Webb telescope detects mysterious water vapor in nearby star system

The James Webb Space Telescope has detected water vapor around a rocky exoplanet orbiting a star 26 light-years from Earth.

Now astronomers are trying to determine whether this water vapor is a sign of what would be the first known presence of an atmosphere near an ancient rocky planet.

Small, cool red dwarf stars are the most common in the universe. Planets that are in the “habitable zone,” the perfect distance from a star for the planet to be hot enough to support liquid water on its surface, tend to orbit very close to red dwarfs because they aren’t as hot as the sun.

Red dwarf stars emit ultraviolet and X-ray radiation capable of destroying fragile layers of gas, leading scientists to wonder whether the rocky planets that orbit them can maintain or recover their atmospheres.

Astronomers have observed a hot, rocky exoplanet called GJ 486 b using the James Webb Telescope. The planet is 30% larger than Earth and has a much stronger surface gravity than our planet.

The planet GJ 486 b is so close to its star that it is able to complete an orbit around it every 1.5 Earth days, and this proximity heats the planet to a surface temperature of up to 430 degrees Celsius.

Astronomers believe the planet is tidally locked, meaning one side always faces the star, while the other is a permanent night side, similar to how the Moon orbits the Earth.

Although extreme temperatures make the exoplanet too hot to be habitable, observations of GJ 486 b with James Webb’s near-infrared spectrograph have revealed hints of water vapour. A study detailing the findings was published in The Astrophysical Journal Letters.

The presence of water vapor might suggest that GJ 486 b has an atmosphere, despite its heat and proximity to the star.

The mystery of water vapor

Although water vapor has already been detected on gaseous planets, scientists have yet to find an atmosphere around a rocky exoplanet, which would be a historic breakthrough as it would somewhat resemble planets in our solar system like Earth and Mars. , which are considered rocky.

“The presence of water vapor in the atmosphere of a hot, rocky planet would be a breakthrough for the science of planets outside our solar system. But we must be careful and make sure the star is not the culprit,” said Kevin Stevenson, co-author and principal investigator of the Webb Observation Program at the Johns Hopkins University Applied Physics Laboratory in Laurel, Maryland.

The team that observed GJ 486 b saw the planet pass in front of its star twice, and then used various methods to analyze the data captured by the telescope’s instruments.

When planets pass in front of their stars, also known as a transit, starlight can filter through a planet’s atmosphere and highlight the chemical imprints of different gases and elements. The results of the analysis of the data collected by Webb pointed to the presence of water vapor around GJ 486 b.

But astronomers are being careful about interpreting the findings because the water vapor could be connected to the star itself.

“We see a signal, and it’s almost certainly due to water. But we still can’t say if this water is part of the planet’s atmosphere, that is, if the planet has an atmosphere, or if we are just seeing a signal of water coming from the star,” said Sarah Moran, lead author of the study and associate researcher. postdoctoral fellow at the University of Arizona in Tucson.

Water vapor exists even on our Sun, in the sunspot regions. Sunspots or star spots are areas that appear darker on stars because they are cooler than other parts of the surface.

Because the red dwarf star that hosts GJ 486 b is much smaller and cooler than the Sun, it may contain even more water vapor in its starspots, enough to create a signal that could be misinterpreted as a planetary atmosphere enveloping it. the exoplanet in close orbit, according to the researchers.

“We saw no indication that the planet passed through star spots during transits. But that doesn’t mean there aren’t spots elsewhere on the star. And that’s exactly the physical scenario that would imprint that water signal on the data and could end up resembling a planetary atmosphere,” said Ryan MacDonald, study co-author and NASA Sagan Fellow at the University of Michigan in Ann Arbor.

The star’s heat and radiation would likely erode GJ 486 b’s possible atmosphere over time. If the extrasolar planet has an atmosphere, it would need to replenish it from a constant source, such as steam from volcanoes.

Future observations of the planet using different instruments on the Webb telescope may reveal additional details about the source of the water vapour.

“It’s the coming together of several instruments that will really determine whether or not this planet has an atmosphere.”