Methane, water revealed in atmosphere of nearby exoplanet

The James Webb Space Telescope has identified methane and water vapour in the atmosphere of a blue planet located 163 light years from our own.

WASP-80 b, considered a ‘warm Jupiter’ with a temperature of 825 kelvins (~551°C) and almost identical in size to the largest planet in Earth’s solar system, was studied by NASA astrophysicists using the JWST pointed at its location in the constellation Aquila.

Performing spectrographic observations as ‘b’ passed in front of and behind its parent star WASP-80 – known as the ‘transit method’ – the NASA team was able to study the dimming of particular light wavelengths to determine what its atmosphere consists of.

They then used an eclipse method – where the planet passes behind the star – to again measure the of dimmed wavelengths observed by the telescope.

The research was led by Taylor Bell of the NASA Ames Research Center and Luis Welbanks of Arizona State University, and the findings are published in Nature.

“This was the first time we had seen such an obvious methane spectral feature with our eyes in a transiting exoplanet spectrum, not too much unlike what could be seen in the spectra of the solar system giant planets a half a century ago,” said Welbanks.

“During this time, a thin ring of the planet’s atmosphere around the planet’s day/night boundary is lit up by the star, and at certain colours of light where the molecules in the planet’s atmosphere absorb light, the atmosphere looks thicker and blocks more starlight, causing a deeper dimming compared (with) other wavelengths where the atmosphere appears transparent.

“This method helps scientists understand what the planet’s atmosphere is made of by seeing which colours of light are being blocked.” 

The identification of methane marks an important milestone for the JWST. The gas has rarely been spotted in the atmospheres of planets other than our solar system’s gas giants Jupiter, Saturn, Uranus and Neptune.

The quality of the telescope and the calculations made by the research team are at such a high quality, there’s a more than 1 in 942 million chance the methane signals were caused by ‘noise’.

The value of detecting both methane and water vapour also gives astrophysicists the ability to calculate the formation history of planets. The ratio between these two substances can indicate where and when a planet formed in relation to its star. The ability to detect these on distant worlds might make it possible to find biomarkers for life.

“Methane is an important gas in tracing atmospheric composition and chemistry in giant planets,” says Welbanks. “It is also hypothesised to be, in combination with oxygen, a possible signature of biology.

“One of the key goals of the Habitable Worlds Observatory, the next NASA flagship mission after JWST and Roman, is to look for gases like oxygen and methane in Earth-like planets around sun-like stars.”