1991 VH orbits the Sun at a distance of 0.98–1.30 AU once every 1.21 years (443 days). Its orbit has an eccentricity of 0.14 and an inclination of 14° with respect to the ecliptic.[3]
Close approaches
The asteroid has an Earth minimum orbital intersection distance of 0.0247 AU (3.70 million km; 2.30 million mi), which translates into approximately 9.6 lunar distances (LD). It has made multiple close approaches to Earth, with the closest being 0.0458 AU (6.85 million km; 4.26 million mi) or 17.8 LD on 15 August 2008.[3]
Physical characteristics
Diameter, shape, and albedo
High-resolution radar imaging from Goldstone and Arecibo Observatory in 2008 show that the 1991 VH primary is a roughly-spheroidal object with an equatorial ridge, bearing resemblance to a spinning top. This shape is not unique to 1991 VH as it been observed in other near-Earth asteroids; most notably 3200 Phaethon, 66391 Moshup, 101955 Bennu, and 162173 Ryugu.[5][16] A number of topographical features, including a 100 m (330 ft)-wide concavity, are present along the object's equatorial ridge. A bright linear feature casting a shadow at the object's mid- to high-latitudes was also seen in the 2008 radar images.[5]
Preliminary modeling of the primary's shape in radar images indicates dimensions of 1.30 km × 1.25 km × 1.18 km (0.81 mi × 0.78 mi × 0.73 mi), or a volume-equivalent diameter of 1.18 km (0.73 mi).[5] The geometric albedo for the primary is 0.17–0.18, considerably lower than infrared-based estimates of 0.30–0.40.[8][4]
Mass and density
The total mass of the 1991 VH system is (1.58±0.08)×1012 kg, based on the orbital motion of the satellite. The mass ratio of the satellite to the primary is 0.086±0.018, corresponding to a primary mass of 1.4×1012 kg—approximately 12 times as massive as the satellite.[a] Given the primary mass and diameter, its density is estimated to be about 1.7±0.8 g/cm3, indicative of a rubble pile internal structure.[5][17]
Spectral type
In the SMASS taxonomy, 1991 VH is classified as a transitional Sk-type, which is an intermediary between the common stony S-type and the less frequent K-type asteroids.[3]
Rotation
Photometric observations in 1997 determined a primary rotation period of 2.624 hours, with a light curve amplitude of 0.08±0.01 magnitudes (U=3).[7] Later photometric observations from 2003–2020 corroborated this result down to a precision of ±0.0001 seconds.[4][18]
As with many binary near-Earth asteroids, the 1991 VH system is thought to have formed through rotational fissioning of a progenitor body due to spin-up by the YORP effect. The resulting mass shed from the progenitor body coalesced in orbit to form the satellite.[17]
This asteroid system was the target of NASA's upcoming Janus Mayhem mission, which was planned to launch in 2022 alongside NASA's Psyche spacecraft, and to arrive in 2026.[12][13]1991 VH became impossible to reach for Janus when the launch of Psyche got delayed in May 2022.[14]
See also
(175706) 1996 FG3, binary near-Earth asteroid and former target of the Janus Serenity mission, until it became inaccessible due to the launch delay
Notes
^ abPrimary mass is calculated from the difference between the system mass and secondary mass: 1.44×1012 kg ≈ 1.58×1012 kg – (0.086 × 1.58×1012 kg).
^Nugent et al's two-parameter H-G model of near-infraredWISEphotometry takes the asteroid's observed opposition surge behavior into account, yielding an absolute magnitude of H = 17.02 and a slope parameter of G = 0.24.[8] An earlier analysis by Pravec et al. used R-band photometry from 2003 observations and obtained similar results: H = 16.95±0.07 and G = 0.26±0.04[9]
^Default fit of photometry from the Minor Planet Center's observations database, assuming a slope parameter of G = 0.15.[1] Because this assumption does not take the asteroid's actual opposition surge behavior into account, the absolute magnitude value H is underestimated.[10]
^Secondary mass is calculated from the product of the system mass and secondary/primary mass ratio: 1.4×1011 kg ≈ 0.086 × 1.58×1012 kg.
References
^ abc"(35107) = 1991 VH". Minor Planet Center. International Astronomical Union. Retrieved 17 November 2021.
^Green, Daniel W. E. (18 November 1991). "IAUC 5390: 1991 VH". International Astronomical Union Circular. Central Bureau for Astronomical Telegrams. Bibcode:1991IAUC.5390....1M. Retrieved 17 November 2021.
^Pravec, Petr; Harris, Alan W.; Kušnirák, Peter; Galád, Adrián; Hornoch, Kamil (September 2012). "Absolute magnitudes of asteroids and a revision of asteroid albedo estimates from WISE thermal observations". Icarus. 221 (1): 365–387. Bibcode:2012Icar..221..365P. doi:10.1016/j.icarus.2012.07.026. S2CID123017048.
^ abJohnston, Wm. Robert (21 September 2014). "(35107) 1991 VH and S/2008 (35107) 1". Asteroids with Satellites Database. Johnston's Archive. Retrieved 18 November 2021.
