In February 2011, few of the humans drew attention to flashed in the media message: an asteroid with a diameter of one meter, named by scientists from NASA CQ1", flew a distance 5480 kilometers from the Earth over the area in the Pacific ocean. The previous record was for "stone" under the code name FU162, which in 2004 procalsol near the Ground only a few hundred kilometers.

Uninvited guests

The small size of these asteroids are not greatly alarmed scientists. They know: "gravitational keyhole" of the Earth, which is a zone that only a little more of the asteroid, under the force of gravity can change their orbit. It happened in this case: the trajectory of the asteroid has been changed to 60 degrees, and "CQ1" with the Earth missed.

Because of the small size prepare such unwelcome "guests" is difficult. In the near-earth space is about a billion objects, and it is quite normal to expect a drop them on the Ground, on average, every few weeks. Penetrating the atmosphere, Tony create a visually impressive effects, but small fragments reach the surface is very rare.

The real threats posed by asteroids with a diameter of 100 metres. "Keyhole" the Earth was not able to change their movement. Such space "boulders" penetrate to the Earth once in 1000 years. A collision with a massive asteroid more than 1 km in diameter - much more rare event, occurring every few million years, however, the consequences can be catastrophic.
Many asteroids remain unnoticed until you are approaching the Earth, and some "open" astronomers after they escaped collision with the Earth, flew past.

Currently, scientists are in control of 10 asteroids approaching with our planet. Their diameter is more than 5 km By estimations of scientists, such heavenly bodies can collide with Earth once in 20 million years. The number of asteroids with a diameter of more than 1 km, cross the Earth's orbit, closer to 500. Getting on the Ground of this asteroid might happen once in 100 thousand years. The fall of a body the size of 1 to 2 km can already lead to a global catastrophe.

In addition, according to the available data, cross the orbit of the Earth around 40 active and 800 extinct "small" comet with a core diameter up to 1 km and 140-270 comets, reminiscent of the comet Halley. These large comets have left their imprints on Earth - 20% of large terrestrial impact craters owe them their existence. In General, more than half of all craters on Earth and comet origin. And now in our atmosphere every minute flies 20 nuclei minicomic 100 tons each.

Scientists estimate that the energy of the collision, the corresponding collision with an asteroid with a diameter of 8 km, should lead to a global catastrophe with shifts of the earth's crust. When etom the size of the crater formed on the surface of the Earth. will be approximately equal to 100 km, and the depth of the crater is only two times less than the thickness of the crust.

According to NASA, approximately every 37 thousand years, our planet risks faced with a large asteroid more than 250 meters. The last few decades we have not once was barely able to avoid such collisions.

The asteroid 4581 Asclepius (23 March 1989)

Astronomers Dr. Henry Holt and Norman Thomas found 300-me-truly space rock, which is said Geophysics, would have led to an explosion in 12 times more powerful than the "Tsar-Bomb" - the most powerful nuclear weapon ever detonated. The calculations showed that ASC-LIPI collided with the Earth at a distance of 430 thousand miles (700000 km), walking right there, where the Land was only 6 hours ago.

Asteroid 2004 FH (18 March 2004)

The LINEAR project discovered a 30-meter asteroid before it passed us by in the distance 42600 kilometres - roughly one tenth of the distance to the moon. As though not large in diameter asteroid in a collision would produce the explosion power of hundreds of kilotons of TNT.

Asteroid 2004 FU (31 March 2004)

Two weeks after the passage of the asteroid 2004 FH, an asteroid named 2004 FU set a new record close of the passage, past the Earth at a distance of 4 thousands of miles. But this is not the worst. Given its small size (6 m), the scientists were able to detect it in just a few hours before he struck the atmosphere. Could he possibly cause serious damage? Not quite. Since the friction of the atmosphere would have burnt it down.

The asteroid 4179 Toutatis (29 September 2004)

This stone is first discovered in 1934, and initially attributed it to an object 1934 ARTICLE. Until then, while the scientists have not lost its trajectory. Seventy years later 4179 Toutatis surfaced again and walked past us at a distance of 1.5 million kilometers. This 4 distance to the moon. One day, dismiss, in the future, as the researchers say, the probability of collision is small.

Asteroid 2004 CHR (3 July 2006)

Because of its projected size from 300 to 900 meters in diameter 2004 HR was classified as a?? a: potentially hazardous asteroid. How close he was to hit us? 268 624 miles (432 308 km). After prolonged observation, the analysis showed that HR went into space, but a collision in the future remains.

The asteroid 2006 VV2 (30 March 2007)

The asteroid passed us at a distance of 2.1 million miles (3.38 million km). Scientists say that an asteroid that size would make a crater so huge that would be erased from the face of the earth the whole country.

Asteroid 2007 TU24 (29 January 2008)

Space rock TU24 was discovered in October 2007, but his close passage occurred three months later, when he walked past us at a speed 9,248 km/sec, and its size was 250 meters in diameter. While travelling that lay at a distance of 1.4 times the distance to the moon, NASA said that there was no chance that TU24 crash or something will affect us.

The asteroid 2009 0045 (2 March 2009)

Australian astronomers from the Observatory Siding Sprint found 35-meter asteroid three days before his very next passage, which was then compared with theoretical object responsible for Tungus ski explosion in 1908. DD45 walked past us at a distance of 74,800 kilometers.

The asteroid 2010 AL30 (13 January 2010)

First Italian scientists Ernesto Guido and Giovanni Sostero documented the object AL30 as proven launch vehicle orbital period of rotation. This theory was later disproved, and it was confirmed that this is a near-earth asteroid 10-15 meters in width. The object was held at the distance of 130 thousand kilometers from the planet. If he collided with the Earth, the explosion would be equal to 100 kilotons of TNT.

Asteroid 2005 YU55 (8 November 2011)

The most recent threat has passed away 604 324 kilometers, becoming the largest asteroid in the last 35 lay down. The size of the asteroid more aircraft carrier (400 metres), but researchers had previously rejected all the risks of exposure to the Ground, and continued to watch his last seen when he, apparently, has started to move in the direction of the Sun. In any case, following its passage by the Earth will take place on 12 November 2041 at a distance of 9 million 300 thousand miles.

New threat

In 2004, scientists PASS announced that there is a probability that the asteroid Apophis, larger than two football fields, can crash into the Earth in 2029. Some additional observations, together with allocations have shown that the chance of collision with the Earth planet killer in 2029 is negligible. But the bitter pill planted the Russian scientists: not so long ago they said that Apophis will hit the Earth on April 13, 2036. Moreover, an important role can play a "gravitational keyhole" of the Earth.
The situation is that in 2029, April 13, Apophis will fly very close, within five degrees of the Earth, that, in General, will be an extraordinary event, but the possibility of a collision at the moment scientists are excluded. On the other hand, if it will pass through the keyhole at the approaching of the Earth... then it really will get the indignation which will return it, and hit the Ground on April 13, 1936. Scientists hope that the asteroid will pass by the Earth and does not hook the keyhole, which instead reflector attack will turn into the instrument precise targeting.

A more likely scenario is the following: Apophis pretty close come to Earth in the end of 2012 and the beginning of 2013, and will be easily seen with ground-based telescopes and radars. If you find that it takes a destructive path, NASA will begin to develop a scheme and equipment necessary to change the orbit of the asteroid, reducing the probability of a collision in 2036 to zero.

There are several ways to change the orbit of the asteroid, the simplest of which is the launch of spacecraft flying straight into the stone. This technology was used on 4 July 2005, when 372-kilogram impactor, previously separated from the American space probe Deep Impact, crashed into comet Tempel I at speeds of 37 thousand kilometers per hour. Although the Deep Impact mission was focused on the collection of scientific data, and not for destruction nobody uragawa comets, this experience may be useful. The calculations show that the probability of collision of an asteroid Apophis Land is 1:250 thousands...

ABtor: Volanic
Source: "Interesting newspaper. The world of the unknown"