Far out cosmology: how much water to make an Earth? (Introduction)

by David Turell , Monday, July 22, 2024, 17:44 (47 days ago) @ David Turell

An estimate from a simulation:

https://www.sciencenews.org/article/earthlike-planets-need-lot-water

"If an Earthlike planet is the goal, the best starting hand might contain three to eight times all the water in Earth’s oceans.

“'There’s kind of a sweet spot,” says Keavin Moore, a planetary scientist at McGill University in Montreal. Less water, and the planet dries out. More water, and it ends up soggy, Moore and colleagues report in a paper submitted June 28 to arXiv.org.

Astronomers think rocky planets orbiting small, dim stars could be the most common abode for life in the galaxy. But those stars have fiery tempers and could strip away a planet’s water with high-energy flares within a few billion years of the planet’s birth.

"Moore and colleagues wondered what would happen if planets could hide the water destined to become oceans and atmospheres in their interiors until their host stars calmed down with age. The team made a simple simulation of a planetary life span, in which a planet is born hot and molten, with some water dissolved in a planet-wide sea of magma. It can start with water in its hand, or be dealt it later, with water delivered by comets or asteroids.

"As the planet cools, water evaporates and forms an atmosphere. Some is lost to space. But some enters a cycle of dissolving into the planet’s mantle and escaping back out into the atmosphere. Storing water in the mantle protects it from the host star’s harsh rays.

"For an Earth-mass planet in Moore’s simulation to end up with oceans and continents after about 5 billion years, it needed to start with three to eight times the amount of water in Earth’s oceans, he and his colleagues found. Planets that started out with up to 12 times Earth’s oceans could wind up as watery worlds, completely covered by ocean with no dry surface whatsoever. Such planets may actually exist, and could theoretically host life even without land."

Comment: Fun and games with numbers. But it makes a major point. This planet got just the right amount of water to set up the hydrological cycle to make rain on land.

https://evolutionnews.org/2018/01/behind-waters-beauty-wondrous-utility/

" [W]e have seen that it is the unique capacity of water to exist in the three stages of matter in the ambient temperature range, in conjunction with the low viscosity of ice and water, that makes possible the hydrological cycle, which has reliably delivered water to the terrestrial ecosystems of planet Earth for millions of years. And because the turning of the hydrological wheel depends largely on the unique properties of water, this means that in effect, water, the very matrix of life, delivers itself to land-based ecosystems by its own capacities."