Mars remains in embryonic state

BBC : Mars grew to its present size in about three million years, which may explain why it is about one-tenth the mass of Earth, writes Jennifer Carpenter for the BBC. It probably stayed relatively small because it avoided colliding with planetary building material during the development of our solar system. Nicholas Dauphas of the University of Chicago and Ali Pourmand of the University of Miami in Florida used the ratio of the radioactive elements hafnium-176 and hafnium-177 to estimate how long it took Mars to form: between two million and three million years—a short time compared with the tens of millions of years it took Earth to reach its current size. They think that Mars was already at its current size before dissipation of the nebular gas, when Earth was just beginning to form.