<blockquote><font class="small">In reply to:</font><hr /><p>other planets moons? Some of these moons seem much more interesting than the planets they orbit. So why haven't we, or if i'm missing something, what projects are in developement to soley monitor another planet's moon(s).<p><hr /></p></p></blockquote><br /><br />Well, most of these moons have siblings, and there's so little known about any of them that it's been more cost effective to send a probe to tour all of the moons in a system than to simply orbit one of them. Basically, it's a case of so many moons, so little time. <img src="/images/icons/wink.gif" /><br /><br />However, new technology is poised to change that. The JIMO mission is probably not going to be resurrected anytime soon (the budget monster ate it) but the concept will probably survive. The idea is to use nuclear-electric ion propulsion (which is very similar in principle to the existing solar-electric propulsion of contemporary ion drives, but much more powerful because of the large electrical source available) to allow a probe to enter orbit around a moon, such as one of the Galilean satellites, loiter in orbit there for a time, then leave orbit and go orbit another moon.<br /><br />The main limiting factor for such missions is the extravagant amount of delta-vee (change in velocity) required over the course of the mission. With chemical rockets, it's just not practical. But with ion propulsion, it's conceivable. It's still very expensive, though, and so such missions tend to be the first on the cutting block.<br /><br />A conventional moon orbiter was planned a while ago: Europa Orbiter. It would've carried ground-penetrating radar to Europa in hopes of determining how big of an ocean Europa actually has and whether or not its accessible from the surface. But it was cancelled along with the rest of the Fire & Ice series, also to have included Solar Probe and Pluto/Kuiper Express. The latter mission was partially resurrected as New Horizons, but <div class="Discussion_UserSignature"> <p> </p><p><font color="#666699"><em>"People assume that time is a strict progression of cause to effect, but actually from a non-linear, non-subjective viewpoint it's more like a big ball of wibbly wobbly . . . timey wimey . . . stuff."</em> -- The Tenth Doctor, "Blink"</font></p> </div>