Pith. sign in

REVIEW 47 references

Activity-Induced Near-Infrared Variability at 29P/Schwassmann-Wachmann 1, 2017-2022

T0 review · reviewed 2026-08-16 · deepseek-v4-flash

Challenge this review Re-run · record.json Download PDF Read on arXiv ↗ Review JSON

Pith's one-line read Near-infrared spectra of 29P taken during quiescence and two outbursts are modeled to show that the two outbursts had effectively different apparent grain size distributions, which the authors attribute to early versus post-outburst sampling of size-sorted dust.

arxiv 2504.12097 v1 pith:J24JDTO7 submitted 2025-04-16 astro-ph.EP

Theodore Kareta , Charles A. Schambeau , Megan Firgard , Yanga R. Fernández This is my paper · ORCID
classification astro-ph.EP
keywords activitydustoutburstoutburstsquiescentappearcometdiscovery
verification ladder T0 review T1 audit T2 compute T3 formal

The pith

A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.

The reading

Comet 29P/Schwassmann-Wachmann 1 sits just outside Jupiter and is famous for dozens of sudden brightness explosions each year. The authors obtained four near-infrared spectra of the comet between 2017 and 2022: one during a large outburst, one after a smaller outburst, and two during quiet periods. They compare these spectra to two kinds of light-scattering models: one for large porous dust grains, and one for a power-law mixture of small grains.

The quiet spectra look alike, and both are modeled by a typical range of grain sizes, so the comet's low-level activity appears stable. The two outburst spectra look very different from each other. The early-outburst spectrum is red and steep, best fit by many tiny grains, while the post-peak spectrum is neutral, best fit by relatively fewer small grains. The authors argue that this difference may not mean the two outbursts ejected different material. Instead, if gas drag accelerates smaller grains faster, the outer edge of the expanding dust cloud is finer-grained. The 2017 observation happened before peak brightness, so it sampled that outer fine-grained shell; the 2022 observation happened after peak, so it saw the whole cloud. They stress this is one possible reconciliation, not a proof, and note that no water ice absorption is clearly seen in any spectrum.

Extended reading notes

Core claim

The paper states: "In essence, we argue that we can explain the differences in our two outburst spectra as an optical depth effect without requiring any intrinsic differences in the kinds of materials ejected during the outbursts." If correct, the apparent grain size distribution of an outburst coma evolves from fine-dominated at early times to more representative at later times because smaller grains are accelerated faster by gas drag, so spectra of a single outburst should change systematically across its rise and fall.

Load-bearing premise

The load-bearing modeling assumption is that the fitted power-law index alpha in the Mie models captures the real grain size distribution rather than model degeneracy or contamination. The authors themselves note in Section 3 that both Hapke and Mie models can fit the quiescent spectra, that the 2017 outburst is poorly fit by Hapke, and in Section 4.2 that possible nuclear light could flatten the inferred size distribution. If alpha is not physically meaningful, the size-sorting interpretation collapses.

Share X Bluesky LinkedIn Reddit HN

Signed reviews

No signed human review yet.

Editorial analysis

A structured set of objections, weighed in public.

Desk editor's note, referee report, and a circularity audit.

Assumptions & free parameters 7 free parameters · 6 assumptions · 0 invented entities

The paper's conclusions rest on a large number of modeling choices and fitted parameters: grain size distribution shape, porosity, ice fraction, ice size, optical constants, and the timing interpretation of when each outburst spectrum was taken relative to peak brightness. These are acknowledged in the text but mean the central interpretation is not a parameter-free derivation; it is a model-dependent scenario inferred from four spectra.

free parameters (7)
  • alpha (Mie grain size power-law index) = 6.94 to 3.14 across epochs
    Free parameter in MCMC fits; the steepness of the size distribution drives the central grain-size interpretation.
  • fvac (dust porosity fraction) = 0.115 to 0.469
    Fitted; for the 2022 outburst it sits at the upper allowed boundary, weakening the result.
  • fice (areal ice fraction) = <0.001 to 0.064
    Fitted; used for the water-ice upper limits.
  • Dice (ice grain diameter) = 1.7 to 21 micrometers
    Fitted; largely unconstrained in most spectra.
  • Deff (Hapke dust grain effective diameter) = 234 to 271 micrometers
    Fitted but unconstrained in most cases, a sign of model degeneracy.
  • Grain radius range for Mie models = 0.5 to 50 micrometers
    Fixed by hand in Section 3.2 and not varied, which affects the inferred alpha values.
  • log(f) MCMC error fudge = approximately 1e-4
    Fitted to test whether the reported errors were reasonable; negligible, but it is an extra free parameter.
assumptions (6)
  • standard math Mie scattering and Hapke (2012) theory with Bruggeman mixing describe the optical behavior of cometary dust and ice grains.
    Used throughout Section 3; both are established scattering models but each carries assumptions about grain size regimes that are not independently verified for this coma.
  • domain assumption The coma can be represented as a mixture of amorphous carbon dust and pure water ice grains, with dust and ice as separate populations.
    Section 3 states this is a required assumption; optical constants are from Edoh (1983), Rouleau and Martin (1991), and Mastrapa et al. (2008).
  • ad hoc to paper The Mie dust size distribution is a single power law with radii between 0.5 and 50 micrometers.
    Section 3.2; the range was not varied and no multiple-population or shape-dependent porosity is considered, which the authors acknowledge may be too simple.
  • domain assumption Wavelength ranges with strong telluric absorption can be excluded without biasing the modeled parameters.
    Section 3; fits use the standard range and tests including and excluding bands. The 2022 February 8 fitted values change when the 1.95 to 2.05 micrometer band is excluded.
  • domain assumption The nucleus contributes negligible or known light to the quiescent and outburst spectra.
    Section 4.2 acknowledges nuclear contamination may be non-negligible and could flatten inferred size distributions, so the claim that the spectra are dust-dominated rests on this assumption.
  • ad hoc to paper The 2017 outburst spectrum was taken before the coma became optically thin, while the 2022 outburst spectrum was taken after peak brightness when the coma was optically thin.
    Section 4.1; this timing interpretation is the premise for the size-sorting explanation and is inferred from light curves, not directly measured at the moment of each spectrum.

how reviews work

0 comments
Cite this review

Pith. "Pith review of Activity-Induced Near-Infrared Variability at 29P/Schwassmann-Wachmann 1, 2017-2022." pith.science (2026). https://pith.science/paper/J24JDTO7

@misc{pith2026250412097,
  author       = {Pith},
  title        = {Pith review of: Activity-Induced Near-Infrared Variability at 29P/Schwassmann-Wachmann 1, 2017-2022},
  year         = {2026},
  howpublished = {\url{https://pith.science/paper/J24JDTO7}},
  note         = {Machine review of arXiv:2504.12097}
}
read the original abstract

29P/Schwassmann-Wachmann 1 (SW1) is both the first-discovered active Centaur and the most outburst-prone comet known. The nature of SW1's many outbursts, which regularly brighten the comet by five magnitudes or more, and what processes power them has been of particular interest since SW1's discovery in the 1920s. In this paper, we present and model four epochs of low-resolution near-infrared spectroscopy of SW1 taken with the NASA Infrared Telescope Facility and Lowell Discovery Telescope between 2017 and 2022. This dataset includes one large outburst, two periods of low activity ("quiescence" or "quiescent activity"), and one mid-sized outburst a few days after one of the quiescent observations. The two quiescent epochs appear similar in both spectral slope and modeled grain size distributions, but the two outbursts are significantly different. We propose that the two can be reconciled if smaller dust grains are accelerated more than larger ones, such that observations closer to the onset of an outburst are more sensitive to the finer-grained dust on the outside of the expanding cloud of material. These outbursts can thus appear very rapid but there is still a period in which the dust and gas are well-coupled. We find no strong evidence of water ice absorption in any of our spectra, suggesting that the areal abundance of ice-dominated grains is less than one percent. We conclude with a discussion of future modeling and monitoring efforts which might be able to further advance our understanding of this object's complicated activity patterns.

Figures

Figures reproduced from arXiv: 2504.12097 by the authors.

Figure 1
Figure 1. Photometric measurements of 29P/Schwassmann-Wachmann 1 are shown from the ATLAS forced photometry server and the British Astronomical Association, corrected for heliocentric and geocentric distances but not for phase angle, relative to the dates on which we obtained near-infrared spectra of the comet. Observations with IRTF/SpeX are shown as black lines in each of the three epochs, and our LDT/NIHTS observations are… view at source ↗
Figure 2
Figure 2. The four low-resolution near-infrared spectra of Schwassmann-Wachmann 1 are shown as black unfilled circles compared against the two classes of models described throughout Section 3 shown as solid colored lines. As before, the light gray regions indicate areas of significant telluric absorption. The models for the 2022 February 8 spectrum are those derived from fitting the data excluding the uncorrected telluric fea… view at source ↗

Discussion (0). Continue with ORCID to comment.

Reference graph

Works this paper leans on

47 extracted references · 11 canonical work pages

  1. [1]

    M., Choi, Y.-J., Weissman, P

    Bauer, J. M., Choi, Y.-J., Weissman, P. R., et al. 2008, PASP, 120, 393, doi: 10.1086/587552

    doi:10.1086/587552 2008

  2. [2]

    M., Grav, T., Fern´ andez, Y

    Bauer, J. M., Grav, T., Fern´ andez, Y. R., et al. 2017, AJ, 154, 53, doi: 10.3847/1538-3881/aa72df Bockel´ ee-Morvan, D., Biver, N.,

    doi:10.3847/1538-3881/aa72df 2017

  3. [3]

    A., et al

    Schambeau, C. A., et al. 2022a, A&A, 664, A95, doi: 10.1051/0004-6361/202243241 —. 2022b, A&A, 664, A95, doi: 10.1051/0004-6361/202243241

    doi:10.1051/0004-6361/202243241

  4. [4]

    Bruggeman, V. D. 1935, Annalen der physik, 416, 636

    work page 1935

  5. [5]

    S., & Cochran, W

    Cochran, A., Barker, E. S., & Cochran, W. 1980, AJ, 85, 474, doi: 10.1086/112699

    work page doi:10.1086/112699 1980

  6. [6]

    L., & Cochran, W

    Cochran, A. L., & Cochran, W. D. 1991, Icarus, 90, 172, doi: 10.1016/0019-1035(91)90077-7

    doi:10.1016/0019-1035(91)90077-7 1991

  7. [7]

    Barker, E. S. 1982, ApJ, 254, 816, doi: 10.1086/159793

    work page doi:10.1086/159793 1982

  8. [8]

    C., Vacca, W

    Cushing, M. C., Vacca, W. D., & Rayner, J. T. 2004, PASP, 116, 362, doi: 10.1086/382907

    doi:10.1086/382907 2004

Show all 47 references
  1. [9]

    1983, PhD thesis, University of Arizona Fern´ andez, Y

    Edoh, O. 1983, PhD thesis, University of Arizona Fern´ andez, Y. R., Kelley, M. S., Lamy, P. L., et al. 2013, Icarus, 226, 1138, doi: 10.1016/j.icarus.2013.07.021

    1983 doi

  2. [10]

    2025, In review at /psj

    Firgard, M., & Kareta, T. 2025, In review at /psj

    2025

  3. [11]

    W., Lang, D., & Goodman, J

    Foreman-Mackey, D., Hogg, D. W., Lang, D., & Goodman, J. 2013, PASP, 125, 306, doi: 10.1086/670067

    2013 doi

  4. [12]

    N., & Nesvorny, D

    Raymond, S. N., & Nesvorny, D. 2023, ApJ, 942, 92, doi: 10.3847/1538-4357/acaa3a

    2023 doi

  5. [13]

    C., et al

    Gustafsson, A., Moskovitz, N., Cushing, M. C., et al. 2021, PASP, 133, 035001, doi: 10.1088/1538-3873/abe2f4

    2021 doi

  6. [14]

    2012, Theory of Reflectance and Emittance Spectroscopy, doi: 10.1017/CBO9781139025683

    Hapke, B. 2012, Theory of Reflectance and Emittance Spectroscopy, doi: 10.1017/CBO9781139025683

    2012 doi

  7. [15]

    N., Tonry, J

    Heinze, A. N., Tonry, J. L., Denneau, L., et al. 2018, AJ, 156, 241, doi: 10.3847/1538-3881/aae47f10. 48550/arXiv.1804.02132

    2018 doi arXiv

  8. [16]

    2019, MNRAS, 486, 5614, doi: 10.1093/mnras/stz1200

    Ivanova, O., Agapitov, O., Odstrcil, D., et al. 2019, MNRAS, 486, 5614, doi: 10.1093/mnras/stz1200

    2019 doi

  9. [17]

    1990, ApJ, 351, 277, doi: 10.1086/168463 SW1 NIR Variability 21

    Jewitt, D. 1990, ApJ, 351, 277, doi: 10.1086/168463 SW1 NIR Variability 21

    1990 doi

  10. [18]

    W., Harris, W

    Kareta, T., Noonan, J. W., Harris, W. M., & Springmann, A. 2023, PSJ, 4, 85, doi: 10.3847/PSJ/accc28

    2023 doi

  11. [19]

    2019, AJ, 158, 255, doi: 10.3847/1538-3881/ab505f

    Kareta, T., Sharkey, B., Noonan, J., et al. 2019, AJ, 158, 255, doi: 10.3847/1538-3881/ab505f

    2019 doi

  12. [20]

    M., Schambeau, C., et al

    Kareta, T., Woodney, L. M., Schambeau, C., et al. 2021, PSJ, 2, 48, doi: 10.3847/PSJ/abe23d

    2021 doi

  13. [21]

    Larson, S. M. 1980, ApJL, 238, L47, doi: 10.1086/183255

    1980 doi

  14. [22]

    M., Steckloff, J

    Lisse, C. M., Steckloff, J. K., Prialnik, D., et al. 2022, PSJ, 3, 251, doi: 10.3847/PSJ/ac9468

    2022 doi

  15. [23]

    E., Binzel, R

    Marsset, M., DeMeo, F. E., Binzel, R. P., et al. 2020, ApJS, 247, 73, doi: 10.3847/1538-4365/ab7b5f

    2020 doi

  16. [24]

    A., et al

    Sandford, S. A., et al. 2008, Icarus, 197, 307, doi: 10.1016/j.icarus.2008.04.008

    2008 doi

  17. [25]

    2022, in AAS/Division for Planetary Sciences Meeting Abstracts, Vol

    Miles, R., & BAA Comet Section 29P Observing Campaign. 2022, in AAS/Division for Planetary Sciences Meeting Abstracts, Vol. 54, AAS/Division for Planetary Sciences Meeting Abstracts, 414.03

    2022

  18. [26]

    A., Mottola, S., et al

    Miles, R., Faillace, G. A., Mottola, S., et al. 2016, Icarus, 272, 327, doi: 10.1016/j.icarus.2015.11.019

    2016 doi

  19. [27]

    2008, A&A, 479, L45, doi: 10.1051/0004-6361:20079130

    Wilke, S., & Carraro, G. 2008, A&A, 479, L45, doi: 10.1051/0004-6361:20079130

    2008 doi

  20. [28]

    W., Rinaldi, G., Feldman, P

    Noonan, J. W., Rinaldi, G., Feldman, P. D., et al. 2021, AJ, 162, 4, doi: 10.3847/1538-3881/abf8b4

    2021 doi

  21. [29]

    2012, ApJ, 752, 15, doi: 10.1088/0004-637X/752/1/15

    Ootsubo, T., Kawakita, H., Hamada, S., et al. 2012, ApJ, 752, 15, doi: 10.1088/0004-637X/752/1/15

    2012 doi

  22. [30]

    B., et al

    Pajola, M., H¨ ofner, S., Vincent, J. B., et al. 2017, Nature Astronomy, 1, 0092, doi: 10.1038/s41550-017-0092

    2017 doi

  23. [31]

    Protopapa, S., Kelley, M. S. P., Yang, B., et al. 2018, ApJL, 862, L16, doi: 10.3847/2041-8213/aad33b

    2018 doi

  24. [32]

    T., Toomey, D

    Rayner, J. T., Toomey, D. W., Onaka, P. M., et al. 2003, PASP, 115, 362, doi: 10.1086/367745

    2003 doi

  25. [33]

    1958, PASP, 70, 272, doi: 10.1086/127223

    Roemer, E. 1958, PASP, 70, 272, doi: 10.1086/127223

    1958 doi

  26. [34]

    Rouleau, F., & Martin, P. G. 1991, ApJ, 377, 526, doi: 10.1086/170382

    1991 doi

  27. [35]

    K., et al

    Sarid, G., Volk, K., Steckloff, J. K., et al. 2019, ApJL, 883, L25, doi: 10.3847/2041-8213/ab3fb3

    2019 doi

  28. [36]

    H., Mueller, B

    Samarasinha, N. H., Mueller, B. E. A., & Woodney, L. M. 2017, Icarus, 284, 359, doi: 10.1016/j.icarus.2016.11.026

    2017 doi

  29. [37]

    H., et al

    Samarasinha, N. H., et al. 2021, PSJ, 2, 126, doi: 10.3847/PSJ/abfe6f

    2021 doi

  30. [38]

    H., Woodney, L

    Samarasinha, N. H., Woodney, L. M., & Kundu, A. 2019, AJ, 158, 259, doi: 10.3847/1538-3881/ab53e2

    2019 doi

  31. [39]

    C., & Jewitt, D

    Senay, M. C., & Jewitt, D. 1994, Nature, 371, 229, doi: 10.1038/371229a0

    1994 doi

  32. [40]

    W., Young, D

    Shingles, L., Smith, K. W., Young, D. R., et al. 2021, Transient Name Server AstroNote, 7, 1

    2021

  33. [41]

    W., Smartt, S

    Smith, K. W., Smartt, S. J., Young, D. R., et al. 2020, PASP, 132, 085002, doi: 10.1088/1538-3873/ab936e10. 48550/arXiv.2003.09052

    2020 doi arXiv

  34. [42]

    K., Graves, K., Hirabayashi, M., Melosh, H

    Steckloff, J. K., Graves, K., Hirabayashi, M., Melosh, H. J., & Richardson, J. E. 2016, Icarus, 272, 60, doi: 10.1016/j.icarus.2016.02.026

    2016 doi

  35. [43]

    K., Sarid, G., Volk, K., et al

    Steckloff, J. K., Sarid, G., Volk, K., et al. 2020, ApJL, 904, L20, doi: 10.3847/2041-8213/abc888

    2020 doi

  36. [44]

    M., Groussin, O., Schultz, P

    Sunshine, J. M., Groussin, O., Schultz, P. H., et al. 2007, Icarus, 190, 284, doi: 10.1016/j.icarus.2007.04.024

    2007 doi

  37. [45]

    L., Denneau, L., Heinze, A

    Tonry, J. L., Denneau, L., Heinze, A. N., et al. 2018, PASP, 130, 064505, doi: 10.1088/1538-3873/aabadf10. 48550/arXiv.1802.00879 Trigo-Rodr´ ıguez, J. M., Garc´ ıa-Hern´ andez, D. A., S´ anchez, A., et al. 2010, MNRAS, 409, 1682, doi: 10.1111/j.1365-2966.2010.17425.x Trigo-Ro...

    2018 doi arXiv

  38. [46]

    Whipple, F. L. 1980, AJ, 85, 305, doi: 10.1086/112676 22 Kareta et al

    1980 doi

  39. [47]

    2020, AJ, 159, 136, doi: 10.3847/1538-3881/ab6e68

    Wierzchos, K., & Womack, M. 2020, AJ, 159, 136, doi: 10.3847/1538-3881/ab6e68

    2020 doi

Pith tools

Reviewed August 16, 2026 · model on record in the stance chip above.