Copyright: 2000, 2008 Bruno Coudoin and others
License: GPLv3
Files:
asteroid*.png

Copyright: Timothée Giet, 2015
License: CC-BY-SA 4.0
Files:
background.svg
space_shuttle.svg
tux_spaceship.svg
saturn.svg  (based on https://openclipart.org/download/118801/saturn-dan-gerhards-01.svg )
netpune.svg (based on https://openclipart.org/download/121843/Neptune-by-Merlin2525.svg )
arrow.svg   (based on https://openclipart.org/detail/113185/ftline_line_arrow_begin-by-dannya )
crash.svg   (based on https://openclipart.org/download/166838/crash.svg )
updown.svg  (based on https://openclipart.org/detail/25007/double-arrow-sign-by-anonymous-25007 )