Press release: What the helium tail of the exoplanet reveals

An international team of researchers with participation from the Institute of Astrophysics at the University of Göttingen has discovered that the gas exoplanet (ie a planet outside our solar system) WASP-69b, drags a comet-like tail of helium particles behind it. Driven by the radiation of its central star, the gas escapes from the atmosphere of the exoplanet. The results were published in the journal Science.

 

The planet was observed during a transit as it passed in front of its own star. The planet and its atmosphere obscured part of the light that reached us from this distant star. "In a region of the spectrum where helium gas absorbs light, we have observed a larger and longer-lasting dimming of starlight," says lead author Lisa Nortmann. The researcher at the Instituto de Astrofísica de Canarias is a former PhD student at the Institute of Astrophysics in Göttingen. "The longer duration of this absorption of light allows us to conclude that the planet has a tail”.

 

In addition, the team studied four other planets outside our solar system and their stars, making a total of five exoplanets. The results indicate that helium is present in the atmospheres of those planets that are exposed to the strongest X-rays and extreme ultraviolet radiation. "This is a first big step towards finding out how the planetary atmospheres evolve over time," says co-author Dr Mathias Zechmeister of the Institute of Astrophysics in Göttingen.  "The results of such studies could confirm that high-energy radiation from the central star can strip away the gaseous shell of gas planets. In this way, they could be transformed into rocky planets with a density similar to that of Venus or Earth."

 

The results open up a new field of research. This makes it possible to compare evaporation processes in a large number of planets. Among other things, the question could be answered whether light planets with a very short orbit time are actually the nuclei of former gas giants like Jupiter, whose atmospheres have evaporated near their stars. To observe the atmosphere of WASP-69b, the Carmenes instrument installed at the 3.5 metre telescope of the Calar Alto Observatory in Almería, Spain, was used. With this spectrograph, both visible and infrared light can be studied with high accuracy. Further information on the project can be found at https://carmenes.caha.es/.

 

Original publication: Nortmann et al. Ground-based detection of an extended helium atmosphere in the Saturn‑mass exoplanet WASP-69b. Science (2018). Doi: 10.1126/science.aat5348

 

Contact:

Dr Mathias Zechmeister

University of Göttingen

Institute for Astrophysics

Friedrich-Hund-Platz 1