Salvador Nogueira

Seen from afar, as if it were an exoplanet, of which only the mass and diameter are normally known, Venus is “similar to Earth”. Since we’re his neighbors, we know he’s anything but. Although it has a similar size and basic composition, in addition to a comparable level of solar radiation incidence, it is an “evil twin” of our planet, an ultra-hot, dry and uninhabitable greenhouse. And one notable difference between the two is that Venus rotates extremely slowly – a fact that is finally beginning to be understood by scientists.

As a general rule, the planets in a system all rotate around their axis in the same direction, and the larger the faster. In the solar family, three of them clash: Uranus, which has its axis of rotation practically “lying” (that is, with the poles in the direction of the Sun), Mercury, which has its rotation gravitationally stopped by the solar gravity and completes two revolutions every three turns on its own axis, and Venus, which has a rotation longer than the translation and clockwise, contrary to the other planets.

Mercury is the easiest to understand: the combination of the flattening of its orbit and the Sun’s tidal effect produced the 2:3 lock. As for Venus and Uranus, it was long speculated that perhaps a giant collision with another celestial body, early in its formation, explained the behavior. Now, for Venus at least, an alternative is more likely.

According to Stephen Kane, a planetary scientist at the University of California at Riverside, the planet was almost gravitationally locked by the Sun in a 1:1 pattern (each revolution around itself accompanies a solar revolution), and then the interaction with its thick atmosphere ( which is practically a hundred times denser than Earth’s and rotates much faster than the planet itself) gave it a slight retrograde rotation of 243 Earth days, longer than the 225 days it takes to circle the Sun.

With this peculiar movement pattern, Venus has lost virtually all the water it had in its formation and has become a desert, with a carbon dioxide greenhouse effect that keeps the surface at 460°C.

As Kane pointed out in article published in Nature Astronomy, there is growing interest in understanding how Venus evolved to its current state. That’s because many of the “terrestrial” exoplanets discovered in recent years, which we are now about to study more closely with equipment like the James Webb Space Telescope, have the potential to be much more like Venus than our planet.

“Venus offers the promise of local data that we will never have from an exoplanet,” says the researcher. “The opportunity to apply a detailed model of Venus’ climate to other worlds is not only attractive but a necessary step in the quest to characterize Earth’s twin analogues around other stars.”

This column is published on Mondays, in Folha Corrida.

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