The space telescope James Webb from the NASA is studying potentially habitable exoplanets in our galaxy, focusing on small planets that could support life due to their position in the habitable zone. Detecting atmospheres, and even more so biosignatures indicative of life, is extremely difficult due to the tiny size of signals from these planets and interference from their host stars.
The transmission spectroscopy of the Webb telescope
The telescope James Webb is engaged in the search for potentially habitable exoplanets, using transmission spectroscopy to analyze their atmospheric compositions. This process is complicated by the small size of the signals and the observation time required, making the detection of biosignatures a significant challenge.
Exoplanets are common in our galaxy, and some orbit in the so-called habitable zone of their star. The telescope James Webb has observed some of these potentially habitable small planets, and astronomers are now analyzing the data collected. Project scientists Webb, Dr. Knicole Colon and Dr. Christopher Stark of the Goddard Space Flight Center from the NASAtell us about the challenges in studying these worlds.
Definition of potentially habitable planets
A potentially habitable planet is often defined as a planet similar in size to the Earth which orbits in the habitable zone of its star, where it could have a temperature sufficient to allow the existence of liquid water on its surface. Currently, we know of about 30 planets that could be small rocky planets like the Earth and which orbit in the habitable zone.
The observation of exoplanet atmospheres
The potentially habitable worlds that the telescope Webb is observing are all transiting exoplanets, that is, with orbits almost perfectly aligned so that they pass in front of their host star. Webb It uses this setup to perform transmission spectroscopy, examining starlight filtered through planets’ atmospheres to learn about their chemical compositions.
However, the amount of starlight blocked by the thin atmosphere of a small rocky planet is tiny, typically much less than 0.02%. Even just detecting an atmosphere around these small worlds is very difficult. Identifying the presence of water vapor, which could increase the possibility of habitability, is even more difficult. Searching for biosignatures, biologically produced gases, is extremely difficult, but also an exciting undertaking.
Currently, there are only a few potentially habitable small worlds accessible to atmospheric characterization with Webbincluding the planets LHS 1140 b And TRAPPIST-1 e.
Technical challenges in biosignature detection
Some recent theoretical work exploring the detectability of gaseous molecules in the atmosphere of the super-Earth-sized planet LHS 1140 b highlight several challenges in biosignature research. The results indicate that approximately 10-50 transits of the planet around its host star would be required, equivalent to 40-200 hours of observation time with Webbto attempt to detect potential biosignatures such as ammonia, phosphine, chloromethane and nitrous oxide, in the optimal scenario of a clear, cloud-free atmosphere.
Exoplanet observation times
Given that Webb cannot observe the system LHS 1140 throughout the year due to the system’s position in the sky, collect 50 transit observations of LHS 1140 b it would take several years, if not almost a decade. Searching for biosignatures could require even more than 50 transit observations if the planet’s atmosphere is cloudy.
Hycean planets: a new avenue for research
One possible avenue in the search for biosignatures is the study of Hycean planets, a theoretical class of super-Earth-sized planets with a relatively thin hydrogen-rich atmosphere and a large ocean of liquid water. The super-Earth planet K2-18 b is a candidate as potentially habitable Hycean, based on current data from Webb and other observers.
Recently, published works have used NIRSpec And NIRISS to detect methane and carbon dioxide in the atmosphere of K2-18 b, but not water. This means that the hypothesis that K2-18 b whether a Hycean world with a liquid water ocean remains based on theoretical models, without yet direct observational evidence.
Disturbing factors in observational data
Another disturbing factor that makes it difficult for small, potentially habitable worlds to be studied Webb is that host stars can also show signs of water vapor. This has been explored in recent observations by Webb of the rocky exoplanet known as GJ 486 b. Therefore, we have the additional challenge of determining whether the water vapor detected by Webb it actually comes from the planet’s atmosphere and not its star.
The future of exoplanet studies
Detecting biosignatures in the atmospheres of small, potentially habitable planets transiting cold stars is an extremely difficult undertaking, requiring ideal conditions (e.g., cloudless atmospheres) or assuming environments similar to those of Earth primordial (i.e. different from Earth modern), the detection of signals significantly lower than 200 parts per million, a well-behaved star without significant amounts of water vapor in the star spots, and a significant amount of observing time to achieve a sufficient signal.
It is also important to remember that the detection of a single biosignature does not constitute the discovery of life. Discovering life on an exoplanet will likely require a large set of unambiguously detected biosignatures, data from multiple missions and observatories, and extensive atmospheric modeling efforts, a process that will likely take years.
