Across
1
Path of a planet around the sun
4
Unit of energy
6
Unit of electric potential
7
Our home planet
8
Center of an atom or cell
9
Gas essential for breathing
Down
2
Nerve cell in the brain
3
Mass per unit volume
5
Icy body with a tail near the sun
6
Hottest planet in solar system
10
The Red Planet
11
Second lightest element