Sand dunes and dry ice on Mars
Time for some more sightseeing on Mars. A recent news release from Mars Reconnaissance Orbiter noted the discovery of seasonal avalanches on Mars. This new image of the northern martian sand dunes illustrate again how the surface of Mars changes seasonally. The white patches on the ridges of the sand dunes is frozen carbon dioxide, dry ice that condenses on the crowns of the dunes every winter. When spring comes, the dry ice evaporates, and as it does so it disturbs the underlying sand, which then tumbles down the sides of the dunes, producing the dark streaks.
The process is less dramatic, however, than the avalanches seen in the previous news release, as suggested by this image below, showing the same dunes in summer without the dry ice. The dark streaks in the second image are not significantly different from the first, indicating that the process that forms them is slow and subtle.
On Christmas Eve 1968 three Americans became the first humans to visit another world. What they did to celebrate was unexpected and profound, and will be remembered throughout all human history. Genesis: the Story of Apollo 8, Robert Zimmerman's classic history of humanity's first journey to another world, tells that story, and it is now available as both an ebook and an audiobook, both with a foreword by Valerie Anders and a new introduction by Robert Zimmerman.
The ebook is available everywhere for $5.99 (before discount) at amazon, or direct from my ebook publisher, ebookit. If you buy it from ebookit you don't support the big tech companies and the author gets a bigger cut much sooner.
The audiobook is also available at all these vendors, and is also free with a 30-day trial membership to Audible.
"Not simply about one mission, [Genesis] is also the history of America's quest for the moon... Zimmerman has done a masterful job of tying disparate events together into a solid account of one of America's greatest human triumphs."--San Antonio Express-News
Readers: the rules for commenting!
No registration is required. I welcome all opinions, even those that strongly criticize my commentary.
However, name-calling and obscenities will not be tolerated. First time offenders who are new to the site will be warned. Second time offenders or first time offenders who have been here awhile will be suspended for a week. After that, I will ban you. Period.
Note also that first time commenters as well as any comment with more than one link will be placed in moderation for my approval. Be patient, I will get to it.