Dart mission

Asteroids sometimes fly near Earth — and we naturally fear that one of them will sooner or later collide with our planet. Can we change the orbit of a celestial body moving toward Earth to save it? Can we change the orbit of a celestial body moving toward Earth that threatens our safety and lives? The DART mission is the first real step toward understanding this. NASA and the Johns Hopkins University Applied Physics Laboratory want to conduct an experiment in space that will explore the possibility of asteroid orbital deflection.

The assembly of the spacecraft, which will try to deflect the orbit of an asteroid, has long been completed, the launch was first scheduled for July 22, 2021, and later postponed. Eventually DART was launched with a Falcon 9 rocket from the Vandenberg Cosmodrome on the night of Nov. 24, 2021. But it still has a long way to go, a full year.

Anti-asteroid defense

Astronomers know many asteroids whose fall to Earth could lead to mass extinction and the collapse of civilization. It is assumed that the orbits of these killer asteroids are realistic to change — if, of course, we detect them in time. How to do this? Perhaps the most obvious answer is to blow up the asteroid or crash into it (to change its trajectory). However, to be sure that this will produce the desired result, scientists need a better understanding of how the asteroid will react to the kinetic impact.

The main task of the spacecraft, created by the project DART (Double Asteroid Redirection Test), whose name can be translated as «Double Asteroid Redirection Test,» is to crash into an asteroid to prove that changing the orbit of killer asteroids is possible.

DART is a specialized spacecraft, an impact probe designed to catch up with an asteroid nearly 11 million kilometers from Earth and collide with it at 6.6 kilometers per second. It was assembled by the Applied Physics Laboratory at Johns Hopkins University (APL). It is noteworthy that it was founded shortly after the beginning of World War II to develop methods to improve the effectiveness of air defense systems. And it is very symbolic that today it is engaged in protecting the Earth from the threat from space — «asteroid defense».

Jet Propulsion Laboratory (JPL), Goddard Space Flight Center (GSFC) and Johnson Space Center (JSC) are also involved in the project.

«Having Two Shapes.»

DART will travel to the 780-meter asteroid Didymos (65803 Didymos). It is a small, fast-rotating asteroid from the Apollo group, a near-Earth asteroid whose orbits cross the Earth’s outer side. Didym has an elongated orbit, which causes it to cross the orbit not only of our planet, but also of Mars during its movement around the Sun.

Didym does not pose a threat to the Earth. In addition, there is no danger that the experiment will create a risk of collision with the planet. At the minimum distance from Earth, it approached in November 2003 and flew 7.2 million kilometers away. A closer approach will take place only in 2123 and will be 5.9 million kilometers. And at the time of the approach probe in October 2022, Didim will be at a distance of 10.9 million kilometers. For comparison, the minimum distance from Earth to Mars — 55.76 million kilometers, and to Venus — 38 million kilometers.

Didim was discovered April 11, 1996 under the asteroid search project «Spacewatch» (Spacewatch) at Kitt Peak Observatory. It was named after the ancient Greek music theorist Didymus the Musician.

Didymus is a double asteroid and has a small satellite, which in June 2020, the International Astronomical Union gave its official name — Dimorphus. It is the one that will be the «target» for the impact. The satellite is only 150 meters in diameter and orbits Didim at a radius of 1.1 kilometers with a period of only 11.9 hours.

Collision

No one knows exactly what will happen when the probe hits its target. The only thing we can say with certainty: the spacecraft will be destroyed. It is estimated that the impact of the 500-kilogram vehicle at six kilometers per second will cause a change in the asteroid’s velocity, about 0.4 millimeters per second, which will cause a slight change in the trajectory of the asteroid system. Over time, however, it will provoke a larger shift in trajectory. Overall, DART is expected to change the speed of Dimorph by about half a millimeter per second, which in turn will change its orbital period by about 10 minutes.

As the scientists point out, there is a chance that ground-based telescopes will even be able to see the collision from Earth. If successful, it will look like a brief flash of light. But even if ground-based telescopes can’t see it, they will still play an important role in observing the aftermath of the collision. After all, the whole point of the mission is to determine how a spacecraft can affect the trajectory of an asteroid by crashing into it. To do this, we only need to note how the asteroid’s brightness changes as the Dimorph circles around its host. Like the LICIACube images, data collected from ground-based telescopes will help researchers refine models of the asteroid impact until the European probe Hera gathers more data.

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