Asteroid Surfaces

Boulder armouring inhibits small-crater formation on the rubble-pile asteroid Bennu, substantially reducing surface age estimates, according to an analysis of the crater size–frequency distribution.

Fractures on the asteroid Bennu imaged by the OSIRIS-REx spacecraft are consistent with cracking induced by diurnal temperature variations over geologically rapid timescales.

Observations of deposits associated with a crater on the rubble-pile asteroid Bennu indicate a surface with low strength that is readily reworked by impact processes.

The surface of the asteroid Bennu is so weakly bonded that rockslide avalanches are easily triggered by small body impacts, and boulders fractured due to diurnal heating and cooling are readily dislodged. The result is a surface under continuous renewal.

Recent missions to the rubble-pile asteroids Bennu and Ryugu have revealed asteroid surfaces that continue to be actively modified by a variety of processes while also recording the geologic history of these small bodies.

Spectral characteristics can be used to link asteroid and meteorite materials. Here, the authors show in-situ mid-infrared data of a boulder on asteroid Ryugu, compared with laboratory spectra of various meteorites, indicate that Ryugu experienced strong aqueous alteration prior to dehydration.

The first robotically obtained samples of a carbonaceous asteroid have been safely returned to Earth. A non-destructive first-look analysis shows that asteroid Ryugu may be a CI chondrite with interesting variations.

Water and hydroxyl enrichment in the solar-wind-irradiated rim of an olivine grain from asteroid Itokawa suggests that its regolith could contain ~20 l m⁻³ of water from solar wind—a potential water source for airless planetary bodies.

The Earth’s most stable quasi-satellite, Kamoʻoalewa, displays an extremely red reflectance spectrum typical of space weathering of lunar-like silicate material which raises the possibility that it is formed of material originating from the Moon

The absence of fine regolith on the asteroid Bennu is due to the high porosity of its rocks, which compress rather than fragment after impacts and exhibit slow thermal cracking.

Both poles of asteroid Ryugu, the target of space mission Hayabusa2, preserve the least processed material by space weathering. Here, the authors show detection of 700 nm absorption band in the polar spectra of Ryugu, that allows to constrain the hydrothermal history of its spectrally blue parent body.

The loss of volatile material from asteroid Ryugu was not caused solely by heating from hypervelocity impacts as previously believed, suggest impact experiments conducted at speeds comparable to those expected in the main asteroid belt

The Hayabusa2 spacecraft found dark boulders with very high porosity (>70%, as high as cometary nuclei) at the bottom of small craters on Ryugu. Such boulders are probably the most pristine parts of the planetesimals that formed Ryugu’s parent body and might have been captured by Hayabusa2 sampling.

Hayabusa2 created an artificial crater on Ryugu to analyse the subsurficial material of the asteroid. Results show that the subsurface is more hydrated than the surface. It experienced alteration processes that can be traced back to Ryugu’s parent body.

Analysis of the size and depth of craters on boulders on the asteroid (101955) Bennu indicates that Bennu has been in near-Earth space for 1.75 ± 0.75 million years.

The distribution of boulders on the surface of top-shaped asteroids such as Bennu or Ryugu tells us about the processes driving their evolution. A model shows that the spin-up induced by the Yarkovsky–O’Keefe–Radzievskii–Paddack (YORP) effect can explain simultaneously both the latitudinal behaviour of the boulders and the regolith migration.

Six bright boulders of exotic material on near-Earth asteroid (101955) Bennu stand out from the average asteroidal surface. This unexpected record of impactors offers clues to the formation history of Bennu.

The Hayabusa2 team has discovered two types of bright boulder on the dark, carbonaceous asteroid Ryugu. One type has a spectrum consistent with material from an anhydrous silicate-rich asteroid, likely introduced by one or more collisions in Ryugu’s past.

In their study, the authors discuss the potential of thermal weathering on airless bodies. As a case study, they use boulder and fracture morphologies on asteroid Bennu.

Asteroid shapes and hydration levels can serve as tracers of their history and origin. Here, the authors show top shape asteroids can form directly through gravitational reaccumulation and rubble piles formed in a single disruption can have similar porosities but variable degrees of hydration.

The surface of active asteroid (3200) Phaethon, parent body of the Geminid meteor shower, reaches temperatures sufficient to destabilize hydrated materials. Here, the authors show that the northern hemisphere and the equatorial region of this asteroid reveal no evidence of hydration in the near-infrared spectra.

The authors here investigate troilite (FeS) grains recovered from the regolith of asteroid Itokawa. Finding wide-spread occurrence of metallic iron whiskers, the authors suggest them to be a decomposition product formed through irradiation of the sulfide by energetic ions of the solar wind.