Spacecraft Orbital Fluctuation Data Colors New Martian Gravity Map

Summary: A new Martian gravity map gleaned feature formation and internal insights from spacecraft orbital fluctuation data, a March 21 NASA article explains.

views of north pole (left) and of south pole (right) via NASA's new Martian gravity map; blue areas = low gravity; red or white areas = high gravity; credit MIT/UMBC-CRESST/GSFC: Generally not subject to copyright in the United States, via NASA

NASA’s new Martian gravity map emerges from orbital fluctuations experienced by three orbiting spacecraft and reveals insights into Martian feature formation and interior makeup, according to NASA’s March 21, 2016, feature article, “New Gravity Map Gives Best View Yet Inside Mars,” by Bill Steigerwald.

“With this new map, we’ve been able to see gravity anomalies as small as about 100 kilometers (about 62 miles) across, and we’ve determined the crustal thickness of Mars with a resolution of around 120 kilometers (almost 75 miles),” explains Antonio Genova, postdoctoral associate at NASA’s Goddard Space Flight Center in Greenbelt, Maryland, and at the Massachusetts Institute of Technology (MIT) in Cambridge. “The better resolution of the new map helps interpret how the crust of the planet changed over Mars’ history in many regions.”

The new Martian gravity map color codes gravity variations. Blue references low-gravity areas. Red and white represent high-gravity areas.

Gravitational pull exerted by the sun and by Mars’ two irregularly-shaped moons, Delmos and Phobos, causes tides in the Red Planet’s crust and mantle. Tidal analysis by scientists at Goddard Space Flight Center (GSFC) confirms the presence of a liquid outer core of molten rock in Mars’ lumpy interior.

Gravity changes on Mars over the 11-year solar magnetic activity cycle lead Goddard scientists to infer that an extreme amount of atmospheric carbon dioxide is deposited onto a polar ice cap during the Martian winter. Seasonal changes in the southern and northern hemispheres drive movement of the carbon dioxide mass between the south and north poles. Up to four trillion tons of carbon dioxide passes annually between the Martian poles. This frozen-out carbon dioxide represents about 12 to 16 percent of the entire mass of the Martian atmosphere.

NASA’s new Martian gravity map colorfully conveys Doppler and range tracking data communicated to NASA’s Deep Space Network telecommunications system by three NASA spacecraft orbiting Mars. About 16 years of data reveal small variations in orbital trajectory and travel time for three spacecraft. Orbital variations affect radio signals communicated by the three spacecraft to the Deep Space Network’s three, longitudinally equidistant global facilities at Goldstone, California; near Madrid, Spain; and near Canberra, Australia.

Mars Global Survey (MRS) circled Mars in a polar orbit over nine years, from arrival on Sept. 11, 1997 (Sept. 12 Coordinated Universal Time), until silence in November 2006. The 2001 Mars Odyssey (ODY) has been in a near-polar orbit since arrival at Mars on Oct. 23, 2001 (Oct. 24 Coordinated Universal Time). Mars Reconnaissance Orbiter (MRO) has been in a near-polar orbit since arrival at Mars on March 10, 2006.

The new Martian gravity map is constructed from crustal thickness and free-air gravity maps as well as from the topography map created by the Mars Orbiter Laser Altimeter (MOLA) onboard the Mars Global Surveyor. The free-air gravity map reveals spacecraft acceleration rates that decrease or increase in response to gravitational variations occasioned by Mars’ surface bumps and interior lumps.

The MOLA topography map helps to create a gravity model of a bumpy, but not lumpy, Mars. Subtracting the MOLA-based gravity model from the free-air gravity map yields a Bouguer gravity anomalies map that reveals Mars’ lumpy interior.

The gravity anomalies identified by the Bouguer gravity map then drive a crustal thickness map. High-gravity places indicate a thin crust with Mars’ dense mantle in surface closeness.

“Gravity maps allow us to see inside a planet, just as a doctor uses an X-ray to see inside a patient,” explains Antonio Genova in NASA’s March 21 feature article. “The new gravity map will be helpful for future Mars exploration, because better knowledge of the planet’s gravity anomalies helps mission controllers insert spacecraft more precisely into orbit around Mars. Furthermore, the improved resolution of our gravity map will help us understand the still-mysterious formation of specific regions of the planet.”

Genova presents the research behind the new Martian gravity map in an article, “Seasonal and static gravity field of Mars from MGS, Mars Odyssey and MRO radio science,” available online as of March 5, for Icarus, a peer-reviewed scientific journal dedicated to Solar System studies. Genova is lead author of the article’s team of seven co-authors representing Goddard Space Flight Center; Massachusetts Institute of Technology’s Department of Earth, Atmospheric and Planetary Sciences; and University of Maryland-Baltimore County’s Center for Research and Exploration in Space Science and Technology (CRESST).

Grants from NASA’s Mars Data Analysis Program and NASA’s Mars Reconnaissance Orbiter mission funded the team’s research.

Martian gravity map shows the Tharsis volcanoes and surrounding flexure, or bending of the lithosphere (the planet's strong, outermost layer); white areas in the center are higher-gravity regions produced by massive Tharsis volcanoes; surrounding blue areas are lower-gravity regions, possibly cracks in the crust (lithosphere); credits: MIT/UMBC-CRESST/GSFC: NASA @NASA, via Twitter March 21, 2016

Acknowledgment

My special thanks to talented artists and photographers/concerned organizations who make their fine images available on the internet.

Image credits:

views of north pole (left) and of south pole (right) via NASA's new Martian gravity map; blue areas = low gravity; red or white areas = high gravity; credit MIT/UMBC-CRESST/GSFC: Generally not subject to copyright in the United States; may use this material for educational or informational purposes, including photo collections, textbooks, public exhibits, computer graphical simulations and Internet Web pages; general permission extends to personal Web pages, via NASA @ http://www.nasa.gov/feature/goddard/2016/mars-gravity-map

Martian gravity map shows the Tharsis volcanoes and surrounding flexure, or bending of the lithosphere (the planet's strong, outermost layer); white areas in the center are higher-gravity regions produced by massive Tharsis volcanoes; surrounding blue areas are lower-gravity regions, possibly cracks in the crust (lithosphere); credits: MIT/UMBC-CRESST/GSFC: NASA @NASA, via Twitter March 21, 2016, @ https://twitter.com/NASA/status/712062234214723584

For further information:

Genova, Antonio, et al. “Seasonal and Static Gravity Field of Mars from MGS, Mars Odyssey and MRO Radio Science.” Icarus, vol. 272 (July 1, 2016): 228-245. DOI: 10.1016/j.icarus.2016.02.050
Available @ http://www.sciencedirect.com/science/article/pii/S0019103516001287

“GMM-3 Mars Gravity Map.” NASA Scientific Visualization Studio. March 21, 2016.
Available @ http://svs.gsfc.nasa.gov/cgi-bin/details.cgi?aid=4436

Marriner, Derdriu. "Gravity May Reshape Innermost Martian Moonlet Phobos Into Rocky Ring." Earth and Space News. Tuesday, Nov. 24, 2015.
Available @ https://earth-and-space-news.blogspot.com/2015/11/gravity-may-reshape-innermost-martian.html

NASA @NASA "New map of Mars’ gravity provides revealing glimpse into hidden interior of the Red Planet." Twitter. March 21, 2016.
Available @ https://twitter.com/NASA/status/712062234214723584

NASA Goddard. “Mars Gravity Map.” YouTube. March 21, 2016.
Available @ https://www.youtube.com/watch?v=iDTDNIh4Qhw

“New Gravity Map Gives Best View Yet Inside Mars.” NASA. March 21, 2016.
Available @ http://www.nasa.gov/feature/goddard/2016/mars-gravity-map

Steigerwald, Bill. “New gravity map gives best view yet inside Mars.” Phys.org. March 21, 2016.
Available @ http://phys.org/news/2016-03-gravity-view-mars.html