High-resolution gravity map confirms Mars’ molten core
NASA has released a newgravity map for Mars stitched together from telemetry data collectedby a trio of spacecraft over the course of 16 years orbiting the RedPlanet. The map has already led to the confirmation that Mars hosts amolten liquid outer core, and insights relating to the titanictransfer of atmospheric material to the polar regions of the RedPlanet during their winter cycle.
The experiment reliedon the transmission of Doppler and range tracking data sent from theagency's Mars Global Surveyor, Mars Odyssey, and Mars ReconnaissanceOrbiter spacecraft. The telemetry was received by a series of radioantennas collectively known as the Deep Space Network.
As the spacecraftorbited Mars, the bumps and ravines that characterize the surface ofthe Red Planet worked to create tiny deviations in the trajectory ofthe spacecraft as they passed over the terrain.
By observing orbitaldeviations from the planet's center of mass, a team of scientists at NASA's Goddard Space Flight Center were able to stitch together a highly detailed Gravity mapof Mars far exceeding the resolution of any that had come before.
In order for theorbital deviations caused by Mars' uneven gravity to be detected,interference from a host of other sources had to be filtered out.This included minute forces such as the pressure exerted on thespacecraft's solar panels by particles emanating from our Sun, anddrag generated via the interaction between the shallow-orbitingprobes and Mars' tenuous atmosphere. The process of removing theinterference took two years of work, involving the use ofsophisticated computer models.
A similar technique wasrecently employed by the team handling ESA's Rosetta spacecraft inorder to map the interior of the comet67P/Churyumov-Gerasimenko. However, the Martian gravity mappingendeavor represented somewhat larger of a challenge.
One of the majorinsights allowed by the gravity map is the confirmation that Marshosts an outer core consisting of liquid molten rock. The idea thatMars hosts a molten liquid outer core is not a new one, howeverprevious gravitational studies had lacked the ability to confirm thediscovery.
The superior resolutionof the new map, which is capable of detecting gravity anomalies only100 km (62 miles) across, has allowed scientists to confirm thetheory by analyzing tides present in the mantle and outer crust ofthe planet created by the gravitational force of our star, and Mars'two moons Phobos and Deimos.
The map is alreadyproving useful in deciphering the geological properties of an unusualregion of the Martian surface located between the northern Martianlowlands and the southern highlands that are known to exhibit a below-average gravity signature.
Previous studies ledscientists to theorize that the gravity depressions owed theirexistence to a network of subsurface channels carved out by runningwater billions of years in the past.
However,NASA's newly-released high-resolution gravity map detected a numberof the channel-like features running along topographical slopes inthe Martian terrain rather than down them. In other words, thefeatures did not correlate with the natural downhill flow of waterrequired to create such a channel, essentially debunking the theory.
Instead,scientists are working on the premise that the current low gravityregion was created when the lithosphere of theplanet flexed and buckled under the titanic weight of the emergingTharsis volcanoes.
Not all of the insightsprovided by the map were limited to the planet's surface. NASAscientists were able to infer the quantity of carbon dioxide thatfreezes out of the atmosphere each winter by analyzing how Mars'gravitational signature has alters over the course of a full cycle ofsolar activity (11 years worth of observations).
It is estimated that aseach hemisphere enters its winter cycle, an astonishing 3 – 4trillion tons of carbon dioxide settles in the polar regions,accounting for around 12 – 16 percent of the Red Planet's tenuousatmosphere. Furthermore, a significant amount of this mass istransferred from pole to poll as the hemispheres alternate throughtheir respective winter cycles
In terms of operationaluses, the map will be instrumental in allowing for a more accurateinsertion of future spacecraft into Mars orbit.