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Day and Night

June 11, 2015

When astronomers contemplate the possibility of life around other stars, they naturally focus on stars that resemble the Sun. But the vast majority of stars are much cooler, smaller, and fainter than the Sun.

Such a star produces so little light that a planet must huddle close to it to stay warm and have a climate that’s suitable for life. But if a planet is too close to its star, then it can become locked so that one side forever faces its sun, and the other side forever faces away — just as one side of the Moon always faces Earth. So one side of such a planet is in perpetual daylight, and the other in perpetual darkness. That’s probably not a good situation for life.

But astronomers recently discovered a possible way out of this problem: In many cases, the planet can still spin freely, the way Earth does — if the planet has an atmosphere that’s as thick as ours.

A study showed that winds in the atmosphere rub against the surface, altering the planet’s rotation so that it spins freely. Because small, faint stars are so common, this finding means that more worlds may have day-and-night cycles than had been thought.

What’s more, a thick atmosphere is good at transporting heat around the entire planet. Venus, for example, has an especially dense atmosphere, and temperatures there are about the same across the entire globe — it’s just as warm on the nightside as the dayside.

We’ll talk about some doomed exoplanets tomorrow.


Script by Ken Croswell, Copyright 2015

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