May 26, 2011
Scientists Explain Why Mars Is Smaller Than Earth
Scientists on Wednesday said they believed they could explain why Mars is smaller than Earth.
They report in the journal Nature that Mars had a growth spurt, developing in as little as two to four million years after the birth of the Solar System, but then suddenly stopped.
Earth grew to its full size over 50 to 100 million years, most likely through agglomeration as it collided with other young space rocks.
"Earth was made of embryos like Mars, but Mars is a stranded planetary embryo that never collided with other small space bodies in the Solar System," said Nicolas Dauphas of the University of Chicago.
The timescale is based on calculations of the time it takes for the radioactive isotope hafnium 182 to decay into tungsten 182.
The source material for this is meteorites that have fallen to Earth and whose chemical signature points to infant Mars as the origin.
Previous estimates of the formation of Mars ranged as high as 15 million years.
Mars is over half of Earth's size. According to NASA's website, its diameter at the equator is 4,245 miles compared with Earth's 7,972 miles.
Image Caption: Mars measures approximately 6,794 kilometers (4,221 miles) in diameter. Earth, with a diameter of 12,750 kilometers (7,926 miles) grew to almost twice the size of Mars via collisions with smaller planetary embryos. Mars is a planetary embryo that escaped such collisions, scientists report in the May 25, 2011, issue of the journal Nature. Credit: NASA/JPL
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