Of the many discoveries and trends that have emerged in our understanding of life in extreme environments on Earth, there can be little doubt in saying that the convergence of polar biology and planetary sciences has been one of the most fruitful and insightful. It has led biologists to other worlds. Space missions are expensive, but recent high resolution cameras and new, sophisticated analytical instruments have continued to support the idea that the planet Mars had, and indeed still has, environments that come close in their physical and chemical extremes to Earth's polar regions.