After years of careful planning and development, last September NASA crashed a spacecraft into a drifting rock in the solar system. It wasn’t my hatred of space rocks or the pleasure of collisions. The purpose of these exercises was to test our ability to deflect an asteroid from course for Earth’s safety. And now we know we can do something. The measurements came in and the course of the rock changed much more than expected.
A series of five articles describing this detour and the mechanisms underlying it have been published in Nature. Now the planet beneath our feet seems to float carelessly in empty space. But it happens that there are a lot of big asteroids out there, and if one of them hits us, we’re going through a tough time.
One way we can deflect large asteroids coming our way is to crash into asteroids in a flying spacecraft. Transferring momentum from a spacecraft to an asteroid can change its trajectory in space.
The Double Asteroid Redirection Test (DART) was an attempt to see if this was possible. The target was carefully chosen: Dimorphos, a moon orbiting a larger asteroid called Didymos. Because the orbital period of the two objects is well characterized, any change in Dimorphos’ orbit can be detected as a change in orbital period. About 160 meters (525 feet) in diameter, Dimorphos orbits the 780-metre-wide Didymos every 11.9 hours. A collision with DART was expected to change this orbital period by about 7 minutes.
As explained in a paper led by planetary astronomer Christina Thomas of Northern Arizona University, the change in orbital period was even more dramatic: Dimorphos orbits Didymos 33 minutes faster than it collides. Two separate measurements of the orbit using different methods gave the same result. This larger-than-expected change in the orbital period of the binary asteroid system can only be explained by the momentum transfer from the DART spacecraft.
Led by astronomer Jian-Yang Li of the Institute of Planetary Sciences, the paper examines in detail ejecta, material ejected from the asteroid by the explosion. It wasn’t just a sudden outburst: Dimorphos continued to spew dust tails like a dry comet for almost two weeks after the impact.
A third paper, led by astronomer Ariel Grajkowski of the SETI Institute in the US, examined the light reflected from Dimorphos before, during and after the collision. A little over three weeks after the collision, Dimorphos’ brightness returned to its pre-crash normal level. The brightness level during this period indicated that the asteroid had lost between 0.3 and 0.5 percent of its total mass.
This emission was responsible for most of the variation in the binary asteroid’s orbit, according to a paper led by astronomer Andrew Cheng of the Johns Hopkins University Applied Physics Laboratory. This ejected material gave Dimorphos more momentum on impact than the DART spacecraft did. “The DART impact,” they write, “shows that the transfer of momentum to a target asteroid can significantly exceed the momentum of a kinetic impactor, confirming the effectiveness of a kinetic impactor in preventing future asteroid impacts on Earth.”
Finally, a team led by planetary scientist Terrick Daley from the Johns Hopkins University Applied Physics Laboratory reconstructed the impact event based on data they collected, including the timescale leading up to the impact, a detailed description of the impact site, and size and shape. of Dimorphos. Their findings are promising.
Humanity can successfully deflect an asteroid from its course with limited knowledge of its composition and surface conditions, without an expensive and lengthy exploration mission. An asteroid deflecting mission should ideally be accomplished decades before a predicted collision. Fortunately, time is a resource we have in abundance right now: No known asteroid will threaten Earth for at least 100 years. This gives us time for a series of reconnaissance missions for any environmental threats, which will increase the chances of a successful diversion should things change in the future. Source
Source: Port Altele
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