Multi-phase volcanic resurfacing at Loki Patera on Io.

The Jovian moon Io hosts the most powerful persistently active volcano in the Solar System, Loki Patera. The interior of this volcanic, caldera-like feature is composed of a warm, dark floor covering 21,500 square kilometres surrounding a much cooler central 'island'. The temperature gradient seen across areas of the patera indicates a systematic resurfacing process, which has been seen to occur typically every one to three years since the 1980s. Analysis of past data has indicated that the resurfacing progressed around the patera in an anti-clockwise direction at a rate of one to two kilometres per day, and that it is caused either by episodic eruptions that emplace voluminous lava flows or by a cyclically overturning lava lake contained within the patera. However, spacecraft and telescope observations have been unable to map the emission from the entire patera floor at sufficient spatial resolution to establish the physical processes at play. Here we report temperature and lava cooling age maps of the entire patera floor at a spatial sampling of about two kilometres, derived from ground-based interferometric imaging of thermal emission from Loki Patera obtained on 8 March 2015 ut as the limb of Europa occulted Io. Our results indicate that Loki Patera is resurfaced by a multi-phase process in which two waves propagate and converge around the central island. The different velocities and start times of the waves indicate a non-uniformity in the lava gas content and/or crust bulk density across the patera.

An infrared flash contemporaneous with the gamma-rays of GRB 041219a.

The explosion that results in a cosmic gamma-ray burst (GRB) is thought to produce emission from two physical processes: the central engine gives rise to the high-energy emission of the burst through internal shocking, and the subsequent interaction of the flow with the external environment produces long-wavelength afterglows. Although observations of afterglows continue to refine our understanding of GRB progenitors and relativistic shocks, gamma-ray observations alone have not yielded a clear picture of the origin of the prompt emission nor details of the central engine. Only one concurrent visible-light transient has been found and it was associated with emission from an external shock. Here we report the discovery of infrared emission contemporaneous with a GRB, beginning 7.2 minutes after the onset of GRB 041219a (ref. 8). We acquired 21 images during the active phase of the burst, yielding early multi-colour observations. Our analysis of the initial infrared pulse suggests an origin consistent with internal shocks.

Discovery of a main-belt asteroid resembling ordinary chondrite meteorites.

Although ordinary chondrite material dominates meteorite falls, the identification of a main-belt asteroid source has remained elusive. From a new survey of more than 80 small main-belt asteroids comes the discovery of one having a visible and near-infrared reflectance spectrum similar to L6 and LL6 ordinary chondrite meteorites. Asteroid 3628 BoZnemcová has an estimated diameter of 7 kilometers and is located in the vicinity of the 3:1 Jovian resonance, a predicted meteorite source region. Although the discovery of a spectral match may indicate the existence of ordinary chondrite material within the main asteroid belt, the paucity of such detections remains an unresolved problem.