Nasa’s Webb telescope finds no atmosphere in Earth-sized planet in solar system thought to have water

Study marks first detection of any form of light emitted by an exoplanet as small as rocky planets in our own solar system

The new James Webb Space Telescope observations of a far away solar system thought to have water found that its innermost planet is devoid of atmosphere, an advance that could lead to better ways of determining whether such celestial bodies host life.

An international team of scientists behind the discovery said the results mark an important step in determining whether planets orbiting small active stars can sustain atmospheres needed to support life.

The findings, published in the journal Nature, indicate that the dayside of the exoplanet Trappist-1b – about 40 lightyears from Earth – has a temperature of about 500 kelvins, or 450 degrees Fahrenheit, and suggests that it has no significant atmosphere.

The study also marks the first detection of any form of light emitted by an exoplanet as small, and as cool as, the rocky planets in our own solar system.

“These observations really take advantage of Webb’s mid-infrared capability. No previous telescopes have had the sensitivity to measure such dim mid-infrared light,” study co-author Thomas Greene said.

Astronomers discovered the planet system orbiting an ultracool red dwarf star (or M dwarf) in 2017.

Later observations revealed that its innermost planet Trappist-1b has an orbital distance about one hundredth that of Earth’s, receiving about four times the amount of energy that Earth gets from the Sun.

While trappist-1b is not within the system’s habitable zone, researchers say observations of the planet can provide important information about its sibling planets, as well as those of other M-dwarf systems.

“It’s easier to characterize terrestrial planets around smaller, cooler stars. If we want to understand habitability around M stars, the Trappist-1 system is a great laboratory. These are the best targets we have for looking at the atmospheres of rocky planets,” Dr Greene explained.

While past observations of the planet found no evidence for a puffy atmosphere, astronomers could not rule out a dense one.

“This planet is tidally locked, with one side facing the star at all times and the other in permanent darkness. If it has an atmosphere to circulate and redistribute the heat, the dayside will be cooler than if there is no atmosphere,” Pierre-Olivier Lagage, another author of the study, said.

In the new study, researchers used a new method to determine the temperature of the planet based on the change in brightness as Trappist-1b moved behind its star during what is called a secondary eclipse.

Scientists analysed data from five separate secondary eclipse observations and compared the results to computer models predicting what the temperature should be in different scenarios.

“The results are almost perfectly consistent with a blackbody made of bare rock and no atmosphere to circulate the heat. We also didn’t see any signs of light being absorbed by carbon dioxide, which would be apparent in these measurements,” Elsa Ducrot, another author of the study, said.

In further observations, scientists hope to see how the temperature changes from the day to the nightside of the planet to confirm if the planet has an atmosphere or not.

“This is the first time we can detect the emission from a rocky, temperate planet. It’s a really important step in the story of discovering exoplanets,” Dr Lagage said.