The reasons why Mars two polar caps are so different
The Martian north pole.
The Martian south pole.
What the colors mean in terms of elevation
A new paper, in review for the past year, has now been published describing the differences between the north and south poles of Mars, the most fundamental of which involve the planet’s orbit and the different elevations of the two poles, with the south pole three to six miles higher in altitude (as indicated by the colors on the maps to the right).
The cumulative data has allowed the researchers to explain why — when the thin winter cap of dry ice sublimates away in the spring — the process at the south pole results in spiderlike features that get enhanced from year to year, but in the north pole that sublimation process produces no such permanent features.
In both cases, the spring sunlight passes through the clear winter mantle of dry ice to heat its base. The sublimated trapped CO2 gas builds up, until the pressure causes the mantle to crack at weak spots. In the south that trapped gas flows uphill each spring along the same paths, carving the riverlike tributaries dubbed unofficially as “spiders” and officially as “araneiform terrain.”
Geophysicist Hugh Kieffer described that process in 2006. A few years later, [Candice] Hansen [the new paper’s lead author] followed up with her own model for the north polar cap, which also displays fans in the spring.
She found that the same phenomena occur in the north, but rather than relatively flat terrain, these processes play out across sand dunes. “When the Sun comes up and begins to sublimate the bottom of the ice layer, there are three weak spots – one at the crest of the dune, one at the bottom of the dune where it meets the surface and then the ice itself can crack along the slope,” Hansen said. “No araneiform terrain has been detected in the north because although shallow furrows develop, the wind smooths the sand on the dunes.”
There is also a lot more dust in the north, including a giant sea of dunes that circles the polar cap. In addition, the northern winter is shorter due to the planet’s orbit, and takes place during the annual dust storm season, causing there to be more dust concentrated within the northern ice. All of these factors make the the dunes and general surface in the north is more easily smoothed by the wind.
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 print edition can be purchased at Amazon or from any other book seller. If you want an autographed copy the price is $60 for the hardback and $45 for the paperback, plus $8 shipping for each. Go here for purchasing details. 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
The Martian north pole.
The Martian south pole.
What the colors mean in terms of elevation
A new paper, in review for the past year, has now been published describing the differences between the north and south poles of Mars, the most fundamental of which involve the planet’s orbit and the different elevations of the two poles, with the south pole three to six miles higher in altitude (as indicated by the colors on the maps to the right).
The cumulative data has allowed the researchers to explain why — when the thin winter cap of dry ice sublimates away in the spring — the process at the south pole results in spiderlike features that get enhanced from year to year, but in the north pole that sublimation process produces no such permanent features.
In both cases, the spring sunlight passes through the clear winter mantle of dry ice to heat its base. The sublimated trapped CO2 gas builds up, until the pressure causes the mantle to crack at weak spots. In the south that trapped gas flows uphill each spring along the same paths, carving the riverlike tributaries dubbed unofficially as “spiders” and officially as “araneiform terrain.”
Geophysicist Hugh Kieffer described that process in 2006. A few years later, [Candice] Hansen [the new paper’s lead author] followed up with her own model for the north polar cap, which also displays fans in the spring.
She found that the same phenomena occur in the north, but rather than relatively flat terrain, these processes play out across sand dunes. “When the Sun comes up and begins to sublimate the bottom of the ice layer, there are three weak spots – one at the crest of the dune, one at the bottom of the dune where it meets the surface and then the ice itself can crack along the slope,” Hansen said. “No araneiform terrain has been detected in the north because although shallow furrows develop, the wind smooths the sand on the dunes.”
There is also a lot more dust in the north, including a giant sea of dunes that circles the polar cap. In addition, the northern winter is shorter due to the planet’s orbit, and takes place during the annual dust storm season, causing there to be more dust concentrated within the northern ice. All of these factors make the the dunes and general surface in the north is more easily smoothed by the wind.
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 print edition can be purchased at Amazon or from any other book seller. If you want an autographed copy the price is $60 for the hardback and $45 for the paperback, plus $8 shipping for each. Go here for purchasing details. 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