Science

How big is the asteroid threat, really?

Is our solar system really a shooting range where the Earth serves as a target for asteroids?

As humanity prepares for its first-ever planetary defense training mission, NASA officials recently assured earthlings that they have nothing to worry about.

The Double Asteroid Redirection Test (DART), in which the probe will crash into the satellite of an asteroid called Didymos on September 27 to try to change its orbit around its parent body, Dimorphos, is just part of our toolbox against potentially threatening asteroids. (Spoiler alert: nothing to worry about now.)

NASA, international agencies and telescopes around the world have been systematically combing the skies for generations looking for any evidence of the presence of asteroids that could pose a serious threat to human civilization. Only a short list of space rocks are considered dangerous at all, and NASA says there is nothing to worry about for at least the next century.

“We are constantly looking in the sky for potential new asteroids and threats,” said Andrea Riley, head of the DART program at NASA, during a September 12 press conference.

Pictured: asteroids in deep space

Dimorphos, 560 feet (170 meters) in diameter, is one of the class of objects that NASA monitors to make sure they are not in a collision course with Earth. The asteroid, however, is not considered a threat at all. Riley also stressed that NASA is more concerned about objects larger than 1 mile (1.6 km) in diameter, for which the agency has already tracked down at least 90% of the population.

Finding objects is one of the obstacles, and learning how to handle them is the next step. The “kinetic strike” strategy that DART will demonstrate is by no means the only way to get an asteroid out of the way. Researchers have proposed a number of other possible methods, from exploding space rocks with nuclear bombs to coloring them to change their brightness so that sunlight can help get them out of the way.

“This test,” Riley said of DART, “will help us make sure we have a mitigation strategy in place if a threat is ever discovered.”

But because space is so big, a space accident remains unlikely, NASA officials said, at least in the near future. There are enough asteroids in the neighborhood of the Earth, so that in the end one of them will definitely head towards our planet. Just ask the dinosaurs.

Related: Darkness caused by dinosaur-killing asteroid wiped out life on Earth in 9 months

Artistic depiction of a DART spacecraft approaching Dimorphos, with the larger Didymos in the background.

Artistic depiction of a DART spacecraft approaching Dimorphos, with the larger Didymos in the background. (Image credit: NASA/JHU-APL)

“If you wait long enough, the object will be found,” Thomas Zurbuchen, Associate Administrator for NASA’s Science Office, told reporters during the same press conference.

“These objects have really affected our history, and we have geological data to support this. [crater] data from the Moon and elsewhere,” he added.

NASA is looking for a low cost solution to any problem now that asteroid defense is not an immediate concern, he said. Thus, if and when the time comes, the agency and its international partners will be ready to solve this problem.

“This actually allows us to advance the level of knowledge along with the international community that wants to continue the mission to really help translate all of our knowledge into a scientific context,” Zurbchen said. “Now is the right time for that. This is not an external schedule that was imposed on us.”

Related: ‘Don’t Look Up’ is a comet-themed satire about climate change

group of astronauts from the movie Armageddon

Bruce Willis (front middle) starred in the 1996 film Armageddon, about miners fighting an asteroid threat. (Image credit: Touchstone Pictures)

DART is just one of the space missions recently tasked with learning more about the orbits of asteroids. For example, NASA’s OSIRIS-REx spacecraft returns to Earth with a sample of the asteroid Bennu. Scientists will study the sample to assess the composition of this asteroid, in part to better refine how to move such objects through space.

The OSIRIS-REx data also helps astronomers better understand the effect of thermal radiation on the asteroid, Zurbuchen said. Over time, the Yarkovsky effect can affect the asteroid’s orbit; so NASA is including thermal effects in its model “to really remove the biggest uncertainties for orbit propagation over long periods,” he said.

According to him, another assistant in this matter is NEO Surveyor. This is an upcoming NASA mission that will look for more asteroids in space and also aim to better predict their paths around the solar system.

On the subject: “Twilight telescopes” find “city-killer asteroids” in an uncharted region of our solar system

Artistic illustration of NASA’s NEO Surveyor spacecraft hunting for asteroids in space. (Image credit: NASA/JPL-Caltech)

While scientists are doing their best to protect the Earth from problems with space rocks, Nancy Chabot of the DART mission called for a perspective on the real threat of asteroids.

There are only four near-Earth asteroids that look like the dinosaur-killing object, which is thought to have been about 6.5 miles (10 km) in diameter, said Chabot, head of DART coordination at Johns Hopkins University. Research laboratory. “We have found them all, we are tracking them, and none of them pose a threat in the foreseeable future,” she stressed.

According to her, even smaller objects are well tracked. According to her, scientists have found more than 95% of objects with a diameter of more than 1 km, and none of them poses an immediate threat.

Now scientists have focused their attention on finding objects several hundred feet in diameter, for which they have found about 50% of the population. While known objects don’t pose the threat that scientists worry about, finding more would bolster our planetary defenses, she said.

By learning to manipulate such objects in space, “regional devastation, [which] it could be the size of a city, a small state, or a small country,” she said. “That’s why Dimorphos is such an ideal target for this first planetary defense mission, because it’s that big.”

Follow Elizabeth Howell on Twitter @howellspace (will open in a new tab). Follow us on Twitter @Spacedotcom (will open in a new tab) and on facebook (will open in a new tab).

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