The Moon Isn’t Two-Faced and Now We Know Why
If I told you that the dark side of the moon has no face like the ‘Man in the Moon’ side and the thought of this made your head explode with dark foreboding, you’re thinking too hard about the Lunar Farside Highlands Problem. Fortunately, the cure is here because the problem has been solved.
We all know it was called the “dark side” because we didn’t know anything about it, right? That changed on October 7, 1959 when the Soviet spacecraft Luna 3 sent back the first images of the lunar backside. They showed less of the large smooth surfaces we call seas or maria. Determining the cause became the Lunar Farside Highlands Problem. In the current edition of Astrophysical Journal Letters, the Penn State research team of Jason Wright, assistant professor of astrophysics, Steinn Sigurdsson, professor of astrophysics and Arpita Roy, graduate student in astronomy and astrophysics, describe how they have solved it.
They started with the assumption that the lack of wide smooth patches is due to differences in crust thickness between the sides and that is was caused by how the moon was formed. After a Mars-sized object hit the Earth, the piece that broke off became the moon. Both were extremely hot and 10 to 20 times closer together than they are now. This resulted in the strong gravitational lock that still exists today.
The molten surface of the far side cooled slowly, allowing the crust to become thick and hard with high concentrations of aluminum and calcium. The near side remained liquid for a much longer period and molten lava stayed present under a thin crust. When meteorites hit this side, the lava boiled out and spread to form the ‘Man in the Moon’ seas. When they hit the far side, craters and valleys were created but the thick crust and cool temperatures kept the lava underground, leaving the surface craggy rather than smooth.
If this news makes you shout and no one seems to hear, you know where to meet me. Ha-ha-ha!