90377 Sedna - Wikipedia

I’ve been reading about Sedna for the past 45 minutes. It’s a dwarf planet that we know exists in our solar system as a trans-Neptunian object, but it sort of defies our understanding of how solar systems develop and function. 

In 2076 it will reach its closest point to the sun along its 11,400 year orbit: about 76 AU (1 AU is the average distance between the Earth and the Sun.) At 76 AU, it’s still about 2.5 times further away than Neptune’s most distant point. At Sedna’s furthest point, it will be about 937 AU away.

To put this in perspective, Voyager 1 the farthest man-made object from Earth. It’s reached the heliospause - the boundary at which the sun’s solar wind is able to push back against the stellar winds of the surrounding stars. This means that for all intents and purposes, it’s just about to pass into interstellar space. Right now, light itself takes about 16.5 hours to travel between Earth and Voyager 1. It’s about 125 AU out. Sedna’s orbit takes it seven and a half times further away from the sun.

Think about that: at its furthest distance out - well into interstellar space - the light from the star it orbits takes more than five full days to reach Sedna’s surface. Sedna actually only spends a relatively small amount of its orbit within what some scientists consider to be the de facto solar system, yet gravity still pulls it back around to make another orbit.

This is because the gravitational influence produced by the sun dominates the gravitational influence of surrounding stars to about 125,000 AU, or about two light-years out.

That’s just fascinating.

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