Comets


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The Younger Dryas impact research debate update

Dr. Martin Sweatman
Ancient Origins
Mon, 28 Sep 2020 18:15 UTC
Ice Age Skeletons
© Jonathan Chen / CC BY-SA 4.0Ice Age Diorama. From left to right: Equus hemionus, Mammuthus primigenius, Coelodonta antiquitatis, Bison exiguous skeletal mounts at the Tianjin Natural History Museum.
The Younger Dryas impact hypothesis has received considerable attention since its publication in 2007 in the prestigious peer-reviewed journal PNAS (Proceedings of the National Academy of Sciences). It suggests the Younger Dryas geological period and mini Ice-Age, from around 10,850 to 9600 BC, along with associated megafaunal extinctions and human societal changes, was triggered by a catastrophic cosmic impact, probably with a fragmented comet from the Taurid meteor stream.

As of now, this paper by Richard Firestone, Allen West and Simon Warwick-Smith and colleagues has amassed over 550 citations in Google Scholar - which is a lot! It is on its way to becoming a classic. But it has also received more than its fair share of criticism, mostly sustained from just a handful of vehement opponents. But has any of their criticism stuck? And what is the status of Firestone et al.'s paper today? Has the dust settled on an outcome? Are we there yet?
Evolution of Temperatures
© Evolution of temperature in the Post-Glacial period according to Greenland ice cores/CC BY-SA 4.0Evolution of temperatures in the post glacial period, after the Last Glacial Maximum (LGM), showing very low temperatures for the most part of the Younger Dryas, rapidly rising afterwards to reach the level of the warm Holocene, based on Greenland ice cores.
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Info

100 million-year-old meteorite crater discovered Down Under

Laura Geggel
Live Science
Wed, 23 Sep 2020 22:30 UTC
Ora Banda Impact Crater
© Resource PotentialsA color-coded gravity image of the Ora Banda Impact Crater site. The crater (deep blue) is in the middle of the image.
Gold miners in the Australian Outback recently discovered a gigantic meteorite crater dating to about 100 million years ago, back when dinosaurs roamed the Earth.

Found near the Western Australian town of Ora Banda, the newly dubbed Ora Banda Impact Crater is about 3 miles (5 kilometers) across. This huge hole was likely created by a meteorite up to 660 feet (200 meters) wide, or longer than the length of two American football fields, according to Resourc.ly, a Western Australia news outlet.

When geologists at Evolution Mining, an Australian gold mining company, came across some unusual rock cores at Ora Banda, they called Jayson Meyers, the principal geophysicist, director and founder of Resource Potentials, a geophysics consulting and contracting company in Perth. Meyers examined the geologists' drill core samples, as well as rock samples from the site, and he immediately noticed the shatter cones — telltale signs of a meteorite crash.

Shatter cones form when high-pressure, high-velocity shock waves from a large impacting object — such as a meteorite or a gigantic explosion (such as would occur at a nuclear testing site) — rattle an area, according to the Planetary Science Institute (PSI), a nonprofit group based in Tucson, Arizona, which was not involved with the new find. These shock waves shatter rock into the unique shatter cone shape, just like a mark that a hard object can leave on a car's windshield.

Because "we know they didn't do any nuclear testing at Ora Banda," the evidence suggests that an ancient impact crater hit the site, Meyers told Resourc.ly.
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Comet 2

Strange, glowing ultraviolet aurora detected around a comet

Michelle Starr
Science Alert
Mon, 21 Sep 2020 05:20 UTC
Comet 67P/Churyumov-Gerasimenko.
© ESA/Rosetta/NAVCAMComet 67P/Churyumov-Gerasimenko.
Aurora - the dancing glow of ionised particles in Earth's upper atmosphere - is not unique to our planet.

The phenomenon has been spotted shining in the atmospheres of every other planet except Mercury. Even Jupiter's moons Ganymede and Europa have auroras.

Never, until now, had an aurora been detected on a comet.

But, in a new analysis of data collected by the Rosetta spacecraft, the space around Comet 67P Churyumov-Gerasimenko (67P/C-G) has been observed glowing with far-ultraviolet auroral radiation.

"I've been studying the Earth's auroras for five decades," said physicist Jim Burch of the Southwest Research Institute.

"Finding auroras around 67P, which lacks a magnetic field, is surprising and fascinating."

Auroras are generated by the excitation of charged particles in an atmosphere.

Here on Earth, for instance, the solar wind blows into the magnetosphere and interacts with charged particles there.

These particles rain down into the upper atmosphere and are funneled up the magnetic field lines to the poles, where they manifest as rippling curtains of light.

It works differently on different bodies, though. The auroras of Ganymede and Europa are generated by interactions with Jupiter's magnetic field.

Venus doesn't have a magnetic field of its own that we know of, but interactions with the solar wind creates one strong enough to trigger auroras.

Mars' atmosphere is extremely thin, but its weak magnetic field can support auroras.
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Comet 2

New Comet C/2020 S3 (Erasmus)

Ernesto Guido
Remanzacco Blogspot
Mon, 21 Sep 2020 18:12 UTC
CBET 4885 & MPEC 2020-S119, issued on 2020, September 20, announce the discovery of a comet (magnitude ~18.5) by Nicolas Erasmus (South African Astronomical Observatory), in four 30-s CCD images taken in 5" seeing on Sept. 17.6 UT with a 0.5-m f/2 Schmidt reflector at Mauna Loa, Hawaii, in the course of the "Asteroid Terrestrial-Impact Last Alert System" (ATLAS) search program. The new comet has been designated C/2020 S3 (Erasmus).

We performed follow-up measurements of this object while it was still on the PCCP webpage.

Stacking of 151 unfiltered exposures, 30 seconds each, obtained remotely on 2020, September 19.1 from L07 (Osservatorio Salvatore di Giacomo, Agerola) through a 0.5 m f/8 Ritchey Chretien + CCD FLI PL4240, shows that this object is a comet with a diffuse coma about 20" in diameter.

Our confirmation image (click on it for a bigger version)

Comet C/2020 S3 Erasmus
© Remanzacco Blogspot
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Fireball 4

Amateur astronomer discovers kilometer-size asteroid

David Dickinson
Sky & Telescope
Fri, 11 Sep 2020 21:58 UTC
Asteroid
© NASAAn artist's conception of a near-Earth asteroid.
We have not yet found all the large, potentially hazardous near-Earth objects, as highlighted by the recent discovery of a kilometer-size asteroid.

Amateur astronomer Leonardo Amaral was scanning the skies on the night of August 27th, imaging a region in the constellation Indus, when he picked up a cosmic interloper: the asteroid 2020 QU6.

Amaral used the 0.3-meter reflector at the Campo dos Amarais observatory near Sau Paulo, Brazil. The observatory had received a recent upgrade thanks to a Planetary Society grant.

Turns out, 2020 QU6 is about a kilometer across — a surprising find given that most such large objects have been found and cataloged. The asteroid orbits the Sun once every 3.26 years on an orbit inclined 23.5° relative to the ecliptic plane. It poses no current threat to Earth, having passed within 40 million kilometers (24 million miles, more than 100 times the Earth-Moon distance) on September 10th. That's the closest the asteroid will come to Earth in the 21st century.
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Fireball 5

The long history of comet phobia

Jess Romeo
JSTOR Daily
Thu, 03 Sep 2020 18:20 UTC
he Book of Miracles, c. 1550
© Wikimedia CommonsThe Book of Miracles, c. 1550.
Nowadays, the appearance of a comet, like the recently soaring NEOWISE, is likely to inspire wonder and excitement. But for much of human history, a comet was more likely to inspire blood-curdling fear.

"Almost always in classical times comets were regarded as portents, generally as warnings of dire events," writes historian Duane Koenig. (They were also sometimes "harbingers of happy things," like the birth of heroes, prophets, or kings.)

Ancient records show that thousands of years ago, "Persians and Koreans viewed comets as of evil nature and often [announced] war with the country in whose direction the tail pointed," writes Koenig. Over in Rome, comets were an object of fear and worship. Historian Geraldine Herbert-Brown finds that Pliny the Elder paid "particular attention to comets, and the terror they had caused humans in the course of history." According to Pliny, a comet would appear at "crucial intervals" starting in 49 BCE, "glaring terribly when Nero succeeded Claudius, and then continuously throughout Nero's principáte."

Comets — also called "bearded stars" — were consistently seen as bad news for rulers. Around 70 CE, the Roman emperor Vespasian was cautioned about a comet. "He contended the bearded star did not concern him because he was bald. It threatened his neighbor, the king of the Parthians, who was hairy," writes Koenig.
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Fireball

Meteor fireball spotted in background of news bulletin in Sydney

Andrew Bucklow
news.com.au
Thu, 03 Sep 2020 02:47 UTC
Meteor on News Broadcast
© Channel 7Meteor spotted in background of Seven news in Sydney.
Channel 7 viewers in Sydney were stunned last night when a meteor shot into the Earth's atmosphere during the news.

Mark Ferguson was presenting the 6pm bulletin when a meteor was visible in the live feed of Sydney's skyline in the background.

Some eagle-eyed viewers noticed the object and posted about it on a Facebook group dedicated to meteor sightings.

Ferguson called into Sunrise this morning and spoke about the incident, telling the breakfast show hosts: "I didn't know too much at the exact time but within a few seconds of throwing to the commercial, Jess our cameraman quickly said, 'Mate, something has just flown behind you. I reckon it's a meteor.'

"We replayed it and had a good look and we couldn't believe it; what a shock!" Ferguson said.
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Comet 2

Space rock turning into a comet observed for the first time

Lisa Goodman
Science News
Wed, 19 Aug 2020 18:25 UTC
Space Rock Turning into Comet
© HEATHER ROPER/UNIV. OF ARIZONASpace rocks called centaurs could someday become brilliant comets, like the one shown in this artist’s illustration. Astronomers have spotted a centaur that is expected to become a comet in about four decades.
Like the mythical half-human, half-horse creatures, centaurs in the solar system are hybrids between asteroids and comets. Now, astronomers have caught one morphing from one type of space rock to the other, potentially giving scientists an unprecedented chance to watch a comet form in real time in the decades to come.

"We have an opportunity here to see the birth of a comet as it starts to become active," says planetary scientist Kat Volk of the University of Arizona in Tucson.
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Comet 2

Triple comet fly-pass imaged by SOHO

Karl Battams
Solar and Heliospheric Observatory (SOHO)
Fri, 14 Aug 2020 18:34 UTC
Sungrazer Comet
© ESA/NASA/SOHO/Karl BattamsStill shot identifying the comet and the fragments and an animation image below.
First appearances can be deceiving, and one of the latest comet discoveries by SOHO is the perfect example of that!

SOHO is no stranger to discovering new comets - via the NASA-funded Sungrazer Project, the observatory has discovered over 4,000 previously unknown comets since launch in 1995. Most of SOHO's comet discoveries can be categorized into families, or groups, the most famous being the "Kreutz" sungrazer group which accounts for over 85% of the Project discoveries. Only around 4% -some 175 comets- do not appear to belong to any known group or comet family. However, these are often among the most interesting comets and this most recent discovery -SOHO's 4,049th comet- was no exception!


The comet was first spotted on August 5th, 2020, by amateur astronomer Worachate Boonplod. At discovery, it was just a tiny faint smudge near the edge of the C3 coronagraph images recorded SOHO's Large Angle Spectrometric Coronagraph (LASCO) instrument. As it neared the Sun over the next day or so, the smudge became increasingly elongated, ultimately hinting that it may be two comets pretending to be one!

This was confirmed as the comets entered the narrower field of view of the LASCO C2 camera, where the improved resolution confirmed that not only was this more than one comet, it was actually THREE comets! The two main components are easy to spot, with the third a very faint, diffuse fragment following alongside the leading piece.
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Comet 2

New Comet C/2020 O2 (Amaral)

Ernesto Guido
Remanzacco Blogspot
Mon, 03 Aug 2020 19:44 UTC
CBET 4822 & MPEC 2020-P10, issued on 2020, August 02, announce the discovery of a comet (magnitude ~18) by Leonardo S. Amaral (Rio de Janeiro, Brazil) on three 60-s CCD exposures taken on July 23 with a 0.3-m f/4 reflector. The new comet has been designated C/2020 O2 (Amaral).

We performed follow-up measurements of this object while it was still on the PCCP webpage.

Stacking of 16 unfiltered exposures, 90 seconds each, obtained remotely on 2020, July 27.05 from X02 (Telescope Live, Chile) through a 0.6-m f/6.5 astrograph + CCD, shows that this object is a comet with a diffuse coma about 8" in diameter (Observers E. Guido, M. Rocchetto, E. Bryssinck, M. Fulle, G. Milani, C. Nassef, G. Savini, A. Valvasori).

Our confirmation image (click on it for a bigger version)

Comet C/2020 O2 Amaral
© Remanzacco Blogspot
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