Exoplanet Observed for First Time With Optical Interferometry

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The ESO (European Southern Observatory) has announced the successful observation of an exoplanet using optical interferometry. It’s the first time an exoplanet has been “seen” in this manner and the technique offers a promising example of how we might discern new information about the atmospheres of exoplanets. Such investigations and characterizations are considered critical to discovering other planets in the galaxy that might support life.

Astronomical interferometry is the process of combining information from multiple separate telescopes to observe a given target in greater detail than any single telescope could offer. Combining multiple smaller mirrors doesn’t offer all the advantages of a single large telescope — the total amount of light collected is smaller than a single large mirror would be — but it allows for very high angular resolutions and avoids the enormous expense associated with casting huge mirrors.

The ESO scientists observed exoplanet HR8799e using the Very Large Telescope (VLT) array in Chile, which combines data from four telescopes using its interferometer. Each individual telescope has an 8.2m meter. While it’s unrelated to the discovery we’ll be discussing, HR8799e is one of the few exoplanets whose movement we’ve confirmed via direct imaging. You can see it in the GIF below (according to Wikipedia, HR8799e is the dot that starts on the right-hand side):


Image by Wikipedia.

Directly observing the exoplanet led to some surprising discoveries. We already knew that HR8799e is a very young planet, at just 30 million years old. The planet is literally still glowing with leftover heat from its formation and an ambient temperature of ~1,000C. The new VLT observations improved our understanding of HR8799e’s spectrum by a full order of magnitude, showing that its atmosphere contains different compounds than we expected.

Our analysis showed that HR8799e has an atmosphere containing far more carbon monoxide than methane — something not expected from equilibrium chemistry,” explains team leader Sylvestre Lacour researcher CNRS at the Observatoire de Paris – PSL and the Max Planck Institute for Extraterrestrial Physics. “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 atmosphere was also found to contain clouds of iron and silicate dust, implying the entire gas giant is engulfed in a colossal storm. Lacour suggests the planet is lit from within, with rays of light penetrating stormy, dark clouds. The silicates and iron then “rain” into the interior. This last process isn’t unique to HR8799e; astronomers believe that diamonds fall like rain within Jupiter and Saturn as well.

Astronomers hope to perform more direct observations of exoplanet atmospheres in the future, as next-generation observatories come online and our observation techniques continue to improve. We may have found nearly 3,000 exoplanets, but our understanding of their atmospheres is still very limited. At this point, every planet we image will likely tell us something we didn’t know before about the likely atmospheric composition of different worlds and where to focus our search for life.

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