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Comet McNaught

From Wikipedia, the free encyclopedia

C/2006 P1 (McNaught)
Comet McNaught as seen from Swift's Creek, Victoria on 23 January 2007
Discovery
Discovery date7 August 2006
Designations
C/2006 P1, Comet McNaught, Great Comet of 2007
Orbital characteristics
Epoch2454113.2961 (20 January 2007)
Observation arc338 days
Number of
observations
331
Orbit typeOort cloud
Aphelion~67,000 AU (inbound)[1]
~4,100 AU (outbound)[a]
Perihelion0.1707 AU (25,540,000 km)
Semi-major axis~33,000 AU (inbound)
~2,000 AU (outbound)[a]
Eccentricity1.000019[2] (hyperbolic trajectory)
Orbital period~6 million years (inbound)[1]
~92,600 yr (outbound)[3][a]
Max. orbital speed101.9 km/s (228,000 mph)[4]
Inclination77.82768004°
Last perihelion12 January 2007[2]
Jupiter MOID0.32 AU

Comet McNaught, also known as the Great Comet of 2007 and given the designation C/2006 P1, is a non-periodic comet discovered on 7 August 2006 by British-Australian astronomer Robert H. McNaught using the Uppsala Southern Schmidt Telescope.[5] It was the brightest comet in over 40 years, and was easily visible to the naked eye for observers in the Southern Hemisphere in January and February 2007.

With an estimated peak magnitude of −5.5, the comet was the second-brightest since 1935.[6] Around perihelion on 12 January, it was visible worldwide in broad daylight. Its tail measured an estimated 35 degrees in length at its peak.[7]

The brightness of C/2006 P1 near perihelion was enhanced by forward scattering.[8]

YouTube Encyclopedic

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  • Comets: Crash Course Astronomy #21
  • January 2007 - Great Comet McNaught (C/2006 P)
  • Comet McNaught C/2009 R1

Transcription

Hey, Phil Plait here and this is Crash Course Astronomy. Since humans have been human we’ve looked to the skies for portents of the future. The Sun, the Moon, the planets, the stars; they’ve all been used for prognostication. And so have comets. A fuzzy blob, moving slowly across the stars? How could soothsayers resist? But now we know a lot more about comets. They’re beautiful, fascinating, and can bring both life and death upon our little world. Comets have been seen the sky since antiquity. Comet Halley, for example, is shown in the Bayeux Tapestry, which depicts the Norman invasion of the British Isles in the year 1066. It was seen by ancient Chinese and Greeks, too. In general, and like everything else in the sky, comets were considered omens or harbingers of human events. Sometimes they were good omens — William the Conqueror liked his chances in 1066 after seeing one — and sometimes bad — that same comet didn’t do so well for King Harold II. A comet bright enough to see with the naked eye shows up in the heavens every few years or so, and some can get spectacularly bright. In 2007, I saw Comet McNaught very near the Sun in broad daylight! When you think of a comet, you probably picture a fuzzy blob and a long tail stretching away from it. Fair enough. But there’s a bit more to them than that. Comets are in many ways similar to asteroids. They’re roughly hewn chunks of stuff left over from the formation of the solar system. Unlike asteroids, which are mostly rock with a dash of ice and maybe metal, comets are a more balanced mixture of ice and rock. And by “ice” I mean frozen water -- but also frozen carbon dioxide, carbon monoxide, methane, ammonia -- things we normally think of as gases on Earth. And by “rock” I do mean rocks, but also gravel and dust. In fact, astronomers sometimes call comets “dirty snowballs,” which isn’t a half-bad term. It’s that ice that makes comets, well, comets. When they’re way out in deep space they’re so cold that they’re basically inert lumps of ice and rock. But many are on elliptical orbits that take them from those sub-freezing depths into our neck of the woods, where the Sun can warm them. As they heat up the ice turns directly into a gas — a process called “sublimation.” The gas then flows away from the comet, creating a cloud around it. This makes the comet look fuzzy, and actually in the past they’ve been called “hairy stars.” I like that term too, and in a sense we still use it. The solid part of the comet is called the nucleus, and the gaseous cloud around it is called the coma — Latin for “hair.” In fact, that’s why we called them “comets.” As the ice sublimates, the bits of rock and gravel and dust embedded in it can be freed and leave the nucleus as well. This material is what forms the comet’s tail, but how that happens depends on which material you’re talking about. The gas and the dust from comets form two different tails. Gas molecules emitted by the comet get ionized by the Sun’s ultraviolet light. That means they lose electrons, becoming charged, and charged particles are highly susceptible to magnetic fields. The solar wind is a stream of charged particles blown out by the Sun, and carries a magnetic field with it. As the wind hits the ionized gas from the comet, it picks up those particles and carries them downstream, away from the Sun. The solar wind is usually moving far, far faster than the comet, so this “ion tail” winds up pointing directly away from the Sun. The dust, on the other hand, is influenced more by sunlight. Light from the Sun exerts a small but inexorable pressure, and this pushes on the dust particles. The dust streams away, but because the pressure isn’t as intense as the solar wind is on the gas tail, the dust tail blows away more lazily, and tends to lag behind the comet in its orbit. That means the two tails usually point in two different directions! In some comets, like 1997’s incredibly bright and gorgeous Comet Hale-Bopp, this is pretty obvious. The dust tails look white or a teeny bit yellowish, due to reflected sunlight, while the ion tail glows blue or green, depending on the primary constituents of the gas. Carbon monoxide tends to emit blue light, while carbon molecules glow a ghostly green. A comet’s tail can stretch for tens of millions of kilometers. But, despite their length, tails are incredibly low density, as low as a few hundred atoms per cubic centimeter. The air you breathe is a million billion times denser! In 1910, Earth passed through the tail of Comet Halley. This caused some public fear because cyanogen, a deadly gas, had been detected in the tail! But of course nothing happened; it turns out getting a gazillionth of the toxic dose isn’t that a big of a problem. Broadly speaking, comets are classified by their orbits. If they have orbital period less than 200 years they’re called short-period comets. These tend to orbit the Sun in the same plane as the planets, and go around the Sun in the same direction as well. From Earth, we see them sticking near the ecliptic, the line across the sky that marks the annual path of the Sun. Comets that take longer than two centuries to go around the Sun are called long-term comets, and have orbits that are tilted every which-way. That means they can appear anywhere in the sky. But this raises an interesting point: Comets go away. Every time they get near the Sun and start outgassing, they lose mass. Over time they get smaller. Eventually, they should… evaporate. Pfffft! Some do this all at once because they dive into the Sun, skimming our star’s surface. We call those Sundivers or Sungrazers. Many of those may actually be pieces from a bigger comet that broke up in space nearly a thousand years ago. But besides those, we know of some comets with orbits that can be short, some with periods of just a few years. Even a century is like a single flap of a mosquito’s wing compared to the lifetime of the solar system! How can comets be billions of years old if their orbits bring them close to the Sun all the time? Astronomers wondered about this very thing. Over the years they came up with an idea: Maybe, out past Neptune, there’s a repository of comets. Chunks of dirty ice, millions of them, billions, orbiting the Sun where it’s perpetually cold. They could have orbits that last for millennia or more. But then something tweaks them, makes them fall toward the Sun. In fact, there may be two such regions, since we have both short period and long term comets. Turns out: this idea is correct! We now know enough about those distant regions of the solar system that they deserves their own episode, so we’ll dive into that topic later. So. What do comets look like up close? Like, really close? Studying them from Earth is hard. The coma obscures the nucleus, making it nearly impossible to see it directly. Ahhh, “from Earth”. If you instead send your telescope to a comet, things change. We first did that in the 1980s, the last time Comet Halley came around. Several nations sent spacecraft to fly past the comet, and the Soviet mission Vega 1 was the first to successfully get pictures of the nucleus. The low-resolution images revealed a dark lump highlighted with two bright spots, later determined to be jets of gas streaming away. These images were used to better determine the position of the nucleus, and a few days later the European probe Giotto zipped past the nucleus at an incredibly close distance of just 600 kilometers. Those pictures were more detailed, and showed us a flying mountain, an irregular chunk 15 x 8 kilometers in size. And it was dark, reflecting only 4% of the light that hit it. That makes the nucleus as black as asphalt! You might think that all that ice would be shiny, but it’s not that simple. Most of Halley’s nucleus is covered in thick dust laced with darker molecules, with only a few spots emitting gas. Most likely, there are deposits of ice under the surface, and only some of them receive enough heat from the Sun to sublimate and blow out gas. This has been seen with other comets as well; the gas is emitted from specific spots on the comet, venting out from cracks in the crusty surface. The surfaces of comets must be inhomogeneous, different in different places. That fact was brought home magnificently in 2014 by another European mission, Rosetta. It went into orbit around the comet 67P/Churyumov- Gerasimenko, and found it to be a bizarre little object. Measuring about 4 kilometers end-to-end, 67P has two lobes connected by a narrow neck, looking very much like a cosmic rubber ducky. The surface is completely devoid of craters; clearly the surface is very young. Images show jets of gas emitted from very specific places on the surface, and there are wide circular pits here and there which may be gas vents, growing wider over time as the ice below is depleted. Surprisingly, the surface is fairly tough and hard, when some scientists expected it to be fluffier. The comet has a very low density, similar to rubble-pile asteroids, so it was expected that the surface would be soft. Rosetta sent down a lander named Philae to set down on the surface, using harpoons to anchor itself, but instead the lander bounced, unable to penetrate the tougher-than-expected material. One idea to explain this is that the ice is porous and fluffier inside the comet, but as it nears the Sun the ice at the surface warms and changes its structure, forming that harder crust. As for the double-lobed thing, well that’s a bit baffling. We see some asteroids shaped that way as well. It’s possible 67P used to be two separate comets that had a low speed collision and stuck together. Or maybe it used to be one big lump, but over the eons the ice in the middle sublimated more, leaving behind the two lobes. Rosetta is the first time in human history we’ve had a probe orbiting a comet, studying it up close and long-term. We’re still learning, still figuring this stuff out. Incidentally, I mentioned earlier that a) comets have lots of ice in them, and 2) they also get really close to Earth sometimes. In fact, they can hit us! Now not to get all technical and scientificy, but that is what we would call “bad,” as we’ll discuss in an upcoming episode. But billions of years ago lots of comets hit the Earth not long after our planet formed. Together with asteroids — many of which are also rich in water ice — they may have brought a significant amount of water to Earth! Scientists are still wrestling over the details of this, and it may be a while before the actual numbers are nailed down, but it’s an intriguing thought. Even more interesting? In 2004, NASA’s Stardust space probe physically passed through the coma of comet Wild 2, collecting samples that were returned to Earth. Careful analysis of the material found the presence of organic, carbon based molecules in them. And not just any random molecules, but complex ones, including amino acids! These are the building blocks of all life on Earth; amino acids are what our bodies use to create proteins. It’s possible that the ingredients of life on Earth didn’t start here, but instead were brought to our planet from comet impacts. Or, at least, there was a mix of the two. If that’s the case, then in a sense, all life on Earth is part alien. How about that? But what gets me are the philosophical ramifications of this. When we look into space, when we examine our celestial neighbors, when we send probes to comets and survey what we find, we’re looking at our own origins. Comets are like time machines, allowing us to investigate our past, four billion years back, hinting at the secrets of the origin of life itself. And you thought astronomy was just lying out in a field and looking up. Well, it is, but if you let it, it’s also a whole lot more. Today you learned that comets are chunks of ice and rock that orbit the Sun. When they get near the Sun the ice turns into gas, forming the long tail, and also releases dust that forms a different tail. We’ve visited comets up close and found them to be lumpy, with vents in the surface that release the gas as ice sublimates. Eons ago, comets (and asteroids) may have brought a lot of water to Earth -- as well as the ingredients for life. Crash Course Astronomy is produced in association with PBS Digital Studios. They have a ton of good shows over on their channel so you should head over there and take a look. This episode was written by me, Phil Plait. The script was edited by Blake de Pastino, and our consultant is Dr. Michelle Thaller. It was directed by Nicholas Jenkins, the script supervisor and editor is Nicole Sweeney, the sound designer is Michael Aranda, and the graphics team is Thought Café.

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.[7] Then, for most of December, the comet was lost in the glare of the Sun.[citation needed]

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).[9] The comet entered SOHO's LASCO C3 camera's field of view on 12 January,[9] and was viewable on the web in near real-time. The comet left SOHO's field of view on 16 January.[9] 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.[citation needed]

As it reached perihelion on 12 January, it became the brightest comet since Comet Ikeya–Seki in 1965.[6] The comet was dubbed the Great Comet of 2007 by Space.com.[10] On 13 and 14 January 2007, the comet attained an estimated maximum apparent magnitude of −5.5.[11] It was bright enough to be visible in daylight about 5°–10° southeast of the Sun from 12 to 14 January.[12] Perigee (closest approach to the Earth) was 15 January 2007, at a distance of 0.82 AU.[13]

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,[14] 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.[citation needed]

Ulysses probe

Animation of Ulysses' trajectory from 6 October 1990 to 29 June 2009
  Ulysses ·   Earth ·   Jupiter ·   C/2006 P1 ·   C/1996 B2 ·   C/1999 T1

The Ulysses spacecraft made an unexpected pass through the tail of the comet on 3 February 2007.[15] Evidence of the encounter was published in the 1 October 2007 issue of The Astrophysical Journal.[16] Ulysses flew through McNaught's ion tail 260 million kilometres (160 million miles) from the comet's core and instrument readings showed that there was "complex chemistry" in the region.[15]

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.[15]

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 kilometres (435 mi) per second at that distance from the Sun, but inside the comet's ion tail, it was less than 400 km (250 mi) per second.[citation needed]

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

— Michael Combi, [15]

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.

Here we got a direct sample of this ancient material which gives us the best information on cometary composition. We're still in the process of figuring out what it tells us. We're contributing part of the whole puzzle. The benefits of such an observation are important. They constrain the interactions of such comets with the Sun, including how the comets lose mass. They also examine the question of how a sudden injection of neutral and cold material interacts with hot solar-like plasmas. That occurs in other places of the universe and we were able to study it right here

Period

Comet C/2006 P1 took millions of years coming directly from the Oort cloud.[1] It follows a hyperbolic trajectory (with an osculating eccentricity larger than 1)[2] during its passage through the inner Solar System, but the eccentricity will drop below 1 after it leaves the influence of the planets and it will remain bound to the Solar System as an Oort cloud comet.[17]

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.[b] 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.[18]

Gallery

See also

Notes

  1. ^ Solution using the Solar System Barycenter
  2. ^ Read osculating orbit for more details about heliocentric unperturbed two-body solutions

References

  1. ^ a b c Horizons output. "Barycentric Osculating Orbital Elements for Comet C/2006 P1 (McNaught)". Solution using the Solar System Barycenter. Ephemeris Type:Elements and Center:@0 (To be outside planetary region, inbound epoch 1950 and outbound epoch 2050)
  2. ^ a b c "JPL Small-Body Database Browser: C/2006 P1 (McNaught)" (2007-07-11 last obs.). Retrieved 17 December 2009.
  3. ^ "Comet C/2006 P1 (McNaught) – facts and figures". Perth Observatory in Australia. 22 January 2007. Archived from the original on 18 February 2011. Retrieved 1 February 2011.
  4. ^ "Horizons Batch for 2007-Jan-12 perihelion velocity". JPL Horizons. Retrieved 22 January 2023.
  5. ^ "Report on the comet discovery and progress from Robert McNaught's homepage". Archived from the original on 19 January 2007. Retrieved 17 January 2007.
  6. ^ a b "Brightest comets seen since 1935". Harvard. Archived from the original on 28 December 2011. Retrieved 12 January 2007.
  7. ^ a b "Kronk's Cometography – C/2006 P1". Retrieved 21 January 2010.
  8. ^ Marcus, Joseph N. (October 2007). "Forward-Scattering Enhancement of Comet Brightness. II. The Light Curve of C/2006 P1" (PDF). International Comet Quarterly. pp. 119–130.
  9. ^ a b c "Brightest Comet in Over Forty Years". SOHO (Hot Shots). 4 February 2007. Retrieved 18 April 2011.
  10. ^ The Great Comet of 2007: Watch it on the Web[permanent dead link] Yahoo News, January by Joe Rao of SPACE.com Skywatching Columnist. Accessed 16 January 2007
  11. ^ "C/2006 P1 ( McNaught )".
  12. ^ "Untitled Document".
  13. ^ "Southern Comets Homepage". Retrieved 17 January 2007.
  14. ^ "C/2006 P1 (McNaught)". Archived from the original on 20 January 2007.
  15. ^ a b c d e "A chance encounter with a comet". Astronomy. 2 October 2007. Archived from the original on 6 February 2012.
  16. ^ Neugebauer, M.; et al. (2007). "Encounter of the Ulysses Spacecraft with the Ion Tail of Comet MCNaught". The Astrophysical Journal. 667 (2): 1262–1266. Bibcode:2007ApJ...667.1262N. doi:10.1086/521019.
  17. ^ "McNaught (C/2006 P1): Heliocentric elements 2006–2050". Jet Propulsion Laboratory. 18 July 2007. Retrieved 10 November 2018.
  18. ^ "McNaught (C/2006 P1): Barycentric elements 2050". Jet Propulsion Laboratory. 18 July 2007. Retrieved 10 November 2018.

External links

This page was last edited on 12 January 2024, at 14:38
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