A European spacecraft has arrived at Venus to study Earth's hot, hazy sister planet. It is only the latest of many space probes trying to understand why our closest planetary neighbor is an unpleasant greenhouse, rather than a more moderate place supporting life.
Astronomers once thought of Venus as Earth's twin. The two are roughly the same size with about the same mass, density, and gravity. Now, after more than 20 U.S. and Soviet missions to the planet between 1961 and 1994, astronomers consider it Earth's "evil" twin.
The European Space Agency's first mission to the planet, the Venus Express, is to gather data to help explain why.
It has entered orbit after a five-month, 400-million-kilometer journey from the Russian space agency launch site in Kazakhstan. The Venus Express will spend the next month adjusting its extremely oval nine-day path to a circular one lasting one day.
"I was a very happy man today, together with my fellow scientists," said the mission's chief scientist, Hakan Svedhem of the Netherlands. "This is really a fantastic experience to see that we end up exactly in the position we wanted to be. Now our work starts. That's very nice work."
Svedhem says the European orbiter will pass through Venus' atmosphere for at least 500 days, using state-of-the-art sensors to answer questions left by previous explorer craft.
"The noble goal of it all is to understand why is Venus such as it is," he explained. "Why is it not more like Earth? We do know we have life on Earth. We think we do not have any life on Venus. Why is that?"
Venus is broiling at 450 degrees Celsius, shrouded by sulfuric acid clouds and a dense carbon dioxide atmosphere nearly 100 times thicker than Earth's. A senior editor with Astronomy magazine, Rich Talcott, says this blanket traps heat from the sun, preventing it from escaping.
"There is excellent evidence that Venus was once much more similar to Earth, but what seems to have happened is that it is just a little bit closer to the sun than Earth is and it receives approximately twice as much heat from the sun as Earth," he explained. "That is enough to keep water from existing as liquid on the surface. Over the course of a few billion years, that has been able to drive off all the water on Venus. That means that any of the carbon dioxide that is in the atmosphere cannot get pulled into the oceans as it has on Earth."
By studying Venus, researchers hope to learn lessons that might apply to Earth, where carbon dioxide pollution and other greenhouse gases from industry and automobiles collect in our atmosphere.
"That has a lot of importance to scientists," he noted. "Here on Earth, we are wondering if increases in carbon dioxide will affect the future of Earth's climate. So they are looking at Venus to see if perhaps how conditions that exist there may relate to Earth."
The science gathering phase of Europe's Venus Express is to begin June 4, once it reaches its final orbit and it instruments have been checked.