IT'S THE END OF THE WORLD AS WE KNOW IT*
by Michael Hammerschlag
I like apocalyptic movies- as I tell friends, I'm good in emergencies. The end of the century has brought us a spate of them: Deep Impact and Armageddon. Of the 2, Deep Impact is far more realistic, but Armageddon is much more fun. In Deep Impact (Dreamworks-director Mimi Leder, who also did Peacemaker) a comet is going to wipe out Earth in an ELE: extinction level event and old salt astronaut Robert Duvall is sent out to blow it up. They keep doing this in these movies: try to blow the objects up. That would, of course, cause a rain of comets or meteors much more devastating than the original.
I know this because I just read probably the most definitive book ever written about earth impactors: Rain of Iron and Ice, John Lewis, 1997. In loving detail it lists every known damage, injury, and death from meteorites and air bursts (basically when a meteor explodes at altitude like a nuclear bomb, without the radiation) back to 1400 BC. Some highlights: Constantinople-472- hissing humming blinding white fireball, fading to yellow and coppery red; turbulent copper cloud; blinded, burned people cowered in terror; blast wave blew out windows and doors, knocking pedestrians to ground and sailboats flat; hot sulfurous wind; 1 hour of fine black dust <> China- Feb 3,1490 Stones fell like rain- over 10,000 killed <> 7/24/1790 Barbotan, France, Meteorite crushed cottage- killed farmer and some cattle <> 3/11/1897 Martinsville W.Virginia- man knocked out, horse killed, walls pierced <> 12/8/1929 Yugoslavia- Meteor hits bridal party, killed 1 (speak now or forever hold your...) <> 7/19/12 Holbrook,Arizona- Building struck, 14,000 stones fell <> Sept 28, 1934 San Francisco- plowing head on at 7000 ft into great shower of meteors, United airliner rocked by some explosions <> 11/28/54 Alabama- Mrs. Annie Hodges struck by 9lb meteorite that crashed through roof, destroying radio <> 12/5/84 Cuneo Italy, Strong explosions, blinding flash, windows broken, daytime fireball "bright as sun" <> 10/9/92 Peekskill, N.Y. Car trunk, floor, pierced by meteorite. The big impacts people know about are the 1908 Tunguska Siberian airburst, that blew down trees for 18 miles and was heard in London, and Arizona's Meteor Crater: about 1 mi. across and 500 ft deep, both explosions about 15 megatons and caused by a rock about 120 ft across.
In Armaggedon (Jerry Bruckheimer, star. Bruce Willis, Liv Tyler, Ben Afffeck) the world-destroying rock is "size of Texas". Forget there's only one asteroid "the size of Texas": Ceres- and only 4 more over 200 miles diameter and they're not coming calling anytime soon. In Deep Impact the comet is 6 miles across. Forget that all it would take to destroy human civilization is a rock 2400 ft across (causing a 12 mi. crater, 100,000 megaton explosion, tidal wave over 1000 ft, global winter and occurring every 250,000 years). Since until 2000 years ago, almost all humans lived within 100 miles of the ocean, all it really would have taken was an 800 ft rock hitting the ocean (1000 megaton explosion, 550 ft. tidal waves moving 450 mph 600 miles away, and happening every 10,000 years). So it's probably not an accident that human civilization is only a paltry 7000 years old out of 3 million years of human habitation and that every religion has legends of brilliant stars, fire, floods, endless dark, and catastrophe. This stuff ain't fiction. It's not if, it's when. A 1 gigaton explosion occurred only 3-5000 years ago in Argentina, leaving a chain of craters 17 miles long. In May '96, a 1000 ft asteroid passed inside the orbit of the Moon- a 2500 megaton impact if it had visited us. There are estimated to be 565,000 near-Earth asteroids (NEA) this big within 1.3 AU (Earth orbit distance) of the Sun, 2000 bigger than 1/2 mile diameter. There are tidal wave deposits 1000 ft. above sea level on Lanai, far higher than any possible earthquake could cause. In 1178, Monks in Canterbury England, witnessed an incredible sight- "The moon's horn split in two, a flaming torch sprang up, spewing out..fire, hot coals, and sparks. The body of the Moon writhed and throbbed like a wounded snake. This phenomenon was repeated a dozen times. After, the Moon, from horn to horn, took on a blackish appearance " Astronomers think this refers to the creation of 12 mile wide crater Bruno by a 120,000 megaton impact(s), 5 times all the world's nukes put together, from a 2 cu. km rock moving 8 mi/s, but we were lucky: it was 20 times more likely to hit Earth!!
Smaller explosions happen even more frequently (~300 ft rock, 100 megaton, 170 ft tidal wave, size of 1863 Krakatoa explosion, every 1600 years), enough to annihilate entire Eastern seaboard and coastal cities around the world. The waves from Krakatoa (Indonesia) shook boats in London and the sound circled the Earth for 9 days. In fact there's a 100 kiloton airburst about once a year somewhere on Earth, about 12 ten kiloton airbursts/year (size of Hiroshima), but the vast majority are over unpopulated areas (ocean). The most amazing film I've ever seen was taken by a tourist in Grand Teton Park in 1972: over 15 seconds a brilliant daytime fireball buzzes from one horizon to the other (in a TV documentary). Passing over Zion Nat. Park, Salt Lake City, Pocatello, Idaho Falls, Helena; it slowly faded from view over Alberta. It was an Earth-grazer, moving 8 mi./sec.and never got closer than 31 miles over Montana, but if it had been a shade closer, it could have annihilated one of those cities in a megaton explosion. In 1972, that could have caused a nuclear war.
Moving up towards the title of this opus, a major killer of 1000 gigatons happens about once every 800,000 years, another reason we have only 7000 years of civilization: man was almost wiped out 2-3 times in his evolution. 65 million years ago a 12 mile wide asteroid or comet slammed into the ocean near the top of the Yucatan and blasted out a 120 mile crater. 100 times the asteroid volume was ripped out of the ground and hurled out at suborbital speeds, to rain down fire and death over the entire globe. The impact punched through the crust, exposing molten lava- vaporizing thousands of cu. miles of ocean water; the seismic pressure waves circling the globe converge in India, where they rip open the crust and erupt massive fields of lava (Deccan Traps). Within hours or days 2 other large fragments smashed into Manson, Iowa (19 mi. crater) and Popagai, Siberia (60 mile crater). Most of the forests and vegetation burned, filling the entire atmosphere with soot, smoke, and toxic gases. Acid nitrogen oxides from the atmosphere reacting with itself in the enormous heat and from burning vegetation, and sulfur oxides from the meteor and from the instant impact vaporization of 80,000 cu. km. of carbonate and sulfate rock acidify rain over the whole planet worse than the worst acid rain ever measured; leaching out deadly mercury, lead, aluminum, cadmium from the soil into rivers and oceans, poisoning most of the life. The acid water kills and dissolves the shells of mollusks and limestone, dumping huge amounts of carbon dioxide in the atmosphere to add to the carbon dioxide from the burning of 3/4 of the world's forests. The worldwide pall of stratospheric dust and sulfur dioxide effectively cuts off the sun for several years; plunging temperatures by up to 72 degrees F: freezing temperatures and darkness, by stopping photosynthesis, cut the food chain off at it's source. Almost all other creatures starve and or freeze. Once the dust settles in 10 years or so, the massive quantities of carbon dioxide, nitrogen oxides, and water vapor kick in a runaway greenhouse effect, raising temperatures 20-50 degrees above normal- baking, drying, and killing most remaining life. When it was over in 100 to 100,000 years..... the dinosaurs, dominant for 160 million years, and 90% of Earth's species were dead and gone. All that was left was a thin layer of gray iridium-rich meteorite dust (Gubbio Clay) all over the world, added up 100,000 cu km of earth. An impact like this one, 1 petaton or 1 billion megatons, happens about every 100 million years. An even worse extinction happened 225 million years ago. In 1994, we had a cosmic demonstration- a string of a dozen comet fragments 1/4-2 miles diameter shelled Jupiter at 28 mps, sending huge fireballs over the visible edge of the gas giant and causing huge black marks several times the size of Earth that lasted weeks and were easily visible in a 8" telescope. The total power in all the explosions was perhaps 30-60 million megatons- we had a grandstand seat for an ELE.
A true planet killer would have to be over 110 miles in diameter (very unlikely, but they just discovered several Chiron comets that size in Jupiter's orbit). Such a monster smiting the Earth at 28 mps would heat the atmosphere to sterilizing temperatures, boiling off the oceans and roasting us into oblivion.
Almost all meteors burn up in the atmosphere, the one's that reach earth are the slow ones: 8/mps or slower. Faster ones crush to dust or explode in the incredible deceleration of the atmosphere. Although they supposedly never hit Earth, meteor showers are among the most impressive events to see. In 1966, the Nov 16-17 Leonid meteor shower provided the greatest show on Earth. For over an hour, watchers saw over 500 meteors a minute, peaking at 40 meteors a second- so many that the watchers felt like they were moving towards the source in a spaceship. This 32-3 year massive storm is reaching us again in 1998-9; even this Nov 16-7, NASA is planning to point all their satellites towards Earth to protect them from the barrage. One major air burst happened the day after my birth day... 30 miles from the hospital in New Haven. Apparently somebody was glad I arrived.
Before we could stop a coming impactor, we'd have to see it, and a new system of 2 telescopes on Kitt Peak, hooked to automated computer comparator programs (Spacewatch) has been discovering dozens of new NEA's/year, as small as 10 feet wide, including one that passed within 80,000 miles of Earth. But we've only discovered 10% of the estimated 2000 1/2 mile diameter killers (each of which could cause a Bruno crater event). Arthur C Clark suggests creating Spaceguard to cover skys across the world; the author says the Maui telescope should be one of the 6 in it. (Arthur Clark suggested communications satellites... in 1946). The most dangerous NEA's are the Appollo, Arjunas, and Aten groups; which intersect or bird-dog Earth's orbit closely. The Atens are really scary: they're inside the orbit of Earth so always in sunlight and undetectable- our likely warning would be 10 seconds. But, with enough warning (more than 2 years), we could, relatively easily, divert an impactor from colliding with us. Especially if we had Liv Tyler.. or Demi Moore to go home to.
*but I feel fine
Michael Hammerschlag worked on the Subaru Telescope on 13,700 ft. Mauna Kea, the world's best place to view the heavens and biggest (13-15 telescopes) and best astronomical complex.