A powerful technique has been used for the first time to assess a planet outside the Solar System.

Direct measurements of exoplanets are difficult, because the relatively dim light from planets blends into the glare of their host star. To solve this problem, astronomers seek approaches to separate a planet’s feeble light from its star’s brilliance.

A team led by Sylvestre Lacour and Mathias Nowak at the Paris Observatory harnessed the GRAVITY instrument at the Very Large Telescope (VLT) in Antofagasta, Chile, to directly observe exoplanets. Each of the VLT’s four 8.2-metre telescopes feeds its light to GRAVITY, which precisely aligns the input. This allows the light to be combined using a technique called optical interferometry.

The protocol created the equivalent of a single telescope that has as much light-collecting power as all four VLT telescopes put together — and a resolution an order of magnitude greater than any one of the four.

An exoplanet (artist’s illustration) orbiting the star HR 8799 is several times more massive than Jupiter, according to new data from the Very Large Telescope.Credit: ESO/L. Calçada

The team measured the spectrum of a hot, young, ‘super-Jupiter’ orbiting the star HR 8799, which is roughly 40 parsecs from Earth. The results suggest that churning winds are disrupting the chemistry of the planet’s atmosphere.