(ORDO NEWS) — Last September, after years of careful planning and development, NASA crashed a spacecraft into a rock drifting through the solar system just minding its own business.
It wasn’t for all the hatred of space rocks or the joy of collisions; The motive for this exercise was to test our ability to knock the asteroid off course in the interests of Earth‘s safety.
And now we know we’re on to something. Measurement data came in, and the course of the stone changed significantly more than expected.
Right now, the planet beneath our feet seems to be floating serenely in empty space.
But it just so happens that there are a lot of big space rocks out there, and if one of them hits us, we’re in for hard times. Just ask the dinosaurs.
One way we could deflect any large asteroids approaching us is by crashing into the approaching rocks in a flying spaceship.
Transferring momentum from a spacecraft to an asteroid can change its trajectory through space just enough to deflect it from its fate on the Earth’s surface.
The Double Asteroid Redirection Test (DART) was an attempt to find out if this was feasible. The target was carefully chosen: Dimorphos, a moon orbiting a larger asteroid called Didymos.
Since the period of revolution of the two objects is well characterized, any change in the trajectory of Dimorphos could be detected as a change in its period of revolution.
Dimorphos is about 160 meters (525 feet) across. Didymos, 780 meters wide, about once every 11.9 hours. The DART collision was expected to change this orbital period by about 7 minutes.
As described in a paper led by planetary astronomer Christina Thomas of Northern Arizona University, the change in orbital period was much more dramatic: Dimorphos is now orbiting Didymos 33 minutes faster than before the impact. Two separate orbit measurements using different methods gave the same result.
This larger-than-expected change in the orbital period of the binary asteroid system cannot be explained by momentum transfer from the DART spacecraft alone.
The article, led by astronomer Jian-Yang Li of the Institute of Planetary Science, examines in detail the ejecta, the material ejected by an asteroid as a result of the explosion.
It wasn’t just an immediate boom: for almost two weeks after the impact, Dimorphos continued to spew dust tails like a very dry comet.
A third paper, led by astronomer Ariel Grajkowski of the SETI Institute in the US, studied the light bouncing off Dimorphos before, during, and after the impact.
A little over three weeks after the impact, Dimorphos’ brightness returned to its normal pre-impact level.
The brightness level over this period suggests that the asteroid has lost between 0.3 and 0.5 percent of its total mass.
According to an article prepared by astronomer Andrew Cheng of the Applied Physics Laboratory at Johns Hopkins University, the ejection was the cause for most of the change in the orbit of a binary asteroid.
This ejected material imparted more momentum to Dimorphos than was transmitted by the DART spacecraft at the moment of impact.
“The DART impact,” they write, “demonstrates that the momentum transfer to the target asteroid can significantly exceed the incident momentum of the kinetic impactor, confirming the effectiveness of the kinetic impact in preventing future asteroid impacts on the Earth.”
Finally, a team led by planetary scientist Terik Daley of the Applied Physics Laboratory at Johns Hopkins University reconstructed the impact an event from the collected data, including the timeline leading up to the impact, a detailed description of the impact site, and the size and shape of Dimorphos.
Their results are promising. Mankind can successfully divert an asteroid from its course with limited knowledge of its composition and surface conditions, without first conducting a costly and lengthy reconnaissance mission.
Ideally, an asteroid deflection mission should take place decades before the predicted impact.
Fortunately, time is a resource that we now have in abundance: no asteroids known to us will threaten the Earth for at least 100 years.
This gives us time for a number of reconnaissance missions for any peripheral threats, which will increase the chances of a successful deflection if something changes in the distant future.
In light of this, the information we have received from DART is invaluable.
This will facilitate modeling and planning for future asteroid deflections, should we need them, to more accurately predict the results of spacecraft exploding into space rocks.
“The successful impact of the DART spacecraft on Dimorphos and the resulting change in Dimorphos’ orbit,” write Daley and his team, “demonstrates that kinetic impact technology is a viable method for potentially protecting the Earth if needed.”
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