Success! NASA knocked an asteroid off course (and now it has a tail) : ScienceAlert

NASA on Tuesday celebrated exceeding expectations during a mission to deflect a distant asteroid, in a science fiction test of humanity’s ability to stop an incoming cosmic object from destroying life on Earth.

The refrigerator-sized Double Asteroid Redirect Launcher (DART) impactor intentionally crashed into the asteroid Dimorph on Sept. 26, pushing it into a smaller, faster orbit around its big brother Gemini, NASA chief Bill Nelson announced.

This changed its orbital period by four percent, or 32 minutes — from 11 hours 55 minutes to 11 hours 23 minutes, bettering the expectation by 10 minutes.

“At some point in the future, if we find an asteroid that threatens to hit Earth and is big enough to actually do some damage, thank God we’d have this successful test,” Nelson told AFP.

The asteroid pair orbits our Sun every 2.1 years and poses no threat to our planet.

But they are ideal for studying the “kinetic strike” method of planetary defense.

DART’s success as a proof-of-concept has made what was once science fiction a reality – notably films such as Armageddon, Deep impactand Don’t look up.

Dimorphos, which has never been photographed before and is 530 feet (160 meters) in diameter, or about the size of a great Egyptian pyramid, appeared as a speck of light about an hour before impact.

Its egg-like shape and craggy, speckled surface of the boulder finally came into clear view in the final moments, as DART raced toward it at about 14,500 miles (23,500 kilometers) per hour.


In the days that followed, astronomers were treated to stunning images of matter spanning thousands of miles – images collected from Earth and space telescopes, as well as a tiny companion satellite that traveled to the belt with DART.

Thanks to its temporary new tail, Dimorphos has turned into a man-made comet.

But quantifying how well the test worked required analysis of light patterns from ground-based telescopes, which took a few weeks to become apparent.

The binary asteroid system, which was about 6.8 million miles (11 million kilometers) from Earth at the time of impact, is only visible as a single dot from the ground.

The brightness of the dot changes as Dimorph passes in front of Gemini, which is significantly larger at half a mile across.

Four optical telescopes were involved in measuring the orbital period – all in Chile and South Africa – while two US-based radar telescopes helped confirm the finding, said NASA planetary scientist Nancy Chabot.

The test also showed scientists that the asteroid looks less like solid rock and more like a “junk pile” of boulders bound together by mutual gravity.

If an asteroid is more compact, the momentum imparted by a spacecraft will be limited. But if significant mass is pushed at high speed in the opposite direction from the impact, there will be an additional thrust.

“It appears that the recoil from the blast of the launch from the surface contributed substantially to the overall thrust imparted to the asteroid,” NASA scientist Tom Statler said in a briefing.

The test will serve as an “anchor point” for simulations and calculations about the outcome of future impacts, he added.

MASS extinction

No known asteroid larger than 140 meters (460 feet) — big enough to destroy a city — has a significant chance of hitting Earth for the next 100 years, according to NASA.

But wait long enough and it will happen.

The geological record shows, for example, that a six-mile-wide asteroid hit Earth 66 million years ago, plunging the world into a long winter that led to the mass extinction of the dinosaurs along with 75 percent of all species.

The agency plans to launch a telescope called the Near-Earth Object (NEO) Surveyor in 2026 to better characterize the potentially hazardous 140-meter asteroids and comets that lie 30 million miles away.

So far, less than half of the estimated 25,000 140m NEOs have been discovered.

Kinetic impact with a starship is only one way to defend the planet, though the only possible method with current technology.

If an approaching object is detected early, a spacecraft could be sent to fly past it long enough to deflect its course using the ship’s gravitational pull, creating a so-called gravity tractor.

Another option would be to launch nuclear explosives to redirect or destroy an asteroid.

NASA believes that the best way to deploy such weapons would be at a distance, to deliver power without blowing the asteroid up stairs, which could further endanger Earth.

© Agence France-Presse

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