vely dry period in Martian history, but the volcanic-breccia nature of NWA 7034 indicates that water played an important role in its eruption.
|Rubidium (Rb)-Strontium (Sr) isotope plot of a sample of the whole rock (WR) and materials separated magnetically from NWA 7034. The important point is that these different separates (labeled Drk-1 etc. and Light-1) have different Rb/Sr ratios. If they fall on a line on this plot, they define a unique age for the sample based on the known rate of radioactive decay. This unique age for NWA 7034 is 2089 ± 81 million years.|
NWA 7034 is one wet rock. It contains about 0.6 wt% H2O, at least ten times more than any other Martian meteorite. Orbital gamma ray and neutron spectrometer data indicate that the upper half meter or so of the Martian surface between about 50 degrees north and 50 degrees south latitudes contains at least 1 wt% water, so NWA 7034 is more like those regions than are typical Martian meteorites, further emphasizing that NWA 7034 is a lot like the typical crust of Mars.
Big questions remain about the source of the water. It might have been in the magma when it ascended from the interior, in which case it contains important information about the source of water to Mars and perhaps explains why the rock is the product of a strong eruption on Mars. (At even modest depths in planets, magma can have considerable water dissolved in it. At the low pressure near the surface the water leaves solution in the magma, forms bubbles, often so many that the magma shoots out of the volcanic vent explosively. Alternatively, the water might represent liquid water (or ice) already in the crust that was mobilized at some point and altered the pre-existing volcanic rock. Even the younger Martian meteorites have a rich record of such alteration. Additional research is needed to determine whether the water was in the magma or added later.
NWA7034 contains igneous rock fragments containing abundant apatite. This mineral contains water in the form of OH in its crystal structure and because it is igneous, contains important information about the water, including the ratio of deuterium to hydrogen in it. Apatite is altered by water relatively easily, so might record a wet weathering event on Mars, but usually we can see evidence for that, such as tattered margins and compositional changes at those margins. NWA 7034 has excellent igneous apatite in unusual rock fragments, such as the one shown below. The value of determining the OH content of apatite is explained more fully in the PSRD article: How Much Water is Inside Mars.
|Backscatter electron image of a rock clast in NWA 7034 that contains ilmenite (white), apatite (light gray crystals), plagioclase feldspar (gray), and potassium feldspar (dark gray). The OH and deuterium to hydrogen ratio can be measured in the apatite crystals by secondary ion mass spectrometry.|
Martian meteorites continued to be found by national Antarctic programs and private collecting expeditions, such as the one that led from Aziz Habibi to Jay Piatek to Carl Agee. Many of the rocks are similar to those we already have, but the unique properties of NWA 7034 show that continuing to search will yield more than the same old, same old Martian meteorites. It is likely that additional new types will be found eventually. Of course, we could always send spacecraft to fetch samples for us!
|Field photograph of the MIL 03346 Martian meteorite [Data Link from the Meteoritical Bulletin] collected by the Antarctic Search for Meteorites Program (ANSMET) on an ice field in the Miller Range, Antarctica in 2003. Click for more information. Continued searches for meteorites are likely to yield additional new types of Martian meteorites, and other types of meteorites as well.|
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