NASA
Scientists suspect that gas giant planets like Jupiter and Saturn started off with rocky and/or icy bodies about 10 times the mass of Earth. At that point, their gravitational muscles would be strong enough to begin pulling gas from the surrounding region, causing them to balloon in size over time.
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updated 8/20/2010 11:21:24 AM ET 2010-08-20T15:21:24

Jupiter sits today as the solar system's king planet, but it has a troubled past.

In a new study, scientists say baby Jupiter was so strongly bashed by giant Earths that it lost part of its core.

That would explain why Jupiter's core is disproportionately smaller today than sibling planet Saturn, says astronomer Douglas Lin, with the University of California in Santa Cruz.

Scientists suspect that gas giant planets like Jupiter and Saturn started off with rocky and/or icy bodies about 10 times the mass of Earth. At that point, their gravitational muscles would be strong enough to begin pulling gas from the surrounding region, causing them to balloon in size over time.

"In principle, all gas giants need to get to a critical core mass before they can start to accrete gas," Lin told Discovery News. "So the question is: Why is Jupiter's core mass so much smaller than Saturn's even though its total mass is so much bigger?"

Working with computer models, astronomers Shu Lin Li of Peking University in China, Craig Agnor with Queen Mary University of London, and Lin came up with one possible answer: Perhaps Jupiter started off like Saturn, but lost part of its core as it evolved.

The scientists calculated that if an object roughly five times the mass of Earth hit Jupiter, the impact would strike all the way to the planet's core. Add another three or four crashes and Jupiter's core would be eroded to roughly what it is today.

"Jupiter has always had this problem because if we believe the numbers... the core seems to be too small — so small that it cannot accrete gas efficiently in the solar nebula. This scenario gets around the problem," Lin said.

NASA plans to launch a spacecraft called Juno next summer to flesh out details about Jupiter's internal structure, gravity and magnetic fields.

"Planets like Jupiter are known to be common in the universe so we would like to understand how they form," astronomer Dave Stevenson, with the California Institute of Technology in Pasadena, told Discovery News.

"They need not all form the way our Jupiter formed, but certainly if we can understand how our Jupiter formed we'd be a long way toward understanding how our solar system formed. Jupiter is the 800-pound gorilla in the room. Once formed, it has a major effect on the architecture of the solar system," Stevenson said.

Li's paper appears online at Cornell University's arxiv.org website.

© 2012 Discovery Channel

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Photos: Jewels from Jupiter

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  1. Jupiter loses a stripe

    The weather on Jupiter is changeable, as these before-and-after pictures show. The photograph on the left shows Jupiter as seen in June 2009. The photo on the right, taken on May 9, 2010, reveals that one of the planet's prominent dark cloud belts has faded away. The lightening of the South Equatorial Belt is due to atmospheric changes. Both pictures were taken by Anthony Wesley, an amateur astronomer in Australia. (Anthony Wesley via The Planetary Society) Back to slideshow navigation
  2. Family portrait

    Launched in 1989, the Galileo spacecraft has photographed Jupiter as well as several of the giant planet's satellites. Here's a montage that shows Jupiter's Great Red Spot and the four largest moons. From top, they are Io, Europa, Ganymede and Callisto. (NASA) Back to slideshow navigation
  3. Cratered Callisto

    Callisto is considered the most cratered celestial body in the solar system. The false-color overlay at right exaggerates the moon's surface features, including the Valhalla impact structure near the center of the disk. (NASA) Back to slideshow navigation
  4. Dark face

    Colors are enhanced in this view of Ganymede's trailing hemisphere, highlighting the moon's polar caps. The violet color indicates where small particles of frost may be scattering light on the blue end of the spectrum. (NASA) Back to slideshow navigation
  5. Cloudy weather

    The mosaic at left shows the true colors of the cloud patterns in Jupiter's northern hemisphere. The rendition at right uses false colors to represent the height and thickness of the cloud cover. (NASA) Back to slideshow navigation
  6. This is the Spot

    A true-color picture captures the subtle shadings of Jupiter's Great Red Spot, a massive, long-lived storm system in the planet's thick atmosphere. (NASA) Back to slideshow navigation
  7. A big splash on Europa

    A computer-generated perspective view shows the Pwyll impact crater on Europa, an ice-covered moon of Jupiter. The heights are exaggerated, but the central peak indicates that the crater may have been modified shortly after its formation by the flow of underlying warm ice. (NASA) Back to slideshow navigation
  8. A blast at Io

    This image of Io, thought to be the solar system's most volcanically active world, shows the plumes of two eruptions. One plume can be seen at the very edge of the disk, the other is puffing up from the dark volcanic ring near the center of the disk. (NASA) Back to slideshow navigation
  9. Lava light

    An active volcanic eruption on Jupiter's moon Io flares in an image taken in February 2000 by the Galileo spacecraft. The dark L-shaped lava flow to the left of center marks the site of energetic eruptions in November 1999 at Tvashtar Catena, which is a chain of giant volcanic calderas. The two small bright spots at left side of image are sites where molten rock is exposed to the surface at the toes of lava flows. (NASA) Back to slideshow navigation
  10. Crazy quilt

    The thin crust of Europa's Conamara region is criss-crossed by craters, cracks and lines - indicating that the surface ice was repeatedly disrupted. The colors, which are enhanced in this view, show where light ice crystals and dark contaminants have settled onto the surface. (NASA) Back to slideshow navigation
  11. A moving moon

    In a picture taken in April 2001 by NASA's Cassini spacecraft, the moon Io looks like a marble set against the background of Jupiter. Io is the giant planet's third-largest satellite. (NASA) Back to slideshow navigation
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