ESO’s GRAVITY instrument, a second generation imaging instrument installed on the Very Large Telescope Interferometer, has made the first direct observation of an extrasolar planet using a light-combining technique called optical interferometry. This innovative method revealed a complex exoplanetary atmosphere on HR 8799e, a super-Jupiter orbiting the young main-sequence star HR 8799.
This artist’s impression shows HR 8799e. Image credit: L. Calçada / ESO.
HR 8799 is a 30 million-year-old star located approximately 129 light-years away from Earth in the constellation Pegasus.
The star is part of a system that also contains a massive debris disk and four giant exoplanets: HR 8799b, c, d and e.
Unlike most exoplanet discoveries, which are inferred from analysis of data, HR 8799 planets are directly visible from Earth.
HR 8799b, c and d were discovered in November 2008 using the Keck and Gemini telescopes in Hawaii.
Further observations in 2009 and 2010 revealed the fourth planet, HR 8799e, which is about 10 times the mass of Jupiter.
It orbits 14.5 times farther from HR 8799 than the Earth is from the Sun and takes about 45 years to orbit the star.
The planet is thoroughly inhospitable — leftover energy from its formation and a powerful greenhouse effect heat HR 8799e to a hostile temperature of 1,611 degrees Fahrenheit (877 degrees Celsius).
“Today’s result, which reveals new characteristics of HR 8799e, required an instrument with very high resolution and sensitivity,” said Observatoire de Paris astronomer Sylvestre Lacour and colleagues.
“GRAVITY can use ESO’s Very Large Telescope’s four unit telescopes to work together to mimic a single larger telescope using a technique known as interferometry.”
“This creates a super-telescope — the Very Large Telescope Interferometer — that collects and precisely disentangles the light from HR 8799e’s atmosphere and the light from its parent star.”
The team’s measurements were able to reveal the composition of HR8799e’s atmosphere.
“Our analysis showed that HR 8799e has an atmosphere containing far more carbon monoxide than methane — something not expected from equilibrium chemistry,” Dr. Lacour said.
“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.”
The astronomers found that the atmosphere of HR 8799e also contains clouds of iron and silicate dust.
When combined with the excess of carbon monoxide, this suggests that the planet’s atmosphere is engaged in an enormous and violent storm.
“Our observations suggest a ball of gas illuminated from the interior, with rays of warm light swirling through stormy patches of dark clouds,” Dr. Lacour said.
“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.”
The findings appear in the journal Astronomy & Astrophysics.
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S. Lacour et al (GRAVITY Collaboration). 2019.First direct detection of an exoplanet by optical interferometry. Astrometry and K-band spectroscopy of HR 8799e. A&A 623, L11; doi: 10.1051/0004-6361/201935253
