Lightcurve of asteroid Nereus

Abstract

An Apollo asteroid (4660) Nereus is one of the most accessible asteroids by spacecraft. Photometric observations of light variation of Nereus were performed in order to support a mission scenario planning and to elucidate the origin of the asteroid. The results revealed that Nereus has a long rotational period, 15.1 ± 1.2 hours, and that the amplitude of light variation is fairly large. Its slow rotation is preferable for a landing or touch down scenario of spacecraft. On the other hand, the comparison of lightcurve data between small main-belt asteroids and comet nuclei suggests that Nereus may be an extinct cometary nucleus, rather than a migrated asteroid from the main-belt. The comparison of the observed data with laboratory impact experiments also implies that the asteroid may not be a fragment from a catastrophic impact event in the main-belt. All the other data already obtained, such as by colorimetry, are not inconsistent with the cometary origin, either.

Radar observations and a physical model of Asteroid 4660 Nereus, a prime space mission target

“…We obtained our first estimate of the long axis (∼500 m) and the intermediate axis (∼250-300 m) from the extent of visible range. The object's rotation appears consistent with the period of 15.1 h as obtained from the lightcurves (Ishibashi et al, 2000a(Ishibashi et al, , 2000b. A very intriguing view of Nereus is along its angular edge (Figs.…”

“…a value slightly lower than suggested inIshibashi et al (2000a) lightcurve analysis (X/Y > 1.7). When compared to other NEA elongations that have been derived from the radar studies (http://echo.jpl.nasa.gov/~lance/nea_elongations.…”

“…However, it was difficult to explain the differences in the inclinations of Nereus (i = 1.4 • ) and the Hungaria region (i > 22 • ). Ishibashi et al (2000a) preferred an hypothesis about the cometary origin of Nereus based on its lightcurve characteristics. The orbit of Nereus is chaotic, heavily influenced by its frequent interaction with the Earth's gravitational field, and therefore it cannot be followed very far away from the present (Michel et al, 1996;Yoshikawa et al, 2000).…”

“…The initial size estimate for Nereus came from an optical R-band study (Ishibashi et al, 2000a(Ishibashi et al, , 2000b which concluded that it is an elongated object with diameter between 1.1-1.3 km. Nereus' spectral classification was not known at that time, so the authors assumed than that Nereus is a C-class object.…”