Titan is the perfect reference to study exoplanet atmospheres, suggests the study

The mission of NASA / ESA Cassini-Huygens explored Saturn and its moons from 2004 to 2017, providing the most detailed images and data on the never taken system. This included the largest moon of Saturn, Titan, that the probe examined closely during its many flies, and with the deployment of the Huygens Lander on its surface.

The mission has provided new information on the Titan atmosphere, its methane cycle and its rich prebiotic environment and the organic chemistry which takes place on its surface. His results have even led to speculations on the possibility of life on Titan, perhaps as methanogenic organisms living in his vast methane lakes.

Closer to home, the deployment of new generation observatories such as the James Webb space telescope (JWST) is revolutionizing the way we study exoplanets. Thanks to advanced webb spectrometers, coronagrapists and optics, this mission affects a transition from discovery to characterization.

According to a new study, Cassini exams of the Titan atmosphere could shed light on these attempts to characterize the atmospheres of exoplanets. The results of the probe, according to the authors, could therefore serve as an ambitious study for future observations, allowing astronomers to anticipate and overcome the potential difficulties interpreting the data of the mission.

The research was led by Prajwal Niraula, a graduate student at the Massachusetts Institute of Technology (MIT) working with the co-author Juliet of Wit, an associate professor at the MIT and leader of her disruptive planet group. They were joined by Robert J. Hargreaves and Iouli E. Gordon of the Division of atomic and molecular physics at the Harvard & Smithsonian Center for Astrophysics and Associate Professor Clara Sousa-Silva of Bard College. The article describing their results is published on the arxiv pre -printed server.

For their study, the team has consulted the data from the Visual and Infrared Cartography Spectrometer of Cassini (VIMS). This instrument made Titan’s high fidelity observations using solar occultations, where sunlight crossing an atmosphere is analyzed with a spectrometer to detect chemical signatures. These observations have confirmed that the Titan atmosphere is composed of nitrogen (95%) and methane (approximately 5%), with traces of other hydrocarbons and organic compounds.

The data also revealed that the Titan undergoes a cycle of methane similar to the water of the earth, where the liquid methane precipitates to form clouds and rained on the surface. As Niraula and de Wit explained to Universe today by e-mail, the success of this mission could shed light on future efforts to characterize the atmospheres of Exoplanet.

In particular, the Cassini mission has demonstrated how the identification of molecules in atmospheres can be difficult because different chemicals can have similar adsorption characteristics. This can lead to poor characterization, which would have drastic implications for scientists who try to determine the habitability of a planet.

As they explained, “in this study, our main objective is to take advantage of the precise transmission spectrum of Titan and our existing knowledge of its atmosphere to study the forces / limits of atmospheric recovery of exoplanet. We focus on the underlying hypotheses concerning the molecules which must be recovered.

“This objective is appropriate because of the existing concerns associated with the possible erroneous interpretation of molecular characteristics. It aims to assess whether the impact is limited to the inferences associated only with the spectroscopic characteristics in question or can lead to a bias on other atmospheric properties.”

The characterization of exoplanet atmospheres has increased considerably in recent years. Previously, astronomers relied on transmission spectra, where sunlight passing through the atmosphere of an exoplanet is analyzed to determine the chemical signatures. This is sometimes possible during planetary transits (transit spectroscopy), when the planets pass by their star compared to the observer.

Thanks to webb and other new generation observatories, astronomers are now to the point where exoplanets can be observed directly (alias. Direct imaging) based on light reflected by their surfaces and atmospheres.

For astronomers, the challenge remains the same: correctly identify the chemical spectra present to determine the existence of biosignatures. The next step in their study was to execute the Tierra model accessible to the public, a 1D spectroscopy code used to characterize the absorption characteristics.

In a previous study, Niraula and Wit were based on the model to take into account seven chemical signatures: methane, carbon monoxide, carbon dioxide, water, hydrogen, nitrogen and ozone. For this latest study, they extended the model to include a larger range of molecules that may exist and the similarity of their signatures, based on existing astronomical data.

Niraula and de Wit said: “It reveals that spectral signatures could not only be easily poorly identified, but that their thesis can also lead to prejudices on other atmospheric parameters, therefore the title connecting the ” detection ” and the` `recovery ” because these two aspects were not connected in the minds of people. atmospheric that they derive).

“Another overview acquired in this study concerns our ability to identify the dominant substantive gas even if it has no strong absorption characteristics (for example, gas nitrogen). This is essential to provide the context of the atmospheric chemistry type which takes place there, among others.”

While more exoplanets are added to the census jet, the search for potentially habitable planets moves in its next phase. The webb instrument has demonstrated its ability to characterize exoplanet atmospheres and has carried out direct detections (including recent TWA 7) since it started operations. In the near future, webb will be joined by the successor of the venerable Hubble, the Roman space telescope Nancy Grace Roman (RST).

Several ground telescopes will also start operations soon, including the extremely large telescope (ELT), the giant Magellan (GMT) telescope and the thirty meter (TMT) telescope. Together, these observatories will allow more direct imaging studies on exoplanets and characterizations. The capacity to correctly identify potential biosignities according to their absorption characteristics is essential if we want to find a land 2.0 or other habitable exoplanets.

In the meantime, Niraula and Wit believe that their work will help the astronomical and astrobiological community transition to a new era of data rich in information. As they have summarized, this will require scientists to ask: “What can we say reliably about these data? This question is in two forms:” What can we say reliably about these data given our current / stellar / atmospheric models? “And” what could we say reliably about these data if we had perfect models? “

“The first helps us to adequately explain the fact that most of our ideas are limited by the models developed to interpret lower quality data in the past, and their limits are now the bottlenecks (not data quality).

“Not taking into account the” noise induced by the model “would cause excessive confidence in our inferences and the probably biased conclusions. The second helps us to identify the dominant limits of existing models and to present the depth of the science that we could make by making guided / targeted improvements.”