Phobos ( or Mars I ) is one of Mars ' moons . The tele-operation of robotic scouts on Mars by humans on Phobos could be conducted without significant time delay , and planetary protection concerns in early Mars exploration might be addressed by such an approach . Phobos has also been proposed as an early target for a manned mission to Mars because a landing on Phobos would be considerably less difficult and expensive than a landing on the surface of Mars itself .