Exoplanets

It is extremely hard to get a direct image of an exoplanet because our instruments are completely blinded by the bright light from the star. For that reason exoplanets are mostly measured by indirect methods like the transit method or radial velocity or gravitational lensing. Direct imaging is the holy grail of exoplanet studies. When astronomers can study exoplanets in detail we can find out information about the planet's atmosphere and composition and even search for biosignature.

One way to solve it is to use an old technique coronagraph invented by the French astronomer Bernard Lyot in 1930 to study the sun's atmosphere. The coronagraph is a telescopic attachment that is designed to block the light from the star.

Some exoplanets have already been directly imaged by blocking the blinding light from the star. An image was taken of the multi-exoplanet system HR 8799 in September 2008. Three planets with masses of ten to seven times Jupiter were observed. The system is young 30 million years and the planets were still glowing from the formation. A fourth planet was discovered around the same system in 2010.

The very first direct image of an exoplanet was already taken in 2004 when a group of astronomers used the VLT telescope to take a picture of a planet (also this planet was several times the size of Jupiter) orbiting a brown dwarf called 2MASS J12073346-3932539 (don't forget the name).

Direct imaging has also been used on Proxima Centauri, our nearest star at 4.25 light-years away. In 2016 an Earth-like planet was discovered in the habitable zone of the system. Measurement by radial velocity in 2019 suggested that the system also has a larger planet Proxima c outside the habitable zone. The image was taken earlier this year by Raffaele Gratton and his colleagues using a VLT telescope and an instrument called SPHERE. The image has some noise and it could be a planet, but the point is brighter than expected. As the planet would not be that large if it exists. One explanation could be that the planet is surrounded by rings like Saturn but with a smaller planet and bigger rings.

One of the most recent news (May 20 2020) is that an image of an exoplanet being born around the star AB Aurigae 520 light-years from Earth has been taken by VLT using SPHERE.

Credit: ESO/Boccaletti et al.

The planet is formatting at the same distance as Neptune from the Sun.