Imaging exoplanets

The James Webb Space Telescope

The most exciting area of planet hunting currently being developed is undoubtedly that of direct imaging. To directly image exoplanets, something known as a coronagraph is used, an instrument present on several telescopes including NASA’s Hubble Space Telescope. This blocks the light of the host star, allowing the scope to see around the star and possibly detect a planet. On the right of this page you can see an incredible composite image of a dust disc around the Fomalhaut star taken by Hubble, and within this disc a planet called Fomalhaut b was discovered on a 2,000-year orbit around the star.

“We knew there was a ring [around Fomalhaut] but we didn’t really have very high hopes of being able to see it, so we were kind of surprised when we actually found this very nice ring,” said Dr Mark Clampin, one of the discoverers of Fomalhaut b and a project scientist working on the JWST. “When we were going through our data we found there was a point source there [indicating a planet] that we were not expecting to find. So we started to study this planet around Fomalhaut and not the ring.”

One of the difficulties, however, is that planets tend to be very dark. Their host star must be sufficiently bright to enable the planet to be seen as it reflects more light, or the planet needs to have characteristics that make it more visible. “The reason we could image [Fomalhaut b] is because it’s a lot brighter than it should be,” continued Dr Clampin. “It looks like the planet has a big ring of dust around it like Saturn, and that dust is boosting the light of the planet so it appears brighter.”

The launch of JWST, though, will provide the biggest boost for planet imaging. “JWST consumes my every waking hour at the moment,” said Dr Clampin. “I’m really looking forward to JWST because I think, while it won’t be able to directly image rocky planets, it will do a really fantastic job of studying planets around younger stars. And using different techniques like transit spectroscopy [studying a planet as it passes in front of its host star] we will be able to make observations of planetary atmospheres around super-Earths.”

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