ANALYSES OF 433EROS FRACTURE PATTERNS: THE GLOBAL LINEAMENT MAP

The observed presence of linear structures on Eros can be interpreted as being solely due to faulting resulting from the transmission of impact shock waves. However, early studies found two large-scale lineaments on Eros (Callisto Fossae and Rahe Dorsum) to be coplanar with a large flat region (the southern “facet”) on one end of the asteroid. This CF-RD-SF plane was interpreted as indicative of a pre-existing structure throughout most of the asteroid, consistent with a fabric inherited from a parent body.

A global database of >2000 linear features Eros lineaments was recently constructed, based on 5-11 m/p resolution NEAR MSI images of the asteroid. These lineaments have been grouped into sets according to location and orientation. Because they were mapped directly onto the Eros shape model, they can be modeled to define planes that cut through the asteroid. We determined the pole of the plane described by each individual lineament. We then compared the poles of the lineaments in each set to determine if they are in fact similarly oriented or if the visual identification was confused by the non-spherical shape of the asteroid.

Lineaments radial to 13 craters have been identified. Given their proximity and orientation relative to the craters it seems most likely that these lineaments were formed as a direct result of the impact event. The most distinct set of lineaments on Eros (Set 1) is also likely to have an impact origin. Aligned roughly with the prime meridian of the asteroid, several of these lineaments are up to 10’s of kilometers long. The orientation of the lineaments is consistent with the pattern expected from fragmentation due to impact on the long side of an ellipsoid target. We infer that these lineaments were formed as a result of the Pysche and/or Himeros impacts.

The set 2 lineaments encircle Eros from 170° -240° E. Their preferred orientation does not obviously follow any predictions of models of lineament formation by impact. We therefore suspect that these lineaments represent a pre-existing internal structure. The set 4 lineaments also do not fit any impact-formation predictions. This set of lineaments describes a plane which may be coplanar to the CF-RD-SF plane. The pole of the set 4 plane is ~60° from the set 2 pole, suggesting that the two sets may represent conjugate fractures.