This is an image where the vertical axis shows the planet's mass as a comparison with the mass of the Earth. This is a logarithmic scale running in powers of ten from 10 to the power minus 2 up to 10 to the power 4 in increments of one power of 10. The horizontal axis shows the orbital radius in terms of astronomical units (AU) again in a logarithmic scale running from 0.01 up to 100 in increments of a multiple of 10. A shaded area of radial velocity is indicated for planetary masses of between values of 10 to the power -4 and 10 Earth masses, with orbital radii between 0.02 and 4 AU. Another shaded area indicated as transits occurs for planetary masses of between 10 to the power 2 and 10 to the power 3 Earth masses, with orbital radii between 0.02 and 0.05 AU. Microlensing occurs for planetary masses between 1 and 10 to the power 4 Earth masses, with orbital radii between 2 and 10 AU. Letters on the graph indicate the relative positions of the planets in the solar system; the largest relative mass is Jupiter (J) and the smallest orbit is Mercury (Me).

6 The habitability of planets