Webb lets researchers use new method to find atmospheres of distant planets

One of the major goals of astronomical research is to find planets other than Earth that might be suitable for supporting life. There are a number of factors that many scientists believe are essential for a planet to be habitable, but one of the most important is whether or not a planet has an atmosphere.

Scientists have discovered other rocky exoplanets similar to Earth, but none that we can say with certainty has an atmosphere. Discovering these planets will reveal insight into how these atmospheres form and are maintained, so we can better predict which planets might be habitable.

A study led by the University of Chicago Ph.D. Student Qiao Xue from Professor Jacob Bean’s group demonstrated a new way to determine whether distant exoplanets have atmospheres and showed that it was simpler and more effective than previous methods.

The new technique, when applied to more planets, has the potential to help us learn more about the patterns of atmosphere formation. The article is published in Letters from the astrophysical journal.

“When we look at a large enough data set, as we will this year with the James Webb Space Telescope, we hope to find trends that will help us better understand how the atmosphere forms and what makes planets habitable,” Xue said.

The search for atmospheres

As scientists try to understand conditions on other distant planets, they would like to know whether or not a planet has an atmosphere, a layer of gas that insulates it and regulates its temperature. On Earth, for example, our atmosphere redistributes heat from the sun around the planet, keeping it a temperate place for life.

However, scientists cannot directly image rocky, Earth-like planets close to their stars. Instead, they must piece together different clues, such as fluctuations in light as the planet moves around its host star.

In the study, scientists used a method proposed in 2019 by a collaboration including Bean and Megan Mansfield (Ph.D. ’21, now at the University of Arizona) to search for atmospheres. The approach uses the temperature difference between an exoplanet measured at its hottest point and the calculated temperature of its theoretical temperature.

Because atmospheres disperse heat across the entire surface of planets, they reduce the temperature of the hottest side of the planet (which faces directly toward the star). Scientists have hypothesized that if an exoplanet’s actual temperature is not as hot as it could be in theory, then we can assume that it has an atmosphere that serves this purpose.

The problem, however, was that we lacked instruments precise enough to provide sufficiently accurate readings of these temperatures. The James Webb Space Telescope has been a game-changer by providing an increased ability to see in infrared, allowing scientists to record the temperature of planets by measuring the intensity of the energy they emit.

When exoplanets pass each other in front of their sun, they obscure some of the star’s light, leading to a slight decrease in the star’s measured brightness. When the planet appears almost behind the star relative to our observing devices, we can capture the maximum brightness of the system, that is, the unobscured star combined with the relatively minimal light emitted by the planet.

When the planet passes behind the star relative to our view, we can record only the light emitted by the star. By subtracting this measurement of light from the measurement of the star’s light combined with that of the planet, we can deduce the brightness – and therefore the temperature – of the planet itself.

In this way, Xue concluded that the first planet to which she applied the new method, the planet GJ1132 b, has no atmosphere: the measured temperature of the planet is too close to the calculated maximum temperature to suggest a temperature regulation. component of the planet. “So it’s not a suitable candidate for life,” she said.

The new method is not the only way to determine whether an exoplanet has an atmosphere or not, but it is a simpler and more reliable way to search for distant planets with an atmosphere. Xue explained that it is less sensitive to false negatives and positives than the other technique.

“This other technique, which measures light filtering through the planet’s atmosphere, is more difficult because it can be confounded by activity on the star and the presence of clouds,” Bean said.

If scientists can understand what gives rise to planets’ atmospheres, it will be easier to rule out uninhabitable planets in their quest for exoplanets suitable for life.

“This study was exciting because I finally had the chance to work with rocky planets, which are every exoplanet scientist’s dream subject because they have enormous potential for life,” Xue said. “Now I’m so excited to see what comes next.”