Icy Worlds

JWST Reveals Varied Origins Between Jupiter’s Irregular Satellites

By Keith Cowing
Status Report
astro-ph.EP
February 5, 2025
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JWST Reveals Varied Origins Between Jupiter’s Irregular Satellites
Irregular satellite orbital inclinations and semimajor axes (normalized to Jupiter’s Hill radius). Family groupings are given as indicated. The prograde population is dominated in mass and number by the Himalia family. The retrograde population is categorized into three orbital families, with the more widely dispersed Pasiphae and Ananke families and the more tightly grouped Carme family. This work studies the Himalia, Carme, Pasiphae, and Ananke families, as well as the isolated satellite Themisto. Orbital parameters from JPL Horizons. — astro-ph.EP

We report observations of eight Jovian irregular satellites with JWST’s NIRSpec instrument: Himalia, Elara, Pasiphae, Sinope, Lysithea, Carme, Ananke, and Themisto. Irregular satellite families, which are presumed to have formed via collisions, contain various Trojan-like and C-type-asteroid-like surfaces.

We sample the three largest members of the Himalia satellite family, detecting the presence of complexed CO2 and a unique absorption band from ∼2.7−3.6 μm whose character correlates with satellite size. The two largest irregular satellites, Himalia family members Himalia and Elara, contain ammoniated phyllosilicates that are not seen in the meteorite inventory.

We propose that the Himalia parent body was heterogeneous and formed with materials similar to Ceres-like ammonium-bearing asteroids. Several small (D∼10km) irregular satellites closely track the colors and absorption bands of “red” Jovian Trojans, demonstrating that these compositions are retained amongst the products of collisions that occurred after Jovian capture.

We report the first detection of aqueous alteration products in the retrograde satellite swarm, finding Ananke’s 3 micron band to closely match phyllosilicates seen in C2 chondrites.

Notably, objects with OH absorption features similar to the Trojan asteroid Eurybates are found in both the retrograde Pasiphae family and the prograde Himalia family, confounding a simple link between such materials and a single surface type. The irregular satellites appear consistent with some materials that experienced alteration from liquid water and others that did not.

Consequently, Jupiter may have captured bodies that formed from different initial compositions, or bodies that experienced different levels of heating, driving differential alteration processes.

Benjamin N. L. Sharkey, Andrew S. Rivkin, Richard J. Cartwright, Bryan J. Holler, Joshua P. Emery, Cristina Thomas

Comments: 20 Pages, 11 Figures, 2 Tables. Submitted to PSJ
Subjects: Earth and Planetary Astrophysics (astro-ph.EP)
Cite as: arXiv:2501.16484 [astro-ph.EP] (or arXiv:2501.16484v1 [astro-ph.EP] for this version)
https://doi.org/10.48550/arXiv.2501.16484
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Submission history
From: Benjamin Sharkey
[v1] Mon, 27 Jan 2025 20:40:54 UTC (1,649 KB)
https://arxiv.org/abs/2501.16484
Astrobiology,

Explorers Club Fellow, ex-NASA Space Station Payload manager/space biologist, Away Teams, Journalist, Lapsed climber, Synaesthete, Na’Vi-Jedi-Freman-Buddhist-mix, ASL, Devon Island and Everest Base Camp veteran, (he/him) 🖖🏻