The Co-formation theory is one of the proposed hypotheses regarding the origin of Earth's Moon, suggesting that the Moon formed at the same time as Earth from the same protoplanetary disk of gas and dust. According to this theory, the Moon and Earth coalesced as distinct bodies in orbit around a common center of mass. The Co-formation theory is one of several explanations for the Moon's formation, alongside the Giant-impact hypothesis, the Capture theory, and the Fission theory. While it was considered a plausible theory in the early stages of lunar research, it has since been largely superseded by the Giant-impact hypothesis due to inconsistencies with the Moon's composition and its orbital dynamics.
Overview[]
The Co-formation theory posits that Earth and the Moon formed simultaneously through the accretion of material from the solar nebula. This material would have existed in the same region of space and, over time, came together to form both bodies. In this model, the Moon is considered a natural satellite of Earth that was never captured or ejected, but rather formed as part of Earth's early accretion process. The theory suggests that both bodies' similar composition, particularly in terms of isotopic signatures, would result from their shared origin.
Historical Context[]
The Co-formation theory was one of the earliest hypotheses proposed to explain the Moon's origin. It emerged as a simpler alternative to other theories, such as the Giant-impact hypothesis, which would require complex events and high-energy collisions. The Co-formation theory was attractive because it suggested that the Earth-Moon system was a natural product of the same material in the early solar system, forming in close proximity. This theory was more widely accepted during the early 20th century, but as lunar exploration and advanced analytical techniques improved, the theory began to lose support.
Supporting Arguments[]
Isotopic Similarity[]
Proponents of the Co-formation theory cite the close isotopic similarity between Earth and the Moon, particularly in terms of oxygen isotopes, as evidence that the two bodies originated from the same material. Studies in lunar geology, particularly those analyzing lunar samples returned by the Apollo missions, showed that the Moon and Earth have nearly identical isotopic ratios, which would be consistent with their co-formation from the same protoplanetary disk.
Stable Orbit[]
The Moon's current orbit around Earth is another point that has been argued in favor of the Co-formation theory. The theory suggests that the Moon formed at a sufficient distance from Earth to avoid gravitational disruptions that could have resulted from a giant impact or capture, allowing it to remain in stable orbit around Earth since its formation.
Formation of Multiple Moons[]
Some versions of the Co-formation theory suggest that multiple moons could have formed around early Earth, with the current Moon being the only one to survive in its orbit. This would have been a natural consequence of the material available in Earth's early environment.
Criticism and Challenges[]
While the Co-formation theory provided an early and simple explanation for the Moon’s origin, it has faced significant challenges over time.
Differing Composition[]
A key argument against the Co-formation theory is the discrepancy in the composition of Earth and the Moon. Although Earth and the Moon share many isotopic similarities, the Moon is notably deficient in volatiles such as water and other light elements, which is difficult to reconcile with the idea that they both formed from the same material. If both bodies formed together from the same disk, they would be expected to have more similar volatile content.
Angular Momentum[]
The Co-formation theory does not adequately explain the current angular momentum of the Earth-Moon system. The Moon’s mass and orbital characteristics suggest that a significant amount of energy was involved in the system's formation, which is more easily explained by a giant impact rather than co-formation. The angular momentum of the Earth-Moon system, in particular, is inconsistent with the expected values for a system formed from a single disk of material.
Lack of a Clear Formation Mechanism[]
Unlike the Giant-impact hypothesis, which is supported by detailed computer models and simulations, the Co-formation theory lacks a comprehensive mechanism for how the Earth and Moon could have formed in such close proximity without interactions that would disrupt their formation processes. Without such a mechanism, the theory is seen as less robust compared to more dynamic models.
Modern Consensus[]
Today, the Co-formation theory is largely considered less viable compared to the Giant-impact hypothesis. The Giant-impact hypothesis, which proposes that the Moon formed from the debris of a collision between Earth and a Mars-sized body, better explains the isotopic differences, angular momentum, and other observed characteristics of the Earth-Moon system. Advances in lunar geology and computational modeling have provided a more detailed understanding of the Moon’s formation, leading to the widespread acceptance of the Giant-impact hypothesis.
Related Theories[]
- Giant-impact hypothesis: The leading explanation for the Moon’s origin, suggesting that the Moon formed from debris ejected after a giant collision between Earth and another planetary body, often called Theia.
- Fission theory: The theory that the Moon was formed by material ejected from a rapidly spinning early Earth.
- Capture theory: The hypothesis that the Moon was a celestial body captured by Earth's gravity after forming elsewhere in the solar system.
See Also[]
References[]
- https://science.nasa.gov/moon/formation/#:~:text=Visiting%20the%20Moon%20with%20the,solar%20system%20began%20to%20form.
- https://en.wikipedia.org/wiki/Giant-impact_hypothesis#:~:text=The%20hypothesis%20suggests%20that%20the%20Early%20Earth,event%20later%20accreted%20to%20form%20the%20Moon.
- https://www.space.com/19275-moon-formation.html#:~:text=Co%2Dformation%20theory%20Under%20such%20an%20explanation%2C%20gravity,and%20would%20explain%20the%20moon's%20present%20location.
- https://news.uchicago.edu/explainer/formation-earth-and-moon-explained#:~:text=Alternate%20theories%20suggested%20by%20scientists%20include:%20*,protoplanetary%20disk%20at%20the%20same%20time%20(%E2%80%9CCo%2Dformation%E2%80%9D)
- https://www.astronomy.com/science/giant-impact-hypothesis-an-evolving-legacy-of-apollo/#:~:text=The%20capture%20theory%20posited%20the%20Moon%20formed,mass%20from%20the%20same%20source%20of%20material.
- https://www.space.com/25322-moon-formation-wild-theories.html#:~:text=Co%2Dformation%20It's%20also%20possible%20that%20the%20moon,moon%2C%20it%20falls%20short%20in%20other%20ways.
- https://www.lpi.usra.edu/education/workshops/unknownMoon/How_Did_the_Moon_Form.pdf#:~:text=The%20co%2Dformation%20hypothesis%20states%20that%20the%20Moon,happened%20later%20to%20change%20one%20of%20them.
- https://www.space.com/moon-giant-impact-theory-chlorine-isotopes#:~:text=The%20terms%20%22heavy%22%20and%20%22light%22%20refer%20to,into%20space%20coalesced%20to%20form%20the%20moon.
- https://study.com/academy/lesson/formation-of-the-moon-theories.html#:~:text=Fission%20means%20breaking%20apart%2C%20and%20the%20fission,a%20rapidly%20spinning%20Earth%20cast%20it%20off.
| Models of the Solar System | ||
|---|---|---|
| Solar Formation | Nebular hypothesis | |
| Dynamical Evolution | ||
| Origin of the Moon | ||
| Early Development | Grand tack hypothesis • Fission theory • Co-formation theory • Capture theory • Migration of Neptune • Jumping-Jupiter scenario | |
| Later Development | Nice model (Nice 2 model • Five-planet Nice model) | |
| Planetary Formation | Giant-impact hypothesis | |
| Placement | Heliocentric model • Geocentric model | |