What is the cosmic equivalent of a scorching heavy metal riff? How about a blisteringly hot exoplanet spraying heavy metals like iron and magnesium into space?

This artist’s illustration shows WASP-121b, a distant world that is losing magnesium and iron gas from its atmosphere. The observations represent the first time that heavy metals have been detected escaping from a “hot Jupiter,” which is a large, gaseous exoplanet that orbits very close to its host star. WASP-121b’s orbit is so close that the star’s gravity is nearly ripping the planet apart, giving the planet an oblique football shape. ( NASA, ESA, and J. Olmsted (STScI))

This heavy metal spitting exoplanet is exactly what the Hubble Space Telescope has discovered in the form of gas exoplanet WASP-121b. The atmosphere of the planet is so hot that metal is vapourising and escaping its gravitational pull.

WASP-121b has been labelled a ‘hot Jupiter’ — which is a large, gaseous exoplanet that orbits very close to its host star.

In addition to this, the scorching hot planet — in the system WASP-121 900 light-years from Earth — has been deformed into a football-shape by the intense tidal forces caused by the gravitational influence of its parent star.

The new observations were made by an international team of astronomers using NASA’s Hubble Space Telescope. The findings — detailed in a paper published in the Astronomical Journal — describe the first known instance of heavy metal gas streaming away from a hot Jupiter.

University of Maryland Astronomy Professor Drake Deming, co-author of the paper, says: “This planet is a prototype for ultra-hot Jupiters. These planets are so heavily irradiated by their host stars, they’re almost like stars themselves.

“The planet is being evaporated by its host star to the point that we can see metal atoms escaping the upper atmosphere where they can interact with the planet’s magnetic field. This presents an opportunity to observe and understand some very interesting physics.”

Breaking the Law — this ‘Hot Jupiter’ is different from the others

Hot Jupiters are usually cool enough internally to ensure that heavier elements such as iron and magnesium that remain in their atmosphere condense into clouds.

WASP-121b defies this trend because its upper atmosphere is an incredible 4,600 degrees Fahrenheit as a result of its close orbit to its star. In fact, this orbit is so tight that the planet is being shredded by the star’s gravity — resulting in the aforementioned oblique shape.

Stellar map showing the position of WASP 121

Lead researcher, David Sing of Johns Hopkins University, explains: “Heavy metals have been seen in other hot Jupiters before, but only in the lower atmosphere.

“With WASP-121b, we see magnesium and iron gas so far away from the planet that they’re not gravitationally bound. The heavy metals are escaping partly because the planet is so big and puffy that its gravity is relatively weak. This is a planet being actively stripped of its atmosphere.”

The researchers used Hubble’s Space Telescope Imaging Spectrograph to search for ultraviolet light signatures of magnesium and iron. These signatures can be observed in starlight filtering through WASP-121b’s atmosphere, as the planet passes in front of its host star.

Sing says: “We picked this planet because it is so extreme.”

“ We thought we had a chance of seeing heavier elements escaping. It’s so hot and so favourable to observe, it’s the best shot at finding the presence of heavy metals.”

Seek and Destroy— stars strip planets of their atmospheres

Artist’s impression of a star stripping the atmosphere of one of its planets

Such observations of WASP-121b just add to the developing story of how planets lose their primordial atmospheres.

When planets form, they gather an atmosphere made of gas from the disk that gave rise to both the planet and its host star.

These young atmospheres consist mostly of hydrogen and helium, the most plentiful elements in the universe. As the planet moves closer to its star, much of this early atmosphere burns off and escapes to space.

Sing explains: “The hot Jupiters are mostly made of hydrogen, and Hubble is very sensitive to hydrogen, so we know these planets can lose the gas relatively easily.

“But in the case of WASP-121b, the hydrogen and helium gas is outflowing, almost like a river, and is dragging these metals with them. It’s a very efficient mechanism for mass loss.”

Back in Black — astronomers aren’t finished with WASP-121b yet

According to the researchers, WASP-121b will be a perfect target for NASA’s James Webb Space Telescope, scheduled for launch in 2021.

The primary mirror of the James Webb Space Telescope (NASA)

The Webb telescope will enable researchers to search for water and carbon dioxide, which can be detected at longer, redder wavelengths of infrared light. The combination of Hubble and Webb observations should give astronomers a more complete inventory of the chemical elements that make up the planet’s atmosphere.

Deming says: “Hot Jupiters this close to their host star are very rare. Ones that are this hot are even rarer still.

“Although they’re rare, they really stand out once you’ve found them. We look forward to learning even more about this strange planet.”