Asteroid Defense

Preventing Comet and Asteroid Impacts

The Threat of Rogue Comets and Asteroids

Introduction, Web Links, Film Reviews, & Bibliography

Compiled by John D. Furber
Updated 6 January 2024

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The following is general background information on the

ASTEROID and COMET Impact Threat

Meteor Crater ArizonaI have become very interested in asteroid and comet impacts because they can threaten the survival of our society and our species. In our Solar System, each of the planets is hit by large, high-velocity rocks at unpredictable times. A striking example occured in July 1994 when we observed Jupiter being struck by a series of large comet fragments.

The chances of a comet or large asteroid heading for Earth are high...
(based upon extrapolations from astronomical observations and past impacts).
We just don't know when...
It could be 6 months or 6,000 years,
so we need to invest in a preparedness plan to locate and divert the big rock
to harmlessly miss us.
This would be common-sense disaster insurance to protect civilization. [John D. Furber, 2017]

The photo at right is the Arizona Meteor Crater, located in the Arizona desert of the United States. It is more than a mile across. Between 20,000 and 50,000 years ago, a small metallic asteroid, about 25 meters (80 feet) in diameter impacted the Earth and formed this crater. (Smithsonian Scientific Series (1929), taken by the U.S. Army Air Service. Public domain.)

Comet HyakutakeComet Hyakutake, pictured at right, was photographed by the Anglo-Australian Observatory as the comet raced by the Earth in March 1996. It was discovered only 7 weeks earlier! If it had been headed for a collision with Earth, 7 weeks would not have given us time to prepare and implement a successful diversion program.

On the other hand, if a comprehensive sky survey were in progress, Comet Hyakutake could have been discovered months or years earlier. And if diversion planning is begun in advance, then the longer lead time could be used to send up a rocket to divert an incoming comet before it strikes the Earth. The expense of such preparations could be justified as buying DISASTER INSURANCE or implementing safety programs.

Calvin Hamilton of the Los Alamos National Laboratory points out that "Earth's atmosphere protects us from the multitude of small debris, the size of grains of sand or pebbles, thousands of which pelt our planet every day. The meteors in our night sky are visible evidence of bodies of this type burning up high in the atmosphere. In fact, up to a diameter of about 10 meters (33 feet), most stony meteoroids are destroyed in the atmosphere in a terminal explosion. Obviously, some fragments do reach the ground, because we have stony meteorites in our museums. Such falls are known to cause property damage from time to time. On October 9, 1992, a fireball was seen streaking across the sky all the way from Kentucky to New York. A 12-kilogram (27-pound) stony meteorite (chondrite) from the fireball fell in Peekskill, New York, punching a hole in the rear end of an automobile parked in a driveway and coming to rest in a shallow depression beneath it. Falls into a Connecticut dining room and an Alabama bedroom are other well documented incursions in this century. A 10-meter (33-foot) body typically has the kinetic energy of about five Hiroshima fission bombs, however, and the shock wave it creates can do considerable damage even if nothing but comparatively small fragments survive to reach the ground.

"Many fragments of a 10-meter (33-foot) iron meteoroid will reach the ground. The only well studied example of such a fall in recent times took place in the Sikhote-Alin Mountains of eastern Siberia on February 12, 1947. About 136 metric tons (150 tons) of fragments reached the ground, the largest intact fragment weighing 1,741 kilograms (3,839 pounds). The fragments covered an area of about 1 to 2 square kilometers (0.4 to .8 square miles), within which there were 102 craters greater than 1 meter (39 inches) in diameter, the largest of them 26.5 meters (87 feet), and about 100 more smaller craters. If this small iron meteorite had landed in a city, it obviously would have created quite a stir. The effect of the larger pieces would be comparable to having a supersonic auto suddenly drop in! Such an event occurs about once per decade somewhere on Earth, but most of them are never recorded, occurring at sea or in some remote region such as Antarctica." (Calvin J. Hamilton, Los Alamos National Laboratory)

On 15 February 2013, the Chelyabinsk meteor entered Earth's atmosphere over the southern Ural region in Russia. It was an approximately 18 m (59 ft) diameter, 10,000ton near-Earth asteroid that entered the atmosphere with a speed relative to Earth of 19 kilometres per second ( 43,000 mph). The light from the meteor was briefly brighter than the Sun, visible as far as 100 km (60 mi) away. It was observed in a wide area of the region and in neighboring republics. Some eyewitnesses also reported feeling intense heat from the fireball.
See Wikipedia
The PBS science documentary NOVA covered this in detail.

The importance of these rather small meteorites is that they remind us of the fact that rocks are bombarding us unannounced, and that one as large as the one that wiped out the dinosaurs could be on its way without our knowledge.

Taking Protective Action

Not only are these facts of fascinating scientific and historical interest, but we are able to take political and technological actions now to DETECT and DEFLECT the next one before it hits us. We can encourage our governments and universities to install the 25 automated, widefield CCD telescopes necessary for the early detection system.
Fear can be an appropriate first reaction, for it can spur people to examine the problem more closely and to take positive, constructive actions. As a society which hopes to endure, two kinds of action are necessary, and fortunately, they are possible with current technology.
  1. We need to scan the entire sky every month to identify and catalog asteroids and comets which cross the orbit of the Earth. With computers, we can plot their future paths (orbits) to identify which ones are on a path to hit the Earth. This requires a modest program of about 25 automated widefield, 1-meter diameter telescopes with CCD detectors and computerized image analyzers, like the one borrowed from the US Air Force on Maui. And of course we need the astronomers to operate them. This would cost maybe $20 million per year, which is a small fraction of the NASA or NSF budget. By identifying the object months or years in advance, it is much easier to take effective action to either divert its path or break it into small enough pieces to safely burn up in the Earth's atmosphere.

  2. Preparations need to be made to respond to an incoming asteroid or comet when it is identified by the astronomers. Some of the scientists and engineers who developed nuclear weapons and missiles are becoming interested in adapting these missiles and bombs to this healthy activity. With enough lead time, even a very small change in momentum will be enough to deflect its path and cause it to miss the Earth. Preliminary studies have been conducted by scientists from:

Deflection proposals have so far included:

An inspiring TED Talk is given by Phil Plait.
He introduces some of the main points, although he misses the problems with the "Gravity Tractor", which I have discussed above.

Additional background information is being compiled on the Wikipedia page:

As individual citizens, we can encourage our government to increase current efforts to scan the skies. Interestingly, in the summer of 1994, the US House of Representatives asked NASA to take these actions, and several months later, NASA refused. We need to remind our government employees how important this is to all of us.

LINEAR GTS-2 Telescope

Private Sponsorship:

If the United States Government remains unresponsive, the telescopes are not too expensive to be built and operated by individual universities, corporations, or private foundations. Their observations could be coordinated via the Smithsonian Institution. The Maui telescope is one of a set of 6 or more that were built for the US Air Force to track satellites and missiles. They have been lending it to the asteroid search for two weeks out of every month. Another, pictured at left, is operated in New Mexico by The LINEAR Project of the MIT Lincoln Laboratory. We could go to the manufacturers, who built them for the Air Force and Lincoln Laboratories, so that we could find out about making more. They cost about $100,000 each. A complete program will need 25 telescopes and would cost about $30 million, including salaries and buildings. This is a small budget, by government standards, and highly worthwhile insurance for human society.Furthermore, we could be do this one-telescope-at-a-time, at different universities or observatories, in different countries, or with funding from different corporate or foundation sponsors.

A more thorough search is planned by the B612 Foundation,, which is soliciting donations to enable their plans to launch satellite-based tracking systems. The B612 Foundation has set up the Asteroid Institute at the University of Washington to study techniques for detecting and diverting near-Earth objects that may threaten our planet.
See this news story (13 June 2017)
One B612 project is, to launch a space telescope, which would orbit the Sun inside the Earth's orbit. This space telescope would look outward, using reflected sunlight to find and track many more asteroids and comets than have been cataloged from Earth-based telescopes to date. Here is a news story about the project (27 April 2015)

Long lead times are essential
to successfully divert these objects
to safely miss us.


PARABOLIC COMETS (Long-period comets)
are a special threat because:


(Photo at right) The ESA/NASA SOHO orbiting solar observatory shows the huge, long-period "Comet NEAT", not visible from Earth, as is approaches from behind the sun.

So, if you have any personal contacts in Government, corporations, academia, or a philanthropic foundation, we need you to talk to them about establishing more telescopes to open our eyes to the rocks and mountains whizzing by us in the Solar System.

Related Web sites:

MAGAZINE Articles:

Four good BOOKS on the subject are:


Additional Reading List:

Contact information:

John D. Furber
G-mail: johnfurber
Landline telephone: 1-352-271-8711
Gainesville, Florida, USA.
[ John D. Furber home page ]

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