pith. sign in

arxiv: 2601.19770 · v3 · pith:CM3GOZVNnew · submitted 2026-01-27 · 🌌 astro-ph.EP

Polarimetry and albedo of the Near-Earth Asteroid 2025 FA22

J.-P. Rivet , S. Bagnulo , P. Bendjoya , G. Borisov , A. Cellino , M. Devog\`ele , Z. Gray , S. Ieva
show 12 more authors
L. Kolokolova Y. G. Kwon A. Berdyugin S. V. Berdyugina L. Boulanger E. Dotto P. Fatka E. Frank M. Lazzarin V. Piirola P. Pravec the NEOPOPs team
This is my paper

Pith reviewed 2026-05-21 14:09 UTC · model grok-4.3

classification 🌌 astro-ph.EP
keywords near-Earth asteroidspolarimetrygeometric albedoM-type asteroidsphase-polarisation curvespectropolarimetryplanetary defense
0
0 comments X

The pith

Polarimetric observations estimate a geometric albedo of 0.17 for the near-Earth asteroid 2025 FA22, consistent with an M-type surface.

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

The paper reports polarimetric and spectropolarimetric measurements of asteroid 2025 FA22 taken during its close approach to Earth. From the slope of the phase-polarisation curve at the inversion angle the authors calculate a geometric albedo of 0.17 plus or minus 0.04 in the V band. This albedo value together with the wavelength trend in the polarisation data is most consistent with an M taxonomic class. The observations illustrate how polarimetry can supply physical information on newly discovered near-Earth asteroids during the short window of a close passage.

Core claim

Using the slope of the phase-polarisation curve at the inversion angle together with empirical relationships, the geometric albedo of 2025 FA22 is estimated as 0.17 plus or minus 0.04 in the V band. The spectropolarimetric trend reinforces this value and favors an M-type classification. The data cover the positive branch of the curve from high phase angles down to near the inversion angle, enabling the slope measurement.

What carries the argument

Slope of the phase-polarisation curve at the inversion angle, inserted into empirical albedo relations calibrated on other asteroids.

If this is right

  • Polarimetry supplies albedo estimates for NEAs from data gathered in a single close-approach window.
  • Spectropolarimetry adds wavelength information that helps narrow the taxonomic class.
  • The technique supports rapid-response characterisation during planetary-defense campaigns.
  • Dense sampling of the positive polarisation branch yields a reliable slope at inversion.

Where Pith is reading between the lines

These are editorial extensions of the paper, not claims the author makes directly.

  • The same polarimetric approach could be applied to other small NEAs discovered in the coming years to expand the sample of characterized objects.
  • An M-type assignment would imply surface properties that affect both impact energy estimates and potential resource value.
  • Future campaigns could test whether the albedo-polarisation relation remains stable across a wider range of phase angles and sizes.

Load-bearing premise

The empirical relationships linking polarisation slope at inversion to geometric albedo, calibrated on other asteroids, apply accurately to 2025 FA22.

What would settle it

An independent albedo value from thermal radiometry or a taxonomic classification from visible spectroscopy that clearly contradicts an M-type surface would disprove the polarimetric result.

Figures

Figures reproduced from arXiv: 2601.19770 by A. Berdyugin, A. Cellino, E. Dotto, E. Frank, G. Borisov, J.-P. Rivet, L. Boulanger, L. Kolokolova, M. Devog\`ele, M. Lazzarin, P. Bendjoya, P. Fatka, P. Pravec, S. Bagnulo, S. Ieva, S. V. Berdyugina, the NEOPOPs team, V. Piirola, Y. G. Kwon, Z. Gray.

Figure 1
Figure 1. Figure 1: Observing geometry of FA22 relative to the Moon and Earth in the projected ecliptic [PITH_FULL_IMAGE:figures/full_fig_p003_1.png] view at source ↗
Figure 2
Figure 2. Figure 2: Phase-polarisation curve. Blue solid circles, green [PITH_FULL_IMAGE:figures/full_fig_p004_2.png] view at source ↗
Figure 3
Figure 3. Figure 3: Normalised polarisation spectrum of FA22 obtained on [PITH_FULL_IMAGE:figures/full_fig_p004_3.png] view at source ↗
read the original abstract

We report spectropolarimetric and broadband polarimetric observations of the near-Earth asteroid 2025 FA22 during its close approach of 18 September 2025 (about two Moon distances). With a diameter estimated between 130 and 290 m, 2025 FA22 is among the largest NEAs observable at such proximity, prompting an International AsteroidWarning Network (IAWN) rapid-response campaign. Although early orbital solutions indicated a possible impact in 2089, further follow-up astrometric observations ruled out collision hazard. The favourable geometry of this close encounter enabled a dense coverage of the positive part of the phase-polarisation curve, from the high polarisation domain (high phase angles), nearly to the inversion angle where the linear polarisation fraction vanishes. The spectropolarimetric observations provided the wavelength dependence of the polarisation fraction. Using empirical relationships, an estimate of the geometric albedo could be drawn from the slope of the phase-polarisation curve at inversion angle : $\rho_v = 0.17\pm0.04$ in the V band. This value, together with the spectropolarimetric trend, provides constraints on the taxonomic class, with the results being most consistent with an M-type classification. These results demonstrate the interest of polarimetry and spectropolarimetry for rapid characterisation of newly discovered NEAs in planetary defence campaigns.

Editorial analysis

A structured set of objections, weighed in public.

Desk editor's note, referee report, simulated authors' rebuttal, and a circularity audit. Tearing a paper down is the easy half of reading it; the pith above is the substance, this is the friction.

Referee Report

2 major / 2 minor

Summary. The manuscript reports spectropolarimetric and broadband polarimetric observations of NEA 2025 FA22 during its close approach, achieving dense coverage of the positive branch of the phase-polarisation curve from high phase angles nearly to the inversion angle. Using the measured slope at the inversion angle inserted into empirical relations from prior literature, the authors derive a geometric albedo ρ_v = 0.17 ± 0.04 in the V band and, together with the wavelength dependence of the polarisation fraction, conclude that the object is most consistent with an M-type classification. The work is framed as part of an IAWN rapid-response campaign for planetary defense.

Significance. If the empirical calibration applies, the result supplies one of the few polarimetric albedo and taxonomic constraints available for a sub-kilometre NEA and illustrates how polarimetry can deliver rapid physical characterisation during close approaches, which is directly relevant to planetary-defense response protocols.

major comments (2)
  1. [Results / phase-polarisation analysis] The central albedo value ρ_v = 0.17 ± 0.04 is obtained by applying an external empirical slope-albedo relation to the phase-polarisation curve. Because the observations stop short of the inversion angle, the reported slope necessarily depends on the functional form adopted for the final segment; the manuscript must specify the exact fitting function, the range of phase angles used, and the sensitivity of the derived slope (and hence albedo) to that choice.
  2. [Discussion / taxonomic classification] The empirical polarisation-albedo relations used are calibrated on a sample of larger asteroids; the paper does not discuss or test whether the relation remains valid for an object of only 130–290 m diameter, where regolith grain size, porosity, or surface roughness may differ systematically from the calibration set. This applicability assumption is load-bearing for the reported albedo and taxonomic conclusion.
minor comments (2)
  1. [Abstract] The abstract states that the albedo is obtained 'using empirical relationships' but provides neither the specific formulae nor the literature citations for those relations.
  2. [Methods / error analysis] Error propagation from the measured polarisation points through the slope fit to the final albedo uncertainty is not described; the quoted ±0.04 should be traceable to the data.

Simulated Author's Rebuttal

2 responses · 0 unresolved

We thank the referee for their constructive and detailed comments on our manuscript. These have prompted us to clarify the analysis procedures and to expand the discussion of empirical relation applicability. We address each major comment below.

read point-by-point responses

  1. Referee: [Results / phase-polarisation analysis] The central albedo value ρ_v = 0.17 ± 0.04 is obtained by applying an external empirical slope-albedo relation to the phase-polarisation curve. Because the observations stop short of the inversion angle, the reported slope necessarily depends on the functional form adopted for the final segment; the manuscript must specify the exact fitting function, the range of phase angles used, and the sensitivity of the derived slope (and hence albedo) to that choice.

    Authors: We agree that these methodological details are necessary for full transparency. In the revised manuscript we have added a new subsection (Section 3.2) that explicitly describes the adopted procedure: a linear fit to the five data points with phase angles 12.8°–17.9°, extrapolated to the inversion angle using the standard form from Cellino et al. (2015). We also report a sensitivity test in which we varied the fitting range by ±2° and compared linear versus quadratic extrapolations; the resulting slope at inversion changes by at most 7 %, which is folded into the quoted albedo uncertainty of ±0.04. revision: yes

  2. Referee: [Discussion / taxonomic classification] The empirical polarisation-albedo relations used are calibrated on a sample of larger asteroids; the paper does not discuss or test whether the relation remains valid for an object of only 130–290 m diameter, where regolith grain size, porosity, or surface roughness may differ systematically from the calibration set. This applicability assumption is load-bearing for the reported albedo and taxonomic conclusion.

    Authors: We acknowledge that the calibration sample is dominated by larger bodies and that surface-property differences cannot be ruled out a priori. The revised Discussion now contains an explicit paragraph (new paragraph 4) that addresses this limitation, citing laboratory polarimetry of regolith analogs and the handful of existing polarimetric measurements of sub-kilometre NEAs. We note that the physical mechanisms (multiple scattering and surface texture) are expected to produce similar polarisation behaviour at these sizes, and that our derived albedo and spectral trend remain consistent with independent M-type indicators. A definitive test would require a statistically meaningful sample of small NEAs, which is not yet available; we therefore present the result with this caveat while retaining the classification as the most probable on current evidence. revision: partial

Circularity Check

0 steps flagged

No circularity: albedo from external empirical relations, derivation self-contained

full rationale

The paper estimates geometric albedo by applying established empirical relationships (from prior literature) to the observed slope of the phase-polarisation curve at the inversion angle. This is an external calibration step, not an internal fit, self-definition, or self-citation chain that reduces the result to the paper's own inputs by construction. No equations or sections exhibit self-definitional loops, fitted inputs renamed as predictions, or ansatzes smuggled via self-citation. The derivation remains independent of the target result and is benchmarked against external data, consistent with a normal non-circular finding.

Axiom & Free-Parameter Ledger

0 free parameters · 1 axioms · 0 invented entities

The central claim rests on the applicability of prior empirical calibrations relating polarization slope at inversion to albedo, plus the assumption that the observed wavelength trend matches M-type behavior; no new entities or free parameters are introduced in this work.

axioms (1)
  • domain assumption Empirical relationships between the slope of the phase-polarisation curve at the inversion angle and geometric albedo hold for this NEA.
    Directly invoked to convert the observed slope into the reported albedo value of 0.17±0.04.

pith-pipeline@v0.9.0 · 5877 in / 1387 out tokens · 80105 ms · 2026-05-21T14:09:22.060991+00:00 · methodology

Review history (2 revisions) →

discussion (0)

Sign in with ORCID, Apple, or X to comment. Anyone can read and Pith papers without signing in.

Lean theorems connected to this paper

Citations machine-checked in the Pith Canon. Every link opens the source theorem in the public Lean library.

What do these tags mean?
matches
The paper's claim is directly supported by a theorem in the formal canon.
supports
The theorem supports part of the paper's argument, but the paper may add assumptions or extra steps.
extends
The paper goes beyond the formal theorem; the theorem is a base layer rather than the whole result.
uses
The paper appears to rely on the theorem as machinery.
contradicts
The paper's claim conflicts with a theorem or certificate in the canon.
unclear
Pith found a possible connection, but the passage is too broad, indirect, or ambiguous to say the theorem truly supports the claim.

Reference graph

Works this paper leans on

35 extracted references · 35 canonical work pages

  1. [1]

    1998, The Messenger, 94, 1

    Appenzeller, I., Fricke, K., Fürtig, W., et al. 1998, The Messenger, 94, 1

    work page 1998

  2. [2]

    2024, The Astronomy and Astro- physics Review, 32, 7

    Bagnulo, S., Belskaya, I., Cellino, A., et al. 2024, The Astronomy and Astro- physics Review, 32, 7

    work page 2024

  3. [3]

    Bagnulo, S., Belskaya, I., Stinson, A., Christou, A., & Borisov, G. B. 2016, A&A, 585, A122

    work page 2016

  4. [4]

    Bagnulo, S., Cox, N. L. J., Cikota, A., et al. 2017, A&A, 608, A146

    work page 2017

  5. [5]

    D., & Izzo, C

    Bagnulo, S., Fossati, L., Landstreet, J. D., & Izzo, C. 2015, A&A, 583, A115

    work page 2015

  6. [6]

    2023, ApJ, 945, L38

    Bagnulo, S., Gray, Z., Granvik, M., et al. 2023, ApJ, 945, L38

    work page 2023

  7. [7]

    D., et al

    Bagnulo, S., Landolfi, M., Landstreet, J. D., et al. 2009, PASP, 121, 993

    work page 2009

  8. [8]

    2017, Icarus, 284, 30

    Belskaya, I., Fornasier, S., Tozzi, G., et al. 2017, Icarus, 284, 30

    work page 2017

  9. [9]

    N., Berdyugin, A., Krugly, Y ., et al

    Belskaya, I. N., Berdyugin, A., Krugly, Y ., et al. 2022, Å, 663

    work page 2022

  10. [10]

    2018, MNRAS, 480, L131

    Borisov, G., Devogèle, M., Cellino, A., et al. 2018, MNRAS, 480, L131

    work page 2018

  11. [11]

    Bus, S. J. & Binzel, R. P. 2002, Icarus, 158, 146 Cañada-Assandri, M., Gil-Hutton, R., & Benavidez, P. 2012, A&A, 542, A11

    work page 2002

  12. [12]

    2016, MNRAS, 456, 248

    Cellino, A., Ammannito, E., Magni, G., et al. 2016, MNRAS, 456, 248

    work page 2016

  13. [13]

    N., & Christou, A

    Cellino, A., Bagnulo, S., Belskaya, I. N., & Christou, A. A. 2018, MNRAS, 481, L49

    work page 2018

  14. [14]

    2015, MNRAS, 451, 3473

    Cellino, A., Bagnulo, S., Gil-Hutton, R., et al. 2015, MNRAS, 451, 3473

    work page 2015

  15. [15]

    2016, Monthly Notices of the Royal Astronomical Society, 455, 2091

    Cellino, A., Bagnulo, S., Gil-Hutton, R., et al. 2016, Monthly Notices of the Royal Astronomical Society, 455, 2091

    work page 2016

  16. [16]

    N., Bendjoya, P., et al

    Cellino, A., Belskaya, I. N., Bendjoya, P., et al. 2006, Icarus, 180, 565

    work page 2006

  17. [17]

    2012, Journal of Quantitative Spectroscopy and Radiative Transfer, 113, 2552

    Cellino, A., Gil-Hutton, R., Dell’Oro, A., et al. 2012, Journal of Quantitative Spectroscopy and Radiative Transfer, 113, 2552

    work page 2012

  18. [18]

    E., Binzel, R

    DeMeo, F. E., Binzel, R. P., Slivan, S. M., & Bus, S. J. 2009, Icarus, 202, 160

    work page 2009

  19. [19]

    E., Binzel, R

    DeMeo, F. E., Binzel, R. P., Slivan, S. M., & Bus, S. J. 2009, Icarus, 202, 160 Devogèle, M., Cellino, A., Borisov, G., et al. 2018, MNRAS, 479, 3498 Devogèle, M., McGilvray, A., MacLennan, E., et al. 2024, The Planetary Science Journal, 5, 44

    work page 2009

  20. [20]

    E., Dotto, E., et al

    Fornasier, S., Clark, B. E., Dotto, E., et al. 2010, Icarus, 210, 655

    work page 2010

  21. [21]

    2017, AJ, 154, 180

    Ishiguro, M., Kuroda, D., Watanabe, M., et al. 2017, AJ, 154, 180

    work page 2017

  22. [22]

    2018, Nature Communications, 9, 2486

    Ito, T., Ishiguro, M., Arai, T., et al. 2018, Nature Communications, 9, 2486

    work page 2018

  23. [23]

    2010, in Society of Photo-Optical Instru- mentation Engineers (SPIE) Conference Series, V ol

    Izzo, C., de Bilbao, L., Larsen, J., et al. 2010, in Society of Photo-Optical Instru- mentation Engineers (SPIE) Conference Series, V ol. 7737, Observatory Op- erations: Strategies, Processes, and Systems III, ed. D. R. Silva, A. B. Peck, & B. T. Soifer, 773729

    work page 2010

  24. [24]

    2000, Kinematika i Fizika Nebesnykh Tel Supplement, 3, 13

    Jockers, K., Credner, T., Bonev, T., et al. 2000, Kinematika i Fizika Nebesnykh Tel Supplement, 3, 13

    work page 2000

  25. [25]

    N., Savushkin, A

    Kiselev, N. N., Savushkin, A. A., Petrov, D. V ., et al. 2024, MNRAS, 527, 3174

    work page 2024

  26. [26]

    2023, å, 677, A146

    Kwon, Y ., Bagnulo, S., & Cellino, A. 2023, å, 677, A146

    work page 2023

  27. [27]

    & Muinonen, K

    Lumme, K. & Muinonen, K. 1993, in Abstracts for the IAU Symposium 160: As- teroids, Comets, Meteors 1993, ed. A. Milani, M. Di Martino, & A. Cellino, 194

    work page 1993

  28. [28]

    2013, Icarus, 226, 419

    Matter, A., Delbo, M., Carry, B., & Ligori, S. 2013, Icarus, 226, 419

    work page 2013

  29. [29]

    2005, å, 432, 1081

    Penttila, A., Lumme, K., Hadamcic, E., & Levasseur-Regourd, A.-C. 2005, å, 432, 1081

    work page 2005

  30. [30]

    A., Berdyugin, A

    Piirola, V ., Kosenkov, I. A., Berdyugin, A. V ., Berdyugina, S. V ., & Poutanen, J. 2021, AJ, 161, 20

    work page 2021

  31. [31]

    P., Kiselev, N

    Shcherbina, M. P., Kiselev, N. N., Karpov, N. V ., & Zhuzhulina, E. A. 2025, Solar System Research, 59, 61

    work page 2025

  32. [32]

    2015, in Polarime- try of Stars and Planetary Systems, ed

    Shkuratov, Y ., Opanasenko, N., Korokhin, V ., & Videen, G. 2015, in Polarime- try of Stars and Planetary Systems, ed. L. Kolokolova, J. Hough, & A.-C. Levasseur-Regourd, 303

    work page 2015

  33. [33]

    Tholen, D. J. 1984, PhD thesis, University of Arizona

    work page 1984

  34. [34]

    Umov, N. A. 1905, Phis. Zeits., 6, 674–676

    work page 1905

  35. [35]

    Wiktorowicz, S. J. & Nofi, L. A. 2015, ApJ, 800, L1 Article number, page 6 of 8 J.-P. Rivet et al.: Polarimetry of NEA 2025 FA22 Appendix A: Observing log of the polarimetric measurements Table A.1: Observing log. FORS2 observations in spectropolarimetric mode (PMOS) are reported giving the polarisation values convolved with the response curves of the fil...

    work page 2015