The Himalia Group

Inside the Hill sphere

The Nearest Carbonaceous Feedstock Is Already in the Jovian System

Four prograde irregular satellites at 11.5 million kilometers, and 22% of Jupiter’s Hill radius.

Jupiter has five irregular-satellite families. The Himalia group — Himalia, Elara, Lysithea and Leda — is prograde, clustered near 11.46 million kilometers at roughly 27° inclination, and is believed to be a single collisional family. Jupiter’s Hill radius is 53.1 million kilometers, so the group sits at 22% of it. These bodies are inside the Jovian system, and a transfer to them never enters heliocentric space.

That geometry is the whole finding. The conclusion that structural feedstock is a permanent Earth import was reached without considering the captured carbonaceous bodies already inside Jupiter’s gravitational domain, and it does not survive their inclusion.

Modeled. The plane change is folded into the arrival burn and costs about 1.9 km/s of the 4.5. Half the Δv and one-thirtieth the transit time of the best Trojan option, with no phasing problem at all, because the transfer never leaves Jupiter’s gravitational domain.

A feedstock shipment from Himalia arrives in two months. From the Trojan swarms it arrives in five to 20 years. From Earth it arrives in 2.73. Modeled

Composition

The Spectroscopy Improved in 2025, and It Improved in the Useful Direction

Bands at 2.7 and 3.05 µm on Himalia and Elara indicate ammoniated phyllosilicates.

Near-infrared spectroscopy of Himalia, Elara and Carme finds surfaces dominated by opaque materials of the kind seen in carbonaceous chondrite meteorites, with magnetite modeled as the dominant mineral phase on Himalia and Elara, and Himalia’s spectral shape resembling the large main-belt C-type asteroid 52 Europa. Carme is spectrally distinct and models as amorphous carbon.

The honest caution is about what magnetite is. It is an iron oxide, not the pre-reduced nickel-iron that made the asteroid belt’s carbonyl-metallurgy story work. This is a carbon-and-nitrogen answer and possibly an iron-ore answer. It is not a free-metal answer, so structural metal may well remain an Earth import even where the carbon problem is solved — unless the structural route is mineral fiber rather than metal, in which case an iron oxide is a normal constituent of the melt and never has to be reduced at all. And these are telescopic spectra of irradiated surfaces. Nobody has been there. Projected

Quantity

This Is Not a Quantity Question

Himalia is 139 kilometers across.

At chondritic density that is 3.7 × 10¹⁸ kilograms — fourteen orders of magnitude more mass than the entire 68-ton first-article manifest at Callisto. No plausible industrial program at Jupiter makes a dent in one of these bodies, and the group has four of them.

So the question is access, and the access is two months. The Trojan verdict was that the material is probably there and cannot be delivered on any schedule that matters. Himalia inverts both halves: delivery is trivial and the material is now partly verified. Modeled

The gap

Nothing Is Planned, Proposed or Funded to Go There

The highest-ranked composition gap in the Jovian system, and it does not close on its own.

Lucy answers the Trojan composition question starting in August 2027, when it encounters 3548 Eurybates and its satellite Queta. The Himalia group has no mission at all. Every Jovian mission ever flown or planned has treated the irregular satellites as a distant-observation target — Galileo, Juno, Europa Clipper, JUICE and Tianwen-4 all go to the Galilean moons, and none of them goes to the bodies that would settle whether the anchor can build anything.

One line in the first-article manifest already anticipates it. Among the landers, hoppers and system tugs, one should be sized to reach the Himalia group. The cost of carrying that capability is small; the cost of not having it is that the anchor never learns whether it can stop importing structure. Projected

Record

Provenance and Data Sources