Atmosphere of vaporized rock discovered on an extraordinarily hot exoplanet.

If you are looking to escape the summer heatwave, WASP-76b would be a poor choice of destination.

Heatwaves on Earth may be uncomfortable and hazardous, but they pale in comparison to the scorching conditions experienced on WASP-76 b, an exoplanet with astonishing temperatures capable of vaporizing iron. Recent research conducted by astronomers delved deeper into this distant world, unveiling the presence of 11 chemical elements in its atmosphere and shedding light on their abundance.

What makes this discovery even more remarkable is the identification of rock-forming elements on WASP-76 b that have yet to be measured in our own solar system’s gas giants, Saturn and Jupiter. According to the team leader, Stefan Pelletier from the Université de Montréal Trottier Institute for Research on Exoplanets, it is rare for a planet hundreds of light years away to provide insights that would otherwise be impossible to obtain about our solar system.

Situated approximately 634 light-years away in the Pisces constellation, WASP-76 b earns its mind-boggling temperatures due to its close proximity to its parent star. As an “ultra-hot Jupiter,” this massive planet orbits a twelfth of the distance between itself and its star, WASP-76, compared to the distance between Mercury and the sun.

These unique circumstances grant WASP-76 b several extraordinary attributes. Despite having approximately 85% of Jupiter’s mass, the exoplanet is nearly twice as wide and six times as voluminous as the solar system’s gas giant. This is a consequence of the planet being “puffed out” by intense radiation from its star.

WASP-76 b has been subject to extensive study since its discovery in 2013 through the Wide Angle Search for Planets (WASP) program. Previous investigations have revealed various elements present in its atmosphere. Notably, in 2020, researchers made a fascinating finding: iron on the tidally locked planet’s scorching side evaporates and migrates to the relatively cooler “night side,” where it condenses and falls as iron rain.

Motivated by these prior studies, Pelletier and the team undertook new observations of WASP-76 b using the MAROON-X high-resolution optical spectrograph on the Gemini North 8-meter Telescope in Hawaii, which is part of the International Gemini Observatory. This advanced technology allowed them to scrutinize the composition of this ultra-hot Jupiter in unprecedented detail.

The extreme temperatures on WASP-76 b prevent elements such as magnesium and iron, which would typically form rocks on Earth-like terrestrial planets, from solidifying. Instead, they exist as gases in the planet’s upper atmosphere, defying conventional expectations.

Studying WASP-76 b offers astronomers an unprecedented opportunity to gain insights into the presence and abundance of rock-forming elements within the atmospheres of giant planets. This knowledge is unattainable for colder giant planets like Jupiter since these elements reside at lower atmospheric levels, rendering them undetectable.

During their investigation of WASP-76 b, Pelletier and his colleagues made a noteworthy discovery. They found that the abundance of elements such as manganese, chromium, magnesium, vanadium, barium, and calcium closely aligns not only with the abundances in the planet’s star but also with those observed in the sun.

The observed elemental abundances are not arbitrary; they result from the hydrogen and helium processing carried out by successive generations of stars over billions of years. As stars create heavier elements until they deplete their nuclear fusion fuel, they eventually die in supernova explosions, releasing these elements into the cosmos. These elements then serve as the building blocks for subsequent stars, while the remaining material forms proto-planetary disks surrounding these young stars, eventually giving rise to planets. Consequently, stars of similar ages possess similar compositions, featuring consistent abundances of elements heavier than hydrogen and helium, commonly referred to as “metals.”

However, terrestrial planets like Earth form through more intricate processes, leading to different abundances of heavy elements compared to their host stars. The fact that the study reveals WASP-76 b has a composition resembling that of its star suggests that its composition also resembles the protoplanetary disk from which it originated. This similarity could potentially extend to other giant planets as well.

Nevertheless, not all of the composition characteristics of WASP-76 b align with expectations. The team discovered a depletion of certain elements within the planet’s atmosphere. Interestingly, these depleted elements are precisely the ones requiring higher temperatures to vaporize, such as titanium and aluminum. Conversely, the elements that matched predictions, like manganese, vanadium, and calcium, vaporize at slightly lower temperatures.

The team interpreted this depletion as an indication of the upper atmosphere of gas giant planets being temperature-sensitive. Depending on the temperature at which an element condenses, it either remains present as a gas in the upper atmosphere or becomes absent as it condenses into a liquid and sinks to lower layers. When located in lower atmospheric regions, the element cannot absorb light, resulting in the characteristic “fingerprint” missing from observations.

If confirmed, this finding implies that two slightly different-temperature giant exoplanets could possess vastly different atmospheres. It can be likened to two pots of water, one frozen at -1°C and the other in a liquid state at +1°C. For instance, while calcium is observed on WASP-76 b, it may not be present on a slightly colder planet.

Another significant discovery made by the team is the presence of vanadium oxide, a chemical compound, within the atmosphere of WASP-76 b. This marks the first time this compound has been identified in the atmosphere of a planet outside our solar system. Astronomers find this discovery intriguing because vanadium oxide can have a significant impact on hot giant planets.

Vanadium oxide plays a similar role to ozone in Earth’s atmosphere, efficiently heating up the upper atmosphere. As a result, temperatures increase with altitude, in contrast to the typical temperature decrease observed on colder planets.

Furthermore, the team detected a higher abundance of nickel around WASP-76 b than initially expected. This finding suggests the possibility that, at some point in its history, the gas giant planet captured a smaller terrestrial world resembling Mercury, which contained a substantial amount of nickel.

The astronomers involved in these breakthroughs plan to continue studying WASP-76 b and similar exoplanets, aiming to unravel how temperatures influence the composition of their atmospheres.

The research is described in a paper published on Wednesday (June 14) in the journal Nature. 

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