Astronomers Investigating Unknown Object That Hit the Earth In 773 AD

KentuckyFC writes "In November 2012, a group of Japanese scientists discovered that the concentration of carbon-14 in Japanese cedar trees suddenly rose between 774 AD and 775 AD. Others have since found similar evidence and narrowed the date to 773 AD. Astronomers think this stuff must have come from space so now the quest is on to find the extraterrestrial culprit. Carbon-14 is continually generated in the atmosphere by cosmic rays hitting nitrogen atoms. But because carbon-14 is radioactive, it naturally decays back into nitrogen with a half-life of about 5700 years. This constant process of production and decay leaves the amount of carbon-14 in the atmosphere relatively constant at about one part in a trillion will be carbon-14. One possible reason for the increase is that the Sun belched a superflare our way, engulfing the planet in huge cloud of high energy protons. Recent calculations suggest this could happen once every 3000 years and so seems unlikely. Another possibility is a nearby supernova, which bathed the entire Solar System in additional cosmic rays. However, astronomers cannot see any likely candidates nearby and there are no historical observations of a supernova from that time. Yet another possibility is that a comet may have hit the Earth, dumping the extra carbon-14 in the atmosphere. But astronomers have ruled that out on the basis that a comet carrying enough carbon-14 must have been over 100 km in diameter and would surely have left other evidence such as an impact crater. So for the moment, astronomers are stumped."

Comments

Some Background

[Anonymous Coward]

Tree Rings, July 30, 2012.

Why unlikely?

[Anonymous Coward]

"Recent calculations suggest this could happen once every 3000 years and so seems unlikely."

Why would it seem unlikely, that at some point 1300 years ago, an event calculated to happen every 3000 years actually happened?

Re:Why unlikely?

[aardvarkjoe]

The actual quote from the article:

The second way carbon-14 can be created in the Earthâ(TM)s atmosphere is if the Sun suddenly belched high energy particles our way. In other words, the Sun might have emitted a superflare 1000 times larger than usual which then engulfed the Earth.

There was a time when astronomers would have immediately ruled out this possibility as well. But last year, astrophysicists calculated that sun-like stars can produce superflares of this size about once every 3000 years.

The "seems unlikely" appears to be an invention of KentuckyFC, enabled by samzenpus.

Re:Why unlikely?

[ShanghaiBill]

If it is as frequent as every 1/3000 years, there definitely be some evidence of it.

But there is evidence: The elevated C14 in the tree rings from 773AD. What other evidence would there be? A lack of historical records is not strong evidence again the solar flare theory, since Europe was in the dark ages and there were few literate people and few records survive from that period. China was thriving and prosperous under the Tang Dynasty, but it may have happened during the night in China, or even on a cloudy, overcast day, which is common in eastern China.

Re:Why unlikely?

[Deadstick]

A lack of historical records is not strong evidence again the solar flare theory, since Europe was in the dark ages and there were few literate people and few records survive from that period. China was thriving and prosperous under the Tang Dynasty, but it may have happened during the night in China, or even on a cloudy, overcast day, which is common in eastern China.

Indeed. The Chinese, and possibly Arabs, Japanese and Anasazi Indians, noted the supernova of 1054 CE that made the Crab Nebula; Europe missed it altogether. Time of day was not an issue for that event, because it lasted a couple of years.

But anyway, it's only TFP that alludes to a lack of historical records: TFA cites two.

Re:Why unlikely?

[Troed]

2000 years of global extreme climate events from historical records: http://www.breadandbutterscien...

773 A.D. In 773 A.D., a severe drought struck Shensi (now Shaanxi province) in central China at Sian.

In 773 A.D., there was a great drought in Shensi province in China.

774 A.D. In Scotland, there was a severe famine with a plague.

Winter of 774 / 775 A.D. In the year 675, there was the greatest frost in England.
[This entry was out of chronological order and I believe Short was referencing the year 775 A.D.]

775 A.D. In England, there was a drought with excessive heat, after a great frost.

The winter was so hard that the Euxine Sea (Black Sea) was quite frozen over. The ice was 30 foot or
cubits thick. People could walk 50 or 100 leagues (150 to 300 miles, 240 to 480 kilometers) on the ice
from the Danube River to the Euphrates River. On the ice fell 30 cubits deep of snow. When the ice
broke, it appeared like great mountains on the sea, which demolished and carried down whole villages
standing on the shore. This winter was succeeded by so excessive heat during the summer that all springs
dried up.72 [The Danube River probably refers to the Danube Delta in Europe, eastern Romania and south
western Ukraine. The Euphrates River rises in Turkey, passes through Syria, and joins with the Tigris
River in southeastern Iraq to form the Shatt al Arab, which empties into the Persian Gulf.]

In the year 775, “Snow fell, and lay 30 Cubits on a Level.”

[In Byzantium], the summer was hot and all the wells dried up.62 [Byzantium at this time included
Turkey, and the western part of the Balkan peninsula.]

In 775 A.D. during the period 1-30 August, floods struck Chekiang (now Zhejiang province) on the east
coast of China at Hangchow.

Article says Not so Unlikely

[glennrrr]

"There was a time when astronomers would have immediately ruled out this possibility as well. But last year, astrophysicists calculated that sun-like stars can produce superflares of this size about once every 3000 years."

I think that if an event happened 14 centuries ago, and one explanation is supposed to happen every 30 centuries or so then it isn't something that can be discarded as an explanation without further evidence.

Misleading title

[daitengu]

While we're arguing about solar flares, or supernovas, we're kind of ignoring the obvious. The title states "an unknown object" "hit the earth". That, also, is ruled out right in the article.

Maybe a better title would have been "Some shit happened in 773 AD and no one really knows what it is, but here's what we have so far!"

Re:Supernova

[The123king]

Here's a link

Actual cause

[fyngyrz]

In 772, Charlemagne began a war of extermination against the heathen Saxons, destroying the Irminsul, the chief seat of their religion. Santa Claus (known as Odin at that time, later Sinterklaus, then Santa) observed this, and at the end of 772, delivered elf-coal, high in carbon-14, to everyone in Charlemagne's forces. In the process, coal dust flew in unprecedented amounts from his sleigh, and this was naturally absorbed by the trees during 773.

I swear, if you people just knew your history a little better, you could maybe make this "science" stuff work better.