Potentially dangerous astronomical objects

Asteroid (99942) Apophis , the danger of which shortly after its discovery in 2004 was estimated at a record 4 points on the Turin scale (later reduced to 1, and then to 0 points )

A potentially dangerous astronomical object ( POAO ) is a space object ( asteroid or comet ) with an orbit that allows an approach to the Earth at a potentially dangerous distance and is large enough for a collision to cause damage.

An object is considered potentially dangerous if it crosses the Earth’s orbit at a distance of less than 0.05 a. e. (approximately 19.5 distances from the Earth to the Moon), and its diameter exceeds 100–150 meters ^[1] . Objects of such sizes are large enough to cause unprecedented destruction on land, or a huge tsunami in the event of a fall into the ocean. Events of this magnitude occur about once every 10,000 years . Based on information obtained from the WISE space telescope, scientists estimate the presence of 4,700 ± 1,500 potentially dangerous objects with a diameter of more than 100 meters ^[2] . By 2012, from 20 to 30% of these objects were discovered ^[2] . Asteroids with a diameter of more than 35 meters can also pose a significant threat - for example, in the event of a fall on a city ^[3] .

The diameters of most small asteroids are unknown, and can only be estimated based on brightness and distance. The NEO program ( Near-Earth Objects Program - “The program [on observing] objects approaching the Earth ”) conducted by NASA and JPL classifies an object as potentially dangerous if its absolute magnitude is 22.0 or less (brighter ) ^[4] . To determine the size of an object with a known absolute stellar magnitude, it is also necessary to know its albedo ^[5] , however, this parameter is usually not known. The NEO program assumes the albedo is 0.13, which gives the lower limit of the size of 150 m ^[4] ; at the same time, the diameter estimates given in the risk table are made on the basis of the albedo 0.154 ^[6] .

As of January 2009, NASA counted 1006 potentially dangerous asteroids and 85 comets approaching Earth ^[7] . The total number of known such objects in the solar system continues to grow, and reached 1360 VET by December 2012 ^{[4] [8]} . Each of the objects found was studied using various instruments, including telescopes , radars and infrared cameras , to determine their characteristics, including size, composition, rotation period around its axis, and a more accurate orbit. Both professional astronomers and amateurs participated in these studies.

During the asteroids approaching the planets and their satellites , gravity acts on them, changing their orbit, and the asteroids can be transferred from the VET list to the safe list, and vice versa. This is a reflection of the dynamic nature of the solar system.

In 2005, the US Congress set a task for NASA to detect by 2020 90% of all objects approaching the Earth and have a size of more than 140 meters . However, even smaller objects can cause significant damage - the Tungus catastrophe caused the fall of an object 50-80 meters in size.

For the classification of the danger of collision of asteroids, there are special scales. The two main ones are the Palermo scale and the Turin scale . In the entire history of the Turin Scale, the highest hazard level (four points) was assigned to the asteroid (99942) Apophis , but subsequent more accurate calculations lowered the estimate of its hazard level, first to one and then to zero points.

The largest VET (based on the absolute stellar magnitude), ordered by year of discovery ^[9] :