Comets


Meteor

Stunning Comet's Size Shocks Scientists

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© Patrick BoomerPatrick Boomer, captured these photographs Southwest of Red Deer, Alberta, Canada. These comparison photos of Comet McNaught, taken on Jan. 6th, Jan. 7th and Jan 9th (2007) shows the difference a day makes. Both photos were taken at 5:36pm local time.
Comet McNaught, the so-called Great Comet of 2007, has been identified as the biggest comet measured to date, according to scientists, whose calculations were based on the comet's overall influence in space.

Instead of using the length of the comet's tail to measure the scale of the comet, astronomers used data from the ESA/NASA Ulysses spacecraft to determine the size of the region of space disturbed by the comet's presence - a cosmic wake across the solar system.

Through analysis of magnetometer data, scientists found evidence of a decayed shockwave surrounding the comet, which was created when ionized gas emitted from the comet's nucleus joined the fast-flowing particles of the solar wind. That, in turn, caused the solar wind around the comet to abruptly slow down.

UFO 2

England: Witness sees a "comet" fly away from him, stop, hover and make a 90 degree turn

Posted: April 13, 2010

Location of Sighting: Anstey leicester
Date of Sighting: 11 04 2010
Time: 21 20hrs

Witness Statement: I'm only making this statement as when I checked this site yesterday, there was no similar statements. But now there's 3 or 4.

My sighting was almost the same as the others in that the object was an orb shaped bright light, covered a large distance in no time at all, silently and there wasn't a a cloud in the sky anywhere.

Sun

Today The Sun Had A Comet For Breakfast

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© SOHO
The icy visitor from the outer solar system appeared with no warning on April 9th and plunged into the sun during the early hours of April 10th. One comet went in, none came out. The Solar and Heliospheric Observatory (SOHO) had a good view of the encounter.

The comet was probably a member of the Kreutz sungrazer family. Named after a 19th century German astronomer who studied them in detail, Kreutz sungrazers are fragments from the breakup of a giant comet at least 2000 years ago. Several of these fragments pass by the sun and disintegrate every day. Most are too small to see but occasionally a big fragment like today's attracts attention.

Meteor

Could a Comet Tail Have Scarred the Earth in the Recent Past?

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© UnknownDrumlins
One of the puzzles that geologists occasionally ponder is the nature of eskers and drumlins.

Eskers are winding ridges a few tens of metres high that look remarkably like railway embankments. Indeed they are often used as readymade roads and run up and down hills over distances that sometimes stretch to hundreds kilometres.

Drumlins, on the other hand, are tear drop-shaped hills a few tens of metres high and a hundreds of metres long. They often appear in large numbers with the same orientation in drumlin fields .

Geologists have long assumed that eskers and drumlins are formed by glaciers and left behind after these ice giants retreated.

There are essentially two problems. The first is the internal structure of these formations. Eskers and drumlins have have an outer layer of water-borne clay and silt with attendant fossil debris. This covers an inner core made of unsorted boulders and rocks which are entirely free of fossils. These inner cores do not appear to have been affected by the action of water. How does this structure arise?

The second is that if glaciers are responsible for eskers and drumlins, they ought to be forming now. And yet nobody can find anywhere on Earth where these structures are currently forming.

Today, Milton Zysman and Frank Wallace publish on the arXiv their explanation for the formation of these objects and it makes for fascinating, if not entirely convincing, reading.

Comment: For more information, read Laura Knight-Jadczyk's"Meteorites, Asteroids, and Comets: Damages, Disasters, Injuries, Deaths, and Very Close Calls".


Meteor

Did a comet trigger a mini Ice Age?

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© U.S. Geological SurveyA sudden plunge of global temperatures 12,900 years ago may have been caused by a comet impact, a British researcher argues.
Paris- A sudden plunge of global temperatures at the dawn of human civilisation may have been caused by a comet impact, a British researcher argues.

Known as 'the Younger Dryas', it has been also called the Big Freeze and the Last Blast of the Ice Age - but for researchers trying to understand the Earth's ancient climate, it's one of the big mysteries of the field.

Around 12,900 years ago, Earth was on a steadily warming trend after almost 100,000 years of harsh glaciation, during which ice sheets placed a swathe of the northern hemisphere under a dead hand, extending their thrall as far as south as New England and Wales.

Meteor

Was a Giant Comet Responsible for a North American Catastrophe in 11,000 BC?

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© NASA05 Hubble Space Telescope image of the breakup of a comet (73/P Schwassmann-Wachmann 3).
Some 13,000 years ago the Earth was struck by thousands of Tunguska-sized cometary fragments over the course of an hour, leading to a dramatic cooling of the planet, according to astronomer Professor Bill Napier of the Cardiff University Astrobiology Centre.

He presents his new model in the journal Monthly Notices of the Royal Astronomical Society.

The cooling, by as much as 8°C, interrupted the warming which was occurring at the end of the last ice age and caused glaciers to re-advance. Evidence has been found that this catastrophic change was associated with some extraordinary extraterrestrial event. The boundary is marked by the occurrence of a "black mat" layer a few centimetres thick found at many sites throughout the United States containing high levels of soot indicative of continental-scale wildfires, as well as microscopic hexagonal diamonds (nanodiamonds) which are produced by shocks and are only found in meteorites or impact craters. These findings led to the suggestion that the catastrophic changes of that time were caused by the impact of an asteroid or comet 4 km across on the Laurentide ice sheet, which at that time covered what would become Canada and the northern part of the United States.

Meteor

Signs of giant comet impacts found in cores

Copious ammonium may be evidence of a 50-billion-ton strike at the end of the ice age

A new study cites spikes of ammonium in Greenland ice cores as evidence for a giant comet impact at the end of the last ice age, and suggests that the collision may have caused a brief, final cold snap before the climate warmed up for good.

In the April Geology, researchers describe finding chemical similarities in the cores between a layer corresponding to 1908, when a 50,000-metric-ton extraterrestrial object exploded over Tunguska, Siberia, and a deeper stratum dating to 12,900 years ago. They argue that the similarity is evidence that an object weighing as much as 50 billion metric tons triggered the Younger Dryas, a millennium-long cold spell that began just as the ice age was loosing its grip (SN: 6/2/07, p. 339).

Precipitation that fell on Greenland during the winter after Tunguska contains a strong, sharp spike in ammonium ions that can't be explained by other sources such as wildfires sparked by the fiery explosion, says study coauthor Adrian Melott, a physicist of the University of Kansas in Lawrence.

The presence of ammonium suggests that the Tunguska object was most likely a comet, rather than asteroids or meteoroids, Melott says. Any object slung into the Earth's atmosphere from space typically moves fast enough to heat the surrounding air to about 100,000° Celsius, says Melott, so hot the nitrogen in the air splits and links up with oxygen to form nitrates. And indeed, nitrates are found in snow around the Tunguska blast. But ammonium, found along with the nitrates, contains hydrogen that most likely came from an incoming object rich in water - like an icy comet.

Comment: For an in-depth study, read Laura Knight-Jadczyk's Meteorites, Asteroids, and Comets: Damages, Disasters, Injuries, Deaths, and Very Close Calls.


Meteor

New Comet Found the Old Fashioned Way

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© Carl Hergenrother/C2A.Orbit of Comet C/2010 F4 (Machholz) and the inner planets. Created with C2A.
Don Machholz of Colfax, CA found his 11th comet on the morning of Tuesday, March 23rd. What sets Don's 11 discoveries apart from the other comets found recently is the way it was found. Nowadays comets are found by computers analyzing thousands of digital images. Only after the computers have sorted through the data is there human intervention to confirm that the object being flagged as a comet is really a comet. Don, on the other hand, has found all 11 of his comets the old-fashioned way. With no help from computers or digital cameras, Don finds his comet by peering through his telescope and identifying faint fuzzies that shouldn't be there. In fact, it is the first visual discovery of a comet since late 2006.

Comet C/2010 F4 (Machholz) is currently 11th magnitude. At this brightness, only observers with moderate-sized telescopes under dark skies will see it. Though the orbit is still somewhat uncertain, the comet appears to reach perihelion in early April at a distance of ~0.6 AU from the Sun. Unfortunately, it will not get much brighter. In fact, seeing it will only get more difficult as the comet moves closer to the Sun. Its increasing proximity to the Sun and the bright Moon now located in the morning sky means even advanced observers will have a hard time seeing it after a few days. It is possible the comet may only be observed for a week or so and then lost for the ages.

Meteor

Tomorrow Includes A Lot Of Asteroids And Comets

Dr.Allan
© DLRThe office at DLR Berlin, number 321, is the hub of all the activities of Dr Alan Harris. It is here that the threads of his largely international research work into comets and asteroids all come together.
"Surprise!" - Alan Harris loves this word. It really suits the character and profession of this 58-year old British scientist. With a Doctorate in Physics, this 'Senior Scientist' at the German Aerospace Center's Berlin-based Institute of Planetary Research (Institut fur Planetenforschung) works in the 'Asteroids and Comets' department. As a scientist, he knows that his research will always lead him to surprises and questions.

"I'll find that out at a later date - right now it's still unknown to me," he says with a grin. Even after 30 years of professional experience, Dr Harris believes that the ability to remain inquisitive and to be positively motivated about things is as important to a researcher as luck and good fortune.

Born in the industrial city of Birmingham, he has had an interest in astronomy since his earliest years: "Even as a child, I took an interest in the stars, and especially in watching the night sky. I kept on asking myself the same questions: what are they, where do they come from, and what do they mean? My mother was unable to answer these questions for me, so I derived most of my knowledge from books," says the man with the lively brown eyes.

Meteor

Giant Comets, Messengers of Life and Death

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A Neolithic comet

(Appeared in an anthology: "God, the universe and men - Why do we exist?" (ed. Wabbel, T.D.), Patmos, Dusseldorf, 2003 (original in German).

Comets are jokers in the celestial pack. They irrupt, usually without forewarning, into the orderly progression of the sky. They cross the celestial sphere in weeks or months, growing one or more tails, before fading and disappearing from sight. On rare occasions a comet may be an awesome sight, and the historical literature of the past two thousand years is sprinkled with accounts of the fear induced when a great comet, its smoky red tail bisecting the heavens, appears in the night sky. In the remote past, tales of such apparitions were often conflated with stories of disaster on Earth. A comet called Typhon in Greek mythology was connected with a mythological flood, and the legend of Phaethon, in which the sun's chariot went off course and the Earth was first burned up and then flooded, may describe an exceptional meteorite impact. There is good evidence that the sky in Neolithic times was dominated by a recurrent, giant comet, and that the Earth annually ran through an associated meteor storm of huge intensity. The origin of religion dates to these times and may be tied up with this spectacular night sky. The prospect that cosmic myths, megaliths and art dating from this time may have been responses on the ground to threats in the sky has in recent years moved from Velikovskian fancy to a subject for serious scholarly discussion. In more scientific times, too, it was often suggested that a comet striking the Earth might create create worldwide havoc. For example past encounters of Halley's comet were supposed to have coincided with Noah's flood in 2342 BC.