Jet Propulsion Laboratory
Scientists Say Mars Has a Liquid Iron Core
New information about what is inside Mars shows the red planet has a
molten liquid iron core, confirming the interior of the planet has some
similarity to Earth and Venus.
This artist's concept of the interior of Mars shows a hot liquid
core that is about one-half the radius of the planet. 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.
JPG (1.4 MB) |
TIFF (7 MB)
Researchers at NASA's Jet Propulsion Laboratory, Pasadena, Calif.,
analyzing three years of radio tracking data from the Mars Global Surveyor
spacecraft, concluded that Mars has not cooled to a completely solid
iron core, rather its interior is made up of either a completely liquid iron
core or a liquid outer core with a solid inner core. Their results are
published in the March 7, 2003 online issue of the journal Science.
"Earth has an outer liquid iron core and solid inner core.
This may be the case for Mars as well," said Dr. Charles Yoder,
a planetary scientist at JPL and lead author on the paper. "Mars is
influenced by the gravitational pull of the Sun. This causes a solid body
tide with a bulge toward and away from the Sun (similar in concept to
the tides on Earth). However, for Mars this bulge is much smaller, less
than 1 centimeter (0.4 inch). By measuring this bulge in the Mars gravity
field we can determine how flexible Mars is. The size of the measured tide
is large enough to indicate the core of Mars can not be solid iron but must
be at least partially liquid."
The team used Doppler tracking of a radio signal emitted by the Global
Surveyor spacecraft to determine the precise orbit of the spacecraft
around Mars. "The tidal bulge is a very small but detectable force
on the spacecraft. It causes a drift in the tilt of the spacecraft's orbit
around Mars of one-thousandth of a degree over a month," said
Dr. Alex Konopliv, a planetary scientist at JPL and co-author on the paper.
The researchers combined information from Mars Pathfinder on the
Mars precession with the Global Surveyor tidal detection to draw
conclusions about the Mars core, according to Dr. Bill Folkner of JPL,
another co-author of the paper.
The precession is the slow motion of the spin pole of Mars as it moves
along a cone in space (similar to a spinning top). For Mars, it takes
170,000 years to complete one revolution. The precession rate indicates
how much the mass of Mars is concentrated toward the center.
A faster precession rate indicates a larger dense core, compared to
a slower precession rate.
In addition to detection of a liquid core for Mars, the results indicate
the size of the core is about one-half the size of the planet, as is the
case for Earth and Venus, and that the core has a significant fraction of
a lighter element such as sulfur.
In addition to measuring the Mars tide, Global Surveyor has been able
to estimate the amount of ice sublimated, changed directly into a gaseous
state, from one pole into the atmosphere and then accreted onto the
opposite pole. "Our results indicate the mass change for the
southern carbon dioxide ice cap is 30 to 40 percent larger than the
northern ice cap, which agrees well with the predictions of the global
atmosphere models of Mars," said Yoder.
The amount of total mass change depends on assumptions about the
shape of the sublimated portion of the cap. The largest mass exchange
occurs if we assume the cap change is uniform or flat over the entire cap,
while the lowest mass exchange corresponds to a conically shaped
JPL manages the Mars Exploration Program for NASA's Office of
Space Science, Washington, D.C. JPL is a division of the California
Institute of Technology in Pasadena.