Spins, shapes, and orbits for near-Earth objects by Nordic NEON

Abstract

Abstract. The observing program of the Nordic Near-Earth-Object Network (NEON) accrues knowledge about the physical and dynamical properties of near-Earth objects (NEOs) using state-of-the-art inverse methods. Photometric and astrometric observations are being carried out at the Nordic Optical Telescope. Here, the NEON observations from June 2004-September 2006 are reviewed. Statistical orbital inversion is illustrated by the so-called Volume-of-Variation method. Statistical inversion for spins and shapes is carried using a simple triaxial shape model yielding analytical disk-integrated brightnesses for both Lommel-Seeliger and Lambert scattering laws. The novel approach allows spin-shape error analyses with the help of large numbers of sample solutions. Currently, such spin-shape solutions have been derived for FF 12, 2003 MS2, 2003 RX7, and 2004 HW. For (1862 Apollo, an unambiguous spin-shape solution has been obtained using the conventional, convex inversion method and, for (1685) Toro and (1981) Midas, the conventional method has been applied repeatedly to map the regime of possible solutions.

Radar and Lightcurve Observations and a Physical Model of Potentially Hazardous Asteroid 1981 Midas

“…There is no unique solution for the rotation period of Midas, but lightcurves from one or two additional apparitions may be sufficient to break this degeneracy. For the sidereal rotation period of Midas, we adopt a best-fit value of 5.2216 hr, with an uncertainty of 0.0017 hr, which is in agreement with rotation periods derived from existing lightcurves (Mottola et al 1995;Wisniewski et al 1997;Muinonen et al 2007;Franco et al 2018). This is one of the shortest known rotation periods of any published NEA contact binary; 10 the only faster rotators are Castalia (4.0 hr, Hudson & Ostro 1994) and 2001 KZ66 (4.99 hr, Zegmott et al 2021).…”

“…Existing lightcurves reported in Mottola et al (1995), Wisniewski et al (1997), Muinonen et al (2007), and Franco et al (2018) revealed a rotation period of 5.22 hr and a large amplitude that suggests an elongated body. The amplitude of about 1.0 mag, seen on several nights, implies an elongation (ratio of maximum to minimum cross sections) of a/b ≈ 2.5 (Harris et al 2014).…”