Comets


Star

Study suggests link between comet bombardment and movement through the galaxy, causing mass extinctions on earth


Science Daily
Fri, 02 May 2008 13:03 UTC
The sun's movement through the Milky Way regularly sends comets hurtling into the inner solar system -- coinciding with mass life extinctions on earth, a new study claims. The study suggests a link between comet bombardment and the movement through the galaxy.

Comets
©Artby Don Davis / Courtesy of NASA
A large body of scientific evidence now exists that support the hypothesis that a major asteroid or comet impact occurred in the Caribbean region at the boundary of the Cretaceous and Tertiary periods in Earth's geologic history. Such an impact is suspected to be responsible for the mass extinction of many floral and faunal species, including the large dinosaurs, that marked the end of the Cretaceous period.
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Bizarro Earth

Sorry to ruin the fun, but an ice age cometh

Phil Chapman
The Australian
Wed, 23 Apr 2008 07:04 UTC
THE scariest photo I have seen on the internet is www.spaceweather.com, where you will find a real-time image of the sun from the Solar and Heliospheric Observatory, located in deep space at the equilibrium point between solar and terrestrial gravity.

What is scary about the picture is that there is only one tiny sunspot.

Image
©SOHO

Comment: Chapman has it only partly right. He excludes the evidence for cometary dust loading that contributed to the last ice age (and most likely previous ones). The increased depositional flux evidenced from Gabrielli's paper shows that it was not the sun alone that caused the last ice age:

Depositional Fluxes
©Nature

And from Victor Clube's talk:
You first take the modern sky accessible to science, especially during the Space Age, and you look at its' darker debris with a view to relating its behavior to the more accessible human history which we can, in principle, really understand. And by this approach you discover from the dynamics of the material in space which I'm talking about that a huge comet must have settled in a Taurid orbit some 20,000 years ago, whose dense meteor stream for 10,000 years almost certainly produced the last Ice Age.
Now the question must be asked, Is there a relationship between the sun's missing spots and a 100,000 year ice age cycle coupled with cometary debris entering the solar system?

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Bell

Planetery Protection: Governments reconsider the risk of Near-Earth asteroid and comet impacts

Lee Billings
Seed Magazine
Wed, 16 Apr 2008 11:38 UTC
Until very recently, the devastating 1908 explosion of a space rock over the isolated Tunguska region of Siberia was thought to be a once-in-a-millennium event. Based on comparisons to nuclear weapon blast effects, many experts estimated the Tunguska object to be 50 to 100 meters. But new simulations by Mark Boslough at Sandia National Laboratories suggest the Tunguska object was much smaller than previously believed. And since smaller near-Earth objects (NEOs) are more common than larger ones, the implication is that the gap between such impacts may be centuries rather than millennia.
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Telescope

The Tagish Lake Meteorite: "Like Sampling the Surface of a Comet"


AstroBiology Magazine
Sun, 02 Jun 2002 00:00 UTC
A scientific consortium of 4 universities and NASA is now trying to uncover the debris and sample the early solar system's unique chemistry.

tagish1
©University Calgary
Close-up of Tagish Lake fragile carbon porousity.
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Telescope

Out of the Blue - Group Searches for Evidence of Recurring Cometary Impacts

Faye Flam
The Philadelphia Inquirer
Mon, 07 Apr 2008 09:09 UTC
Magnified 25,000 times under Drexel University's scanning electron microscope, a couple of flecks of dirt offer up a landscape full of crags, valleys, ridges - and, to Dee Breger's eyes, a window back in time.

Microspherule
©Dee Breger
Colorized scanning electron micrograph shows a tiny spherule that is believed to have formed from a vaporized or melted fragment when a piece of a comet slammed into the Indian Ocean an estimated 4,800 years ago. Marine geophysicist Dallas Abbott hypothesizes that such an impact was the source of deluge legends like Noah's ark and Gilgamesh.
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Star

Saturn Moon Resembles Comets


Aviation Week
Fri, 28 Mar 2008 21:26 UTC
Saturn's bizarre moon Enceladus is a little more mysterious after the recent Cassini flyby found it to be remarkably like a comet in its internal chemistry.

"A completely unexpected surprise is that the chemistry of Enceladus, what's coming out from inside, resembles that of a comet," says Hunter Waite of the Southwest Research Institute, principal investigator for the Cassini Ion and Neutral Mass Spectrometer. "To have primordial material coming out from inside a Saturn moon raises many questions on the formation of the Saturn system."
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Star

Saturn's moon Enceladus surprisingly comet-like

Stephen Battersby
New Scientist
Thu, 27 Mar 2008 15:14 UTC
Saturn's curious moon Enceladus appears to have the same chemical makeup as a comet, according to the latest results from the Cassini probe. That's a big surprise, as Enceladus should have formed in very different conditions from those of comets.

On 12 March, Cassini flew through the huge plume of steam and other gases that spews from fissures at the moon's south pole. A glitch prevented the spacecraft's dust analyser from studying the makeup of the plume, but another instrument, called the Ion and Neutral Mass Spectrometer (INMS), did sample its chemistry.

As well as water vapour, the INMS detected carbon dioxide, methane and a range of more complex organic chemicals such as propane.

Image
©NASA/JPL/GSFC/SwRI/SSI
Heat radiates from the entire length of 150-kilometre-long fractures on the south pole of Saturn's icy moon Enceladus
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Hourglass

Op-Classic, 1994: Arthur C. Clarke on Killer Comets

Arthur C. Clarke
The New York Times
Sun, 23 Mar 2008 02:13 UTC
Every week, the Opinion section presents an essay from The Times's archive by a columnist or contributor that we hope sheds light on current news or provides a window on the past.

This week's offering comes from Arthur C. Clarke, the science fiction novelist, who died on Wednesday. In 1994, he urged Op-Ed readers to look to the skies--or risk going the way of the dinosaurs.
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Star

Comet Hale-Bopp Still Lives


Sky and Telescope
Sun, 23 Mar 2008 14:14 UTC
Although it has been more than a decade since Comet Hale-Bopp blazed in the night sky, it's still sputtering as it continues to head into cold, trans-Neptunian space.

In a paper submitted to the Astrophysical Journal Letters, a trio of Hungarian and Australian astronomers describe capturing the most distant cometary activity ever seen.

Image
©Dennis di Cicco
Comet Hale-Bopp amid its glory on March 17, 1997. The comet still shines in the outer solar system, but at a mere 20th magnitude.
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Star

A Cloudy Comet and a Wispy Nebula

Alan MacRobert
Sky and Telescope
Thu, 06 Mar 2008 17:17 UTC
I love celestial coincidences. There are just so many of them.

Why do some of the closest bright stars to the solar system lie in front of the bright stars of the winter Milky Way? This foreground and background have nothing to do with each other, but they combine to make our winter evening sky especially starry-bright.

Why, from Earth's viewpoint, do planets shine just about as bright as the brightest stars?

Why are the apparent sizes of the Moon and Sun so nearly alike? They're just right to give us the most spectacular-looking (if rather rare) total solar eclipses.

Image
©S&T: Dennis di Cicco & Sean Walker
On the evening of March 5th, big dim Comet Holmes was passing big dim NGC 1499, the California Nebula in Perseus. For this image Dennis di Cicco took 30-minute exposures through blue and green filters and a 50-minute exposure through a red filter, using a 5-inch Tele Vue NP127is refractor and an Apogee U16M CCD camera. Click image for larger view. (Look carefully at the large view and you'll see the faint nucleus of the comet as a tiny red-green-blue streak; it moved between the three exposures.) The field is roughly 3° tall, with north up.
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