GRAVITY instrument breaks new ground in exoplanet imaging

Cutting-edge VLTI instrument reveals details of a storm-wracked exoplanet using optical interferometry.

This artist’s impression shows the observed exoplanet, which goes by the name HR8799e. Credit: ESO/L. Calçada
This artist’s impression shows the observed exoplanet, which goes by the name HR8799e. Credit: ESO/L. Calçada

GRAVITY, a second generation instrument on the ESO’s Very Large Telescope Interferometer (VLTI) used optical interferometry and observed an exoplanet named HR8799e with clouds of iron and silicates swirling in a planet-wide storm.

The exoplanet ‘HR8799e’ is also dubbed as ‘super-Jupiter’, a world unlike any found in our Solar System, that is both more massive and much younger than any planet orbiting the Sun. It was originally discovered in 2010 orbiting the young main-sequence star HR8799, which lies around 129 light-years from Earth in the constellation of Pegasus.

At just 30 million years of age, this infant exoplanet is young enough to give researchers a window onto the development of planets and planetary systems. The exoplanet is completely inhospitable— extra energy from its development and a powerful greenhouse effect heat HR8799e to a hostile temperature of roughly 1000 °C.

This wide-field image shows the surroundings of the young star HR8799 in the constellation of Pegasus. This picture was created from material forming part of the Digitized Sky Survey 2. The location of HR 8799 is shown.  Credit: ESO/Digitized Sky Survey 2
This wide-field image shows the surroundings of the young star HR8799 in the constellation of Pegasus. This picture was created from material forming part of the Digitized Sky Survey 2. The location of HR 8799 is shown.
Credit:
ESO/Digitized Sky Survey 2

Team leader Sylvestre Lacour researcher CNRS at the Observatoire de Paris – PSL and the Max Planck Institute for Extraterrestrial Physics said, “Our analysis showed that HR8799e has an atmosphere containing far more carbon monoxide than methane — something not expected from equilibrium chemistry. We can best explain this surprising result with high vertical winds within the atmosphere preventing the carbon monoxide from reacting with hydrogen to form methane.”

For this observation, an instrument with very high resolution and sensitivity were required. GRAVITY a use ESO’s VLT’s four unit telescopes to work simultaneously to act as a super telescope using a method called interferometry. The telescope thus was able to collect and precisely disentangles the light from HR8799e’s atmosphere and the light from its parent star.

This is the first time that optical interferometry has been used to reveal details of an exoplanet, and the new technique furnished an exquisitely detailed spectrum of unprecedented quality — ten times more detailed than earlier observations. The team’s measurements were able to reveal the composition of HR8799e’s atmosphere — which contained some surprises.

Astronomers also detected that the HR8799e has clouds of iron and silicate dust. When combined with the excess of carbon monoxide, this suggests that HR8799e’s atmosphere is engaged in an enormous and violent storm.

Lacour said, “Our observations suggest a ball of gas illuminated from the interior, with rays of warm light swirling through stormy patches of dark clouds. Convection moves around the clouds of silicate and iron particles, which disaggregate and rain down into the interior. This paints a picture of a dynamic atmosphere of a giant exoplanet at birth, undergoing complex physical and chemical processes.”

This result was announced today in a letter in the journal Astronomy and Astrophysics by the GRAVITY Collaboration.