COLLISION COURSE: COSMIC IMPACTS AND LIFE ON EARTH by Fred Bortz (A REVISED AND UPDATED ebook from StarWalk Kids Media, 2014)
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Originally published in library binding by the Millbrook Press, 2001
Cosmic Collision Links and Updates Since 2001
These notes are in reverse order by the date added to this webpage.
Another Comet Crash on Jupiter
On the fifteenth anniversary of the "Great Comet Crash," an amateur astronomer discovered a fresh impact site on Jupiter
Heidi Hammel and other astronomers immediately arranged for telescope time to study how the impact is developing. In a Saturday 25 July 2009 e-mail from the Keck observatory on Mauna Kea to "Dr. Fred" called "Jupiter whacked again," Heidi wrote the following about her observations through the overnight of July 24-25:
You by now probably know of the Gemini and Hubble observations.
Heidi's excitement is obvious. We will be adding updates to the Heidi Hammel update pages of "Dr. Fred's Place" as this encore performance from Jupiter plays out.
We also got some great Keck images tonight. I still have another
night at Keck tomorrow, and then Sunday at Gemini. Hubble
observations sporadically as well. Tiger by the tail!
To Deflect or Destroy? That is the Question
In December 2008, an article appeared describing the research of a group of scientists at Tel Aviv University in Israel who are studying the composition and structure of asteroids to determine the best way to save Earth from a dangerous impact? Do you try to change its orbit or blow it to pieces? The problem with blowing it up is that some large pieces could still strike Earth and cause lots of damage. But if you try to push the space rock into a slightly different orbit, you'll need to know whether it is solid or a loose collection of rocky, icy, or metallic pieces. They haven't come up with a definite answer to that big question yet, but they are definitely making progress. Stay tuned!
Italian Research Team Claims to Have Found Crater from Tunguska Impact Event
Collision Course! has a chapter devoted to the famous Tunguska Event of 1908 in which a small comet or asteroid is suspected of causing the devastation of a forested area of Siberia. One of the continuing mysteries about that event is that no one has found even a fragment of the impactor. Now, according to a National Geographic report, a team of Italian researchers have found evidence that a small lake, known as Lake Cheko, was formed when a piece of the supposed space object broke off and plowed into the mud near the Podkamennaya Tunguska River. The event killed two people and wiped out entire herds of reindeer in that area.
The researchers plan another expedition to the lake in 2008 to sample its sediments and search its bottom for pieces of the as yet undiscovered impactor from outer space.
European Space Agency's Don Quixote Project
The techniques to save the planet as described in Collision Course! are outdated, and the European Space Agency has developed some very interesting techniques to change the orbits of threatening space rocks, turning potential collisions into harmless near misses.
Apollo IX Astronaut Eyes Near-Earth Asteroid
Apollo IX astronaut Rusty Schweikert was the first pilot of the Apollo Lunar Module, but his 1969 mission was never designed to go to the Moon. Now in 2005, he has his eyes on a different space mission. He wants NASA to put an electronic tag on 1000-foot-wide Asteroid 2004NM4. First spotted near the horizon not long after sunset from the Steward Observatory of the University of Arizona on June 19 and July 20, 2004, the asteroid's orbit seemed to put it on a near collision course with Earth on Friday, April 13, 2029. The scientists couldn't rule out a possible impact, but the calculations had a large uncertainty. They could not do better because the asteroid was nearing its farthest point from Earth, about 106 million miles away, and its orbit was taking it to the daylight side of Earth where it would not be visible.
It was not spotted again until late December, when it was observed from Australia for five days around Christmas. This time it was much closer, only about 9 million miles away. With more data to compute its orbit more precisely, the results were scary. On December 26, new calculations gave the space rock a possibility of impact in 2029 of one in 38. That probably would have been front page news if the reporters hadn't been preoccupied with the great Asian tsunami that occurred the same day.
Meanwhile, scientists kept watching and kept calculating. By the time the asteroid was out of view, they could say for certain that it would miss, but only by 15-25,000 miles, at most a tenth of the way to the Moon. That close encounter with Earth is certain to change its orbit, and might make it an even greater threat than it is now. That's why Schweikert is proposing a mission to put a small device called a transponder on the asteroid. Then, whenever people know want to know where Asteroid 2004MN4 is, they can send out a radio signal and listen for the transponder's reply. Even when it is on the daylight side of Earth, they will be able to keep track of it like a grizzly bear with an electronic tag attached to its ear.
No matter what, Friday, April 13, 2029, will be a lucky day for scientists who study asteroids. Read this NASA Science News story about that close approach and the great opportunities it brings those scientists. They won't have to send a spacecraft to get a good closeup view of the space rock. They'll just have to aim their instruments in the right direction as it comes close to us. They're already planning to see how the asteroid's shape changes as it experiences Earth's gravity at close range.
This NASA image, which exaggerates height differences as measured from space, shows the edge of the nearly worn-down 65 million-year-old Chicxulub crater as a darker green circular arc in the Northwest (upper left) of Mexico's Yucatan Peninsula. That crater was formed when a ten-kilometer wide asteroid or comet collided with Earth, which most scientists believe led to the extinction of more than half of the life-forms on the planet, including the dinosaurs.
But Maybe That Theory Is Wrong!
A March 2, 2004 news story describes one scientific team's analysis that the Chicxulub impact happened 300,000 years before the great extinction. The team leader, Gerta Keller of Princeton University is quoted as saying, "The Chicxulub impact was not the only thing making life horrible at the end of the Cretaceous."
Find Out the Effects of a Cosmic Collision Close to Where You Live
I just discovered a link to an on-line program for computing the effects of a large cosmic impact near you. I live in Western Pennsylvania near Pittsburgh, the state's second largest city. I wondered what might happen if Philadelphia, the state's largest city, was hit by an asteroid. I knew it would be bye-bye to Independence Hall, the Liberty Bell, and the steps of the Philadelphia Art museum, made famous as the place where boxer Rocky Balboa of the Rocky movies got his exercise. But what would we feel all the way across the state?
I followed that link and made the following choices: Distance from impact, 500 kilometers (310 miles); Projectile diameter (how large the asteroid is across) 2 kilometers (1.24 miles); Projectile density - dense rock; Impact velocity 10 kilometers per second (6.21 miles per second), which is only a little faster than the speed of an artificial satellite in low Earth orbit; Impact angle, 45 degrees; Target density (what material it hits) - porous rock.
The program calculated the energy of impact and told me that impacts of that size happens somewhere on Earth once in about 1.1 million years. It would immediately form a crater 17 kilometers (10.6 miles) across, which would ultimately grow to nearly 25 kilometers (15.4 miles) when all the shaking ended.
The fireball, which is all that would remain of the city of Philadelphia, would not be visible from Pittsburgh; but a mere 100 seconds later, Pittsburgh would feel the shaking as if an earthquake of magnitude 8.1 had struck Philadelphia. Buildings would shake but not fall down, windows and dishes in cabinets would rattle, and people would be awakened in their beds. Five and a half minutes after the impact, particles averaging about 2.3 millimeters (about a tenth of an inch) in size would start raining from the sky. The ground would soon be coated with these rocky bits to a depth of 7.1 millimeters or more than a quarter-inch.
At about 28 minutes after the impact, the air blast will reach Pittsburgh. By then, it won't be much of a blast. It would produce a 5.4 mile per hour breeze and sound about as loud as heavy traffic.
To try another example for yourself, follow this link.
Did a Cosmic Impact Cause "The Great Dying" 250 Million Years Ago?
Many people are fascinated by the extinction of the dinosaurs and many other animals and plants at the end of Cretaceous Period 65 million years ago, but not as many know that a much greater extinction event took place 185 million years earlier. Scientists commonly call the extinction at the end of the Permian Period "The Great Dying" because 90 percent of all species were wiped out.
As catastrophic as the event was, it paved the way for the rise of giant reptiles. The Permian was followed by the Triassic Period, in which the first dinosaurs appeared. As scientists became more confident that the dinosaurs were wiped out by a cosmic impact, they began to ask, did a cosmic impact cause "The Great Dying" and thus pave the way for the dinosaurs just as a cosmic impact ended their reign and made way for humans?
Dr. Luann Becker of the University of California, Santa Barbara and other researchers think so, and they have identified a crater called Bedout (pronounced Bed-OO) in Northwestern Australia as the likely impact point. You can read an excellent article describing the work of Dr. Becker's team in the on-line Astrobiology Magazine.
Skywatchers Focus Binoculars on Near-Miss Asteroid 2004 FH
On Monday, March 13, 2004, observers from the Spaceguard Survey in New Mexico detected and reported an asteroid in an orbit that would bring it close enough to Earth to be seen with binoculars as it passed by at a distance of 26,500 miles, a little more than a tenth as far away as the Moon, on Thursday March 18 at 5:08 p.m. Eastern time. Designated 2004 FH, the space rock was approximately 100 feet across and was close and bright enough to be visible through binoculars in the Southern hemisphere. Had it hit Earth's atmosphere, it would have created a spectacular fireball but not surface damage. Spaceguard scientists estimated that asteroids of that size hit Earth every two to three years. The importance of this observation is that it came early enough to respond if it had been on a collision course.
For instance, if it had been as large as the 200-300 foot asteroid or comet that devasted many square miles of forest in the Tunguska region of Siberia in 1908, it would have been seen even sooner, and its point of impact could have been determined many days in advance. Though such an impact would not be preventable with current technology on such short notice, the impact area could be evacuated and many lives and valuables could be saved. Also, the incoming body could be studied so that future engineers and scientists could devise strategies to minimize or even prevent the damage by modifying the orbit of a threatening impactor or by breaking it into pieces that are small enough to burn up before reaching the ground.
Those future engineers and scientists may include young readers of Collision Course! Cosmic Impacts and Life on Earth.
You may be able to read a newspaper account of the near-miss asteroid in the online archives of the Washington Post.
Important New Research on How to Save Humanity
The April 19, 2003 issue of New Scientist magazine had three articles on current research about the Chicxulub impact that led to the mass extinction at the end of the Cretaceous period. The first article presented the opinion of a professor who stated that although science is doing a good job looking for dangerous comets and asteroids, very little research is aimed at need to learning more about the physical makeup of asteroids, which will be very important if we hope to deflect a Doomsday rock on collision course with Earth.
The second article presented a detailed description of what happened on Earth in the days after that impact. It explains in detail which places on Earth were most likely to have suffered forest fires and how it is likely that Europe and the northern reaches of North America would have escaped the worst immediate damage. That work may explain how certain animals managed to survive the catastrophe. It also may be a useful tool for predicting safe havens on Earth if another such rock ever heads our way and we are unable to turn it back.
The third article discusses why "nuking" a space rock may be ineffective. The latest evidence indicates that asteroids may be loose piles of rubble that would crush but not be deflected much by a nuclear blast. Other techniques to gradually change the orbital velocity of such a rock, like using the Yarkovsky Effect discussed below ("The Most Significant Threat Yet"), would probably be necessary.
That magazine is available in many libraries, or can be purchased as a back issue from the New Scientist website.
Tunguska Event a Once-a-Millennium Occurrence
On November 21, 2002, a story in the Los Angeles Times described a scientific study of asteroid impacts on Earth as seen by orbiting spy satellites. The scientists concluded that impacts as large as the one that flattened trees over an area half the size-of Rhode Island in the Tunguska region of Siberia on June 30, 1908 occur about once in a thousand years. Since most of the Earth is ocean or sparsely populated land, city-destroying space rocks would be expected to fall about once in 30,000 years.
Did More Than One Impact End the Age of the Dinosaurs?
On November 5, 2002, my morning paper carried a story from the New York Times news service about a challenge to the theory that a single cosmic impact was responsible for the end of the dinosaurs. Several impacts of large space rocks may have been to blame.
I'll be updating this page with more complete information as it becomes available.
The Most Significant Threat Yet
On April 4, 2002, Washington Post staff writer Guy Gigliotta reported, "An asteroid nearly a mile wide could be headed for an apocalyptic collision with Earth." The space rock -- first seen in 1950, rediscovered at the end of 2000, and tracked until August of 2001 -- is known as 1950 DA. It follows a 2.2-year path around the sun that crosses Earth's orbit. That, says Gigliotta, is "the bad news. The good news is that it won't arrive for 878 years, and it might be pretty easy for our descendants to move it out of the way."
The article goes on to describe a number of techniques that might be used to save civilization from the asteroid, which is given a one in three hundred chance of colliding with Earth on March 16, 2880. One alternative, according to University of Arizona planetary scientist Joseph N. Spitale, is to change its surface so it absorbs and responds to sunlight differently, taking advantage of a phenomenon known as the Yarkovsky Effect.
Fred Bortz, author of Collision Course! Cosmic Impacts and Life on Earth will be following developments concerning 1950 DA, though he isn't personally worried about its effects. Unless his locality suffers a direct hit, he expects to remain undisturbed in a small sealed chamber about six feet underground.
The Nearest Miss of the New Millennium (That We Know Of)
On June 14, 2002, an asteroid the size of a football field came within 75,000 miles of Earth -- less than one third the distance to the Moon -- and we didn't know about it for three days. In an Associated Press story, near-Earth asteroid researcher Grant Stokes stated that an asteroid of that size "passes within a lunar distance of Earth" about once a week on the average, but most of them escape notice since the major projects searching for near-earth objects concentrate on larger bodies.
This object, designated 2002 MN, was probably comparable in size to the "Tunguska Object" that devastated nearly 800 square miles of Siberian forest on June 30, 1908. Had it struck a populated area, it would have caused "considerable loss of life," Stokes said. The impact would have released an amount of energy comparable to "a large nuclear weapon."
New Evidence of a Very Old, Very Big Impact Event
In the August 23, 2002, issue of Science, a team of geologists led by Gary R. Byerly of Louisiana State University and Donald R. Lowe of Stanford University reported evidence that an asteroid twice as big across as the one that wiped out the dinosaurs struck Earth about three-and-one-half billion years ago, when the most complex life-forms on the planet were single-celled bacteria. The impact produced about ten times as much energy as the asteroid that ended the Cretaceous Period sixty-five million years ago and set the stage for the emergence of mammals -- including humans -- as the world's dominant life form.
The evidence comes from two sites, one in South Africa and one in Australia, known to contain some ot the oldest rocks in the world that have not been "cooked, heated, twisted, and folded," according to Lowe. The rocks at both places have layers of the same geological age that contain an excess of iridium, the same rare metal that provided the first evidence of the Cretaceous catastrophe. In addition, they contain "spherules," solidified droplets of once vaporized rock that are created in massive volcanic eruptions or impact events. Analysis of the chromium in the spherules confirmed that it did not originate on earth.
The Biggest "To Do" About a "Probably Won't"
In late July, 2002, newspapers made a big deal about two-kilometer (1.2 mi.) wide asteroid 2002 NT7, first detected on July 9. After it had been observed for about two weeks, scientists calculating its orbit reported that it will cross Earth's orbit at about the place Earth will be on February 1, 2019. It will be moving at about 100,000 kilometers per hour (60,000 miles per hour) relative to Earth, which means that the Earth will be in the target zone for about eight minutes.
That sounds scary, but all scientific measurements have uncertainties. Taking all the uncertainties of the measurements into account, they compute a one in 200,000 chance that Asteroid 2002 NT7 will strike Earth in 2019. It will also come close to Earth in 2044, 2053, 2060, and 2078.
Dr. Donald K. Yeoman's of the Jet Propulsion Laboratory told reporters that scientists will have a much better calculation of its orbit after a few more weeks of observing. At that point, he expects that the results will rule out any impact in 2019 or those later years. On the 0-to-10 Torino scale of asteroid hazards, 2002 NT7 is currently ranked at 1, meaning that it should be watched carefully but its chance of impact is small. A 0 on the Torino scale means that the object poses no danger to Earth, while a 10 means that an impact is certain, and it will cause devastation around the world.
You can find up-to-date information about 2002 NT7 and other dangerous space rocks at the NASA asteroid and comet impact pages and The Planetary Society's Near Earth Objects Page
Collision Course! couldn't include every story of great cosmic impacts, so you might enjoy reading this award-winning series of newspaper articles about an impact that reshaped the Virginia coastline 35 million years ago in the Virginian-Pilot. The author, Diane Tennant, was awarded the 2002 Walter Sullivan award for science journalism by the American Geophysical Union.
As Collision Course! Cosmic Impacts and Life on Earth went to press, scientists at NASA's Near-Earth Object Program announced the discovery of Object 2000 SG234, which is traveling around the
Sun every 354 days. The object is probably an asteroid about the size of an office building, but it may be a smaller, brighter human-made object: a rocket booster from one
of the Apollo missions to the moon.
The scientists' first estimate of its orbit gave one chance in five hundred of a collision on September 21, 2030. No other known near-Earth object had ever posed such a serious risk. Fortunately, as was the case for Asteroid 1997 XF11 (see the Prologue) , other images of the object soon revealed that we will be safe a while longer. It will miss Earth by 2.7 million miles in 2030, but it has one chance in a thousand of colliding with our planet on September 16, 2071.
If it is an Apollo booster on collision course, it will burn up harmlessly
in the atmosphere. If it is an asteroid, it could cause severe damage; but
the NASA scientists are confident that they could send a rocket from Earth
to divert its path enough for it to miss.
On February 23, 2001, scientists announced evidence that the greatest mass extinction of all, the "Great Dying" at the end of the Permian Era about 250 million years ago, may have been caused by a cosmic impact. Thus the same kind of event that killed the dinosaurs 65 million years ago set the stage for their emergence. Humans, beware!
The "Science at NASA" web site has an article about that discovery. The article points out that Earth was already undergoing great geological changes -- powerful collisions between continents and volcanic eruptions that unleashed more than a million times as much lava as the famous Mount St. Helens eruption of 1980 -- when that space rock hit. Life on Earth was already in trouble at the end of the Permian Era, and the cosmic impact may have been the final blow.
On July 24, 2001, a meteor bright enough to be seen in daylight, attracted plenty of attention in the northeastern United States and national news coverage. Scientists suspect the object was a piece of an asteroid that exploded into several fireballs as it neared the ground.
This link to the San Francisco Chronicle article may still be "live," although there may be a charge to retrieve it from the archives after a few days.
On December 16, 2001, near-Earth asteroid 1998 WT24 came close enough to see with a backyard telescope.This NASA headline story link, if it is still "live," tells the story of the asteroid and another "potentially hazardous asteroid" called Toutatis that will be even brighter in 2004, and what we know about their dangerous orbits. This time, Asteroid 1998 WT24 came close enough to Earth -- about five times the distance to the Moon -- for powerful radars to map its orbital path more precisely and to measure its shape and size.
On January 7, 2002, less than two weeks after its discovery on December 26, 2001, near-Earth asteroid 2001 YB5 zipped by our planet at a speed of 68,000 miles per hour and came within 520,000 miles of a collision. That's a bit more than twice the distance to the Moon.
Scientists estimated that the space rock is about 1000 feet across and would have completely devastated an area about as large as Texas or France had it hit.
If you want to read a fuller story, this link to the Nando Times article (the online Charlotte News and Observer) may still be "live."
Another NASA headline story talks about another collossal cosmic impact on another planet. Collision Course! has a chapter about the collsion between Comet Shoemaker-Levy 9 and Jupiter, but this collision would have been much bigger. The rings of Saturn may have been created in a giant cosmic collision. The article describes two possible explanations for the rings. A Moon-sized rock that passed too close to Saturn might have been pulled to pieces just as Jupiter broke apart Comet Shoemaker-Levy 9, or an asteroid might have collided with a mon of Saturn and blasted it to bits. Scientists think that could have happened during the age of the dinosaurs on Earth. In the lifetime of the Solar System, that wasn't very long ago!
On March 8, 2002, unseen because it was hidden by the glare of the Sun, a dangerous asteroid narrowly missed Earth, coming within 1.5 times the distance to the Moon. It was probably larger than the famous Tunguska object that devasted over 2000 square kilometers (800 square miles) of Siberian forests in 1908. The object, now known as 2002 EM7, has been added to the list of near-Earth objects to watch. Scientists are still observing its 323-day orbit in order to get a better estimate of future near-miss or impact possibilities. The chances of its making a direct hit on Earth in the twenty-first century are probably one in several million.
More information may be live on this link to the New Scientist web site.
Links to Websites Related to Collision Course!
Click for summary of Collision Course! Cosmic Impacts and Life on Earth
Click to read the Prologue, "Target Earth."
Text copyright 2001-2004 by Alfred B. Bortz, all rights reserved
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