Lander (spacecraft) 2012. Planned for 2018, NASA's Mars Astrobiology Explorer-Cacher lander mission was cancelled due to budget cuts. Exploration of Mars including the use of landers continues to this day. Amongst them, Russia has planned a Mars sample return mission Mars-Grunt for near 2026, and China for near 2030. While several flybys conducted by Mars orbiting probes have provided images and other data about the Martian moons Phobos and Deimos, only few of them intended to land on the surface of these satellites. Two probes under the Soviet Phobos program were successfully launched in 1988, but in 1989 the intended landings on
Moons of Mars satellites, Earth had one and Jupiter had four (known at the time), that Mars by analogy must have two. Furthermore, as they had not yet been discovered, it was reasoned that they must be small and close to Mars. This would lead Swift to making a roughly accurate estimate of their orbital distances and revolution periods. In addition Swift could have been helped in his calculations by his friend, the mathematician John Arbuthnot. Voltaire's 1752 short story "Micromégas", about an alien visitor to Earth, also refers to two moons of Mars. Voltaire was presumably influenced by Swift. In recognition of