Water Vapour Discovered around Rocky Exoplanet GJ 486 b, But is it From the Planet or its Host Star?
Astronomers have discovered hints of water vapour around a rocky exoplanet called GJ 486 b, using the James Webb Space Telescope. This is significant because the planet is too close to its star to be within the habitable zone, where liquid water could persist on its surface. The planet’s surface temperature is about 800 degrees Fahrenheit (430 degrees C), which means it is too hot for water to exist in liquid form. Despite this, data from Webb’s Near-Infrared Spectrograph (NIRSpec) suggests that water vapour exists on the exoplanet, which could mean that it has an atmosphere, a discovery that would be a major breakthrough for exoplanet science.
However, the presence of water vapour on GJ 486 b is not conclusive evidence that it has an atmosphere. Another possibility is that the water vapour originated in the atmosphere of the planet's host star, Wolf 437, a red dwarf. Water vapour can sometimes exist in sunspots on our own Sun because these regions are cooler than the surrounding surface of the star. Wolf 437 is much cooler than the Sun, so even more water vapour could accumulate in its own sunspots. This could create a signal that mimics a planetary atmosphere, making it difficult for astronomers to determine the source of the water vapour.
To determine whether the water vapour on GJ 486 b is associated with the planet or its host star, astronomers will need to conduct further observations using other instruments on the James Webb Space Telescope, such as the Mid-Infrared Instrument (MIRI). This will allow them to look at the planet's day side and determine whether it has an atmosphere that can circulate heat from the tidally locked world's day side to its night side. If the hottest point on the day side is shifted, this would indicate an atmosphere that can circulate heat.
GJ 486 b's proximity to its star is what has scientists so puzzled by the discovery of water vapour in space, possibly on the rocky planet. If the water vapour is associated with the planet, that would suggest that it has an atmosphere, despite being so close to the star and having a scorching surface temperature. Rocky exoplanets are most likely to be found orbiting red dwarf stars, which are the most common stars in the universe. To be in the habitable zone, a planet must orbit a red dwarf star closely as these stars emit less heat, and the planet needs to remain warm enough to potentially support liquid water. However, such stars are also active, particularly when they are young, releasing ultraviolet and X-ray radiation that could destroy planetary atmospheres. This raises the question of whether a rocky planet could maintain or reestablish an atmosphere in such a harsh environment.
The study's results have been accepted for publication in The Astrophysical Journal Letters. The James Webb Space Telescope is the world's premier space science observatory. Webb's mission is to unravel the enigmas of our solar system, explore far-off worlds orbiting alien stars, and delve into the enigmatic structures and beginnings of the cosmos, as well as our position within it. The Webb initiative is a global project spearheaded by NASA in collaboration with the European Space Agency (ESA) and the Canadian Space Agency.
0. “Webb Finds Water Vapor, But From a Rocky Planet or Its Star?” WebbTelescope.org, 1 May. 2023, https://webbtelescope.org/contents/news-releases/2023/news-2023-120
1. “Water vapor mystery puzzles astronomers” Courthouse News Service, 1 May. 2023, https://www.courthousenews.com/water-vapor-mystery-puzzles-astronomers/
2. “Webb Finds Water Vapor, But From A Rocky Planet Or Its Star? – Astrobiology” Astrobiology News, 1 May. 2023, https://astrobiology.com/2023/05/webb-finds-water-vapor-but-from-a-rocky-planet-or-its-star.html
3. “This Piping-Hot Rocky World Looks Surprisingly Wet” Gizmodo, 1 May. 2023, https://gizmodo.com/webb-telescope-water-vapor-rocky-exoplanet-red-dwarf-1850391696
4. “Water Vapor Detected Near Distant Planet by JWST” Mirage News, 1 May. 2023, https://www.miragenews.com/water-vapor-detected-near-distant-planet-by-jwst-997011/
5. “Webb discovered water vapor around a rocky planet that shouldn’t have an atmosphere” Yahoo Entertainment, 1 May. 2023, https://www.yahoo.com/entertainment/webb-discovered-water-vapor-around-200909829.html