For Science!
Scorched or Frozen: What is the Earth's Ultimate Fate?

CJ Miozzi | 4 Jun 2014 19:00
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What will happen when the Earth loses its magnetic field?


If the Earth's magnetic field protects the atmosphere from being stripped away by the solar wind, then wouldn't the greenhouse effect stop once the Earth loses its magnetosphere?

Mars' magnetic field died out four billion years ago. While the planet presently lies in the Sun's habitable zone, the reason its surface is so cold is because its atmosphere is too thin for any appreciable greenhouse effect to keep it warm. It is believed that Mars had a thicker atmosphere in the past, and the loss of its magnetosphere is at least partially responsible for the loss of its atmosphere.

A planet's magnetosphere is generated by the motion of a liquid core layer. Once that liquid cools into a solid, it stops generating a magnetic field. Mars, being smaller than the Earth, cooled much faster. It'll take another 3-4 billion years for the Earth's liquid outer core to solidify.

Does that mean that temperatures will then cool as the Earth's atmosphere is stripped away? Not quite. It turns out that a planet's mass is far more important to retaining its atmosphere than its magnetic field. That's why Venus, which is about as massive as the Earth, has a dense atmosphere despite its lack of a magnetosphere.

What will happen to the Earth when the Sun becomes a Red Giant?

Solar Prominence

Red is a colder color than yellow, so won't the Sun generate less heat once it becomes a red giant, cooling the Earth?

The Sun's current surface temperature is about 5505 °C, whereas red giants have temperatures of under 4800 °C. But while it is true that red giants are cooler, they are also significantly larger.

When the Sun enters the final stages of its life in 6.5 billion years, it will swell up into a red giant, swallowing Mercury and Venus and reaching a radius of 1.2 AU. By that time, the Earth will have drifted to at most 1.5 AU due to the Sun's mass loss, meaning it will be significantly closer to the surface of the Sun than it is today - and possibly even within the Sun.

Optimistic scenarios involve the Earth's atmosphere being stripped away and surface temperatures reaching more than 2,130 °C, bathing our planet in a magma ocean. The grimmest outcome sees drag forces from the Sun's atmosphere slow down the Earth, decreasing its orbital distance and sucking it deeper and deeper into the Sun until it completely vaporizes like a small meteor in the Earth's atmosphere.

Ultimately, no matter which way you look at it, there is only one vision for the Earth's distant future.

Global warming: it is our destiny.

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