James Webb Space Telescope

It is a major goal of astronomical research to find planets other than Earth that might be suitable for sustaining life. There are a number of factors which many scientists agree are essential to a planet being habitable, but an important one is whether or not a planet has an atmosphere.

Scientists have found other rocky, Earth-like exoplanets, but none that we can definitively say have atmospheres. Finding these planets will reveal insights into how such atmospheres are formed and retained, so that we can better predict which planets could be habitable.

A study conducted by University of Chicago Ph.D. student Qiao Xue with Prof. Jacob Bean's group has demonstrated a new way to determine if faraway exoplanets have an atmosphere—and showed that it was simpler and more efficient than previous methods.

The new technique, when applied to more planets, has the potential to help us learn more about patterns in atmosphere formation. The paper is published in The Astrophysical Journal Letters.

"When we look at a large enough data set, as we will this year with the James Webb Space Telescope, we are hoping to find trends to help us understand more about atmosphere formation—and what makes planets habitable," said Xue.

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

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

In the study, the scientists used a method that was proposed in 2019 by a collaboration including Bean and Megan Mansfield (Ph.D.'21, now with the University of Arizona) to look for atmospheres. The approach uses the difference in temperature between an exoplanet measured at its hottest and the calculated temperature of how hot it could theoretically be.

Since atmospheres disperse heat around the entire surface area of planets, they reduce the temperature of the hottest side of the planet (which faces the star directly). The scientists hypothesized that if an exoplanet's actual temperature is not as hot as it could theoretically be, then we can presume it has an atmosphere performing this function.

The trouble was, however, that we have lacked instruments precise enough to provide accurate enough readings for these temperatures. The James Webb Space Telescope has changed that—offering an increased capacity to see in the infrared, which allows for scientists to record the temperatures of the planets by measuring the intensity of energy they emit.

When exoplanets cross in front of their suns, 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 viewing devices, we can capture the maximum brightness of the system—that is, the unobscured star combined with the comparatively minimal light emitted from the planet...........

https://phys.org/news/2024-10-webb-method-atmospheres-distant-planets.html