While most of us know about rings around Saturn and Jupiter, some scientists
believe there once were rings of rock debris around our own planet. Two
scientists – Peter J. Fawcett, of the University of New Mexico, and Mark
B.E. Boslough, of the U.S. Department of Energy’s Sandia National
Laboratories – have suggested that a geologically “recent” collision (about
35 million years ago) may have caused such a temporary debris ring.

The two also suggest that such temporary rings – lasting from 100,000 to a
few millions of years – may explain some patterns of climate change observed
in the earth’s geological record. These conclusions are spelled out in an
article in the Journal of Geophysical Research, Atmospheres, August 16

Lore of the Rings

“One way to get a ring,” says Sandia’s Boslough, “is with an impact.” There
is a growing body of evidence showing that the earth has been subjected to
numerous impacts by comets and asteroids throughout its history. Among these
impacts are the Meteor Crater, in Arizona, the buried Chixulub crater, in
the Yucatan Peninsula of Mexico, and a chain of at least five craters spread
across several continents.

Several studies, both theoretical and with laboratory data, suggest that
some large impacts are capable of ejecting material into space in the form
of debris rings, if the mechanics of the impact meet certain requirements.
The authors conclude that the mostly likely scenario for ring creation is a
low-angle impact by a large asteroid. Some earth materials and melted
meteoric debris, called “tektites” would form the ring materials.

Boslough describes an impact where the collision object ricochets back into
the atmosphere. The ricochet becomes part of an expanding vapor cloud,
setting up an interaction that allows some of the debris to attain orbit
velocity. The orbiting debris will collapse into a single plane by the same
mechanics that led to the rings of Saturn and other planets, Boslough
explains. Such a ring would most likely form near the equator, because of
the dynamics involved with the moon and the earth’s equatorial bulge.

Speculation on climates past

The effects of the larger impact events on earth’s environment and climate
have been the subjects of much speculation and research over the past two
decades. “Clearly, large impacts have affected the evolution of the earth,
life on it and its atmospheric environment,” says Fawcett.

Much of the work has focused on the Cretaceous-Tertiary (K-T) boundary
event, which marked a mass extinction and the end of the age of the
dinosaurs about 65 million years ago. A number of these studies suggest an
impact resulting in the suspension of a layer of dust in the upper
atmosphere blocking sunlight and cooling the earth. The two researchers
asked could other impacts result in different atmosphere-altering phenomena?

An equatorial ring would cast a shadow primarily in the tropics, as it does
for Saturn. Depending on location, surface area, and darkness of the ring
shadow, the amount of incoming solar warmth, or insolation, could be
significantly altered, the two authors conclude. To test their theory, the
two assumed an opaque ring, like Saturn’s B-ring, scaled to earth-size and
tested global climate affects using a climate model.

The model selected and modified for the simulation was developed by the
National Center for Atmospheric Research (NCAR.) The Center’s “Genesis”
climate model includes atmospheric circulation information and layers of
vegetation, soil, snow, sea temperature and land ice data. The goals of the
internally funded project were for Sandia to adapt a popular climate code to
run on distributed-memory parallel computers and to establish relationships
with the climate change research community, Boslough explained. The Labs
made use of its Sandia University Research Program to fund Fawcett’s efforts
to analyze the data from the adapted code.

A Ring World

“The equatorial debris ring has a profound effect on climate, because it
reflects a significant fraction of tropical insolation back to space before
it can interact with the atmosphere,” the authors conclude. Surface and
atmospheric temperatures, changes in temperature ranges from equator to
poles, circulation patterns and the rain and snow cycles were all impacted
by the ring, the model shows.

The two scientists looked at changes shown in the model to predict changes
that might be found in the earth’s geologic record as a way to test their
work. In addition to the K-T boundary event, they looked at a more recent
impacts and a much older one.

The most recent event – about 35 million years ago – is identified by an
iridium layer (often associated with meteors) and two pronounced
mico-tektite fields, where these melted meteor-related materials have been
found and dated. Climatic records from sedimentary materials just above the
iridium/micro-tektite interval indicate a 100,000-year cooling interval.
Orbiting debris in a ring, casting its shadow in the subtropics could have
sustained such a cooling trend, the authors suggest.

The K-T boundary impact – about 65 million years ago – was much larger than
the more recent impact and had a much larger immediate effect on the
environment as measured by extinctions and atmospheric changes. But there
were no long-term effects on the climate, leading the authors to conclude
the event probably did not generate a debris ring.

Snowball Earth

Another interesting aspect of the modeling work is its implications for the
so-called “Snowball Earth” theory. This theory holds that the earth was
completely frozen over at the surface as many as four times in the
neoproterozoic period – 750 to 580 million years ago. While much remains to
be learned about the geologic evidence for this theory, “an opaque ring
could have acted as the trigger to at least one episode of global
glaciation,” the two researchers say. This would address one difficult
question for the theorists: how did earth come to be frozen?

Sandia is a multiprogram laboratory operated by Sandia Corporation, a
Lockheed Martin Company, for the United States Department of Energy’s
National Nuclear Security Administration under contract DE-AC04-94AL85000.
With main facilities in Albuquerque, N.M., and Livermore, Calif., Sandia
has major research and development responsibilities in national security,
energy and environmental technologies, and economic competitiveness.

Sandia media contact: Will Keener, rwkeene@sandia.gov, (505) 844-1690

Sandia technical contacts: Mark Boslough, mbboslo@sandia.gov, (505)
845-8851; or Peter Fawcett, fawcett@unm.edu, (505) 277-3867