Exactly one hundred and ten years ago, the Tunguska meteorite fell in Siberia, destroying an area of forest the size of Hong Kong. RIA Novosti tells how much mankind has come close to creating global planetary defense systems and taming guests from space.
Today is Asteroid Day - an unofficial holiday dedicated to the danger posed by "heavenly stones" for the Earth. It was on June 30 in 1908 that the Tunguska meteorite fell. The idea of the holiday belongs to the director Gregory Richters and Brian May, British astrophysicist and guitarist of the Queen band.
This anniversary of the Tunguska disaster is especially interesting. Firstly, 2018 is the fifth anniversary of the fall of the Chelyabinsk meteorite.
Second, this week the Japanese probe Hayabusa 2 arrived at the asteroid Ryugu. Studying it, scientists hope, will help clarify the origin of the solar system and how large and small asteroids formed in it.
The magic of small numbers
Astronomers have been dealing with near-Earth asteroids and the danger associated with them for several decades, but the public and politicians became interested in this problem only in February 2013, after the space fireworks in the Urals.
The Chelyabinsk meteorite clearly showed what the fall of even relatively small celestial bodies can lead to, which, as planetologists used to believe, should always completely burn up in the atmosphere and not pose any threat to human life and economic infrastructure.
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Although the guest from space did not collide with the Earth's surface, having exploded in the air, and, fortunately, there were no human casualties, the economic damage, according to the Chelyabinsk region authorities, exceeded one billion rubles. If the meteorite was several meters larger, the amount would have increased by tens or hundreds of times.
The Earthlings got off with only a slight fright, but legislators and officials on both sides of the ocean had to take some measures. The budget for NASA's asteroid unit has tripled, and the Russian authorities have promised to develop an early warning system for asteroid hazards by the early 2020s.
Weak interest in this problem in the past decades is explained, on the one hand, by the lack of reliable data on how many asteroids are in near-Earth space and what are the chances of their collision with the Earth, on the other hand, by a lack of understanding of the threats associated with them.
This is how the artist imagined the European AIM mission near the asteroid Didyma / ESA.
“NASA and our partners have discovered more than 95% of asteroids, whose fall to Earth will cause a catastrophe on a global scale. None of these celestial bodies pose a threat to our planet in this and the next century. Nevertheless, asteroids are constantly falling to Earth, and we need to be prepared for this,”explained Aaron Miles, deputy head of the Office of Science and Technology under the US President, speaking at a meeting with reporters at NASA headquarters.
The recently published National Strategy to Prepare the United States for Combating the Asteroid Threat has summarized the results of these studies and identified plans for the future.
“Since May 1998, we have been hunting for objects that can be dangerous for people and all earthly life in general. In 2010, we successfully achieved the first goal - we identified almost all asteroids (about 98%) with a diameter of about a kilometer or more. Only about 40 unknown objects remain,”adds Lindley Johnson, head of planetary defense at NASA.
Only two asteroids from this list, which includes about two thousand objects, were considered relatively dangerous to life on Earth - Apophis (2004 MN4) and Bennu (1999 RQ36), discovered in 2004 and 1999.
The probability of their fall in 2029 and in the second half of the next century was estimated at 2.3% and 0.07% - quite a lot by the standards of astronomy. This is orders of magnitude higher than the hazard level of all other near-earth objects. After clarifying the orbits, sizes and shapes, these asteroids ceased to stand out and lost their status as potential killers of civilization.
The fall of the "black swan"
“Back in 2005, long before the Chelyabinsk meteorite, the US Congress officially asked NASA to start searching and 'censoring' smaller objects with a diameter of 140 to 1000 meters. At the moment, there are 19 410 asteroids in our catalog, about half of which fall within this range, which is dangerous for us. None of them threaten the Earth, but a third of the asteroids are not yet known to us,”Johnson continues.
Scientists continue to observe celestial bodies, and NASA, Roscosmos and ESA are investing more and more efforts and funds in the development of ground-based and space telescopes, early warning systems, and even send missions to asteroids.
The readiness of both the authorities and scientists to deal with this problem, as noted by the famous Russian planetary scientist Alexander Rodin in an interview with RIA Novosti, is associated with a philosophical concept, which he calls a "black swan", and computer game lovers - "the syndrome of instant death."
In its most general form, this is understood as a very unlikely event, but with extremely serious, catastrophic consequences. The collision of the Earth with a large asteroid is precisely the "black swan".
The Tunguska meteorite and its Chelyabinsk "cousin" in this case serve as bad examples, creating a false sense of security. By a happy coincidence, they caused minimal damage to the planet and humanity.
American probe OSIRIS-REx / NASA / NASA's Goddard Space Flight Center / Conceptual Image Lab.
Another similar event, which happened only 13 thousand years ago - and these are moments by the standards of geology and astronomy - led to the beginning of a new ice age and fires that covered ten percent of the planet.
Traces of the culprit of this catastrophe, the so-called Dryas comet, were recently found at the bottom of one of the dried up ancient lakes in Mexico and in the ice of Greenland, as well as on all other continents of the Earth.
Because of the fires and the cooling of the climate, according to scientists today, giant sloths, mastodons and other representatives of the megafauna of America, as well as the first Indians of the New World, the peoples of the Clovis culture, have died out. And the Earth was still lucky - the comet disintegrated into parts upon entering the atmosphere, and not all of its fragments reached the surface.
Scientists can still only very approximately predict the consequences of such disasters for one simple reason - there is no complete understanding of what the guests from outer space are and how they interact with each other.
“The anniversary of the Tunguska meteorite will continue in August, when the OSIRIS-REx probe reaches the asteroid Bennu. The samples that he will deliver to Earth will help us understand how such objects work. The Japanese mission Hayabusa-2, in which we also participate, is already solving similar problems,”Johnson notes.
Tractor, Painter and Kamikaze
In addition to the scientific search and study of asteroids, NASA and other space agencies are also creating early warning systems that allow detecting yet unknown small celestial bodies at the moment when they begin to approach the Earth.
The development of such a system, as the head of Roskosmos, Dmitry Rogozin, said, remains one of the three main space priorities for Russia. The first such system, Dozor, could go into space after 2019.
A similar NASA project, the Scout system, has been in operation since November 2016. It is now capable of detecting relatively small asteroids, 30 meters in diameter, a few days before their approach to Earth, using automated telescopes of the PAN-STARRS network.
But her capabilities are not limited to this. The meter-long asteroid 2018 LA, which burned up in the skies over Africa in early June, showed that, with a successful coincidence, this system will detect even very small celestial bodies even before they approach the Moon and Earth.
This keeps the hope that the rescue services will have time to prepare for the fall of the asteroid, and the space defense systems and space forces will try to knock it off its trajectory.
Asteroid Ryugu and an unusual mountain on its surface / JAXA, University of Tokyo & collaborators.
“Today we are seriously developing projects for three planet protection systems designed for different situations. For example, if there is an immediate threat to the Earth, we can send a heavy probe to an asteroid and crash into it at high speed, which will cause the celestial body to change its orbit,”Johnson says.
And this, as the astronomer emphasized, is no longer a fantasy. NASA recently approved plans to build a DART probe that will travel to the asteroid Didyma in December 2020 and collide with one of its halves in October 2022. The impact of a metal "blank" weighing 500 kilograms, as calculated by scientists, will reduce the speed of the asteroid by 0.4 millimeters per second.
As a result, the position of Didyma's moon will change, and the nature of the movement of both objects in orbit. The results of this experiment, Johnson and his colleagues hope, will help evaluate how heavy such kamikaze probes should be and whether they should be equipped with nuclear weapons, as suggested by Brent Barby of NASA - one of the authors of the HAMMER project.
“If we have several decades before the collision, then we can use less radical methods - for example, send a special 'probe-tractor' to the asteroid. The gravitational interaction between them will speed up or slow down the celestial body, and its orbit will change,”says Johnson.
The "painter" probe can play the same role, painting the asteroid with patterns of white or black. Such a repainting, the scientist explains, will enhance or weaken the heating of a celestial body by the sun's rays, which will change its speed and prevent a catastrophe.
The cause of the whole Earth
Scientists and politicians are increasingly aware that the cooperation of all countries is required to protect the planet. The first project of this kind, the International Asteroid Hazard Warning Network IAWN, was created in 2013 by the UN Committee on the Peaceful Uses of Outer Space.
In addition to NASA and its divisions, the network includes the European Space Agency, the National Space Administration of China, the European Southern Observatory and a number of Russian academic institutions - the Institute of Astronomy, the Special Astrophysical Observatory, the Institute of Solar-Terrestrial Physics of the Russian Academy of Sciences, and the Ural Federal University.
The main task of the IAWN is to join forces for round-the-clock observation of near-earth space. Almost all asteroids discovered in the past five years have been discovered as part of this global program.
While the lion's share of these findings falls on NASA employees and telescopes, however, the role of international partners in this "whole Earth business", as the scientist stressed, is constantly increasing.
For example, one meter and two meter telescopes of the Crimean and Special Astrophysical Observatory in Nizhny Arkhyz are constantly involved in observations. Their large size and sensitivity make it possible to detect relatively small and faint objects that cannot be seen by smaller telescopes of the PAN-STARRS network and other members of the IAWN.
“Experience with NEOWISE has shown that launching a space-based infrared telescope capable of tracking even the dimmest asteroids would greatly assist in detecting the remaining medium-sized asteroids and in finding countless objects similar in size to the Chelyabinsk meteorite. We are now discussing such plans with our international partners,”Johnson explained.
As the scientist noted in an interview with RIA Novosti, he does not exclude the participation of Russia and other space powers in missions like DART, if they have the financial capabilities and political desire to join NASA's current plans.