 |
| Image Credit: http://www.thesilverink.com/wp-content/uploads/2015/04/Earth_and_moon.png |
Our Moon has a special place in our Solar System. Yes, it is our Moon, but more interestingly, it is the largest known moon compared to its host planet. Some astrobiologists believe that the large size of the moon and the resulting tides were what allowed life to form several billion years ago. Sadly, the moon is receding from the Earth by a few centimeters every year.
A question we are still pondering is how the Moon got there to begin with. The currently accepted theory is the giant impact theory, which claims that around 4.5 billion years ago, a Mars-sized protoplanet, Theia, collided with the Earth creating a disk of molten rock, gas, and debris which combined to become the Moon. This theory works well in explaining the similar orientations of the spins of the Earth and Moon and the lack of iron on the Moon. Simulations of this theory have been able to accurately recreate the Earth-Moon system.
 |
| An artists rendition of the giant impact theory. Image Credit: http://upload.wikimedia.org/wikipedia/commons/4/4a/Artist's_concept_of_collision_at_HD_172555.jpg |
This theory also used to be supported by the similarities in composition between the Earth and Moon. We have found that the Earth and Moon have the same quantities of certain isotopes while our observations of other planets and their moons show that there are very different proportions of these isotopes. This would imply that the Earth and Moon have a common origin, and that perhaps the Moon formed from material from the Earth. This could have been a result of the collision with Theia. However, simulations of the giant impact theory actually show that most of the material that forms into the Moon comes from Theia, and not Earth. If this were true, that would mean that Theia would have to have formed in a part of the planetary disk that has similar composition as Earth in order to create a Moon with similar composition as the Earth.
Two recent papers discuss the likelihood that Theia could have been isotopically similar to Earth, coming to different conclusions. Some of the reasons these two studies could have differed include their assumptions on the orbital characteristics big planets. It isn't necessarily true that these planets would have orbited in the same way back then as they do now. Both studies found that different configurations of the planets Jupiter and Saturn would have affected the regions in the planetary disk where developing planets would acquire their material, thus changing the outcomes in the formations of the Earth and Theia. Also, the distribution of the isotope, oxygen-17, is unknown, though both studies used the same assumption of a linear distribution. Perhaps a significant cause to the difference in the conclusions of the two papers' is the amount that they allowed the Earth to contribute to the formation of the Moon. The study that concluded that the similar composition of Theia was likely also allowed a larger percentage of the Moon to be made from the Earth. Finally, the study which concluded in the unlikeliness of the similar composition of Theia only considered models that were analogous to the Earth and Theia, while the other study considered all possible collisions.
Both studies require more research and analysis to come to a strong conclusions, though they offer interesting questions to consider. You can find more information on the research papers for each study. The paper concluding that such conditions for the formation of the moon are unlikely can be found here, and the paper concluding that such conditions are plausible can be found here.
Citations:
No comments:
Post a Comment