About life-destroying asteroids, the way to discover them and options for eradicating the danger from them. First article in the series by Dr. Noah Brosh
Published in Galileo - Issue 96, August 2006
Close to midnight, on Friday April 13, 2029 (not a "Black Friday" that brings bad luck, but the opposite, as will become clear later), viewers in the sky of Israel will be privileged to see a celestial object moving quickly among the stars. Although the body will not be particularly bright, and may not be visible at all from the heart of a large and bright city, it will be clearly visible to an observer in a dark place, as if it were another one of the artificial satellites visible after dark or towards dawn. The apparent brightness of the body will be like that of one of the pale stars of the Big Dipper, a well-known constellation in the northern part of the sky.
The artificial satellites are visible to our eyes after sunset or before sunrise because they return sunlight to us: a satellite 800 km above the ground is illuminated by sunlight even though the point on the ground from which it is seen is in the dark. The difference between the body that will be visible on April 13, 2029 and the usual satellites is its distance from us: at that time, its distance from the Earth will change significantly. The apparent movement, of 42 degrees per hour, will be slower than that of the low satellites, but fast for a body more than 30,000 km from the earth. At the maximum approach, when the body will look like a star with brightness 3 or 4, the celestial gram will be found "only" 36,350 km above the ground, a little higher than the level of the geosynchronous satellites (35,786 km) that complete one lap around the earth exactly in a day, Therefore they appear to be standing above a fixed point on the equator.
The strange star in the sky was named "Apophys". The meaning of the name, and the connection between it and the nature of the body, will become clear later. But already here it is important to mention that the vigorous studies done regarding Apophis clearly show that April 13, 2029 is, in this case, an exceptionally lucky day for the inhabitants of the Earth! The space rock, whose size is several hundred meters and whose speed relative to the Earth will at this time be greater than 10 km per second, will not collide with the Earth, but will pass by it at a safe distance. If a collision had occurred, we would not have suffered a renewed "dinosaur extinction", as occurred 65 million years ago, but only a disaster on a "local" scale: a crater several kilometers in diameter and one kilometer deep would have erupted in the ground, heavy destruction would have been caused to buildings at a distance of Many tens of kilometers from the impact site, the intense noise of the penetration into the atmosphere and the impact on the ground would have caused earaches at that range, and so on. Impacts of this type on the Earth occur every few tens of thousands of years, that is, it is not a rare event in its history. At the same time, after the series of disasters that happened recently (the tsunami in Southeast Asia, huge floods due to the hurricanes in the southeastern United States) today's crowded world is sensitive even to "minor" injuries.
The body we will write about here belongs to a family of celestial bodies that are members of our solar system and is known as the "Near-Earth Objects" (NEOs) family. These are comets or asteroids whose orbits have been altered by the influence of the major planets in the solar system or collisions with other asteroids, and now occasionally approach Earth. Asteroids are rocky bodies that mostly travel between the orbits of Mars and Jupiter, although some travel in much different orbits. Comets are bodies usually made of water ice and other frozen gases, in which dust grains and rocks of various sizes are mixed. The frozen materials evaporate as the comet approaches the Sun along its elliptical orbit.
detection and alarm
For the past two decades, the astronomical world has been paying a lot of attention to small bodies that come very close to Earth. These bodies are members of the solar system, along with the planets, of which our earth is one. Like the planets (or planets), the small bodies also orbit the sun in elliptical orbits (when the sun is at one of the foci of the ellipse, as required by Kepler's first law of motion). The motive for the great interest in the small bodies is the recognition that bodies that come very close to the earth may damage it and cause serious damage, perhaps even the extinction of all humanity. In fact, the focus on the great extinction that occurred 65 million years ago, when most of the dinosaurs left the world, brought the possibility of a fatal strike from space into the consciousness of the political ranks. This was also helped by several horror films ("Armageddon", "Deep Impact", "Meteor", etc.) along with science fiction books on similar topics, and of course vigorous public pressure.
Since the Great Extinction of the Dinosaurs, there have been several impacts of celestial bodies on Earth that have been recorded throughout human history. One of them, which took place in China in 1490, probably killed about 10,000 people. Another impact, closer to the present day, occurred on June 30, 1908 over Siberia. A body whose mass is estimated at about 100,000 tons entered the atmosphere and disintegrated in an explosion when it was at an altitude of about six kilometers. Trees fell in an area of about 2,000 square kilometers below the point of the explosion, and in an area twice as large, trees that remained upright also caught fire. The energy released in this impact is equivalent to the explosion of 50,000 nuclear bombs the size of the Hiroshima bomb (each weighing 5,000 tons). In 2000, a much smaller body, probably about 20 meters in diameter, appeared over northern Canada, over Lake Tagish. The energy released in this impact was equivalent to only about 2,000 tons of TNT, but the explosion, which occurred at a height of about 25 km above the ground, was recorded in the Canadian electricity grid.
The public pressure exerted in the United States in light of a history of non-negligible injuries led in 1998 to a congressional decision to task NASA with discovering by 2008 90% of the bodies in the solar system whose size exceeds XNUMX km, which could harm the earth and cause very heavy damage . This decision, of mapping the dangers from space, is a matter of "know the enemy" for humanity. To meet this discovery task, several stargazers in the United States and around the world joined forces to discover as many near-Earth bodies as possible. The discovery was made by photographing a section of the sky and repeating the same photograph about half an hour later and about a full hour later. By comparing the three photographs, it is possible to find out if in the area of the sky that was photographed there is a celestial element belonging to the solar system and not a distant star in the background; The body will be seen in each of the images in a different place, due to its movement around the sun and the movement of the earth in its orbit (the place from which we observe changes). Special computer programs analyze "triplets" of photographs and automatically detect most moving bodies, while accurately measuring their location. The location is reported to the "Minor Planet Center, MPC" established by the International Astronomical Union at Harvard University in the United States. This is the official body that centralizes and distributes the observations, and calculates the future position of the various bodies.
The observations of one observatory must be made for two close nights, even consecutive ones, during which the celestial body changes its position according to its orbit around the sun and the movement of the earth. Each night three photographs must be collected to ensure that it is indeed an asteroid, and to obtain a celestial orbit close to the real one. These measurements allow for an approximate determination of the body's orbit around the sun, according to which it is possible to calculate where the body will be a few weeks later - although not the exact orbit around the sun, which allows a position to be determined at any time. To determine an exact route, more observations must be made, at times as far apart as possible.
On June 19, 2004, the American astronomers Roy Tucker (Tucker), David Tholen (Tholen) and Fabrizio Bernardi (Bernardi) operated a telescope at the Kitt Peak Observatory in Arizona, in search of near-Earth bodies. Among their other discoveries that night was a body that was awarded from the center to small bodies for a temporary number only, but not there, as it was observed for only two nights (due to bad weather the other nights). Tolan and his colleagues turned to other studies and abandoned the body they observed for only two nights. About half a year later, beginning on December 18 and during five nights near Christmas 2004, astronomers from Australia and the rest of the world watched the southern sky for the same target. The Center for Small Bodies connected their observations to those of Tolan and his friends when it became clear that it was the same body, which was then given the temporary nickname "2004 MN4". The observations in a time interval of six months made it possible for the first time to determine a route with a reasonable level of accuracy.
The trajectory, and its expected development over the years, were fed into computers operating at NASA's Jet Propulsion Laboratory (JPL) and at the University of Pisa in Italy to predict approaches to Earth. The role of the "Near-Earth Object Center" at JPL is to coordinate the American detection and tracking activities for these objects, according to NASA's directive and the resolution of Congress. The role of the center in Italy, known as "NEODYS", is to provide data on entities close to the country in an accessible and easy way, while calculating the chances of damage. The computers at the two centers independently showed that the body 2004 MN4 comes very close to the Earth from time to time, and that on April 13, 2029 the body will even collide with the Earth...
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Turin scale
It is possible to estimate the expected damage from the collision of a celestial body with the Earth. The calculation is based on the kinetic energy the body has due to its movement and size, and the form of its passage through the atmosphere until it hits the ground. The more solid the body, the greater the chance that it will reach the ground almost intact, although part of it will evaporate during the passage through the atmosphere. Evaporation occurs because bodies from space reach the earth at a very high speed. The minimum speed is that of a free fall from an infinite distance to the earth, 11.2 km per second, which is also equal to the "escape speed" from the earth. If we simplify the calculation, the maximum speed, 72 km per second, is the sum of the highest speed that a body belonging to the solar system can have when it is close to the Earth (42 km per second; at this speed the orbit of the body is very eccentric) and the speed of the Earth in its orbit around the sun (30 km per second). The simple summation of the two speeds is true if the trajectories of the celestial body and the Earth are in the same plane and in the opposite direction of movement, that is, the bodies move opposite each other - a head-on collision.
In order to express the combination of the factors of the chances of injury together with the dangers associated with this injury, two scales were formulated, in which a higher rating is a reason for greater concern. One scale was drawn up in the city of Turin at a gathering of scientists dealing with the subject. On the Torino scale, a rating of 0 is given to meteors that do not reach the ground at all and space bodies that do not collide with the earth. Rating 2 to 5 (indicated in yellow in the graphic description of the scale) deserves the attention of astronomers, because the chance of impact exceeds one percent and according to the known characteristics of the body, the impact could cause a regional disaster. The level of severity increases up to ratings 8 to 10 (marked in red), which express a definite injury; At level 10, the damage could bring about the end of human civilization. A level 10 impact probably occurs every 100,000 years.
Normally, a near-Earth body does not receive a rating higher than 0. It is easy to understand the excitement that gripped the astronomical world when, for several days, at the end of 2004, the near-Earth asteroid 2004 MN4 reached an alarming rating of 4 on the Torino scale, with a collision chance of one in 37!
