(35107) 1991 VH
Binary near-Earth asteroid with a chaotically tumbling satellite.
(35107) 1991 VH is a binary asteroid that orbits near Earth and is classified as a potentially hazardous member of the Apollo group. Its most unusual feature is a highly unsettled dynamic state: the satellite tumbles in a non-synchronous rotation, chaotically swapping energy and angular momentum with its own eccentric, precessing orbit. The cause remains unknown, though a likely explanation is a close pass by Earth within roughly 50,000 to 80,000 kilometers. A far less probable scenario involves a major collision within the last million years. This system was one of two targets for NASA’s Janus Mayhem mission, but a launch delay made both targets unreachable.
The minor planet received its number from the Minor Planet Center on 27 February 2002, but has not yet been given a name.
Its orbit around the Sun ranges from 0.98 to 1.30 AU, completing one circuit every 1.21 years (443 days). The orbit has an eccentricity of 0.14 and an inclination of 14° relative to the ecliptic.
The asteroid’s minimum orbital intersection distance with Earth is 0.0247 AU (about 3.70 million kilometers, or 9.6 lunar distances). The closest recorded approach occurred on 15 August 2008, at 0.0458 AU (6.85 million kilometers, or 17.8 lunar distances).
High-resolution radar imaging from Goldstone and Arecibo Observatory in 2008 shows the primary body is roughly spheroidal with an equatorial ridge, resembling a spinning top—a shape seen in other near-Earth asteroids like 3200 Phaethon, 66391 Moshup, 101955 Bennu, and 162173 Ryugu. Along the ridge lie several topographical features, including a 100-meter-wide concavity. A bright linear feature casting a shadow appears at mid- to high-latitudes. Preliminary modeling gives the primary dimensions of 1.30 km × 1.25 km × 1.18 km, equivalent to a sphere about 1.18 km in diameter. Its geometric albedo is 0.17–0.18, notably lower than infrared-based estimates of 0.30–0.40.
The total system mass is (1.58±0.08)×10¹² kg, derived from the satellite’s orbital motion. The satellite-to-primary mass ratio is 0.086±0.018, giving the primary a mass of about 1.4×10¹² kg—roughly 12 times that of the satellite. With that mass and diameter, the primary’s density is about 1.7±0.8 g/cm³, suggesting a rubble pile structure.
In the SMASS classification, 1991 VH is a transitional Sk-type, intermediate between common stony S-type and rarer K-type asteroids.
Quick Facts
- Minorplanet
- yes
- Background
- #FFC2E0
- Discoverer
- R. H. McNaught
- Discovery Site
- Siding Spring Obs.
- Discovered
- 9 November 1991
- Mpc Name
- (35107) 1991 VH
- Mp Category
- NEOApolloPHA
- Epoch
- 21 January 2022 (JD 2459600.5)
- Uncertainty
- 0
- Observation Arc
- 29.34 yr (10,717 days)
- Aphelion
- 1.3014 AU
- Perihelion
- 0.9732 AU
Facts from the source article.
Lore & Background
The asteroid was discovered on 9 November 1991 by Australian astronomer Robert McNaught at Siding Spring Observatory. It was numbered by the Minor Planet Center on 27 February 2002 but has not yet been named. The binary system consists of a roughly-spheroidal primary about one kilometre in diameter and an elongated satellite less than half a kilometre in diameter. High-resolution radar imaging from Goldstone and Arecibo Observatory in 2008 revealed that the primary has an equatorial ridge, resembling a spinning top, with a 100 m-wide concavity and a bright linear feature casting a shadow at mid- to high-latitudes. The primary's shape is modeled as 1.30 km × 1.25 km × 1.18 km, with a geometric albedo of 0.17–0.18. In the SMASS taxonomy, 1991 VH is classified as a transitional Sk-type. The satellite, S/2008 (35107) 1, was discovered on 27 February 1997 by Petr Pravec, Marek Wolf, and Lenka Šarounová at Ondřejov Observatory through photometric observations of mutual eclipses. It was not officially confirmed until resolved by adaptive optics at Keck II on 9 August 2008, and was given its provisional designation on 19 September 2008.
Reader's Guide
The 1991 VH system is significant for its unusual dynamical state: the satellite has a tumbling, non-synchronous rotation that chaotically exchanges energy and angular momentum with its precessing, eccentric orbit. The cause is not known, but a likely scenario is a close planetary encounter with Earth within ~50,000 to 80,000 kilometers; a collision event within the past million years is considered very unlikely. The system was one of two targets of NASA's Janus Mayhem mission, planned to launch in 2022 alongside the Psyche spacecraft and arrive in 2026, but became inaccessible when the Psyche launch was delayed in May 2022. The total mass of the system is (1.58±0.08)×10¹² kg, with a primary mass about 12 times that of the satellite. The primary's density of about 1.7±0.8 g/cm³ suggests a rubble pile internal structure. The system is thought to have formed through rotational fissioning of a progenitor body due to spin-up by the YORP effect.
Did You Know?
- The satellite was among the first near-Earth asteroid satellites discovered, alongside those of (385186) 1994 AW1 and 3671 Dionysus.
- The primary's shape resembles a spinning top, similar to 3200 Phaethon, 66391 Moshup, 101955 Bennu, and 162173 Ryugu.
- The asteroid has an Earth minimum orbital intersection distance of 0.0247 AU (about 9.6 lunar distances).
- The satellite's discovery was reported on 29 March 1997 but not confirmed until August 2008.
Frequently Asked Questions
Who discovered (35107) 1991 VH and when?
Robert McNaught identified the asteroid on 9 November 1991 while conducting observations at Siding Spring Observatory in Australia.
What makes the satellite of (35107) 1991 VH so unusual?
Instead of settling into a stable synchronous spin like most asteroid moons, this satellite tumbles chaotically, continuously trading energy and angular momentum with its own eccentric, precessing orbit. The exact trigger for this unsettled dynamic state is still not fully confirmed.
What is the official designation of (35107) 1991 VH's moon?
The companion carries the designation S/2008 (35107) 1, reflecting its identification as a satellite in 2008.
Why is (35107) 1991 VH classified as potentially hazardous?
It belongs to the Apollo near-Earth group, meaning its orbit crosses Earth's path and brings it close enough to our planet to warrant monitoring as a theoretical impact risk.
What likely caused the satellite's chaotic tumbling state?
The leading hypothesis points to a close gravitational encounter with Earth at a distance of roughly 50,000 to 80,000 kilometers, which would have perturbed the moon's rotation. A major collision within the last million years is considered a far less probable alternative.
More in Notable Asteroids, Part 4 1-24
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