The production of dipolar waves by electric charge implies that quadrupolar waves are possible. Quadrupolar gravity waves imply that the second mass moment can have a non-zero second order time derivative . Other higher order wave structures are allowed for gravity, but we expect that quadrupolar waves to predominate, since its the simplest one can get. The above discussion gives us rules for assigning the spin for the graviton, a theoretical particle which transmits the gravitational force, analogous to the photon transmitting the electromagnetic force. Since the lowest order wave possible for gravity is quadrupolar, we expect most gravitons to have a spin of two.
Photons have a spin of one since they can be dipolar.
No single book seems to have enough information about planets for me. Here you can find info like the mass of Mars, the size of Jupiter, and the correct pronounciation of the name of the 7th planet of the Solar System. This gives a great opportunity to see the Orion Nebula. Look at the Orion Belt, and go a bit down towards the greenish fuzzy patch.