When it comes to interstellar work, don’t forget the Kuiper Belt. Although amateur astronomer Kenneth Edgeworth was the first to predict its existence, the Belt was named for Gerard Kuiper, who analyzed it in 1951. It is a region of thousands (and perhaps millions) of small, icy moons and cometary debris that exists from the orbit of Neptune well into deep space. Our first interstellar missions will be explorations of this area and the vast Oort cloud of comets that may extend as much as a light year out from the Sun.
And yes, in a true sense, the Voyager probes could be considered interstellar missions, still reporting data as they move on toward the heliopause. But we may learn a good deal about Kuiper Belt objects by studying the findings of a spacecraft considerably closer, the Cassini Saturn orbiter.
Cassini’s Ultraviolet Imaging Spectrometer tells us that Phoebe, a tiny world about one-fifteenth the diameter of Earth’s moon, is probably itself a Kuiper Belt object that was captured long ago by Saturn’s gravity. A University of Colorado at Boulder professor named Larry Esposito has been discussing Phoebe at the 36th annual Division of Planetary Sciences Meeting held in Louisville, KY from today until November 12. From a UC Boulder press release:
“UVIS sees the absorption signature of water ice on its surface, showing Phoebe was born in the outer solar system,” Esposito said. Exhibiting an unusual retrograde, or backward, orbit, Phoebe likely was lassoed by Saturn’s powerful gravitational field during the planet’s formative years, he said.
One powerful clue about Phoebe: its unusual retrograde (backward) orbit. “UVIS sees the absorption signature of water ice on its surface, showing Phoebe was born in the outer solar system,” Esposito added.
We may well find that other outer-system moons, like Neptune’s Triton, have their origin in the Kuiper Belt. Other UVIS data include high-detail images of Saturn’s rings that show the influence of the planet’s moons in creating density waves — ripples — in the so-called Cassini Division, the gap between the bright A and B rings of Saturn. UVIS also found, according to Esposito, a bright glow in Titan’s upper atmosphere that appears to be “…the glow of nitrogen atoms, molecules and ions energized by electrons striking the upper atmosphere.”
Centauri Dreams will have more in the next few days on the meeting’s other sessions with interstellar implications. They include an advanced propulsion meeting tomorrow and discussions on extrasolar planets to be held on Friday. Particularly fascinating from the latter should be “Specular Reflection of Starlight off Distant Planetary Oceans,” to be presented by D.M. Williams (Penn State Erie, The Behrend College) and E. Gaidos (U. Hawaii). More as information comes in.
