Observations of Loki Patera by Juno during close flybys

TL;DR

Using Juno spacecraft data, this study reveals unique thermal properties and resurfacing dynamics of Loki Patera on Io, including evidence of magma volume, resurfacing waves, and persistent lava islands that challenge existing models.

Contribution

First detailed infrared analysis of Loki Patera from Juno data, identifying new resurfacing wave patterns and persistent lava islands that challenge current geological models.

Findings

Loki shows a distinct thermal structure with perimeter brightening but no hot ring.

A resurfacing wave propagates at 2-3 km per day, possibly originating from a point source.

Persistent lava islands have remained unchanged for over 45 years, challenging erosion models.

Abstract

We used data from the Juno spacecraft to investigate both the spatial and temporal properties of Loki Patera on Io, acquired in two infrared bands between December 2022 and April 2024, at spatial resolutions ranging from 400 m to 15 km. Loki shows a thermal structure unlike other active lava lakes previously reported, with some brightening near the perimeter of the lake but lacking the continuous hot ring seen at other paterae. Modeling the slow rate of cooling suggests there is a significant volume of magma beneath the crust to provide the latent heat necessary to decelerate the cooling rate. A thermal propagation that may represent the signature of a resurfacing wave, going from the southwest of the lake to the north, was observed with a velocity of about 2-3 km per day. Data collected in 2024 may indicate the onset of a new resurfacing wave originating from a point source, rather than the foundering of a linear section of the crust. We also observed many small (about 3 km wide), closely spaced (about 10 km apart) islands that have persisted in the same locations for at least 45 years, since first being imaged by Voyager 1. The persistence of these islands challenges resurfacing models of Loki, as they have remained fixed - likely anchored to the lava lake floor - and have not noticeably changed in size, arguing against large-scale thermal erosion. The central island of Loki shows a few thermal structures associated with the fractures that cross the island, indicating that the fractures most likely contain molten lava.