15P/Finlay
Jupiter-family comet with one of the smallest Earth-MOIDs.
15P/Finlay is a Jupiter-family comet that orbits the Sun every 6.58 years. It was first spotted by William Henry Finlay on 26 September 1886 from the Royal Observatory at the Cape of Good Hope in South Africa. Among all known numbered periodic comets, its orbit brings it unusually close to Earth’s path, giving it one of the smallest minimum orbit intersection distances (E-MOID).
Early orbit calculations in 1886 suggested a resemblance to the lost comet of Francesco de Vico from 1844, but Lewis Boss later showed the orbits were too different for them to be the same object. During its 1906 return, the comet brightened to magnitude 6. A close pass by Jupiter in 1910 lengthened its orbital period, and in 1919 the comet was found off its predicted path—rediscovered by Sasaki at Kyoto Observatory on 25 October of that year. After 1926, the comet faded, and it was not seen again until 1953; since then, it has been observed at every return.
In the 2014–2015 apparition, the comet underwent two outbursts. On 16 December 2014, it jumped from magnitude 11 to 9, becoming visible in standard 50 mm binoculars. On 23 December 2014, it appeared only one-sixth of a degree from Mars in the evening sky, though by then it had dimmed. A second outburst on 16 January 2015 brought it back to magnitude 8.
The comet’s current Earth-MOID is 0.009 AU (about 1.3 million km). After six more perihelion passages, on 22 October 2060, 15P/Finlay will pass roughly 0.0334 AU (5 million km) from Earth, with an uncertainty of about ±2300 km. This will be one of the closest comet approaches to our planet on record.
The nucleus is small. In 2004, Jakub Cerny estimated an upper size limit of 1.5 km using non-gravitational forces, but this assumed nearly 10% of the surface was active near perihelion. Photometric data from 2000 gave an absolute magnitude of 17.2, implying a larger nucleus of 2.42 km if its geometric albedo is about 0.035.
Dust ejected during the 1995 perihelion produced a meteor shower on 29–30 September 2021, radiating from the southern constellation Ara. Additional outbursts were expected on 7 October 2021 from the 2008 and 2014 streams. A 2026 study confirmed that the Mauna Kea Observatory in Hawaii detected this shower, tracing its source to dust from the 2014 apparition.
Quick Facts
- Discoverer
- William Henry Finlay
- Discovery Site
- Royal Observatory, South Africa
- Discovery Date
- 26 September 1886
- Mpc Name
- P/1886 S1, P/1893 K1
- Designations
- 1886 VII, 1893 III, 1906 V · 1919 II, 1926 V, 1953 VII · 1960 VIII, 1967 IX, 1974 X · 1981 XII, 1988 IX
- Orbit Ref
- jpldata · MPC
- Epoch
- 21 November 2025 (JD 2461000.5)
- Observation Arc
- 135.43 years
- Obs
- 2,062
- Perihelion
- 0.997 AU
- Aphelion
- 6.025 AU
- Semimajor
- 3.511 AU
Facts from the source article.
Lore & Background
Initial orbit calculations in 1886 showed a similarity to Francesco de Vico's lost comet of 1844, but Lewis Boss noted large discrepancies and concluded they were not the same. During the 1906 apparition the comet brightened to magnitude 6. A close pass with Jupiter in 1910 increased its orbital period, and in 1919 the comet was found off predictions; a new comet discovered by Sasaki at Kyoto Observatory on 25 October 1919 was identified as Finlay's. After 1926 its magnitude declined, and it was not until 1953 that it was observed on every return.
During the 2014 perihelion passage, the comet underwent an outburst on 16 December 2014 from magnitude 11 to magnitude 9, becoming visible in common binoculars with a 50 mm objective lens. On 23 December 2014, 15P and Mars were only 1/6 of a degree apart in the sky after sunset, though the comet had dimmed considerably by then. Another outburst to magnitude 8 occurred on 16 January 2015.
Debris ejected during the 1995 perihelion passage generated a meteor shower on 29–30 September 2021 radiating from the southern constellation Ara. More outbursts were expected on 7 October 2021 from the 2008 and 2014 streams. A 2026 study confirmed detection of this meteor shower at Mauna Kea Observatory, attributing the source to dust from the 2014 apparition; the 2008 apparition was exceptionally quiet and unlikely to have contributed high-velocity dust.
Reader's Guide
15P/Finlay holds significance as a Jupiter-family comet with a notably close Earth approach potential. Its Earth-MOID of 0.009 AU is among the smallest for numbered periodic comets, and on 22 October 2060 it will pass roughly 0.0334 AU (5.00 million km) from Earth with an uncertainty of about ±2300 km, making it one of the closest comet approaches to Earth. The comet has been considered as a potential target for space exploration: a 2020 study placed Finlay as one of ten backup targets for the European Space Agency's Comet Interceptor mission, and in 2025 the proposed JAXA Next Generation Small-Body Sample Return mission selected it as one of five backup targets. Assuming a 2029 launch, Comet Interceptor could make a flyby by September 2034; if NGSR targets 15P, it could launch by 2037 and rendezvous following an Earth-Venus-Earth-Earth trajectory. The comet also produced a detectable meteor shower in 2021 from debris ejected during its 1995 and 2014 perihelion passages, confirmed by observations at Mauna Kea Observatory.
Did You Know?
- 15P/Finlay was discovered by William Henry Finlay at the Royal Observatory at Cape of Good Hope on 26 September 1886.
- The comet has one of the smallest minimum orbit intersection distances with Earth's orbit among known numbered periodic comets.
- On 22 October 2060, 15P/Finlay will pass about 5 million km from Earth, one of the closest comet approaches to Earth.
More in Named Comets, Part 5 1-24
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