Comet McNaught

Discovery

McNaught discovered the comet in a CCD image on 7 August 2006 during the course of routine observations for the Siding Spring Survey, which searched for Near-Earth Objects that might represent a collision threat to Earth. The comet was discovered in Ophiuchus, shining very dimly at a magnitude of about +17. From August through November 2006, the comet was imaged and tracked as it moved through Ophiuchus and Scorpius, brightening as high as magnitude +9, still too dim to be seen with the unaided eye. Then, for most of December, the comet was lost in the glare of the Sun.

Upon recovery, it became apparent that the comet was brightening very fast, reaching naked-eye visibility in early January 2007. It was visible to northern hemisphere observers, in Sagittarius and surrounding constellations, until about 13 January. Perihelion was 12 January at a distance of 0.17 AU. This was close enough to the Sun to be observed by the space-based Solar and Heliospheric Observatory (SOHO). The comet entered SOHO's LASCO C3 camera's field of view on 12 January, and was viewable on the web in near real-time. The comet left SOHO's field of view on 16 January. Due to its proximity to the Sun, the Northern Hemisphere ground-based viewers had a short window for viewing, and the comet could be spotted only during bright twilight.

As it reached perihelion on 12 January, it became the brightest comet since Comet Ikeya–Seki in 1965. The comet was dubbed the Great Comet of 2007 by Space.com. On 13 and 14 January 2007, the comet attained an estimated maximum apparent magnitude of −5.5. It was bright enough to be visible in daylight about 5°–10° southeast of the Sun from 12 to 14 January. The closest approach to the Earth occurred on 15 January 2007, at a distance of 0.82 AU.

After passing the Sun, McNaught became visible in the Southern Hemisphere. In Australia, according to Siding Spring Observatory at Coonabarabran, where the comet was discovered, it was to have reached its theoretical peak in brightness on Sunday 14 January just after sunset, when it would have been visible for 23 minutes. On 15 January the comet was observed at Perth Observatory with an estimated apparent magnitude of −4.0.

Exploration

The Ulysses spacecraft made an unexpected pass through the tail of the comet on 3 February 2007. Evidence of the encounter was published in the 1 October 2007 issue of The Astrophysical Journal. Ulysses flew through McNaught's ion tail 260 e6km from the comet's core and instrument readings showed that there was "complex chemistry" in the region.

The Solar Wind Ion Composition Spectrometer (SWICS) aboard Ulysses measured Comet McNaught's tail composition and detected unexpected ions. It was the first time that O3+ oxygen ions were detected near a comet. This suggested that the solar wind ions, which did not originally have most of their electrons, gained some electrons while passing through the comet's atmosphere.

SWICS also measured the speed of the solar wind, and found that even at 260 million kilometres (160 million miles) from the comet's nucleus, the tail had slowed the solar wind to half its normal speed. The solar wind should usually be about 700 km per second at that distance from the Sun, but inside the comet's ion tail, it was less than 401 km per second.

This was very surprising to me. Way past the orbit of Mars, the solar wind felt the disturbance of this little comet. It will be a serious challenge for us theoreticians and computer modellers to figure out the physics

Prof. George Gloeckler, the principal investigator on the Solar Wind Ion Composition Spectrometer (SWICS), said the discovery was important as the composition of comets told them about conditions approximately 4.5 billion years ago when the Solar System was formed.

Orbit

Comet C/2006 P1 took millions of years coming directly from the Oort cloud.

Given the orbital eccentricity of this object, different epochs can generate quite different heliocentric unperturbed two-body best-fit solutions to the aphelion distance (maximum distance) of this object. For objects at such high eccentricity, the Sun's barycentric coordinates are more stable than heliocentric coordinates. Using JPL Horizons, the barycentric orbital elements for epoch 2050 generate a semi-major axis of 2050 AU and a period of approximately 92,700 years.

Gallery

Image:Comet McNaught.jpg| Over Iceland on 9 January Image:McNaughtComet.jpg|Just after sunset from Perth, Western Australia on 16 January Image:Cometperth3.jpg|Over Perth, Western Australia at 9 p.m. on 17 January File:Comet McNaught at South Beach.jpg|Seen from South Beach, Fremantle, Western Australia on 17 January. The lights at the bottom are navigation lights in Gage Roads. Image:Comet McNaught Windhoek 2007 Jan 17.jpg|Windhoek, Namibia on 17 January at 8 p.m. local time File:Comet McNaught (2).jpg|Setting behind the Andes, at Bariloche, Argentina, on 17 January Image:Cometmcnaughtchrisn1.jpg| 18 January from Pukekohe, New Zealand Image:Comet McNaught from La Perouse 3.JPG| 19 January from La Perouse, Sydney, Australia Image:Comet McNaught Signal Hill 20070119 1.jpg|From Signal Hill, Cape Town on 19 January. The silhouette of Lion's Head is visible on the left, while on the right Venus sets over the Atlantic Ocean. Image:sat comet WEB.jpg|20 January from Lawlers, Western Australia Image:Villa Alemana Region of Valparaiso, Chile.jpg|Villa Alemana Region of Valparaiso, Chile on 20 January Image:2007 01 21 Comet McNaught Canberra Red Hill.jpg|from Red Hill, Canberra on 21 January Image:Mcnaught daylight20070113.jpg|Comet McNaught in broad daylight while it was visible by naked eye. Taken on 13 January at 14:00 UTC in Gais, Switzerland. Image:Comet tail.jpg|The tail of the comet Comet McNaught was still seen in the Northern Hemisphere after the comet itself was long gone. The picture also shows the Moon and Venus. Image:Inferior mirage of sunset comet.jpg|A very rare sequence of the inferior Mirage of the comet set

References

Notes

Citations

| doi-access= free | arxiv= 1204.2285

| access-date= 12 January 2007 }}

| access-date= 17 December 2009 }}

| archive-date= 16 September 2024 | archive-url= https://web.archive.org/web/20240916003236/http://sehrg.at.ua/_ld/0/29_Striated_Featur.pdf | url-status= dead }}

| display-authors= etal | doi-access= free }}

| access-date= 1 February 2011 | archive-date= 18 February 2011 | archive-url= https://web.archive.org/web/20110218054618/http://www.perthobservatory.wa.gov.au/information/comet_mcnaught_info.html | url-status= dead }}

| access-date= 18 April 2011 }}

| access-date= 16 January 2007 }}

| access-date= 16 June 2025 }}

References

1. "Report on the comet discovery and progress from Robert McNaught's homepage".
2. "Kronk's Cometography – C/2006 P1".
3. "Untitled Document".
4. "Southern Comets Homepage".
5. "C/2006 P1 (McNaught)".
6. (2007). "McNaught Captures McNaught". Astronomy Online.
7. (18 July 2007). "McNaught (C/2006 P1): Heliocentric elements 2006–2050". Jet Propulsion Laboratory.
8. (18 July 2007). "McNaught (C/2006 P1): Barycentric elements 2050". Jet Propulsion Laboratory.