Protecting Earth from asteroids is complicated and requires global cooperation

An artist's depiction of comets passing Earth.
If an asteroid ever did threaten Earth, the response would be global. (Image credit: Christoph Burgstedt/Science Photo Library via Getty Images)

PARIS — NASA's DART spacecraft is closing in on its appointment with Dimorphos, but the energetic encounter is just the very speartip of global efforts to keep life on Earth safe from asteroid impacts.

The Double Asteroid Redirection Test (DART) is set to smash into Dimorphos, a moonlet of the larger asteroid Didymos, on Monday (Sept 26). The mission will measure whether the impact can alter the orbit of Dimorphos around Didymos, testing out the kinetic impact approach to planetary defense of hitting an asteroid that threatens Earth with enough force to nudge its orbit and avert catastrophe. 

At the International Astronautical Congress 2022 in Paris, representatives from NASA; the Johns Hopkins University Applied Physics Laboratory (APL), which manages the mission; the European Space Agency (ESA) and ESA's Hera mission outlined plans to coordinate and build up our ability to respond to potential asteroid hazards. Planetary defense efforts spread across many countries, take place on all continents and extend into space, the speakers emphasized.

Related: NASA's DART asteroid-impact mission explained in pictures

Monday will mark a violent end for DART, and will be "one of the only times that loss of signal will be celebrated and cheered," Betsy Congdon, DART mechanical lead engineer at APL, told the conference.

Celebration notwithstanding, follow-up work in a number of areas begins right away. The Light Italian Cubesat for Imaging of Asteroids (LICIA Cube) recently separated from DART and will fly past three minutes after impact, returning images of ejecta and plume from the asteroid.

Back on Earth, observations will be made using telescopes on all seven continents to determine whether and by how much the orbit of Dimorphos around Didymos has changed.

The European Space Agency will launch a follow-up surveyor mission in 2024, called Hera, arriving at the Didymos system in 2026. That spacecraft will fully investigate the pair of space rocks to determine the effects of the impact, Patrick Michel, the principal investigator for Hera at the French Scientific Research National Center (CNRS), said at the panel discussion. 

The Hera spacecraft will also carry a pair of breadbox-sized cubesats named Juventas and Milani. These tiny spacecraft will make radar observations of the two asteroids and decode the makeup of boulders on their surfaces using an imager capable of seeing a wider range of colors than the human eye. 

Eyes on the sky 

But planetary defense is more than just deflection. In a broader sense, work is ongoing across the world to find and implement the best ways to detect, track and characterize asteroids, coordinate responses to potential hazards and mitigate any effects.

The focus now is not on the larger, kilometer-wide-scale (0.6 miles) and above asteroids that would cause global devastation and feature in sci-fi films. The vast majority of these rarer large objects have been spotted and are not a threat to Earth. 

Instead, it is asteroids from roughly tens to hundreds of meters across that are hard to detect and largely unaccounted for. Rocks of this size impact the Earth much more frequently and can cause local and even regional damage and inflict mass casualties. The 2013 Chelyabinsk meteor that exploded over Russia, for instance was not spotted until it entered the atmosphere.

Richard Moissl, head of the Planetary Defense Office at ESA, outlined ground-based facilities for detecting and tracking asteroids, including a challenging new system of compound observatories. Moissl told IAC that scientists are developing so-called "Flyeye" telescopes, going on a "toe-to-toe battle with the laws of physics and what is feasible in optics trying to optimize the field of view, sensitivity and resolution all at the same time." 

These compound eye telescopes split each image into 16 smaller subimages, increasing the total amount of sky that can be observed at once and expanding the field of view. These telescopes would conduct nightly sky surveys, automatically flagging potential hazards.

Finding and tracking the smaller, more numerous threats, requires scanning the skies in the infrared, particularly to pick up darker asteroids. For this, NASA's Near-Earth Object Surveyor (NEO Surveyor) will detect infrared wavelengths using a nearly 20-inch (50 centimeters) diameter telescope. NEO Surveyor is scheduled for launch in 2026 but may be delayed two years by low funding levels depending on Congressional decisions about appropriations.

Additionally, ESA has established its Near-Earth Object Mission in the Infrared (NEOMIR) space telescope concept and is seeking support for the mission from its member states. The telescope would "scan objects which come from directions too close to the sun to be observed from the Earth, thereby closing a vital observational gap which exists to this day," Moissl told via email after the panel. "Our current roadmap foresees a launch in the 2029-2030 timeframe."

Who's in charge 

In the event that a hazardous asteroid is spotted on a collision course with Earth, it won't just be NASA — or whoever discovers a threat — that decides on what happens next. 

NASA established the Planetary Defense Coordination Office (PDCO) in 2016. In the event that an asteroid is likely to hit, the office would have to work domestically with the Department of Homeland Security and the Federal Emergency Management Agency (FEMA), Bhavya Lal, NASA's associate administrator for technology, policy and strategy, told the IAC audience. These national agencies would then work with local government agencies on mitigation efforts.

Internationally, NASA would coordinate with planetary defense bodies from other agencies, such as ESA's Planetary Defence Office, and also work with the Space Mission Planning Advisory Group (SMPAG) facilitated by the United Nations. The main purpose of SMPAG is to prepare an "international response to a threat by a near-Earth object through the exchange of information, development of options for collaborative research and mission opportunities, and to conduct NEO threat mitigation planning activities," according to the group's homepage. This group would also be responsible for informing the U.N. in the case of a credible asteroid threat.

DART is testing just one method of deflecting an asteroid and is designed to show that if a threat is ever detected, humans can take action. Although it is still early days for planetary defense, DART would be one more tool than the dinosaurs had.

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Andrew Jones
Contributing Writer

Andrew is a freelance space journalist with a focus on reporting on China's rapidly growing space sector. He began writing for in 2019 and writes for SpaceNews, IEEE Spectrum, National Geographic, Sky & Telescope, New Scientist and others. Andrew first caught the space bug when, as a youngster, he saw Voyager images of other worlds in our solar system for the first time. Away from space, Andrew enjoys trail running in the forests of Finland. You can follow him on Twitter @AJ_FI.