Japanese scientists found that, about 4 billion years ago, large-scale magnetic field existed on the Moon, just as that of the Earth today. At that time, the spin axis of the Moon was several dozens degrees different from that of today, which means that the Moon showed its other side to the Earth at that time.

Palaeomagnetic measurements suggest that an active core dynamo operated on the Moon from 4.2 to 3.56 billion years ago. Since the Apollo era, many magnetic anomalies have been observed on the Moon. The magnetization of the lunar crust in some of these regions could preserve the signature of an early dipolar magnetic field generated by a core dynamo. Thus, the magnetic anomalies may yield information about the position of the palaeomagnetic pole during the time that the dynamo operated.

Researchers present a comprehensive survey of magnetic anomalies on the lunar surface using magnetometer data obtained by the Lunar Prospector and Kaguya lunar orbiters. They extract magnetization vectors from 24 magnetic anomalies using an iterative inversion method and derive the palaeomagnetic poles, and find that the north poles, as well as the antipodal south poles, cluster in two distinct locations: one near the present rotation axis and the other at mid-latitude.

The clustering is consistent with a dipole-dominated magnetic field generated in the lunar core by a dynamo that was reversing, much like that of Earth. Furthermore, the two pole clusters imply that the Moon experienced a polar wander event during its ancient history due to the reorientation of the Moon with respect to its spin axis by 45°-60°.

Bus-Size Asteroid Buzzes Earth, Comes Closer Than the Moon

A small asteroid about the size of a city bus zipped by Earth at a range closer than the moon early Saturday (May 3), but posed no threat to our planet.

The newly discovered asteroid 2014 HL129 came within 186,000 miles (299,338 kilometers) of Earth when it made its closest approach on Saturday morning, which is close enough to pass between the planet and the orbit of the moon. The average distance between the Earth and moon is about 238,855 miles (384,400 km).

You can watch a video animation of asteroid 2014 HL129's orbit around the sun on Space.com. The asteroid is about 25 feet (7.6 meters) wide, according to NASA's Asteroid Watch project based at the agency's Jet Propulsion Laboratory in Pasadena, Calif. It made its closest approach to Earth at 4:13 a.m. EDT (0813 GMT).

Saturday's close shave by asteroid 2014 HL129 came just days after its discovery on Wednesday, April 28, by astronomers with the Mt. Lemmon Survey team, according to an alert by the Minor Planet Center, an arm of the International Astronomical Union that chronicles asteroid discoveries. The Mt. Lemmon Survey team scans the night sky with a telescope at the Steward Observatory atop Mt. Lemmon in Arizona's Catalina Mountains.

NASA scientists and researchers around the world constantly monitor the sky for potentially dangerous asteroids that could pose a risk of impacting the Earth.

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