NASA -- Scientific understanding is often a matter of making the right comparisons. In terms of studying the Earth, one of the best comparative laboratories exists one planet over —- on Mars.

Jet Propulsion Lab -- Living too close to a neighbor may not be very appealing, but when Earth’s neighboring red planet moves closer than it’s been in 50,000 years, observers expect nothing but acclaim.

Earth and Mars are converging for a close encounter in August. The red planet is already an appealing target for sky watchers.Science@NASA -- Count slowly: one one-thousand, two one-thousand, three one-thousand....