# (35107) 1991 VH

(35107) 1991 VH (provisional designation 1991 VH) is a binary near-Earth asteroid and potentially hazardous asteroid of the Apollo group. It was discovered on 9 November 1991, by Australian astronomer Robert McNaught at Siding Spring Observatory. This binary system is composed of a roughly-spheroidal primary body about one kilometre in diameter, and an elongated natural satellite less than half a kilometre in diameter. The 1991 VH system is unusual for its dynamically excited state; the satellite has a tumbling, non-synchronous rotation that chaotically exchanges energy and angular momentum with its precessing, eccentric orbit. This asteroid system was one of the two targets of NASA's Janus Mayhem mission, until the delay of the rocket launch made both targets inaccessible.

## Numbering and naming

This minor planet was numbered by the Minor Planet Center on 27 February 2002. It has not yet been named.

## Orbit

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.

### 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.

## 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. 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.
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). The geometric albedo for the primary is 0.17–0.18, considerably lower than infrared-based estimates of 0.30–0.40.

### Mass and density

The total mass of the 1991 VH system is (1.58±0.08)×10$^{12}$ 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 1.4×10$^{12}$ kg—approximately 12 times as massive as the satellite. Given the primary mass and diameter, its density is estimated to be about 1.7±0.8 g/cm$^3$, indicative of a rubble pile internal structure.

### 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.

### 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). Later photometric observations from 2003–2020 corroborated this result down to a precision of ±0.0001 seconds.

## Satellite

S/2008 (35107) 1 is the secondary component and natural satellite of the 1991 VH system.

### Discovery

S/2008 (35107) 1 is among the first near-Earth asteroid satellites discovered, alongside those of (385186) 1994 AW1 and 3671 Dionysus. It was discovered on 27 February 1997, by astronomers Petr Pravec, Marek Wolf, and Lenka Šarounová at Ondřejov Observatory. The satellite was detected through photometric observations of periodic dips in the system's brightness, caused by mutual eclipses and occultations of the components. The discovery of the satellite was reported in a notice published by the International Astronomical Union on 29 March 1997, but was not officially confirmed until it was individually resolved in adaptive optics imaging by the Keck II telescope at Mauna Kea Observatory on 9 August 2008. The satellite was given the provisional designation S/2008 (35107) 1 on 19 September 2008.

### Origin

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.

## Exploration

This asteroid system was the target of NASA's Janus Mayhem mission, which was planned to launch in 2022 alongside NASA's Psyche spacecraft, and to arrive in 2026. 1991 VH became impossible to reach for Janus when the launch of Psyche got delayed in May 2022.