As we know, one of the key factors for the evolution of life is the presence of “volatile substances”, that is, elements and compounds that can easily evaporate at relatively low temperatures. This means that understanding where these volatiles come from and whether Earth is unusually rich in volatiles is important to understanding what makes life and new life possible. means that studypublished on October 11th scientific progressmost of which suggests that the planets originate from a relatively small proportion of the material that formed.
Planets are formed by the gradual accretion of tiny pieces of material called planetesimals. There are two basic categories of planetesimals: differentiated and undifferentiated. Both begin as “large pieces of dust and other small rock fragments stuck together (often loosely),” as the study’s lead author Leissa Martins explains. Undifferentiated planetesimals basically remain as they are. In contrast, differentiated planetesimals are characterized by being exposed to enough heat that all of their components melt together.
This melting is caused by the radioactive decay of aluminum-26 (Al-26), an unstable isotope of aluminum. As Al-26 decays, it generates so much heat that it essentially melts the surrounding material. “This process degasses a lot of the volatiles,” Martins explains. Once evaporated, the volatile materials simply drift into space. ”[They are] They were lost because of the low gravity of these small objects. ”
Thankfully for us, all the Al-26 in our solar system decayed very early on, leaving enough undifferentiated material to supply Earth with the volatile compounds necessary for the evolution of life. . And when Al-26 disappears, so does it. Isotopes form in the core of a star that has burned off all its hydrogen and is hurtling toward its final moments of explosion.
This means that they are found in star-forming regions, where new stars coalesce from the scattered remnants of their dead predecessors, but not in relatively quiet and benign environments like today’s solar system. “Al-26 is continuously produced in regions of the galaxy where new stars and planets are forming, but it is not necessarily continuously injected into the same planetary system over its lifetime,” Martins said. If supernova explosions occur repeatedly, it will be very inconvenient for us.”
Martins and her team’s research investigated the earth’s sources of zinc. They found that while about 70% of Earth’s mass comes from the accretion of differentiated planetesimals, that differentiated material provides only 10% of the planet’s zinc. This means that 30% of the earth I didn’t Forms from differentiated planetesimals are the source of most of the volatile compounds on Earth. “Without this substance, we would be left with much more modest volatile compounds.”
The question of how lucky this was, and whether Earth is unusually rich in volatile materials compared to similar planets in other star systems, remains open. “There are other factors that play a role in determining that amount. [differentiated and undifferentiated material] Planets accrete outside of time (i.e. mixing and transfer of material between different heliocentric distances). There is also still debate as to whether Al-26 was evenly distributed throughout the solar system, or whether it was concentrated in some parts and not in others. ”
Similarly, it’s certainly possible that other solar systems could find Earth-like planets that could theoretically support life but formed without the materials to do so, Martins said. “This study highlights that there are many criteria that must be met to form a habitable planet. When looking for life, we typically look for planets in the so-called Goldilocks zone. That’s because those planets are likely able to maintain liquid water on their surfaces, but that assumes they had water and other volatile substances to begin with, when in fact the planets were there to begin with. It could be quite dry. Our study doesn’t really tell us about the possibility of such a scenario, but it’s at least possible.”
