The orbits of Jupiter's four tiny inner moons -- Amalthea, Adrastea, Metis, and Thebe -- are seen in an artist's cutaway view of the gas giant's ring system. These moons are thought to be the sources of the dust that forms Jupiter's faint rings.
Posted on 10/30/2007 7:02:07 PM PDT by SunkenCiv
Perhaps the most surprising find for astronomers was an absence of tiny moonlets within the planet's rings. Prior missions had revealed four small moons orbiting inside the orbit of the large moon Io. The smallest of these are Adrastea, at 12 miles (20 kilometers) in diameter, and Metis, at 25 miles (40 kilometers) in diameter. Earlier instruments weren't sensitive enough to spot moons much smaller than these. But scientists presumed that moonlets existed, because where there are big objects, there are usually lots of smaller ones. "That's sort of how these things work," said Mark Showalter, a planetary scientist at the SETI Institute and lead author of a study on the "missing" moonlets. Looking for moonlets is important, Showalter said, because they are thought to be the source of the dust that forms Jupiter's faint rings. Such dust can be created when meteorites hit small moons within the rings, forming puffs of smokelike particles. But despite the probe's ability to spot objects as small as 0.6 mile (a kilometer) in diameter, New Horizons found no new moons. "It was really a surprise," Showalter said. The most likely explanation, he continued, is that meteorite bombardment has battered such small bodies to the point that they are too small for New Horizons to detect. But the new pictures did produce an unexpected find: clumps of debris within the planet's main ring. While clumps of material aren't unusual, Jupiter's clumps were found in clusters that should have been rapidly dispersed by orbital forces. "We haven't seen anything like this in any other planetary rings," Showalter said.
(Excerpt) Read more at news.nationalgeographic.com ...
The orbits of Jupiter's four tiny inner moons -- Amalthea, Adrastea, Metis, and Thebe -- are seen in an artist's cutaway view of the gas giant's ring system. These moons are thought to be the sources of the dust that forms Jupiter's faint rings.
More Climate Change — on Jupiter
National Geographic News | 9 Oct 2007 | Anne Minard
Posted on 10/10/2007 2:09:55 PM EDT by docbnj
http://www.freerepublic.com/focus/f-news/1909310/posts
 |
||
| · join · view topics · view or post blog · bookmark · post new topic · | ||
Have Jupiter's smallest moons been obliterated?The Long Range Reconnaissance Imager (LORRI) camera on New Horizons should have been able to spot moons down to a diameter of about 1 kilometre. But it saw nothing smaller than Adrastea, a 16-kilometre-wide resident of Jupiter's faint ring system (see image at right). This is puzzling, because scientists expected the number of objects to increase at smaller size scales, as they do in the rings of Saturn. The missing moons may have been eroded away by micrometeoroids, say researchers led by Mark Showalter of the SETI Institute in Mountainview, California, US. A steady rain of small objects - probably between the sizes of a grain of sand and a pebble - would destroy small moons while leaving larger ones mostly intact, they say. For example, a 27-kilometre-wide moon could survive having its outer 5 km worn away over time, whereas an object just 5 km across would be eroded away to nothing in the same time period... But why did this process spare Saturn's small moons? Showalter thinks the answer has to do with the fact that Saturn is simply less massive than Jupiter.
by David Shiga
New Scientist
October 9, 2007
Disclaimer: Opinions posted on Free Republic are those of the individual posters and do not necessarily represent the opinion of Free Republic or its management. All materials posted herein are protected by copyright law and the exemption for fair use of copyrighted works.
