Venus became the solar system's baking hellhole by making a classic real estate mistake: building in the wrong neighborhood, according to research released Wednesday presenting the first comprehensive findings from Europe's Venus Express spacecraft.
Instruments aboard the craft, which has been orbiting the haze-shrouded planet for almost 20 months, show that Venus and Earth are not just sister planets, but are nearly twins in important ways.
They are comparable in size and mass, have similar amounts of carbon dioxide and once probably possessed nearly equal amounts of water.
But while Earth matured into the solar system's beauty queen, replete with forests, rivers and oceans, Venus, about 30% closer to the sun, lost nearly all its water. Its clouds today are filled with sulfuric acid.
The reason? Location, location, location.
"It's a sobering little tale," said Andrew Ingersoll, an astronomer at Caltech in Pasadena, who wrote one of the nine research articles published in the current issue of the journal Nature. "Venus is just too close to the sun."
Much of this was known, or suspected, about the planet before the European Space Agency launched Venus Express in November 2005. It's the 30th spacecraft to visit the solar system's second planet from the sun, beginning with NASA's Mariner 2 mission in 1962.
The craft is the first European mission to Earth's closest planetary neighbor, and the first of any kind to tour Venus in a decade.
With a suite of modern instruments, including spectrometers and imagers capable of piercing the thick clouds down to the planet's surface, the 1,300-pound spacecraft is probing Venus' poisonous atmosphere in unprecedented detail.
"They've made some progress on questions that have been around for a while," Ingersoll said.
Specifically, Venus Express was able to confirm a much-debated measurement by the Pioneer mission in 1978, which found large amounts of deuterium -- a heavier isotope of hydrogen -- in the atmosphere.
This is consistent with a massive loss of hydrogen to space, Ingersoll said. The mechanism probably involved intense radiation from the sun, 67 million miles away, breaking the enormous quantities of water vapor in the atmosphere into its constituents of hydrogen and oxygen.
The hydrogen then escaped to space, while the oxygen and deuterium, along with carbon dioxide, stuck around, heating the atmosphere and making the surface, at about 870 degrees Fahrenheit, hotter than the innermost planet, Mercury.
