taylormemer
24th July 2004, 14:44
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Puzzling Differences In Jupiter And Saturn
By Robert Roy Britt
Senior Science Writer
posted: 06:52 am ET
20 July 2004
Scientists aren't sure what the interiors of Jupiter and Saturn look like or how the planets formed. But a new study of their insides suggests they took different paths to giant status.
Researchers modelled 50,000 what-ifs of internal structure using real data from the two planets and lab experiments that show how material behaves under extreme pressure. They found Saturn has a huge core and Jupiter may have none.
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http://a52.g.akamaitech.net/f/52/827/1d/www.space.com/template_images/scienceastronomy/i_scitues_images_icon.gif Images
http://www.space.com/images/040720_saturn_globe_02.jpg
Saturn seems to have a significant core of iron, carbon and other elements heavier than hydrogen. Credit: NASA/ESA/Hubble
http://www.space.com/images/040720_jupiter_globe_02.jpg
Jupiter appears not to have a significant core. It's bulk -- 318 times the mass of Earth -- my have something to do with that. Credit: NASA/Cassini
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"Heavy elements are concentrated in Saturn's massive core, while those same elements are mixed throughout Jupiter, with very little or no central core at all," said Didier Saumon of the Los Alamos National Laboratory.
The result, published last week in the Astrophysical Journal, agrees with similar studies but is far more comprehensive. "These conclusions are now very firm," Saumon said in a telephone interview.
Why So different?
Both planets are about 70 percent hydrogen. Most of the rest of their makeup is helium. The remaining "heavy elements" include iron, silicon, carbon, nitrogen and oxygen.
But why would only Saturn end up with a heavy core? The question is a troubling one for planet-formation theorists.
The leading model for giant planet formation involves first growing a core of rock and ice several times the mass of Earth. Once big enough, this core easily attracts and holds onto gas, sweeping through the nascent solar system and glomming on to hydrogen and other elements left behind in the Sun's formation.
But this so-called core-accretion model has a problem. It takes millions of years to build a gas giant, and observations of other star systems suggests the gas swirling around a newborn star doesn't hang around that long.
An alternative theory (http://www.space.com/scienceastronomy/solarsystem/planet_formation_020709-1.html) has a gas giant collapsing out of a knot of gas. This method can form the seed of a Jupiter-like planet in just 1,000 years or so. But the theory hasn't allowed full modeling of a finished planet so far, Saumon said, and only a handful of researchers embrace it.
As Saumon points out, if Jupiter has little or no core, it would seem to lend credence to the gravitational collapse idea. He's not ready to give up on the standard model of core accretion, however, in part because scientists prefer common solutions to explain similar-looking, neighboring objects.
"We don't really believe the two planets would have formed by two processes so different," he said.
Crushing Pressure
Saumon speculates on what might have happened with Jupiter: The king of the nine planets contains 318 times more mass than Earth (Saturn contains about 95 Earth masses). Jupiter's core would have been melted to liquid under intense pressure during formation.
"If it accreted gas very, very fast, this large amount of mass would come crashing down fast enough to induce mixing of the core," he said. The sort of heavy elements which, in the center of Saturn form a core, were instead mushed around and spread throughout Jupiter.
He cautions that more observations are needed to settle the case.
"You can't see the core," Saumon said. "The measurements we have are very indirect." Rapid rotation the giants -- each spins around once about every 10 Earth-hours -- causes them to bulge at their midsections in a way that depends on internal structure, and space probes have measured the bulges in the gravity fields of the planets during flybys. "It's a very indirect way of determining the internal structure. But that's all we have."
Gravity measurements of Saturn by the Cassini (http://www.space.com/cassini/) spacecraft, especially if it is allowed to operate beyond the four years of the planned primary mission, could improve understanding of its deep mysteries, Saumon said.
_____________________________________________________________
http://a52.g.akamaitech.net/f/52/827/1d/www.space.com/template_images/scienceastronomy/i_scitues_morestories_icon.gif More Stories
Cassini Struck by Hailstorm of Ring Particles at Saturn (http://www.space.com/scienceastronomy/cassini_dust_040712.html)
Cassini Finds Mud in Saturn's Rings (http://www.space.com/scienceastronomy/saturn_rings_040708.html)
Wild New Theory for Building Planets (http://www.space.com/scienceastronomy/solarsystem/planet_formation_020709-1.html)
Did Jupiter Bully Other Planets In Sibling Rivalry? (http://www.space.com/scienceastronomy/solarsystem/jupiter_pushy_991208.html)
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CREDIT: SPACE.com
Image Of The Day
July 23, 2004
http://a52.g.akamaitech.net/f/52/827/1d/www.space.com/template_images/iod/iod_viewer_photoicon_text.gif Spectacular Detail
http://a52.g.akamaitech.net/f/52/827/1d/www.space.com/images/040723_iod_rings_04.jpg
Saturn's rings have been seen in many colors. Attempts to highlight the contrast resulted in a garish image from the Voyager mission. Infrared or ultraviolet imagery is colorized so otherwise invisible radiation reflected by the ring particles are pleasing to our eyes.
This new view from the Cassini spacecraft captures the true colors of the rings, according to astronomers at the Space Science Institute, which manages the probe's camera.
Cassini was beneath the rings on June 21, about 4 million miles (6.4 million kilometers) from Saturn when it took this picture. It was released yesterday.
Saturn has several rings separated by distinct gaps. The ring system begins from the inside out in this order: D, C, B, A, F, G, E.
The brightest part of the rings in this image, curving from the upper right to the lower left, is the B ring. Many bands throughout the B ring have a pronounced sandy color. Cassini's images show that color variations in the rings are more pronounced in this viewing geometry than they are when seen from Earth.
The rings are made primarily of water ice with, as Cassini showed recently, rock or mud sprinkled in. Since pure water ice is white, it is believed that different colors in the rings reflect different amounts of contamination by other materials such as rock or carbon compounds.
The Cassini-Huygens mission is a cooperative project of NASA, the European Space Agency and the Italian Space Agency
Credit: NASA/JPL/Space Science Institute
_____________________________________________________________
http://a52.g.akamaitech.net/f/52/827/1d/www.space.com/images/scitues_jupsaturncores_ff.jpg
Puzzling Differences In Jupiter And Saturn
By Robert Roy Britt
Senior Science Writer
posted: 06:52 am ET
20 July 2004
Scientists aren't sure what the interiors of Jupiter and Saturn look like or how the planets formed. But a new study of their insides suggests they took different paths to giant status.
Researchers modelled 50,000 what-ifs of internal structure using real data from the two planets and lab experiments that show how material behaves under extreme pressure. They found Saturn has a huge core and Jupiter may have none.
_____________________________________________________________
http://a52.g.akamaitech.net/f/52/827/1d/www.space.com/template_images/scienceastronomy/i_scitues_images_icon.gif Images
http://www.space.com/images/040720_saturn_globe_02.jpg
Saturn seems to have a significant core of iron, carbon and other elements heavier than hydrogen. Credit: NASA/ESA/Hubble
http://www.space.com/images/040720_jupiter_globe_02.jpg
Jupiter appears not to have a significant core. It's bulk -- 318 times the mass of Earth -- my have something to do with that. Credit: NASA/Cassini
_____________________________________________________________
"Heavy elements are concentrated in Saturn's massive core, while those same elements are mixed throughout Jupiter, with very little or no central core at all," said Didier Saumon of the Los Alamos National Laboratory.
The result, published last week in the Astrophysical Journal, agrees with similar studies but is far more comprehensive. "These conclusions are now very firm," Saumon said in a telephone interview.
Why So different?
Both planets are about 70 percent hydrogen. Most of the rest of their makeup is helium. The remaining "heavy elements" include iron, silicon, carbon, nitrogen and oxygen.
But why would only Saturn end up with a heavy core? The question is a troubling one for planet-formation theorists.
The leading model for giant planet formation involves first growing a core of rock and ice several times the mass of Earth. Once big enough, this core easily attracts and holds onto gas, sweeping through the nascent solar system and glomming on to hydrogen and other elements left behind in the Sun's formation.
But this so-called core-accretion model has a problem. It takes millions of years to build a gas giant, and observations of other star systems suggests the gas swirling around a newborn star doesn't hang around that long.
An alternative theory (http://www.space.com/scienceastronomy/solarsystem/planet_formation_020709-1.html) has a gas giant collapsing out of a knot of gas. This method can form the seed of a Jupiter-like planet in just 1,000 years or so. But the theory hasn't allowed full modeling of a finished planet so far, Saumon said, and only a handful of researchers embrace it.
As Saumon points out, if Jupiter has little or no core, it would seem to lend credence to the gravitational collapse idea. He's not ready to give up on the standard model of core accretion, however, in part because scientists prefer common solutions to explain similar-looking, neighboring objects.
"We don't really believe the two planets would have formed by two processes so different," he said.
Crushing Pressure
Saumon speculates on what might have happened with Jupiter: The king of the nine planets contains 318 times more mass than Earth (Saturn contains about 95 Earth masses). Jupiter's core would have been melted to liquid under intense pressure during formation.
"If it accreted gas very, very fast, this large amount of mass would come crashing down fast enough to induce mixing of the core," he said. The sort of heavy elements which, in the center of Saturn form a core, were instead mushed around and spread throughout Jupiter.
He cautions that more observations are needed to settle the case.
"You can't see the core," Saumon said. "The measurements we have are very indirect." Rapid rotation the giants -- each spins around once about every 10 Earth-hours -- causes them to bulge at their midsections in a way that depends on internal structure, and space probes have measured the bulges in the gravity fields of the planets during flybys. "It's a very indirect way of determining the internal structure. But that's all we have."
Gravity measurements of Saturn by the Cassini (http://www.space.com/cassini/) spacecraft, especially if it is allowed to operate beyond the four years of the planned primary mission, could improve understanding of its deep mysteries, Saumon said.
_____________________________________________________________
http://a52.g.akamaitech.net/f/52/827/1d/www.space.com/template_images/scienceastronomy/i_scitues_morestories_icon.gif More Stories
Cassini Struck by Hailstorm of Ring Particles at Saturn (http://www.space.com/scienceastronomy/cassini_dust_040712.html)
Cassini Finds Mud in Saturn's Rings (http://www.space.com/scienceastronomy/saturn_rings_040708.html)
Wild New Theory for Building Planets (http://www.space.com/scienceastronomy/solarsystem/planet_formation_020709-1.html)
Did Jupiter Bully Other Planets In Sibling Rivalry? (http://www.space.com/scienceastronomy/solarsystem/jupiter_pushy_991208.html)
_____________________________________________________________
CREDIT: SPACE.com
Image Of The Day
July 23, 2004
http://a52.g.akamaitech.net/f/52/827/1d/www.space.com/template_images/iod/iod_viewer_photoicon_text.gif Spectacular Detail
http://a52.g.akamaitech.net/f/52/827/1d/www.space.com/images/040723_iod_rings_04.jpg
Saturn's rings have been seen in many colors. Attempts to highlight the contrast resulted in a garish image from the Voyager mission. Infrared or ultraviolet imagery is colorized so otherwise invisible radiation reflected by the ring particles are pleasing to our eyes.
This new view from the Cassini spacecraft captures the true colors of the rings, according to astronomers at the Space Science Institute, which manages the probe's camera.
Cassini was beneath the rings on June 21, about 4 million miles (6.4 million kilometers) from Saturn when it took this picture. It was released yesterday.
Saturn has several rings separated by distinct gaps. The ring system begins from the inside out in this order: D, C, B, A, F, G, E.
The brightest part of the rings in this image, curving from the upper right to the lower left, is the B ring. Many bands throughout the B ring have a pronounced sandy color. Cassini's images show that color variations in the rings are more pronounced in this viewing geometry than they are when seen from Earth.
The rings are made primarily of water ice with, as Cassini showed recently, rock or mud sprinkled in. Since pure water ice is white, it is believed that different colors in the rings reflect different amounts of contamination by other materials such as rock or carbon compounds.
The Cassini-Huygens mission is a cooperative project of NASA, the European Space Agency and the Italian Space Agency
Credit: NASA/JPL/Space Science Institute
_____________________________________________________________