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Scientists who are investigating how the Earth formed think the best bet for figuring that out is to study Jupiter. Really, Jupiter. It made enough sense to NASA that the agency launched a billion-dollar mission to the giant planet five years ago. The spacecraft, named Juno, arrives at Jupiter today. NPR's Joe Palca has this preview of what the mission hopes to find.
JOE PALCA, BYLINE: Jupiter is the big kahuna of the solar system. More than a thousand earths could fit inside Jupiter. And Jupiter is a totally different kind of planet from Earth.
JONATHAN LUNINE: It's a hydrogen-helium ball of gas.
PALCA: Jonathan Lunine is a planetary scientist at Cornell University and one of the scientists on the Juno mission. Jupiter is what's known as a gas giant.
LUNINE: But deep inside, there might be a core of material like the Earth is made of.
PALCA: Rocks and metals and stuff.
LUNINE: How big it is is anybody's guess.
PALCA: Juno should help reveal how big, as well as a lot of other information about Jupiter. Lunine is particularly interested in one measurement, how much water there is in Jupiter. Some theories say there was a lot of water floating around in the outer solar system when Jupiter was forming and that was ultimately the water that form showed up on Earth - or maybe not.
LUNINE: We might find that water's very depleted in Jupiter. And maybe water was relatively rare in the outer solar system, in which case it would lead us to a big question mark as to where the Earth got its water.
PALCA: But before Juno can collect the data Lunine and other scientists are looking forward to, it has to get into orbit around Jupiter. Guy Beutelschies is director of space exploration systems at Lockheed Martin, the company that built and operates Juno. He says the space probe will be traveling extremely fast when it reaches Jupiter.
GUY BEUTELSCHIES: We're over 130,000 miles an hour.
PALCA: And so it's got to slow down.
BEUTELSCHIES: As we come in right close to the planet, we're going to fire the main engine. It'll fire for about 35 minutes.
PALCA: That will only slow Juno down by about a thousand miles an hour. But that will be enough for Jupiter to capture Juno in its gravitational field.
BEUTELSCHIES: We've only got one shot. If we miss this, we fly by, you know, we're assuming the mission's over.
PALCA: That would be very bad. But even if everything goes well, orbiting near Jupiter is hazardous. Jupiter is surrounded by powerful radiation that can fry any spacecraft that comes near.
BEUTELSCHIES: Once we get into orbit, the timer is ticking. We know, eventually, the radiation is going to damage the electronics.
PALCA: So mission scientists have come up with a plan to minimize Juno's exposure to those radiation belts.
FRAN BAGENAL: We skim over the clouds. And we duck under the radiation belts. And we go from pole to pole.
PALCA: That's Fran Bagenal from the University of Colorado Boulder. She's another Juno scientist. During these close passes, Juno's instruments will be collecting and storing data. But Juno only spends part of each orbit near the planet. After each close-up look, Juno scampers off to safety in a long, loping orbit that will only bring it back to Jupiter weeks later.
BAGENAL: We send all the data back. We sort of recover (imitating sharp exhale). We survived that one. Let's see if we can do it again, trim the orbit a little bit and then come back and then zoom from pole to pole again.
PALCA: Juno won't orbit Jupiter indefinitely. Mission managers expect they'll get about 30 orbits before the planet's radiation starts to take its toll on the spacecraft. And rather than risk losing control of Juno and have it crash into one of Jupiter's icy moons, moons that NASA hopes to someday explore for signs of life, mission managers will send Juno plunging into Jupiter, where it will be swallowed up without so much as a hiccup.
Now, it's not surprising that a planetary scientist like Fran Bagenal is excited about all the information Juno will provide about Jupiter. But she thinks everyone has a reason to be interested in the mission.
BAGENAL: I think we all want to know where we came from, how the solar system got to be the way it is. And key to that is understanding Jupiter.
PALCA: In the coming weeks, Juno should start providing some answers. Joe Palca, NPR News.
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