Astronomers Confirm First Exoplanet “Thermometer Molecule” that is Typically Used to Study Brown Dwarfs

Artist impression of "hot Jupiter" exoplanet, WASP-31 b. (Credit: ESA/Hubble & NASA)

A recent study published in The Astrophysical Journal Letters examines a rare alloy molecule known as chromium hydride (CrH) and its first-time confirmation on an exoplanet, in this case, WASP-31 b. Traditionally, CrH is only found in large quantities between 1,200 to 2,000 degrees Kelvin (926.85 to 1,726.85 degrees Celsius/1700 to 3,140 degrees Fahrenheit) and used to ascertain the temperature of cool stars and brown dwarfs. Therefore, astronomers like Dr. Laura Flagg in the Department of Astronomy and Carl Sagan Institute at Cornell University refer to CrH as a “thermometer for stars”.

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This Brown Dwarf is 2,000 Degrees Hotter Than the Sun

exoplanet hot jupiter transiting its star
This artist’s impression shows an ultra-hot exoplanet as it is about to transit in front of its host star. Credit: ESO

Astronomers have discovered an intense binary star system located about 1,400 light years away. It contains a brown dwarf with 80 times the mass of Jupiter which is bound closely with an incredibly hot white dwarf star. Observations have shown the brown dwarf is tidally locked to the white dwarf, allowing the daytime surface temperatures on the brown dwarf to reach 8,000 Kelvin (7,700 Celsius, 14,000 Fahrenheit) — which is much hotter than the surface of the Sun, which is about 5,700 K (5,427 C, 9,800 F). The brown dwarf’s nightside, on the other hand, is about 6,000 degrees K cooler.

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A Brown Dwarf is Getting Hit With So Much Radiation it's Hotter Than the Sun

Artist view of a hot Jupiter closely orbiting its star. Credit: NASA/JPL-Caltech/T. Pyle (IPAC)

Hot Jupiters are large gas planets that orbit their star closely. Unlike our Jupiter, which radiates more heat than it gets from the Sun, hot Jupiters get more heat from their star than from their interior. As a result, they can have a surface temperature of 1,000 K rather than the 160 K that Jupiter has. They are one of the more common types of exoplanets and the easiest type of exoplanet to discover.

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This Hot Jupiter is Leaving a Swirling Tail of Helium in its Wake

Image from the computer simulation of HAT-P-32 b (bright dot left of star) leaving a trail of helium during its 2.2-day, clockwise orbit (dashed line). (Credit: M. MacLeod (Harvard-Smithsonian Center for Astrophysics) and A. Oklopčić (Anton Pannekoek Institute for Astronomy, University of Amsterdam)

In a recent study published in Science Advances, a team of researchers commissioned the Hobby-Eberly Telescope (HET), which is designed to study exoplanetary atmospheres, to examine how a “hot Jupiter” exoplanet is losing its helium atmosphere as it orbits its parent star, leaving tails of helium that extend approximately 25 times the diameter of the planet itself.

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This Exoplanet Orbits Around its Star’s Poles

Astronomers have found another hot Jupiter in a polar orbit around its star. This illustration shows the exoplanet WASP-79 b following a polar orbit around its star. Image Credit: NASA/GSFC

In 1992, humanity’s effort to understand the Universe took a significant step forward. That’s when astronomers discovered the first exoplanets. They’re named Poltergeist (Noisy Ghost) and Phobetor (Frightener), and they orbit a pulsar about 2300 light-years away.

Even though we thought there must be other planets around other stars, and entire science fiction franchises were built on the idea, we didn’t know for sure and couldn’t just assume it to be true. A quick glance at human history shows how wrong our assumptions about nature can be.

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Giant Exoplanet is Spiraling Inward to its Doom

Kepler 1658b may spiral in to its aging star in the distant future.
Kepler 1658b may spiral in to its aging star in the distant future. Credit: Gabriel Perez Diaz/Instituto de Astrofísica de Canarias

“Death by star” is a fate awaiting most planets in star systems. That includes our Sun, Venus, and Mercury a few billion years from now. And, astronomers now see that same fate awaiting Kepler-1658b. It’s a hot Jupiter exoplanet orbiting an evolved F-type yellow-white dwarf star about 2600 light-years away from Earth.

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Planets Make it Harder to Figure out a Star’s age

Active star, nearby exoplanet, and inactive companion star for NASA's Chandra X-ray Observatory. 2022

Estimating stellar age has always been a challenge for astronomers. Now, a certain class of exoplanets is making the process even more complicated. Hot Jupiters – gas giants with orbital periods smaller than that of Mercury – appear to have an anti-aging effect on their stars, according to a new study. These enormous planets inflict both magnetic and tidal interference on their host star, speeding up the star’s rotation and causing them to emit X-rays more energetically, both of which are hallmarks of stellar youth. The result calls into question some of what we previously believed about stellar age, and offers a glimpse at the ongoing interconnectivity between a star and its planets long after their formation.

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How Do Hot Jupiters Get So Close to Their Stars?

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

In this age of exoplanet discovery, we’ve discovered thousands of exoplanets of different types. The hot Jupiter is one of the most unusual types. There’s nothing like it in our Solar System.

Hot Jupiters are massive gas planets, and they attract a lot of attention because they’re so close to their stars and reach blistering temperatures. Their existence spawns a lot of questions about their formation and evolution. A new study is trying to answer some of those questions by determining hot Jupiters’ ages.

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Hubble has Characterized 25 Hot Jupiters. Here’s What we Know so far

Archival observations of 25 hot Jupiters by the NASA/ESA Hubble Space Telescope have been analysed by an international team of astronomers, enabling them to answer five open questions important to our understanding of exoplanet atmospheres. Amongst other findings, the team found that the presence of metal oxides and hydrides in the hottest exoplanet atmospheres was clearly correlated with the atmospheres' being thermally inverted.

Hot Jupiters are giant exoplanets – even more massive than Jupiter – but they orbit closer to their star than Mercury. When they were first discovered, hot Jupiters were considered oddballs, since we don’t have anything like them in our own Solar System. But they appear to be common in our galaxy. As exoplanets go, they are fairly easy to detect, but because we don’t have up-close experience with them, there are still many unknowns.

A new study used archival data from the Hubble and Spitzer space telescopes to study this class of giant gas exoplanets, and undertook one of the largest surveys ever of exoplanet atmospheres. The researchers said they employed high performance computers to analyses the atmospheres of 25 hot Jupiters using data from about 1,000 hours of telescope observations. Their findings, published in the Astrophysical Journal Supplement Series, help to answer several long-standing questions about hot Jupiters.

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