domingo, 25 de septiembre de 2011

Massive Impact Crater on Earth May Yield Clues to Ancient Climate Change on Mars

MarsHemispheresThe prehistoric Chicxulub crater left by an asteroid collision in Mexico's Yucatan Peninsula could yield clues about what Mars was like billions of years ago, according to NASA planetary geologist Adriana Ocampo, an expert about what impact craters can reveal about planet formation. Her work could shed light on a giant crater on the surface of Mars -the largest in the Solar System- that was created by an impact from an object the size of Pluto.

Astronomers have been puzzled for decades about a huge dent on the surface of Mars -- the largest known crater in the solar system -- and new evidence suggests it was caused by the impact of an asteroid the size of Pluto.

The Mexican crater, known as Chicxulub, was created when an asteroid that smacked into Earth 65 million years ago in a catastrophe that wiped out around half the planet's species and was perhaps responsible for the dinosaurs becoming extinct.

Studying the debris spewed by the collision may answer questions about radical changes in atmosphere that can result from massive asteroid hits, Ocampo, has been studying the Yucatan crater for a decade, told Reuters.

"It's a natural laboratory because of its similarities to what we can find on other planets like Mars where humans can't go," Ocampo said of Mexico's smaller crater.

The crater on Mars, measuring 5,300 miles across, is so big that it has left half the planet at a lower elevation.

NASA's Mars Reconnaissance Orbiter and Mars Global Surveyor have provided detailed information about the elevations and gravity of the Red Planet's northern and southern hemispheres. A new study using this information may solve one of the biggest remaining mysteries in the solar system: Why does Mars have two strikingly different kinds of terrain in its northern and southern hemispheres? The huge crater is creating intense scientific interest.

The mystery of the two-faced nature of Mars has perplexed scientists since the first comprehensive images of the surface were beamed home by NASA spacecraft in the 1970s. A giant northern basin that covers about 40 percent of Mars' surface, sometimes called the Borealis basin, is the remains of a colossal impact early in the solar system's formation, the new analysis suggests. At 8,500 kilometers (5,300 miles) across, it is about four times wider than the next-biggest impact basin known, the Hellas basin on southern Mars.

Astronomers from UC Santa Cruz, Caltech and MIT proposed that a giant meteorite or comet more than 1,200 miles in diameter - sped toward Mars at up to 21,600 miles an hour, crashed at a steep slant into the planet about 3.9 billion years ago, and blasted out the huge elliptical scar that now forms all of the planet's northern lowlands, while leaving the southern highlands relatively undamaged. And the giant crash, the scientists agreed, could even have happened without melting any large part of the planet. It must have been the biggest blast in the history of our solar system - the impact of a planetary bomb as powerful as a billion tons of TNT.

If the theories are right, it blasted out the biggest crater that any planet has ever survived. It was a convulsion far bigger than the puny one that drove the dinosaurs to extinction on Earth only 65 million years ago. One region of the surface is the huge oval-shaped scar of the impact itself, covering more than a third of the Martian surface and including all the vast low-lying lands of the planet's far north where the Phoenix spacecraft is now digging up buried nuggets of ice. The other is the even larger highland region to the south, marked by deep canyons, high mountains and the remains of giant volcanoes.

The huge, dark elliptical scar with its thinner Martian crust in the north is more than 6,500 miles long and 5,300 miles wide, and few craters have punctured its smooth plains. Astronomers call it the Borealis Basin.

The other, covering virtually the entire southern hemisphere, averages up to 5 miles higher in elevation and is heavily cratered - an indication that its surface, untouched by the impact, is older than the northern lowlands, scientists believe.

An accompanying report calculated that the impacting object that produced the Borealis basin must have been about 2,000 kilometers (1,200 miles) across. That's larger than Pluto. It appears to have held an ocean in crater the size of the combined areas of Asia, Europe and Australia,the early days of the planet, before Mars lost so much of its atmosphere and the water either sublimated away or froze beneath the surface.

Mexico's crater is a much smaller 100 miles in diameter and is now half a mile underground, where rocks and earth have buried it over millions of years. Space geologists believe the asteroid hit in the Caribbean Sea, probably causing a huge tsunami.

Information from Chicxulub could also give clues about whether or not there was water on the surface of Mars long after the planet was dented by the massive asteroid hit.

Scientists have detected frozen water on the surface of the red planet. Martian seas could have disappeared when the planet was bombarded by smaller meteors that changed its atmosphere and dried it out, Ocampo said.

The Daily Galaxy

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