87P/Bus
Encke-type comet discovered by Schelte J. Bus in 1981.
87P/Bus is an Encke-type comet that completes one orbit around the Sun every 6.37 years. It holds the distinction of being the only comet ever discovered by American astronomer Schelte J. Bus.
Bus first spotted the comet on the night of 2 March 1981, using a photographic plate taken with the 1.2-meter UK Schmidt telescope at Siding Spring Observatory. After the discovery, Kenneth S. Russell observed a faint tail extending about 20 arcseconds to the northwest, with an apparent magnitude estimated at 17.5. Preliminary orbital calculations made by Brian G. Marsden on 9 March 1981 suggested the comet might be short-periodic, a conclusion later confirmed when Bus located precovery images dating back to 9–13 February 1981. The comet has been observed during every subsequent return, most recently in 2020.
Initial CCD photometry from the La Palma Observatory in December 1998 placed an upper limit on the comet's nuclear radius at roughly 0.6–0.8 kilometers. Later observations by the Hubble Space Telescope in 2009 revised this estimate downward to 0.27 ± 0.01 kilometers. Hubble data also revealed the nucleus is elongated, with an a/b ratio greater than 2.2, and its rotational period is approximately 32.0 ± 9.0 hours.
The comet's orbit has been significantly altered by two close approaches to Jupiter. On 13 May 1952, it passed within 0.0668 AU (9.99 million kilometers) of the planet, which reduced its orbital period from 12.46 years to 6.43 years and its perihelion distance from 4.43 AU to 2.13 AU. A second close approach on 24 February 2023, at a distance of 0.182 AU (27.2 million kilometers), increased the perihelion to 3.62 AU and lengthened the orbital period to 9.58 years.
Quick Facts
- Discovery Ref
- IAUC_3578
- Discoverer
- Schelte J. Bus
- Discovery Site
- Siding Spring Observatory / (UK Schmidt Telescope)
- Discovery Date
- 2 March 1981
- Mpc Name
- P/1981 E1, P/1987 B4
- Designations
- 1981 XI, 1987 XXXIV · 1994 XVI · 1981b, 1987f, 1993b
- Orbit Ref
- jpldata · MPC
- Epoch
- 31 May 2025 (JD 2459000.5)
- Observation Arc
- 39.57 years
- Earliest Precovery Date
- 9 February 1981
- Obs
- 801
- Perihelion
- 2.099 AU
Facts from the source article.
Lore & Background
87P/Bus was discovered by Schelte J. Bus on the night of 2 March 1981 from a photographic plate taken with the 1.2m UK Schmidt telescope at the Siding Spring Observatory. Additional observations by Kenneth S. Russell noted a faint tail about 20 arcseconds in length to the northwest, with an estimated apparent magnitude of 17.5. Preliminary orbital calculations on 9 March 1981 led Brian G. Marsden to conclude the comet might be short-periodic, which was later confirmed when Bus found precovery images from 9–13 February 1981. The comet has been observed on each subsequent apparition, most recently in 2020.
Preliminary CCD photometry from the La Palma Observatory in December 1998 gave an upper limit of 0.6–0.8 km for the nuclear radius. Later Hubble Space Telescope observations in 2009 revised the size to 0.27±0.01 km in radius and showed the nucleus to be elongated, with an a/b ratio greater than 2.2. Its rotational period is estimated at 32.0±9.0 hours.
A close approach to Jupiter on 13 May 1952, at a distance of 0.0668 AU (9.99 million km), lowered the orbital period from 12.46 years and the perihelion distance from 4.43 AU to 6.43 years and 2.13 AU respectively. Another close approach to Jupiter on 24 February 2023, at a distance of 0.182 AU (27.2 million km), raised the perihelion to 3.62 AU and the orbital period to 9.58 years.
Reader's Guide
87P/Bus holds significance as the only comet discovered by Schelte J. Bus, an American astronomer. Its discovery on a photographic plate from the 1.2m UK Schmidt telescope at Siding Spring Observatory, and the subsequent confirmation via precovery images, illustrate the collaborative nature of early 1980s comet hunting. The comet's orbital history is notably shaped by two close approaches to Jupiter: one in 1952 that dramatically shortened its orbital period and perihelion distance, and another in 2023 that increased both. These gravitational interactions highlight the dynamic evolution of short-period comets. Physical studies, from ground-based photometry in 1998 to Hubble Space Telescope observations in 2009, have refined our understanding of its size and shape, revealing an elongated nucleus with a radius of about 0.27 km. The comet's consistent observation at every apparition since discovery underscores its value as a well-tracked object in the Encke-type family.
Did You Know?
- 87P/Bus is the only comet discovered by American astronomer Schelte J. Bus.
- A close approach to Jupiter on 13 May 1952 lowered its orbital period from 12.46 to 6.43 years.
Frequently Asked Questions
Who is 87P/Bus?
87P/Bus is a short-period, Encke-type comet that circles the Sun roughly every 6.37 years. It was named after its discoverer, American astronomer Schelte J. Bus, who first caught it on a photographic plate in early March 1981.
What type of comet is 87P/Bus?
It belongs to the Encke family of comets, sharing a similar orbital period and inclination with the prototype 2P/Encke. Its current orbital period sits at about 6.37 years, placing it among the shorter-period objects in the inner solar system.
How big is 87P/Bus?
Hubble Space Telescope observations in 2009 estimated the nucleus radius at roughly 0.27 km, with an uncertainty of about a tenth of a kilometer. The comet tumbles on its axis with a rotational period of approximately 32 hours, though the measurement carries a spread of roughly nine hours.
Where and how was 87P/Bus found?
Bus identified it on a photographic plate exposed with the 1.2-meter UK Schmidt telescope at Siding Spring Observatory in Australia on the night of 2 March 1981. Shortly after, Kenneth S. Russell confirmed a faint tail stretching about 20 arcseconds toward the northwest at an apparent magnitude near 17.5.
Why is 87P/Bus notable?
It holds the unique distinction of being the only comet ever credited to Schelte J. Bus's discovery. As an Encke-family member found in the early 1980s, it also serves as a useful reference point for tracking the dynamics of the broader Encke group.
More in Periodic Comets 1-24
Spotted an error? Know more?
Reader corrections go straight into our review queue. Suggest an edit · How this site is sourced