Jupiter Scientific Reports on
Threats from Heaven: Dangers to Earth from Solar System Debris

ON MAY 8, 1998, A COMET STRUCK EARTH! Yes, it happened. Not in one of Earth's oceans or on one of its continents but on theater screens throughout the United States. May 8 marked the release of "Deep Impact." Its "star-studded" cast included the premier appearance of a new, monumental "imp-actor."

      Critics call the film a "smash hit," guaranteed to leave a lasting impression (scientists call this a crater). Others say that the movie makes a big splash. And newspaper headlines employ the double-entendre "Steven Spielberg produces deep impact." Indeed, this film has created renewed interest in the threat of an extraterrestrial object hitting Earth.

      Tongue-in-cheek aside, this is a serious issue. The extinction of the human race is at stake.

      Could an asteroid strike Earth during our lifetime? The answer is yes, but the probability is low. However, the consequence of an impact of an asteroid a mile in diameter or larger would be catastrophic.

      Few people realize it but small objects zoom by quite frequently. Most go undetected. However, sometimes astronomers do spot them. For example, on January 18, 1991, asteroid 1991BA whizzed by our planet reaching a closest approach of 100,000 miles (160,000 kilometers). To put this number into perspective, the mean distance between the Earth and the Moon is 240,000 miles and Earth's diameter is about 8,000 miles (13,000 kilometers). The near miss in 1991 was not anticipated and surprised not only astronomers but the public when it was subsequently reported in newspapers throughout the world. On December 9, 1994, asteroid 1994XM1 passed even nearer at a distance of 70,000 miles. Other known "close encounters" during this last decade of the second millennium also took place on May 20, 1993 and March 15, 1994. None of these objects were large -- about ten meters wide -- nor were they a threat to life since asteroids of this size burn up in the atmosphere. Nonetheless, for the millions of stony objects in our solar system, planet Earth is target Earth. Anyone for darts?

      Even small asteroids -- 100 yards (100 meters) in diameter and larger -- can cause significant local destruction. This is because asteroids and comets typically travel so fast: about 10 miles per second (16 kilometers per second), that is, 600 miles a minute or 36,000 miles per hour! In other words, it takes them a single second to travel the length of Manhattan. No traffic jams in outer space! No speed limits either (except for the speed of light).

      On March 12, 1998, the New York Times and other newspapers around the world announced that, on October 26, 2028, asteroid 1997XF11 would pass dangerously near to Earth, possibly striking our planet. Preliminary observations indicated that 1997XF11 was somewhat less than a mile in diameter. The impact from such an asteroid would cause widespread damage and death; probably hundreds of millions of people would die. However, the chances for an actual collision were small according to an initial scientific March 11 report. Subsequently, some scientists, who got hold of 1997XF11 data, even concluded that it posed no danger. The uncertainty was definitively cleared up the next day when it was announced that 1997XF11 would fly by at a "safe" distance of 600,000 miles. Apparently, some astronomers had discovered old 1990 photographic plates containing images of 1997XF11. Incorporating this information with 1998 observations allowed them to determine the asteroid's orbit more precisely. There is virtually zero chance of an impact with Earth in 2028. Thank Heaven!

      The false alarm was mainly caused by two factors: (1) a hasty public release of scientific information and (2) zeal on the part of the press.

      With only preliminary conclusions available, results were disseminated. It is irresponsible on the part of any scientist to HASTILY provide the press with a potentially horrific story when the life-threatening event is to happen so far in the future. There is also a tendancy for some reporters to ask leading, speculative questions and for newspapers to publish before corroborating information. A moderate amount of sensationalism by the press then created a "hit story" for March 12th news. March 13 was a "different story": Embarrassment.

      People with telescopes will have an opportunity to see "THE ASTEROID THAT SCARED THE WORLD FOR JUST ONE DAY," when 1997XF11 makes a "return visit" in October 2002. On the last day of that month, it will be about 6 million miles from Earth. When they observe it, amateur astronomers will hold their breath, not out of fear but from excitement.

      Deep Impact was not the first film of its kind to "hit the screen." NBC's two-part series "Asteroid" lit up television sets across the United States on February 16 and 17 in 1997. The movie was scientifically inaccurate in many places. It is virtually impossible that a comet could cause several asteroids to head toward the Earth: one, yes; two or more, no. Furthermore, it is laughable to think that these asteroids would travel with the comet. In the late 21st century, it may be possible to create Star-Trek-like lasers, but using such phasers in the 20th century to break up the asteroid is bad science fiction. And at the end of the movie, the comet's tail is pointing in the wrong direction! The tail should be aimed away from the Sun and not behind the comet's motion. Even worse is that the comet is seen moving across the sky like a jet; every amateur astronomer knows that it takes days for a comet to travel a few degrees of arc even at a distance of 6 million miles.

      The explosions during the film must have raised TV viewers' pulse rates. But after the drama ended, people probably relaxed and stretched their legs, while couch potatoes went calmly back to sleep in the "safety" of their homes.

      The creators of Deep Impact used technical advisors to avoid any major scientific slip-ups. It is perhaps nitpicking to point out that the comet's tail was always behind its direction of motion; this is possible if it was heading at the Sun as well as the Earth. In such a case, the object would be visible only during the night. But in the movie, the comet is seen during the day. The end of the film is not realistic from a technical viewpoint: it is impossible to pulverize a comet with four nuclear devices, thereby avoiding at the last moment an ELE or "extinction level event" [not standard scientific jargon]. But this is Hollywood, where even "nature's most powerful extraterrestrial missiles" can be defused without turning a movie into "a dud."

      And brace yourselves for the next attack. On July 1, the film Armageddon will be released, in which Earth will be threatened by a deadly asteroid, and the forces of good and evil will once more be pitted against each other. If 1998 seems like a year full of Hollywoodish apocalyptic events, then what is in store for 1999, the last year of this millennium?

      Moving from the imaginary world of cinema to the harsh reality of truth, asteroids and comets DO pose serious threats to life on Earth. Even during the nineteenth century, our planet has been struck. On June 30, 1908, a small object -- estimated to be half the size of a football field -- exploded several miles above a forest near the Tunguska River, destroying 900 square miles (2000 square kilometers) of pines. The power of the blast was about 10 megatons of TNT. If such a blast were to happen without warning over one of the world's most densely populated cities, millions of people would die.

      Scientists use acronyms for "menacing" asteroids and comets. In increasing danger to us, they are NEOs or "near-earth objects," ECAs or "earth-crossing asteroids," and PHAs or "potentially hazardous asteroids." People have heard of carcinogens such as PCBs that are hazardous to their health, but they probably have not heard of NEOs, ECAs and PHAs that are hazardous to our planet. During the past few decades, astronomers have searched for NEOs, ECAs and PHAs. Of the estimated 2000 ECAs, only about 200 have been found. Slightly more than 100 PHAs have been tabulated. Solar system scientists think that comets comprise about 10% of potentially hazardous objects. Because most PHAs are not tabulated, there is more of a chance of a "surprise strike" than an "anticipated strike" if a collision with Earth occurs.

      On July 17, 1994, an explosion equivalent to about a million megatons of TNT took place not on Earth but on Jupiter. It was created when fragment G of comet Shoemaker-Levy pounded into the planet. The day before, the smaller fragment A had struck. Previously, Jupiter's gravity had caused the comet to break up into 21 pieces. In a week-long period, each slammed into the planet with enormous explosive power. Astronomers on Earth watched the display in awe.

      During the Mesozoic Era (245 million years ago to 65 million years ago), reptiles "ruled" Earth: Ocean-dwelling creatures such as ichthyosaurs, nothosaurs, mosasaurs, plesiosaurs and crocodiles dominated the seas and swamps; the flying-reptiles, the pterosaurs, "patrolled" Earth's air; and dinosaurs dominated the land. Although angiosperms, or flowering plants, appeared about 130 million years ago, no grass existed during the Mesozoic. At the start of this era, the continents were all connected in a supercontinent called Pangaea. By the end of the era, Pangaea had broken up. South America and Africa, for example, had separated. Sixty-five million years ago, these two continents were drifting apart and the Atlantic Ocean was half its modern size. Earth possessed no polar caps because the average temperature was considerably warmer. In short, the geography, climate and life of the Mesozoic were very different from today.

      The Mesozoic Era ended when an asteroid six miles (10 kilometers) in diameter pummeled Earth in the western Gulf of Mexico with a force equivalent to 10,000 times the modern world's stockpile of nuclear weapons. The fireball explosion incinerated all life within hundreds of miles of the blast. Enormous mile-high waves flooded continents. Incandescent ash set Earth's vegetation ablaze. For months thereafter, a curtain of darkness prevailed over Earth. Not only were the dinosaurs wiped out but 90% of land life.

      Needless to say, this catastrophe had a dramatic effect on evolution. It paved the way for the emergence of mammals and eventually man. Had the asteroid not struck Earth, reptiles probably would still be ruling our planet today and mammals probably would still be furry little creatures the size of moles. In a real sense, we humans owe our existence to this haphazard act of nature. Thank goodness for this catastrophe!

      But we have more to thank. Impacts played an important role in the formation of our planet some 4.6 billion years ago. At that time, a giant cloud of gas and dust collapsed. As the material fell in upon itself, it grew dense and heated up. Most material ended up in the central region as a star, our Sun. But some of it continued to circle around. Through the processes of cohesion and accretion, boulders and asteroids were built. At this time, our solar system was littered with debris. Eventually, some planetesimals (diminutive planets) formed. At that point, their gravity drew in nearby rocky material. Planetesimals were pelted continuously as objects rained down on them. These impacts made the planetesimals grow in size until they became planets. The third one from the Sun became Earth. The energy released from all the bombardments left our planet so hot that it was almost entirely liquid rock. For the next several hundred million years, comets and asteroids pounded our planet. Eventually, Earth cooled enough so that oceans could form. As the saying goes, "the rest is history," although it is a history that few people completely know.

      Turning from the past to the future, could our demise be the same as that of the dinosaur's? What are the chances of the extinction of the Homo sapiens due to an extraterrestrial impact? Astronomers have estimated that roughly every 100 million years, a multi-kilometer-sized asteroid strikes Earth. Since each of lives for about 100 years, the probability that we shall all die from a large asteroid is about 1 out of a million, which is roughly the same chances as winning a state lottery. Please place your bets!

      What about a smaller object? An asteroid several hundred yards wide would cause significant local damage and some global disruptions. Tens of millions of people would die. A DHO ("definitely hazardous object" [not standard scientific jargon]) of this size is estimated to strike Earth every million years. In terms of probabilities, this is like playing and winning the "numbers lotto" of a typical metropolis newspaper.

      Los Alamos scientists have recently performed computer simulations on the effects of ocean slamming asteroids. If an object three miles in diameter were to smash into the Atlantic Ocean, waves would overwhelm the East Coast of the United States and reach the Appalachian Mountains. New York City, for example, would be underwater for hours. Even a smaller ocean-slamming impact would create widespread coastal damage and kill millions of people. Perhaps now is the time to invest in some scuba gear!

      An estimate has been made that there is about 1 chance in 5,000 that an individual during his or her life will be killed by some type of extraterrestrial object. And we are not talking about aliens; we are talking about a meteorite, a comet or an asteroid.

      Can science and technology prevent a catastrophe from a large asteroid or comet? The answer is yes if it is detected sufficiently early. A rocket full of (probably nuclear) explosives would have to be launched. One would not try to destroy the object since this would cause it to fragment into pieces leading to an equally destructive "multiple warhead," much like the case of Comet Shoemaker-Levy. Instead, the explosion needs to take place next to the object. This would create a small change in its direction of motion, causing a significant deviation in its orbit for much later times. With current technologies, an Earth-striking asteroid or comet would have to be detected years and perhaps decades in advance in order for preventative measures to be effective. The lead-time is determined by the size of the object and its trajectory. The required explosive power of the human-launched device depends on the object's weight. In regard to comets, it is important for planetary scientists to learn more about these icy bodies since their detailed structure and composition is not so well understood.

      In the situation with a warning time of a few years or less, the only recourse would be to evacuate the impact area. And in the case of a "surprise attack," well . . . well, at least if you are among the "lucky ones" in fate's way, there's probably no quicker way to die.

      Let us hope that if the big one comes, we will be ready.

Note: Most of the historical information for this report was obtained from The Bible According to Einstein.

This report was prepared by the staff of Jupiter Scientific, an organization devoted to the promotion of science through books, the internet and other means of communication.

This web page may NOT be copied onto other web sites, but other sites may link to this page.

People acting or using this information, do so at their own risk. Jupiter Scientific shall not be liable to any individual or entity claiming damage or loss by the contents of this report.

Selected Web Sites on Comet/Asteroid Impacts

Copyright ©1998 by Jupiter Scientific

To Jupiter Scientific's Information Page