The Source of Saturn's G Ring

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Science  03 Aug 2007:
Vol. 317, Issue 5838, pp. 653-656
DOI: 10.1126/science.1143964

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  • RE: "The Source of Saturn's G Ring" by Matthew M. Hedman, Joseph A. Burns, Matthew S. Tiscareno, Carolyn C. Porco, Geraint H. Jones, Elias Roussos, Norbert Krupp, Chris Paranicas, Sascha Kempf

    The picture of the Cosmic Horseshoe on page 45 of Astronomy magazine (December 2016) makes me think of the picture of Neptune's ring arcs on page 49. Page 45 shows gravitational lensing by one galaxy of another. They're almost – but not quite – perfectly aligned to make an arc of 300 plus degrees, an almost complete ring. The arc's 4 or 5 bright spots appear to be represented on p. 49. This "solar-system horseshoe" shows Neptune's ring arcs which are actually the 4 or 5 brightest spots in the outer Adams ring. The solar-system horseshoe may be caused by Neptune gravitationally lensing the light from the hypothetical Planet 9 proposed a year ago by astronomers Mike Brown and Konstantin Batygin. The lensing would create the bright spots on the dusty Adams ring. To produce this optical effect, Planet 9 would have to be at a point in its orbit that's either above or below the plane of Neptune's orbit: and from Earth's viewpoint, Planet 9 and Neptune would be almost – but not quite – perfectly aligned. The first part of the previous sentence is easily accomplished since Planet 9's orbital inclination is estimated at 20 to 40 degrees while Neptune's is only 1.77 degrees. The second part raises a potential problem for optical astronomers on Earth – Planet 9 might be hiding behind Neptune, and they'll have to wait a few years before it shows itself (maybe infrared astronomers can detect the extra heat).

    The arcs a...

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    Competing Interests: None declared.

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