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Fri, 27 Nov 2020
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Comets

Star

Saturn Moon Resembles Comets

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."

Star

Saturn's moon Enceladus surprisingly comet-like

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

Hourglass

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

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.

Star

Comet Hale-Bopp Still Lives

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.

Star

A Cloudy Comet and a Wispy Nebula

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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Scientists Say Comet Smashed Into Southern Germany In 200 BC

A comet or asteroid smashed into modern-day Germany some 2,200 years ago, unleashing energy equivalent to thousands of atomic bombs, scientists reported on Friday.

crater Chiemgau
© Chiemgau Impact Research Team
The largest crater in the Chiemgau field in Bavaria is water-filled Tuttensee, located near the village of Marwang. At the water surface, Tüttensee measures 1,200 feet across. but the original crater may have been twice as large. Photo credit: Chiemgau Impact Research Team.

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Evidence Confirms Electric Comet Model

It appears that predictions made by Wal Thornhill and the Electric Comet model are being quickly confirmed, whether mainstream astronomers like it or not. In the end, it seems nature will be the arbiter of which model is the most accurate and predictive.

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Comets in History: The Journal of Hamel and Korea

At the end of the year [1664] we saw shortly after each other two tail-stars or comets arising in the sky. The first one, in the southeast, was to be seen for almost two months. After that another one appeared in the southeast. The appearance of these celestial bodies, caused a big panic in the country. The war-fleet was standing by, the guards of the ports were reinforced, all fortresses were provided with extra provisions and extra munitions, while cavalry and infantry were exercising daily. Also was it not allowed to light any lamps, especially not in the cities along the coast. This fear was caused by the fact that when the Tartarians invaded the country, there were also similar signs in the firmament, as well as at the beginning of the war with the Japanese.

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Today in Cape history: Third comet visible in 12 years



Comet 1664
©Unknown

On this day in 1664, as described in the book "Cape Cod Historical Almanac" by Donald G. Trayser, "the people of Cape Cod and other parts of New England saw the last of a great comet which excited fear and awe. It appeared November 8th last, and continued to this date, the third comet witnessed by early settlers in the space of 12 years.

Telescope

Boston University Astronomers Map Full Extent Of Mercury's Comet-Like Tail

Boston University astronomers released new images of Mercury that capture both the source regions of and, for the first time, the extraordinary length of the planet's comet-like tail. Earlier research had mapped-out Mercury's sodium gas tail to approximately 40,000 kilometers, but planetary scientists from BU's Center for Space Physics (CSP) have found that the tail can extend more than 2.5 million kilometers, or 1.5 million miles, from the planet.

mercury comet like tail
©Center for Space Physics, Boston University
Mercury's tail of sodium gas captured by a wide-angle telescope showing an enormous extent of the atoms escaping from the planet's surface. The insert shows the source regions of the tail gases imaged at a different time using a very narrow field of view telescope. The source regions occur at high latitudes, probably related to solar wind access to Mercury's surface along specific magnetic field lines. The impacts of the solar wind ions and electrons result in sputtering sodium from the surface. Since Mercury is close to the Sun, the sputtered atoms are pushed away by the pressure of light, with this photon radiation pressure leading to the long tail. The brightness of the source regions is about 1 million times greater than the faintest part of the distant tail. The sizes of the source regions span about 1/2 of the planet's radius, while the tail extends to about 1500 times the radius of the planet, about 1.5 million miles.