Nine of them circle Jupiter in a wide,
retrograde orbit, which means they move in the opposite direction that the planet rotates.
For the asteroids in
retrograde orbit, there are at least 50 known moons of Jupiter's that are retrograde, some of which are thought to be asteroids or comets that originally formed near the gas giant and were captured when they got too close.
The most important, with respect to the primary science objectives, was the sunrise terminator, which was when the spacecraft was passing from the lighted portion of the moon to the dark portion of the moon, since the spacecraft was in a
retrograde orbit. The science phase orbit was designed such that when crossing the sunrise terminator, the spacecraft would be approximately 50 kilometers above the surface of the moon, in order to satisfy mission requirements.
The study also showed that if Earth revolved around the sun in the opposite direction, called a
retrograde orbit, it wouldn't need a moon at all to have a climate about as stable as it has today.
Like 1P/Halley, stream meteoroids have a
retrograde orbit around the Sun, meaning that they enter the upper atmosphere at a high velocity of around 66 km/sec.
Just one other known trans-Neptunian object has a
retrograde orbit: 2008 [KV.sub.42], whose path is inclined 103[degrees].
This planet is quite particular because it has a
retrograde orbit and, evenmore, its orbit is quite inclined in angle respect to the star's equator.