Privileged Planet: our tilt helps life (Introduction)

by David Turell , Thursday, June 21, 2018, 14:50 (2347 days ago) @ dhw

We are tilted 23.5 degrees from upright. it makes seasons and makes life here much easier to survive:

https://www.nytimes.com/2018/06/20/science/summer-solstice-2018-meaning-sunset.html?emc...

"The solstice occurs because Earth does not spin upright but leans 23.5 degrees on a tilted axis. Such a slouch, or obliquity, has long caused astronomers to wonder whether Earth’s tilt — which you could argue is in a sweet spot between more extreme obliquities — helped create the conditions necessary for life.

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"If the planet had no slouch, it wouldn’t have seasons. The hemispheres would never dip toward or away from their star. Instead, the poles (which always point toward the frigid depths of space) would be so cold that carbon dioxide would be pulled from the sky, an effect, Dr. Heller argues, that would cause the planet to lose its precious greenhouse gas so that liquid water could never form.

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"David Ferreira, an oceanographer at the University of Reading in England, invoked a similar argument. In 2014, he and his colleagues found that even an Earth 2.0 with a slouch as low as Uranus’s could potentially support life — so long as the planet had a global ocean.
An ocean will absorb heat during summer, then when winter arrives it will release that heat, allowing the planet to stay relatively temperate.

“'It’s a bit like when you put a stone in the fire and it gets really hot,” Dr. Ferreira says.
“'If you take that stone out of the fire, it’s going to release that heat slowly.” That allows the water world to experience balmy springlike temperatures year-round.

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"Take Earth as an example. Although our planet’s obliquity is relatively constant, it does change by a mere few degrees. Such slight variations have sent vast sheets of glaciers from the poles to the tropics and entombed Earth within a frozen skin of solid ice. Luckily, Earth has managed to escape these so-called snowball states. But scientists are not sure whether the same will be true for planets like Mars with larger variations in their tilts.

"In 2018, a team of astronomers argued that wild variations could push a planet toward an inescapable snowball state, even if it resided within a star’s habitable zone — that goldilocks band where liquid water can typically exist.

"As such, a stable tilt just might be a necessary ingredient for life. It’s an interesting finding given that the Earth’s tilt never changes drastically thanks to the Moon. And yet astronomers don’t know how common such moons are within the galaxy, said John Armstrong, an astronomer at Weber State University in Utah. If they turn out to be uncommon across the galaxy, it could mean that such stability — and therefore life — is hard to come by.

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“'This planet is really on the verge of destruction all the time,” he said. Although Earth is considered stable, it has still suffered global glaciations and meteorite impacts — and yet life has survived. That could mean that life is hardier than you might expect. But it could also mean that further variations would push it over the edge."

Comment: More evidence that the Earth might be specifically designed so life could start.