The Cosmic Connection: An Extraterrestrial Perspective by Carl Sagan

Author:Carl Sagan
Language: eng
Format: mobi, epub
Tags: Life Sciences, Science, Solar system, Biology, General, Outer space, Astronomy
ISBN: 9780333324745
Publisher: Papermac
Published: 1981-01-15T10:00:00+00:00

And running out of Coprates were features that were very curious indeed –sinuous channels, meandering through the highlands above the Coprates Valley and graced with beautiful little tributaries. If such channels had been seen on Earth, they would unhesitatingly have been attributed to running water. But on Mars the surface pressures are so low that liquid water would instantly vaporize, just as the pressures on Earth are so low that liquid carbon dioxide vaporizes instantly. On Earth we have solid carbon dioxide and gaseous carbon dioxide, but not liquid carbon dioxide. On Mars this absence of the liquid phase is true as well for water.

But as the Mariner 9 photographic mission continued, a variety of additional channels were discovered: Channels with second- and third-order tributary systems, channels without a crater at their beginning or end, channels with teardrop-shaped islands in their midst, channels with braided termini, like those cut on Earth by episodic flooding.

There seems to be little doubt that most of the several dozen longest such channels (the longest are hundreds of miles long), and hundreds of smaller ones, were cut by running water. But since there can be no liquid water on Mars today, the channels must have been cut in a previous epoch of Martian history – when the total pressures were larger, the temperatures higher, and the availability of water greater.

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