Earth was formed over 4.5 billion years ago. Earth's building blocks were made of different sizes of rock. Everything from dust to planetesimals. Scientists think that many of the chunks of rock were carbonaceous meteorites, which came from asteroids in the outer reaches of the main asteroid belt.
Some evidence doesn't line up with the conclusion. Some of the Earth-forming meteorites came from further out in the Solar System, according to a new study.
The Solar System's formation was explained by the nebular hypothesis. A rotating disk was formed when a mass of gas and dust collapsed. Everything else formed from what remained after the Sun formed in the center of the disk.
The Solar System has a frost line. The Solar System is divided into two regions by the frost line. It is cold enough for volatiles to form ice grains. Water, ammonia, carbon dioxide, carbon monoxide, and methane are volatiles. The Sun's energy breaks apart the volatiles inside the frost line. The solar wind pushes them away from the inner regions. They can solidify once past the frost line. The inner material is dry and rocky, while the cold outer regions are warm.
The frost line has been in different places. As the Solar System evolved, the frost line was pushed further outward by the Sun. Initially, the Sun was less energetic than it is now. The solar nebula was not as transparent as it could have been.
The first body to form in the solar system was the Sun. The planets are not. Their positions relative to the frost line and types of materials inside and outside of the frost line dictated their formation. The outer planets beyond the frost line are mostly composed of lighter elements, such as hydrogen, carbon, nitrogen and oxygen, while the inner planets are mostly composed of heavier elements, such as iron, magnesium and Silicon.
Carbonaceous chondrites played a role in the planet's formation. The outer regions of the main asteroid belt are thought to be the source of carbonaceous chondrites. Each family of CCs has the same parent body. Individual CCs are fragments of the parent body.
There might be more going on. Some of the carbonaceous chondrites came from asteroids that formed far away from the main asteroid belt and beyond the frost line, according to the researchers behind it.
The study was led by researchers at the Earth-Life Science Institute at the Tokyo Institute of Technology. The journal AGU Advances has a study in it.
The asteroid belt between Mars and Jupiter is the focus of the study. Observations of asteroids in the outer part of the belt show a feature that indicates water ice and/or Ammonium clays on their surfaces. The materials are stable at lower temperatures and can easily form in their current location. Evidence shows that the asteroids are the parent bodies of CCs. meteorites recovered on Earth do not have the same feature.
One of the puzzling features of the asteroid belt is this discrepancy.
There is new research suggesting a solution to this puzzle. The results suggest that asteroids formed in the more distant reaches of the Solar System.
These asteroids were large enough to be differentiated, meaning they had cores and mantles with different compositions. The mantles were rich in water, and the cores were denser. “Ammoniated phyllosilicates form within the water-rich mantles of the differentiated bodies containing NH3 and CO2 under high water-rock ratios (>4) and low temperatures (<70°c),”>
The asteroids have dense rocky cores. The heavier the cores, the more likely they are to be meteorites.
As planets do, asteroids form via accretion. That is represented in 1 in the figure. Some of them formed beyond the frost line, where they added NH3 and CO2 to the water ice. The asteroids are shown in 2. The differentiated asteroid is shown in part 3. The mantle lacks the CCs on Earth display. The parent asteroid can be disrupted by a collision. The features of meteorites from the hydrated core are the same as those on Earth.
The study points out a quirk in the formation of the Solar System. Astronomers think that Jupiter moved to within 1.5AU of the Sun before moving outward again. A migration took place with Saturn. The Grand Tack hypothesis is about these movements.
The asteroid belt was affected by the migrations of the Solar Systems. Many of the asteroids ended up in positions they didn't form in. CCs were created during those scattering events. The asteroids that formed Earth were originally from beyond the frost line.
The study is based on both observations and modelling. JAXA, the Japan Aeronautical Exploration Agency, leads many observations from the AKARI satellite. The all-sky survey was performed by the astronomy satellite. There were more than 5,000 asteroids in the catalogue.
The authors propose that several, if not all, C-complex asteroids and CC parent bodies formed beyond NH 3.
Scientists have more to do than just observe and model. They will soon have pieces of asteroids to study.
Hayabusa 2 asteroid sampling mission collected samples from the asteroid. The asteroid samples were returned in December 2020. NASA collected samples from the asteroid Bennu. The samples should be back on Earth in September.
Scientists will be able to compare their predictions with the samples. Hayabusa 2's samples should contain ammoniated salts and minerals, according to the distant origins of these asteroids. OSIRIS-REx samples are a test of these predictions.
One of the questions in astronomy is if the Solar System is representative of other solar systems. Is formation processes similar to all systems? How similar? How different?
Whether our solar system's formation is a typical outcome remains to be determined, but numerous measurements suggest we may be able to place our cosmic history in context soon.
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