5905 Johnson
Binary Hungaria asteroid discovered by Eleanor Helin in 1989.
5905 Johnson (provisional designation 1989 CJ1) is a binary asteroid belonging to the Hungaria group, located in the innermost region of the main asteroid belt. It was discovered on 11 February 1989 by American astronomer Eleanor Helin at Palomar Observatory in California. The primary body is roughly 4 kilometers (2.5 miles) in diameter, and its moon is about 1.6 kilometers (1 mile) across, completing an orbit every 21.8 hours.
This stony S-type asteroid is part of the dynamical Hungaria group, the densest concentration of asteroids near the inner edge of the belt, but it is not a member of the collisional Hungaria family. Instead, based on its proper orbital elements, it belongs to the background population of the main belt. It orbits the Sun at a distance of 1.8 to 2.0 AU, taking 2 years and 8 months (964 days) to complete one revolution, with a semi-major axis of 1.91 AU. Its orbit has an eccentricity of 0.07 and an inclination of 28° relative to the ecliptic. No precovery images or earlier identifications exist, so the observation arc begins with its discovery at Palomar in February 1989.
Measurements from NASA’s Spitzer and WISE telescopes, along with the NEOWISE mission, give Johnson a diameter between 3.62 and 4.791 kilometers and an albedo ranging from 0.19 to 0.44. The Collaborative Asteroid Lightcurve Link (CALL) uses revised WISE data from Petr Pravec, adopting an albedo of 0.1524 and a diameter of 4.80 kilometers for an absolute magnitude of 14.255.
The first rotational lightcurve of Johnson was obtained between 1 and 11 April 2005 through photometric observations by Brian Warner at the Palmer Divide Observatory, Petr Pravec and Peter Kušnirák at Ondřejov Observatory, Adrián Galád and Štefan Gajdoš at Modra Observatory, and P. Brown and Z. Krzeminski at the University of Western Ontario. These observations revealed that Johnson is a synchronous binary asteroid, with its moon orbiting every 21.785 hours. Mutual occultation and eclipsing events showed a magnitude change of 0.15 to 0.18, indicating the satellite’s diameter is about 40% that of the primary (a secondary-to-primary diameter ratio of 0.4), corresponding to a mean diameter of 1.4 to 1.9 kilometers.
Subsequent lightcurves by Warner and Pravec gave a revised rotation period for the primary of 3.7814 to 3.7824 hours, with a brightness variation of 0.10 to 0.20 magnitude.
Quick Facts
- Minorplanet
- yes
- Background
- #D6D6D6
- Discovered
- 11 February 1989
- Discoverer
- E. F. Helin
- Discovery Site
- Palomar Obs.
- Mpc Name
- (5905) Johnson
- Named After
- Lindley N. Johnson / (astronomer, engineer)
- Mp Category
- main-belt(inner) / Hungariabackground
- Epoch
- 23 March 2018 (JD 2458200.5)
- Uncertainty
- 0
- Observation Arc
- 28.96 yr (10,576 days)
- Aphelion
- 2.0476 AU
Facts from the source article.
Lore & Background
5905 Johnson is a stony S-type asteroid and member of the dynamical Hungaria group, forming the innermost dense concentration of asteroids in the Solar System. It is not a member of the collisional Hungaria family but a non-family asteroid of the main belt's background population. It orbits the Sun at a distance of 1.8–2.0 AU every 964 days, with an eccentricity of 0.07 and an inclination of 28°. No precoveries or prior identifications exist; its observation arc begins with its discovery in February 1989.
Between 1 and 11 April 2005, the first rotational lightcurve was obtained by astronomers Brian Warner, Petr Pravec, Peter Kušnirák, Adrián Galád, Štefan Gajdoš, P. Brown, and Z. Krzeminski at multiple observatories. These observations revealed Johnson is a synchronous binary asteroid with a moon orbiting every 21.785 hours. Mutual occultation and eclipsing events had a magnitude of 0.15–0.18, indicating the satellite's diameter is 40% of the primary's, or 1.4–1.9 km. Later lightcurves by Warner and Pravec gave a primary rotation period of 3.7814–3.7824 hours and confirmed the satellite's orbital period of 21.78–21.797 hours. The asteroid was named after American astronomer and engineer Lindley N. Johnson, instrumental for the Near-Earth Asteroid Tracking program.
Reader's Guide
5905 Johnson holds significance as a well-studied binary asteroid within the Hungaria dynamical group, providing insights into the formation and evolution of small asteroid systems. Its discovery by Eleanor Helin at Palomar Observatory in 1989 added to the catalog of near-Earth and main-belt objects. The 2005 lightcurve campaign involving multiple astronomers and observatories established its binary nature, with a satellite about 40% the size of the primary. The asteroid's naming after Lindley N. Johnson honors his contributions to the Near-Earth Asteroid Tracking program, which became operational in December 1995. The range of diameter and albedo values from Spitzer, WISE, and NEOWISE surveys, along with the revised data by Petr Pravec, highlight the ongoing refinement of physical parameters. Its fast but not extreme rotation period and synchronous binary configuration make it a valuable object for studying asteroid dynamics and satellite formation. The naming citation was published by the Minor Planet Center on 3 May 1996.
Did You Know?
- 5905 Johnson is a synchronous binary asteroid with a moon that orbits every 21.8 hours.
- The satellite's diameter is about 40% of the primary's, measuring 1.4–1.9 km.
- The asteroid is named after Lindley N. Johnson, who was instrumental for the Near-Earth Asteroid Tracking program.
More in Notable Asteroids, Part 3 1-24
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