If you already own Universe Sandbox ², just run Steam to update to Alpha 17.
What's New in Alpha 17?
Alpha 17 introduces better looking star glows, a new Halley’s Comet simulation, and two values which show how similar a planet is to Earth and the speculative chance of it forming basic life. There’s also a “Make Pulsar” tool, better crash handling and reporting, and some bug fixes.
You can read about some of the other features we are working on for future updates on our blog:
What Are We Working On? | Alpha 17 & Beyond[universesandbox.com]
For a full list of what's new in 17, please see our release notes.
Let us know what you think of Universe Sandbox ² Alpha 17 via the in-game feedback tools or the forums.

翻译：如果您已经拥有宇宙沙盒² ，只需运行steam更新到alpha17 。
什么是新的Alpha17 ？
Alpha17引入了更美观的星发光，一个新的哈雷彗星模拟，两个值展示了行星与地球的相似度和它形成基本生命的机会。还有一个“脉冲星”的工具，更好的撞击处理和报告，以及一些bug修复。