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newscientist 00448.txt

#Japanese probe to sniff out why planets lose gases Update 16 september: Epsilon took off at 2pm local time on 14 september. About an hour later the Spectroscopic Planet Observatory for Recognition of Interaction of Atmosphere (SPRINT-A) separated from the launch rocket. Update 27 august 2013: JAXA today cancelled the planned launch of Epsilon due to an abnormality detected 19 seconds before the planned lift off at 1. 45 pm local time. Original article published 26 august 2013bigger isn't always better: Japan's newest rocket scheduled for its maiden voyage this week is designed to be a smaller cheaper way to get science satellites into space. Advances in pre-flight automation mean that the rocket dubbed Epsilon can be ready to lift off in about a week with fewer people in mission control helping to slash costs to about $38 million per launch much cheaper than its heavier labour-intensive predecessors. But perhaps the most exciting aspect of the inaugural launch will be Epsilon's cargo: the world's first space telescope designed to study the planets from afar. The Spectroscopic Planet Observatory for Recognition of Interaction of Atmosphere or Sprint-A will look at Venus and Mars to find out why some worlds lose their atmospheres while others manage to keep a grip on their gases. This will in turn help exoplanet hunters figure out which distant worlds are capable of hosting atmospheres that might support life. Sprint-A will also peer at Jupiter's moon Io the most volcanically active body in the solar system to see how the tiny moon influences Jupiter's mighty auroras. If all goes to plan the Epsilon rocket will launch from Japan's Uchinoura Space center on 27 august at 0445 UTC. It will deploy Sprint-A into low Earth orbit where the spacecraft will take aim at the planets using cameras and sensors that record extreme-ultraviolet light. Extreme UV is a range of light suitable for observing planetary atmospheres says Shujiro Sawai of the Japan aerospace exploration agency (JAXA. Extreme UV from the sun gets bent at the boundary where a planet's atmosphere meets space and the way it is redirected can reveal the atmospheric composition. But extreme UV radiation coming from space is absorbed by the Earth's atmosphere so it is not observable from the ground says Sawai. Very little outer space observation with extreme UV has been done so scientists are expecting new discoveries that no one has imagined ever before. So far our best clues to the original atmospheres of Mars and Venus come from the composition and structure of ancient rocks either meteorites that made it to Earth from those planets or rocks examined by rovers and orbiters. Based on the evidence it seems that Mars Earth and Venus probably had similar atmospheres long ago. But we also know that the sun pumps out a constant stream of charged particles called the solar wind which can ionise gases in a planet's upper atmosphere and pick up the newly charged particles effectively sweeping them away. Earth is protected from the solar wind by a relatively strong global magnetic field which repels charged particles from the sun explains Nick Schneider of the Laboratory for Atmospheric and Space Physics in Boulder Colorado who has worked on Sprint-A. Still the solar wind would have been much stronger when the sun was young and more active. Because Venus is closer to the sun the solar wind might have stripped gaseous water from its early atmosphere leaving a thick haze of mostly carbon dioxide that turned the planet's surface into a hellish desert. And while Mars is farther away it has no global magnetic field. It is thought the solar wind thinned the Red planet's atmosphere over time making it cold and dry. It turns out that most atmospheres have lost a lot of gas over their lifetimes. On Mars it may be as much as 99 per cent. What drives the escaping is a big question says Schneider. Solar stripping is a leading hypothesis but it is not the only runner. For instance others have suggested that Mars lost its atmosphere all of a sudden during a powerful collision with an asteroid or comet. A NASA probe called Maven due to launch in November will orbit Mars to study its atmosphere up close to try to solve the puzzle. Sprint-A will help from afar by looking for the extreme UV radiation generated as the solar wind slams into the upper atmospheres of both Mars and Venus says Sawai. By observing this phenomenon we will investigate how the solar wind affects the upper atmosphere of planets and how the planetary atmosphere escapes into outer space. The results may add a new twist to the search for exoplanets that can support life says Schneider. Until recently a planet's habitability was defined largely by its distance from its star which hints at whether its surface would be warm enough to support liquid water. But it is clear from our solar system that a lot of other factors come into play says Schneider d

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