Feasibility study of a mission to Sedna – Nuclear propulsion and solar sailing

They know its radius is ~1000km but interestingly, there is no way to determine its mass without a flyby or other gravitational interaction. I guess you could swag it by using the lunar density, which gives ~~~ 10^22 kg.

https://www.wolframalpha.com/input?i=4.189%C3%9710%5E9+km%5E...

Wouldn't it's composition be of more ice and rock (like pluto), therefore lower density than the moon?

That's a reasonable assumption, but given Sedna's unusual orbit, its origin could also be quite different from Pluto's.

In the wikipedia post you are replying to has the chemical composition of the surface of the planet, obviously we can't know what is beneath that, but to me, indicates this is closer to Pluto than it is to our Moon.

> Detailed spectroscopic analysis has revealed Sedna's surface to be a mixture of the solid ices of water (H2O),[15] carbon dioxide (CO2), and ethane (C2H6), along with occasional sedimentary deposits of methane (CH4)-derived,[16] vividly reddish-colored organic tholins,[15] a surface chemical makeup somewhat similar to those of other trans-Neptunian objects.[17]

It's actually the diameter that is 1,000 km, so I guess that changes the mass if assuming Lunar density to around 1.74×10^21 kg.