Across
1
Particle of light
3
Center of an atom or cell
4
Ball of burning gas in space
8
Curved glass that refracts light
9
The Red Planet
Down
2
Icy body with a tail near the sun
3
Unit of force
5
Nerve cell in the brain
6
Smallest unit of an element
7
Fourth state of matter
10
Element found in all living things