Astronomers Spot Giant Exoplanet Losing Its Atmosphere In A Comet-Like Tail

The gas tail is made up of helium particles that escape the planet's atmosphere and streak out into space.

Artist’s rendition of exoplanet WASP-69b losing its atmosphere in a comet-like tail.
Gabriel Perez Diaz / IAC

The gas tail is made up of helium particles that escape the planet's atmosphere and streak out into space.

Astronomers studying a famous exoplanet that goes by the name of WASP-69b have stumbled upon a peculiar find. It seems that the massive exoplanet, a gas giant first sighted in 2014, is sporting a comet-like tail composed of helium particles that originated in its own atmosphere, reports Phys.org.

This puzzling discovery was made by scientists from the Instituto de Astrofísica de Canarias (IAC) in the Canary Islands, Spain, who scoped out the planet’s atmosphere with the help of the 3.5-meter telescope stationed at the Calar Alto Observatory in Almeria.

The scientists used the telescope’s CARMENES instrument to take a good look at WASP-69b and found out that the exoplanet is losing helium gas, which is agitated by the radiation coming from its parent star and breaking through the planet’s gravitational field.

In a paper published today in the journal Science, the team argued that this strange occurrence is due to a phenomenon called atmospheric escape, in which gas particles from a planet’s atmosphere leak into outer space. A similar thing is happening to Earth’s atmosphere as well, the Inquisitr recently reported, and an orbital mission is gearing up to launch later this month to study the phenomenon in depth.

According to NASA, WASP-69b weighs slightly more than Jupiter and circles its parent star once every 3.9 days. The IAC team observed the exoplanet while it was passing in front of its star. This passage is also known as transit and normally causes the starlight to dim, which typically leads to new exoplanet discoveries via what astronomers call the transit method.

Artist's rendition of exoplanet WASP-69b losing its atmosphere in a comet-like tail.
Artist’s rendition of exoplanet WASP-69b transiting its parent star. Gabriel Perez Diaz / IAC

As expected, WASP-69b blocked the star’s light during transit. While this is nothing out of the ordinary, the revelation came once the team noticed that the starlight was blocked at specific wavelengths of the spectrum associated with helium absorption.

“We observed a stronger and longer-lasting dimming of the starlight in a region of the spectrum where helium gas absorbs light,” said IAC astronomer Lisa Nortmann, who led the research.

“The longer duration of this absorption allows us to infer the presence of a tail.”

Since CARMENES is capable of seeing both visible and near-infrared light simultaneously and at high resolution, the observations enabled the team to determine the composition of the exoplanet’s atmosphere. At the same time, the astronomers were able to infer the speed of the helium particles that were escaping the planet’s gravity and to estimate the length of the gas trail left behind.

The video below, released by IAC earlier today, shows a simulation of WASP-69b in transit around its star, displaying the comet-like tail of helium particles that trail behind it.

The case of WASP-69b was measured up against those of four other exoplanets: two hot Jupiters, HD 189733b and HD 209458b; a hot Neptune called GJ 436b; and the hottest planet ever discovered, the ultrahot Jupiter KELT-9b.

As the Inquisitr previously reported, KELT-9b was found in 2017 and has smoldering surface temperatures of up to 7,800 degrees Fahrenheit. Meanwhile, HD 189733b is the first exoplanet whose transit was sighted in X-rays, notes NASA, whereas HD 209458b is the first alien world whose atmosphere was detected by Earth-bound scientists.

Artist's rendition of the exoplanet HD 209458b passing in front of its parent star.
Artist’s rendition of the exoplanet HD 209458b passing in front of its parent star. NASA/ESA/Alfred Vidal-Madjar/CNRS

After comparing the transits of all five exoplanets, Nortmann’s team uncovered traces of helium in the atmospheres of the planets most battered by X-rays and extreme ultraviolet radiation coming from their parent stars. However, the analysis showed that only WASP-69b and HD 189733b exhibited “a clear signal of absorbing helium” — although, in the case of HD 189733b, “the helium envelope is more compact and does not form a tail,” explains the IAC.

The findings suggest that it could be possible for highly active stars to strip gas giants, such as Jupiter and Neptune, of their gaseous envelope, turning them into rocky worlds with the same kind of density as Venus or Earth. By extrapolation, it might also be feasible for planets with ultra-short orbital periods, that are nestled very close to their parent stars, to actually be the evaporated nuclei of ancient hot Jupiters.

“In the past, studies of atmospheric escape, like the one we have seen in WASP-69b, were based on space-borne observations of hydrogen in the far ultraviolet, a spectral region of very limited access and strongly affected by interstellar absorption,” said study co-author Michael Salz, a researcher at the University of Hamburg. “Our results show that helium is a very promising new tracer to study atmospheric escape in exoplanets.”

A separate study focusing on the discovery regarding HD 189733b is due for publication in the journal Astronomy & Astrophysics.