Scientists using images from Mars Reconnaissance Orbiter (MRO) collected over six Martian years (6.5 Earth years) have found that the mid-sized dunes dubbed mega-dunes near the north pole actually do move from year to year, unlike similar sized dunes elsewhere on the planet.
Megaripples on Mars are about 1 to 2 meters tall and have 5 to 40 meter spacing, where there size falls between ripples that are about 40 centimeters tall with 1 to 5 meter spacing and dunes that can reach hundreds of meters in height with spacing of 100 to 300 meters. Whereas the megaripples migration rates are slow in comparison (average of 0.13 meters per Earth year), some of the nearby ripples were found to migrate an average equivalent of 9.6 meters (32 feet) per year over just 22 days in northern summer – unprecedented rates for Mars. These high rates of sand movement help explain the megaripple activity.
Previously it was believed that such dunes were static planetwide, left over from a time when Mars’ atmosphere was thicker and could then move them more easily. This data however suggests that the winds produced over the north pole when the carbon dioxide in the atmosphere freezes in winter and sublimates back to a gas in summer are sufficient to shift these dunes in the surrounding giant Olympia Undae dune sea.
Now available in hardback and paperback as well as ebook!
From the press release: In this ground-breaking new history of early America, historian Robert Zimmerman not only exposes the lie behind The New York Times 1619 Project that falsely claims slavery is central to the history of the United States, he also provides profound lessons about the nature of human societies, lessons important for Americans today as well as for all future settlers on Mars and elsewhere in space.
Conscious Choice: The origins of slavery in America and why it matters today and for our future in outer space
, is a riveting page-turning story that documents how slavery slowly became pervasive in the southern British colonies of North America, colonies founded by a people and culture that not only did not allow slavery but in every way were hostile to the practice.
does more however. In telling the tragic history of the Virginia colony and the rise of slavery there, Zimmerman lays out the proper path for creating healthy societies in places like the Moon and Mars.
“Zimmerman’s ground-breaking history provides every future generation the basic framework for establishing new societies on other worlds. We would be wise to heed what he says.” —Robert Zubrin, founder of founder of the Mars Society.
All editions available at Amazon, Barnes & Noble, and all book vendors. The ebook can be purchased direct from my ebook publisher, ebookit, in which case you don't support the big tech companies and I get a bigger cut much sooner. Note that the price for the ebook, $3.99, goes up to $5.99 on September 1, 2022.
Autographed printed copies are also available at discount directly from me (hardback $24.95; paperback $14.95). Just email me at zimmerman @ nasw dot org.