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Let's go to Mars

Lowell builds an observatory to prove Mars is alive

A wealthy Bostonian put a telescope on a 7,200-foot ridge in Arizona to map a Martian irrigation network. The work was meticulous and entirely wrong.

A printed black-and-white map of Mars in a ruled rectangular frame, wider than it is tall, with longitude marked 0 to 360 degrees along the top, latitude down the left edge, and a book gutter running down the middle. Pale desert and darker stippled regions are crossed by a dense mesh of fine lines, most ruled straight and a few drawn as long arcs, with small numbers printed along the lines, beside the dark spots where lines meet, and in open pale ground. "Plate XXIV" appears above the frame and "North" at the bottom inside it; below the frame, "MAP OF MARS on Mercator's Projection" and "Lowell Observatory, Flagstaff, A. T. 1895".
Plate XXIV of Percival Lowell's Mars (1895): his map of the planet on Mercator's projection, from observations at Lowell Observatory in Flagstaff, Arizona Territory. Most of the canal lines are ruled straight, and the numbers run to 288, keying each named feature — canal, oasis or region — to an index at the back of the book. · Image: Percival Lowell, Mars (Houghton, Mifflin, 1895), Plate XXIV, via Wikimedia Commons

Percival Lowell, rich and finished with careers in business and Far Eastern diplomacy, decided the next favourable Mars opposition was worth a private observatory. He sent an assistant, Andrew Douglass, to test the air in Arizona Territory, and picked a ridge above Flagstaff at about 7,200 feet: high, dry and steady. He was observing from it by May 1894 with borrowed lenses. His own 24-inch Alvan Clark refractor, still in use today, arrived in the summer of 1896.

He reported a system: hundreds of canals in a global net, dark "oases" at the junctions, and a wave of seasonal darkening spreading from the polar caps toward the equator each spring. Lowell's reading was that Mars was an old, drying world whose inhabitants had built planetary-scale irrigation to move meltwater from the poles to the deserts. He argued it in three books — Mars (1895), Mars and Its Canals (1906) and Mars as the Abode of Life (1908) — and drew the plates himself.

Some of his conclusions hold up: Mars is dry and has lost most of its water. His 1908 estimate of surface pressure, 64 millimetres of mercury or about 85 millibars, was wrong by a factor of fifteen, but in line with everyone else's until a spacecraft measured the pressure in 1965. His observatory's hunt for a trans-Neptunian planet found Pluto in 1930, thirteen years after he died.

Evans and Maunder demonstrated the mechanism in 1903, while Lowell was still working: the straightness came from human vision rather than from Mars. Lowell dismissed it. His own assistants confirmed him: Lampland was announced in 1905 as having photographed the canals, and E. C. Slipher claimed them in his 1907 plates. Agreement between observers was read as independent confirmation; two decades of corroboration came out of a closed loop.

No spacecraft has found anything resembling a canal. Lowell's lasting effect was the audience: he made "is there life on Mars?" a question ordinary people argued about.