With some 20,000 near-Earth asteroids and comets orbiting the Sun, NASA and other space agencies have been constantly tracking these near-Earth objects (NEOs) since the 1990s in a joint initiative called ‘Spaceguard.”
However, merely chasing these potential threats is not going to save Earth from another mass extinction and, probably, thousands of years of ice age, should one of them slam into us.
The good news is that NASA has been working on a planetary-defense mission called DART, an acronym for Double Asteroid Redirection Test, to save us from exactly such an eventuality.
DART is essentially an impactor spacecraft that NASA plans to crash into an asteroid satellite at 13,500 miles per hour in an effort to change its course.
The idea is to find out how much the car-sized impactor can change the trajectory of the flying space rock and whether it’s enough to redirect an Earth-bound asteroid safely away from us.
The space rock that NASA has in its crosshairs for the planned Oct 2022 smash-up is, in fact, a satellite moonlet nicknamed Didymoon, about seven million miles away from Earth.
The moonlet, which is about 150 meters across, orbits an 800-meter-wide asteroid called Didymos, from where it gets its nickname.
While Didymoon is not on a collision course with Earth and poses no threat to us whatsoever, a detailed study of the space object and then slamming into it to bump it off its bearings should provide the DART team with useful data that can come in handy in averting a real asteroid threat if ever it comes to that.
Speaking to Space.com at the annual meeting of the American Geophysical Union, Nancy Chabot – a planetary scientist at Johns Hopkins University’s Applied Physics Laboratory and project scientist for DART – said that “science-driven” space missions were largely focused on understanding the origins of our solar system and its building blocks, but planetary defense was all “about the present solar system and what are we going to do in the present.”
Chabot says that tracking the moonlet and knowing its exact location, instead of having a ballpark idea of its whereabouts, is going to be crucial to the mission because the DART team wants to hit it head-on for maximum impact.
“It’s interesting because it’s a space mission, but the telescopes are such a huge, important part of the mission succeeding,” Chabot told space news website.
“We have to know where this moon is in order to impact it, to make this maximum deflection,” she said.
“We kind of take for granted that we know where everything is at all times,” she continued
“We understand where the system is as a whole, but specifically where that moon’s gonna be [requires tracking] because we want to try to hit it head-on,” Chabot added.
However, at least ten to twenty years’ advance warning will be needed to pull off something like redirecting a huge asteroid in a real-threat scenario, according to Chabot.
She says that “the idea of a kinetic impactor is definitely not like [the movie] ‘Armageddon,’ where you go up at the last hour and you know, save the Earth.”
She adds: “This is something that you would do five, 10, 15, 20 years in advance — gently nudge the asteroid so it just sails merrily on its way and doesn’t impact the Earth.”
The 14 radar images below, captured by the Arecibo Observatory radio telescope in Puerto Rico in November 2003, show Didymos (65803) and its moonlet.
If all goes according to plan, the mission will launch as early as June 2021, with an expected collision date in Oct 2022, as mentioned earlier.
While ground telescopes will track the new course of the twin objects post-impact, an Italian Space Agency CubeSat called Light Italian CubeSat for Imaging of Asteroids will accompany DART on its mission to keep an eye on proceedings.
Additionally, as part of an international Asteroid Impact Deflection Assessment (AIDA) mission, the European Space Agency (ESA) will launch two CubeSats, APEX (Asteroid Prospection Explorer) and Juventas, onboard the agency’s Hera spacecraft, in time to reach the binary asteroid system sometime in 2026 to record the effects of the DART collision, according to NASA.
“To test potential techniques in “deflecting” an asteroid – one of the preferred methods for mitigating a threat – DART will travel to the Didymos binary asteroid system via its a xenon-based electric propulsion system, steering with an onboard camera and sophisticated autonomous navigation software,” says the U.S. space agency.
DART is expected to send back a close-up shot of the Didymoon surface – its last transmission to Earth – before it is pulverized into space dust.
For any Solar System body to qualify as a near-Earth object, its closest approach to the Sun has to be less than 1.3 astronomical units (AU), the equivalent of nearly 121 million miles.
Among the 20,000 near-Earth asteroids and comets orbiting the Sun is a 500-meter-wide asteroid called Bennu, which has a 1-in-2,700 chance of smashing into Earth sometime between 2175 and 2196, say scientists.
The potentially hazardous object (PHO), “listed on the Sentry Risk Table with the second-highest cumulative rating on the Palermo Technical Impact Hazard Scale,” is currently 54 million miles from Earth.
The Sun-orbiting asteroid has been in NASA’s crosshairs ever since its discovery by the Lincoln Near-Earth Asteroid Research (LINEAR) project in 1999.
So focussed has the space agency been on Bennu that in 2016 it sent its ORISIS-REx (Origins, Spectral Interpretation, Resource Identification, Security, Regolith Explorer) spacecraft to the asteroid on a sample-return mission.
After traveling through space for more than two years, the spacecraft finally reached the proximity of Bennu last month.
Over the coming months, the NASA spaceship will map the asteroid to identify the best possible sample-collection site before making a slow descent to the surface to collect samples using its robotic arm.
OSIRIS-REx will begin its return journey after it has safely tucked away its precious cargo of Bennu samples inside a Sample-Return Capsule (SRC).
The SRC is expected to re-enter Earth’s atmosphere and land at the U.S.
Air Force Utah Test and Training Range on Sep 24, 2023 – about a year after DART smashes into Didymoon, hopefully, achieving the desired results.
For all we know, Bennu might just turn out be the asteroid that NASA has to knock off-course to save the planet in the future; that’s when the knowledge gained from the DART mission will come in handy – unless the 500-meter flying rock hits us sooner.
Time will tell.