13P/Olbers

Lore & Background

Heinrich Wilhelm Matthias Olbers discovered the comet on 6 March 1815, describing it as small. It came to perihelion on 26 April 1815 and reached an apparent magnitude of about 5, faintly visible by naked eye. Its orbit was first computed by Carl Friedrich Gauss on 31 March as parabolic, and Friedrich Bessel calculated an orbital period of 73.9 years using observations from June; other astronomers of the era produced periods between 72 and 77 years. Modern solutions give an orbital period of 74.9 years for the 1815 epoch.

Unsuccessful searches for the comet throughout 1887 ended when William Robert Brooks accidentally found it on 25 August 1887. He described it as an easy object through a 9-inch reflector, with a brightish nucleus and a faint tail; it continued to brighten for a few days after perihelion, reaching an apparent magnitude of about 9. On 28 July 1887 the comet passed 0.081 AU from Mars, then passed perihelion on 8 October 1887.

The comet was recovered on 4 January 1956 by Antonín Mrkos, then located in Eridanus at an estimated magnitude of 16. He later found it in plates from the McDonald Observatory dated 12 November 1955. It passed perihelion on 19 June 1956 and reached magnitude 6.5, with a tail about one degree long.

Recovered on 24 August 2023 by Alan Hale using the Las Cumbres Observatory at Siding Spring, with pre-recovery images from 13 August. The comet then had an estimated magnitude of about 22. It came to opposition on 16 November 2023. By 14 January 2024 its magnitude was 15.3, with a strongly condensed coma 0.9 arcminutes across and a faint tail one arcminute. By 10 March 2024 it had brightened to magnitude 11.4 with a coma 4 arcminutes across. On 12 April it was observed visually at magnitude 9.2, a magnitude brighter than the ephemeris. It reached perihelion on 30 June 2024 at 1.18 AU from the Sun and 1.94 AU from Earth, expected to brighten to magnitude 7–8 but peaking at 6–7.

Before the 2023 recovery, Kinoshita calculated a future perihelion on 22 March 2094; accounting for 2023–4 observations, the nominal time is now 20 March 2094.

Reader's Guide

13P/Olbers is notable as the third comet discovered by Heinrich Olbers and as a Halley-type periodic comet with a 69-year orbit. Its observational history spans more than two centuries, with recoveries in 1887, 1956, and 2023–2024, each adding to the understanding of its orbit and behavior. The comet's 2024 apparition was well observed, reaching a peak magnitude of 6–7, and its water production rate was measured by the SWAN instrument on SOHO, reaching a maximum of 1.1×10^29 sec−1 on 3 June 2024. Infrared spectroscopy at the NASA Infrared Telescope Facility revealed abundances of H2O, OCS, C2H6, CH3OH, and H2CO, with significantly enriched CO and CH4. The unusual CO enrichment implies an upper limit on the nucleus radius of 20–30 km, but given the water production rate comparable to comets 1P/Halley and 23P/Brorsen–Metcalf at similar distances, the actual nucleus size is likely smaller, ranging from several to about 10 km in radius. There is speculation that 13P/Olbers produces an annual meteor shower on Mars, coming from the direction of Beta Canis Majoris, with a minimum orbit intersection distance of 0.0266 AU and an impact velocity of 27 km/s.

Did You Know?

• 13P/Olbers is the third of three comets discovered by Heinrich Olbers.
• The comet passed 0.081 AU from Mars on 28 July 1887.
• The comet's next perihelion is calculated for 20 March 2094.