A planet for all seasons
"The analogy between Mars and the earth is, perhaps, by far the greatest in the whole solar system. The diurnal motion is nearly the same; the obliquity of their respective ecliptics, on which the seasons depend, not very different … the bright polar spots are owing to the vivid reflection of light from frozen regions; and that the reduction of those spots is to be ascribed to their being exposed to the sun."
“Mars has an atmosphere; we have reason to believe this atmosphere to be very thin,--thinner at least by half than the air upon the summit of the Himalayas,--and in constitution not to differ greatly from our own.”
“After air, water. If Mars be capable of supporting life, there must be water upon his surface; for, to all forms of life, water is as vital a matter as air. On the question of habitability, therefore, it becomes all-important to know whether there be water on Mars.”