DART impact date : Sept 26, 2022
Ryugu impact date : April 5, 2019
Ryugu impactor diameter : 0.073 m (baseball size)
Resulting crater diameter : 14.5 m
Damage factor - 200x (approx)
Damage factor for comet Tempel 1 : 50x
(estimated, not measured. 1 m impactor, 50 m crater from poor resolution pics)
NASA's 15 m prediction : May 2, 2019 (damage factor - only 7.5x)
(1 month after Ryugu impact. Its crater size was known by then)
ESA's 20 m prediction : Aug, 2019 (damage factor - only 10x)
(5 months after Ryugu impact. Ryugu's crater size was known by April end, 2019)
So despite knowing that an impactor can create a crater 190 times bigger, on a low gravity, rubble pile asteroid Ryugu, both NASA & ESA, shockingly did not expect a big damage on a similar but smaller asteroid Dimorphos. Prior to impact, they knew very well that Dimorphos was a rubble pile asteroid. Damage factor of 7.5-10x was impossibly low.
My pre-impact predicted damage factor for Dimorphos : 20x
My post-impact predicted damage factor for Dimorphos : 20x to 40x
It cannot be more than 57x since it is only 115 m wide on the short side (115m/2m). A crater larger than 100 m can trigger the collapse of the crater walls & cause a shape deformation. After that stage, the crater growth will stall & it won't be recognizable any further.
Pre-impact papers on crater sizes :
Ryota Nakano et al, July 2022
Others : Masatoshi Hirabayashi, Harrison Agrusa, Fabio Ferrari, Alex Meyer, Patrick Michel, Sabina Raducan, Paul Sánchez, Yun Zhang
"5 different crater diameters are considered: 20, 40, 60, 80 and 100m. Based on earlier studies the craterʼs depth-to-diameter ratio (d/D) is set to 0.1"
"Therefore, we anticipate that the mutual dynamics of the Didymos system (and thus the orbital period) will be generally unaffected as long as the crater diameter is smaller than 100 m."
"The β is expected to be in a range from 1 to 5,depending on Dimorphos’s structural properties and impact conditions."
"Importantly, if Dimorphos experiences a global deformation, it implies that its structure is weak (Raducan & Jutzi 2022; Stickle et al. 2022)."
"We found that a crater with a diameter of less than ∼80 m would only cause an orbital period change smaller than the observation accuracy. Thus, the effect of a crater on the mutual dynamics will be negligible."
Date : 2019
At the same time DART’s collision will also leave a 20-metre-wide crater on Didymoon’s surface. Hera will map the shape of this crater to gather unique information to design asteroid deflection missions in future. In addition, the mission will shed light on the asteroid’s surface properties and internal structure. Is the asteroid a monolithic mass or a rubble pile?
Date : 2019
DART’s collision has also been modelled to have possibly left a sizeable (20 m diameter scale) crater on Dimorphos’s surface.
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Post-impact papers on crater sizes :
Angela Stickle et al, Feb 2025
"Simulations here suggest that Dimorphos has near-surface strength ranging from a few Pascals to tens of kPa, which corresponds to crater sizes of 40–60 m."
Sabina Raducan et al, Feb 2024
Our simulations indicate that the DART impact caused global deformation and resurfacing of Dimorphos. ESA’s upcoming Hera mission may find a reshaped asteroid rather than a well-defined crater.
Bern SPH’s fast-integration scheme has been validated against laboratory experiments18 and was recently successfully applied to model the impact of the Hayabusa2 Small Carry-on Impactor (they recreated the Ryugu cratering).
On Dimorphos, for a cohesion lower than Y0 ≈ 4 Pa, the impact occurs in the gravity-dominated regime in which crater growth is halted by the asteroid’s small gravity rather than its cohesion.
The bulk density of Dimorphos is less than the current best estimate of the asteroid’s bulk density of 2,400 kg m−3 (ref. 1). Thus, Dimorphos is probably more porous and, therefore, may have a rubble-pile structure throughout the whole body.
In all impact scenarios simulated here, the DART impact does not produce a conventional impact crater but instead causes global deformation of the target.
For a cohesionless target, the ratio of the major to intermediate axes a/b could have changed from the reported pre-impact value of 1.02 to as much as 1.2. Such a large change in the a/b ratio is detectable with the highest-quality post-impact light curve data. (lightcurve based shape estimation is a pseudoscience & she is getting misled by its interpretation).
However, our best-fitting scenarios indicate that Dimorphos, the satellite of Didymos, exhibits a cohesive strength of less than a few pascals. This observed disparity in cohesive strength between Didymos and Dimorphos suggests a potential scarcity of fine grains within Dimorphos’s structure as well as a weak and fragmented internal structure.
The solar arrays made contact with Dimorphos’s surface before the spacecraft bus; however, the majority of the impact energy was transferred through the bus, which made up most of the spacecraft’s mass at the time of impact.
NOTE : There is no mention of crater diameter in this paper surprisingly. Even if the asteroid had deformed, it would happen only after the crater had reached its maximum possible size (width of its short axis, the side of a thick disc). So for shape deformation to happen, the crater diameter would have to exceed 116 m, which is the thickness of the disc. After this stage, the collapse could begin.
The ejecta plume for the cohesionless target (Y0= 0 Pa) is more massive than that for the cohesive target (Y0 = 500 Pa).
For the cohesive target (Y0 = 500 Pa), crater growth ceases about 100 s after the impact, before the crater grows large enough for the ejection angle to be influenced by target curvature. In this case, the maximum ejecta opening angle is ~120°.
On the other hand, for the low-cohesion targets (Y0= 0 Pa), there is a larger cratering efficiency and crater growth continues to later times, resulting in a wider cone opening angle influenced by target curvature.
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General info from Google on depth-to-diameter ratios for craters
(d/D ratio)
Class 1 (Deep): d/D > 0.1
Class 2 (Average): 0.05 < d/D < 0.1
Class 3 (Shallow): d/D < 0.05
40m, 4m (0.1)
40m, 5.2m (0.13)
40m, 8m (0.2)
Ryugu : Large craters (diameter > 50 m) have maximum d/D values close to 0.13. The largest natural craters on Ryugu, such as Urashima, have d/D ratios of around 0.2. Smaller craters (diameter < 50 m) tend to have shallower d/D ratios, generally less than 0.09, suggesting they are more easily degraded by the surface environment and seismic shaking. The artificial crater created by the Hayabusa2 mission's Small Carry-on Impactor (SCI) has a d/D ratio of about 0.159.
Bennu : Craters with diameters less than 80 meters show a wide variation in their d/D ratios. The smallest craters tend to be shallower. For craters larger than approximately 80 meters, the d/D ratio levels off and tends to be small, generally ranging only from 0.02 to 0.09. Studies of 108 craters larger than 10 meters on Bennu found a mean d/D ratio of 0.10-0.13. The low d/D ratios and variations indicate that the craters are largely affected by mass movement and the asteroid's "rubble-pile" nature, where the surface material is very weak and highly porous, rather than a solid, strong rock. This weak surface inhibits craters from becoming as deep as those on more solid bodies.
Phobos : Craters generally have higher d/D ratios (0.05 to 0.24) than typical craters on the Moon or Mars, which is likely due to Phobos' very low gravity and the target material properties (such as the presence of a deep regolith layer). The low gravity likely prevents significant slumping or wall collapse that would typically shallow craters on larger bodies.
Itokawa : The average depth-to-diameter (d/D) ratio for its impact craters is 0.08, which is significantly shallower than craters on other asteroids. This low ratio is a key indicator of its "rubble-pile" nature. The unusual shallowness is attributed to several factors related to Itokawa's composition as a rubble pile, a loosely aggregated collection of boulders and fine materials held together by weak gravity.
