https://www.techradar.com/news/windows-10-has-a-new-exclusive-emjoi-the-astro-cat

Microsoft has worked out another exclusive emoji for Windows 10, the infinitely awesome Astro Cat. Found by Emojipedia, the emoji is achieved by joining the ‘Cat Face’ and ‘Rocket’ emojis by a small string of characters in between.

Specifically, this technique is known as the ‘zero width joiner’ (ZWJ), a specific string of characters that, when placed between two emojis in the proper order, will produce a whole new emoji. However, at this point only Windows 10 supports the zero width joiner.