sábado, 24 de novembro de 2012

Study Suggests Earth, Mars Share Primordial Water Source, Chondritic Meteorites

In their earliest eras, the Earth, Mars and the solar system's other rocky planets drew water from the same source, chondritic meteorites -- not usually credited comets, suggest recent studies of two primitive space rocks of Martian origin.

The findings also suggest the Earth and Mars evolved quite differently, supporting wider evidence of a significant surface water presence in the distant Martian past that disappeared over time along with a more substantial atmosphere.

NASA's closely watched Curiosity rover has been at work on similar "habitability" questions on the red planet since its much heralded landing at the base of Mount Sharp in Gale Crater
nearly four months ago (Aug. 6).

On Earth, researchers from the Tokyo Institute of Technology, NASA's Johnson Space Center, the Lunar and Planetary Institute and the Carnegie Institution for Science drew their conclusions from the 79 gram Larkman Nunatak 06319 meteorite, which was recovered from Antartica in 2006, and the 82 gram Yamato 980459 Martian rock found in Antarctica in 1998, two of 62 rocks listed in NASA's Martian Meteorite Compendium.

Their findings are set for publication in the Earth and Planetary Science Letters of Dec.1, as "Origin of water and mantlecrust interactions on Mars inferred from hydrogen isotopes and
volatile element abundances of olivine-hosted melt inclusions of primitive shergottites."

The two volcanic rocks differ in the richness of their elemental composition, affording telltale comparisons between their ratios of elemental hydrogen and deuterium, the isotope of hydrogen with a neutron added to the nucleus.

"These meteorites contain trapped basaltic liquids, not unlike the basalts that erupt on Hawaii," John Jones, an experimental petrologist from NASA/Johnson, a study co-author and a member of the Curiosity science team, explained in a statement. "They are pristine samples that have sampled various Martian volatile element environments."

Yamato 980459's H/D ratio was Earth-like, suggesting a similar primordial origin for Martian water.

But the amount of water trapped in Yamato's crystalline structures was quite dry, 15 to 47 parts per million. Yamato, the "depleted" meteorite, made its way from the Martian mantle to the crust little altered before it was blasted away on a trajectory that would bring it to Earth, the five member research team led by Tomohiro Usui, of the Tokyo Institute of Technology and a former NASA/ LPI postdoctoral fellow, surmises.

Lar 03619, the "enriched" meteorite, exhibited 10 times as much trapped water and an H/D ratio that suggested interactions with a surface reservoir in the Martian crust as well as the atmosphere, according to researchers.

The sculpted channel features in the ancient terrain of the Martian southern hemisphere suggest as much, they note in a collection of pre-publication announcements from the four study institutions.

Source: www.aviationweek.com

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