Privileged Planet: our tilt helps life (Introduction)

by David Turell , Tuesday, July 03, 2018, 18:29 (2118 days ago) @ David Turell

An article on exoplanets explains how our tilt is maintained:

https://www.sciencedaily.com/releases/2018/06/180628151708.htm

"How important is axial tilt for climate? Large variability in axial tilt could be a key reason why Mars transformed from a watery landscape billions of years ago to today's barren desert.

"'Mars is in the habitable zone in our solar system, but its axial tilt has been very unstable -- varying from zero to 60 degrees," said Georgia Tech Assistant Professor Gongjie Li, who led the study together with graduate student Yutong Shan from the Harvard-Smithsonian Center for Astrophysics. "That instability probably contributed to the decay of the Martian atmosphere and the evaporation of surface water."

"As a comparison, Earth's axial tilt oscillates more mildly -- between 22.1 and 24.5 degrees, going from one extreme to the other every 10,000 or so years.

"The orientation angle of a planet's orbit around its host star can be made to oscillate by gravitational interaction with other planets in the same system. If the orbit were to oscillate at the same speed as the precession of the planet's spin axis (akin to the circular motion exhibited by the rotation axis of a top or gyroscope), the spin axis would also wobble back and forth, sometimes dramatically.

"Mars and Earth interact strongly with each other, as well as with Mercury and Venus. As a result, by themselves, their spin axes would precess with the same rate as the orbital oscillation, which may cause large variations in their axial tilt. Fortunately, the moon keeps Earth's variations in check. The moon increases our planet's spin axis precession rate and makes it differ from the orbital oscillation rate. Mars, on the other hand, doesn't have a large enough satellite to stabilize its axial tilt."

Comment: Earth is carefully controlled to allow life. I would strongly suggest designed for life.