Numeracy: "orbits" (circles amp; ellipses), scale, distance, sorting (categorisation). Number bases (if aliens have three fingers on each hand they will count in numbers with a base 6!) Very large numbers.
Science: discuss suitable environments to promote life and growth, structure of the solar system. Travel and rockets.
Artwork: landscapes, models of aliens, planets. Looking at everyday objects through alien eyes.
PE: alien movements through different terrain (an outing for apparatus!).
ICT: support all the above. Look at websites mentioned. Search for other information on the internet. Send "alien" emails!