* Astronomy

Title: How Sedna and family were captured in a close encounter with a solar sibling
Author: Lucie Jilkova, Simon Portegies Zwart, Tjibaria Pijloo, Michael Hammer

The discovery of 2012VP_113 initiated the debate on the origin of the Sedna family of planetesimals in orbit around the Sun. Sednitos roam the outer regions of the Solar System between the Egeworth--Kuiper belt and the Oort cloud, in extraordinary wide (a>150 au) orbits with a large perihelion distance of q>30 au compared to the Earth's (a=1 au and eccentricity e=(1-q/a)~0.0167 or q~1 au). This population is composed of a dozen objects, which we consider a family because they have similar perihelion distance and inclination with respect to the ecliptic i=10--30 deg. They also have similar argument of perihelion of (340±55) deg. There is no ready explanation for their origin. Here we show that these orbital parameters are typical for a captured population from the planetesimal disk of another star. Using the orbital parameters of the Sednitos we reconstruct the encounter that led to their capture. We conclude that they might have been captured in a near miss with a 1.8 solar mass star that impacted the Sun at ~340 au at an inclination with respect to the ecliptic of 17--34 deg with a relative velocity at infinity of ~4.3 km/s. We predict that the Sednitos-region is populated by 930 planetesimals and the inner Oort cloud acquired about 440 planetesimals through the same encounter.

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