A giant exoplanet that is about the mass of Jupiter and is about 163 light-years away from Earth is excreting a helium trail.

Astronomers from the Instituto de Astrofisica de Canarias (or IAC) spotted WASP-69b's comet-like tail using a 3.5-meter telescope at the Calar Alto Observatory in Almeria, Spain.

Their findings were published in the journal Science.

Observing WASP-69b's Tail From The Ground

WASP-69b gets its tail as comets do — whenever it passes near its small but active star, it is bombarded with radiation, and it leaves behind a trail of helium that is almost as wide as itself. In fact, the exoplanet's tail is wide enough that astronomers were able to spot and study it from the ground.

At the Calar Alto Observatory, astronomers observed WASP-69b during transit when it passed in front of its host star, partially eclipsing its light.

"We observed a stronger and longer lasting dimming of the starlight in a region of the spectrum where helium gas absorbs light," explained Lisa Nortmann, the lead author of the study. "The longer duration of this absorption allows us to infer the presence of a tail."

To detect the atmosphere, the astronomers took advantage of the CARMENES instrument, which is installed on the telescope at the Calar Alto Observatory. The instrument, which consists of two spectrographs, is used to detect and observe main sequence stars in order to detect low-mass exoplanets within the habitable zone.

The CARMENES instrument enabled astronomers to see the composition of the atmosphere of the exoplanets. They concluded in the study that WASP-69b's tail is made up of helium particles that escape from the exoplanet's atmosphere because of the pressure of ultraviolet rays emitted by its host star.

Study Of Atmospheric Escape

The team also investigated four other exoplanets using the same technique and data from the European Space Agency's Multi-Mirror X-Ray Mission (XMM-NEWTON). They found that helium particles are present in the atmospheres of exoplanets that get bombarded with large amounts of X-ray and ultraviolet radiation from their host planets.

The observation confirms that extreme radiation can strip giant planets, such as Jupiter and Neptune, of their gaseous envelope, turning them into rocky worlds similar to Earth and Mars.

Michael Salz, the first author of a companion publication by the same team of astronomers, explained that their work is significant because previous studies on atmospheric escape 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." However, their findings are proof that helium can also be used to study atmospheric escapes of planets.

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