One recent discovery made by NASA’s James Webb Space Telescope (JWST) is truly revolutionary as it unveils a new class of exoplanets entirely! This intriguing planet is located roughly 244 light years from Earth in the constellation Lepus. This finding represents a significant leap forward in exoplanet science. It is truly groundbreaking in its focus on exoplanets, particularly sub-Neptunes, which are well-established as being intermediate in size and mass between Earth and Neptune.
TOI-421 b orbits a sun-like star that is somewhat smaller and cooler than our Sun. The most violent planet, as we discovered, is so hot its surface reaches an average temperature of 1,340 degrees Fahrenheit. What’s really incredible is its proximity to its host star. It orbits at just 0.056 astronomical units, about 5.6% of the distance from Earth to the Sun.
The JWST’s spectroscopic observations have revealed strong evidence of water (H2O) in TOI-421 b’s hydrogen-rich atmosphere. Additionally, we inferred levels of sulfur dioxide (SO2) and carbon monoxide (CO). This was very exciting for us, but at the same time we still didn’t see any evidence for carbon dioxide (CO2) or methane (CH4). These new findings offer a significant look into the planet’s atmospheric makeup and how it may change over time.
Insights from Spectroscopic Observations
The observations made by the JWST using its NIRISS and NIRSpec instruments have allowed scientists to analyze the atmospheric makeup of TOI-421 b in unprecedented detail. According to Brian Davenport, a researcher involved in the study, “We saw spectral features that we attribute to various gases, and that allowed us to determine the composition of the atmosphere.”
What’s particularly striking about TOI-421 b’s atmosphere is how much clearer it is than other sub-Neptunes Webb has observed. Davenport noted, “Whereas with many of the other sub-Neptunes that had been previously observed, we know their atmospheres are made of something, but they’re being blocked by [haze].” This absence of haze in TOI-421 b’s atmosphere makes it easier to study its composition.
The impacts of these findings go well beyond just detecting new gases in the atmosphere. The new data they collected supports the prediction of that hypothesis. It indicates that hot and highly irradiated types of planets like TOI-421 b, are clear atmospheres without clouds and/or haze. This result is important for astronomers who want to understand the atmospheric dynamics and evolution of exoplanets.
The Unique Composition of TOI-421 b
Eliza Kempton, another researcher on the project, expressed her excitement about the potential of JWST to characterize smaller planets: “I had been waiting my entire career for Webb so that we could meaningfully characterize the atmospheres of these smaller planets.” Her enthusiasm underlines how important this mission will be for addressing knowledge gaps about these sub-Neptunes.
Kempton stressed how important it is to study these atmospheres. This foundational inquiry sheds light on how sub-Neptunes formed and evolved, including their absence in our own solar system. “By studying their atmospheres, we’re getting a better understanding of how sub-Neptunes formed and evolved,” she stated. “Part of that is understanding why they don’t exist in our solar system.”
Interestingly, Kempton noted that TOI-421 b was selected for observation due to prior data suggesting it might not have hazes: “Why did we observe this planet, TOI-421 b? It’s because we thought that maybe it wouldn’t have hazes.” Considering the timescale of the mission, their strategic focus paid off, as the results showed a strong contrast from previous assumptions about atmosphere composition.
Understanding Atmospheric Formation
TOI-421 b’s atmosphere appears to develop similarly to the giant planets in our own solar system. It’s not playing by the rules of what we expect sub-Neptunes to do. Kempton explained a crucial aspect of this process: “If you just took the same gas that made the host star, plopped it on top of a planet’s [atmosphere], and put it at the much cooler temperature of this planet, you would get the same combination of gases.”
One important temperature threshold is around 1,070 degrees Fahrenheit. It allows us to make judgements about whether a detected sub-Neptune has a clear atmosphere or not. TOI-421 b is well above this threshold. This allows it to be a particularly interesting case to investigate further, examining atmospheric clarity on many more exoplanets.
Davenport concluded by stating, “We’ve unlocked a new way to look at these sub-Neptunes.” Whether these conclusions about TOI-421 b hold as we study more exoplanets remains to be seen. In addition, they chart a course for future exploration of even more intriguing similar small bodies.