Astronomers believe that planets revolve around every star, of which our sun is only one. About five thousand of such ‘exoplanets’ are now known, a tiny fraction of the total number. But direct observations of exoplanets are rare: In the bright light of the parent star, an exoplanet is as dull as a fly on a lighthouse. Add to that the gigantic distance – no less than four hundred light-years in this case – and it is understandable why there are only twenty portrait photos of the five thousand known exoplanets.
Yet the planet in question, aptly named ‘HIP 65426 b’, had already been photographed in 2017. This ‘second’ observation nevertheless stirs up a lot in the astronomical world. If not by the model, then by the photographer: the James Webb Space Telescope. With the latest instruments and the largest lens ever for a space telescope, James Webb can make completely new observations, even on known planets.
Previously invisible light
This is partly because the telescope is not affected by the scattering particles in the Earth’s atmosphere, which telescopes on the ground still have to peer through. In addition, James Webb is at a strategic distance from Earth, so that the space telescope is less affected by the disturbing radiation from the earth.
This allows James Webb to perceive light that was previously invisible, even to Webb’s predecessor Hubble. Much information about exoplanets, for example about clouds in the atmosphere, is hidden precisely in those unattainable ‘colours’ of light. That’s why planetary scientists eagerly awaited Webb’s first shots of exoplanets.
‘It’s as if you want to look into a room, but you can only look through the keyhole in the door,’ says Ignas Snellen, professor of exoplanets at Leiden University and not involved in the research. “With James Webb, we can finally throw open the door and really look inside.”
History
For example, astronomers can now collect information about the chemical composition of exoplanets. This was also apparent when James Webb recently found carbon dioxide in the atmosphere of an exoplanet, a first. Researchers are interested in these kinds of chemical discoveries because they can provide valuable information about the evolution of exoplanets.
The photographed planet is relatively young – ‘only’ 14 million years old. By comparison, the Earth was formed about 4.5 billion years ago. Therefore, traces of the formation can still be seen in the system, such as a dust ring around the parent star. It had not yet appeared in the sighting five years ago during the first observation.
All of this may sound more interesting than the blocky photo would suggest at first glance. It will be many decades before photos of exoplanets will resemble Google Maps. But that should not spoil the fun for Snellen and his colleagues all over the world: ‘The images are beautiful, they show in one fell swoop that we can have high expectations of James Webb over the next twenty years.’