Modelling the polarization properties of Comet 1P/Halley using a mixture of compact and aggregate particles
Bibliographic record
Abstract
Both the in situ measurement of Comet 1P/Halley and the Stardust-returned samples of Comet Wild 2 showed the presence of a mixture of compact and aggregate particles, with both silicates and organic refractory being in the composition of the cometary dust. Results obtained recently from the Stardust mission suggest that the overall ratio of compact to aggregate particles is 65:35 (or 13:7) for Comet 81P/Wild 2. In the present work, we propose a model that considers cometary dust as a mixture of compact and aggregate particles, with a composition of silicate and organic. We consider compact particles as spheroidal particles and aggregates as both ballistic cluster–cluster aggregate (BCCA) and ballistic agglomeration with two migrations (BAM2) aggregate with a certain size distribution. The mixing ratio of compact to aggregate particles is taken to be 13:7. For modelling Comet 1P/Halley, the power-law size distribution n(a) ∼a−2.6, obtained from a re-analysis of the Giotto spacecraft data, for both compact and aggregate particles, is used. We consider a mixture of BAM2 and BCCA aggregates with a lower cut-off size of about 0.20 μ m and an upper cut-off of about 1 μ m. We also consider a mixture of prolate, spherical and oblate compact particles with an axial ratio (E) of 0.8–1.2 where a lower cut-off size of about 0.1 μ m and an upper cut-off of about 10 μ m are considered. Using a T-matrix code for polydisperse spheroids (0.1 μ m ≤a≤ 10 μ m) and superposition T-matrix code for aggregates (0.2 μ m ≤av≤ 1 μ m), the average simulated polarization curves are generated, which can best fit the observed polarization data at the four wavelengths: λ= 0.365, 0.485, 0.670 and 0.684 μ m. The suitable mixing percentages of aggregates obtained from the present modelling are 50 per cent BAM2 and 50 per cent BCCA particles, and the silicate-to-organic mixing percentages are 78 per cent silicate and 22 per cent organic, in terms of volume. The present model successfully reproduces the observed polarization data, especially the negative branch, for Comet 1P/Halley at the above four wavelengths, more effectively as compared to other work done in the past. It is found that among the aggregates, the BAM2 aggregate plays a major role in deciding the cross-over angle and depth of the negative polarization branch.
Fetched live from OpenAlex and de-inverted. Abstracts are not stored in this database: the inverted indexes are 8.6 GB of the frame’s 9.3 GB of text, and the host has 13 GB free.
How this classification was reachedexpand
Full frame distilled prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. Learned from the 10,348 direct Codex labels and 10,348 direct Gemma labels. Candidate is the union of thresholded teacher heads; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels or direct frontier model labels.
Codex and Gemma teacher scores by category
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.000 | 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 teacher head, 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".