Discovering Five New Exoplanets and Their Atmospheric Mysteries
The quest to uncover the atmospheres of exoplanets is one of the groundbreaking objectives of the James Webb Space Telescope (JWST). Researchers aim to determine whether these distant worlds could harbor life. However, this endeavor comes with significant challenges: scientists must first identify where to look, and the exoplanet in question must possess an atmosphere to analyze. Currently, astronomers have located nearly 6,000 exoplanets, but many lack atmospheres. Furthermore, a considerable number of those that do exist aren’t Earth-sized. Additionally, numerous exoplanets orbit stars that are too luminous for today’s telescopes to discern their atmospheres. These limitations mean that, despite having thousands of candidates, the actual number of Earth-sized planets with detectable atmospheres is relatively low. This makes the recent publication by Jonathan Barrientos from Cal Tech and his colleagues, detailing five new exoplanets orbiting M-dwarf stars—two of which may have atmospheres—particularly exciting news for astrobiologists and exoplanet researchers.
The Transiting Exoplanet Survey Satellite (TESS) was responsible for discovering these five potential candidates. However, confirming their existence necessitates further investigations, which are presented for the first time in this new study. When TESS identifies a signal that hints at an interesting exoplanet, it issues a TESS Object of Interest (TOI) alert, informing the public about this new candidate. To validate a candidate's presence, follow-up observations are typically needed, including transit photometry or even high-resolution imaging.
Verifying the existence of these newly identified planets required a collaborative effort, utilizing data from at least nine different telescopes, such as the Keck II Observatory and the Hale Telescope. This extensive dataset confirmed the presence of five planets across four distinct systems, with one system containing two planets that are gravitationally resonant with each other. Among these, four are classified as “Super-Earths,” possessing sizes ranging from 1.28 to 1.56 times that of Earth, while the fifth planet, identified as TOI-5716b, has a size comparable to our own planet.
Fraser engages in a discussion about exoplanet atmospheres with Dr. Joanna Barstow.
A key distinction between our planet and these extraterrestrial bodies lies in their orbital periods, which span from a mere 0.6 days to 11.5 days. Such rapid orbits are quite common among current exoplanet candidates, largely due to the limited telescope time available for observation. More critically, all these newfound planets orbit M-dwarf stars, which play a significant role in their atmospheric potential.
Why are M-dwarfs so important? First, these stars are relatively dim, allowing telescopes like the JWST to more effectively block out their brightness while searching for signs of an atmosphere. However, they also have a reputation for being unstable, frequently emitting massive X-ray and ultraviolet flares that can strip away a planet's atmosphere if it’s situated too close to the star.
To account for the potential atmospheric loss caused by these stellar phenomena, scientists use a concept known as the "cosmic shoreline." This theoretical framework maps the relationship between a planet's insolation (the amount of sunlight and radiation it receives) and its gravity. Planets with higher insolation are more susceptible to losing their atmospheres, whereas greater mass aids in retaining atmospheric layers. The resulting plot illustrates a clear linear relationship, designated as the cosmic shoreline.
In the research paper, the five newly discovered planets are categorized into three distinct groups. Three of these planets lie significantly "above" the cosmic shoreline, suggesting that their star’s energy likely eroded any atmospheres they might have possessed. The fourth planet, TOI-5736b, distinguished by its short orbital period, belongs to a unique category. Despite receiving substantial radiation, its considerable size and mass imply that it could theoretically maintain a volatile-rich atmosphere simply due to its dimensions.
This leaves us with one notable exception—exoplanet TOI-5728b. Remarkably, this planet appears capable of retaining its atmosphere, even while orbiting an active M-dwarf star. The combination of its atmospheric retention and the dimness of its host star positions this planet as a prime candidate for future observations using the James Webb Space Telescope (JWST) to directly detect its atmosphere.
Realistically, given its lengthy 11.5-day orbital period, the chances of finding complex life on this newly confirmed planet are minimal. However, some extremophiles—organisms thriving under extreme conditions—might still manage to survive if they have adequate protection. The only way we’ll know for sure is through observation, and the process from discovering TOIs to confirming and characterizing them, eventually leading to study by world-class observatories, exemplifies the scientific method in action.
It may take some time before the JWST, which is currently occupied with various projects, can focus on this particular planet. However, we anticipate that eventually, data regarding its atmosphere will emerge, generating excitement among planetary scientists and astrobiologists alike. For now, patience will be essential as the wheels of scientific progress continue to turn.
