmospheres, and those atmospheres contain a lot of strangeness, like clouds made of aluminum oxide, and titanium rain.

A team of astronomers has created a cloud atlas for Hot Jupiters, detailing which type of clouds and atmospheres we’ll see when we observe different Hot Jupiters.

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Your Umbrella is Insufficient on a Planet Where it Rains Iron

Work by the Geneva cartoonist Frederik Peeters: «Singing in the Iron Rain: An Evening on WASP-76b». (Detail - © Frederik Peeters)

Imagine a planet where it rained iron. Sounds impossible. But on one distant exoplanet, which is tidally locked to its star, the nightside has to contend with a ferrous downpour.

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Here are the First Pictures from CHEOPS

First image of the star chosen as target for CHEOPS after cover opening. The star, at the centre of the image, is located at a distance of 150 light-years from us, in the constellation of Cancer. Image Credit:ESA/Airbus/CHEOPS Mission Consortium

The CHEOPS spacecraft is taking the first tentative steps in its mission. Back on January 29th, the spacecraft opened the cover on its lens. Now, we have the first images from CHEOPS.

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Two Newly-Discovered Exoplanets are Probably the Result of a Catastrophic Collision

Simulation of a collision between two 10 Earth-mass planets. Image Credit: Zoe Leinhardt and Thomas Denman, University of Bristol
Simulation of a collision between two 10 Earth-mass planets. Image Credit: Zoe Leinhardt and Thomas Denman, University of Bristol

How can two planets so similar in some respects have such different densities? According to a new study, a catastrophic collision may be to blame.

In our Solar System, all the inner planets are small rocky worlds with similar densities, while the outer planets are gas giants with their own similar densities. But not all solar systems are like ours.

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The Power of the Wobble: Finding Exoplanets in the Shifting of Starlight

Artist's concept of the hot Jupiter WASP-121b, which presents the best evidence yet of a stratosphere on an exoplanet - generated using Engine House VFX. Credit: Bristol Science Centre/University of Exeter

They say there’s more than one way to skin an interstellar cat, and in astronomy there’s more than one way to find alien exoplanets orbiting a distant star. With the recent shut-down of NASA’s prolific Kepler mission and its windfall of discoveries, it’s time to look towards the future, and towards alternatives.

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Surprising Discovery. Four Giant Planets Found Around a Very Young Star

Researchers have identified a young star with four Jupiter and Saturn-sized planets in orbit around it, the first time that so many massive planets have been detected in such a young system. Image Credit: Amanda Smith, Institute of Astronomy
Researchers have identified a young star with four Jupiter and Saturn-sized planets in orbit around it, the first time that so many massive planets have been detected in such a young system. Image Credit: Amanda Smith, Institute of Astronomy

What exactly is a “normal” solar system? If we thought we had some idea in the past, we definitely don’t now. And a new study led by astronomers at Cambridge University has reinforced this fact. The new study found four gas giant planets, similar to our own Jupiter and Saturn, orbiting a very young star called CI Tau. And one of the planets has an extreme orbit that takes it more than a thousand times more distant from the star than the innermost planet.

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This Planet is so Metal. Iron and Titanium Vapour Found in the Atmosphere of an “Ultra-Hot Jupiter”

Artist impression of a sunset over KELT-9b, where the planet’s atmosphere is hot enough to vaporize heavy metals such as iron and titanium. Credit and ©: Denis Bajram

In the course of discovering planets beyond our Solar System, astronomers have found some truly interesting customers! In addition to “Super-Jupiters” (exoplanets that are many times Jupiter’s mass) a number of “Hot Jupiters” have also been observed. These are gas giants that orbit closely to their stars, and in some cases, these planets have been found to be so hot that they could melt stone or metal.

This has led to the designation “ultra-hot Jupiter”, the hottest of which was discovered last year. But now, according to a recent study made by an international team of astronomers, this planet is hot enough to turn metal into vapor. It is known as KELT-9b, a gas giant located 650 light-years from Earth that has atmospheric temperatures so hot – over 4,000 °C (7,232 °F) – it can vaporize iron and titanium!

The international team was led by Jens Hoeijmakers, a postdoctoral student at the University of Geneva (UNIGE) and the the University of Bern (UNIBE). The team included members from the National Center of Competence in Research (NCCR) PlanetS group and UNIGE’s Future of Upper Atmospheric Characterization of Exoplanets with Spectroscopy (FOUR ACES1) team.

Artist’s impression of KELT-9b, an ultra-hot Jupiter that orbits a hot, young star about 650 light years from Earth. Credit: NASA/JPL-Caltech

These groups, which are dedicated to characterizing exoplanets, are made up of researchers from UNIGE, UNIBE, the University of Zurich (UZH) and the University of Lausanne (UNIL). Additional support came from researchers from Cambridge University’s Cavendish Astrophysics and MRC Laboratory of Molecular Biology, the Cagliari Observatory, and the Roque de los Muchachos Observatory.

The study which describes their findings – “Atomic iron and titanium in the atmosphere of the exoplanet KELT-9b” – recently appeared in the scientific journal Nature. For the sake of their study, the team sought to place constraints on the chemical composition of an ultra-hot Jupiter since these planets straddle the boundary between gas giants and stars and could help astronomers learn more about exoplanet formation history.

To do this, they selected KELT-9b, which was originally discovered in 2017 by astronomers using the Kilodegree Extremely Little Telescope(s) (KELT) survey. Like all ultra-hot Jupiters, this planet orbits very close to its star – 30 times closer than the Earth’s distance from the Sun – and has a orbital period of 36 hours. As a result, it experiences surface temperatures in excess of 4,000 °C (7,232 °F), making it hotter than many stars.

Based on this, Dr. Hoeijmakers and his colleagues conducted a theoretical study that predicted the presence of iron vapor in the planet’s atmosphere. As Kevin Heng, a professor at the UNIBE and a co-author on the study, explained in a recent UNIGE press release:

“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.”

By examining KELT-9b during a transit, the team was able to observe spectra from its atmosphere. Credit: NASA/JPL-Caltech

To test this prediction, the team relied on data from the High Accuracy Radial velocity Planet Searcher for the Northern hemisphere (HARPS-North or HARPS-N) spectrograph during a single transit of the exoplanet. During a transit, light from the star can been seen filtering through the atmosphere, and examining this light with a spectrometer can reveal things about the atmosphere’s chemical composition.

What they found were strong indications of not only singly-ionized atomic iron but singly-ionized atomic titanium, which has a significantly higher melting point – 1670 °C (3040 °F) compared to 1250 °C (2282 °F). As Hoeijmakers explained, “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.”

In addition to revealing the composition of a new class of ultra-hot Jupiter, this study has also presented astronomers with something of a mystery. For example, scientists believe that many planets have evaporated due to being in a tight orbit with a bright star in the same way that KELT-9b is. And, as their study indicates, the star’s radiation is breaking down heavy transition metals like iron and titanium.

Although KELT-9b is probably too massive to ever totally evaporate, this new study demonstrates the strong impact that stellar radiation has on the composition of a planet’s atmosphere. On cooler gas giants, elements like iron and titanium are believed to take the form of gaseous oxides or dust particles, which are difficult to detect. But in the case of KELT-9b, the fact that these elements are in atomized form makes them highly detectable.

Artist impression of a sunset over KELT-9b, where the planet’s atmosphere is hot enough to vaporize heavy metals such as iron and titanium. Credit and ©: Denis Bajram

As David Ehrenreich, the principal investigator with the UNIGE’s FOUR ACES team and a co-author on the study, concluded,“This planet is a unique laboratory to analyze how atmospheres can evolve under intense stellar radiation.” Looking ahead, the team’s study also predicts that it should be possible to observe gaseous atomic iron in the planet’s atmosphere using current telescopes.

In short, astronomers need not wait for next-generation telescopes in order to study this unique planetary laboratory, which can teach astronomers much about the process of exoplanet formation. And in by learning more about the formation of gas giants in other star systems, astronomers are likely to gain vital clues as to how our own Solar System formed and evolved.

Who knows? Perhaps our own Jupiter was hot at one time, and lost mass before it migrating to its current position. Or perhaps Mercury is the burnt-out husk of a once giant planet that lost its gaseous layers. As the study of exoplanets is teaching us, such strange things are known to happen in this Universe!

Further Reading: University of Geneva, Nature