90377 Sedna - Population

Population

Sedna's highly elliptical orbit means that the probability of its detection was roughly 1 in 80, suggesting that, unless its discovery was a fluke, another 40–120 Sedna-sized objects would exist within its region. Another object, 2000 CR₁₀₅, has a similar but less extreme orbit: it has a perihelion of 44.3 AU, an aphelion of 394 AU, and an orbital period of 3,240 years. It may have been affected by the same processes as Sedna.

Each of the proposed mechanisms for Sedna's extreme orbit would leave a distinct mark on the structure and dynamics of any wider population. If a trans-Neptunian planet was responsible, all such objects would share roughly the same perihelion (≈80 AU). If Sedna were captured from another planetary system that rotated in the same direction as the Solar System, then Sedna's population would all possess relatively low inclinations and possess semi-major axes ranging from 100–500 AU. If it rotated in the opposite direction, then two populations would form, one with low inclinations and one with high. The gravity of perturbing stars would produce a wide variety of perihelia and inclinations, each dependent on the number and angle of such encounters.

Gaining a larger sample of such objects could therefore help in determining which scenario is most likely. "I call Sedna a fossil record of the earliest Solar System", said Brown in 2006. "Eventually, when other fossil records are found, Sedna will help tell us how the Sun formed and the number of stars that were close to the Sun when it formed." A 2007–2008 survey by Brown, Rabinowitz and Megan Schwamb attempted to locate another member of Sedna's hypothetical population. Although the survey was sensitive to movement out to 1,000 AU and discovered the dwarf planet candidate 2007 OR₁₀, it detected no new bodies in Sedna-like orbits. Subsequent simulations incorporating the new data suggested about 40 Sedna-sized objects probably exist in this region.