$ sudo apt-get remove planets 

Uninstall planets including dependent package

If you would like to remove planets and it's dependent packages which are no longer needed from Ubuntu,

$ sudo apt-get remove --auto-remove planets 

Use Purging planets

If you use with purge options to planets package all the configuration and dependent packages will be removed.

$ sudo apt-get purge planets 

If you use purge options along with auto remove, will be removed everything regarding the package, It's really useful when you want to reinstall again.

$ sudo apt-get purge --auto-remove planets 

See Also,