- The second closest planet to the Sun rotates on itself from west to east.
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| Why does Venus rotate backward from the rest of the planets in the Solar System? |
Of the planets of the Solar System, Venus has a peculiarity. All planets rotate from east to west, except for the second closest to the Sun. Venus rotates from west to east, and really, it shouldn't.
A new study argues that the reason for the inverted spin is its powerful atmosphere. As Gizmodo reports, if it weren't for the thick, fast-moving atmosphere on Venus, the planet probably wouldn't rotate.
The gravity of a large object in space can prevent a smaller object from rotating, a phenomenon called tidal lock. Because it bypasses this blockage, a University of California, Riverside scientist argues that the atmosphere should be a more prominent factor in studies of Venus and other planets.
These arguments, as well as descriptions of Venus as a partially tidally locked planet, have just been published in a Nature Astronomy article.
Standing on the surface of Venus would be like standing at the bottom of a very hot ocean.
"We think of the atmosphere as a thin, almost separate layer on top of a planet that has minimal interaction with the solid planet," said Stephen Kane, an astrophysicist at UCR and lead author of the paper.
"Venus' powerful atmosphere teaches us that it is a much more integrated part of the planet that affects absolutely everything, including the speed of the planet's rotation," adds Kane.
Venus takes 243 Earth days to rotate once, but its atmosphere circles the planet every four days. Extremely fast winds cause the atmosphere to drag along the planet's surface as it circulates, slowing its rotation while also loosening the Sun's grip on gravity.
The slow rotation, in turn, has dramatic consequences for Venus' sweltering climate, with temperatures averaging up to 480 degrees Celsius, hot enough to melt lead.
"It's incredibly strange, a tremendously different experience than being on Earth," Kane said. "Standing on the surface of Venus would be like being at the bottom of a very hot ocean. You couldn't breathe in it," adds the author.
The Venusian atmosphere also prevents energy from the sun from leaving the planet, which prevents it from cooling or from having liquid water on its surface, a state known as the runaway greenhouse effect.
It's unclear whether being partially tidally locked contributes to this runaway greenhouse state, a condition that ultimately renders a planet uninhabitable for life as we know it.
Not only is getting clarity on this question important to understanding Venus, but it's also important to studying exoplanets that are likely to be targeted by future NASA missions.