Webb finds traces of water on a planet 400 light years away

June 1 () –

A team of astronomers identified water vapor in the atmosphere of the exoplanet WASP-18 and mapped the planet’s temperature as it slipped behind and reappeared from its star.

This event is known as a secondary eclipse.. Scientists can read the combined light from the star and planet, and then refine measurements of just the star as the planet moves behind it.

The new investigation of the atmosphere of this ultrahot gas giant 10 times more massive than Jupiter was made possible by the NIRISS instrument on the James Webb Space Telescope.

At 400 light-years, WASP-18 b is so enticing that astronomers have been studying it since its discovery in 2009. An orbit for WASP-18 b around its star, which is slightly larger than our Sun, takes just 23 hours. There is nothing like it in our Solar System.

The same side, known as the day side, of WASP-18 b always faces its star, just as the same side of the Moon always faces Earth. This is called tidal lock. The exoplanet’s temperature map, or brightness, shows a large temperature change, of up to 1,000 degrees, from the hottest point in front of the star to the terminator, where the day and night sides of the tidally locked planet meet at a permanent twilight.

“JWST gives us the sensitivity to make much more detailed maps of hot giant planets like WASP-18 b than ever before.. This is the first time a planet has been mapped with JWST, and it’s really exciting to see that some of what our models predicted, such as a sharp drop in temperature away from the point of the planet directly facing the star, is actually seen. in the data said it’s a statement Megan Mansfield, a fellow at the University of Arizona, and one of the authors of the paper describing the results.

The team mapped temperature gradients on the day side of the planet. Given how much colder the planet is at the terminator, it’s likely something is preventing the winds from efficiently redistributing heat to the night side. But what is affecting the winds remains a mystery.

‘WASP-18 b’s brightness map shows a lack of east-west winds that corresponds better to models with atmospheric resistance. One possible explanation is that this planet has a strong magnetic field, which would be an exciting discovery!” said co-author Ryan Challener, of the University of Michigan.

One interpretation of the eclipse map is that magnetic effects force winds from the planet’s equator up over the north pole and down over the south pole, rather than east-west as might be expected.

The researchers recorded temperature changes at different elevations in the layers of the gas giant planet’s atmosphere.. They saw temperatures increase with elevation, varying by hundreds of degrees.

The spectrum of the planet’s atmosphere clearly shows multiple small but precisely measured forms of water, present despite extreme temperatures of nearly 2,700 degrees Celsius. It’s so hot that it would tear most water molecules apart, so continuing to see its presence speaks to Webb’s extraordinary sensitivity in detecting any remaining water. The amounts recorded in the atmosphere of WASP-18 b indicate that water vapor is present at various elevations.