|Discovered by||Alan Hale|
|Discovery date||July 23, 1995|
|The Great Comet of 1997,|
|Orbital characteristics A|
|Observation arc||8.48 years|
|Orbit type||Long period comet|
|Semi-major axis||186 AU|
|Orbital period||2520–2533 yr|
(Barycentric 2391 yr)
|Last perihelion||April 1, 1997|
|Next perihelion||4385 ± 2.0 AD|
Comet Hale–Bopp (formally designated C/1995 O1) is a comet that was perhaps the most widely observed of the 20th century and one of the brightest seen for many decades.
Alan Hale and Thomas Bopp discovered Comet Hale–Bopp separately on July 23, 1995, before it became visible to the naked eye. It is difficult to predict the maximum brightness of new comets with any degree of certainty, but Hale–Bopp met and exceeded most predictions when it passed perihelion on April 1, 1997, reaching about magnitude –1.8. It was visible to the naked eye for a record 18 months, twice as long as the Great Comet of 1811, the previous record holder. Accordingly, Hale–Bopp was dubbed the great comet of 1997.
Hale had spent many hundreds of hours searching for comets without success, and was tracking known comets from his driveway in New Mexico when he chanced upon Hale–Bopp just after midnight. The comet had an apparent magnitude of 10.5 and lay near the globular cluster M70 in the constellation of Sagittarius. Hale first established that there was no other deep-sky object near M70, and then consulted a directory of known comets, finding that none were known to be in this area of the sky. Once he had established that the object was moving relative to the background stars, he emailed the Central Bureau for Astronomical Telegrams, the clearing house for astronomical discoveries.
Bopp did not own a telescope. He was out with friends near Stanfield, Arizona, observing star clusters and galaxies when he chanced across the comet while at the eyepiece of his friend's telescope. He realized he might have spotted something new when, like Hale, he checked his star maps to determine if any other deep-sky objects were known to be near M70, and found that there were none. He alerted the Central Bureau for Astronomical Telegrams through a Western Union telegram. Brian G. Marsden, who had run the bureau since 1968, laughed, "Nobody sends telegrams anymore. I mean, by the time that telegram got here, Alan Hale had already e-mailed us three times with updated coordinates."
Hale–Bopp's orbital position was calculated as 7.2 astronomical units (AU) from the Sun, placing it between Jupiter and Saturn and by far the greatest distance from Earth at which a comet had been discovered by amateurs. Most comets at this distance are extremely faint, and show no discernible activity, but Hale–Bopp already had an observable coma. A precovery image taken at the Anglo-Australian Telescope in 1993 was found to show the then-unnoticed comet some 13 AU from the Sun, a distance at which most comets are essentially unobservable. (Halley's Comet was more than 100 times fainter at the same distance from the Sun.) Analysis indicated later that its comet nucleus was 60±20 kilometres in diameter, approximately six times the size of Halley.
Its great distance and surprising activity indicated that comet Hale–Bopp might become very bright when it reached perihelion in 1997. However, comet scientists were wary – comets can be extremely unpredictable, and many have large outbursts at great distance only to diminish in brightness later. Comet Kohoutek in 1973 had been touted as a 'comet of the century' and turned out to be unspectacular.
Hale–Bopp became visible to the naked eye in May 1996, and although its rate of brightening slowed considerably during the latter half of that year, scientists were still cautiously optimistic that it would become very bright. It was too closely aligned with the Sun to be observable during December 1996, but when it reappeared in January 1997 it was already bright enough to be seen by anyone who looked for it, even from large cities with light-polluted skies.
The Internet was a growing phenomenon at the time, and numerous websites that tracked the comet's progress and provided daily images from around the world became extremely popular. The Internet played a large role in encouraging the unprecedented public interest in comet Hale–Bopp.
As the comet approached the Sun, it continued to brighten, shining at 2nd magnitude in February, and showing a growing pair of tails, the blue gas tail pointing straight away from the Sun and the yellowish dust tail curving away along its orbit. On March 9, a solar eclipse in China, Mongolia and eastern Siberia allowed observers there to see the comet in the daytime. Hale–Bopp had its closest approach to Earth on March 22, 1997, at a distance of 1.315 AU.
As it passed perihelion on April 1, 1997, the comet developed into a spectacular sight. It shone brighter than any star in the sky except Sirius, and its dust tail stretched 40–45 degrees across the sky. The comet was visible well before the sky got fully dark each night, and while many great comets are very close to the Sun as they pass perihelion, comet Hale–Bopp was visible all night to northern hemisphere observers.
After its perihelion passage, the comet moved into the southern celestial hemisphere. The comet was much less impressive to southern hemisphere observers than it had been in the northern hemisphere, but southerners were able to see the comet gradually fade from view during the second half of 1997. The last naked-eye observations were reported in December 1997, which meant that the comet had remained visible without aid for 569 days, or about 18 and a half months. The previous record had been set by the Great Comet of 1811, which was visible to the naked eye for about 9 months.
The comet continued to fade as it receded, but is still being tracked by astronomers. In October 2007, 10 years after the perihelion and at distance of 25.7 AU from Sun, the comet was still active as indicated by the detection of the CO-driven coma. Herschel Space Observatory images taken in 2010 suggest comet Hale–Bopp is covered in a fresh frost layer. Hale–Bopp was again detected in December 2010 when it was 30.7 AU away from the Sun, and on August 7, 2012, at a 33.2 AU distance from the Sun. Astronomers expect that the comet will remain observable with large telescopes until perhaps 2020, by which time it will be nearing 30th magnitude. By this time it will become very difficult to distinguish the comet from the large numbers of distant galaxies of similar brightness.
The comet likely made its previous perihelion 4,200 years ago, in July 2215 BC. The estimated closest approach to Earth was 1.4 AU, and it may have been observed in ancient Egypt during the 6th dynasty reign of the Pharaoh Pepi II (Reign: 2247 – c. 2216 BC). Pepi's pyramid at Saqqara contains a text referring to an "nhh-star" as a companion of the pharaoh in the heavens, where "nhh" is the hieroglyph for long hair.
Hale–Bopp may have had a near collision with Jupiter in early June 2215 BC, which probably caused a dramatic change in its orbit, and 2215 BC may have been its first passage through the inner Solar System from the Oort cloud. The comet's current orbit is almost perpendicular to the plane of the ecliptic, so further close approaches to planets will be rare. However, in April 1996 the comet passed within 0.77 AU of Jupiter, close enough for its orbit to be measurably affected by the planet's gravity. The comet's orbit was shortened considerably to a period of roughly 2,533 years, and it will next return to the inner Solar System around the year 4385. Its greatest distance from the Sun (aphelion) will be about 370 AU, reduced from about 525 AU.
The estimated probability of Hale-Bopp's striking Earth in future passages through the inner Solar System is remote, about 2.5×10−9 per orbit. However, given that the comet nucleus is around 60 km in diameter, the consequences of such an impact would be apocalyptic. Weissman conservatively estimates the diameter at 35 km; an estimated density of 0.6 g/cm3 then gives a cometary mass of 1.3×1019 g. At a probable impact velocity of 52.5 km/s, impact energy can be calculated as 1.9×1032 ergs, or 4.4×109 megatons, about 44 times the estimated energy of the K-T impact event.
Over many orbits, the cumulative effect of gravitational perturbations on comets with high orbital inclinations and small perihelion distances is generally to reduce the perihelion distance to very small values. Hale–Bopp has about a 15% chance of eventually becoming a sungrazing comet through this process.
Comet Hale–Bopp was observed intensively by astronomers during its perihelion passage, and several important advances in cometary science resulted from these observations. The dust production rate of the comet was very high (up to 2.0×106 kg/s), which may have made the inner coma optically thick. Based on the properties of the dust grains—high temperature, high albedo and strong 10 μm silicate emission feature—the astronomers concluded the dust grains are smaller than observed in any other comet.
Hale–Bopp showed the highest ever linear polarization detected for any comet. Such polarization is the result of solar radiation getting scattered by the dust particles in the coma of the comet and depends on the nature of the grains. It further confirms that the dust grains in the coma of comet Hale–Bopp were smaller than inferred in any other comet.
One of the most remarkable discoveries was that the comet had a third type of tail. In addition to the well-known gas and dust tails, Hale–Bopp also exhibited a faint sodium tail, only visible with powerful instruments with dedicated filters. Sodium emission had been previously observed in other comets, but had not been shown to come from a tail. Hale–Bopp's sodium tail consisted of neutral atoms (not ions), and extended to some 50 million kilometres in length.
The source of the sodium appeared to be the inner coma, although not necessarily the nucleus. There are several possible mechanisms for generating a source of sodium atoms, including collisions between dust grains surrounding the nucleus, and "sputtering" of sodium from dust grains by ultraviolet light. It is not yet established which mechanism is primarily responsible for creating Hale–Bopp's sodium tail, and the narrow and diffuse components of the tail may have different origins.
While the comet's dust tail roughly followed the path of the comet's orbit and the gas tail pointed almost directly away from the Sun, the sodium tail appeared to lie between the two. This implies that the sodium atoms are driven away from the comet's head by radiation pressure.
The abundance of deuterium in comet Hale–Bopp in the form of heavy water was found to be about twice that of Earth's oceans. If Hale–Bopp's deuterium abundance is typical of all comets, this implies that although cometary impacts are thought to be the source of a significant amount of the water on Earth, they cannot be the only source.
Deuterium was also detected in many other hydrogen compounds in the comet. The ratio of deuterium to normal hydrogen was found to vary from compound to compound, which astronomers believe suggests that cometary ices were formed in interstellar clouds, rather than in the solar nebula. Theoretical modelling of ice formation in interstellar clouds suggests that comet Hale–Bopp formed at temperatures of around 25–45 kelvins.
Spectroscopic observations of Hale–Bopp revealed the presence of many organic chemicals, several of which had never been detected in comets before. These complex molecules may exist within the cometary nucleus, or might be synthesised by reactions in the comet.
Detection of argon
Hale–Bopp was the first comet where the noble gas argon was detected. Noble gases are chemically inert and vary from low to high volatility. Since different noble elements have different sublimation temperatures, and don't interact with other elements, they can be used for probing the temperature histories of the cometary ices. Krypton has a sublimation temperature of 16–20 K and was found to be depleted more than 25 times relative to the solar abundance, while argon with its higher sublimation temperature was enriched relative to the solar abundance. Together these observations indicate that the interior of Hale–Bopp has always been colder than 35–40 K, but has at some point been warmer than 20 K. Unless the solar nebula was much colder and richer in argon than generally believed, this suggests that the comet formed beyond Neptune in the Kuiper belt region and then migrated outward to the Oort cloud.
Comet Hale–Bopp's activity and outgassing were not spread uniformly over its nucleus, but instead came from several specific jets. Observations of the material streaming away from these jets allowed astronomers to measure the rotation period of the comet, which was found to be about 11 hours 46 minutes.
Binary nucleus question
In 1997 a paper was published that hypothesised the existence of a binary nucleus to fully explain the observed pattern of comet Hale–Bopp's dust emission observed in October 1995. The paper was based on theoretical analysis, and did not claim an observational detection of the proposed satellite nucleus, but estimated that it would have a diameter of about 30 km, with the main nucleus being about 70 km across, and would orbit in about three days at a distance of about 180 km. This analysis was confirmed by observations in 1996 using Wide-Field Planetary Camera 2 of the Hubble Space Telescope which had taken images of the comet that revealed the satellite.
Although observations using adaptive optics in late 1997 and early 1998 showed a double peak in the brightness of the nucleus, controversy still exists over whether such observations can only be explained by a binary nucleus. The discovery of the satellite was not confirmed by other observations. Also, while comets have been observed to break up before, no case had been found of a stable binary nucleus until the subsequent discovery of P/2006 VW139.
In November 1996, amateur astronomer Chuck Shramek (1950–2000) of Houston, Texas took a CCD image of the comet which showed a fuzzy, slightly elongated object nearby. His computer sky-viewing program did not identify the star, so Shramek called the Art Bell radio program Coast to Coast AM to announce that he had discovered a "Saturn-like object" following Hale–Bopp. UFO enthusiasts such as remote viewing proponent, and Emory University political science professor Courtney Brown soon concluded that there was an alien spacecraft following the comet.
Several astronomers claimed that the object was simply the 8.5-magnitude star SAO141894, including Alan Hale. They noted that the star did not appear on Shramek's computer program because the user preferences were set incorrectly. Art Bell claimed to have obtained an image of the object from an anonymous astrophysicist who was about to confirm its discovery. However, astronomers Olivier Hainaut and David Tholen of the University of Hawaii stated that the alleged photo was an altered copy of one of their own comet images.
Nancy Lieder, who claims to receive messages from aliens through an implant in her brain, stated that Hale–Bopp was a fiction designed to distract the population from the coming arrival of "Nibiru" or "Planet X", a giant planet whose close passage would disrupt the Earth's rotation, causing global cataclysm. Her original date for the apocalypse was May 2003, which passed without incident, but various conspiracy websites continued to predict the coming of Nibiru, most of whom tied it to the 2012 phenomenon. Lieder and others' claims of the planet Nibiru have been repeatedly debunked by scientists.
Its lengthy period of visibility and extensive coverage in the media meant that Hale–Bopp was probably the most-observed comet in history, making a far greater impact on the general public than the return of Halley's Comet in 1986, and certainly seen by a greater number of people than witnessed any of Halley's previous appearances. For instance, 69% of Americans had seen Hale–Bopp by April 9, 1997.
Hale–Bopp was a record-breaking comet—the farthest comet from the Sun discovered by amateurs, with the largest well-measured cometary nucleus known after 95P/Chiron, and it was visible to the naked eye for twice as long as the previous record-holder. It was also brighter than magnitude 0 for eight weeks, longer than any other recorded comet.
Carolyn Shoemaker and her husband Gene, both famous for co-discovering comet Shoemaker–Levy 9, were involved in a car crash after photographing the comet. Gene died in the crash and his ashes were sent to the Moon aboard NASA's Lunar Prospector mission along with an image of Hale–Bopp, "the last comet that the Shoemakers observed together".
- "JPL Small-Body Database Browser: C/1995 O1 (Hale–Bopp)" (2007-10-22 last obs). Retrieved December 5, 2008.
- JPL SBDB Epoch 1996
- Syuichi Nakano (February 12, 2008). "OAA computing section circular NK 1553". OAA Computing and Minor Planet Sections. Retrieved December 17, 2009.
- Horizons output. "Barycentric Osculating Orbital Elements for Comet C/1995 O1 (Hale-Bopp)". Retrieved January 31, 2011. (Solution using the Solar System Barycenter and barycentric coordinates. Select Ephemeris Type:Elements and Center:@0)
- Marsden, B. G. (1997). "Orbit Determination and Evolution of Comet C/1995 O1 (Hale-Bopp)". Earth, Moon, and Planets. 79 (1): 3–15. Bibcode:1997EM&P...79....3M. doi:10.1023/A:1006268813208. S2CID 121368997.
- "Solex 10 estimate for Next Perihelion of C/1995 O1 (Hale-Bopp)". Archived from the original on August 10, 2012. Retrieved December 18, 2009.
- Shanklin, Jonathan D. (2000). "The comets of 1995". Journal of the British Astronomical Association. 110 (6): 311. Bibcode:2000JBAA..110..311S.
- Hale, A.; Bopp, T.; Stevens, J. (July 23, 1995). "IAU Circular No. 6187". IAU. Retrieved July 5, 2011.
- Mobberley, Martin (2013), It Came From Outer Space Wearing an RAF Blazer!: A Fan's Biography of Sir Patrick Moore, Springer Science & Business Media, p. 483, ISBN 978-3319006093
- Lemonick, Michael D. (March 17, 1997). "Comet of the decade Part II". Time. Retrieved October 30, 2008.
- Newcott, William (December 1997). "The Age of Comets". National Geographic Society. Retrieved December 7, 2009.
Nobody sends telegrams anymore...
- Bopp, Thomas (1997). "Amateur Contributions in the study of Comet Hale–Bopp". Earth, Moon, and Planets. 79 (1–3): 307–308. Bibcode:1997EM&P...79..307B. doi:10.1023/A:1006262006364. S2CID 117124838.
- Marsden, B. G. (1995). "Comet C/1995 O1 (Hale-Bopp)". Minor Planet Electronic Circular. 1995-P05.
- Kidger, M. R.; Serra-Ricart, Miquel; Bellot-Rubio, Luis R.; Casas, Ricard (1996). "Evolution of a Spiral Jet in the Inner Coma of Comet Hale-Bopp (1995 O1)". The Astrophysical Journal Letters. 461 (2): L119–L122. Bibcode:1996ApJ...461L.119K. doi:10.1086/310008.
- McNaught, R. H.; West, R. M. (August 2, 1995). "Circular No. 6198". IAU. Retrieved July 5, 2011.
- Biver, N.; Rauer, H; Despois, D; Moreno, R; Paubert, G; Bockelée-Morvan, D; Colom, P; Crovisier, J; et al. (1996). "Substantial outgassing of CO from Comet Hale–Bopp at large heliocentric distance". Nature. 380 (6570): 137–139. Bibcode:1996Natur.380..137B. doi:10.1038/380137a0. PMID 8600385. S2CID 4342525.
- Fernández, Yanga R. (2002). "The Nucleus of Comet Hale-Bopp (C/1995 O1): Size and Activity". Earth, Moon, and Planets. 89 (1): 3–25. Bibcode:2002EM&P...89....3F. doi:10.1023/A:1021545031431. S2CID 189899565.
- Kidger, M.R.; Hurst, G.; James, N. (2004). "The Visual Light Curve Of C/1995 O1 (Hale-Bopp) From Discovery To Late 1997". Earth, Moon, and Planets. 78 (1–3): 169–177. Bibcode:1997EM&P...78..169K. doi:10.1023/A:1006228113533. S2CID 120776226.
- Browne, Malcolm R. (March 9, 1997). "Comet Holds Clues to Birth of Time". The New York Times.
- "The Trail of Hale-Bopp". Scientific American. March 17, 1997. Retrieved October 23, 2008.
- McGee, H. W.; Poitevin, P. (1997). "The total solar eclipse of 1997 March 9". Journal of the British Astronomical Association. 107 (3): 112–113. Bibcode:1997JBAA..107..112M.
- "Comet Hale-Bopp". Stardust. Jet Propulsion Laboratory, NASA. November 26, 2003. Retrieved October 9, 2008.
- West, Richard M. (April 13, 1997). "Comet Hale-Bopp (April 13, 1997)". European Southern Observatory. Archived from the original on May 24, 2011. Retrieved November 23, 2008.
- Shylaja, B. S. (1997). "What's New With Hale Bopp?". Bulletin of the Astronomical Society of India. 25: 155–156. Bibcode:1997BASI...25..155S.
- West, Richard M. (March 7, 1997). "Comet Hale-Bopp (March 7, 1997)". European Southern Observatory. Archived from the original on May 24, 2011. Retrieved November 25, 2008.
- Szabó, Gy. M.; Kiss, L. L.; Sárneczky, K. (2008). "Cometary Activity at 25.7 AU: Hale-Bopp 11 Years after Perihelion". Astrophysical Journal Letters. 677 (2): 121. arXiv:0803.1505. Bibcode:2008ApJ...677L.121S. doi:10.1086/588095. S2CID 13344162.
- Szabó, Gy. M.; Kiss, L. L.; Kiss, Cs.; Pál, A.; Sárneczky, K.; Juhász, A.; Hogerheijde, M. R. (2012). "Evidence for fresh frost layer on the bare nucleus of comet Hale—Bopp at 32 AU distance". Astrophysical Journal. 761 (1): 8. arXiv:1210.2785. Bibcode:2012ApJ...761....8S. doi:10.1088/0004-637X/761/1/8. S2CID 119197339.
- Szabó, M.; Sárneczky, K.; Kiss, L. L. (2011). "Frozen to death? – Detection of comet Hale-Bopp at 30.7 AU". Earth and Planetary Astrophysics. 1104: 4351. arXiv:1104.4351. Bibcode:2011A&A...531A..11S. doi:10.1051/0004-6361/201116793. S2CID 119113598.
- Dave Herald (August 7, 2012). "Comet Hale-Bopp C/1995 O1 - observed tonite". Yahoo Groups. Retrieved August 9, 2012.
- West, Richard M. (February 7, 1997). "Comet Hale-Bopp (February 7, 1997)". European Southern Observatory. Archived from the original on January 12, 2015. Retrieved January 12, 2015.
- Yeomans, Don (April 10, 1997). "Comet Hale-Bopp Orbit and Ephemeris Information". JPL/NASA. Retrieved October 23, 2008.
- "The Lost Tomb", Kent Weeks, ISBN 0-297-81847-3, page 198
- Williams, David R. (December 23, 2005). "Comet Fact Sheet". NASA (National Space Science Data Center). Retrieved December 5, 2008. (pre-perturbation orbit: semi-major axis 250AU; period 4000yr)
- Weissman, Paul R. (2007). "The cometary impactor flux at the Earth". Proceedings of the International Astronomical Union. Cambridge University Press. 2 (S236): 441–450. Bibcode:2007IAUS..236..441W. doi:10.1017/S1743921307003559. ISBN 978-0-521-86345-2.
- Bailey, M. E.; Emel'Yanenko, V. V.; Hahn, G.; Harris, N. W.; Hughes, K. A.; Muinonen, K.; Scotti, J. V. (1996). "Orbit Determination and Evolution of Comet C/1995 O1 (Hale-Bopp)". Monthly Notices of the Royal Astronomical Society. 281 (1): 916–924. Bibcode:1996MNRAS.281..916B. CiteSeerX 10.1.1.29.6010. doi:10.1093/mnras/281.3.916.
- Jewitt, David; Matthews, Henry (1999). "Particulate Mass Loss from Comet Hale-Bopp". The Astronomical Journal. 117 (2): 1056–1062. Bibcode:1999AJ....117.1056J. doi:10.1086/300743. S2CID 120740179.
- Fernández, Yanga R.; Wellnitz, Dennis D.; Buie, Marc W.; Dunham, Edward W.; Millis, Robert L.; Nye, Ralph A.; Stansberry, John A.; Wasserman, Lawrence H.; a'Hearn, Michael F.; Lisse, Carey M.; Golden, Meg E.; Person, Michael J.; Howell, Robert R.; Marcialis, Robert L.; Spitale, Joseph N. (1999). "The Inner Coma and Nucleus of Comet Hale–Bopp: Results from a Stellar Occultation". Icarus. 140 (1): 205–220. Bibcode:1999Icar..140..205F. doi:10.1006/icar.1999.6127. S2CID 43229796.
- Mason, C. G.; Gehrz, R. D.; Jones, T. J.; Woodward, C E.; Hanner, M. S.; Williams, D. M. (2001). "Observations of Unusually Small Dust Grains in the Coma of Comet Hale-Bopp C/1995 O1". The Astrophysical Journal. 549 (1): 635–646. Bibcode:2001ApJ...549..635M. doi:10.1086/319039.
- Ganesh, S.; Joshi, U. C.; Baliyan, K. S.; Deshpande, M. R. (1998). "Polarimetric observations of the comet Hale-Bopp". Astronomy and Astrophysics Supplement. 129 (5): 489–493. Bibcode:1998A&AS..129..489G. doi:10.1051/aas:1998201.
- Cremonese, G; Boehnhardt, H; Crovisier, J; Rauer, H; Fitzsimmons, A; Fulle, M; Licandro, J; Pollacco, D; et al. (1997). "Neutral Sodium from Comet Hale–Bopp: A Third Type of Tail". The Astrophysical Journal Letters. 490 (2): L199–L202. arXiv:astro-ph/9710022. Bibcode:1997ApJ...490L.199C. doi:10.1086/311040. S2CID 119405749.
- Wilson, J. K.; Baumgardner, J.; Mendillo, M. (1998). "Three tails of comet Hale-Bopp". Geophysical Research Letters. 25 (3): 225–228. Bibcode:1998GeoRL..25..225W. doi:10.1029/97GL03704.
- Cremonese, G.; Fulle, Marco (1997). "Sodium In Comets". Earth, Moon, and Planets. 79 (1): 209–220. Bibcode:1997EM&P...79..209C. doi:10.1023/A:1006245619568. S2CID 118693620.
- Meier, Roland; Owen, Tobias C. (1999). "Cometary Deuterium". Space Science Reviews. 90 (1–2): 33–43. Bibcode:1999SSRv...90...33M. doi:10.1023/A:1005269208310. PMID 11543290. S2CID 34317575.
- Rodgers, S. D.; Charnley, S. B. (2002). "Organic synthesis in the coma of Comet Hale–Bopp?". Monthly Notices of the Royal Astronomical Society. 320 (4): L61–L64. Bibcode:2001MNRAS.320L..61R. doi:10.1046/j.1365-8711.2001.04208.x.
- Stern, S. A.; Slater, D. C.; Festou, M. C.; Parker, J. Wm.; Gladstone, G. R.; A'hearn, M. F.; Wilkinson, E. (2000). "The Discovery of Argon in Comet C/1995 O1 (Hale-Bopp)". The Astrophysical Journal. 544 (2): L169–L172. arXiv:astro-ph/0011327. Bibcode:2000ApJ...544L.169S. doi:10.1086/317312. S2CID 16759616.
- Krasnopolsky, Vladimir A.; Mumma, MJ; Abbott, M; Flynn, BC; Meech, KJ; Yeomans, DK; Feldman, PD; Cosmovici, CB (1997). "Detection of Soft X-rays and a Sensitive Search for Noble Gases in Comet Hale-Bopp (C/1995 O1)". Science. 277 (5331): 1488–1491. Bibcode:1997Sci...277.1488K. doi:10.1126/science.277.5331.1488. PMID 9278508.
- "Bergeron Comet Hale-Bopp Animation". Stardust. Jet Propulsion Laboratory, NASA. Retrieved October 14, 2008.
- Warell, J.; Lagerkvist, C.-I.; Lagerros, J. S. V. (1999). "Dust continuum imaging of C/1995 O1 (Hale-Bopp): Rotation period and dust outflow velocity". Astronomy and Astrophysics Supplement Series. 136 (2): 245–256. Bibcode:1999A&AS..136..245W. doi:10.1051/aas:1999213.
- Sekanina, Z. (1997). "Detection of a Satellite Orbiting The Nucleus of Comet Hale–Bopp (C/1995 O1)". Earth, Moon, and Planets. 77 (3): 155–163. Bibcode:1997EM&P...77..155S. doi:10.1023/A:1006230712665. S2CID 122481110.
- Sekanina, Z. (1998). "Detection of a Satellite orbiting the Nucleus of Comet Hale-Bopp (C/1995 O1)". Proceedings of the First International Conference on Comet Hale-Bopp. European Organisation for Astronomical Research in the Southern Hemisphere. 77 (3): 155–163. Bibcode:1997EM&P...77..155S. doi:10.1023/A:1006230712665. S2CID 122481110.
- Marchis, F.; Boehnhardt, H.; Hainaut, O. R.; Le Mignant, D. (1999). "Adaptive optics observations of the innermost coma of C/1995 O1. Are there a "Hale" and a "Bopp" in comet Hale-Bopp?" (PDF). Astronomy & Astrophysics. 349: 985–995. Bibcode:1999A&A...349..985M. Archived from the original (PDF) on October 31, 2008. Retrieved October 29, 2008.
- McCarthy, D. W.; Stolovy, S; Campins, H; Larson, S; Samarasinha, N; Kern, S (2007). "Comet Hale–Bopp in outburst: Imaging the dynamics of icy particles with HST/NICMOS". Icarus. 189 (1): 184–195. Bibcode:2007Icar..189..184M. doi:10.1016/j.icarus.2007.01.019.
- Weaver, H. A.; Feldman, P. D.; a'Hearn, M. F.; Arpigny, C.; Brandt, J. C.; Stern, S. A. (1999). "Post-Perihelion HST Observations of Comet Hale–Bopp (C/1995 O1)". Icarus. 141 (1): 1–12. Bibcode:1999Icar..141....1W. doi:10.1006/icar.1999.6159.
- Sekanina, Z. (1997). "The problem of split comets revisited". Astronomy and Astrophysics Letters. 318: L5–L8. Bibcode:1997A&A...318L...5S.
- Jaroff, Leon; Willwerth, James (April 14, 1997). "The man who spread the myth". Time. Retrieved October 30, 2008.
- Hale, Alan (1997). "Hale-Bopp Comet Madness". Skeptical Inquirer. 21 (2): 25–28. Archived from the original on February 8, 2010. Retrieved December 6, 2009.
- Burnham, Robert; Levy, David H. (2000). Great Comets. Cambridge University Press. p. 191. ISBN 978-0-521-64600-0.
- Tholen, David J. (January 15, 1997). "Fraudulent use of an IfA/UH picture". European Organisation for Astronomical Research in the Southern Hemisphere. Archived from the original on September 30, 2007. Retrieved October 14, 2008.
- Robinson, Wendy Gale (2006). "Heaven's Gate: The End". Journal of Computer-Mediated Communication. 3 (3). doi:10.1111/j.1083-6101.1997.tb00077.x.
- George Johnson (March 28, 1997). "Comets Breed Fear, Fascination and Web Sites". The New York Times. Retrieved September 27, 2009.
- David Morrison. "The Myth of Nibiru and the End of the World in 2012". Skeptical Inquirer. Archived from the original on April 21, 2009. Retrieved April 28, 2009.
- "Nibiru: The Nonexistent Planet". Space.com. December 4, 2018. Retrieved July 17, 2020.
- Aguirre, Edwin L. (July 1997). "The Great Comet of 1997". Sky and Telescope.
- "Eugene Shoemaker Ashes Carried on Lunar Prospector". www2.jpl.nasa.gov.
|Wikimedia Commons has media related to Comet Hale-Bopp.|
- CometBase: Comet Hale-Bopp
- Cometography.com: Comet Hale-Bopp
- NASA Hale-Bopp page
- Shadow and Substance.com: Static orbital diagram
- Comet Nucleus Animation
- Kramer, Emily A.; Fernandez, Yanga R.; Lisse, Carey M.; Kelley, Michael S.P.; Woodney, Laura M. (2014). "A dynamical analysis of the dust tail of Comet C/1995 O1 (Hale–Bopp) at high heliocentric distances". Icarus. 236: 136–145. arXiv:1404.2562. Bibcode:2014Icar..236..136K. doi:10.1016/j.icarus.2014.03.033. S2CID 119201510.
- Hale-Bopp at the JPL Small-Body Database