Large Interferometer for Exoplanets: VIII. Where Is the Phosphine? Observing Exoplanetary PH₃ with a Space-Based...

Area of Science:

• Exoplanetary science
• Astrochemistry
• Planetary atmospheres

Background:

• Phosphine (PH3) is a key molecule for understanding exotic planetary chemistry.
• While detected in Solar System giants, phosphine remains unobserved in exoplanets.
• Phosphine is theorized as a potential biosignature in exoplanetary atmospheres.

Purpose of the Study:

• To identify observable science cases for phosphine (PH3) chemistry using a space-based mid-infrared nulling interferometric observatory.
• To assess the detectability of phosphine in various exoplanetary scenarios with the Large Interferometer for Exoplanets (LIFE) concept.

Main Methods:

• Utilized chemical kinetics and radiative transfer calculations.
• Developed forward models for prototypical observational cases using LIFEsim, a LIFE observation simulator.
• Simulated phosphine detection scenarios across LIFE's dynamic range.

Main Results:

• Phosphine detection is feasible in warm giants (1 hr) and temperate super-Earths (10 hrs) around G and M stars, respectively.
• Detection in Venus-Twin exoplanets with extreme PH3 concentrations appears unlikely even within 100 hrs.
• Phosphine is detectable in 2 out of 3 scenarios, approximately 10 times faster than with the James Webb Space Telescope.

Conclusions:

• The Large Interferometer for Exoplanets (LIFE) mission shows significant potential for detecting phosphine in diverse exoplanetary atmospheres.
• These findings will guide LIFE mission design and prioritize future observational strategies.
• LIFE's capabilities offer a substantial advantage for exoplanetary phosphine detection, advancing the search for biosignatures.