161P/Hartley–IRAS is a Halley-type comet in a retrograde orbit with an orbital period of 21 years. This is the sixth and final comet discovered by the infrared space telescope IRAS, and the third of twelve comets discovered overall by Australian astronomer, Malcolm Hartley.
Observational history
1983 apparition and discovery Malcolm Hartley first detected the trail of this comet on a photographic plate exposed from the Siding Spring Observatory on 4 November 1983. At the time it was a 15th-magnitude object within the constellation Capricornus. However, before he could obtain a confirmation plate, John K. Davies and Simon F. Green reported that the Infrared Astronomical Satellite (IRAS) detected a comet on 10 November 1983. Kenneth S. Russell later confirmed that it was the same object as the one observed by Hartley by 23 November. The discovery was publicly announced on 25 November 1983.
Follow-up observations were conducted by Brian A. Skiff, James B. Gibson, Richard E. McCrosky and others in December 1983, reporting a weak condensation and a short tail. John E. Bortle reported that the comet reached peak brightness at magnitude 7.8 on 24 February 1984, indicating that it produced an outburst that brightened it by two magnitudes. It faded gradually in the coming months, and by 27 May 1984, Hartley–IRAS had a total visual magnitude of 12.2. The comet was last observed on 4 June 1984.
2005 apparition Robert H. McNaught recovered Comet Hartley–IRAS on 3 November 2004, ahead of its next perihelion on 20 June 2005. The comet was subsequently given an official numerical designation (161P) by the Minor Planet Center on 24 November 2004. It reached magnitude 11.3 on 16 June 2005.
2026 apparition
The comet was recovered from the Siding Spring Observatory by on 18 July 2026 at nearly 2–3 times fainter than predicted from its previous apparition in 2005. , the comet is around apparent magnitude 12. It reached opposition on 27 September 2026. The closest approach to Earth was on 2 October 2026 at a distance of . At perihelion on 27 November 2026, the solar elongation will be 61 degrees at a magnitude of approximately 11.
Physical characteristics On March 1984, Stephen M. Larson measured the spectroscopy of the comet, detecting emissions of OH, NH, CN, and from its coma, where it was noted to be comparable to that of 27P/Crommelin.
Orbit Brian G. Marsden confirmed Hartley–IRAS as a periodic comet on December 1983, where he suspected that the comet may have been near Jupiter sometime in 1957, although this was later refuted by Shuichi Nakano and in 1984 and 1998, respectively. , this comet currently completes a 21.4-year orbit around the Sun, reaching perihelion at a distance of and aphelion of around . It has retrograde, near-polar orbit around the Sun, with only a few close encounters with Jupiter between 1921 and 2171. Orbital calculations show that while the comet has a nominal Lyapunov time of around 650 years, non-gravitational accelerations caused by its cometary activity will likely perturb its orbit enough to make close encounters with the inner planets (particularly Venus, Earth, and Mars) in the next 5,000 years or so.
Notes
References
External links
at the Minor Planet Center database 161P/Hartley–IRAS at Gary W. Kronk's Cometography 161P/Hartley–IRAS at Seiichi Yoshida's website 161P/Hartley–IRAS at Gideon van Buitenen's website 161P/Hartley–IRAS at the Comet Observations Database (COBS)
Minor Planet Electronic Circulars (MPEC) MPEC 2004-V25: Comet P/1983 V1 = 2004 V2 Hartley–IRAS (Bibcode: 2004MPEC....V...25M) MPEC 2004-W19: Comet P/1983 V1 = 2004 V2 Hartley–IRAS (Bibcode: 2004MPEC....W...19H)