Across
1
The Red Planet
4
Gas essential for breathing
5
Smallest unit of an element
6
Fourth state of matter
9
Precious yellow metallic element
Down
2
Icy body with a tail near the sun
3
Center of an atom or cell
4
Compound containing oxygen
7
Preserved remains of ancient life
8
Ball of burning gas in space
10
Tissue that contracts for movement
11
Tectonic landmass section