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Lightning crackles in the atmosphere of Earth's "evil twin" Venus, while the meagre remnants of suspected bygone oceans continue to be whipped off the planet and lost to space, say scientists.
They unveiled yesterday a series of findings from the European Space Agency's Venus Express mission to the
planet closest to Earth not just in distance but also in size.
Venus, the second planet from the Sun, and Earth, the third, started out as virtual twins, according to scientists.
But at some point in their 4.5-billion-year histories, something went horribly wrong on Venus. The greenhouse effect ran amok, making Venus a hellish kiln - its surface hot and dry, its crushing atmosphere made up of carbon dioxide permeated by clouds of sulfuric acid that cloak the planet.
"The findings show, of course, that the planet as it stands now is different from the Earth - the high temperatures, the high pressures and the composition. But the processes, we now understand, are much more Earth-like," said Hakan Svedhem, Venus Express team project scientist.
"The two planets were, in fact, very similar in the earlier days of the solar system. And they have then evolved in different directions, but according to the same rules and explanations."
The findings were published in the journal Nature.
A previous mission to Venus had detected hints that lightning was flashing through the planet's atmosphere. The instruments aboard Venus Express were able to unambiguously confirm the presence of lightning, the scientists said.
"They look like lightning bursts, very short discharges of electrical energy," said Christopher Russell of the Institute of Geophysics and Planetary Physics at the University of California, Los Angeles.
Long ago, Dr Svedhem said, Venus was a much wetter place, probably with liquid water oceans like those on Earth and like those that scientists think were once on Mars.
"Eventually the oceans boiled off, and all the water ended up as water vapour in the atmosphere."
Equipment aboard the spacecraft allowed scientists to observe how particles are escaping from the atmosphere. The dominant escaping ions, the scientists found, include oxygen and hydrogen in the ratio that corresponds to water, which may help to explain how Venus lost its original water to space.
Venus, unlike Earth, lacks a magnetic field to protect its atmosphere from the solar wind, the stream of electrically charged particles emitted by the Sun. Thus, the solar wind interacts directly with the upper atmosphere of Venus, causing Venus' atmosphere to lose its gases in the form of ionised particles, the scientists said.
Liquid water oceans may have been present on Venus as recently as one billion to three billion years ago, Dr Svedhem said.
The scientists also gathered three-dimensional images of a vast rotating vortex of clouds at the South Pole and compiled the best global map of atmospheric temperatures to date.
Some scientists dub Venus Earth's "evil twin". Its surface temperatures top 400C and its surface pressure is 100 times that of Earth.
"How did it all go wrong?" asked Andrew Ingersoll of the California Institute of Technology in a commentary accompanying the findings.
- Reuters
