First exoplanet discovered by the James Webb Space Telescope

NASA’s James Webb Space Telescope keeps breaking records. Now it has broken another with the discovery of its first new exoplanet – the smallest ever directly imaged.

The research, published in Nature, focuses on a special type of star system which scientists identified as promising for imaging exoplanets. These are young star systems that are “pole on”, meaning the stellar disc which includes planets is face on, rather than viewed from the side.

A key advantage of targeting young systems is that recently formed planets in these discs are still hot, making them brighter than those in older systems.

TWA 7 is a young star less than half the size of our Sun and 111 light-years from Earth, sitting in the constellation Antila. At just 6.5 million years old, the star is in the very early stages of its life. Astronomers noticed a debris disc around the star when it was discovered in 1999. Since then, they have wondered if the star could be host to forming planets.

It ticks all the boxes to be targeted in the search for a new exoplanet.

The star’s debris disc has 3 rings – one of which is quite narrow. The James Webb Space Telescope (JWST) images – taken using a coronagraph attachment on the telescope’s MIRI instrument – revealed a source within the rings which looked a little bit like a planet.

The astronomers eliminated other possibilities including observation bias and concluded that the source must be a planet. Computer simulations confirmed that the ring and gap where the planet is believed to sit corresponds to the JWST images.

Disc around star glowing red
Image of the disk around the star TWA 7 recorded using ESO’s Very Large Telescope’s SPHERE instrument. We can clearly see the empty area around TWA 7 B in the R2 ring (CC #1). Credit: © JWST/ESO/Lagrange.

The planet, dubbed TWA 7 b, is about the same mass as Saturn – roughly 30% the mass of Jupiter, or nearly 100 times the mass of Earth. This makes it the lightest exoplanet ever directly imaged.

Most exoplanets are discovered through the transit method. This works best when a planet’s orbital plane is flat to the observer, rather than pole on. When the exoplanet passes directly between its host star and a telescope, this is registered as a dip in the star’s brightness.

Exoplanets must be fairly large to be directly imaged because, unlike stars, they are generally not very bright. TWA 7 b is the smallest exoplanet to be directly observed, highlighting the power of the JWST’s infrared imaging instruments.

TWA 7 b, the authors say, is probably cold and orbits its star at a distance about 52 times greater than Earth’s orbit around the Sun.

Targets for future coronagraph observations are already being drawn up to find and image more exoplanets around other young stars.

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