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S. A. Stern (SwRI)
The discovery of the large (H=1.7) distant object, 2003 VB12, aka Sedna (Brown, Trujillo, and Rabinowitz 2004), is exciting on several grounds, not the least of which are the implications of its large size (D~2000 km) and distant, excited orbit (q~76 AU, a~532 AU, i~12 deg, e~0.86). Sedna's highly eccentric orbit clearly suggests it has been severely dynamically disturbed since its accretion, which must have occurred with e~0 and i~0. Early commentary on Sedna's origin (e.g., Brown et al., 2004; Morbidelli & Levison 2004) has centered on a formation location at <50 AU, with transport to the present orbit having resulted from a strong scattering event by a massive planet or a nearby star. Here I examine the viability of an alternate, in situ accretion (e.g., near 76 or 500 AU, Sedna's q and a) scenario, which would have been followed by dynamical evolution to the present orbit. Consider first a ``primordial formation" scenario taking 100-300 Myr, consistent with current accretion model results in the Kuiper Belt (e.g., Stern & Colwell 1997; Kenyon 2002). Doing so, we estimate that as little as 10 Earth masses of solids could have been required in a disk stretching from 70 to 100 AU region to produce Sedna-scale objects. If however Sedna formed in a very wide disk extending from 70 to 500 AU, then a significantly less plausible outer disk mass of 80-240 Earth masses in solids is implied. The implications of these results, which would require a more extended and massive Kuiper Disk, reminiscent of some broad extrasolar disks 100s of AU in extent, will be discussed.
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Bulletin of the American Astronomical Society, 36 #2
© 2004. The American Astronomical Soceity.