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Planet Venus slowing down

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February 14, 2012

Visualization of the Venus Express in orbit above Venus (Image: ESA)

Visualization of the Venus Express in orbit above Venus (Image: ESA)

The rotation of the planet Venus is slowing down, according to recent data gathered by the European Space Agency's Venus Express satellite. Peering through the planet's dense atmosphere with infrared imaging, the orbiter saw surface features up to 20 km (12.4 miles) from their expected location. The discrepancy could be explained if the Venusian day has lengthened by six and a half minutes since the planet's speed of rotation was established 16 years ago.

Venus' accepted rate of rotation was established by NASA's Magellan mission in the 1990s, when a day on Venus (or one rotation) was clocked at being equal in duration to 243.0185 Earth days. Slow, in other words. But it would appear that the rotation has slowed further still in recent years.

"When the two maps did not align, I first thought there was a mistake in my calculations as Magellan measured the value very accurately, but we have checked every possible error we could think of," said planetary scientist Nils Müller of the DLR German Aerospace Centre. Long-duration radar measurements from Earth appear to corroborate the findings, according to the ESA.

Fluctuating weather patterns are believed to affect planetary rotation through friction with the surface. An Earth day can vary by a millisecond, depending on seasonal wind patterns and temperatures. But this phenomenon has been discounted as the cause for the Venusian discrepancy because such small, random fluctuations should average out over longer periods.

However, the ESA claims that other atmospheric modeling has shown that Venus might undergo decades-long weather cycles which might perhaps cause more lasting changes to the planet's rotational speed. It's an explanation that might account for the 390-second lengthening of the Venusian day.

Pinning down the precise rate of the planet's rotation is not without practical application. "An accurate value for Venus' rotation rate will help in planning future missions, because precise information will be needed to select potential landing sites," said Venus Express scientist Håkan Svedhem.

Venus Express has monitored the planet's atmosphere since 2006 and will continue to do so until at least December 31 2014, though further project funding may be allocated before then.

Source: ESA

About the Author
James Holloway James lives in East London where he punctuates endless tea drinking with freelance writing and meteorological angst. Unlocking Every Extend Extra Extreme’s “Master of Extreme” achievement was the fourth proudest moment of his life.   All articles by James Holloway
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9 Comments

Isn't Venus in a locked orbit with one side facing Earth? If so, wouldn't you expect the rotation period to slow down and speed up as the Earth and Venus change distances in their orbits?

MBadgero
14th February, 2012 @ 07:11 am PST

You appear to be thinking of the moon. Venus is a bit bigger and a bit further away.

Also it goes around the sun, not the earth.

Dave Cross
14th February, 2012 @ 10:22 am PST

:) no, I know the moon is in a locked orbit around the Earth and Venus orbits the Sun, not the Earth.

I thought I read a long time ago that astronomers were surprised that Venus was not in a locked orbit around the Sun, but that radar images of Venus from Earth always showed the same side, and that was how they first determined that Venus' rotation was retrograde.

MBadgero
14th February, 2012 @ 12:23 pm PST

MBadgero, you're thinking of Mercury, not Venus. Mercury is tidally locked around the sun.

Mary Della Valle
14th February, 2012 @ 01:17 pm PST

I'd have appreciated some suggested implications and further details. Presumably it can't recover the speed without drifting closer to the sun? Would the slowing of its rotation cause that to happen anyway? Would the orbiter not have recognised this as well as the slowing? An interesting article, but not as informative as I'd hope for.

Marcus Carr
14th February, 2012 @ 04:22 pm PST

@mbadgero: yesm, that is what I heard those many years ago. That the mystery of the rotation of Venus, was that it was not locked, but mysteriously patterned its rotation to exactly match the position of earth with its rotational displacement. Very strange but true. Would almost certainly have to be something in the dynamic collapse of the nebulous cloud during formation I would think. These other blokes just are not up on science is all.

Paul Higginbotham Sr.
14th February, 2012 @ 06:39 pm PST

@Paul Higgibotham: Yes, that's true, but that's not tidal locking.

@Marcus Carr: No, the increase in the venusian day length will not affect it's orbit around the Sun. However, if Venus had any moons that would affect their orbits around Venus.

This is what's happening to Earth's core but at a much slower rate.

hyperspaced
15th February, 2012 @ 02:31 am PST

@Mary, Mercury also is not tidally locked with one face always to the sun (as Earth's moon is to Earth), but in a 3:2 synchronous rotation.

@Paul, while it's known to many that Venus rotates backwards, I think the history of what was expected before this was known and how it was discovered may lost to the Internet.

MBadgero
15th February, 2012 @ 05:28 am PST

GULP

Fluctuating weather patterns

decades-long weather cycles

Must be manmade global warming!

Goomba
21st February, 2012 @ 08:30 am PST
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