Washington: Venus is spinning on its axis so slowly that, for any survivor, a day in Venus would seem interminable, as it is the equivalent of 243 days on Earth, researchers say.
To make things worse, French astronomers have discovered that a day on Venus is getting even longer.
A team from the Paris Observatory evaluated data from a spectrometer aboard a European orbiter, the Venus Express.
Called VIRTIS, the instrument measures infrared and visible light and is used to scan the planet’s surface beneath the thick, roiling atmosphere.
The astronomers were shocked when they checked landmarks against the last mapping of Venus, carried out between 1990 and 1994 by the US probe Magellan.
At a given point in the Venusian day, landmarks were a full 20 kilometres behind where they should have been, the Sydney Morning Herald reported.
The team has asserted that they have been over the observations again and again.
“After eliminating possible sources of error, we believe that the duration of the Venusian day must have changed over the 16 years,” the researchers said.
Their estimate is that an extra six and a half terrestrial minutes have been added to the Venusian day during this time.
“On the astronomical scale, this is a major change,” said investigator Pierre Drossart.
The astronomers’ hypothesis is that friction by Venus’ atmosphere is braking the movement of the terrain below.
The atmosphere is apparently 100 kms thick, with extremely dense clouds of 96 per cent carbon dioxide, driven by superwinds reaching some 350 kilometres per hour.
Atmospheric pressure at the surface is 92 times that of Earth - the equivalent of being more than 900 metres below the ocean.
“A braking effect from the atmosphere also occurs erratically on Earth, but the discrepancy is only a matter of a few tenths of a second and it is imperceptible,” Drossart said.
Drossart also said that it was difficult to predict if Venus would stop spinning eventually or even go into reverse rotation.
“It’s difficult to say, given that we only have two points of measurement,” said Drossart.
“But theoretical models suggest that this is probably just a cyclical phenomenon. If the atmosphere speeds up, the planet slows. Then the energy goes into reverse, in a pendulum effect,” Drossart added.
The study has been published in the journal Icarus.