Do you happen to know what issue of S&T that was? I'd like to read it. I did a simulation of this object. Screen shots:
More info from my website:
Here's another simulation where the Sun captures Sedna after a Brown Dwarf passes close to the Sun. S&T magazine also had a short article on this:
There are many ways the Sun could capture an interstellar object. The odds are very low, but it could happen. Think of a capture as an ejection in reverse. If you want to capture a planet into a round stable orbit inbetween Mars and Jupiter, first imagine an object in this stable orbit. What would it take to eject it? If its orbit is stable, not much. Another interstellar massive object could pass through the solar system, making a close pass to this planet and ejecting it. So the reverse of that would be that two interstellar planets, completely unrelated, pass through the solar system at the same time, make a close encounter to each other at the position of the desired stable orbit, exchanging energy, causing one to be inserted into a round stable orbit while the other one continues on a hyperbolic trajectory out of the solar system. Possible? Yes! Probable? I doubt this has ever happened anywhere in the galaxy.
If you are willing to settle for a non-stable orbit, the possibilities grow. A non-stable orbit means that the object will probably one day be ejected. The reverse of this is that the object gets captured into an unstable orbit.
Another method is for a binary planet to encounter the solar system. As they pass through, they get split apart, leaving one in solar orbit while the other one continues on a hyperbolic trajectory to infinity. Some theorize that this is how Neptune captured Triton.