Did Mars cool more slowly than first thought?

[MeteorWayne]

The magnetosphere collapsed when the dynamo at Mars' center shut down.<br />The dynamo at the center of planets is sustained by rotation and convection in a mettalic liquid layer beneath the surface.<br />Since Mars is so small, the core solidified, and poof, no more dynamo, ergo no more magnetic field.<br /><br />That's the quick explanation. Like most things, the details are a lot messier, but that gives you the idea. <div class="Discussion_UserSignature"> <p><font color="#000080"><em><font color="#000000">But the Krell forgot one thing John. Monsters. Monsters from the Id.</font></em> </font></p><p><font color="#000080">I really, really, really, really miss the "first unread post" function</font><font color="#000080"> </font></p> </div>

 

[JonClarke]

Venus presumably had hotspots and possibly an aesthenosphere, like Earth. This is different to a magma ocean, which is substantially molten.<br /><br />the original magama ocean idea was defined from Moon, where the upper part of the moon was completely molten to a depth of several 100 km. As this cooled, crystallising olivine and pydroxene settled while plagioclase floated, forming a scum on the surface several 10's of km thick. Eventually the whole thing froze, resulting in an anorthositic crust, peridotite upper mantle, and a noritic transition zone.<br /><br />this is probably my last post for a week or so, as I am off to the field soon.<br /><br />Jon <div class="Discussion_UserSignature"> <p><em>Whether we become a multi-planet species with unlimited horizons, or are forever confined to Earth will be decided in the twenty-first century amid the vast plains, rugged canyons and lofty mountains of Mars</em>  Arthur Clarke</p> </div>

 

[h2ouniverse]

Venus is thought to have been resurfaced almost entirely as recently as one billion years ago by a massive outflow of magma. Although there is no more plate tectonics since the oceans vaporized long ago, the core is very hot, comparable to Earth's a priori. The absence of tectonics slows down the cooling process (by decreasing the exchanges with the surface).<br /><br />Best regards.