Across
1
Particle of light
5
Naturally occurring inorganic solid
7
Second lightest element
8
Ball of burning gas in space
9
Unit of heredity
10
Infectious microscopic agent
Down
2
Compound containing oxygen
3
Mass per unit volume
4
Blocking of light by a celestial body
6
Fourth state of matter
11
Icy body with a tail near the sun
12
Force that attracts objects together