After one year in orbit around Mercury, Messenger’s scientists have concluded that Mercury is not only dense but odd.
After one year in orbit around Mercury, Messenger’s scientists have concluded that Mercury is not only dense but odd.
The [proposed gravity] model, when combined with topography data and measurements of the planet’s spin, reveals that as much as 85% of Mercury’s radius is taken up by its dense iron core — an upward revision. “We knew Mercury had a large core,” says [Maria Zuber of MIT]. “Now we think it’s even larger.” What’s more, to compensate for a crust that’s enriched in sulphur and depleted in iron, the team has proposed a solid shell of iron sulphide that sits between the core and the mantle. While the shell satisfies the gravity constraints, it also makes it more difficult for a lot of convection to occur in the thin mantle that overrides it — which presents problems for those that invoke convection as a driver of the observed tectonic and volcanic features at the surface. “There isn’t a whole lot of mantle to be doing this lifting up,” says Zuber.
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. from any other book seller, or direct from my ebook publisher, ebookit.
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
After one year in orbit around Mercury, Messenger’s scientists have concluded that Mercury is not only dense but odd.
The [proposed gravity] model, when combined with topography data and measurements of the planet’s spin, reveals that as much as 85% of Mercury’s radius is taken up by its dense iron core — an upward revision. “We knew Mercury had a large core,” says [Maria Zuber of MIT]. “Now we think it’s even larger.” What’s more, to compensate for a crust that’s enriched in sulphur and depleted in iron, the team has proposed a solid shell of iron sulphide that sits between the core and the mantle. While the shell satisfies the gravity constraints, it also makes it more difficult for a lot of convection to occur in the thin mantle that overrides it — which presents problems for those that invoke convection as a driver of the observed tectonic and volcanic features at the surface. “There isn’t a whole lot of mantle to be doing this lifting up,” says Zuber.
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. from any other book seller, or direct from my ebook publisher, ebookit. 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
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