Across
1
Biological catalyst
5
Ball of burning gas in space
6
Positive particle in nucleus
7
Fourth state of matter
11
Mass per unit volume
13
Precious yellow metallic element
Down
2
Curved glass that refracts light
3
Smallest unit of an element
4
Our home planet
8
Gas essential for breathing
9
Amplified beam of light
10
Disturbance that transfers energy
12
The Red Planet