The James Webb Space Telescope's Quest for Atmospheres: A New Discovery and Its Implications
The James Webb Space Telescope (JWST) is on a mission to detect atmospheres around exoplanets, a crucial step in determining their potential for supporting life. However, this quest is not without its challenges. While scientists have identified approximately 6000 exoplanets, many of them lack atmospheres, and those that do often have atmospheres that are not Earth-sized. Moreover, the stars around which these exoplanets orbit can be too bright for current telescopes to observe their atmospheres. These constraints significantly limit the number of Earth-sized exoplanets that can be studied for atmospheres.
A recent paper by Jonathan Barrientos from Caltech and his colleagues introduces five new exoplanets orbiting M-dwarf stars, with two of them potentially possessing atmospheres. The Transiting Exoplanet Survey Satellite (TESS) discovered these candidates, and the paper details the confirmation process, which involved data from at least nine telescopes, including the Keck II Observatory and the Hale Telescope. This collaborative effort confirmed the existence of five planets in four systems, with one system featuring two planets in resonance with each other. Four of these planets are "Super-Earths" ranging from 1.28 to 1.56 times the size of Earth, while the fifth, TOI-5716b, is similar in size to our planet.
One significant difference between Earth and these distant exoplanets is their orbital periods, which range from 0.6 to 11.5 days. This is relatively quick, but it's a normal range for current exoplanet candidates due to limited telescope time. More importantly, these exoplanets orbit M-dwarf stars, which are relatively dim, making it easier for telescopes like the JWST to block the star's light and study the exoplanet's atmosphere. However, M-dwarfs are also known for their volatility, with massive X-ray and ultraviolet flares that can strip away a planet's atmosphere if it's too close to the star.
To account for this, scientists estimate a "cosmic shoreline," which is a plot between the planet's insolation (sunlight/radiation) and its gravity. Higher insolation makes it easier for atmospheres to be blown off, while higher masses help planets retain their atmospheres. This plot creates a clear, linear line, earning the name "cosmic shoreline."
The paper categorizes the five exoplanets. Three are clearly above the cosmic shoreline, indicating that their atmospheres have likely been stripped away by their star's energy. TOI-5736b, the planet with the shortest period, is unique due to its high radiation exposure and large radius and mass, which could theoretically allow it to hold onto a heavy atmosphere. The standout exoplanet is TOI-5728b, which seems to retain its atmosphere despite orbiting an active M-dwarf star. Its dim star makes it an ideal candidate for further study by the JWST to attempt a direct atmospheric detection.
While TOI-5728b's 11.5-day orbital period makes complex life unlikely, some extremeophiles might survive if properly protected. The process of discovering and characterizing these exoplanets, eventually leading to observations by the world's most advanced telescopes, is a testament to how science should work. The JWST's attention to this particular planet may be a while away, but the data it collects will undoubtedly excite planetary scientists and astrobiologists, even if they have to wait a little longer for the wheels of science to turn.
