DART is one "important step" in the long road towards functional planetary defense

• NASA's DART mission changed the orbital period of an asteroid orbiting another asteroid last month.
• The mission "was designed with the purpose of making accurate measurements possible" for calculations regarding planetary defense, NASA's DART program scientist Dr. Tom Statler told IE.
• Follow-up analyses and missions are in the works as humanity gears up its planetary defense capabilities.

NASA’s Double Asteroid Redirection Test (DART) mission successfully altered the orbital period of an asteroid, Dimorphos, orbiting a larger asteroid, Didymos, last month.

That impressive feat constituted the first planetary defense test ever carried out in space, and it determined that we should be able to avert a hazardous space rock on a collision course with Earth, should we need to.

While it's tempting to draw a collective sigh of relief, the situation's not quite so simple, and NASA warns that there's still much more work to be done.

"Keep in mind that DART was designed with the purpose of making accurate measurements possible,” NASA’s DART program scientist, Dr. Tom Statler told IE in an interview. "If we were ever in a situation where we had to deflect an asteroid, many other factors would influence the design of a deflection mission and what kind of spacecraft would be needed."

NASA's DART impact was "exciting beyond words"

The Double Asteroid Redirection Test (DART) spacecraft smashed into Dimorphos on September 26. It first captured a now-iconic shot of the asteroid coming closer into view in the final moments before impact.

"It was exciting beyond words," Statler explained, adding that when he saw the impact, he "felt incredibly proud and happy for our engineering team that built and operated the spacecraft and accomplished the impact, and excited along with the rest of the investigation team and eager to find out how Didymos was going to react."

A few days later, on October 11, NASA announced the results of the DART mission. The DART spacecraft impact altered Dimorphos’ orbital period from 11 hours and 55 minutes to a shorter 11 hours and 23 minutes — meaning it caused a total 32-minute change. Thankfully, Dimorphos and Didymos, located about some 7 million miles (11 million km) from Earth, aren't headed our way. Still, the calculations show that we should be able to alter the trajectory of a hazardous space rock on a collision course with Earth.

NASA has pointed out that the orbital period calculations do factor in a margin of error of two minutes in either direction. As Statler pointed out, "the DART investigation team is still acquiring data with ground-based observatories around the world to further refine the precision of this measurement."

Still, Statler added that "Long before DART was launched, NASA defined a successful orbital period change of Dimorphos as 73 seconds or greater, based on the smallest change that could be reliably measured from Earth. This means that even accounting for the plus or minus 2 minutes of uncertainty, DART surpassed this minimum benchmark by more than 25 times."

NASA's dramatic DART mission is only the beginning

It's hard not to marvel at a scientific achievement as impressive as DART — the sci-fi-like mission is the first in history to alter the trajectory of a non-human-made object in space. However, shortly after NASA announced the results of its DART mission, Statler did provide a word of caution to the world’s press. In a press conference following the announcement, he stated, "we should not be too eager to say one test on one asteroid tells us exactly how every other asteroid would behave in a similar situation."

Statler reiterated this concern to IE, stressing that humanity is still very much in the early stage of development regarding planetary defense technology. “Prior to impact, computer models estimated that Dimorphos’ orbital period around Didymos would change by roughly a few percent as a result of DART’s collision, and the measured change of 32 minutes is in accord with this broad expectation,” he told IE. “[But] more work is in progress to understand how the ejecta from Dimorphos’ surface affected the overall momentum transfer.”

In the case of DART, the effects of the kinetic impact event exceeded NASA’s expectations. It’s worth noting, however, that Dimorphos is the smallest asteroid ever visited by a spacecraft — it measures 170 meters (560 ft) in diameter, compared to Didymos at 780 meters (2,560 ft). Asteroids come in many different shapes and sizes, and there are many “factors [that] would influence the design of a deflection mission” as well as the “kind of spacecraft [that] would be needed,” Statler said.

"DART’s successful kinetic impact represents an important step toward a working planetary defense method," Statler continued, "but there are more steps needed before we get there. In the short term, there is still a lot to learn about the efficiency of momentum transfer from DART’s impact, which the DART investigation team is continuing to study."

Ultimately, the DART mission is a crucial reference point by which NASA can test its physics calculations in computer simulations for asteroids of different shapes and sizes.

What next for planetary defense missions?

The next step for NASA and the global scientific community is to continue to analyze Dimorphos from ground-based observatories and space — the Hubble Space Telescope and the James Webb Space Telescope both worked in tandem for the first time last month in order to capture observations of Dimorphos and Didymos.

Meanwhile, the European Space Agency (ESA) is also planning its Hera mission, which will send three spacecraft to Dimorphos in about four years to carry out follow-up observations and investigate the long-term effects of the DART mission. New data from these future missions "will help planetary defense experts better understand the effectiveness of kinetic impact and how this technique could be used in the future if ever needed," Statler said.

Statler also explained that "the next priority for NASA’s Planetary Defense Coordination Office – the entity that oversees the agency’s ongoing planetary defense efforts – is the Near-Earth Object Surveyor, NEO Surveyor."

The NEO Surveyor is an infrared space telescope “designed to substantially improve NASA’s ability to discover and characterize most of the potentially hazardous asteroids and comets that come within 30 million miles of Earth’s orbit,” Statler continued, adding that, "for a mission like DART to work in the future, we must first find any potential impact hazards to the Earth with as much warning time as possible."

At the time of writing, scientists estimate the probability of a 5-10 kilometer wide asteroid — like the one that wiped out the dinosaurs — hitting Earth is almost negligible at 0.000001 percent every year. For all we know, though, after NEO Surveyor takes to the skies — it is expected to launch in 2026 — new observations could dramatically change the landscape. It is, after all, better to be overly cautious in the face of a potential extinction event.