Water from Asteroids, Water the Chances?
Brian Sousa, Applied Physics, 2020
Though water makes up over 70 percent of our planet, we still do not know where it originally came from. Research has shown that the early universe was full of water, but the process of how it came to our planet is one that is still up for debate.
Initial evidence gathered on the creation of Earth has led many astronomers to believe that water must have been brought from somewhere else.Through simulations run to model Earth’s early history, it has been found that the temperatures would have been too high for surface waters to form and not evaporate. Researchers have also used these simulations to calculate the flavor of water that the Earth would have had when it was first forming. The term flavor refers to the ratio of heavy water, water composed of deuterium instead of hydrogen, to normal water. Assuming that water originated on Earth, this ratio should have stayed constant, but current measurements of the ratio is higher. However, if water was also delivered to Earth, this would explain the different ratio. This led astronomers to begin looking at different sources, with comets and asteroids being the most likely.
Assuming that water originated on Earth, this ratio should have stayed constant, but current measurements of the ratio is higher.
To investigate the possibility of comets, NASA began the Rosetta mission. Rosetta is a space probe that was sent to catch and soft land on the comet 67P/Churyumov-Gerasimenko, where samples would be collected and brought back to Earth. After measuring the water vapors on 67P, we learned that the water vapors on the comet were significantly different from those found on Earth, suggesting that these types of comets could not provide Earth with its water. In response, research shifted to focus on asteroids.
To investigate this possibility, NASA launched the Osiris-REx mission. The Osiris-REx is a spacecraft travelling to the carbonaceous asteroid Bennu, with the purpose to be the first U.S. mission to bring an asteroid sample to Earth. Bennu is already known to contain water and could collide with Earth one day, indicating that similar colliding asteroids could have delivered water to Earth in its early history. The spacecraft will take a detailed survey of Bennu where it will map out potential sample sites. Once a site is determined in July of 2020, Osiris REx will touch onto Bennu and retrieve a sample to potentially provide more information about the early creation and evolution of our planet and solar system.
Most planets lose some of their atmosphere to space, and it would be easier for the lighter hydrogen to escape than the heavier deuterium.
While many astronomers believe that asteroids are responsible for delivering Earth’s water, there is some suspicion about this idea. The belief that asteroids delivered Earth’s water is based on the idea that the ratio of heavy water to regular water on Earth today doesn’t match what it should have been during its early life. However, some astronomers argue that this ratio could be expected to change over time. Most planets lose some of their atmosphere to space, and it would be easier for the lighter hydrogen to escape than the heavier deuterium. This, along with other geological processes, could have caused the ratio on Earth to gradually increase. A recent study of primordial water, water that has been undisturbed through Earth’s lifetime, collected in the Earth’s mantle has shown a 25 percent lower ratio of deuterium to hydrogen than what is found now. This lower ratio suggests that asteroids would not be a good fit as the source of Earth’s water. At this time, the results from the study are not yet widely accepted, but they have sparked interest into further research into this idea.
Although the question of the origin of our planet’s water will remain unanswered for now, promising research has allowed a discussion to develop. As we learn more we will gain a deeper understanding of the origin of our planet and how life on Earth came to be.