Venus mysteries blamed on colossal collision

New proposition explains lack of water on planet

NASA

A radar image of Venus' surface in false color, as depicted by the Magellan spacecraft. While not molten any longer, Venus' atmosphere blankets the planet to maintain lead-melting air temperatures — a similar effect scientists think helped keep Mars molten for tens of millions of years.

By Dave Mosher

updated 1:28 p.m. ET Feb. 28, 2008

Venus is made of the same stuff of Earth, but is bone-dry, hot enough to melt lead and has a chokingly thick atmosphere. It even spins backwards.

Astronomers have spent decades trying to explain Venus' mysterious properties. Now one scientist thinks the planet's formation may explain all: Two huge, protoplanetary bodies collided head-on and merged to form our planetary neighbor, but obliterated nearly all water in the process.

"The probability that two protoplanets collided to form Venus is not at all implausible," said John Huw Davies, a geodynamicist at Cardiff University in the U.K. who developed the idea.

Story continues below ↓

A majority of scientists think Earth's moon formed when a protoplanet about the size of Mars smacked into the planet at an angle. Davies thinks Venus was born of a far worse cosmic train wreck.

"What if the moon-Earth collision isn't that big in planetary terms?" Davies told SPACE.com. "A head-on blow between two similarly sized bodies would have been about twice as energetic."

Astronomers have had little time to react to Davies' proposition, which is detailed in a recent issue of the journal Earth and Planetary Science Letters, but already some are wary. Despite the cautionary responses from other scientists, Davies thinks his idea is worth exploring.

Over-baked
Earth harbors an enormous volume of water, even in its searing interior. The life-giving molecule emerges as a vapor with molten lava, carrying with it a radioactive gas known as argon-40. The isotope is generated from radioactive potassium deposits inside of our planet, as well as in Venus.

Davies thinks the relatively low amount of such argon detected in Venus' atmosphere — about 400 times scarcer than on Earth — is a sign that water never really seeped out of the parched, volcano-covered planet.

"The only way water could have out-gassed is very early in Venus' history," Davies said. "The argon-40 gives us a timescale of water leaving the ground because it's produced over time, and only a little of it has been released."

A mega-collision between two bodies of roughly equal size could have provided the energy necessary to rip water, which is made of two hydrogen and one oxygen, into pieces. The hydrogen would escape into space while oxygen would bond with iron and sink to the planet's core.

Click for related content

Images reveal Venus' chaotic atmosphere
Scientists probe mysteries of Venus
Soviet-era Venus images get new life

Although the Earth suffered a catastrophic impact that formed the moon, Davies explained that the process did not dry out the two bodies.

"It wasn't as energetic, limiting the reaction of iron and water," he said.

CONTINUED: "You have to explain that ..."

1 | 2 | 3 | Next >