5477 Holmes
Binary Hungaria asteroid with a 1-km moon discovered in 2005.
5477 Holmes (provisional designation 1989 UH2) is a binary system and a member of the Hungaria family, located in the innermost region of the asteroid belt. Roughly 3 kilometers across, it was discovered on 27 October 1989 by American astronomer Eleanor Helin at Palomar Observatory in California. The asteroid is thought to be an E-type, likely spherical, and rotates quickly—once every 2.99 hours. In November 2005, astronomers announced the discovery of a moon about 1 kilometer in size, making Holmes a synchronous binary system.
Holmes belongs to the Hungaria family (003), a dense cluster of bright asteroids in the inner belt, distinct from the sparser Mars-crosser and near-Earth populations. It orbits the Sun at distances between 1.8 and 2.1 AU, completing a circuit every 2 years and 8 months (970 days) on a semi-major axis of 1.92 AU. Its orbit has an eccentricity of 0.08 and an inclination of 23° relative to the ecliptic. The observation arc begins with its discovery at Palomar in October 1989.
The asteroid is assumed to be E-type, consistent with other Hungaria members. Photometric lightcurves obtained since 2005 by Brian Warner, Petr Pravec, and others show a well-defined rotation period of 2.9940 hours and a brightness variation of 0.10 to 0.12 magnitude, indicating a nearly spherical shape. Its rotation is close to that of a fast rotator.
According to NEOWISE data from the WISE mission, Holmes measures 3.147 kilometers in diameter with an albedo of 0.31. The Collaborative Asteroid Lightcurve Link uses a revised WISE-derived albedo of 0.2849 and a diameter of 3.21 kilometers, based on an absolute magnitude of 14.445. Johnston's Archive gives a diameter of 2.95 km for the primary and 3.15 km for the combined system.
The satellite was discovered through photometric observations by Brian Warner and collaborators from 2–12 November 2005. It orbits the primary every 24.4 hours at an estimated average distance of 6.7 km. Mutual occultation events showed the moon is about 37% the size of the primary, corresponding to a diameter of 1.09–1.19 km, depending on the primary's size estimate. The discovery was announced on 15 November 2005.
The minor planet was named for American amateur astronomer Robert E. Holmes Jr. (born 1956), director of the Astronomical Research Observatory (H21) in Westfield, Illinois.
Quick Facts
- Minorplanet
- yes
- Background
- #D6D6D6
- Discoverer
- E. F. Helin
- Discovery Site
- Palomar Obs.
- Discovered
- 27 October 1989
- Mpc Name
- (5477) Holmes
- Named After
- Robert Holmes / (American astronomer)
- Mp Category
- main-belt(inner) / Hungaria
- Epoch
- 23 March 2018 (JD 2458200.5)
- Uncertainty
- 0
- Observation Arc
- 27.60 yr (10,082 d)
- Aphelion
- 2.0613 AU
Facts from the source article.
Lore & Background
5477 Holmes is a core member of the Hungaria family (003), a large group of bright asteroids that forms the innermost dense concentration of asteroids in the Solar System. It orbits the Sun at a distance of 1.8–2.1 AU every 970 days, with an eccentricity of 0.08 and an inclination of 23°. The asteroid is an assumed E-type, consistent with the Hungaria family's spectral type. Photometric lightcurves obtained since 2005 by Brian Warner and Petr Pravec show a well-defined rotation period of 2.9940 hours and a brightness amplitude of 0.10–0.12 magnitude, indicating a nearly spherical shape. The asteroid's short period is near that of a fast rotator. Its diameter and albedo vary across surveys: NEOWISE gives 3.147 km and an albedo of 0.31; Pravec's revised WISE-data yields 3.21 km and albedo 0.2849; Johnston's Archive reports 2.95 km for the primary and 3.15 km for the combined system. The satellite was discovered from photometric observations during 2–12 November 2005, announced on 15 November 2005. It orbits every 24.4 hours at an estimated average distance of 6.7 km, and mutual occultation events indicate it is 37% the size of the primary, corresponding to a diameter of 1.09–1.19 km. The asteroid was named for American amateur astronomer Robert E. Holmes Jr, who directs the Astronomical Research Observatory in Westfield, Illinois; the naming citation was published on 18 February 2011.
Reader's Guide
5477 Holmes is significant as a binary system within the Hungaria family, a region of the asteroid belt that is the innermost dense concentration of asteroids. Its discovery as a binary asteroid in 2005 added to the growing catalog of small bodies with moons, providing insights into the formation and evolution of such systems. The asteroid's short rotation period of 2.9940 hours and nearly spherical shape, inferred from low lightcurve amplitude, make it a useful object for studying the physical properties of E-type asteroids. The satellite's size, about 37% of the primary, and its synchronous orbit offer constraints on binary formation mechanisms, such as rotational fission or gravitational capture. The naming after amateur astronomer Robert Holmes highlights the contributions of non-professional observers to asteroid research. The multiple diameter estimates from different surveys (NEOWISE, Pravec, Johnston) reflect ongoing refinement of physical parameters for small asteroids. As a Hungaria family member, Holmes helps characterize the composition and dynamics of this inner-belt population, which is distinct from the main belt and near-Earth objects.
Did You Know?
- 5477 Holmes was discovered on 27 October 1989 by Eleanor Helin at Palomar Observatory.
- It has a moon about 1.09–1.19 km in diameter, discovered in November 2005.
- The asteroid's rotation period is 2.9940 hours, indicating a nearly spherical shape.
- It is named after American amateur astronomer Robert E. Holmes Jr, who runs the Astronomical Research Observatory in Illinois.
More in Notable Asteroids, Part 3 1-24
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