If you already own Universe Sandbox ², just run Steam to update to the latest version.
Or you can buy Universe Sandbox ² here:
http://universesandbox.com/buy/
What's new?
Alpha 15 is the biggest update yet for Universe Sandbox ². We redesigned the user interface for a cleaner, more intuitive experience, rewrote physics for better performance, and introduced a dynamic soundtrack. There are also magnetic fields, light pulses, fireworks, custom keybindings, and a ton of smaller improvements, changes, and bug fixes.
In Alpha 15.1 we updated the look of Ceres based on the latest photos from NASA, added a random asteroid feature, new moons of Pluto, pulsar jets, and improved the look of brown dwarfs. We also re-introduced the ability to customize launch bodies. Hover over bodies in the Add panel then press a number key to assign the body to that launch slot. There are also a handful of other improvements and bug fixes.
In Alpha 15.2 we've added a simulation for New Horizons' Pluto flyby, including a model of the New Horizons spacecraft. We've also made it possible to draw trails relative to a body and made additional tweaks and fixes.
Let us know what you think! And please report any problems either with the in game feedback tool or by starting a new thread...