161P/Hartley–IRAS

Halley-type comet the other comets of the same name Comet Hartley (disambiguation)Comet Hartley Comet IRAS July 2026 161P/Hartley–IRAS 161P-20260930BC.jpg 161P/Hartley–IRAS on 30 September 2026 11PM PDT with a 6" refractor and combined stacks on the comet and stars. IAUC_3894 Malcolm HartleyIRAS 4–10 November 1983 P/1983 V1P/2004 V2 1984 III, 1983vICQ1 jpldata MPC 9 June 2026(JD 2461200.5) 42.77 yearsobs_arc 425 1.265 AU 14.178 AU 7.722 AU 0.83616 21.457 years 95.791° 1.475° 47.068° 352.14° 0.540 0.442 AU 0.112 AU 7.8(1983 apparition) 11.5 15.0 20 June 2005 27 November 2026Horizons2026 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,Marsden_1986 and the third of twelve comets discovered overall by Australian astronomer, Malcolm Hartley.hartley_comet Observational history thumb|left|Comet 161P/Hartley–IRAS, photographed on 6 October 2026 in Tallinn, Estonia. The star-aligned stack shows the comet’s movement during the imaging session. 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.Kronk_2017 At the time it was a 15th-magnitude object within the constellation Capricornus.Reported initial position upon discovery was: α 21 53.6, δ –21 18Kronk_2017 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.Kronk_2017 The discovery was publicly announced on 25 November 1983.IAUC_3894 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.IAUC_3896 John E. Bortle reported that the comet reached peak brightness at magnitude 7.8 on 24 February 1984,IAUC_3918 indicating that it produced an outburst that brightened it by two magnitudes.Kronk_2017 It faded gradually in the coming months, and by 27 May 1984, Hartley–IRAS had a total visual magnitude of 12.2.IAUC_3952 The comet was last observed on 4 June 1984.Kronk_2017 2005 apparition Robert H. McNaught recovered Comet Hartley–IRAS on 3 November 2004, ahead of its next perihelion on 20 June 2005.IAUC_8428 The comet was subsequently given an official numerical designation (161P) by the Minor Planet Center on 24 November 2004.IAUC_8445 It reached magnitude 11.3 on 16 June 2005.IAUC_8555 2026 apparition thumb|left| 161P/Hartley–IRAS on 11 September 2026. Images stacked on the moving comet creating star trails around it. The comet was recovered from the Siding Spring Observatory by Hirohisa Sato de Hirohisa Sato on 18 July 2026 at nearly 2–3 times fainter than predicted from its previous apparition in 2005.CBET_5718 2026 10, the comet is around apparent magnitude 12.cobs Van_Buitenen It reached opposition on 27 September 2026.Opposition The closest approach to Earth was on 2 October 2026 at a distance of 0.505 AU e6km unit.Van_Buitenen At perihelion on 27 November 2026, the solar elongation will be 61 degrees at a magnitude of approximately 11.Van_Buitenen Physical characteristics On March 1984, Stephen M. Larson measured the spectroscopy of the comet, detecting emissions of OH, NH, CN, C3 and C2 from its coma, where it was noted to be comparable to that of 27P/Crommelin.IAUC_3926 Orbit Brian G. Marsden confirmed Hartley–IRAS as a periodic comet on December 1983,IAUC_3903 where he suspected that the comet may have been near Jupiter sometime in 1957,IAUC_3898 although this was later refuted by Shuichi Nakano and Kazuo Kinoshita ja 木下一雄 in 1984 and 1998, respectively.Kronk_2017 2026 08, this comet currently completes a 21.4-year orbit around the Sun, reaching perihelion at a distance of 1.27 AU e6km unit and aphelion of around 14.2 AU e9km unit.MPC It has retrograde, near-polar orbit around the Sun,Kankiewicz_2021 with only a few close encounters with Jupiter between 1921 and 2171.jpldatajupiter_encounters Orbital calculations show that while the comet has a nominal Lyapunov time of around 650 years,Kankiewicz_2021 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.Kankiewicz_2021 Notes "hartley_comet" Malcolm Hartley previously recovered 79P/du Toit–Hartley and 80P/Peters–Hartley in February and July 1982 respectively, both of which he is credited as co-discoverer. "jupiter_encounters" Comet Hartley–IRAS encountered Jupiter in 1921 (0.385 AU), and will make further close flybys by 2028 (0.397 AU) and 2171 (0.645 AU) respectively. "obs_arc" Observation arc from the Minor Planet Center database covering dates from 4 November 1983 until 13 August 2026. References H. Sato M. Masek S. Nakano etal D. W. Green Comet 161P/Hartley–IRAS http://www.cbat.eps.harvard.edu/iau/cbet/005700/CBET005718.txt Central Bureau Electronic Telegrams 2026-07-18 5718 1 TXT J. K. Davies S. F. Green K. S. Russell M. Hartley B. G. Marsden Comet Hartley–IRAS (1983v) http://www.cbat.eps.harvard.edu/iauc/03800/03894.html IAU Circular 1983-11-25 3894 1 1983IAUC.3894....1D K. S. Russell J. B. Gibson B. A. Skiff etal B. G. Marsden Comet Hartley–IRAS (1983v) http://www.cbat.eps.harvard.edu/iauc/03800/03896.html IAU Circular 1983-12-05 3896 2 1983IAUC.3896....2R N. G. Thomas E. Bowell E. Everhart D. W. Green B. G. Marsden Comet Hartley–IRAS (1983v) http://www.cbat.eps.harvard.edu/iauc/03800/03898.html IAU Circular 1983-12-09 3898 2 1983IAUC.3898....2T B. G. Marsden Periodic Comet Hartley–IRAS (1983v) http://www.cbat.eps.harvard.edu/iauc/03900/03903.html IAU Circular 1983-12-21 3903 2 1983IAUC.3903....2M J. C. Marlin C. S. Morris J. E. Bortle B. G. Marsden Periodic Comet Hartley–IRAS (1983v) http://www.cbat.eps.harvard.edu/iauc/03900/03918.html IAU Circular 1984-02-24 3918 1 S. M. Larson D. W. Green J. E. Bortle B. G. Marsden Periodic Comet Hartley–IRAS (1983v) http://www.cbat.eps.harvard.edu/iauc/03900/03926.html IAU Circular 1984-03-09 3926 2 C. S. Morris D. W. Green Periodic Comet Hartley–IRAS (1983v) http://www.cbat.eps.harvard.edu/iauc/03900/03952.html IAU Circular 1984-06-14 3952 4 1984IAUC.3952....4M R. H. McNaught D. W. Green Comet P/2004 V2 (Hartley–IRAS) http://www.cbat.eps.harvard.edu/iauc/08400/08428.html IAU Circular 2004-11-05 8428 1 2004IAUC.8428....1M D. W. Green Comets 161P/Hartley–IRAS and 162P/Siding Spring http://www.cbat.eps.harvard.edu/iauc/08400/08445.html IAU Circular 2004-11-24 8445 6 2004IAUC.8445....6G J. J. Gonzalez N. Biver D. W. Green Comet 161P/Hartley–IRAS http://www.cbat.eps.harvard.edu/iauc/08500/08555.html IAU Circular 2005-07-01 8555 4 2005IAUC.8555....4G Comet Names and Designations http://www.icq.eps.harvard.edu/names1.html International Comet Quarterly 2026-07-07 161P/Hartley–IRAS – JPL Small-Body Database Lookup https://ssd.jpl.nasa.gov/tools/sbdb_lookup.html#/?sstr=161P ssd.jpl.nasa.gov Jet Propulsion Laboratory 2012-07-26 P. Kankiewicz I. Włodarczyk Impact of non-gravitational effects on chaotic properties of retrograde orbits https://www.aanda.org/articles/aa/pdf/2021/02/aa37738-20.pdf Astronomy & Astrophysics 2021 646 182–197 2021A&A...646A.182K 2101.04364 10.1051/0004-6361/202037738 free G. W. Kronk M. Meyer D. A. J. Seargent Cometography: A Catalog of Comets 6: 1983–1994 2017 Cambridge University Press Cambridge 978-0-521-87216-4 56–60 B. G. Marsden Comets in 1983 Quarterly Journal of the Royal Astronomical Society 1986 27 102–113 1986QJRAS..27..102M 161P/Hartley–IRAS Orbit http://www.minorplanetcenter.net/db_search/show_object?object_id=161P Minor Planet Center 2014-06-18 COBS Observation list: 161P https://www.cobs.si/obs_list?id=393 Crni Vrh Observatory 2026-08-10 Comet 161P Lightcurve G. van Buitenen 161P/Hartley–IRAS https://astro.vanbuitenen.nl/comet/161 astro.vanbuitenen.nl 2026-04-14 Horizons Batch for 161P/Hartley–IRAS on 2026-Sep-27 JPL Horizons https://ssd.jpl.nasa.gov/horizons_batch.cgi?batch=1&COMMAND=%27161P%27&START_TIME=%272026-Sep-27%27&STOP_TIME=%272026-Sep-28%27&STEP_SIZE=%273%20hours%27&QUANTITIES=%271,20,23,29%27 2026-08-13 Horizons Batch for 161P/Hartley–IRAS on 2026-Nov-27 JPL Horizons Perihelion occurs when rdot flips from negative to positive https://ssd.jpl.nasa.gov/horizons_batch.cgi?batch=1&COMMAND=%27161P%27&START_TIME=%272026-Nov-24%27&STOP_TIME=%272026-Nov-30%27&STEP_SIZE=%273%20hours%27&QUANTITIES=%2719%27 2022-06-22 (JPL#60 Soln.date: 2021-Apr-15) External links 1000042 161P 161P/Hartley–IRAS 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) 160P/LINEAR 162P/Siding Spring Category:Periodic comets 161P 161P 0161 Category:Discoveries by Malcolm Hartley Category:Discoveries by IRAS 0161 * *