6615 Plutarchos
A Florian asteroid with a suspected moon discovered in 2007.
6615 Plutarchos, with the temporary designation 9512 P-L, is a stony asteroid from the inner main belt, belonging to the Flora family and suspected of having a moon. It measures roughly 3.1 kilometers across. The asteroid was found during the Palomar–Leiden survey in 1960 and later named for the Greek philosopher Plutarch. Its possible satellite was identified in 2007.
The discovery occurred on 17 October 1960. Dutch astronomers Ingrid and Cornelis van Houten at Leiden Observatory analyzed photographic plates taken by Dutch-American astronomer Tom Gehrels at Palomar Observatory in California. The "P-L" in its designation refers to the Palomar–Leiden collaboration, a productive survey in the 1960s. Gehrels used Palomar's 48-inch Schmidt telescope, then shipped the plates to Leiden for astrometric work. The three astronomers are credited with finding thousands of minor planets.
This S-type asteroid orbits with an eccentricity of 0.13 and an inclination of about 2° relative to the ecliptic. No earlier observations or precovery images exist, so its observation arc begins with the 1960 discovery.
In April 2007, astronomers Julian Oey, Donald Pray, and Petr Pravec obtained a lightcurve from photometric data. It showed a rotation period of 2.3247 hours and a brightness variation of just 0.06 magnitude, suggesting a nearly spherical shape. For an object its size, this rotation is rapid, near the 2.2-hour threshold for fast rotators.
During the same 2007 observations, mutual eclipses and occultations indicated that Plutarchos might be a synchronous binary asteroid, with a moon orbiting every 40.02 hours. However, no diameter estimate for the satellite or follow-up studies have been published since.
NASA's NEOWISE survey measured the asteroid's diameter at 3.139 kilometers, with a very high surface albedo of 0.412. In contrast, the Collaborative Asteroid Lightcurve Link assumes an albedo of 0.24—derived from 8 Flora, the family's largest member—and calculates a diameter of 3.11 kilometers based on an absolute magnitude of 14.7.
The minor planet was named for Plutarch (c. AD 45–125), the Greek writer and Platonic philosopher known for *Parallel Lives* and *Moralia*. He studied mathematics and philosophy at the Academy of Athens. Roughly half of his philosophical writings survive. The naming citation was published by the Minor Planet Center on 4 April 1996 (M.P.C.
Quick Facts
- Minorplanet
- yes
- Background
- #D6D6D6
- Discovered
- 17 October 1960
- Discoverer
- C. J. van Houten / I. van Houten-G. / T. Gehrels
- Discovery Site
- Palomar Obs.
- Mpc Name
- (6615) Plutarchos
- Pronounced
- p · l · uː · ˈ · t · ɑr · k · ə · s
- Adjective
- Plutarchian p · l · uː · ˈ · t · ɑr · k · i · ə · n
- Named After
- Plutarch / (Greek philosopher)
- Mp Category
- main-beltFlora
- Epoch
- 4 September 2017 (JD 2458000.5)
- Uncertainty
- 0
Facts from the source article.
Lore & Background
Plutarchos was discovered on 17 October 1960 by Dutch astronomer couple Ingrid and Cornelis van Houten at Leiden, on photographic plates exposed by Dutch–American astronomer Tom Gehrels at Palomar Observatory in California. The survey designation 'P-L' stands for Palomar–Leiden, named after Palomar Observatory and Leiden Observatory, which collaborated on the Palomar–Leiden survey in the 1960s. Gehrels used Palomar's Samuel Oschin telescope and shipped the plates to Leiden for astrometry. The trio are credited with discovering several thousand minor planets.
The S-type asteroid is a member of the Flora family, one of the largest groups of stony asteroids in the main-belt. Its orbit has an eccentricity of 0.13 and an inclination of 2° with respect to the ecliptic. No precovery images were taken, and no prior identifications were made, so the observation arc begins with its discovery in 1960.
A rotational lightcurve obtained from photometric observations in April 2007 by astronomers Julian Oey, Donald Pray and Petr Pravec gave a well-defined rotation period of 2.3247 hours with a brightness variation of 0.06 magnitude, indicating a nearly spheroidal shape. For an asteroid of its size, Plutarchos rotates rapidly, close to the 2.2-hour threshold spin rate for fast rotators. During those same observations, mutual eclipse/occultation events suggested that Plutarchos is a synchronous binary asteroid with a minor-planet moon orbiting it every 40.02 hours. However, neither a diameter estimate for the suspected satellite nor any follow-up observations have been published since 2007.
Reader's Guide
The significance of 6615 Plutarchos lies in its suspected binary nature, discovered through photometric observations in 2007 that revealed mutual eclipse/occultation events consistent with a synchronous moon orbiting every 40.02 hours. This makes it a candidate for further study among binary asteroids, though no follow-up observations or satellite diameter estimates have been published. Its rapid rotation period of 2.3247 hours, near the 2.2-hour fast-rotator threshold, adds to its interest for understanding asteroid spin dynamics. As a member of the Flora family, one of the largest stony asteroid groups, it contributes to knowledge of the inner main-belt population. The asteroid's naming after the Greek philosopher Plutarch connects it to cultural history, and its discovery as part of the prolific Palomar–Leiden survey highlights the collaborative effort that led to the discovery of thousands of minor planets. The discrepancy in diameter estimates—3.139 km from NEOWISE with a high albedo of 0.412 versus 3.11 km from an assumed albedo of 0.24—underscores the uncertainty in physical characterization without direct measurements.
Did You Know?
- Plutarchos was discovered on 17 October 1960 by Ingrid and Cornelis van Houten at Leiden, using plates exposed by Tom Gehrels at Palomar Observatory.
- Its rotation period of 2.3247 hours is close to the 2.2-hour threshold for fast rotators.
- A suspected moon was discovered in 2007, but no diameter estimate or follow-up observations have been published.
- The asteroid is named after the Greek philosopher Plutarch, known for Parallel Lives and Moralia.
More in Notable Asteroids, Part 3 1-24
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