Mars observed in 1976 by the Viking Orbiter then observed again by Mars Odyssey mapping (2001-04).


Viking Orbiter Image Themis, Thermal Emission Imaging System

Comparing these two images there are significant differences in the geology of Mars, 1976 compared to 2001-2004. Mariner 9 images from 1971 also show geological changes on Mars compared to the present Odyssey mapping images.
I found it amazing the changes in the geology of Mars when considering observed and photographed observations of Mars from the middle to late 1800’s.
Putting all these pieces together illustrates the historical changes on Mars to be within about the last 150 years. Astronomers Saw!

Craterchains
As a boy I remember all the speculation about the canals on Mars. Reading about them in science magazines and the science fiction books was fascinating. As noted by many astronomers in their drawings, photos, and notes over the past couple hundred years there have been some major changes.
When FieryIce brought to my attention this APOD of Mars, Mars Then and Now and questioned about the canals I suggested she do some research and see what comes up. Her investigations have produced some interesting observations made by astronomers and we offer our combined effort for your comments and ideas about these easily observable changes to Mars.