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| Comet Hartley 2 | |
|---|---|
| Name | 103P/Hartley |
| Other names | Hartley 2 |
| Discoverer | Malcolm Hartley |
| Discovery date | 1986 |
| Epoch | 2010 |
| Semimajor | 3.47 AU |
| Perihelion | 1.06 AU |
| Aphelion | 5.88 AU |
| Eccentricity | 0.695 |
| Period | 6.46 yr |
| Inclination | 13.6° |
Comet Hartley 2 is a short-period Jupiter-family comet discovered in 1986 by Malcolm Hartley during observations at the UK Schmidt Telescope on behalf of the Siding Spring Observatory program. The comet returned predictably on a ~6.5-year orbit and became the target of the NASA EPOXI mission in 2010, providing high-resolution data that linked its activity to sublimation of volatiles and rotational dynamics observed by spacecraft and ground observatories. Its repeated apparitions allowed coordinated campaigns across facilities including Hubble Space Telescope, Spitzer Space Telescope, Arecibo Observatory, and numerous professional and amateur observatories worldwide.
Discovered by Malcolm Hartley in March 1986 during a survey conducted at the UK Schmidt Telescope, the object received the periodic designation 103P from the Minor Planet Center according to conventions used by the International Astronomical Union. Initial observations were communicated via the Central Bureau for Astronomical Telegrams and followed up by teams at European Southern Observatory and Cerro Tololo Inter-American Observatory, confirming its cometary nature with visible coma and low surface brightness. Subsequent recoveries at returns were reported through observatory networks such as Mauna Kea Observatories and programs like the LINEAR and NEAT surveys, refining orbital elements and activity history.
Hartley 2 follows a Jupiter-family trajectory influenced by repeated encounters with Jupiter that modify its orbit through gravitational perturbations similar to dynamics studied in the Kirkwood gaps and resonances discussed for small bodies in the Solar System. With a semimajor axis near 3.47 AU and eccentricity about 0.695, its perihelion approaches roughly 1.06 AU from the Sun while its aphelion extends beyond the orbit of Jupiter. Orbital solutions maintained by the Jet Propulsion Laboratory and the Minor Planet Center show a period near 6.46 years and an inclination ~13.6°, situating it among Jupiter-family comets catalogued alongside objects such as 2P/Encke and 9P/Tempel. Close approaches led to notable perturbations documented in ephemerides used by the Deep Space Network and mission planners at NASA.
Imaging and spectroscopic results from the EPOXI flyby, combined with infrared data from Spitzer Space Telescope and submillimeter observations at facilities like James Clerk Maxwell Telescope, indicate a small, highly active nucleus with an elongated, peanut-like shape roughly 1.2 km in overall length. Thermal modeling tied to data products from the Infrared Astronomical Satellite and radiometric studies produced estimates of low bulk density and high porosity consistent with rubble-pile or aggregate structures discussed in studies of Comet 67P/Churyumov–Gerasimenko. Spectroscopy revealed abundant water ice, carbon dioxide, carbon monoxide, and organic-bearing compounds previously identified in spectra from Rosetta, Giotto, and ground-based campaigns using the Very Large Telescope and Keck Observatory.
Hartley 2 exhibited hyperactive behavior with localized jets and coma features driven predominantly by sublimation of H2O and CO2 ices, as interpreted from narrowband photometry and mass-loss rates derived during the flyby and from monitoring at Haleakala Observatory and Kitt Peak National Observatory. The EPOXI dataset showed kilometer-scale icy grains lofted into the coma, analogous to phenomena inferred for C/1995 O1 (Hale–Bopp) and studied in cometary coma dynamics literature associated with Giotto observations. Gas production rates varied with rotation and insolation patterns, with temporal changes linked to non-gravitational forces cataloged for comets by researchers at CERN-affiliated groups and teams at the Max Planck Institute for Solar System Research.
The NASA EPOXI mission, repurposing the Deep Impact spacecraft originally launched to study 9P/Tempel 1, executed a close flyby of the comet on 4 November 2010, providing high-resolution imaging, infrared spectroscopy, and particle data. The encounter was coordinated by scientists at the Jet Propulsion Laboratory, NASA Ames Research Center, and instrument teams including members from Cornell University and the University of Maryland. EPOXI revealed the nucleus morphology, active jets, and distribution of icy grains, producing datasets integrated with ground campaigns at Gemini Observatory and space-based observations from Hubble Space Telescope that informed models of spin state evolution and outgassing-driven torques seen also in analyses of Comet 1P/Halley.
Since discovery, Hartley 2 has been monitored across multiple apparitions by professional observatories such as Subaru Telescope, Palomar Observatory, La Silla Observatory, and networks of amateur astronomers coordinated through organizations like the International Astronomical Union and the American Association of Variable Star Observers. Radio and radar observations at Arecibo Observatory and Goldstone Deep Space Communications Complex contributed constraints on nucleus size and activity; spectroscopy at Keck Observatory and Very Large Telescope characterized volatile composition. Long-term photometric series contributed to rotational period determinations and seasonal activity models comparable to those developed for Comet 103P-class bodies and studies published by teams at Harvard–Smithsonian Center for Astrophysics and Institut de Mécanique Céleste et de Calcul des Éphémérides.
Named after discoverer Malcolm Hartley following conventions of the International Astronomical Union and Minor Planet Center nomenclature, the comet's public profile increased with the EPOXI flyby, receiving coverage in outlets linked with NASA public affairs and media organizations such as BBC News, The New York Times, and National Geographic. Educational programs at institutions like the Smithsonian Institution and planetaria across the United States and Europe used the encounter to illustrate small-body science alongside historical cometary missions including Vega, Giotto, and Rosetta, inspiring outreach collaborations with amateur societies such as the Royal Astronomical Society and the Association of Lunar and Planetary Observers.
Category:Comets