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Size of Mars said down to early birth

Size of Mars said down to early birth
NASA's Hubble Space Telescope took this close-up of the red planet Mars when it was just 55 million miles (88 million kilometers) away on December 17, 2007. Mars will be at its brightest on December 24, 2007 as it aligns directly opposite of the sun, and will not be as visible for another nine years. This color image was assembled from a series of exposures taken within 36 hours of the Mars closest approach with Hubble's Wide Field and Planetary Camera 2. (UPI Photo/NASA/ESA/Hubble Heritage Team) | License Photo

CHICAGO, May 25 (UPI) -- U.S. scientists studying Mars say its rapid creation during the formation of the solar system explains its small size relative to Earth, which formed later.

Geophysicists Nicolas Dauphas at the University of Chicago and Ali Pourmand at the University of Miami said Mars probably is not a terrestrial planet like Earth, which grew to its full size over 50 million to 100 million years via collisions with other small "embryo" bodies in the solar system, a National Science Foundation release said Wednesday.

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"Earth was made of embryos like Mars, but Mars is a stranded planetary embryo that never collided with other embryos to form an Earthlike planet," Dauphas said.

Mars developed far more quickly than Earth, in as little as 2 million to 4 million years after the birth of the solar system, the researchers said.

The study provides evidence for this idea, first proposed 20 years ago on the basis of planetary growth simulations.

"We thought that there were no embryos in the solar system to study, but when we study Mars, we are studying embryos [of the kind] that eventually made planets like Earth," Pourmand said.

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Computer models suggest Mars must have reached half its present size less than 2 million years after the formation of the solar system, the researchers said.

The results of their study, funded by the National Science Foundation, were published in the journal Nature.

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