you should end the ellipses to the middle of the planets
no moons?
it's for a RPG : players will need a few information about the viability of each planet. Maybe you should add a few infomation : giant gazeous, earthly like with arid weather, unsuitable for leaving, 3,5G on the ground (ouch, i'm so heavy)
No scale . A map with no scale and no legend is not a map (i think my geographic teacher when i was 12 learn me a least this thing ;-) )
planets can have gradients, that can be interesting, making the solar system not flat

these are only a few thought, just ideas