This is our big question: How did life on earth begin? Anyone who claims to have the answer tells great stories. We just don’t know yet.
Even if a final answer is still a long way off – or can never be found – there are some clever ways to nibble on the edges of this big question. A group of researchers from Kobe University in Japan are addressing this compelling question with their own question: Did the heat from asteroid impacts help life?
This team of researchers is not the first to think about asteroid impacts and their role in creating life on Earth. But instead of focusing on asteroids that hit Earth and provide water and chemicals, they are studying the impacts between asteroids and other small bodies. It is possible that the heat from these impacts could create water and life-producing chemicals on the surface of the asteroid and then be given off to Earth.
The group of scientists started with an asteroid proxy made of porous plaster as a target. They placed thermocouples in their asteroid to measure heat. Then they made high-speed impacts by accelerating projectiles from the Kobe University gas cannon. Your two-stage gas cannon is special physics equipment that can accelerate things to extremely high speeds.
On the left is the Kobe University gas pistol. Gas cannons can propel projectiles at extremely high speeds for physical research. The picture on the right is from a gas pistol in a GM / Delco facility. It is the result of a 7 gram plastic projectile fired from a gas pistol at 7,000 meters per second into an aluminum block. Photo credit: (L) Yasui et al. 2021, Kobe University. (R) From cameraman: RD Ward. Depicted service: Other service ID: DDSC8513609, Public Domain, https://commons.wikimedia.org/w/index.php?curid=876520
A critical idea behind their experiment is the change in the water and the heat required to create it. Aqueous alteration is when minerals in the rock change due to chemical reactions with water. These reactions can produce organic solids. But for these reactions to take place, the asteroid’s ice must melt. In larger bodies, scientists believe that the decay of aluminum 26, a radioactive isotope, can provide heat for changing water. However, this only occurs in larger asteroids around 10 km in diameter and may have only occurred in the solar system’s first 10 million years before all of Al 26 decayed. Could the water change due to impacts on smaller asteroids much later in the life of the solar system?
They monitored the temperature generated by the impacts as they increased the speed of their projectiles. Not only did they want to know how much heat is being generated, but also how long that heat lasts. Could asteroid impacts generate enough heat to create chemicals that spring from life without destroying the asteroids themselves? How widespread are these conditions in the solar system and could these chemicals still be produced in older solar systems like ours?
In their work, the team pointed out that in the main asteroid belt, the relative speed between the asteroids is around 4 to 5 km / s. The shock of these collisions would have immediately increased the temperature around the resulting crater. Collisions like this were common in the youth of our solar system long after all of Al 26 had disintegrated. The heat from these impacts would have been most pronounced with more porous asteroid bodies. There have been many numerical studies of the heat from these impacts, but the authors of this paper say theirs may have been the first to be examined directly.
The researchers used different types of projectiles moving at different speeds to develop a model of impact heating. The picture below shows some of their experimental results.
The graph on the left shows the impact results of a polycarbonate projectile flying at 1.7 km / s. The graphic on the right shows the impact results of an aluminum projectile flying at 4.3? Km? S? 1. The points marked with i = 1 to 4 represent the thermocouples. Image source: Yasui et al. 2021.
Using their experimental data, the team developed a rule of thumb for the effects of impact heating on asteroids. The thermal conduction model based on this rule enabled them to calculate the heat distribution around the impact crater. Then they compared their model with what is known about water changes and the formation of organic solids from meteorite analyzes.
This picture shows the heat distribution around the crater floor of asteroid mother bodies, calculated with the calculated heat conduction model
The dashed lines are isothermal contour lines. The numbers corresponding to the isotherm contour lines indicate the value obtained when the distance from the point of impact is normalized by the radius of the crater. Each panel shows results for objects at different distances from the earth. Image source: Yasui et al., 2021.
Overall, the researchers found that the potential of asteroid impacts to create vital chemicals is more widespread than thought. It is more widespread in space and time, and the necessary heat can be generated by impacts that create craters up to 100 m in diameter. The team says their results increase the number of astronomical bodies that water and organic matter may have supplied the origin of life on earth.
Another interesting result of their work are organic solids, which were formed in the nebula cloud at the very beginning of the formation of our solar system. The team showed that the heat from impacts can be like a double-edged sword. Not only can this heat forge new organic materials, but it can also destroy the same type of materials that have been present on asteroids and asteroid mother bodies since the early days.
We may never know exactly what gave birth to life on earth. But we can at least build a trail of evidence leading to the necessities for it to appear. If this paper is correct in its conclusion, then the manufacture of some of the vital chemicals may occur more frequently than expected.
But that doesn’t mean that life is.
The paper presenting these results is entitled “Actions can provide heat for aqueous changes and organic solid formation on asteroid mother bodies”. It was published in the journal Nature Communications Earth and Environment. The first author is Minami Yasui, a lecturer at the Graduate School of Science at Kobe University.