The Phoenix Lander may have dominated Mars news in recent weeks, but a new study performed here on Earth has turned up a whopper of a finding: The Red Planet seems to have been the victim of a massive hit and run more than four billion years ago.
That is the conclusion of researchers who have finally mapped the edges of something known as the Martian hemispheric dichotomy.
That feature—in which the crust thickness drops from 30 to about 10 miles (50 to 20 kilometers) over a large area that is the most visible feature on Mars—has been known to astronomers for more than 30 years and was long suspected to be due to an asteroid impact that flung most of the crust out the area.
Scientists could not say for sure, however, because the dichotomy's exact shape was unclear: As much as a third of its edge was obscured beneath a 20-mile- (30-kilometer-) high pile of volcanic rock (the second largest feature on Mars) known as the Tharsis Rise.
To uncover the dichotomy's true edge, researchers from the Massachusetts Institute of Technology (M.I.T.) and NASA's Jet Propulsion Laboratory in Pasadena, Calif., used geologic data to probe the structure of the crust underneath Tharsis.
They combined data on the surface height, or topography, with variations in mass revealed by disparities in the surface's gravitational force, looking for telltale changes in mass under Tharsis.
The analysis revealed an elongated round shape measuring about 6,600 by 5,300 miles (10,600 by 8,500 kilometers) and covering 42 percent of the planet. The team calls it the Borealis basin.
"There's basically only one process we know of that will produce a giant elliptical depression...and that's a giant impact," says M.I.T. planetary scientist Jeffrey Andrews-Hanna, lead author of the report, published in Nature.
One longstanding puzzler that did not quite fit with the asteroid idea was that although the asteroid would have left a circular crater or impact basin, the dichotomy seemed at best elliptical in shape. But according to a second Nature study, an asteroid impact still could have caused that shape.
A separate team from the California Institute of Technology in Pasadena and the University of California, Santa Cruz, simulated the effect of impacts made at different energies, speeds and angles on the Martian crust.
They found that the dichotomy's newly revealed shape matched an impact by an asteroid measuring 1,000 to 1,700 miles (1,600 to 2,700 kilometers) wide, moving at about four to six miles (six to 10 kilometers) per second and striking at an angle of 30 to 60 degrees with the ground, with the most likely angle being 45 degrees.
The study also throws cold water on a second objection to the impact hypothesis: Scientists have thought that rock melted by the powerful strike would have simply filled in the basin and erased any record of its effects. According to the new simulation, the impactor would have thrown clear enough of the crust to leave a marked depression.
In yet another consistency check, a second simulation paper in Nature reports that reverberations through the crust caused by the collision could account for a known decline in magnetism in Martian rock on the opposite side of the planet from the dichotomy.
That a large asteroid would have hit Mars is not unexpected: Craters that pepper the inner planets and moons of the solar system indicate that space rocks crashed together like pool balls when the planets were young. For example, researchers believe that our moon was formed when a Mars-size object crashed into a young Earth.
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7 Comments
Add CommentAmazing, how do they come up with this stuff?
Reply | Report Abuse | Link to thishttp://www.FireMe.To/udi
"both more than 1,30 miles (2,000 kilometers) wide."
Reply | Report Abuse | Link to thisProbably this should be 1300 miles, not 130.
-Petri-
Perhaps the impact ripped away much of Mar's atmosphere. Mar's lower mass and gravity would not recapture the atmosphere, the way Earth would. Mars is small, but so is Venus and that planet has a substantial atmosphere.
Reply | Report Abuse | Link to thisThe asteroid size bigger than our moon, from where it came? Is it possible
Reply | Report Abuse | Link to thisthat asteroid of that size can come to so closure and does not got impact with other planet such as jupiter,saturn , urenus & Neptune if it is not from
our solar system .If it is from our solar system than it must be satelite of Mars. Than only it speed before collision was 10km/sec. otherwise it would
be more than 1,40,000km/hr.
rcdohare25@yahoo.co.in
Reply | Report Abuse | Link to thisHave they determined the age of the two ?
could it be that we are not the first intelligent life in the solar system and mars was like earth teeming with life until that asteroid came along?
Reply | Report Abuse | Link to thisI think this catastrophe explanation for all kinds of crust formation on the inner planets (Earth, Moon, Mars etc.) is becoming some kind of an obsession for some scientists. I wonder why, when there are much more probable explanation for the formation of the features in question.
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