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Percival Lowell’s lasting contribution to research of Mars was his observation of a “wave of darkening” on the surface of Mars that began when the polar caps of Mars began to melt. As water vapour was progressively transported away from the pole in the martian atmosphere, the surface on the planet underwent a gradual darkening, beginning at the pole and travelling toward the equator then into the opposite hemisphere of the planet. The appearance of this surface phenomena was like a wave travelling over the surface and it was so precise that Lowell was able to accurately measure the speed of the wave to be about thirty kilometers per day.

Astronomers of Lowell’s day widely believed that the Hourglass Sea region on the planet was an ocean. The feature, renamed by Giovanni Schaparelli as Syrtis Major, has a blue-green hue. However, it appeared to grow in size between the martian springtime and summer, peaking with a green and blue colour that would change through to brown and dull gray in autumn and winter. This led Lowell to consider that this was driven by the melting ice caps during the changing seasons on Mars:

“[T]he ocean-like character of Syrtis Major must pass with other charming myths into the limbo of the past. For the great blue green area is no ocean, no sea, no anything connected with water, but something very far removed from water: namely a vast track of vegetation… the color of Syrtis Major in places fades out. Just such an effect would follow the change of vegetation from green to yellow and ocher, as spring passed towards autumn” – Percival Lowell, Popular Astronomy, No. 36, 1906

Lowell’s theory of a wave of water vapour being transported through the atmosphere from the poles that created vast colour changes was the first evidence that indicated that Mars had an ecosphere and could in fact be a living planet.

© Anthony Beckett 2019

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