Zodiacal Light Spectroscopy with JWST/MIRI

Interplanetary dust particles (IDPs), the source materials of the zodiacal light, are supposed to originate from comets and some asteroids (Vernazza et al. 2015 [1]). So far, our comprehension of their composition relies primarily on the analysis of IDPs collected in the stratosphere (e.g. Sandford 1989 [2]).

The Mid-InfraRed Instrument (MIRI) of the James Webb Space Telescope (JWST) has the capability to provide spectra of the zodiacal light at an unprecedented spectral resolution and across a broad spectral range, assuming it has a good signal-to-noise ratio (SNR), and therefore a sufficiently long acquisition time. Rather than dedicating observation time to zodiacal dust, it is possible to exploit backgrounds with long exposures times, such as those in the Cycle 2 GO program GO  2820 (PI: Pierre Vernazza).

This program includes six background fields associated with observations of the small objects (1) Bienor, (2) Chariklo, (3) 2020 VF1, (4) 2013 LU28, (5) 2002 GG166 and (6) 1999 OX3.

The data are reduced through the JWST calibration pipeline last version, which significantly reduces the fringing effect, especially for channels 3 and 4. In order to remove the thermal contribution from JWST, a synthetic background is generated based on JWST Backgrounds Tool (Rigby et al. 2023 [3]), depending on the time and location of the observation, and is rescaled to match the total observed background flux. Through these steps, the average SNR between 7µm  and 25 µm is above 100 across all datasets, thus allowing the detection of relatively weak spectral features.

Olivine and pyroxene features between 8 µm and 12 µm are detected and consistent with prior measurements from AKARI/IRC (Takahashi et al. 2019 [4]) , thereby enhancing the reliability of the features observed in MIRI spectra. Several significant features not related to olivine and pyroxene are detected. Over these six backgrounds, close in latitude, variation of intensity and shape of features are observed. These spectral differences are being assessed in relation to the DIRBE zodiacal model (Kelsall et al.1998 [5]) modelised by the ZodiPy Python package (San et al. 2022 [6]). 

This investigation will involve a comparison of these spectra with those of various IDPs (anhydrous and hydrous ; e.g. Sandford and Bradley 1989 [2]) and an exploration of potential links with major dust bands produced by recent asteroid break-ups (Brož et al. 2024 [7]) and Marsset et al. 2024 [8]).

References

[1] Vernazza et al. 2015, Interplanetary Dust Particles as Samples of Icy Asteroids. The Astrophysical Journal, 806(2):204, June 2015.

[2] Sandford and Bradley 1998, Interplanetary dust particles collected in the stratosphere: Observations of atmospheric heating and constraints on their interrelationship and sources. Icarus, 82(1):146–166, 1989.

[3] J. Rigby et al. 2023, How Dark the Sky: The JWST Backgrounds. Publications of the Astronomical Society of the Pacific, 135(1046):048002, April 2023.

[4] Takahashi et al. 2019, Mid-infrared spectroscopy of zodiacal emission with AKARI/IRC. Publications of the Astronomical Society of Japan, 71(6):110, 11 2019.

[5] Kelsall et al.1998, The COBE Diffuse Infrared Background Experiment Search for the Cosmic Infrared Background. II. Model of the Interplanetary Dust Cloud. The Astrophysical Journal, 508(1):44, nov 1998.

[6] San et al. 2022, COSMOGLOBE: Simulating zodiacal emission with ZodiPy.  A & A, 666:A107, 2022.

[7] Brož et al. 2024, Young asteroid families as the primary source of meteorites. Nature, 634(8034):566–571, Oct 2024. 

[8] Marsset et al. 2024,  The Massalia asteroid family as the origin of ordinary L chondrites. Nature, 634(8034):561–565, Oct 2024.