The James Webb Space Telescope took the first direct image of a planet orbiting a distant star.
The telescope observed the faint glow of the gas giant near a young star 350 light-years away from us; This was a demonstration that the telescope can directly observe exoplanets. It is technically difficult, but it offers a much different tool for studying exoplanets than the indirect methods currently used.
“It’s a turning point, not just for the Web, but for astronomy in general,” says physicist and astronomer Sasha Hinckley of the University of Exeter in Britain.
To date, 5,000 planets orbiting other Milky Way stars have been officially discovered outside the solar system. Most of them have only been observed indirectly through the effects they have on their parent star.
When an exoplanet passes between its star and us, the star’s light dims slightly; If we observe such eclipses at regular intervals, it means that an exoplanet is moving there.
In addition, the exoplanet has the slightest gravitational influence on its star, which can be observed in the form of regular changes in the wavelengths of the star’s light. Both of these methods work best for planets close to the star.
Direct observations of exoplanets are rare; So far, only 20 of them have been photographed with high contrast. Exoplanets are very far from our instruments, and are extremely small and faint, especially against the brightness of their star.
An exoplanet may be much fainter than the diffracted light halo of its star; However, it is the best tool we have for characterizing exoplanets in long-distance, multiyear orbits around a star.
Exoplanet scientists have high hopes for James Webb because of its high sensitivity. It seems that their hopes are justified.
The exoplanet imaged by the telescope is named HIP 65426 b, and it orbits an A-type main sequence star called HIP 65426, or HD 116434. The planet orbits the star at a distance of 110 AU, or 110 times the distance between Earth and the Sun.
It was discovered in 2017 by the European Southern Observatory’s (ESO) Very Large Telescope (VLT) instrument called SPHERE. This instrument is equipped with a tool called a coronagraph, which reduces the star’s light to a minimum so that we can see the glow of the exoplanet.
In the near-infrared wavelengths observed by the VLT, the exoplanet is about 10,000 times fainter than the star.
Because James Webb is in space and unobstructed by Earth’s atmosphere, while seeing longer infrared wavelengths than the VLT, his observations of the exoplanet revealed new details.
For example, the researchers found that HIP 65426 b has about 7.1 times the mass of Jupiter. Therefore, it is likely to be a gas giant and therefore unlikely to be conducive to life as we know it.
Exoplanet detection proved challenging Even after observing in mid-infrared wavelengths with the James Webb instrument MIRI, the exoplanet still appeared several thousand times fainter than the star.
Nevertheless, James Webb observed HIP 65426 b with all seven of his observational filters, making it the first time to detect an exoplanet at wavelengths longer than 5 micrometers.
“Getting this picture was like digging for space treasure. At first, I could only see light from the star, but after careful image processing, I was able to remove the light and see the planet,” says Erin Carter, an astronomer at the University of California, Santa Cruz.
According to the team, the telescope exceeded the expected contrast performance by a factor of ten, which is extremely important for high-contrast direct imaging of an exoplanet. Based on such capabilities, the team predicts that James Webb will be able to see planets less than three times the mass of Jupiter, and even more than 100 AU away from the star.
“I think the most exciting thing is that this is just the beginning. In the future, we will see many images of exoplanets that will improve our understanding of their physics, chemistry, and formation. We may even discover previously unknown types of exoplanets,” says Carter.
The study is available on the peer-reviewed server arXiv.