Does the Evolution of Complex Life Depend on the Stellar Spectral Energy Distribution?

Area of Science:

• Astrobiology
• Planetary Science
• Stellar Astrophysics

Background:

• The evolution of complex life is a key question in astrobiology.
• Understanding the conditions necessary for complex life is crucial for identifying habitable exoplanets.
• Stellar properties significantly influence the energy available to orbiting planets.

Purpose of the Study:

• To introduce the proportional evolutionary time (PET) hypothesis.
• To propose a link between stellar mass and the time required for complex life evolution.
• To define the 'biological available window' as a key factor in energy availability for life.

Main Methods:

• Defining the 'biological available window' (200–1200 nm) of stellar spectra.
• Calculating total incident energy within this window over planetary history.
• Formulating the PET hypothesis based on energy availability and evolutionary rates.

Main Results:

• The PET hypothesis posits that mean evolutionary time to complex life is a function of stellar mass.
• Planets receiving less than Earth's total incident energy (∼10^34 J) may not host complex life.
• Late K- and M-dwarf stars (M < 0.7 M☉) are predicted to be too young for complex life.

Conclusions:

• F-, G-, and early K-dwarf stars (M > 0.7 M☉) are optimal targets for detecting biosignatures of complex life.
• Future space telescopes should focus on these stars for exoplanet atmosphere analysis.
• The PET hypothesis provides a framework for prioritizing exoplanet searches for complex life.