Did DART, the Double Asteroid Redirection Test come true?
The core promise of planetary defence, that a spacecraft can change an asteroid's motion, was kept in 2022 and beat its own bar by more than 25 times. The rest of the chain is unfinished: the survey that finds the rock, a repeatable and predictable method, a spacecraft that could be built in the warning time, and a body with the authority to launch it.
Read the review · 8.3/10 →How this P(n) was calculated
Each prediction is weighted 1–5 by how pivotal it is to the story: 5 is the core premise, 1 is background detail. Arrived scores 1, arriving 0.5, everything else 0. P(n) is the weighted points divided by the total weight.
| Claim | Prediction · why this weight | Weight | Status | Value | Points |
|---|---|---|---|---|---|
| DART-1 | A spacecraft can measurably change the motion of an asteroid by hitting it (the kinetic impactor). Core premise: the whole mission, and the idea of planetary defence by impact, rests on this. |
5 | ARRIVED | 1 | 5 |
| DART-2 | The outcome of a deflection can be predicted well enough in advance to plan one against a real threat. Supporting: the test only becomes a method if the result can be predicted, but the headline deflection stands without it. |
3 | NEAR | 0 | 0 |
| DART-3 | Most asteroids big enough to devastate a region are found years or decades before they could hit. Major: a deflection is only possible against a rock that has been found, so the whole defence depends on the survey. |
4 | NEAR | 0 | 0 |
| DART-4 | A real deflection mission can be designed, built and launched within the warning time a newly found asteroid would give. Supporting: this is the gap between a demonstration and a defence, but the test itself did not need it. |
3 | NEAR | 0 | 0 |
| DART-5 | An agreed international process exists to decide on, fund and launch a deflection before an impact. Supporting: the story of planetary defence is as much about who decides as about the rocket. |
3 | ARRIVING | 0.5 | 1.5 |
| Total | 18 | 6.5 |
P(n) = 6.5 ÷ 18 = 36% · unweighted average 30%
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DART-1
A spacecraft can measurably change the motion of an asteroid by hitting it (the kinetic impactor).
Weight 5/5 · Core premise: the whole mission, and the idea of planetary defence by impact, rests on this.
DART hit Dimorphos on 26 September 2022 and shortened its orbit around Didymos from 11 hours 55 minutes to 11 hours 23, a change of about 32 minutes (later put at about 33). The pre-set success threshold was 73 seconds. The pair do not threaten Earth, so this was a test, not a rescue. 123
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DART-2
The outcome of a deflection can be predicted well enough in advance to plan one against a real threat.
Weight 3/5 · Supporting: the test only becomes a method if the result can be predicted, but the headline deflection stands without it.
The momentum factor depends on Dimorphos's mass and density, which have not been measured; the main paper allows a range of about 2.2 to 4.9. ESA's Hera arrives in November 2026 and starts a science phase of around six months, and ESA says the open questions include why the deflection was so much greater than simulations predicted. Understanding one asteroid is not understanding all of them. 45
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DART-3
Most asteroids big enough to devastate a region are found years or decades before they could hit.
Weight 4/5 · Major: a deflection is only possible against a rock that has been found, so the whole defence depends on the survey.
Congress set a goal in 2005 of finding 90 per cent of near-Earth asteroids over 140 metres. NASA's infrared survey telescope, NEO Surveyor, is scheduled to launch no earlier than September 2027, after earlier proposals were not selected between 2006 and 2017. Small objects such as the 17 to 20 metre one that burst over Chelyabinsk in 2013 arrive unseen. The 2024 YR4 case showed discovery and follow-up working, over about two months. 678
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DART-4
A real deflection mission can be designed, built and launched within the warning time a newly found asteroid would give.
Weight 3/5 · Supporting: this is the gap between a demonstration and a defence, but the test itself did not need it.
DART flew as a planned test against a known, harmless target. No interceptor is standing ready, and the 2024 YR4 episode ended before any mission had to be started. Space agencies' stated plan is reference missions and test flights to prove the technology before a threat appears; a second kinetic test or a standing reference design would move this claim. 910
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DART-5
An agreed international process exists to decide on, fund and launch a deflection before an impact.
Weight 3/5 · Supporting: the story of planetary defence is as much about who decides as about the rocket.
The International Asteroid Warning Network and the Space Mission Planning Advisory Group exist, with UN backing, to coordinate warning and to develop reference plans. As described by the UN and ESA, they coordinate and recommend. I found nothing giving either the authority or the money to launch, which would remain a national decision. 1112
- FOR NASA Confirms DART Mission Impact Changed Asteroid's Motion in Space. Johns Hopkins Applied Physics Laboratory, 2022-10-11. Period cut from 11 h 55 min to 11 h 23 min, about 32 minutes, against a 73-second minimum.
- FOR Momentum transfer from the DART mission kinetic impact on asteroid Dimorphos. Nature (open-access copy on PubMed Central), 2023-03-01. Cheng and colleagues report a momentum enhancement factor of 3.61 and conclude the impact was highly effective.
- CONTEXT DART mission page. NASA Science, 2026-11-03. NASA's own mission page: launch 24 November 2021, impact 26 September 2022.
- FOR First light: Hera resolves two asteroids instead of one. European Space Agency, 2026-10-27. Hera has slowed to 20 m/s relative to the pair; first detailed images of Dimorphos due 25 November.
- AGAINST Momentum transfer from the DART mission kinetic impact on asteroid Dimorphos. Nature (open-access copy on PubMed Central), 2023-03-01. Dimorphos's mass is poorly constrained, so the factor spans roughly 2.2 to 4.9; Hera is expected to narrow it.
- FOR NEO Surveyor. NASA Science, 2026-11-03. Infrared space telescope in development; launch no earlier than September 2027.
- AGAINST NEO Surveyor. Wikipedia, 2026-11-03. Records the 2005 congressional mandate and the repeated non-selection of survey proposals from 2006 to 2017.
- CONTEXT 2024 YR4. NASA Science, 2026-03-05. No significant Earth impact risk in 2032 and beyond; lunar impact in 2032 ruled out with Webb data.
- CONTEXT 2024 YR4. Wikipedia, 2026-11-03. Records no deflection mission for YR4 and says one would have been difficult to prepare in the time available.
- CONTEXT Getting ready for asteroids. European Space Agency, 2014-01-01. SMPAG is to develop reference missions, including precursor test missions, to fly before a real threat arises. Page undated in text; year approximate.
- FOR Media advisory: Open Forum on near-Earth Object impact hazards. United Nations Information Service Vienna, 2016-02-17. Says IAWN and SMPAG were established after UN General Assembly resolution 68/75 endorsed recommendations for an international response.
- CONTEXT Getting ready for asteroids. European Space Agency, 2014-01-01. SMPAG's task is to coordinate expertise and capabilities and recommend measures; it is not described as a launch authority.
Ledger updated 3 Nov 2026. All works on the P(n) Board · Method