Observatory. Acceleration of free fall on a surface

Confirmatory observations of the near-Earth asteroid 2012 PW were also made from the NEOCP page, and the observations were published in MPEC 2012-P19. And astrometry was obtained for several asteroids discovered in July at the ISON-Kislovodsk observatory, as part of a new asteroid survey.

06/18/12 * On the night of June 16-17, an attempt was made to observe the occultation of the 12.7m star by trans-Neptune (5145) Pholus, the band uncertainty was quite large, and the occultation could not be detected. Successful observations of two new near-Earth asteroids 2012 LE11 and 2012 LF11 were also carried out, the observation results were published in MPEC 2012-M06 and MPEC 2012-M07.

13.06.12 * Last night observed the recently discovered comets C/2012 K5 (LINEAR) and C/2012 L3 (LINEAR).

05.27.12 * This night I specially went to the observatory to observe the near-Earth asteroid 2012KP24. An asteroid with a diameter of 20m should approach our planet at a distance of 50,000 km on May 28, having a magnitude of about 12m and moving almost a degree across the sky in an hour. Astrometry and photometry were also obtained for the new comet C/2012 K1 (PANSTARRS), which in 2014 may be available for observation with the naked eye.

05/11/12 * Short starts bright nights. Last night we managed to observe only 4 comets.

04/29/12 * For April 26 and 27, CCD observations were received for 6 more comets, comet C/2011 UF305 (LINEAR) was also observed visually. In addition, a confirmatory observation was made for supernova 2012by, discovered on April 25 in the interacting galaxy UGC 8335 CBET 3096. Complex astrometry was performed for the near-Earth asteroid 2012HM at the moment of approach to the Earth up to 1.4LD, during observation angular velocity the asteroid was 105"/min, magnitude 15.5m, astrometry had to be done along a very elongated track.

04/25/12 * Only observations of comets were carried out that night. Astrometry and photometry were obtained for 7 comets; comet C/2009 P1 (Garradd) was observed only visually.

04/14/12 * We successfully tested the operation of a new focuser, traditionally manufactured independently.

04/13/12 * Last night observational material was received on several comets. In particular, we were able to visually observe comets C/2009 P1 (Garradd) and C/2011 F1 (LINEAR), comet Garad is beginning to gradually weaken. Observed Comet 49P/Arend-Rigaux, this is my second observed return of this comet! In addition, confirmatory astrometry was obtained for 2 new near-Earth asteroids discovered by the Catalina automatic survey: 2012 GC2 and 2012 GD2. The observations were published in MPEC 2012-G37 and MPEC 2012-G38.

02/15/12 * Last night, the results of observations of several more comets were received, as a result, 11 comets have already been observed in this lunation. We were able to obtain visual data on comet 78P/Gehrels; it still retains a brightness of 11.8m. An attempt was also made to find comet 238P/Read, but without success, the comet is weaker than 20.5m. The first two search sites of this year were received, but unfortunately, at 2 a.m. the sky was filled with haze.

02/13/12 * 2 tests were carried out at the observatory good nights February 10 and 12, although the Moon was still very much in the way. Observations of comets were mainly carried out; observational material was obtained on 8 comets. A confirmatory observation of the new comet C/2012 C2 (Bruenjes) was also made; the comet is accessible for visual observation and has a magnitude of 11.5m. The observations were published in MPEC 2012-C44 and CBET 3019.

12/28/11 * Perhaps December 26th was our last good night of the past year. Observations of several comets have been made, one near-Earth asteroid has been observed from the NEO confirmation page, observations were published in MPEC 2011-Y40.

11.21.11 * Last night, as usual, observations of several comets were carried out, several search sites were also received, the data is still being processed. In general, the night was ideal in all respects, an example of this is the image of the M1 nebula in Taurus, the shining in individual frames was a record in the entire history of CCD observations at the observatory, the values ​​reached 1.4 ".

01.11.11 * On October 21, 25, 27 and 30, observations of comets were carried out at the observatory, and confirmatory observations of possible supernova explosions were made in the galaxies PGC 2692384 and UGC 12410, the observation results were published in CBET 2891 and CBET 2887. Several search sites for asteroids and supernovae were obtained, but to no avail, except for a few discovered asteroids that had not been observed for 2 or more years. In general, the last ten days of October pleased with the weather, there were very good nights, the brightness at times amounted to 1.7-2", and the faintest of the observed asteroids, 2008 FE1, had a magnitude of 21.2V!

10/19/11 * Last night there was a couple of hours before the moon rose. Observed several comets, and a confirmatory observation of a possible supernova explosion was made in the galaxy NGC7485, the observation results were published in CBET 2866. One bright asteroid was observed from the NEO confirmation page, but in the end its orbital elements fell slightly short of a near-Earth asteroid.

03.10.11 * The coming autumn does not spoil the weather; yesterday we managed to catch some light for a few hours. I visually observed comets C/2009 P1 (Garradd) and 78P/Gehrels, and also observed comets 213P/Van Ness and 131P/Mueller on a CCD. Several searches were made, but this time to no avail.

09/06/11 * On September 3 and 5, visual and CCD observations of comets were carried out at the observatory. Information about the discovery of 2 new asteroids, which received preliminary designations 2011 QN51 and 2011 QM51, was confirmed. Both are classic main belt objects.

09/01/11 * Observations of several comets were obtained last night. I spent a couple of hours searching for new objects; 2 new asteroids were previously found.

08.27.11 * Over two nights, August 24 and 26, observational material was obtained on several comets. The fragmentation of comet 213P/Van Ness remains. We even managed to do astrometry of the second fragment. Visual estimates of comets C/2009 P1 (Garradd), 213P/Van Ness and 78P/Gehrels were also obtained. A supernova was observed in the bright galaxy M101.

08/06/11 * Two wonderful nights were spent at the observatory, at times with a very good atmosphere. On the night of August 5-6, flashes of the northern lights could be observed in the northern sector of the sky, which sometimes became brighter Milky Way, and the colors were even perfectly distinguishable. Unfortunately, I didn’t have a camera with me. For me, this is not the first observation of this phenomenon in our latitudes. Observational material was also obtained on several comets, including several visual assessments and several comets were observed on CCD. It is worth noting the observation of the fragmentation of comet 213P/Van Ness, and the observation of comet 78P/Gehrels - I am already observing this comet in the 3rd return to perihelion!

08/02/11 * The last two short nights were partially spent on technical adjustments of the telescope for the upcoming observing season. Nevertheless, I visually observed the relatively bright comet C/2009 P1 (Garradd), the comet now has a magnitude of 7.6m, and CCD images of it and several other comets were also obtained.

This is not quite a thematic article for me, but I thought it would be interesting to talk about the asteroid danger. In principle, this is a hackneyed topic, but in recent years It is gradually acquiring a different content, so I think it will be interesting.

Impact

Simulation of the atmospheric explosion of the Tunguska meteorite. Modern estimates give the power of this impact at 5..15 megatons.

An impact is the impact of an asteroid (in principle, of any size) on the Earth, with the subsequent release of its kinetic energy in the atmosphere or on the surface. The smaller the impact in energy, the more often it occurs. The impact energy is in a good way determine whether a cosmic body is dangerous for the earth or not. The first such threshold is about 100 kilotons of TNT equivalent of energy release, when an arriving asteroid (which upon entering the atmosphere begins to be called a meteorite) ceases to be limited to getting into YouTube, but begins to bring trouble. A good example such a threshold event is Chelyabinsk meteorite 2014 - a small body with characteristic dimensions of 15...20 meters and a mass of ~10 thousand tons shock wave caused damage worth a billion rubles and injured ~300 people.

However, the Chelyabinsk meteorite aimed very well, and in general it did not particularly disrupt the life of even Chelyabinsk, not to mention the entire Earth. The probability of accidentally falling into a densely populated area during a collision with our planet is about a few percent, so the real threshold of dangerous objects begins with a power 1000 times greater - on the order of hundreds of megatons, the characteristic impact energy for bodies with a caliber of 140-170 meters.

Unlike nuclear weapons, the energy release of meteorites is more spread out in space and time, therefore slightly less lethal. The photo shows the explosion of the Ivy Mike nuclear installation, 10 megatons.

Such a meteor has a radius of destruction of a hundred kilometers, and if it lands successfully, it can end many millions of lives. Of course there are rocks in space and bigger size- A 500-meter asteroid will cause a regional catastrophe, affecting areas thousands of kilometers from the place of its fall, a one and a half kilometer asteroid can wipe out life from a quarter of the planet’s surface, and a 10-kilometer one will cause a new mass extinction and will definitely destroy civilization.

Now that we've calibrated the Armageddon level from size, we can get down to science.

Near-Earth asteroids

Calculation of probable impact frequency depending on energy. By vertical axis frequency of “cases per year”, horizontally - impact power in kilotons. Horizontal stripes are size tolerances. Red marks are observations of real impacts with an error.

However, qualitative and quantitative growth leads to a rapid increase in the number of detected near-Earth objects. The appearance of CCD matrices on telescopes in the 90s (which increased their sensitivity by 1-1.5 orders of magnitude) and at the same time automatic algorithms for processing images of the night sky led to an increase in the rate of detection of asteroids (including near-Earth ones) by two orders of magnitude at the turn of the century.

In 1998-1999, the LINEAR project came into operation - two robotic telescopes with an aperture of only 1 meter, equipped with only a 5-megapixel (later you will understand where “everything” comes from) matrix, with the task of detecting as many asteroids and comets as possible, including .h. near-Earth. This was not the first project of this type (NEAT was quite successful a couple of years earlier), but the first one specifically designed for this task. The telescope featured the following features, which would later become standard:

• A special astronomical CCD matrix with back-illuminated pixels, which increased its quantum efficiency (the number of registered incident photons) to almost 100%, versus 30% for standard non-astronomical ones.
• A wide-angle telescope that allows you to photograph a very large surface of the sky overnight.
• A private cadence telescope photographed the same area of ​​the sky 5 times during the night with a gap of 28 minutes and repeated this procedure two weeks later. The frame exposure was only 10 seconds, after which the telescope moved to the next field.
• Special algorithms that subtracted stars from the frame according to the catalog (this was an innovation) and looked for moving groups of pixels with certain angular velocities.

LINEAR will become a star of the first magnitude in the asteroid search, discovering 230 thousand asteroids over the next 12 years, including 2300 crossing the Earth’s orbit. Thanks to another MPC (Minor Planet Center) project, information on the found asteroid candidates is distributed to different observatories for additional orbital measurements. In the 2000s, a similar automated sky survey, Catalina, came into operation (which will be more aimed at searching for near-Earth objects, and will find hundreds of them per year).

Number of near-Earth asteroids discovered by different projects by year

Gradually, estimates of the probability of Armageddon in general begin to yield to estimates of the probability of death from a specific asteroid. Among first hundreds, and then thousands of near-Earth asteroids, approximately 10% stand out whose orbits are closer than 0.05 astronomical units from the Earth’s orbit (approximately 7.5 million km), while the size of the asteroid should exceed 100-150 meters (the absolute magnitude of the solar system body H>22).

At the end of 2004, NASA told the world that asteroid Apophis 99942, discovered at the beginning of the year, had a 1 in 233 chance of hitting Earth in 2029. Asteroid, by modern measurements has a diameter of about 330 meters and an estimated mass of 40 million tons, giving approximately 800 megatons of explosion energy.

Radar image of the asteroid Apophis. Measuring the trajectory with radar at the Arecibo Observatory made it possible to clarify the orbit and eliminate the possibility of a collision with the Earth.

Probability

An illustration of how the tube of possible orbits of the asteroid Apophis was compressed at the moment of a possible collision as the orbital parameters were refined. As a result, the Earth was not affected.

Another interesting illustration from Apophis is the calculation of possible impact points (taking into account uncertainty) for a collision in 2036. It can be seen, by the way, that the trajectory passed near the crash site Tunguska meteorite.

By the way, to quickly assess the comparative danger of near-Earth asteroids, two scales were developed - the simple Turin scale and the more complex Palermo scale. Turinskaya simply multiplies the probability of a collision and the size of the body being assessed, assigning it a value from 0 to 10 (for example, Apophis at the peak of the probability of a collision had 4 points), and Palermskaya calculates the logarithm of the ratio of the probability of an impact of a particular body with the background probability of an impact of such energy from today to the moment of possible impact collisions.

At the same time positive values on the Palermo scale means that one single body becomes a more significant potential source of disaster than all the others - discovered and undiscovered - combined. Another important point The Palermo scale is an applied convolution of the probability of impact and its energy, giving a rather counterintuitive curve of the degree of risk from the size of the asteroid - yes, 100 meter rocks do not seem to be capable of causing significant damage, but there are many of them and they fall relatively often, generally causing a greater number of potential victims than the 1.5 kilometer “killer of civilizations”.

However, let us return to the history of the discovery of near-Earth asteroids and potentially dangerous objects among them. In 2010, the first telescope of the Pan-STARRS system came into operation, with an ultra-wide-field telescope with an aperture of 1.8 meters, equipped with a matrix of 1400 megapixels!

A photograph of the Andromeda Galaxy from the Pan-STARRS 1 telescope, allowing one to evaluate its wide angle. For comparison, drawn in the field full moon and colored squares - the “usual” field of view of large astronomical telescopes.

Unlike LINEAR, it takes 30 second pictures with a viewing depth of 22 stars. magnitude (i.e. could detect an asteroid 100-150 meters in size at a distance of 1 astronomical unit, against the kilometer limit at such a distance for LINEAR), and a high-performance server (1480 cores and 2.5 petabytes of hard drives) turns 10 taken every night terabyte to the list of transient phenomena. It should be noted here that the main purpose of Pan-STARRS is not the search for near-Earth objects, but stellar and galactic astronomy - the search for changes in the sky, for example distant supernovae, or catastrophic events in close dual systems. However, this nonsense telescope also discovered hundreds of new near-Earth asteroids over the course of a year.

Server Pan-STARRS. Generally speaking, the photo is from 2012, today the project has expanded quite a lot, a second telescope has been added, and two more are being built.

One more mission must be mentioned - space telescope NASA WISE and its extension NEOWISE. This device took images in the far infrared, detecting asteroids by their IR glow. Generally speaking, it was originally aimed at searching for asteroids beyond the orbit of Neptune - Kuiper belt objects, scattered disk and brown dwarfs, but in an extension mission, after the telescope ran out of coolant and its temperature became too high for the original task, this The telescope found about 200 near-Earth bodies.

As a result, over the past 30 years, the number of known near-Earth asteroids has grown from ~50 to 15,000. Today, 1,763 of them are included in the list of potentially dangerous objects, none of which have ratings greater than 0 on the Turin and Palermo scales.

Lots of asteroids

Here in the picture the known near-Earth asteroids (not only dangerous objects), contours - an assessment of existing, but not yet found. Situation for 2012.

Currently, estimates of the proportion of detected asteroids are made through model synthesis of the population and calculation of the visibility of bodies of this population from Earth. This approach makes it possible to well estimate the proportion of detected bodies not only through extrapolation of the “size-number of bodies” function, but also taking into account visibility.

Here in the table the sizes of asteroids are given in units of H - absolute stellar magnitudes for solar system objects. A rough conversion to size is made using this formula and from it we can conclude that we know more than 90% of near-Earth objects larger than 500 meters in size and about half the size of Apophis. For bodies between 100 and 150 meters, only about 35% is known.

However, we can remember that a measly 30 years ago, about 0.1% of dangerous objects were known, so the progress is impressive.

However, this is not the end of the story. Today, the LSST telescope is being built in Chile, another monster survey telescope that will be armed with 8-meter optics and a 3.2 gigapixel camera. Over the course of several years, starting in 2020, having taken approximately 50 petabytes (in general, the project’s motto is “turning the skies into a database”) of LSST images, it should detect ~100,000 near-Earth asteroids, determining the orbits of almost 100% of bodies of dangerous sizes. By the way, in addition to asteroids, the telescope should produce several billion more objects and events, and that same database should ultimately amount to 30 trillion rows, which poses a certain complexity for modern DBMSs.

To accomplish its task, LSST has a very unusual optical design, where a third mirror is placed in the center of the first.

A 3.2 gigapixel camera with a 63 cm pupil, cooled to -110 C, is a working tool for LSST.

Is humanity saved? Not really. There is a class of stones located in orbits internal to the Earth in a 1:1 resonance, which are very difficult to see from Earth, there are long period comets- usually relatively large bodies, which have very high velocities relative to the Earth (i.e., potentially very powerful impactors), which we can today notice no more than 2-3 years before the collision. However, in fact, for the first time in the last three centuries, since the idea of ​​a collision between the Earth and a celestial body was born, in a few years we will have a database of trajectories of the overwhelming number of dangerous bodies carrying Earth.

In the next part I will describe the scientific point of view on methods of influencing dangerous asteroids.

Tags:

• asteroid-comet danger
• astronomy
• telescopes

The Earth can be threatened by objects that approach it at a distance of at least 8 million kilometers and are large enough not to collapse when entering the planet’s atmosphere. They pose a danger to our planet.

Until recently, the asteroid Apophis, discovered in 2004, was called the object with the highest probability of colliding with the Earth. Such a collision was considered possible in 2036. However, after Apophis passed by our planet in January 2013 at a distance of about 14 million km. NASA specialists have reduced the likelihood of a collision to a minimum. The chances, according to Don Yeomans, head of the Near-Earth Object Laboratory, are less than one in a million.
However, experts have calculated the approximate consequences of the fall of Apophis, whose diameter is about 300 meters and weighs about 27 million tons. So the energy released when a body collides with the Earth’s surface will be 1717 megatons. The strength of the earthquake within a radius of 10 kilometers from the crash site can reach 6.5 on the Richter scale, and the wind speed will be at least 790 m/s. In this case, even fortified objects will be destroyed.

Asteroid 2007 TU24 was discovered on October 11, 2007, and already on January 29, 2008 it flew near our planet at a distance of about 550 thousand km. Thanks to its extraordinary brightness - 12th magnitude– it could be seen even through telescopes medium strength. Such a close passage of a large celestial body from Earth is a rare phenomenon. The next time an asteroid of the same size will approach our planet will only be in 2027.
TU24 is a massive celestial body comparable to the size of the University building on Vorobyovy Gory. According to astronomers, the asteroid is potentially dangerous because it crosses the Earth's orbit approximately once every three years. But, at least until 2170, according to experts, it does not threaten the Earth.

Space object 2012 DA14 or Duende belongs to near-Earth asteroids. Its dimensions are relatively modest - a diameter of about 30 meters, a weight of approximately 40,000 tons. According to scientists, it looks like a giant potato. Immediately after the discovery on February 23, 2012, it was found that science was dealing with an unusual celestial body. The fact is that the asteroid’s orbit is in a 1:1 resonance with the Earth. This means that the period of its revolution around the Sun approximately corresponds to an Earth year.
Duende may remain close to Earth for a long time, but astronomers are not yet ready to predict the behavior of the celestial body in the future. Although, according to current calculations, the probability of Duende colliding with the Earth before February 16, 2020 will not exceed one chance in 14,000.

Immediately after its discovery on December 28, 2005, asteroid YU55 was classified as potentially dangerous. The diameter of the space object reaches 400 meters. It has an elliptical orbit, which indicates the instability of its trajectory and unpredictability of behavior.
In November 2011, the asteroid already alarmed scientific world, flying up to a dangerous distance of 325 thousand kilometers from the Earth - that is, it turned out to be closer than the Moon. Interestingly, the object is completely black and almost invisible in the night sky, for which astronomers nicknamed it “Invisible”. Scientists then seriously feared that a space alien would enter the earth's atmosphere.

An asteroid with such an intriguing name is a long-time acquaintance of earthlings. It was discovered by German astronomer Carl Witt back in 1898 and turned out to be the first near-Earth asteroid discovered. Eros also became the first asteroid to acquire artificial satellite. It's about about the NEAR Shoemaker spacecraft, which landed on a celestial body in 2001.
Eros is the largest asteroid in the inner Solar System. Its dimensions are amazing – 33 x 13 x 13 km. Average speed giant 24.36 km/s. The asteroid's shape is similar to a peanut, which affects uneven distribution gravity is on it. The impact potential of Eros in the event of a collision with the Earth is simply enormous. According to scientists, the consequences of an asteroid hitting our planet will be more catastrophic than after the fall of Chicxulub, which allegedly caused the extinction of the dinosaurs. The only consolation is that the chances of this happening in the foreseeable future are negligible.

Asteroid 2001 WN5 was discovered on November 20, 2001 and later fell into the category of potentially dangerous objects. First of all, one should be wary of the fact that neither the asteroid itself nor its trajectory have been sufficiently studied. According to preliminary data, its diameter can reach 1.5 kilometers.
June 26, 2028 will happen another approach of the asteroid to the Earth, and the cosmic body will approach its minimum distance - 250 thousand km. According to scientists, it can be seen through binoculars. This distance is enough to cause satellites to malfunction.

This asteroid was discovered by Russian astronomer Gennady Borisov on September 16, 2013 using a homemade 20 cm telescope. The object was immediately named almost the most dangerous threat among celestial bodies for the Earth. The diameter of the object is about 400 meters.
The asteroid's approach to our planet is expected on August 26, 2032. According to some assumptions, the block will sweep just 4 thousand kilometers from the Earth at a speed of 15 km/s. Scientists have calculated that in the event of a collision with the Earth, the explosion energy will be 2.5 thousand megatons per TNT equivalent. For example, the power of the largest thermonuclear bomb, blown up in the USSR - 50 megatons.
Today, the probability of an asteroid colliding with the Earth is estimated at approximately 1/63,000. However, with further refinement of the orbit, the figure may either increase or decrease.

Scales

There are several scales for assessing the danger of VET.

Turin scale

• Asteroids (0 points) - consequences of a collision: they have no chance of meeting the Earth.
• Asteroids (10 points) - consequences of a collision: the number of species inhabiting our planet should be reduced by orders of magnitude.

Judging by geological data (several hundred impact craters have been explored), collisions with large celestial bodies have happened more than once in the history of our planet. By the fall of one large meteorite some scientists explain the mass extinction of living organisms (about 250 million years ago). Another meteorite, according to the hypothesis of U. Alvarez, led to the extinction of dinosaurs.

Sources

The closest to Earth was a small asteroid 2004 FU 162 (diameter about 6 meters) - about 6500 km from Earth (March 2004).

Discovery History

Historically, the first of the asteroids with an orbit close to the Earth was discovered by Eros (Amur group). Most large asteroid in the Amur group - Ganymede (which should not be confused with the moon of Jupiter of the same name), its diameter is approximately 32 km (Eros has about 17 km).

• Asteroid 2008 TC 3 - discovered 20 hours before it burned up in the atmosphere over Sudan on October 7, 2008.
• Asteroid 2009 DD 45 - discovered on February 28, 2009 (three days before its closest approach to Earth) by astronomer Robert McNaught, who studied photographs taken using the Schmidt telescope at Siding Springs Observatory in Australia. The asteroid came closest to the Earth on March 2, 2009 (16:44 Moscow time, according to representatives of the Planetary Society - 13:44 GMT). Could be seen with the naked eye in the sky above southern part Pacific Ocean. Dimensions - 20-50 (27-40) meters. Distance to Earth - 66 (72) thousand km. The spread of numbers is due to the fact that the diameter of asteroids is calculated based on their albedo - reflectivity. Since astronomers don't know exactly how much light is reflected by the surface of 2009 DD45, they rely on averages. Movement speed - (at the moment of being at a minimum distance from the Earth - 20 km/s. In the event of a collision, the explosion energy would be equal to 1 megaton (one nuclear bomb high power) in TNT equivalent. For comparison: the impact of the Tunguska meteorite (exploded in the atmosphere over Siberia on June 30, 1908) felled 80 million trees over an area of ​​about 2000 square kilometers, which corresponds to an explosion of 3-4 megatons of TNT.

Difficulty in detection

Financial

Scientists note that even small objects pose a threat to the Earth, since their explosions near the planet as a result of heating can lead to significant destruction. However, NASA is currently tracking mainly the largest space objects, whose diameter is more than a kilometer (as of 2007, 769 known asteroids and comets, the diameter of which does not exceed 140 meters, are not observed so closely).

Technical

Current Status

In total, about 6,100 objects have been registered that pass at a distance of up to 1.3 astronomical units from the Earth.

As of April 2009 in solar system not a single PEO was observed (a list of a little more than a thousand positions, where 90% are asteroids, 10% are comets, the distance from them to the Earth is less than 0.05 astronomical units) that could overcome the threshold of zero points.

The danger that asteroids pose to the planet is not considered serious. By modern estimates, collisions with similar bodies(according to the most pessimistic forecasts) are unlikely to occur more often than once every hundred thousand years. If a celestial body of sufficient size is directed towards Earth to cause serious destruction, astronomers will be able to detect it.

See also

Notes

Links

• Zheleznov N. B. Asteroid-comet hazard: current state of the problem.
• Finkelstein A., corresponding member RAS. Asteroids threaten the Earth. Science and Life, No. 10, 2007, pp. 70-73.
• Earth's Impact Craters Database.
• Near-Earth Asteroid Database (English).

Wikimedia Foundation. 2010.