Researchers are still piecing together how the initial inner Solar System planetesimals came into being.
There’s a possibility they originated close to either the silicate condensation line or the water snowline within the solar protoplanetary disk.
The crucial question remains: do their chemical makeups align more with those originating near the silicate condensation line (devoid of water and in a reduced state) or those near the water snowline (containing water and in an oxidised state)?
Scientists delve into the world of iron meteorites as snapshots from the early days of our solar system, to answer this question.
Firstly, what are planetesimals?
A planetesimal is a celestial entity crafted from dust, rock, and various materials. The term draws inspiration from the notion of infinitesimal, signifying an object so minute that it eludes visibility or precise measurement. These entities can span a considerable range in size, ranging from several meters to hundreds of kilometres.
Coined in the context of planetary genesis, the term planetesimal encapsulates the idea of compact celestial bodies emerging in the course of planet formation. While likened to miniature planets, their significance extends beyond mere size, playing a pivotal role in the universe.
Why did the scientists delve into meteorites?
In a recent study, scientists have merged meteorite information with thermodynamic modelling, leading to a significant revelation. The findings suggest that the initial inner solar system planetesimals likely developed in the presence of water, posing a challenge to the existing astrophysical models of the early solar system.
These meteorites serve as remnants of the metallic cores belonging to the initial planetesimals that didn’t evolve into planets but orbited the solar system before eventually reaching Earth. By scrutinising the chemical compositions of these meteorites, researchers gain insights into the circumstances surrounding their formation.
This investigation aids in addressing the longstanding query of whether the fundamental constituents of Earth took shape at a considerable distance from the Sun, fostering the existence of water ice, or if they originated in closer proximity, resulting in arid planetesimals.
Despite the absence of visible water in the meteorites, scientists can infer its historical presence by examining its impact on other chemical elements.
Breaking down the chemistry of water, which comprises two hydrogen atoms and one oxygen atom, reveals its oxidation potential when interacting with other elements. During this process, water relinquishes its oxygen atom. Take the reaction of iron metal with water, for instance, resulting in the formation of iron oxide. Given sufficient water exposure, this sequence can create rust, characterised by Fe2O3 and FeO(OH). Detecting rusty iron oxide on Mars strongly implies a watery history for the Red Planet.
Damanveer Grewal, the study’s lead author and a former postdoctoral scholar at Caltech, brings specialised knowledge in deciphering chemical signatures from iron meteorites to unveil secrets of the early solar system.
Despite the disappearance of any iron oxide from the initial planetesimals over time, researchers can gauge the extent of iron oxidation by scrutinising these meteorites’ metallic nickel, cobalt, and iron contents. Maintaining a balance among these three elements in comparison to other primitive materials is crucial, as any deviation suggests a certain degree of iron oxidation has taken place.
The research team stumbled upon a fascinating revelation when examining iron meteorites thought to have originated from the solar system’s inner and outer reaches. Surprisingly, these meteorites displayed a comparable level of missing iron metal.
This intriguing similarity suggests that the planetesimals giving rise to both sets of meteorites came into existence in a solar system region where water was present, implying that the elemental building blocks of planets carried water right from their inception.
What do the lead authors say?
Paul Asimow emphasised the often-overlooked significance of iron meteorites in understanding the early solar system. He pointed out that these meteorites contain a wealth of information about the earliest solar system history, provided one can decipher their signals. The discrepancy between the measurements from inner solar system meteorites and the expected values suggests an oxygen activity approximately 10,000 times higher than anticipated.
Damanveer Grewal added a layer to this understanding, noting that if water existed in the initial building blocks of our planet, it’s plausible that other crucial elements, such as carbon and nitrogen, were also present.
This implies that the essential ingredients for life might have been embedded in the foundations of rocky planets right from their inception.
Paul Asimow, however, offered a word of caution, highlighting that the method employed in the study explicitly detects water utilised in oxidising iron and does not account for excess water that could contribute to the formation of oceans.
Why is this finding important?
These findings pose a challenge to established astrophysical models of the solar system. If the planetesimals formed in the current orbital location of Earth, the existence of water would suggest a considerably cooler inner solar system than what current models propose. An alternative hypothesis suggests that these planetesimals originated farther out, where temperatures were lower, and subsequently migrated inward over time.
The research findings have been officially published in the journal Nature Astronomy.
