Describe the possible history of a typical Plutino as astronomers now believe it occurred. What ...

Answer to q. 1

More than a hundred of the Kuiper Belt Objects are caught with Pluto in a 3:2 resonance with Neptune. That is, they orbit the Sun twice while Neptune orbits three times. This subset of KBOs have been named plutinos. The plutinos formed in the outer solar nebula, but how did they get caught in resonances with Neptune? As you learned earlier, some models of the formation of the planets suggest that Uranus and Neptune may have migrated outward early in the Solar System's history. As Neptune moved farther from the Sun, its orbital resonances could have swept up small objects like a kind of planetary snow plow. The plutinos are caught in the 3:2 resonance, and other KBOs are caught in other resonances. The evidence appears to support those models which predict that Uranus and Neptune migrated outward. The migration of the outer planets would have dramatically upset the motion of some of these Kuiper Belt Objects, and some could have been thrown inward where they could interact with the Jovian planets. Some of those objects may have been captured as moons, and astronomers wonder if moons such as Neptune's Triton could have started life as KBOs. Other objects may have hit bodies in the inner Solar System and caused the late heavy bombardment episode especially evident on the surface of Earth's Moon.

Answer to q. 2

A bit of comparative planetology shows that Pluto is not related to the Jovian or Terrestrial planets; it is obviously a member of a newfound family of worlds that orbit beyond Neptune. These bodies must have formed at about the same time as the eight classical planets of the Solar System, but they did not grow massive enough to clear their orbital zones of remnant planetesimals and consequently remain embedded among a swarm of other objects in the Kuiper Belt.

Answer to q. 3

By counting craters on Triton, planetary scientists conclude that the surface has been active as recently as a million years ago and may still be active.

Answer to q. 4

Traces of methane absorb red light and thus make the atmosphere look green-blue.

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