a team of scientists, including carnegie's conel alexander and jianhua wang, studied the hydrogen in water from the martian interior and found that mars formed from similar building blocks to that of earth, but that there were differences in the later evolution of the two planets. this implies that
terrestrial planets（类地行星）, including earth, have similar water sources--
chondritic（球粒状陨石的） 2. however, unlike on earth, martian rocks that contain
3 volatiles such as water, do not get recycled into the planet's deep interior. their work will be published in the december 1 issue of earth and planetary science letters.
much
5 surrounds the origin, abundance and history of water on mars. the
6 channels of the martian southern hemisphere speak loudly of flowing water, but this
7 is ancient. consequently, planetary scientists often describe early mars as "warm and wet" and current mars as "cold and dry."
debate in the scientific community focuses on how the interior and crust of mars formed, and how they differ from those of earth. to investigate the history of martian water and other volatiles, scientists at nasa's johnson space center in houston, carnegie, and the lunar and planetary institute in houston studied water concentrations and hydrogen
8 compositions trapped inside crystals within two martian meteorites. the meteorites, called shergottites, were of the same
9 nature, but one was rich in elements such as hydrogen, whereas the other was
10.
the meteorites used in the study contain trapped
basaltic（玄武岩的） liquids, and are
11 samples that sampled various martian
4 element environments. one
1 appears to have changed little on its way from the martian
12 up to the surface of mars. it has a hydrogen isotopic composition similar to that of earth. the other meteorite appears to have sampled martian crust that had been in contact with the martian atmosphere. thus, the meteorites represent two very different sources of water. one sampled water from the deep interior and represents the water that existed when mars formed as a planet, whereas the other sampled the shallow crust and atmosphere.
"there are competing theories that account for the diverse compositions of martian meteorites," said lead tomohiro usui. "until this study there was no direct evidence that primitive martian
13 contained material from the surface of mars."
because the hydrogen isotopic compositions of the two meteorites differ, the team inferred that martian surface water has had a different
14 history than martian interior water. most likely, atmospheric water has preferentially lost the
15 hydrogen
16 to space, and has preferentially retained the heavier hydrogen isotope (deuterium).
that the enriched
meteorite（陨星） has incorporated crustal and atmospheric water could help to solve an important mystery. are martian meteorites that are enriched in
17, such as water, coming from an enriched, deep mantle, or have they been overprinted by interaction with the martian crust?
"the hydrogen isotopic composition of the water in the enriched meteorite clearly indicates that they have been overprinted, so this meteorite tells scientists more about the martian crust than about the martian mantle," alexander said. "conversely, the other meteorite yields more information about the martian interior."
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