The chemical composition of Martian surface material is deduced using two different approaches: Direct measurements by the Alpha-Proton-X-Ray Spectrometer (APXS) flown to Mars by the Pathfinder mission, and by analyses of SNC meteorites, which are believed to be rocks from Mars. Several surface rocks of Mars measured by the APXS have different chemical compositions than those of SNC meteorites. Both compositions are also different from the Martian soil found at the Pathfinder landing site. However, this soil, which covers the surface of Mars, seems to be a mixture of local rocks, SNC meteoritic material, and an iron-rich component. From selected element correlations found in SNC meteorites and Martian surface samples, the bulk chemical composition of the planet is obtained. According to this model, Mars has an iron rich core of about 22 wt.%, which is relatively smaller than the Earth's core of about 33.5 %.

We report noble gas data for 37 H chondrites collected from the Allan Hills by EUROMET in the 1988-1989 field season. Among these are 16 specimens with high levels (>100 krad) of natural thermoluminescence (NTL), originally interpreted as signaling their derivation from a single meteoroid with an orbit that became Earth-crossing similar to 100 ka ago. One of these 16 is an H3 chondrite with a cosmic-ray exposure age of similar to 33 Ma and clearly represents a separate fall. The other 15 H4-6 chondrites derive from three separate meteoroids, each of which is represented by a five or six member group. These groups have mean exposure ages of 3.7, 4.1, and 6.6 Ma: the middle-group members all contain solar Ne. The two younger groups also seem to each include a few H chondrites with normal NTL levels.Measurements of cosmogenic Be-10 (1.5 Ma), Al-26 (710 ka), and Cl-36 (301 ka) in 14 of the high-NTL chondrites indicate that all reflect a simple irradiation history. In contrast, many of a different (38 member) randomly selected suite of Antarctic H chondrites seem to have different cosmic-ray irradiation histories. The 3.7 and 6.6 Ma groups from the 37 member Allan Hills suite come from about 5-30 and about 5-10 cm depths in 80-125 and 60-125 cm radius meteoroids, respectively.

Meteoritics & Planetary ScienceVolume 32, Issue 1 p. 4-5 Free Access In the tracks of the martians Ludolf Schultz, Ludolf SchultzSearch for more papers by this authorDerek Sears, Derek Sears EditorsSearch for more papers by this author Ludolf Schultz, Ludolf SchultzSearch for more papers by this authorDerek Sears, Derek Sears EditorsSearch for more papers by this author First published: 04 February 2010 https://doi.org/10.1111/j.1945-5100.1997.tb01230.xAboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat No abstract is available for this article. Volume32, Issue1January 1997Pages 4-5 ReferencesRelatedInformation

Cosmic-ray-exposure ages of meteorites provide information on the collisional history of their parent bodies and the delivery mechanism of meteorites to Earth. The exposure-age distributions of ordinary chondrites show distinct patterns for H, L, and LL types, consistent with their origin on different parent bodies. The exposure-age distributions of howardites, eucrites. and diogenites (HEDS) show a common pattern with major peaks at 22 Ma and 38 Ma This provides additional evidence for a common origin of the HED meteorites, possibly 4 Vesta, although orbital dynamics calculations showed that the delivery of meteorites from Vesta to Earth is difficult. However, the discovery of several kilometer-sized Vesta-like asteroids in the region between Vesta and the 3:1 resonance suggested that these seem more likely parent bodies of the HEDs than Vesta itself. This implies that the exposure-age clusters may represent samples of several parent bodies. Therefore, the near-absence of diogenites with ages <20 Ma might be of interest for the composition of these kilometer-sized fragments of Vesta. Here we present cosmic-ray-exposure ages of 20 diogenites, including 9 new meteorites. In addition, we calculate the probability for each peak to occur by chance, assuming a constant production rate of HED fragments.

Eleven meteorites suggested to belong to a meteoroid stream of 17 H chondrites (cluster 1) have been analyzed for their noble gases. Together with literature data, the noble gas record of all these stones is discussed. Cluster 1 chondrites belong to different chemical‐petrologic types, and three are regolith breccias, as proven by solar type gases. The thermal history of the parent body of cluster 1 stones is not the same for all (as seen in the radiogenic 40Ar), and diffusive loss of helium in four of them suggests small perihelion distances for these specimens and thus different orbits from the rest of this group. Exposure ages vary between about 4 and 70 Ma. Thus the orbital elements of the stream must have been undisturbed for about 70 Ma. The exposure age distribution of cluster 1 chondrites is not distinct from that of “normal” H chondrites. These data appear inconsistent with the suggestion that cluster 1 chondrites belong to a specific meteoroid stream with very similar orbits.