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The small planetesimals of our Solar System are
BBC News Online Science Editor Dr David Whitehouse wrote, on 22 July 1999:
"The most detailed study of an asteroid shows that it contains precious metals worth at least $20,000bn. The data were collected last December by the Near Earth Asteroid Rendezvous (Near) spacecraft which passed close to the asteroid Eros. ... The first conclusions from that encounter are now published the journal Science. ... Eros is believed to have been formed from the wreckage of a collision with a larger body. Its composition appears to be similar to the stony meteorites that frequently fall to Earth. That means Eros is a goldmine in space, as well as a platinum mine, a zinc mine and many more minerals besides.
If Eros is typical of stony meteorites, then it contains about 3% metal. With the known abundance's of metals in meteorites, even a very cautious estimate suggests 20,000 million tonnes of aluminium along with similar amounts of gold, platinum and other rarer metals. In the 2,900 cubic kms of Eros, there is more aluminium, gold, silver, zinc and other base and precious metals than have ever been excavated in history or indeed, could ever be excavated from the upper layers of the Earth's crust.
That is just in one asteroid and not a very large one at that. ... How much is Eros worth? Today's trading price for gold is about $250 per ounce or about $9m per tonne. It means the value of the gold in asteroid Eros is about $1,000bn. That is just the gold. Platinum is even more expensive, $350 per oz. Work it out yourself. Since it contains a lot of rare elements and metals that are of use in the semiconductor industry for example, at today's prices Eros is worth more than $20,000bn. ... One way to get the metals back would be to mine them on Eros and send the refined iron back to Earth. ...
It takes about 2,000 calories to boil a gram of iron so the equivalent of between 20 to 200 thousand megatons of TNT would be needed to start liberating substantial quantities of iron from the asteroid. But this energy could be obtained from the Sun. If you wanted to mine only a section of Eros at a time then a huge solar energy collector - a sheet only a few kilometres in size - could collect enough energy from sunlight to power a smelting plant on the surface of Eros. These are all "guesstimate" figures. But they serve to demonstrate just how plentiful are the resources of the Solar System, in terms of minerals, metals and energy, once we decide to go out and get them. It shows how mining one fairly small asteroid like Eros would revolutionise the availability of many raw materials on Earth. ...
According to a 24 July 2002 BBC article by David Whitehouse and by Ivan Noble: "...
... [ This image
is from a 24 July BBC article by Ivan Noble. ] ...
... It was first seen on the night of 5 July, picked up by the Linear Observatory's automated sky survey programme in New Mexico, US. ... NT7 circles the Sun every 837 days and travels in a tilted orbit ...[that]... is rather highly inclined to the Earth's orbit ... from about the distance of Mars to just within the Earth's orbit. ... NT7 will be easily observable for the next 18 months or so ... Observations made over that period - and the fact that NT7 is bright enough that it is bound to show up in old photographs - mean that scientists will soon have a very precise orbit for the object. ... From its brightness, astronomers estimate it is about two kilometres wide ... Researchers estimate that on 1 February, 2019, its impact velocity on the Earth would be 28 km a second - enough to wipe out a continent and cause global climate changes. ...".
According to a 23 December 2000 BBC article: "...
The 50-yard space rock travelled over London at more than 20 miles per second before missing the planet by just 480,000 miles - twice the distance to the moon but a near miss in astronomical terms. If it had collided with Earth it would have left a hole three quarters of a mile across. The asteroid, still visible through a reasonably powerful telescope in the constellation of Ophiuchus, appeared without warning above the capital at 2400GMT on Friday [22 December 2000]. Robin Scagell, vice-president of the Society for Popular Astronomy, said astronomers can track kilometre-wide asteroids - but spotting smaller objects is much harder. ... he said. "Now with the advanced image detectors available today we are beginning to realise that we're in a bit of a shooting gallery." The asteroid ... has been given the name 2000 YA ... Professor Duncan Steel, the author of Target Earth - a book about asteroids, told the BBC Radio 4's Today programme: "The last time the Earth was hit by something like this was in 1908 above Siberia. "It released energy equivalent to about 20 megatonnes of TNT. If it was to enter the atmosphere above London, it would take out the whole of the city out to the M25." ...".
According to an Associated Press article by Paul Recer on 11 March 1998:
"... Asteroid 1997 XF11 was discovered Dec. 6 by the University of Arizona Spacewatch program and was added to a list of 108 asteroids considered to be "potentially hazardous objects." ... [Asteroid] specialist Jack G. Hills said the space rock ... poses a real danger to Earth. ... Steven Maran of the American Astronomical Society ... noted that no asteroid the size of 1997 XF11 has ever been predicted to pass so close to the Earth. Hills said an asteroid the size of 1997 XF11 colliding with the Earth at more than 17,000 miles an hour would explode with an energy of about 320,000 megatons of dynamite. That equals almost 2 million Hiroshima-sized atomic bombs. Such an asteroid hitting the ocean, said Hills, would create a tidal wave hundreds of feet high, causing extreme flooding for thousands of miles of coast line. "If one like this hit in the Atlantic Ocean, all of the coastal cities would be scoured by the tsunami," said Hills. "Where cities stood, there would be only mudflats." If such an asteroid hit on land, he said, it would instantly dig a crater 20 miles across and so clog the sky with dust and vapor that the sun would be darkened "for weeks, if not months." Maran said the best estimate is that the mile-wide 1997 XF11 will pass inside the orbit of the moon, with the most likely separation from the center of the Earth of about 30,000 miles. The Earth has a radius of about 4,000 miles. The estimate, said Maran, has a margin of error of more than 180,000 miles. This means a collision with Earth is theoretically possible, but uncertain at this time, he said. ... Observations made earlier this month by University of Texas astronomers indicated the asteroid would make its nearest approach to the Earth on Oct. 26, 2028, at about 1:30 p.m. EDT. ... The notice said the asteroid, which is on a wide-swinging, independent orbit of the sun, will move out of view to all but the largest telescopes over the next few months. It will become more visible once again in 2000. And in 2002, it is expected to pass within about 6 million miles of Earth on Halloween Eve. Hills said the asteroid is lost from view when it passes behind the sun, but that it will emerge into telescope range about every two years. Astronomers eventually will be able to track the object using radar, he said, and this will enable them to establish a precise orbital path years ahead of the possible impact. Only then, said Hills, will the true risk of collision be known. Experts long concerned about the potential danger of asteroids have said the Earth could be protected by exploding a missile near the speeding rock while it was far away. The intent would be to nudge the asteroid onto a path that would send it safely away from the planet. ... "
According to the Eros description in the web pages of the NEAR (Near Earth Asteroid Rendezvous) program, one of the largest and best observed near-Earth asteroids is 433 Eros, discovered in 1898 independently by G. Witt (Germany) and A. Chalois (France). Eros accounts for half of the volume of all near-Earth asteroids. The potato-shaped Eros is one of the most elongated asteroids, with estimated dimensions of 35 x 15 x 13 kilometers, so it almost fits within the Baltimore Beltway. Eros orbits around the Sun with a perihelion of 1.13 AU (169,045,593 km) and 1.78 AU (266,284,209 km), and it rotates once every 5.27 hours. Though it is an S type asteroid, it is somewhat varied in its chemical composition. Its opposite sides have slightly different mineralogies. The gravity on Eros is very weak but enough to hold a spacecraft. There is no air and no evidence of water. The day time temperature of Eros is about 100 C while at night in plunges to -150 C.
This montage of the asteroid Eros was assembled from images acquired by the Near Earth Asteroid Rendezvous (NEAR) spacecraft on Dec. 23, as the spacecraft flew by the asteroid at a distance of 2,500 miles (4,100 kilometers) at 1:43 p.m. EST. This montage shows the first nine of 28 views of Eros that were obtained during the flyby. The images were taken between 10:44 AM and 12:44 PM EST as the spacecraft range closed from 7300 miles (11,100) km to 3300 miles (5300 kilometers). During that time, the asteroid completed nearly half of a rotation. The smallest resolved detail is approximately 1650 feet (500 meters) across. ... Options for rescheduling firing of the main spacecraft engine are currently being examined, and could lead to Eros rendezvous and orbit insertion as early as mid-1999 or as late as May 2000. Eros is NEAR's second asteroid encountered. On June 27, 1997, NEAR flew by the main-belt asteroid Mathilde at a range of 1212 kilometers (750 miles).
According to the Mathilde information in the web pages of the NEAR (Near Earth Asteroid Rendezvous) program, asteroid 253 Mathilde has been sstudied by scientists in the Science Data Center at the Johns Hopkins University Applied Physics Laboratory in Laurel, Md.
A 25-minute flyby of the asteroid by the Near Earth Asteroid Rendezvous (NEAR) spacecraft on June 27 has resulted in spectacular images of a dark, crater-battered little world assumed to date from the beginning of the solar system. The Mathilde flyby is the closest encounter with an asteroid to date and the first with a C-type asteroid. The asteroid's mean diameter was found to be 33 miles (52 kilometers), which is somewhat smaller than researchers originally estimated. A study of the asteroid's albedo (brightness or reflective power) shows that it reflects three percent of the sun's light, making it twice as dark as a chunk of charcoal. Such a dark surface is believed to consist of carbon-rich material that has not been altered by planet-building processes, which melt and mix up the solar system's original building block materials.
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