Comets


Meteor

North America Comet Theory Questioned

Rex Dalton
Nature News
Mon, 12 Oct 2009 10:00 UTC
San Jon site
© Vance HollidaySediments at the San Jon site, in eastern New Mexico, contained very low abundances of magnetic spherules said to be evidence of an impact.
No evidence of an extraterrestrial impact 13,000 years ago, studies say.

An independent study has cast more doubt on a controversial theory that a comet exploded over icy North America nearly 13,000 years ago, wiping out the Clovis people and many of the continent's large animals.

Archaeologists have examined sediments at seven Clovis-age sites across the United States, and did not find enough magnetic cosmic debris to confirm that an extraterrestrial impact happened at that time, says the report in the Proceedings of the National Academy of Sciences (PNAS). It is the latest of several studies unable to support aspects of the impact hypothesis.

In 2007, a team led by Californian researchers announced a theory that a comet or asteroid had exploded over the North American ice sheet, creating widespread fire and an atmospheric soot burst followed by a cooling period known as the Younger Dryas.

Sometime after this, the Clovis people, sophisticated large-animal hunters known for their spear points, mysteriously disappeared; the team linked their vanishing to the environmental effects of the proposed impact.

Comment: For a more in-depth view, read: The Younger Dryas Impact Event and the Cycles of Cosmic Catastrophes - Climate Scientists Awakening

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Meteor

What (Maybe) Didn't Kill the Dinosaurs: Comets

John Matson
Scientific American
Thu, 01 Oct 2009 00:01 UTC
Comet
© Bettmann CorbisCometary commotion: A new mechanism for how icy bodies get past Jupiter and Saturn suggests that comet showers did not play a big role in Earth's extinctions.
A new model for comet production revises the theory of their origins

The chunks of ice and dust that make their home in the Oort cloud, far beyond the orbit of Pluto, sometimes become dislodged and head into the solar system as streaky comets. Some disruptions, caused by passing stars and other interactions with the Milky Way galaxy, are severe enough to send Oort comets into orbits that buzz or even collide with Earth. New simulations have revealed a novel mechanism for their entry into our part of the solar system, a method that also suggests that comet showers may not have been strongly involved in major extinctions on Earth.

Comet dynamics depend heavily on Jupiter and Saturn: their huge gravitational fields tend to keep objects away from Earth. Comets that manage to skirt Jupiter and Saturn, the conventional thinking goes, had to have originated in the outer reaches of the Oort cloud, where perturbations from outside the solar system can be felt most strongly and are writ large across vast cometary orbits that take hundreds of years to complete. Only during comet showers caused by close stellar passages, the theory holds, have extreme gravitational disruptions brought inner Oort cloud comets into the mix.
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Meteor

Zadunaisky's Math Determined Halley's Comet Orbit


Associated Press / Boston.com
Wed, 07 Oct 2009 20:20 UTC
Buenos Aires, Argentina - Pedro Elias Zadunaisky, an Argentine astronomer and mathematician whose calculations helped determine the orbit of Saturn's outermost moon, Phoebe, as well as Halley's Comet, died Wednesday. He was 91.

Zadunaisky was a pioneer in celestial mechanics, applying mathematical models to determine how gravity and other forces alter the orbits of other objects in the solar system.

Zadunaisky also was a Senior Astronomer at the Smithsonian Astrophysical Observatory and in the 1960s researched the orbits of celestial bodies at NASA's Goddard Space Flight Center, calculating the orbits of the first U.S. Earth satellite, Explorer I, as well as other satellites during the U.S. space race against Russia.

Born in the Argentine city of Rosario on Dec. 10, 1917, Zadunaisky earned a civil engineering degree at the National University of Rosario, then pursued applied mathematics and specialized in celestial mechanics. He earned three Guggenheim fellowships for research at Columbia University in 1957, Princeton University in 1958 and at the University of Texas at Austin in 1977.
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Telescope

Astronomical Birth Event Results in a Multitude of 'Baby' Comets

Helen Altonn
Honolulu Star Bulletin
Thu, 17 Sep 2009 01:03 UTC
Image
© NASAThis 2007 image taken from the Hubble Space Telescope shows a jellyfish-shaped Comet Holmes
Astronomers who were dazzled by the 2007 explosion of a comet into the largest object in the solar system have discovered it gave birth to a bunch of baby comets.

Reporting the "largest comet birth ever seen" were David Jewitt, Rachel Stevenson and Jan Kleyna, who observed the event through a Mauna Kea telescope.

Jewitt, a professor, and Stevenson, his graduate student, left the University of Hawaii Institute for Astronomy this summer to join the University of California, Los Angeles. Kleyna is an astrobiology postdoctoral researcher at the institute.
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Telescope

Mini-Comets Within a Comet Lit Up 17P/Holmes During Megaoutburst


PhysOrg
Wed, 16 Sep 2009 13:41 UTC
Image
© Jewitt/Stevenson/KleynaReveals the expansion of the coma of comet Holmes over 9 nights in 2007 November.
Astronomers from the University of California, Los Angeles and the University of Hawaii have discovered multiple fragments ejected during the largest cometary outburst ever witnessed. Images and animations showing fragments rapidly flying away from the nucleus of comet 17P/Holmes will be presented by Rachel Stevenson at the European Planetary Science Congress in Potsdam, Germany, on Wednesday 16 September.

Stevenson, together with colleagues Jan Kleyna and David Jewitt, began observing comet Holmes in October 2007 soon after it was reported that the small (3.6 km wide) body had brightened by a million times in less than a day. They continued observing for several weeks after the outburst using the Canada- France- Hawaii Telescope in Hawaii and watched as the dust cloud ejected by the comet grew to be larger than the Sun.

The astronomers examined a sequence of images taken over nine nights in November 2007 using a digital filter that enhances sharp discontinuities within images. The filter, called a Laplacian filter, is particularly good at picking out faint small-scale features that would otherwise remain undetected against the bright background of the expanding comet. They found numerous small objects that moved radially away from the nucleus at speeds up to 125 metres per second (280 mph). These objects were too bright to simply be bare rocks, but instead were more like mini-comets creating their own dust clouds as the ice sublimated from their surfaces.
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Meteor

Jupiter Captured Comet as Temporary Moon

Nancy Atkinson
Universe Today
Sun, 13 Sep 2009 00:00 UTC
Image
© NASA
Jupiter's gravity well has been known to capture objects - evidenced by the recent impact on the gas giant discovered by amateur astronomer Anthony Wesley. But one object captured by Jupiter in the mid 1900's was later able to escape from the planet's clutches.

Researchers have found comet 147P/Kushida-Muramatsu was captured as a temporary moon of Jupiter, and remained trapped in an irregular orbit for about twelve years. "Our results demonstrate some of the routes taken by cometary bodies through interplanetary space that can allow them either to enter or to escape situations where they are in orbit around the planet Jupiter," said team member Dr. David Archer.

With this discovery, five such objects have now been discovered where the phenomenon of temporary satellite capture (TSC) has occurred, but this new research suggests it might happen more frequently than was expected. Kushida-Muramatsu orbited Jupiter between 1949 and 1961, the third longest capture period of the five objects.
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Meteor

Found: first amino acid on a comet

Maggie McKee
New Scientist
Mon, 17 Aug 2009 23:59 UTC
Image
© NASA/Jet Propulsion LaboratoryAn amino acid called glycine has been found in dust collected by the Stardust spacecraft, which flew by Comet Wild 2 in 2004
An amino acid has been found on a comet for the first time, a new analysis of samples from NASA's Stardust mission reveals. The discovery confirms that some of the building blocks of life were delivered to the early Earth from space.

Amino acids are crucial to life because they form the basis of proteins, the molecules that run cells. The acids form when organic, carbon-containing compounds and water are zapped with a source of energy, such as photons - a process that can take place on Earth or in space.
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Meteor

NASA Researchers Make First Discovery of Life's Building Block in Comet

Bill Steigerwald
NASA Goddard Space Flight Center
Tue, 18 Aug 2009 01:06 UTC
Image
© NASA/JPL This is an artist's concept of the Stardust spacecraft beginning its flight through gas and dust around comet Wild 2. The white area represents the comet. The collection grid is the tennis-racket-shaped object extending out from the back of the spacecraft.
NASA scientists have discovered glycine, a fundamental building block of life, in samples of comet Wild 2 returned by NASA's Stardust spacecraft.

"Glycine is an amino acid used by living organisms to make proteins, and this is the first time an amino acid has been found in a comet," said Dr. Jamie Elsila of NASA's Goddard Space Flight Center in Greenbelt, Md. "Our discovery supports the theory that some of life's ingredients formed in space and were delivered to Earth long ago by meteorite and comet impacts."
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Meteor

Comet Swarm Delivered Earth's Oceans?

Ker Than
National Geographic News
Wed, 05 Aug 2009 20:00 UTC
Comet
© Nicolle Rager-Fuller, NSFA comet slams into what is now Chesapeake Bay in an artist's conception.
A barrage of comets may have delivered Earth's oceans around 3.85 billion years ago, a new study suggests.

Scientists have long suspected that Earth and its near neighbors were walloped by tens of thousands of impactors during an ancient event known as the Late Heavy Bombardment.

This pummeling disfigured the moon, leaving behind massive craters that are still visible, preserved for millennia in the moon's airless environment. But it's been unclear whether the impactors were icy comets or rocky asteroids.

Now, based on levels of a certain metal in ancient Earth rocks, a team led by Uffe Jorgensen of the Niels Bohr Institute in Denmark says comets were the culprits.

Whether Earth had oceans before any comets arrived has been intensely debated, Jorgensen noted.
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Meteor

Shuttle Plumes Hint at Comet Crash in Siberia

Irene Klotz
Discovery News
Fri, 31 Jul 2009 16:07 UTC
Image
© NASANight-Shining Clouds
Tracking plumes from space shuttle launches provided researchers with one of the strongest pieces of evidence that a comet crash was responsible for flattening a Siberian forest in 1908.

The crash, which leveled trees for hundreds of miles in Siberia, was followed by the appearance of extremely bright clouds, visible by night.

Similar clouds triggered by the flights of space shuttles through atmosphere were found over the planet's poles two days after a launch from Florida, research published in last week's Geophysical Research Letters shows.

Comment: For more in-depth reading on Tunguska read: Tunguska, Psychopathy and the Sixth Extinction

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