Space weathering effects in Bennu asteroid samples
Bibliographic record
Abstract
The OSIRIS-REx mission deployed contact pad samplers to collect regolith from the uppermost surface of the asteroid Bennu that was exposed to the space environment. Space weathering processes, dominated by micrometeoroid impacts and solar irradiation, modify the mineralogy and chemistry of exposed surfaces to produce solar wind-amorphized layers on clays, metallic whiskers associated with high temperature melts and Fe nitride created by the reaction of indigenous N-bearing gases with space-weathered surfaces. Here, we use cosmogenic noble gases and radionuclides to suggest that the upper metre of Bennu's regolith has been exposed to cosmic rays for 2-7 million years, consistent with remote sensing observations indicating that the asteroid's surface is dynamic and regularly modified by mass movement. Solar energetic particle track and microcrater densities constrain the space weathering spectral changes observed in Hokioi crater to <50,000 years. These spectral changes are driven largely by the accumulation of impact melt deposits on particle surfaces, although compositional or grain size effects may also occur. Comparison of Bennu samples with those collected from the asteroids Ryugu and Itokawa suggest that micrometeoroid impacts might play a more active and rapid role in the space weathering of asteroidal surfaces than was initially suggested, particularly for carbonaceous bodies.
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How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.002 | 0.001 |
| Science and technology studies | 0.001 | 0.000 |
| Scholarly communication | 0.001 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.001 | 0.000 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one source (direct Gemma or distilled Codex), not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".