Astronomers have spotted CO2 on a planet outside the solar system for the first time. how they did

Bengaluru: NASA’s James Webb Space Telescope (JWST) has detected the first definitive evidence of carbon dioxide in the atmosphere of an extra-solar planet. The alien planet outside our solar system is a gas giant that orbits a sun-like star 700 light-years away in the constellation Virgo.

The planet, WASP-39b, has a mass equivalent to a quarter of Jupiter’s (or about the same as Saturn’s) and is 1.3 times the diameter of Jupiter. Its surface temperature is estimated at 900 degrees Celsius and it orbits very close to its host star.

The planet completes its orbit in just four Earth days, about one-eighth the distance from its star as Mercury is from the sun.

The planet was discovered in February 2011 by the Wide Angle Search for Planets (WASP) project and already made news in 2018 when Hubble and Spitzer space telescopes discovered large amounts of water vapor in its atmosphere.

Carbon absorbs light at longer and greater infrared wavelengths than water vapor. Therefore, the JWST was able to detect carbon dioxide in its atmosphere while Hubble and Spitzer could not.

By knowing the proportion of carbon and oxygen present in WASP-39b’s atmosphere, scientists can gain an understanding of how the planet formed and evolved relative to its star.

“The detection of such a clear carbon dioxide signal on WASP-39b bodes well for detecting atmospheres on smaller, Earth-sized planets,” said Natalie Batalha of the University of California, Santa Cruz, and team leader of Webb’s Transiting Exoplanet Group, in a press release.


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Exoplanets in transit

WASP-39b was detected by the transit method, which means that seen from Earth, it can be seen passing in front of its star in its orbit. Such planets attenuate the light of the star they pass by very slightly, but enough so that scientists on earth can perform complicated calculations about the nature of the planet.

While some starlight is attenuated, some passes through the planet’s atmosphere as it passes in front of the star. The atmosphere filters certain colors according to its composition. This can also be seen in our own skies which display fiery and colorful sunsets when there are particles or increased pollution in the atmosphere.

Different gases absorb different combinations of colors across a spectrum of wavelengths, and this can be seen in the spectrum of starlight transmitted behind the exoplanet. By observing the missing colors, astronomers can infer exactly what gases are present in a planet’s atmosphere.

This method is known as transmission spectroscopy.

The spectrum of the planet itself is the most accurate obtained for an exoplanet to date, showing great detail and differences at a sensitivity never seen before, particularly in the 3 to 5.5 micrometer range.

“As soon as the data appeared on my screen, the massive carbon dioxide feature grabbed me,” said Zafar Rustamkulov, a graduate student at Johns Hopkins University and a member of the Transiting Exoplanets team. “It was a special moment, crossing an important threshold in exoplanet science.”

(Editing by Nida Fatima Siddiqui)


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Arline J. Mercier