4% is baryonic matter, the stuff we call something. (Atomic Matter is the stuff that planets and people are made of)
22% is dark matter particles we cannot see. (Dark Matter is a mysterious form of matter not made of atoms or known particles)
74% of the universe is "nothing," or what physicists call dark energy. (Dark Energy is an even more enigmatic form of energy that is causing the universe's expansion to accelerate)
more science:
Climate change hits Mars
Scientists from Nasa say that Mars has warmed by about 0.5C since the 1970s. This is similar to the warming experienced on Earth over approximately the same period.
more images: Postcards From Mars
note: hat-tips to Metro Newspaper