[meteorite-list] Did the Celts See a Comet Impact in 200 B.C.?

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Fri Oct 15 12:55:33 2004
Message-ID: <200410151655.JAA05260_at_zagami.jpl.nasa.gov>

http://www.astronomy.com/default.aspx?c=a&id=2519

Did the Celts see a comet impact in 200 B.C.?

A new-found field of impact craters may mark the site of a recent comet
strike.

The Chiemgau Impact Research Team
Astronomy Magazine
October 14, 2004

We have identified an exceptional field of meteorites and impact craters
stretching from the town of Alt??tting to the area around Lake Chiemsee
in southeastern Bavaria, Germany. While there are many meteorite
"strewnfields" known around the world, few contain significant craters.
The Chiemgau field, which falls within an ellipse 36 miles long and 17
miles (58 by 27 kilometers) wide, holds at least 81 impact craters
ranging from 10 to 1,215 feet (3 to 370 meters) in size. Many more
craters may lie hidden in heavily forested areas within the ellipse, and
farming activities in the region may have destroyed others.

In autumn 2000, a group of amateur archaeologists working the area
around Lake Chiemsee discovered pieces of metal containing minerals not
found previously in the region. Werner Mayer, the independent scholar
who led the amateur team, noticed that the material was associated with
what appeared to be impact craters, most of which showed clear rims. In
2004, four other scientists joined Mayer to form the Chiemgau Impact
Research Team: Kord Ernston, a geologist at the University of W??rzburg;
independent scholar Gerhard Benske; Michael Rappengl??ck, an astronomer
with the Institute for Interdisciplinary Sciences in Gilching; and
Ulrich Sch??ssler, a University of W??rzburg mineralogist.

Meteorite strewnfields with craters

name location crater no. width of largest crater

Chiemgau Germany 81 1,215 feet (370m)
Henbury Australia 13 607 feet (158m)
Wabar Saudi Arabia 4 380 feet (116m)
Kaalijarvi Estonia 9 360 feet (110m)
Campo del Cielo Argentina 9 328 feet (100m)
Morasko Poland 8 312 feet (95m)
Sikhote Alin Russia 159 87 feet (26.5m)

Geological evidence makes clear the site's extraterrestrial connection.
Sandstone boulders and small, weathered rock fragments called cobbles in
and around the craters are completely coated by silica glass, which
requires unusually high temperatures. We believe the cobbles were
superheated and ejected in the impact. We found bluish-gray, dark green,
and black glass-like material in unusual shapes - such as teardrops and
dumbbells - indicating rapid cooling and solidification during flight.

The peculiar minerals found throughout the site include the iron-silicon
alloys gupeiite (Fe3Si) and xifengite (Fe5Si3), both of which were
identified in a meteorite discovered in the Yanshan Mountains of China
in 1984. Gupeiite was also found in FRO 90036, a ureilite-class
meteorite found in the Frontier Mountains of Antarctica, and related
minerals were found in Dhofar-280, a meteorite that probably came from
the Moon.

When did the impact occur? Archaeological finds in the area, as well as
the ages of trees within the craters, tell us the impact occurred in
historical times. The oldest tree we found rooted in a crater wall is at
most 500 years old, and we found xifengite and gupeiite beneath the
retaining walls of Burghausen Castle, which has been dated to the 15th
century a.d. At another site, we unearthed impact-related minerals along
with Celtic artifacts. The artifacts seem to have been strongly heated
on one side. This pushes the earliest date for the impact to the late
Roman period, between 480 b.c. and 30 b.c. Radiocarbon dates from ash
samples we removed from layers in several craters are not yet available.

The growth patterns of Irish oaks slowed dramatically between a.d. 536
and 545, indicating a much cooler climate. Historical records refer to
famine and a dimmed Sun during this period. Many have argued this
so-called "dust-veil event" was the aftermath of a large (0.3 mile, or
500m) comet fragment exploding high in Earth's atmosphere. To date, no
craters related to such an event have been found.

However, the rings also show slowed growth around 207 b.c. Roman authors
wrote about showers of stones falling from the sky and terrifying the
populace. In 205 b.c., because of these events, the Senate ordered that
a conical meteorite known as the Needle of Cybele (which had been
worshipped in Asia Minor in connection with the fertility goddess
Cybele) be brought to Rome. On the rim of the largest crater, named
T??ttensee, archaeologists have found Roman relics from about a.d. 200.
This, in addition to the heated coins from the late Roman period we
found at the Chiemgau impact site, lead us to favor this early date.

We believe an asteroid or comet fragment exploded above southeastern
Germany in the late Roman period. Our candidate impactor is a
low-density object, perhaps something like the C-class asteroid 253
Mathilda. Astronomers believe Mathilda was once completely shattered but
reassembled as a loose aggregate of material - that is, a rubble pile.
Given the material we recovered and the length of the ellipse of
scattered debris, we suggest the impacting body was more likely a comet
fragment - rich in methane, ammonia, and water, with a relatively small
fraction of rocky matter.

We estimate the projectile had a diameter of about 0.7 mile (1.1 km) and
a mean density about 30 percent greater than water (1.3 g/cm3). It
entered Earth's atmosphere at a speed of 27,000 miles per hour (43,000
km/h) and broke up at an altitude of 43 miles (70 km). The main mass of
the projectile struck the ground at 2,200 miles per hour (3,500 km/h),
releasing an amount of energy equivalent to 106 million tons of TNT.
Based on the size distribution of the craters - the larger ones are in
the southern part of the field, the smaller ones in the northern part -
we conclude the meteoroid came out of the northeast and moved southwest.
Multiple fragmentation events may account for the cratered area's large
size.

What would people on the ground have experienced? About 2 seconds after
the strike, people 6 miles (10 km) away would have felt the ground shake
as it would in a magnitude 6.0 earthquake. The air blast, arriving 30
seconds after impact, would have swept through at a speed of 500 miles
per hour (800 km/h) and produced a peak pressure of about 1.4
atmospheres (142,000 Pa), easily collapsing buildings, especially wooden
ones. Even from 10 km away, sound from the impact would have reached 103
decibels - loud enough to cause strong ear pain. Up to 90 percent of the
trees would have blown over; the rest would have lost their branches.

We found a thin layer of ash in and between the craters. The forest
beneath the blast would have ignited suddenly, burning until the
impact's blast wave shut down the conflagration. Dust may have been
blown into the stratosphere, where it would have been transported around
the globe easily, so it may be possible to trace the event in ice cores
from Greenland or Antarctica.

In any case, the impact undoubtedly had a major effect on the
environment and people then living in the vicinity of
Altoetting-Chiemgau. The region must have been devastated for decades.
We are currently looking for gaps in the historical and archaeological
records during the time we propose for the impact to better understand
both the event itself and its cultural effects.

The Chiemgau Impact Research Team consists of Kord Ernston, Werner
Mayer, Gerhard Benske, Michael Rappengl??ck, and Ulrich Sch??ssler. For
more information, visit the Ernston Claudin Impact Structures
<http://www.impact-structures.com/> web site.
Received on Fri 15 Oct 2004 12:55:24 PM PDT