The Martian Anomaly

The Martian Anomaly Mars may be hiding a major temperature imbalance deep beneath its surface, with a new study suggesting that the planet’s southern interior is up to 750 degrees warmer than the north. A research team uncovered the anomaly after analyzing archival data from three NASA spacecraft – Mars Global Surveyor, Mars Odyssey and Mars Reconnaissance Orbiter – looking for subtle changes in their orbital speeds caused by variations in Mars’ gravitational field. Using a technique called “tidal tomography,” lead author Alexander Berne and his colleagues accounted for how the Sun’s gravitational pull on Mars changes as the planet follows its elliptical orbit. The resulting model revealed an interior that looks considerably less uniform than scientists generally assume. "Scientists usually assume that the interiors of planetary bodies are generally spherically symmetric, but this is not necessarily true," Berne explained in a statement. To account for the gravitational differences, the researchers calculated that the mantle beneath the southern hemisphere must be between 390 and 750 degrees Fahrenheit hotter than its northern counterpart – which suggests that parts of it could even remain partially molten. Mars already has a striking north-south divide on the surface: Its northern hemisphere consists largely of lowland plains that may once have contained a vast ocean, while the southern crust is on average 15.5 miles (25 kilometers) thicker and dominated by cratered highlands. The newfound heat difference could help explain other Martian mysteries. NASA’s InSight lander previously found that seismic waves dissipate faster in the south, something a hotter mantle could account for. It could also shed light on unusual magnetic remnants in southern iron-bearing minerals. Mars lost its global magnetic field billions of years ago, but hot material rising from the mantle could have heated parts of the crust beyond their “Curie temperature,” altering their magnetic properties, according to Space.com. But why exactly the southern interior is hotter remains uncertain. One possibility is that a colossal impact more than four billion years ago carved out the northern lowlands and allowed heat to escape, cooling the northern mantle faster. Alternatively, the south’s thicker crust may have acted as an insulating lid, trapping heat below. "The dichotomy that we see between north and south is important to understand because it gives information about processes that may have influenced the hydrology of Mars, including the formation of basins that may have held water," co-author Amirhossein Bagheri said in the statement. The technique could eventually be used to probe other worlds, including Mercury and Jupiter’s large moons, giving scientists another way to investigate planetary interiors without ever touching the surface.