Eros is a very elongated (34 kilometers by 11 kilometers by 11 kilometers) asteroid, most of the surface of which is saturated with craters smaller than 1 kilometer in diameter. The largest crater is 5.5 kilometers across, but there is a 10-kilometer saddle-like depression with attributes of a large degraded crater. Surface lineations, both grooves and ridges, are prominent on Eros; some probably exploit planes of weakness produced by collisions on Eros and/or its parent body. Ejecta blocks (30 to 100 meters across) are abundant but not uniformly distributed over the surface. Albedo variations are restricted to the inner walls of certain craters and may be related to downslope movement of regolith. On scales of 200 meters to 1 kilometer, Eros is more bland in terms of color variations than Gaspra or Ida. Spectra (800 to 2500 nanometers) are consistent with an ordinary chondrite composition for which the measured mean density of 2.67 +/- 0.1 grams per cubic centimeter implies internal porosities ranging from about 10 to 30 percent.

Abstract1. The importance of vision for efficient agonistic communication was investigated in the rusty crayfish, Orconectes rusticus, a species active both day and night. Agonistic bout dynamics were analyzed from isosexual pairs of males and females interacting under moderate (350 lux) and dim (11 lux) light levels, and in complete darkness (using infra-red video recording). Under dim light we determined the effect of visual light and dark adaptation on communication. 2. As light diminished, bouts became less frequent, but longer, and the crayfish invested more time and performed more acts when resolving bouts. Thus, communication efficiency was clearly lower in the dark than under moderate light, for both sexes. Males performed more acts than females overall, and were generally more aggressive than females. 3. The frequency of visually-mediated behaviours (e.g. Lunge, Follow) decreased in the absence oflight, while tactile behaviours (e.g. Antenna Tap, Chela Strike, Push) were performed more frequently. Males especially performed more highly aggressive tactile behaviours in the dark. It was shown that some behaviours previously considered to be visually mediated (e.g. Meral Spread) are also tactually or proprioceptively mediated, and some behaviours assumed to be tactually mediated (e.g. antennal movements) are probably also visually mediated. 4. Under dim light, crayfish with light-adapted eyes resolve bouts more efficiently in terms of time and energy investment than do dark-adapted animals. This is consistent with the effects of pigment migrations during dark adaptation in the crayfish superposition compound eye, which enhance visual sensitivity, but decrease acuity. We suggest that dark adaptation diminishes a crayfishes ability to deal with the subtleties of visual communication, but may well enhance its ability to detect predators.

On 25 October 2000, the Near Earth Asteroid Rendevous (NEAR)-Shoemaker spacecraft executed a low-altitude flyover of asteroid 433 Eros, making it possible to image the surface at a resolution of about 1 meter per pixel. The images reveal an evolved surface distinguished by an abundance of ejecta blocks, a dearth of small craters, and smooth material infilling some topographic lows. The subdued appearance of craters of different diameters and the variety of blocks and different degrees of their burial suggest that ejecta from several impact events blanketed the region imaged at closest approach and led to the building up of a substantial and complex regolith consisting of fine materials and abundant meter-sized blocks.

We determined the mass of asteroid 433 Eros, its lower order gravitational harmonics, and rotation state, using ground-based Doppler and range tracking of the Near Earth Asteroid Rendezvous (NEAR)-Shoemaker spacecraft and images of the asteroid's surface landmarks. The mass of Eros is (6.687 +/- 0.003) x 10(18) grams, which, coupled with our volume estimate, implies a bulk density of 2. 67 +/- 0.03 grams per cubic centimeter. The asteroid appears to have a uniform density distribution. The right ascension and declination of the rotation pole are 11.37 +/- 0.05 and 17.22 +/- 0.05 degrees, respectively, and at least over the short term, the rotation state of Eros is stable with no measurable free precession of the spin pole. Escape velocities on the surface vary from 3.1 to 17.2 meters per second. The dynamical environment of Eros suggests that it is covered with regolith and that one might expect material transport toward the deepest potential wells in the saddle and 5.5-kilometer crater regions.

The terminal navigation of the Near Earth Asteroid Rendezvous (NEAR) spacecraft during its close flyby of asteroid 253 Mathilde involved coordinated efforts to determine the heliocentric orbits of the spacecraft and Mathilde and then to determine the relative trajectory of the spacecraft with respect to Mathilde. The gravitational perturbation of Mathilde on the passing spacecraft was apparent in the spacecraft tracking data. As a result of the accurate targeting achieved, these data could be used to determine Mathilde's mass as 1.033 (+/- 0.044) x 10(20) grams. Coupled with a volume estimate provided by the NEAR imaging team, this mass suggests a low bulk density for Mathilde of 1.3 grams per cubic centimeter.