[extropy-chat] Mars core: soft, and maybe hard at the pip

Avatar Polymorph avatar at renegadeclothing.com.au
Fri Feb 13 00:38:16 UTC 2004

Further to years earlier discussion on the Martian (near-vacuum) atmosphere,
the solar wind, planetary chemistry and the lack of a magnetosphere: new
information. A good reason to get to Mars for more research. Nanotech
transformation can resculpture the planet in decades: perhaps
hitech/nanotech may be required to resculpture the interior - and create a
permanent atmosphere. (If we don't hold it in via a nanomembrane.) (Makes me
think of the novel 'Bloom.')


Molten martian core

The more researchers study Mars, the more similarities they seem to find
between the Red Planet and Earth. The latest parallels come from the planet'
s enigmatic interior. As is the case with Earth's, the martian core appears
to be about half the size of the planet and, to some extent, liquid iron,
according to new research out of NASA.

Writing in the March 7 online edition of Science, Chuck Yoder and others
report on three years of radio tracking data from the Mars Global Surveyor,
which reveals a surface bulge on Mars and the first direct evidence of a
liquid martian core.

This artist's concept of the interior of Mars shows a hot liquid core about
half the radius of the planet. Like Earth's, the core is mostly made of iron
with some possible lighter elements such as sulfur. The mantle is the darker
material between the core and the thin crust. NASA/JPL.

"The gravitational pull of the Sun causes a bulge in Mars toward the Sun and
away from the Sun," says co-author Alex Konopliv. "Because we are measuring
the gravity field of Mars, we see the bulge not only on the surface of Mars
but also throughout the planet including the bulge in the core." Yoder's
team found a surface bulge of 0.7 centimeters, much smaller than the tidal
bulge on Earth but large enough to indicate that Mars' core cannot be solid.
A solid core would not deform and would show very little gravitational tide.

The findings, however, do not reveal whether the martian core is entirely
liquid or has a solid inner core with a liquid outer shell. "It may have a
solid inner core, like Earth. However, this measurement is insensitive to
that possibility," Yoder says.

Twenty years ago, David Stevenson, a planetary sciences professor at
Caltech, favored a Mars with no inner core, one entirely liquid, but now he
sees the core differently, with a solid inner core and a thin liquid outer
core, much like Earth's. The presence of sulfur in the core, he says, would
dramatically lower the melting point of iron. "So if the core were pure
iron, it would indeed freeze with its high freezing point, but because we
expect the core from general chemical considerations to have elements, such
as sulfur - which is an antifreeze, like salt on an icy road - the outermost
part of it should be liquid," he says.

On Earth, seismological and geomagnetic evidence give researchers clues to
the planet's interior. No seismological evidence from Mars exists to help
determine the composition of its core. And unlike Earth, which has a large
magnetic field generated by the motion of its outer fluid core, Mars
currently has no magnetic field. This absence has generated speculation on
the core's structure. "One of the possible explanations suggested decades
ago for that absence was that Mars has a solid core; if you have a solid
core, you cannot generate a magnetic field because it's not enough to have
an electrical conductor - you have to have a dynamo process," Stevenson

Yoder and others' research rules out that possibility, he says, but further
complicates the puzzle as to why Mars has no magnetic field. Stevenson
thinks it has something to do with a lack of heat flow needed to set the
core in motion. Because Mars is smaller than Earth and has no plate
tectonics, the planet lacks an efficient way of losing heat to the exterior,
he says - a feature that separates Earth not only from Mars but also from
the rest of the solar system. "I've speculated that there's a direct link
between whether a planet has plate tectonics and whether it has a magnetic
field. Earth is the only terrestrial planet with both a magnetic field and
plate tectonics."

Lisa M. Pinsker

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