This exoplanet could change our understanding of the edge of habitability

"Looking at this planet will tell us what's happening on this inner edge of the habitable zone."
Tejasri Gururaj
An artist's impression of exoplanet LP 890-9c’s possible evolution from a hot Earth to a desiccated Venus.
An artist's impression of exoplanet LP 890-9c’s possible evolution from a hot Earth to a desiccated Venus.

Credit: Carl Sagan Institute/R. Payne 

The search for habitable terrestrial planets or exoplanets is an active and ever-evolving field. Scientists are keen to find planets outside our solar system that have conditions conducive to supporting life as we know it- or something different.

Discovering and characterizing such planets is a significant step towards answering the age-old question of whether we are alone in the universe. One of the many unanswered questions in this search is the ideal distance a rocky planet can be to a star while sustaining water and life. 

Scientists believe that they may have found an exoplanet that could answer this question. 

Researchers led by Lisa Kaltenegger, director of the Carl Sagan Institute, have discovered an exoplanet (LP 890-9c or SPECULOOS-2c) that could shed light on the conditions at the inner edge of a star's habitable zone and the different evolutionary paths of Earth and Venus. 

The research team also included Laetitia Delrez, a postdoctoral researcher at the University of Liège, Belgium, who led an international team of scientists that discovered LP 890-9c, and scientists from the Massachusetts Institute of Technology and Pennsylvania State University.

Exoplanet LP 890-9c

LP 890-9c is a super-Earth, meaning it has a mass greater than but less than ten times the Earth's mass. It is part of a system that hosts another super-Earth called LP 890-9b, with both orbiting a red dwarf star about 100 light-years away from Earth. 

LP 890-9c is roughly 40 percent larger than the Earth and takes 8.5 days to orbit its star. Previous studies have suggested that liquid water or an atmosphere rich in water is possible on the exoplanet. 

Kaltenegger and her team designed a unique model that analyzes the chemical signatures emitted by rocky planets towards the inner edge of the habitable zone. 

From a hot Earth with potentially life-sustaining conditions to a barren Venus-like planet having carbon dioxide in the atmosphere, the model accounts for different scenarios depicting the stages of rocky planet evolution. 

By examining these scenarios, astronomers seek to obtain insights into the timescales of these evolutionary processes, which are currently uncertain.

Observing the exoplanet using James Webb

The model, however, requires data about the composition of the exoplanet's atmosphere. This is where the James Webb Space Telescope (JWST) comes in. 

In an accompanying paper led by Jonathan Gomez Barrientos, a graduate student at the California Institute of Technology, NASA's JWST has been highlighted as potentially being able to identify the composition and characteristics of the exoplanet's atmosphere. 

According to this study, JWST might prove the presence of an atmosphere, especially one dominated by water vapors, after just three transits of LP 890-9c across its host star. Additionally, JWST could show evidence of a Venus-like atmosphere with just eight transits and a potentially habitable hot Earth with just 20 transits. 

The calculations from Kaltenegger and her team's model help to estimate the times required for JWST to establish the composition of LP 890-9c's atmosphere, assuming one exists.

In addition to the TRAPPIST-1 system, LP 890-9c is one of the best candidates for the JWST to study for potentially habitable planets. 

Explaining the significance of studying this exoplanet, Kaltenegger said in a press release, "Looking at this planet will tell us what's happening on this inner edge of the habitable zone – how long a rocky planet can maintain habitability when it starts to get hot. It will teach us something fundamental about how rocky planets evolve with increasing starlight and about what will one day happen to us and Earth."

The findings of the study are published in the journal Monthly Notices of the Royal Astronomical Society: Letters.

Study abstract:

Venus and Earth provide astonishingly different views of the evolution of a rocky planet, raising the question of why these two rocky worlds evolved so differently. The recently discovered transiting Super-Earth LP 890-9c (TOI-4306c, SPECULOOS-2c) is a key to the question. It circles a nearby M6V star in 8.46 d. LP890-9c receives similar flux as modern Earth, which puts it very close to the inner edge of the Habitable Zone (HZ), where models differ strongly in their prediction of how long rocky planets can hold onto their water. We model the atmosphere of a hot LP890-9c at the inner edge of the HZ, where the planet could sustain several very different environments. The resulting transmission spectra differ considerably between a hot, wet exo-Earth, a steamy planet caught in a runaway greenhouse, and an exo-Venus. Distinguishing these scenarios from the planet’s spectra will provide critical new insights into the evolution of hot terrestrial planets into exo-Venus. Our model and spectra are available online as a tool to plan observations. They show that observing LP890-9c can provide key insights into the evolution of a rocky planet at the inner edge of the HZ as well as the long-term future of Earth.

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