Sidereal Messenger: Webb discovers his first exoplanet, but doesn’t get used to it

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Last week saw another of the traditional meetings of the American Astronomical Society. Among the many results presented, we had the first exoplanet officially discovered by the James Webb Space Telescope. But it’s good not to get used to it.

The work, led by Kevin Stevenson and Jacob Lustig-Yaeger, from Johns Hopkins University, in Laurel, Maryland (USA), was only possible because there was a concrete clue to its existence, taken by the Tess satellite – indeed a specialist in discovering extrasolar worlds. .

In theory, Webb is perfectly capable of discovering planets using the transit method, in which the telescope detects the momentary reduction in brightness of a star when a planet orbiting it passes in front of it, like a minieclipse. More than capable, the Webb would be better than any other telescope for this.

However, the effective application of the technique requires constant observation over a long period of time, since it is not known in advance when a hitherto unknown planet will transit in front of the star. And that doesn’t match Webb’s management. Telescopes like this have every second of observation disputed by astronomers, with research proposals in the style of “each hoe, a worm”: every glimpse of the satellite has to bring relevant scientific results. It was this strategy that made Hubble the most productive telescope in the history of astronomy, and it will certainly do the same for Webb now.

So how, in those terms, did the discovery of the exoplanet LHS 475 b happen? Tess had already made the possible detection, albeit uncertain, of the star, and the satellite data allowed inferring the exact moment of subsequent transits. All that was left was to take a peek at the time to confirm the prediction. Done and done: Webb was pointed and saw the luminosity curve of the star LHS 475 decrease and then increase, as the planet passed in front of it, denouncing its own existence.

What impresses is the quality of the data. The light curve shows with unrivaled clarity a mere 0.1% decrease in brightness from the star, a red dwarf 41 light-years from here in the constellation of the Octant. This translates to a rocky planet 99% the diameter of Earth. But the similarities end there: completing a revolution around its modest sun every two days, it must be too hot to support life.

However, it may have an atmosphere, and one of Webb’s greatest strengths is its ability to detect the potential composition of these worlds. The team tried hard, but it was impossible to match any model to the spectrum (signature of light) collected by the telescope. You can already tell that LHS 475 b does not have a dense methane-based atmosphere like that of Saturn’s moon Titan. But one cannot rule out other compositions, in particular one dominated by carbon dioxide. By the way, the data are also not incompatible with a total absence of atmosphere. Perhaps, with a closer look, on a later occasion, Webb can reveal more. But let astronomers fight to get more time with him.

This column is published on Mondays in Folha Corrida.

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