The danger from space is one of the main threats to humanity: a collision with an asteroid 300 meters in diameter is comparable to the explosion of an atomic bomb. In this regard, NASA announced the development of a new planetary defense system: scientists propose to "shoot down" the asteroid with a ram, changing its trajectory.
Forewarned is forearmed
Talk about the fact that the Earth is actually defenseless against a possible asteroid threat has been raised for a long time. Someone says that the danger is greatly exaggerated, because only in 2016 was the first death of a person in 200 years from a meteorite fall, which, however, was denied by NASA, and someone - that we still cannot be sure predict the fall of celestial bodies to the surface of the Earth. Confirmation is the famous Chelyabinsk meteorite, which made a lot of noise and caused huge losses. And we cannot not only predict, but even more so prevent.
As part of solving the first problem, scientists consider it necessary to commission new observatories, both space and ground. One example is the Mobile Astronomical System of Robot Telescopes (MASTER), created on the basis of Moscow State University. The main goal of the project is to obtain up-to-date information of the entire visible sky within one night. In addition to the search for dark matter, new exoplanets and the discovery of small bodies in the solar system, the data will also help track potentially dangerous asteroids moving towards the planet. NASA also has its own observatories, the purpose of which is to detect potentially dangerous objects for the Earth. One of the main such centers is the Arecibo Observatory, located in Puerto Rico, at an altitude of 497 meters above sea level, and has one of the world's largest radio telescopes using only one aperture.
At the same time, none of the modern radars has sufficient power to cover such a vast space even relatively close to the Earth and ensure the return of a signal to detect unknown near-Earth objects. With optical telescopes, it is easier to detect light from the Sun that is reflected by an object, and ground-based radar can be used to more accurately track and determine the orbits of objects detected by these telescopes, their physical characteristics and body dynamics as they approach the Earth.
Radar observations can correct our asteroid position data from several thousand kilometers, provided by optical observations, to several meters. The risk of impact posed by a potentially hazardous asteroid can be resolved relatively quickly with radar observations, while using only optical observations, we may not be aware of its position for many years.
This was the case with the asteroid (99942) Apophis, which was discovered in 2004. Initially, it was assumed that in April 2029 it could collide with the Earth, but radar observations carried out by Arecibo Observatory in 2005 practically ruled out this possibility. After the asteroid on January 9, 2013 approached the Earth at a distance of almost 14, 5 million kilometers, which is less than a tenth of the distance to the Sun, scientists found that the volume and mass of this asteroid is 75 percent more than expected.
Research shows that the best way to defend against an asteroid by changing its trajectory depends on each specific scenario. The choice of mitigation method depends on the object's orbit, composition, relative velocity, as well as the likelihood of impact and the expected impact location. Some near-Earth objects can be in such an orbit, which is very difficult to work with if not detected over several decades. Other asteroids are essentially a collection of small debris, making it difficult to correct their trajectory without destroying them. Some objects are too small or fragile to reach the Earth's surface, such as the meteorite that collapsed over Chelyabinsk in 2013. They require more rapid response to emergencies. Therefore, each specific case presupposes special planetary protection measures.
Planetary protection is a term used by astronomers to describe all the capabilities needed to detect and warn of probable collisions of asteroids or comets with the Earth, and then either to prevent them or to mitigate the consequences. It is necessary to accurately characterize these objects by determining their orbital trajectories, size, shape, mass, composition, rotation dynamics, and other parameters. This information will help professionals determine the hazard of potential exposure.
With projects of active impact on potentially dangerous asteroids, which could minimize damage from their impact in advance, everything is a little more complicated. Various ideas were proposed: from sending a compact nuclear or traditional chemical charge to an asteroid in order to destroy it to using a gravitational tug and rocket engines capable of deflecting the asteroid's course from Earth. However, most of these ideas have not yet gone beyond theoretical developments: these projects are too expensive and have quite a lot of controversial issues - up to the unresolved issue of using nuclear charges in outer space. However, NASA has come up with another way to actively influence the object threatening the Earth.
We are talking about the space mission Double Asteroid Redirection Test (DART) - this is the first real attempt to actively influence an asteroid. The goal is to develop ways to protect the planet from the impact of objects from space. The project is being co-created with the Johns Hopkins Applied Physics Laboratory with support from NASA's Jet Propulsion Laboratory (JPL), Goddard Space Flight Center (GSFC) and Johnson Space Center (JSC).
“We have many scientific missions aimed at understanding the past of the solar system and its formation. The Planetary Defense Project refers to the present solar system and our immediate immediate plans and actions. To carry out our plans and physically correct the trajectory of the object, it will take a lot of time in stock. The idea of a kinetic ram is, of course, not at all what is shown in the movie "Armageddon", where people were alarmed at the last moment and saved the Earth. We will need to take care of this 10 or even 20 years before the impact: slightly push the asteroid so that it flies by and does not hit the planet,”explains planetary scientist Nancy Chabot of the Applied Physics Laboratory at Johns Hopkins University.
The target of the DART mission was a binary asteroid system, which received the name (65803) Didymos, which is translated from Greek as "twin". Didymos A is 780 meters in size, while its "little brother" Didymos B is only 160 meters. He will become the main goal of the mission. The Didymos system has been carefully studied since 2003: the primary body is an S-type rocky object, the composition of which is similar to that of many asteroids, and the composition of Didymos B is not yet known. The double asteroid itself does not pose a danger to the Earth: in 2003 it flew over a distance of more than seven million kilometers, and next time it will approach our planet in 2123.However, this mission will help scientists obtain important information that will be invaluable in the future for protection from dangerous objects.
Shoot down and trace
Preparations for the launch of the DART spacecraft will begin at the end of December 2020 and will last until May 2021. The launch is planned to be carried out in June 2022, and in early October, the space ram will collide with an object at a distance of 11 million kilometers from Earth. Near-Earth asteroid (185851) 2000 DP107 is largely considered an analogue of Didymos.
DART is believed to use an airborne autonomous targeting system to target Didymos B and then plunge into the asteroid at six kilometers per second - about nine times faster than a bullet. Ground-based observatories will be able to capture this impact and the change in Didymos B's orbit, allowing scientists to better identify the potential for kinetic forcing as an asteroid mitigation strategy. The kinetic impact technique works by changing the speed of the threatening asteroid by a small fraction of its total speed, but doing so well before the predicted impact, so that this small impact over time is added to the large displacement of the asteroid's trajectory.
In this case, an important part of the mission will be to observe the asteroid both before and after the impact. It will be monitored by a small artificial satellite, Light Italian Cubesat, which the Italian Space Agency will launch simultaneously with DART. The European Hera mission, in turn, will reach the binary asteroid by 2026 and document the size and destruction patterns that DART has done.
Despite the fact that Didymos does not threaten our planet, it is important for humanity to learn how to prevent collisions with potentially dangerous space bodies, because if we plan to continue living on Earth, taking care of the climate and the safety of its resources, we must also think about external threats that are capable of overnight put an end to all living things.