If all goes well, a spacecraft NASA launched last November will crash into an asteroid on Monday.
If everything goes absolutely perfectlythat impact will push the asteroid into a slightly different orbit, meaning that for the first time, humans will have changed the trajectory of a celestial object.
Making history, however, is incidental. The real mission is to defend the planet.
There’s no need to panic: The target space rock has no chance of hitting Earth, nor any other known asteroid for at least half a century. This NASA mission, operated by the Johns Hopkins University Applied Physics Laboratory in Laurel, Maryland, is testing a technique to redirect an asteroid in case future Earth people really need to move one out of the way.
The basic idea couldn’t be simpler: Hit it with a hammer! But the degree of difficulty is high, in part because no one has ever seen the asteroid that NASA plans to push. It is a small moon called Dimorphos that is about the size of a football stadium.
Sky watchers operating the world’s highest-powered telescopes detect the small moon only as a shadow crossing the larger orbiting asteroid, Didymos, as the two revolve around the sun together. The pair form a “double asteroid,” a common arrangement in our solar system.
Here’s how the $330 million Double Asteroid Redirection Test (DART) is designed to work:
Why just hit him instead of blowing him to bits?”ArmageddonBecause blowing up an ancient rock pile, especially one that may contain metal or giant rocks, as many asteroids do, would be tricky and unpredictable, said Nancy Chabot, a planetary scientist and mission coordination lead. deviation means we have time for a bit of finesse: a little nudge now could ensure an asteroid sails a long way from Earth many years later.
“You don’t necessarily want to make this more complicated than it has to be, do you? You would do this way ahead of time, like decades, 10, 20, 30 years ahead,” she said. “Small changes add up to big changes in that amount of time.”
Asteroids in our neighborhood
Thousands of asteroids are big enough and come close enough to Earth’s orbit for researchers to keep an eye on them.
[The chances of this asteroid hitting Earth are tiny, NASA says — but not zero]
No known asteroid large enough to cause ground damage has a significant chance of reaching our planet in the next 50 years, according to NASA Director Paul Chodas. Center for Near Earth Object Studies. His team catalogs and tracks asteroids and comets whose orbits bring them close to Earth’s general neighborhood, defined as within 121 million miles of the sun.
Most of these known asteroids were identified by ground-based optical telescopes, and some were located by an infrared space telescope called NEOWISE which detected its heat signatures from its perch in low Earth orbit.
Nearly two-thirds of them are so small that they would burn up in Earth’s atmosphere if they came at us. But of course some asteroids are huge and dangerous, ask any dinosaur.
Chodas said that scientists have discovered 95 percent of near-Earth asteroids that are large enough to create a global catastrophe, that is, one kilometer (about six-tenths of a mile) or more. The largest is about four miles wide, much smaller than the six-mile behemoth that wiped out the dinosaurs.
the unknown some are wildcards.
Asteroids that are slightly smaller but still large enough to cause a lot of regional damage are harder to detect with current technology. Models estimate that we’ve found only 40 percent of those that are 460 feet wide (140 meters) and larger, like Didymos and its small moon. That’s well short of NASA’s goal of identifying at least 90 percent.
“Some asteroids are sneaky and have orbits that make an asteroid very hard to find,” Chodas said.
Some may be in orbits that often don’t bring them close to Earth. Some are made of dark material that doesn’t reflect much light, making it hard for ground-based telescopes to detect them. Others may lurk on the opposite side of the sun.
The truck-sized rock that caused a fireball and shock wave over Russia in 2013 came without warning because it was coming from the direction of the sun, a huge blind spot for existing telescopes.
[Don’t panic: Scientists are practicing for a killer asteroid impact]
Fortunately, more high-powered eyes are on the way.
In 2026, NASA plans to launch a very sensitive infrared telescope called NEO Surveyorsthat you will have a wide view of the skies from a stable point of view about a million miles between the earth and the sun. Like its predecessor NEOWISE, it will detect heat signals instead of visible light.
Amy Mainzer, principal investigator for the Surveyor team, said it should be able to spot a 460-foot asteroid from at least 50 million miles away.
At about the same time, a new ground telescope in Chile it is expected to come online with a huge 28-foot mirror that will be able to detect objects that are much fainter and farther away than any current ground-based telescope.
“The two of them together will get us to 90 percent very quickly,” Chodas said.
Why did NASA choose this asteroid?
The small moon Dimorphos is an ideal target because of its ordinary composition and extraordinary location close enough, but not too close, to Earth.
It’s probably chondrite, Chabot said, a common type of asteroid made of rock and metal debris left over from when the planets formed 4.5 billion years ago. No one knows its shape, but it’s about the size of something that people would definitely want to redirect if it were headed toward Earth.
About a sixth of all near-Earth asteroids are linked by gravity in pairs or small groups in the same way that Dimorphos is linked to Didymos. This is how we know the moon exists: Earth-based telescopes detect Didymos’s regular dimming and brightening as the moon passes in front and behind every 11 hours and 55 minutes.
The spacecraft’s head-on collision is expected to slow the tiny moon enough that Didymos’s gravity pulls it a little closer, speeding up its orbit. The column of rock that is blown out of the crater at the moment of impact can also provide an additional push.
Contact will occur about 6.7 million miles from Earth, about 28 times the distance between Earth and the Moon. That’s close enough for high-speed data transmission and for ground-based telescopes to detect a change in the tiny moon’s orbit, but far enough away that the whole effort presents a significant technological challenge.
If the ship fails, the asteroid won’t be around for decades.
The technology being tested
The DART spacecraft carries quite a bit sophisticated equipmentincluding some that NASA is testing for future missions.
Whats Next? We’ll see.
In 2024, the European Space Agency will launch a spacecraft called herah to visit Dimorphos and investigate the crater that, fingers crossed, will be left by DART. What he discovers will help planetary defense experts figure out how the diversion technique can be refined, and perhaps gain insight into what other methods might work, too.
Future techniques could include using gravity to pull asteroids out of orbit, removing them with lasers or even moving them with tractor beams, NASA planetary defense officer Lindley Johnson said at a pre-mission press conference.
“This,” he said, “is just a start.”