Roughly three billion years ago, moon shifted from its axis, most probably due to violent volcanoes, according to a research paper published in the journal Nature. The strong volcanic activity might have released a tremendous amount of energy, resulting in heating up of lunar surface, according to research paper.
Southern Methodist University, Dallas Planetary scientist Matt Siegler and his team examined data collected by NASA. After checking in detail about hydrogen detected by orbital instruments, astronomers believe that it could be in form of ice. It might have remained safe from solar heat in the craters noticed around moon’s north and south poles.
The study team analyzed data collected by NASA’s Lunar Prospector and Lunar Reconnaissance Orbiter missions. During exposure to sunlight, the hydrogen in ice form could have boiled-off into space. The research team added that odd offset of the ice from the moon’s current north and south poles was a tell-tale indicator about shift in lunar axis. However, this might have happened billions of years ago. Lunar poles are permanently cloaked in shadow. The presence of hydrogen at lunar poles was first reported in the late 1990s.
The research team noticed that distance between the true poles and to ice caps is around 125 miles or six degrees. The shift in axis might have started around three billion years ago. And, it could have continued at a very slow speed for a billion years.
Due to volcanic activity, the giant mass of molten material could have caused a change in internal balance of lunar center of gravity.
Talking about the shift in lunar axis, Siegler said, “This was such a surprising discovery. We tend to think that objects in the sky have always been the way we view them, but in this case the face that is so familiar to us — the Man on the Moon — changed.”
Planetary bodies settle into their axis based on their mass: A planet’s heavier spots lean it toward its equator, lighter spots toward the pole. On the rare occasion mass shifts and causes a planet to relocate on its axis, scientists refer to the phenomenon as “true polar wander.”
Discovery of lunar polar wander gains the moon entry into an extremely exclusive club. The only other planetary bodies theorized to have permanently shifted location of their axis are Earth, Mars, Saturn’s moon Enceladus and Jupiter’s moon Europa.
What sets the moon apart is its polar ice, which appears to effectively “paint out” the path along which its poles moved.
On Earth, polar wander is believed to have happened due to movement of the continental plates. Polar wander on Mars resulted from a heavy volcanic region. The moon’s change in mass was internal—the shift of a large, single mantle “plume.” Ancient volcanic activity some 3.5 billion years ago melted a portion of the moon’s mantle, causing it to bubble up toward its surface, like goo drifting upward in a lava lamp.
“The moon has a single region of the crust, a large basaltic plain called Procellarum, where radioactive elements ended up as the moon was forming,” Siegler said. “This radioactive crust acted like an oven broiler heating the mantle below.”
Some of the material melted, forming the dark patches we see at night, which are ancient lava, he said.
Siegler compares true polar wander to holding a glass filled with water. Most planets are like a steady hand holding a glass, their axis doesn’t shift and the water stays put. A planet whose mass is changing is like a wobbly hand, causing its axis to shift and the water to spill out. Similarly, as Earth’s moon changed its axis, much of its ice ceased to be hidden from the sun and was lost.
Co-author Richard Miller mapped the moon’s remaining ice by using data from NASA’s Lunar Prospector mission, which orbited the moon from 1998 to 1999. The presence of ice is inferred by measuring the energy of neutrons emitted from the lunar surface. Instruments on NASA’s satellite, including a neutron spectrometer, measured neutrons liberated from the moon by a rain of stellar particles scientists call cosmic rays. Low energy neutrons indicate the presence of hydrogen, the dominant molecule in water and ice.