UW: Orbital Variations Can Trigger 'Snowball' States on Exoplanets

[bystander]

Orbital Variations Can Trigger 'Snowball' States in Habitable Zones around Sunlike Stars
University of Washington | 2018 May 14

Artist’s impression of Earth as a frigid 'snowball' planet. Credit: NASA

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Aspects of an otherwise Earthlike planet’s tilt and orbital dynamics can severely affect its potential habitability — even triggering abrupt “snowball states” where oceans freeze and surface life is impossible, according to new research from astronomers at the University of Washington.

The research indicates that locating a planet in its host star’s “habitable zone” — that swath of space just right to allow liquid water on an orbiting rocky planet’s surface — isn’t always enough evidence to judge potential habitability.

Russell Deitrick ... and co-authors set out to learn, through computer modeling, how two features — a planet’s obliquity or its orbital eccentricity — might affect its potential for life. They limited their study to planets orbiting in the habitable zones of “G dwarf” stars, or those like the sun.

A planet’s obliquity is its tilt relative to the orbital axis, which controls a planet’s seasons; orbital eccentricity is the shape, and how circular or elliptical — oval — the orbit is. With elliptical orbits, the distance to the host star changes as the planet comes closer to, then travels away from, its host star. ...

Exo-Milankovitch Cycles II: Climates of G-dwarf Planets in Dynamically Hot Systems - Russell Deitrick et al

• arXiv.org > astro-ph > arXiv:1805.00283 > 01 May 2018

[Ann]

So the stability of the Earth's axial tilt (at less than 35 degrees) is another factor that has helped make the Earth so eminently habitable. Obviously a very eccentric orbit can be deadly to life on a planet.

Ann

[Chris Peterson]

So the stability of the Earth's axial tilt (at less than 35 degrees) is another factor that has helped make the Earth so eminently habitable. Obviously a very eccentric orbit can be deadly to life on a planet.

I'd say deadly (or preventing the formation of) complex life. It's not at all clear that simple life couldn't weather huge climatic variation.

[Ann]

So the stability of the Earth's axial tilt (at less than 35 degrees) is another factor that has helped make the Earth so eminently habitable. Obviously a very eccentric orbit can be deadly to life on a planet.

I'd say deadly (or preventing the formation of) complex life. It's not at all clear that simple life couldn't weather huge climatic variation.

Okay, Chris. I believe that scientists agree that the Earth was once "Snowball Earth", and this happened when the Earth already had a flourishing microbial fauna (or whatever collective noun you'd use to describe a biosphere of bacteria). Not only did the unicellular organisms not become extinct, but not too long afterwards the Cambrian explosion came to the Earth.

Ann