A new study suggests that Earth and Mars didn't grow according to the same formula, offering crucial clues about planet formation and the conditions necessary for the creation of potentially habitable worlds .
“The most surprising thing is that Earth and Mars appear to have formed in different ways. We can expect that two planets that formed next to each other in the same Solar System would have more similar formation histories,” said Professor Anders Johansen, a planet formation expert at the Globe Institute of the University of Copenhagen. He co-led the research team with Assistant Professor Haiyang Wang.
Two rocky planets, two paths of formation.
Rocky planets like Earth and Mars are thought to have formed from leftover matter around a young sun. In the process, these clumps of matter grew larger, collided, coalesced, and eventually formed planets.
There are two main mechanisms that may play a role in this process. The first is the collision and merger between relatively large objects called planetesimals, or microplanets.
The second mechanism is gravel accretion, in which smaller particles of matter drifting in the protoplanetary disk are drawn in by growing celestial bodies.
New research suggests that both mechanisms contributed to the formation of Earth and Mars. However, their contribution rates differ significantly on the two planets.
According to Haiyang Wang, at least 75% of Earth's mass appears to originate from two young planets, also known as protoplanets, which have grown to large sizes through gravel accretion. Microplanets contribute a maximum of about 25% of Earth's mass.
Meanwhile, the story of Mars is almost reversed. About three-quarters of Mars' mass appears to originate from microplanets, while the remaining quarter comes from gravel accretion.
This means that although Earth and Mars are neighbors in the Solar System, the "materials" and the way they accumulate matter to become planets are very different.
The chemical composition retains traces from 4.5 billion years ago.
To understand what happened in the early stages of the Solar System, researchers cannot directly observe the formation of Earth or Mars. Instead, they must search for "fossil traces" preserved within these planets.
The research team focused on volatile elements such as sodium, zinc, and potassium in the crust and mantle of Earth and Mars.
These elements can evaporate at high temperatures, so the amount of them remaining on the planet today may reflect the conditions the planet experienced during its formation.
Scientists then combined these chemical traces with computer models to test various formation scenarios, thereby determining which scenario best fits the characteristics of Earth and Mars today.
“This is really like a large-scale criminal investigation to find out what happened at that time, when most of the evidence has long since disappeared. But even after 4.5 billion years, the composition of the Earth's and Mars' mantle is still preserved. It can be seen as a testament to the formation process,” Anders Johansen explains.
These markers are particularly important because the process of planet formation can dramatically alter its chemical composition.
Temperature, growth rate, and the amount of matter a planet accumulates all influence whether volatile elements are retained or lost into space.
Of course, reconstructing the process of planet formation 4.5 billion years ago cannot be entirely accurate. Scientists still don't know the exact composition of the original materials that made up the Solar System.
Therefore, the research model must rely on certain assumptions about the composition of the "building materials" of planets. When these assumptions are changed, the proportion of gravelly and microplanetary accretion may also change.
However, it is noteworthy that the core conclusion remains unchanged.
"The exact ratios may vary slightly, but our analysis consistently shows that Earth and Mars were formed in two different ways," said Haiyang Wang.
According to him, this method also provides a more direct and accurate approach to understanding planet formation compared to the previously commonly used isotope-based method.
Isotope methods can provide a great deal of important information, but in some cases, the same data can be interpreted in different ways.
The new research therefore not only helps explain the differences between the two neighboring planets but also contributes to clarifying how rocky planets develop in the early stages of a star system.
How did the Earth form relate to life?
This discovery has even greater significance: it could help scientists better understand why some planets become habitable worlds, while others become barren and harsh.
The formation process determines the amount of volatile matter a planet can retain.
These include water and many other compounds that are essential for life.
If a planet forms in a way that causes it to lose most of its volatile elements, its ability to sustain water or other components necessary for future life may be limited.
Conversely, a suitable formation history can help the planet retain the resources necessary for a habitable environment.
"If we understand how planets lose volatile elements during formation, we can also better predict the amount of water and other life-supporting substances they eventually retain," said Anders Johansen.
Clues to the hunt for habitable planets.
The methods used in this study could also be applied in the future to study rocky planets outside our Solar System.
Thousands of exoplanets have been discovered, but determining whether a world is truly suitable for life remains an extremely difficult problem.
Instead of focusing solely on a planet's size, temperature, or distance from its host star, scientists may need to look deeper into how that planet formed.
Earth and Mars demonstrate that two planets may have formed close together but possess very different formation histories.
That very history may determine the chemical composition, water content, and environmental conditions they will maintain for billions of years to come.
Therefore, studying the process of planet formation not only helps answer the question of how Earth and Mars came into existence.
Furthermore, it could become a crucial tool in the hunt for "second Earths" and an answer to one of astronomy's biggest questions: Does life exist anywhere else besides Earth?
(According to SciTechDaily, Earthsky, LiveScience)