NASA's DART Spacecraft Impact Altered Asteroid's Solar Orbit

On September 26, 2022, a 570-kilogram NASA spacecraft traveling at 22,530 kilometers per hour slammed into a small asteroid moonlet called Dimorphos, 10.9 million kilometers from Earth. The collision was deliberate — the culmination of the $324.5 million Double Asteroid Redirection Test, or DART, designed to answer a question that has haunted planetary scientists for decades: Can humanity actually deflect an asteroid?

The immediate results were dramatic. Dimorphos's 12-hour orbit around its companion asteroid Didymos shortened by 33 minutes, far exceeding the 73-second threshold NASA had set for mission success [1]. But three and a half years later, a new study has revealed something even more profound: the impact didn't just nudge Dimorphos around its parent — it permanently rearranged both asteroids' orbit around the Sun [2].

It is the first time in recorded history that humans have measurably changed a natural object's path through the solar system.

The Discovery No One Expected

When DART's planners designed the mission, the primary metric was simple: measure how much the spacecraft's kinetic impact changed Dimorphos's orbit around Didymos. That measurement came quickly. Ground-based telescopes confirmed the 33-minute orbital period reduction within weeks [1].

But the heliocentric effect — the change in how the entire Didymos-Dimorphos binary system orbits the Sun — was far subtler. It required years of painstaking observation and an unlikely coalition of professional and amateur astronomers scattered across the globe.

The findings, published March 6, 2026 in the journal Science Advances, were led by Rahil Makadia of the University of Illinois Urbana-Champaign and Steve Chesley, a senior research scientist at NASA's Jet Propulsion Laboratory [2][3]. Their team combined radar measurements with a technique called stellar occultation — tracking the precise moments when asteroids pass directly in front of distant stars, temporarily blocking their light.

Between October 2022 and March 2025, volunteer astronomers worldwide recorded 22 such occultations of Didymos. Each observation provided an extraordinarily precise fix on the asteroid's position and velocity, allowing researchers to reconstruct its orbital trajectory with enough accuracy to detect a change measured in microns per second [2][3].

The result: the DART impact slowed the Didymos system's orbital velocity around the Sun by approximately 11.7 microns per second — roughly 1.7 inches per hour, or about 370 meters per year [2][4]. The system's 770-day solar orbital period permanently decreased by less than a second [3].

"If [an asteroid] is ever on its way to hitting the Earth, we can more confidently now say that we have the ability to push them around and away from the Earth," Makadia said [4].

How Debris Did the Heavy Lifting

One of the most significant findings from the DART mission — reinforced by this latest study — is that the spacecraft itself was only part of the equation. The real force multiplier was the debris.

When DART struck Dimorphos at roughly 6.1 kilometers per second, it displaced more than 1 million kilograms of rocky material into space — enough to fill six or seven rail cars [5]. This ejecta plume, spraying outward from the impact site, acted like a rocket exhaust in reverse, pushing Dimorphos in the opposite direction with considerably more force than the spacecraft's direct impact alone.

Scientists quantify this effect using a metric called the momentum enhancement factor, or beta. A beta of 1 would mean the asteroid absorbed the spacecraft's momentum and nothing more. For Dimorphos's orbit around Didymos, the beta was measured at approximately 3.6 — meaning the ejecta transferred roughly 2.6 times more momentum than the spacecraft itself [5][6].

For the heliocentric orbit change, the new study calculated a momentum enhancement factor of approximately 2.0, meaning ejected debris effectively doubled the spacecraft's direct pushing force on the Sun-orbiting trajectory [2][3]. The difference between the two beta values reflects the complex dynamics of how momentum is distributed between the binary system's internal orbit and its path around the Sun.

The study also yielded another scientific dividend: by analyzing the orbital dynamics, researchers were able to independently calculate the bulk densities of both asteroids for the first time. Didymos came in at approximately 2,600 kilograms per cubic meter, while Dimorphos measured roughly 1,540 kilograms per cubic meter [2][3] — supporting the hypothesis that Dimorphos may have originally formed from material flung off its rapidly rotating companion.

Source: GDELT Project

Data as of Mar 11, 2026CSV

A Squashed Ball Becomes a Watermelon

The impact didn't just change orbits. It reshaped Dimorphos entirely.

Before DART arrived, Dimorphos was a roughly symmetrical oblate spheroid — shaped, in colloquial terms, like a squashed ball, wider than it was tall. Images from the DRACO camera aboard DART and the Italian Space Agency's LICIACube, which flew alongside to document the collision, showed a rubble-pile asteroid approximately 170 meters across [7].

After the impact, ground-based radar observations and dynamical modeling revealed that Dimorphos had been deformed into a triaxial ellipsoid — an elongated shape more resembling a watermelon [8]. The collision created a substantial crater and ejected so much surface material that the moonlet's overall geometry was fundamentally altered.

A 2024 study published in the Planetary Science Journal, led by Shantanu Naidu of JPL, confirmed that both the shape deformation and the orbital changes appear to be permanent [8]. Dimorphos's orbit around Didymos is no longer circular but has become slightly eccentric, and the moonlet's rotation has become more complex.

These findings carry important implications for future planetary defense scenarios. If a kinetic impactor can reshape a rubble-pile asteroid this dramatically, mission planners will need to account for how structural changes might affect subsequent deflection attempts on the same body.

The Bigger Picture: Why Planetary Defense Matters

The DART mission did not target a threatening asteroid. Neither Didymos nor Dimorphos poses any danger to Earth. But the binary system served as an ideal test case — close enough to observe in detail, with Dimorphos's orbit around Didymos providing a measurable change that ground-based telescopes could detect.

The urgency behind the test, however, is real. As of late 2025, astronomers have catalogued more than 36,000 near-Earth objects, with approximately 2,400 classified as potentially hazardous asteroids — those large enough and passing close enough to Earth to warrant monitoring [9]. While more than 99% of known potentially hazardous objects pose no impact threat over the next century, the search is far from complete. Congress mandated in 2005 that NASA identify 90% of near-Earth objects 140 meters or larger — a threshold still unmet two decades later [10].

The consequences of an undetected impact could be catastrophic. The Chelyabinsk event of February 2013 — when a roughly 20-meter asteroid exploded in Earth's atmosphere over Russia — shattered windows in six cities and injured over 1,500 people, despite being too small to have been detected in advance [9]. An impact from a Dimorphos-sized object (170 meters) could devastate a region.

NASA's planetary defense budget reflects growing recognition of the threat. Annual spending has grown from $3.7 million in 2009 to $341 million in fiscal year 2026, a nearly hundredfold increase [10][11]. The bulk of current funding supports the NEO Surveyor space telescope, an infrared observatory designed to accelerate the discovery of potentially hazardous asteroids from its planned orbital vantage point. Originally targeted for a 2026 launch, NEO Surveyor has been delayed to 2028 due to funding constraints and a cost increase from $1 billion to $1.6 billion [10].

Source: The Planetary Society / Congressional Appropriations

Data as of Mar 11, 2026CSV

What Comes Next: The Hera Investigation

The next chapter in the DART story is already underway. The European Space Agency's Hera spacecraft launched on October 7, 2024, aboard a SpaceX Falcon 9, and is en route to the Didymos system [12].

Hera is expected to arrive in November 2026 — a month earlier than originally planned, thanks to favorable spacecraft performance and efficient trajectory design [12][13]. The mission will perform the first-ever rendezvous with a binary asteroid, conducting a detailed survey of both Didymos and Dimorphos.

The spacecraft carries two suitcase-sized CubeSats — Milani and Juventas — that will be deployed for close-up investigations. Juventas will use a low-frequency radar to probe the internal structure of Dimorphos, providing the first-ever look inside an asteroid [12]. This data will be crucial for understanding whether DART's impact created internal fractures or merely rearranged surface material.

Hera's observations will also independently verify the ground-based measurements of orbital and shape changes, providing a critical cross-check on the stellar occultation data that underpins the new heliocentric deflection study.

"From 2022 to 2026, a question of time," ESA titled one of its mission updates — a nod to the fact that understanding the full consequences of DART's 2022 impact has required years of observation, and the most detailed answers are still months away [13].

The Road From Proof of Concept to Planetary Shield

DART has proven that kinetic impact works. The technology is real, the physics is understood, and the measurements are in hand. But significant challenges remain before humanity can claim a reliable planetary defense capability.

First, DART targeted a small moonlet in a binary system — an ideal scenario where the orbital change was easy to measure and the momentum enhancement from ejecta was maximized. Deflecting a solitary asteroid on a collision course with Earth would present different dynamics, and the decades of advance warning needed for a kinetic impactor to accumulate sufficient deflection may not always be available [6].

Second, the rubble-pile composition of Dimorphos — a loosely bound collection of rocks and dust — proved highly responsive to kinetic impact, producing enormous amounts of momentum-enhancing ejecta. A denser, monolithic asteroid might absorb more of the impact energy without producing the debris spray that doubled DART's effectiveness [5][6].

Third, detection remains the fundamental bottleneck. No defense strategy works against an asteroid we haven't found yet. The delayed NEO Surveyor mission and the still-incomplete census of 140-meter-plus near-Earth objects represent gaps in a defense architecture that DART has shown can work — if we know the threat is coming [10].

Nevertheless, the latest finding — that DART measurably altered an asteroid's path around the Sun — represents a milestone that extends beyond scientific achievement. Over sufficient time and distance, even a change of 370 meters per year in an asteroid's position accumulates. For a threatening asteroid detected decades in advance, that kind of nudge could mean the difference between impact and a near miss.

As Makadia and his colleagues demonstrated with 22 flickering starlight observations from backyards and observatories around the world, humanity has — for the first time — reached out and rearranged the furniture of the solar system.

Source: NASA / Nature / Science Advances

Data as of Mar 11, 2026CSV