TRAPPIST-1 Planets Have No Large Moons, Study Argues - Seeker
https://www.seeker.com/space/planets/trappist-1-planets-have-no-large-moons-study-argues
The conditions for habitable exoplanets in the TRAPPIST-1 system might depend on the presence of large moons — and Earth reveals clues to why.
A new study looks at the possibilities of large moons in TRAPPIST-1, a notoriously crowded exoplanet system that may have habitable planets within it.
Earlier this year, observations from NASA's Spitzer Space Telescope indicated that seven planets here could be rocky and have liquid water on their
surfaces, making TRAPPIST-1 the system with the most potentially habitable planets.
But even before NASA's discovery, TRAPPIST-1 was known and pondered by scientists, including the author of the new paper, Stephen Kane, an associate
professor of astronomy at San Francisco State University who specializes in exoplanets.
"I have several publications now on exomoons, and for many years I've been thinking about how the ability of a planet to host a moon scales with
the presence of nearby planets and proximity to the host star," Kane said in an e-mail. "The discovery of the TRAPPIST-1 system prompted me to finally
calculate whether or not planets in compact planetary systems can actually harbor moons."
For TRAPPIST-1, Kane found that the planets are so tightly packed together that large moons would likely be impossible. While the rotational axes of
the planets would quickly change and have more chaotic climates, he said, life could still evolve — it just might take a longer time.
Kane's methodology involved studying the influences of two parameters: the Hill radius, or the area in space in which a planet exerts gravitational
influence based on its mass and distance from the host star, and the Roche limit, which identifies where the gravitational effect near a planet is
too strong for a moon to survive.
