4765 Wasserburg
Bright Hungaria asteroid, suspected binary and asteroid pair.
4765 Wasserburg, provisionally designated 1986 JN1, is a bright asteroid belonging to the Hungaria group. It sits in the innermost part of the main asteroid belt, measures about 3 kilometers (1.9 miles) across, and is considered a suspected binary system as well as an asteroid pair. American astronomer Carolyn Shoemaker spotted it on 5 May 1986 from Palomar Observatory; the object was later named for geologist Gerald J. Wasserburg. Its orbit places it between 1.8 and 2.1 astronomical units from the Sun, completing one lap every 2 years and 9 months (991 days). The orbit has a low eccentricity of 0.06 and a high inclination of 24° relative to the ecliptic. Before its official discovery, it had already been recorded as 1983 EA1 at Palomar in 1983, pushing its observation arc back by three years. Wasserburg forms an asteroid pair with (350716) 2001 XO105 and was included in Petr Pravec’s study on asteroid pair formation through rotational fission, published in *Nature*. The minor planet honors Gerald J. Wasserburg (1927–2016), a Caltech professor of geology and geophysics. He pioneered radiometric dating methods in isotope geochemistry, famously producing precise age measurements of Moon rocks that helped clarify the Moon’s origin and supported the Late Heavy Bombardment hypothesis. He also analyzed meteorite isotopes, built a timeline for the Solar System’s formation and evolution, and contributed to nucleosynthesis theory. The naming citation appeared on 27 June 1991 (M.P.C. 18464). Preliminary data from NASA’s WISE and NEOWISE surveys give Wasserburg a diameter of 1.777 kilometers and an outstandingly high albedo of 1.000. In contrast, the Collaborative Asteroid Lightcurve Link assumes it is an E-type asteroid with an albedo of 0.40 (based on 434 Hungaria) and calculates a larger diameter of 3.82 kilometers from an absolute magnitude of 13.7. Between 2006 and 2014, Brian Warner (Palmer Divide Observatory), Petr Pravec (Ondřejov Observatory), and Julian Oey (Blue Mountains Observatory) gathered several rotational lightcurves. The best analyses yield a rotation period between 3.6231 and 3.6280 hours, with brightness variations ranging from 0.07 to 0.60 magnitude (rated U=3/3/3/3-). The changing amplitude suggests Wasserburg is likely one of the more elongated primary asteroids among known smaller binaries under 10 kilometers.
Quick Facts
- Minorplanet
- yes
- Background
- #D6D6D6
- Discovered
- 5 May 1986
- Discoverer
- C. Shoemaker
- Discovery Site
- Palomar Obs.
- Mpc Name
- (4765) Wasserburg
- Named After
- Gerald J. Wasserburg / (American geologist)
- Mp Category
- main-belt (inner)Hungaria
- Epoch
- 4 September 2017 (JD 2458000.5)
- Uncertainty
- 0
- Observation Arc
- 33.15 yr (12,108 days)
- Aphelion
- 2.0621 AU
Facts from the source article.
Lore & Background
Wasserburg is a bright member of the Hungaria family, which form the innermost dense concentration of asteroids in the Solar System. It orbits the Sun in the inner main-belt at a distance of 1.8–2.1 AU once every 2 years and 9 months (991 days). Its orbit has an eccentricity of 0.06 and an inclination of 24° with respect to the ecliptic. It was first identified as 1983 EA1 at Palomar in 1983, extending the body's observation arc by 3 years prior to its official discovery observation. Wasserburg forms an asteroid pair with (350716) 2001 XO105, and was part of Petr Pravec's sample study 'Formation of asteroid pairs by rotational fission', published in the journal Nature. Between 2006 and 2014, several rotational lightcurves of Wasserburg were obtained from photometric observations by astronomers Brian Warner, Petr Pravec, and Julian Oey. Best rated lightcurve analysis gave a well-defined rotation period between 3.6231 and 3.6280 hours with a brightness variation between 0.07 and 0.60 magnitude. Due to the changing amplitude, Wasserburg is likely one of the more elongatedly shaped primary asteroids of all known smaller binaries with a diameter of less than 10 kilometers. After being already recognized as an asteroid pair, American astronomer Brian Warner observed faint mutual eclipsing and occultation events in April 2013. After repeated lightcurve subtraction, he was able to show that Wasserburg is likely a binary system with a minor-planet moon orbiting it every 15.97 hours. Assuming a depth of 0.03 magnitude, he estimated a secondary-to-primary mean-diameter ratio of 0.16±0.02. The Johnston's archive derives a diameter of 280±80 meters for the satellite, based on the primary diameter given by WISE. A semi-major axis of 2.9 kilometers is also estimated for the moon's orbit. However, photometric observations taken in 2015 could not detect the presence of a satellite and Wasserburg remains only a suspected binary.
Reader's Guide
Wasserburg is notable as a bright Hungaria asteroid and a suspected binary system, part of an asteroid pair with (350716) 2001 XO105. Its inclusion in Petr Pravec's study 'Formation of asteroid pairs by rotational fission' in Nature highlights its significance for understanding how asteroids split into pairs. The suspected satellite, indicated by mutual eclipsing events observed in April 2013, adds to its interest, though 2015 observations failed to confirm it, leaving its binary status uncertain. The asteroid's high albedo (1.000 from WISE) and elongated shape, inferred from changing lightcurve amplitudes, make it a candidate for studying binary formation and rotational fission. Its naming after Gerald J. Wasserburg, a pioneer in radiometric dating and isotope geochemistry who analyzed Moon rocks and meteorites, connects it to lunar and solar system science. The conflicting diameter measurements (1.777 km from WISE vs. 3.82 km from assumed albedo) underscore the challenges in characterizing small asteroids.
Did You Know?
- It was discovered by Carolyn Shoemaker at Palomar Observatory on 5 May 1986.
- The asteroid's suspected moon orbits every 15.97 hours, with an estimated diameter of 280±80 meters.
- Its surface albedo was measured at 1.000 by the WISE survey, an outstandingly high value.
Frequently Asked Questions
What is 4765 Wasserburg?
It is a bright asteroid belonging to the Hungaria group, orbiting in the innermost stretch of the main asteroid belt. Originally catalogued under the provisional designation 1986 JN1, it was later named in honor of geologist Gerald J. Wasserburg.
Who discovered 4765 Wasserburg and where?
American astronomer Carolyn Shoemaker identified the object on 5 May 1986 while observing from Palomar Observatory in California. The naming decision pays tribute to geologist Gerald J. Wasserburg.
What is distinctive about 4765 Wasserburg's orbit?
It circles the Sun between roughly 1.8 and 2.1 AU with a notably low eccentricity, completing one full revolution in about 991 days (2 years and 9 months). This keeps it anchored to the innermost band of the main belt as a member of the Hungaria family.
Is 4765 Wasserburg a binary or asteroid pair?
Yes — it is flagged as both a suspected binary system and an asteroid pair, indicating that two smaller bodies likely share a common barycenter rather than one large body dominating. The precise geometry is still being refined by ongoing observations.
How large and fast-spinning is 4765 Wasserburg?
WISE measurements place its diameter near 1.8 km, while a lower-albedo model stretches the estimate to about 3.8 km. It rotates once every 3.62–3.63 hours, and its high reflectivity makes it one of the brighter members of the Hungaria group.
More in Notable Asteroids, Part 3 1-24
Spotted an error? Know more?
Reader corrections go straight into our review queue. Suggest an edit · How this site is sourced