The formation of the moon has remained a mystery to this day, with a number of different hypotheses postulated to try to explain the age-old question of where Earth’s companion came from. While none of the hypotheses are without flaws, the one favoured within the scientific community right now postulates a giant impact, early on in the history of the formation of our planet, some 4.5 billion years ago.
The early inner solar system was populated with several Mars-sized bodies which crossed orbits with each other and other planets. In the giant impact hypothesis, one of these bodies, named Theia, collided with the Earth, resulting in the formation of a disc of debris circling the Earth after the collision.
Some of the material from this debris disc would have then coalesced to form the moon. This could have been the last in a series of impacts which our planet could have possibly experienced from such cosmic bodies.
Such a hypothesis also aims to explain observations that can be made today, resulting directly from such a collision. One of these observations is the abnormally high angular momentum in the Earth-moon system, when comparing the Earth to the other terrestrial planets. Indeed, such a giant impact could have provided the excess momentum observed in the system, and it is estimated that right after the collision, one Earth day would have been approximately five hours long.
A second observation came from imaging the far side of the moon, which showed a lot more craters and almost no maria (flat plains) than the near side of the moon. Since lunar maria are thought to have formed from flows of magma resulting after asteroids penetrated the lunar crust, this seems to suggest that a thicker crust is present on the far side of the moon.
A number of possibilities from the giant impact scenario could explain this. The prevailing idea is that a second smaller moon could have formed from the debris of the initial giant impact with Theia, further out than the moon itself, which would have eventually collided with them on the far side, increasing the amount of surface material on that side. Hence, the crust on the far side would be thicker, meaning that asteroids would not be able to puncture the crust all the way to the magma below, and no magma flows resulting in surface maria could form.
Josef Borg completed a PhD in Astronomy at the Institute of Space Sciences and Astronomy, University of Malta, and is currently a researcher at the Faculty of Health Sciences at the University of Malta. He is also Malta’s representative on the European Astrobiology Network Association (EANA) council.
Sound Bites
• James Webb Space Telescope to release its first science-quality images on July 12: Following a period of six months of commissioning in space, NASA will release the first operational images taken by the $10 billion James Webb Space Telescope on July 12, according to an agency statement posted Wednesday (June 1). Although the Webb team has shared several images already, these were all interim alignment images taken to evaluate the observatory’s capabilities. The July 12 images will come after each instrument is “calibrated, tested, and given the green light by its science and engineering team,” according to NASA.
• NASA selects two companies to build next-gen spacesuits for future lunar and ISS missions: NASA has selected two companies to make spacesuits for its Artemis moon programme and future International Space Station (ISS) missions. Teams led by Axiom Space and Collins Aerospace (with ILC Dover as a major contributor) received access to a contract worth up to a total of $3.5 billion to supply spacesuits for future NASA missions through 2034, agency officials announced today (June 1).
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DID YOU KNOW?
• The Artemis programme – back to the moon by 2025! The Artemis missions will be the first crewed missions to the moon since 1972. The program has the mid-term goal of establishing a sustainable human presence on the moon, with the long-term objective being that of establishing a lunar base for resource extraction and eventual exploration of other solar system bodies.
• Gravity on the lunar surface is about one-sixth that on Earth! There is some gravity on the noon, albeit much weaker than that on Earth, with an acceleration due to gravity of around 1.6 metres per second squared (compared to Earth’s 9.8 metres per second squared). That means that someone on the moon will only weigh around 16.6 per cent of their weight on Earth!
For more trivia, see: www.um.edu.mt/think.