Astronomers don't know the answer to the dreaded question
In the spring of 2015, the famous astronomical resource astrowatch.net first attracted the attention of the general public to the asteroid 2012 TC4 (the number 2012 in the name of the asteroid indicates the year of its discovery).
Astronomers' interest in the asteroid was due to the fact that, according to calculations, its next passage near the Earth was supposed to occur on October 12, 2017.
Like all celestial bodies of this kind, the asteroid has a very elongated orbit, so the distance to which it will approach the Earth can never be predicted in advance with great accuracy.
The generally accepted unit for measuring the distance to asteroids that can threaten the planet is the average distance to the Moon, that is, 384 467 km or 30 Earth diameters. In astronomy, this unit of measurement is referred to as LD (Lunar Distance).
During the last passage near the Earth (in 2012), the asteroid 2012 TC4 approached the planet at a distance of 0.247 LD (Lunar Distance), which is approximately 94,800 km.
According to the calculations of astronomers who observed the orbit of the asteroid in the period 2012-2015, the next time it should approach the Earth on October 12, 2017, having passed at the same significant distance as the last time.
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According to the laws of classical mechanics, which relatively accurately describe the motion of celestial bodies, for an asteroid to fall to the Earth, it must pass at a distance of 0.079 LD from the planet. Since on October 12, 2017, 2012 TC4 was supposed to be at a significantly greater distance from the Earth, the probability of its collision with the planet was estimated as 0.00055%.
However, as it has now become clear, these were erroneous calculations. According to the latest data, the asteroid 2012 TC4 may come as close as 4,000 miles to Earth. This is an almost guaranteed collision of a celestial body with a planet:
In this dramatic situation, it is now becoming extremely important for astronomers to accurately determine the size of the asteroid and its composition.
According to official estimates in 2012, the size of the asteroid is estimated at 10-40 meters in diameter. For comparison, the Chelyabinsk meteorite, which fell in February 2013, had a maximum diameter of 20 meters. Therefore, a 40 x 40 meter rock will be quite a lot.
However, the problem is that astronomers can determine the exact size of an asteroid only knowing the reflection coefficient of the substance that makes up its surface. If it is a block of cometary ice that glitters very brightly, the size of the asteroid can be calculated to within centimeters. But if it is a huge coal rock, its size will be estimated as the size of a spot of shiny rock interspersed on the surface.
It is also very important to know what the asteroid consists of, that is, what is its core? If it is a piece of ice or loose rock, then even having 100 meters in diameter such an asteroid does not pose a particular threat, it will fall apart even when braking against the atmosphere. But if there is a 40-meter piece of refractory rock or iron in general, it will fly to the surface almost all of it
Perhaps in such a situation a powerful infrared telescope would greatly help, but there is no data on this in the open press. It remains to follow the development of events.