January 24, 2019 at 4:10 am #25053
So it might be that all the exoplanets we’re discovering could be a lot more like Venus; Earth might be the outlier. [LINK]
Akatsuki may have discovered why Venus’s atmosphere rotates so fast. The reason may play a vital role in the habitability of Earth-sized exoplanets.
As a planet nearly the same size and mass as the Earth, Venus is an essential study for understanding the range of possible conditions on rocky planets. A defining feature of our neighbouring world is a thick atmosphere whose reflective properties enticed ancient astronomers to name the planet after the mythological goddess of beauty, but whose ability to trap heat renders the surface temperature capable of melting lead.
Yet perhaps the strangest feature of the Venusian atmosphere is its speed. Winds whip around the planet up to sixty times faster than the surface rotates; a phenomenon known as atmospheric super-rotation.
Exceeding 100 m/s (360 km/h) in the upper clouds, wind speeds on Venus are legitimately fast. However, the surface of the planet also rotates extremely slowly. The planet orbits the Sun in 225 Earth days but takes 243 Earth days to rotate on its axis, making the Venusian day (one complete rotation) longer than its year.
Such slow rotation may be a common feature among Earth-sized exoplanets such as the TRAPPIST-1 system and Proxima Centauri-b, whose close orbits to their star have likely resulted in tidal lock. Like the Moon orbiting the Earth, a tidally locked world rotates once per orbit so that one side permanently faces the star while the other experiences perpetual night. Slow rotators with Earth-like atmospheres need to transport heat efficiently around the planet or risk the atmosphere collapsing as it freezes on the cold night side of the world. Such a catastrophic end could be avoided if tidally-locked worlds typically had the fast winds of a super-rotating atmosphere.
Seems to me like that would really play hell with life developing anywhere unless it’s already really robust.
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