through it. The bloom of the main ring may be a beginning of the halo. The halo ring's inner boundary is not far from the strongest 2:1 Lorentz resonance. In this resonance the excitation is probably very significant, forcing particles to plunge into the Jovian atmosphere thus defining a sharp inner boundary. Being derived from the main ring, the halo has the same age. Gossamer rings Amalthea gossamer ring The Amalthea gossamer ring is a very faint structure with a rectangular cross section, stretching from the orbit of Amalthea at (2.54 RJ) to about (). Its inner boundary is not clearly defined because of the presence of the much brighter main ring and halo. The thickness of the ring is approximately 2300 km near the orbit of Amalthea and slightly decreases in the direction of Jupiter. The Amalthea gossamer ring is actually the brightest near its top and bottom edges and becomes gradually brighter towards Jupiter; one of the edges is often brighter than another. The outer boundary of the ring is relatively steep; the ring's brightness drops abruptly just inward of the orbit of Amalthea, although it may have a small extension beyond the orbit of the satellite ending near 4:3 resonance with Thebe. In forward-scattered light the ring appears to be about 30 times fainter than the main ring. In back-scattered light it has been detected only by the Keck telescope and the ACS (Advanced Camera for Surveys) on HST. Back-scattering images show additional structure in the ring: a peak in the brightness just inside the Amalthean orbit and confined to the top or bottom edge of the ring. In 2002–2003 Galileo spacecraft had two passes through the gossamer rings. During them its dust counter detected dust particles in the size range 0.2–5 μm. In addition, the Galileo spacecraft's star scanner detected small, discrete bodies (< 1 km) near Amalthea. These may represent collisional debris generated from impacts with this satellite. The detection of the Amalthea gossamer ring from the ground, in Galileo images and the direct dust measurements have allowed the determination of the particle size distribution, which appears to follow the same power law as the dust in the main ring with q=2 ± 0.5. The optical depth of this ring is about 10−7, which is an order of magnitude lower than that of the main ring, but the total mass of the dust (107–109 kg)