How Dangerous are Earth-Crossing Objects?
and other near-Earth object search programs demonstrate that
the Earth is surrounded by a swarm of asteroids and comets that threaten
us with collision and world-wide destruction.
The danger from near-Earth objects has sparked research into the probability
of occurrence of damaging impacts as well as the possibility of deflecting
potential impactors before they strike the Earth.
The extent of the damage
even a small impactor can cause is exemplified by the asteroid or
comet fragment which exploded in the air over Tunguska in Siberia in June
of 1908 with a force equivalent to between ten and twenty megatons of TNT.
(Such an explosion in the air in which the impactor does not reach the
ground intact is called an airburst or airblast.) The resulting blast wave leveled
hundreds of square kilometers of forest. The area was sparsely
inhabited so only two people are reported to have been killed:
Vasiliy son of Okhchen died from wounds sustained after being hurled
against a tree by the blast, and the aged hunter Lyuburman of Shanyagir
died from shock.
The Tunguska object was probably a stony body
about 50-70 meters (around 200 feet) in diameter. An object of this
size could easily destroy a large metropolitan center. This nearly
happened with Tunguska; a difference in arrival time of a few hours might
have seen populous St. Peterburg or another European city destroyed.
In fact, at about the same time as the Tunguska object exploded,
a small object struck near the city of Kiev. The coincidence in time
leads some scientists to speculate that the Kiev object may be a fragment
of the Tunguska impactor, or at least, a fragment of the same parent object
as the Tunguska impactor.
Smaller scale airbursts over populated areas have caused minor damage.
For example, an airburst over Madrid, Spain in 1896 smashed windows
and leveled a wall. There are many reports of airbursts causing
tremors and minor damage in inhabited areas. John Lewis's book
Rain of Iron and Ice lists a couple of dozen such
incidents over the past century.
A small airburst which occurred over El Paso, Texas, USA on October 9, 1997
caused no apparent damage but did alarm residents.
Another which occurred
July 7, 1999 over New Zealand was captured on videotape.
Fortunately, most airbursts occur over
the oceans, so no damage to human habitations results.
What size impactor makes it through the atmosphere to the lower
atmosphere or the ground with enough remaining velocity to produce
a damaging airburst or crater-forming impact?
It turns out that the Earth's atmosphere is ineffective in preventing
ground impact damage for stony meteorites greater than 200 meters
(about 650 feet) in diameter. For iron meteorites that impact at
greater than 20 km/sec (12.5 mi/sec), the critical diameter is about
40-60 meters (130-200 feet). Stony bodies greater than 60 meters
and less than 200 meters can cause significant airburst damage as at Tunguska.
The greatest danger from an ocean impact occurs when the incoming body
does not disintegrate in the atmosphere but instead strikes the water
relatively intact. The impact raises a tsunami which, if the object
is large enough, can devastate coastal areas hundreds of miles away.
Tsunamis of unknown origin are usually attributed to earthquakes and
volcanos, but it is likely that some -- including the largest and
most damaging -- result from cosmic impacts.
An asteroid of sufficient size to raise a tsunami with an
average height of 100 meters along the entire coast of the ocean
strikes once every few thousand years on average.
Stony bodies less than 200 meters in diameter do not produce tsunamis,
while those larger than 200 meters can produce catastrophic tsunamis.
Water waves generated by such an impactor are two-dimensional
disturbances that fall off in height only inversely with
distance from the point of impact. The average runup in height
of a tsunami as it reaches the continental shelf is more than
an order of magnitude. An impact anywhere in the Atlantic of a
stony asteroid more than 400m (1,300 feet) in diameter would
devastate coasts on both sides of the ocean. Tsunami runups would
exceed 60m (200 feet).
Frequently it is asserted than there have been no recorded deaths caused
by meteorite strikes. In fact, as John Lewis points out in his book
Rain of Iron and Ice, there have
been a number of injuries and deaths attributed to meteorite impacts
throughout history. See the
listing some instances of such injurious impacts taken from Lewis's book.
Walter Branch offers another
list of meteorites that have struck man-made objects,
humans, and animals
The well-known Richter scale is often used to gauge the severity of
an earthquake. The recently developed Torino Scale
measures the potential damage from a cosmic impact on a scale on
0 (no damage) to 10 (an impact event capable of causing a global
climatic catastrophe). The Torino scale was developed by
Richard P. Binzell of MIT.
The idea of deflecting impactors before they strike the Earth
goes back at least to Lord Byron, who in 1822 wrote:
Who knows whether, when a comet shall approach this globe to destroy
it, as it often has been and will be destroyed, men will not tear
rocks from their foundations by means of steam, and hurl mountains,
as the giants are said to have done, against the flaming mass? - and
then we shall have traditions of Titans again, and of wars with Heaven.
A few ideas for deflecting a threatening near-Earth comet or asteroid include:
- Attach rockets to the NEO's surface with the engines pointed
away from the object. Fire the rocket engines for a sufficiently
long time to nudge the NEO into a new non-threatening orbit.
- Build a mass driver on the NEO's surface. A mass drive accelerates
fragments of the NEO into space. The reaction would nudge
the NEO into a different non-threatening orbit.
- Attach a thin solar sail several square kilometers in size to
the NEO with strong cables. Solar wind pressure would eventually
nudge the NEO into a new non-threatening orbit.
- Detonate sizable nuclear weapons near the NEO. The energy pulse
released by the bombs would vaporize part of the NEO's surface.
The vaporized material blown away from the surface would propel
the NEO in the opposite direction, again moving the the NEO into
a non-threatening orbit.
All of these methods -- and many more which have been proposed -- rely
on sufficiently early detection of the threat from a particular
near-Earth object. That is why the NEO search programs are so important.
If we don't know a threatening object is coming, we can't prepare to
deflect it. If we don't deflect the NEO, the impact may destroy
out civilization. A sufficiently large impactor we extinguish us and
most life on Earth. We could go the way of the dinosaurs without even
knowing what hit us.
- Asteroid and Comet Impact Hazard
by David Morrison, Ken Bollinger, and Richard Gerber at
NASA/Ames offers an overview of this topic, the Spaceguard
Survey Report of 1992, Congressional testimony and statements,
an impact hazard scale, a list of known NEOs with orbital
elements, a list of future close passages of NEOs,
bibliographies, and links to related web sites.
- Asteroid And Comet Impact Hazard Bibliography (1992-1997)
offers a short list of important papers and books on this
subject from 1992-1997 collected by David Morrison.
- Asteroid / Comet - Earth Impacts
by David A. Rideout calculates the approximate kinetic energy
of an impacting asteroid and comet along with the consequences
of the impact.
- Asteroids, Comets, Death, and Extinction
by J. Z. Ponder discusses the danger posed by earth-crossing
- Impact Hazard: Predictability and Policy Issues
by Clark Chapman discusses the history of work on the impact
threat and deflection strategies.
- Lesson Plans on Possible Asteroid Impacts
offers a teacher's guide for grades 8-12.
- Orbit Diagrams
from the Minor Planet Center at the Smithsonian Astrophysical
Observatory provides orbital diagrams for a selection of
near-Earth asteroids and comets, including comet 2P/Encke and
- Probability of Collisions with Earth
by Ray Newburn discusses the likelihood of impact events of
offers a comparative list of the probabilities of various
occurrences such as losing your job, dying in an asteroid
impact, and being sucked through your computer monitor into
another space/time continuum (!). A bit tongue-in-cheek but
Detection of, Dangers of, and Defenses against, Impacts
- ABCs Of NEOs
by Richard P. Binzel discusses the origin of near-Earth
objects and the dangers those pose.
- Alpha Space Foundation
is a not-for-profit organization seeking to build a
space-based network of telescopes for detecting threatening
objects; a space shield to divert or destroy such objects; and
several self-sufficient space settlements to ensure the
continued existence of the human race should a large object
penetrate the shields and collide with the Earth.
(Air Force Maui Optical Station), in collaboration with
scientists from the Jet Propulsion Laboratory (JPL), conducts
follow-up observations of newly discovered and multiple
apparition Near Earth and Main Belt Asteroids. These
observations are designed to update the orbital elements, and
to determine the rotation rates, shapes, and spin axis
orientation of the observed asteroids.
- "And now a word from Chicken Little ..."
offers an interview with David Morrison conducted by Kate Rix
which discusses the impact danger.
- Asteroid Avoidance
by Arthur Krispin surveys several methods of averting
catasclysmic impacts of asteroids with the Earth.
- Asteroid Collisions with Earth
summarizes a NASA research project by Owen B.Toon, Kevin
Zahnle, and David Morrison to study the environmental
repercussions of asteroid and comet impacts on the Earth.
- Asteroid and Comet Tracking
by John Walker allows you to plot the orbit and current
position of an asteroid (minor planet) or comet by pasting its
orbital elements into the text box provided for that purpose
on his page. You enter the orbital elements, which permit
calculation of the position of the object for a period of time
surrounding the Epoch for which they are computed, in the form
currently published in the International Astronomical Union
(IAU) and Minor Planet Electronic Circulars.
- Asteroid Collisions
offers background information on collisional outcomes as well
as a laboratory impact experiment database.
- Asteroid/Comet Earth Impacts
by David A. Rideout calculates the approximate kinetic energy
of an asteroid and a comet released on impact with the
- Asteroid Hunters Scan The Sky
is a CBS news article about the Massachusetts Institute of
Technology's Lincoln Laboratory team headed by Grant Stokes.
This team searches for near-Earth objects using technology
originally designed by the United States Air Force to track
- Asteroid Impact
reports on a class project to decide whether or not it would
be a good idea to build a research center to study Near Earth
- Asteroid Insurance
offers a policy against an asteroid impact. I think it's
supposed to be a joke, but you never know.
- Asteroid Radar Research
by Keith Rosema and Steven J. Ostro discusses ongoing
projects to determine asteroid physical properties and orbits
using radar. This includes Earth-crossing asteroids.
- Asteroids and Comets Threat
by Victor D. Noto offers constantly updated news about
impact-related research and events. Includes annotated links
to a variety of catastrophism, astronomy, and space
- Asteroids and us
discusses the origin and evolution of asteroids, their
relationship to comets, and the danger asteroids pose to
- Asteroids, Comets, and Meterorites: Their Intimate Relation with Life on Earth
by Stephen P. Broker discusses impacts of comets and
asteroids, among other things.
- Asteroids -- Effects of an Impact on Earth
by Mark Prado discusses Tunguska, reports and detection
methods of small asteroid hits, effects of impacts on Earth,
defense methods, and more.
- Avoiding Armageddon by redirecting space debris
by Nick Nuttall is adapted from his article in The Times of
London. Nuttall discusses proposed methods for deflecting
potentially destructive incoming objects.
- On June 10, 1997, Space Development Corporation's founder and chairman James W. Benson announced the Benson Prize for the Amateur Discovery of Near-Earth Asteroids
, which offers $500 for each of the next 10 discoveries of
near-Earth asteroids by amateur astronomers. "The purpose of
the Benson Prize," said Benson, "is to encourage backyard
astronomers to seek out previously unknown near-Earth
- Catalina Sky Survey
at the Lunar and Planetary Lab of the University of Arizona
has been carrying out "a systematic survey of the
near-opposition sky at ecliptic latitudes 30 to 60 degrees on
a monthly basis with the f/3 0.41m University of Arizona
Catalina Schmidt. A total of 16260 square degrees have been
scanned to date, resulting in the discoveries of 62 new
asteroids and 1 new comet."
- Citizens' Protection Against Near Earth Objects (Cpaneo)
" is an international forum for discussing the issues and
bringing to the forefront the most current information
available from the educational, governmental, environmental,
and scientific communities. Our mission therefore is to serve
as a buffer between the scientists and the rest of the global
community to help convey the importance of this matter."
- Collisions With Asteroids and Comets
from Strasenburgh Planetarium discusses the kinds of objects
which could strike the Earth, what would happen if a comet or
asteroid did hit us, what the changes are of a major impact,
what is being done to find potentially dangerous space
objects, what we could do if a collision were immiment, and
where to find reliable information about impacts.
- Comet and Asteroid Risks to Earth
offers extracts from several articles and books which discuss
the impact threat and means to divert potential
- Comet and Asteroid Search
by Gil Esquerdo discusses this program, currently in a "wait
and see" position, at the Planetary Science Institute.
- Comet Busters
by Peter Tyson is an article from Technology
Review which discusses the dangers posed by
earth-crossing objects. Tyson discusses some of the proposals
for diverting such objects.
- Comet or asteroid impact with the earth: How real is the threat?
by Bob Hawkes offers a brief look at the impact danger.
- Comets and Asteroids and Catastrophes
by Glen W. Chapman excerpts material from several sources
including Frank Close's book Apocalypse When.
Describes sources of potential dangerous impactors and
includes some ancient texts which may describe impact
- Cosmic Collisions
by Sally Stephens offers a primer on asteroid collisions with
- A Cosmic trail with destruction in its wake
by Nick Nuttall is an article from "The Times" of London, May
24, 1990. Nuttall interviews Victor Clube, who discusses the
danger of impacts, especially from the Taurid stream.
- Could a Comet Lead To a Killer Flood
reports on research from Los Alamos National Laboratory which
looked at the effects of an asteroid or comet impact in the
middle of the Atlantic or Pacific ocean.
- Defense System Aiming At Asteroids
is an article by Ellen Hale from the Salt Lake Tribune of
Sunday, June 2, 1996. Hale discusses the search for near
earth objects and ways to deflect them. Includes comments
from John Lewis, David Morrison, and Tom Gehrels. A longer
version of this article is also available from Florida
Today Space Online.
- Destination Earth! - The Threat From Space
by C. M. Raffrey discusses the threat from NEOs and methods
for deflecting them.
- DoD vs. Asteroids
by Brian Friel reports on comments from U.S. Defense
Department spokemen Kenneth Bacon and Defense Undersecretary
Paul Kaminski about how the Defense Department is approaching
the impact danger.
- Doomsday Asteroid
offers the transcript of a television program about the
impact danger. The program included snippets from interviews
with scientists like Victor Clube, Gene Shoemaker, and Duncan
- Earth can servive
suggests we need to start building a system to protect our
planet from destruction. Includes links to various
catastrophism resources including some religiously oriented
- Earth-crossing asteroids
by Scott Hudson discusses how and why people study asteroids,
the nature of the impact hazard, spacecraft missions to
asteroids, what research has told us about asteroids, and
- Earth Crossing Objects
by Douglas Clarkson briefly summarizes the danger from NEOs,
the extinction of the dinosaurs, periodic extinctions and
Nemesis, Chiron, and Spaceguard. Also offers links to related
web sites and a short bibliography.
- Educator's Guide to NEAR
by Steve Bowser and Joy Maloney tells what the Near Earth
Asteroid Rendezvous program is all about. Includes
information for teachers, lesson plans, a project to design a
discovery mission, and information about the NEAR
- EUNEASO Project
(European Near-Earth Asteroids Search Observatories) is a
European near-Earth object search, followup, and physical
- Hunting Asteroids from Your Backyard
by Dennis di Cicco discusses how other amateur astronomers
can discover asteroids with telescopes as small as 8" in
aperture using digital technology and CCD cameras.
- Impact Apocalypse
by Stacey Hayde offers interviews with Gerrit Verschuur and
Alan Hale about the danger from NEOs.
- IMPACT: Death From Above
by William Jessee offers an introduction to the dangers of
impacts and methods for defending against impacts.
- Is the Sky Falling?
by David Morrison is an article from the May/June 1997 issue
of Skeptical Inquirer
magazine. Morrison discusses the impact threat and offers
reviews of a number of books on this subject.
- Jupiter Scientific Reports on Threats from Heaven
discuses the dangers posed to the Earth by solar system
- Klet Observatory
in Southern Bohemia in the Czech Republic operates a search
program for minor planets and performs follow-up astrometry of
NEOs and other unusual minor planets and comets.
- Kollisjoner med asteroider og kometer
(in Norwegian) by Trond Erok Hillestad discusses the impact
- Kuiper Belt
Home Page by David C. Jewitt and Jing Li discusses this
trans-Neptunian belt of objects which is considered to be the
source of short-period comets. Includes photos and lists of
Kuiper belt objects discovered so far, information on
"Plutinos," a bibliography,
(Lincoln Near Earth Asteroid Research) is an MIT Lincoln
Laboratory program funded by the United States Air Force. "The
goal of the LINEAR project is to demonstrate the application
of technology originally developed for the surveillance of
earth orbiting satellites, to the problem of detecting and
cataloging Near Earth Asteroids (also referred to as Near
Earth Objects, or NEOs) that threaten the Earth."
- List Of The Larger Potentially Hazardous Asteroids (PHAs)
is from the Minor Planet Center at the Smithsonian
- LONEOS: Lowell Observatory Near-Earth Object Search
supplements the Spacewatch and NEAT programs Currently only
about 100 of the estimated 1600 earth-crossing asteroids
larger than 1 km in diameter are known. LONEOS hopes to scan
the entire dark sky accessible from Flagstaff, Arizona three
times per month to locate more of the earth-crossing asteroids
visible down to about 20th magnitude.
- Meteor Defense
by Bob Kobres
discusses possible methods for deflecting incoming
- Meteoroids Threaten Satellites
is an Associated Press story by Jane E. Allen reporting the
concerns raised by the damage to satellites which might result
from the possible Leonid meteor storm expected in November
1998 or November 1999.
- Minor Planet Center
at the Smithsonian Astrophysical Center is a nonprofit
organization which is responsible for the collection,
computation, checking, and dissemination of astrometric
observations and orbits for minor planets and comets.
- The Near Earth Asteroid Rendezvous (NEAR)
mission intends to rendezvous with the asteroid Eros, the
largest of the near Earth asteroids
- Near-Earth Asteroid Tracking
(NEAT) by S. Pravdo at NASA/JPL has observed almost 29,000
asteroids, of which nearly 14,000 were previously
- Near-Earth Asteroids
offers a statement by Eugene M. Shoemaker to the United
States Congress, presented on April 10, 1997. Shoemaker
discusses the danger from near-Earth objects.
- The Planetary Society's Near-Earth Object Grant Program
"seeks to encourage the discovery and exploration of NEOs by
supporting observation projects and related research around
the world. The Society intends these grants to accelerate the
NEO discovery rate, to improve and increase observations, and
to encourage international cooperation in this field." Also
for the Gene Shoemaker Near-Earth Object Grant
- Near Earth Object Map
, by Scott Manley of the Armagh Observatory, displays an
up-to-date map of the solar system showing the orbits of the
terrestrial planets and the estimated position of several
- Near Earth Object Program
at the Jet Propulsion Laboratory (NASA) was established in
mid-1998 "to help coordinate, and provide a focal point for,
the study of those comets and asteroids that can approach the
- Near Earth Objects Page
by The Planetary Society offers "current information about
the science, discovery, and tracking of comets and
- The NEO Page
(near-Earth objects) page of the International Astronomical
Union (IAU) Minor Planet Center (MPC) at the Smithsonian
Astrophysical Observatory offers a wealth of information
including the NEO confirmation page, the dates of last
observations of NEOs, a list of known NEOs and orbital
diagrams for some of them, lits of close approaches to the
earth, and links to related sites.
- NEO Petition
by Jim Simpson discusses the impact threat and provides
boilerplate for a petition to members of the United States
Senate, requesting an increase in funding for near-Earth
object detection and discovery.
- NEOs: Friends or Foes
by Richard P. Binzel discusses the effects of global versus
local impacts, how to look at the risks associated with impact
events, and offers a probability table relating the risk of an
impact to that of other types of events.
- NPR's January 17, 1997 Talk of the Nation: Science Friday
offers a one hour discussion with harold Levison and Steve
Prado about the dangers posed by near Earth objects.
- OCA - DLR Asteroid Survey
or O. D. A. S. "is a dedicated program to search for
asteroids and comets, with special emphasis on NEOs within
the framework of the EUNEASO project."
- Perturbing the Oort Cloud
is an article by Michael Szpir which appeared in the
January/February 1997 issue of American
Scientist. Szpir describes recent research into the
idea of a 28 to 32 million year comet shower and extinction
cycle caused by galactic disk tides.
- Planetary Defense: Catastrophic Health Insurance for Planet Earth
is a research paper, presented as part of the United States
Air Force 2025 Project, by Colonel John M. Urias and his
colleagues. This report dicusses the danger from cosmic
impacts and possible methods of defense.
- Planetary Defense Watch Advisory Page
offers information on impacts, possible defenses,
publications, and a list of scientists working on the impact
- Planetary Defense Workshop Proceedings
offers the proceedings of a meeting held May 22-26, 1995 at
at the Lawrence Livermore National Laboratory. The papers are
in Adobe Acrobat format (PDF).
- On the lighter side, The Worldwide Institute for the Preservation of Everything offers some thoughts about a Protective satellite force shield
- Quail Hollow Asteroid Discovert and Astrometry Program
discusses the work this private astronomical observatory does
into discovering and tracking asteroids.
- Report of the Near-Earth Objects Survey Working Group
from NASA's Near-Earth Object Survey Working Group discusses
a program to "discover, characterize, and catalog within ten
years (to the extent practicable), the potentially threatening
comets and asteroids larger than 1 km in diameter."
- Sky and Telescope's Impact Hazards Web Site
offers an article on the impact hazard by Gerrit L. Verschuur
and annotated links to web sites about impacts by Stuart J.
- Sky is Falling
by George H. Lenz discusses the energy of impactors, the
Cretaceous/Tertiary boundary impact, and offers a short
- Solar System Collisions
by Doug Hamilton allows you to calculate the approximate
crater size and energy released by an impacting body on
various bodies in the solar system.
- The Space Shield Foundation
"is a totally private, non-commercial Foundation organized in
Russia with international participation. It was established in
1994 mainly as Russian public foundation to promote, support
and provide scientific research and technology development on
hazards due to space objects (asteroids and comets) impact
with the Earth and protection of the planet against such
- Australian Spaceguard Survey
by Michael Paine is an unofficial homepage seeking to
drum up support for the reestablishment of Spaceguard
Australia. Includes information on the risk and
consequences of cosmic impacts, Near Earth Object news,
a discussion of the Shiva Hypothesis for a thirty
million year cycle of mass extinctions brought on by
comet showers induced by the passage of the solar system
up and down through the galactic plane. Also includes a
running up-to-date list of NEO-related news items.
- Japan Spaceguard Association
is the Japanese affiliate of The Spaceguard Foundation.
Most information here is in Japanese.
- Spaceguard Canada
"the University of Victoria/ Dominion Astrophysical
Observatory near-Earth object astrometry program is
designed to provide real-time astrometric confirmation,
recovery, and follow-up of newly-discovered Earth
approaching objects (comets and asteroids)."
- Spaceguard Croatia
- The Spaceguard Foundation
is an association aimed at the protection of Earth's
environment against bombardment by comets and asteroids.
The association was officially set up on March 26, 1996
in Rome, Italy.
- Spaceguard Foundation (U. S. Mirror)
- Spaceguard Foundation e.V.
is the German affiliate of The Spaceguard
- Spaceguard UK
offers the charter for Spaceguard UK and discusses the
June 1996 proposal concerning the establishment of a
coordinating office to study the threat posed to the
United Kingdom by the possibility of an impact by an
asteroid or a comet. The proposal was sent to the
Minister for Science and Technology and to the Secretary
of State for Defence.
- The Spacewatch Project
at the University of Arizona "is an ongoing research project
whose ultimate goal is to survey the Solar System to
completion. One of our primary goals is to develope a system
to automatically discover the hazardous asteroids and comets
which can impact Earth, causing widespread devastation."
- Stray Asteroids
is a one-hour RealAudio transcription of a National Public
Radio broadcast of January 17, 1997 in which Harold Levison
and Steve Prado discuss the impact threat and programs to
detect near-Earth objects.
- Target: Earth
by Peter Jedicke discusses the impact danger and possible
- TASS, The Amateur Sky Survey
"hopes to construct low-cost drift-scan cameras and
distribute them to sites around the world; the idea is to
monitor bright objects across a large section of the sky."
This includes NEOs.
- Threat and Promise of Asteroids and Comets.
by Alex Michael Bonnici offers links to web pages on the NEO
threat. Bonnici says "he future of the human species is tied
in a very deep way to the coming and passing of Asteroids and
- Threat of Asteroids
by D. J. Dave discusses the impact threat.
- Torino Impact Hazard Scale
was developed by Richard P. Binzell of MIT to gauge the
potential damage from a cosmic impact.
- Uppsala-ESO Survey of Asteroids and Comets
(UESAC) searches for previously undetected comets near
- White Paper on Planetary Defense
from Air University 2020 discusses the detection and
inteception of asteroids on collisions courses with the
- Why Study Near Earth Objects
by Carl Sagan offers a list of reasons for studying
Impacts on Earth
- Archive of DOD Press Releases
provides press releases/announcements from the Air Force
Technical Applications Centre (AFTAC) Office of Public Affairs
and elsewhere. These releases relate to satellite observations
of fireballs detected in the atmosphere by optical and
infrared sensors aboard United States Department of Defense
- Australian mystery impact?
Bob Edwards talks with Gregory Van Der Vink on National
Public Radio's January 29, 1997 Morning
Edition program about "the unexplained events nearly
four years ago in the Australian outback. Was the huge
explosion, felt hundreds of miles away, a small earthquake, a
meteorite crashing or worst of all, a nuclear blast?" Van Der
Vink suggests the evidence supports the possibility of an
impact, but no crater has yet been found. You will need a
RealAudio client to listen to the interview.
A May 28,
release from the National Science Foundation offers
another summary of this event, along with images of the
seismic signal and a map of the area from which the signal
- Catalogue of Meteorites and Fireballs, from A.D. 2 to A.D. 1860 by R.P. Greg, Esq., F.G.S
by R. P. Greg was originally published in 1861 as part of the
Report of the Thirtieth Meeting of the British
Association for the Advancement of Science.
- Chesapeake Bay Bolide: Modern Consequences of an Ancient Cataclysm
by C. Wylie Poag discusses the impact of a large bolide,
about 35 million years ago, in the vicinity of Chesapeake Bay,
Virginia, USA. The impact carved a roughly circular crater
twice the size of the state of Rhode Island (around 6,400
square kilometers) and about 1.3 kilometers deep.
- Close Encounters of the Bolide Kind, Of meteorites and Mainers
by Herbert Adams discusses several impact events witnessed by
inhabitants of the state of Maine in the United States.
- Cosmic Collisions
by Joseph Robert Jochmans from Atlantis
Rising discusses misses and near-misses from
near-Earth objects. Includes comments on the theories of Otto
Muck who suggested Atlantis was destroyed by an asteroid
- Damage by Impact at Meteor Crater
by Linda M. V. Martel discusses research by David Kring on
the environmental effects of the impact which created Meteor
Crater in Arizona.
- The Day the Sands Caught Fire
by Jeffrey C. Wynn and the late Eugene M. Shoemaker is a
Scientific American feature article from the November 1998
issue discussing the dating of the Wabar craters in Saudi
Arabia. This impact event may have occurred as recently as
135 years ago.
Greenland, December 9, 1997
- Impact Cratering on Earth
from Natural Resources Canada offers a introduction to the
subject. Includes sections on crater morphology (with
images), crater identification, the impact hazard, and
suggestions for further reading.
offers a list of identified terrestrial impact craters.
- Norwegian Astronomical Society Meteor Section
includes data on confirmed
impact craters and structures in the Nordic countries.
- Peekskill Meteorite
is a 972K MPEG movie showing the fall of this meteorite on
October 8, 1992. An impacting fragment weighing 12 kilograms
(26 pounds) damaged a car in Peekskill, New York State, USA.
This may be the first movie of a fireball for which an
associated meteorite was located.
- Shock Therapy: How Earth Responds to Impacts From Outer Space
by Randall T. Cygan discusses the impact of large bolides on
the Earth and on Jupiter.
- Small Comets
discusses the "small comets" theory of Louis Frank. He
suggests that, every few seconds, a house-sized "snowball"
approaches Earth and deposits a large cloud of water vapor in
the Earth's upper atmosphere. This idea continues to be very
new evidence (May 28, 1997) from the Polar spacecraft's
Visible Imaging System confirms the existence of some new
phenomenon in Earth's upper atmosphere which appears to be the
arrival of objects containing a lot of water. This is likely
to be a topic of intense debate over the coming months.
- Terrestrial Impact Craters Slide Set
was compiled by Christian Koeberl and Virgil L.
Impacts that weren't
- A news report from Chambery, France
stated that a meteorite struck a car in this Alpine French
town on April 11, 1997. Meteorite experts at the Paris museum
who examined fragments of the purported impactor discovered it
was composed of combustible plastic.
- Expedition to Honduras
by Jiri Borovicka talks about am expedition to a site in
Honduras in which a meteor was claimed to have created a
165-foot wide crater in November, 1996. The impact was also
supposed to have damaged part of a main highway, and ignited
a fire which destroyed several acres of coffee plants. The
expedition found no evidence for an impact at this site.
- Meteorite blasts 165-foot-wide crater in Honduras
presents an Associated Press wire story about a small impact
in Honduras in November, 1996. The impactor is claimed to
have left a 165 foot crater, damaged part of a main highway,
and ignited a fire which destroyed several acres of coffee
plants. More details and a picture of the devastated area
appear in an
article (in Spanish) from the Honduran newspaper "La
Prensa". just_li This incident, IF
CONFIRMED, would offer a useful counterexample to
critics who maintain that small impactors cannot start fires
because, for example, the meteoroid is "cold." just_li As of
March, 1997, reseachers who have visited the San Luis site of
the landslide do not believe there was an impact at this
location. Rather, a bright fireball was observed, and an
unrelated landslide occurred. However, fragments from this
bolide may have impacted elsewhere in Honduras, as
suggested by the article Scientists
confirm fireball in Northwest Honduras was meteorite.
Asteroid 1997 XF11
- Asteroid 1997 XF11 (Earth Close-Approach)
from the Solar System Dynamics group at the Jet
Propulsion Laboratory includes a summary of the close
approach to Earth in 2028, plots showing positions of
the asteroid in the Earth target plane at closest
approach, a table of all Earth close approachers between
1990 and 2029, and geocentric ephemerides for 1997
- Close Approach Of Asteroid 1997XF11
by David Morrison discusses the media blitz
accompanying the announcement in March, 1998 that
near-Earth asteroid 1997XF11 might strike the Earth in
2028. This asteroid was discovered on December 6, 1997
Scotti of the
Spacewatch Project at the University of Arizona's
Lunar and Planetary Laboratory. The asteroid will
pass near the Earth in 2028, but miss the Earth by a
comfortable margin of about twice the distance to the
Moon. It is possible that 1997XF11 may collide with
the Earth at some time in the distant future. This is
also true of the many other earth-crossing
- Close calls with comets
by Johnny Horne discusses the near approach of asteroid 1996
JA1 to the earth on May 19, 1996.
- TWA 800: did a meteorite strike cause it to crash?
offers responses by David J. Helfand and Gerrit Verschuur to
the question about the possibility that the crash of TWA
flight 800 resulted from the plane being struck by a
meteorite. Also see the comments by David
Tunguska and similar events
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pib on July 6, 2003.