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Comets

Star

Stardust comet dust resembles asteroid materials

Contrary to expectations for a small icy body, much of the comet dust returned by the Stardust mission formed very close to the young sun and was altered from the solar system's early materials.

When the Stardust mission returned to Earth with samples from the comet Wild 2 in 2006, scientists knew the material would provide new clues about the formation of our solar system, but they didn't know exactly how.

©NASA/JPL
Combined long- and short-exposure images captured during the Stardust flyby of the comet Wild 2.

Star

Electric Comet Theory: The Enduring - Yet Downplayed - Mysteries of Comets

"Mysteries are due to secrecy."
-Francis Bacon


On December 24, 2007, the website Space.com published a report entitled, "The Enduring Mysteries of Comets." The premise is intriguing, since it is rare for science media to acknowledge that "mysteries" of any real significance exist for conventional theories. Unfortunately, the report mentions few of the recent discoveries that have thrown the popular "dirty snowball" model of comets into disarray.

"We have now had four close encounters with comets, and every one of them has thrown astronomers onto their back foot." -Stuart Clark, New Scientist, September 09, 2005.

Star

Old Comets for a New Year

As we kick off the year 2008, Comet Tuttle is putting on a nice show for backyard skywatchers. It had not been seen since 1994, but you'll have an excellent opportunity to pick it up with binoculars or small telescopes during the next two weeks.

Tuttle can even be glimpsed by sharp-eyed observers under pristine skies without any optical aids, for it is one of the brightest of the short-period comets, those that orbit the sun often enough to be seen again and again from Earth and identified as such.

Telescope

Comet Shoemaker-Levy Home Page

From July 16 through July 22, 1994, pieces of an object designated as Comet P/Shoemaker-Levy 9 collided with Jupiter. This is the first collision of two solar system bodies ever to be observed, and the effects of the comet impacts on Jupiter's atmosphere have been simply spectacular and beyond expectations. Comet Shoemaker-Levy 9 consisted of at least 21 discernable fragments with diameters estimated at up to 2 kilometers.

©NASA JPL

Latest Images of Comet Shoemaker-Levy

Telescope

Comet Shoemaker-Levy 9 About to Smash into Jupiter

For a period of about six days centered on July 19, 1994, fragments of Comet Shoemaker-Levy 9 are expected to collide with Jupiter, the solar system's largest planet. Such an event has never before been available for study. The energy released by the larger fragments will be more than 10,000 times the energy released by a 100-megaton hydrogen bomb! Unfortunately for observers, the collisions will occur on the night side of Jupiter, the back side as seen from Earth. How did this comet fragment? And what do astronomers think will happen when it hits?

©D.A. Seal/JPL
Artist's conception of the collision of Comet Shoemaker-Levy 9 with Jupiter, as seen from the Galileo spacecraft. At the time of the first impact, the comet fragments will be much farther apart than shown in this illustration.

Better Earth

The Hazard to Civilization from Fireballs and Comets

Image
© SVM Clube
Having recently written a review of New Light on the Black Death: The Cosmic Connection by dendrochronologist Mike Baillie of Queen's University, Belfast, Ireland, I decided to go deeper into the subject. Over the past few weeks a whole case of books I ordered have been arriving and getting piled on my desk after a quick thumb-through... so much to do, so little time.

In the meantime, a friend of mine (who is a climate scientist at a major U.S. research facility) turned me on to an interesting find, a paper addressed to the European Office of Aerospace Research and development, dated June 4, 1996, entitled: "The Hazard to Civilization from Fireballs and Comets" by S.V.M. Clube. (For the uninitiated, Clube is an astrophysicist at the University of Oxford).

In this short (4 pages) letter and summary statement, Clube writes (emphases in the original, make of them what you will):
Asteroids which pass close to the Earth have been fully recognized by mankind for only about 20 years. Previously, the idea that substantial unobserved objects might be close enough to be a potential hazard to the Earth was treated with as much derision as the unobserved aether. Scientists of course are in business to establish broad principles (eg relativity) and the Earth's supposedly uneventful, uniformitarian environment was already very much in place. The result was that scientists who paid more than lip service to objects close enough to encounter the Earth did so in an atmosphere of barely disguised contempt. Even now, it is difficult for laymen to appreciate the enormity of the intellectual blow with which most of the Body Scientific has recently been struck and from which it is now seeking to recover.

Comment: Continue to Part Three: Cosmic Turkey Shoot


Telescope

University of Minnesota physicist reads the history of the solar system in grains of comet dust

Four years ago, NASA's Stardust spacecraft chased down a comet and collected grains of dust blowing off its nucleus. When the spacecraft Comet Wild-2 returned, comet dust was shipped to scientists all over the world, including University of Minnesota physics professor Bob Pepin. After testing helium and neon trapped in the dust specks, Pepin and his colleagues report that while the comet formed in the icy fringes of the solar system, the dust appears to have been born close to the infant sun and bombarded by intense radiation from these and other gases before being flung out beyond Neptune and trapped in the comet. The research appears in the Jan. 4 issue of the journal Science.

Star

The Enduring Mysteries of Comets

For millennia, comets were believed to be omens of doom. Instead, solving the mysteries regarding these "dirty snowballs" could help reveal the part they played in the birth of life on Earth, as well as secrets concerning the rest of the galaxy.

Comment: According to the gathered data and research, pretty soon Jewitt will have an opportunity to observe up close and personal many of those interstellar comets.


Star

Human Memories of the Doomsday Comet

For several weeks in the fall of 2007, amateur astronomers and sky watchers around the world were entranced by the mysterious, energetic display of Comet Holmes 17P. The Internet still abounds with exotic theories about the comet's nature -- some have claimed it is the "Blue Kachina" foretold in Hopi Prophecy, others assert that the secret government shot it with a nuclear missile, and still others say its nucleus is acquiring mass and turning into a PLANET.

Garish and unfounded speculations aside, it is interesting that Comet Holmes, while providing a remarkable cometary "light show" and inciting great interest, never appeared to the naked eye as more than a tiny, luminous "fluff ball" of light. Certainly, without the aid of telescopes and space satellites, its unremarkable glow amongst a vast network of stars and planets would not have captured the average person's attention. Nor would anyone observing it have had any reason to feel terror.

Bizarro Earth

Did a massive comet kickstart plate tectonics on Earth?

It's such a simple idea that it's surprising no one seems to have thought of it before. Did a massive asteroid or comet impact kick-start plate tectonics on Earth?

For much of our planet's history, rocky plates have been sliding over a viscous, molten mantle, colliding to build mountain ranges or spreading apart to make way for oceans. In a neat piece of recycling, an oceanic plate dives, or "subducts", underneath a less dense continental plate, and eventually melts into the hot mantle.

Geologists estimate that plate tectonics began during the Archean period, between 2.5 and 3.8 billion years ago - but they don't know what triggered it. Ancient Earth was too hot for the crust to solidify completely, and the lightest minerals would have floated to the surface over the entire planet, making the subduction of denser plate material unlikely.