Mars is closer to the Earth than Jupiter. I was expecting it to look brighter than Jupiter but it didn't. Giving an accurate distance to a planet from Earth is difficult because it depends on whereabouts on its orbit it is at the time you're asking. However, there is a large gap in distance from the Sun between Mars and Jupiter and the ball-park figures I've seen suggest Jupiter is 10x further from Earth than Mars. That would make Jupiter 100x dimmer by the inverse square law. However Jupiter has 21x the radius of Mars and thus 440x the area. It will in theory send back 440x as much light. Now it gets tricky. Jupiter is so much further from the Sun so it will receive less in the first place to reflect. It is 3x further so would receive 9x less light by the inverse square law. Although fewer photons would reach out as far as Mars, it would gather more of them due to its size. Also it is likely that the sand on Mars is not as reflective as the clouds on Jupiter. Also Mars was lower down in the sky so the Earth's atmosphere would absorb more. Also my eyes might not pick up red as well as the white coming back from Jupiter.
