Falling Diamonds From A Long-Lost Planet

Our ancient Solar System was a violent place, where primordial objects crashed into one another, blasting each other into a multitude of fragments. This chaotic, turbulent mess of primordial crashes, occurring between rampaging objects, has inspired some planetary scientists to refer to our ancient, still-forming Solar System as a “cosmic shooting gallery”. Indeed, some of these invading objects wreaked havoc when they crashed into the newborn Earth, often contributing more and more of their material to our still-forming planet. Planetary formation models show that the solid, terrestrial inner planets of our Sun’s familiar family–Mercury, Venus, Earth and Mars–were born as a result of the accretion of tens of Moon-to-Mars-sized planetary embryos through raging, energetic giant impacts. In April 2018, a team of astronomers published their new findings suggesting that a space rock that fell to Earth may have come from a long-lost proto-planet from the early Solar System–and that tiny bits of iron and sulfur embedded in diamonds within this meteorite likely were created under high pressures found only deep within planets the size of Mercury or Mars.

Alas, tattle-tale relics of these large, lost proto-planets have been difficult to find. Ureilites are one of the major families of achondritic meteorites and their parent body is thought to have been catastrophically blasted to pieces by an impact during the first 10 million years of our 4.56 billion-year-old Solar System. Achondrites lack chondrules and originate in differentiated bodies–such as planets. A chondrule is a spheroidal mineral grain, that is present in large numbers, within some stony meteorites 먹튀검증. In the April 17, 2018 issue of Nature Communications, a team of planetary scientists published their report announcing that they had studied a chunk of the Almahata Sitta ureilite using transmission electron microscopy. The scientists found, scattered within this chunk, large diamonds that could only have formed at high pressure deep within a parent body. The team of researchers detected chromite, phosphate, and (Fe,Ni)-sulfide (iron, nickel, sulfide) inclusions embedded in diamond, and they reported that the composition and morphology of the inclusions can only be explained if the formation pressure was greater than 20 GPa. These pressures indicate that the ureilite parent-body was a Mercury-to-Mars-sized planetary embryo.

Sulfide inclusions in diamonds are the most common of all inclusions, and they contain important information about the timing and physical/chemical conditions prevailing during diamond formation.

The story of the Almahata Sitta ureilite began when an asteroid, designated as Asteroid 2008 TC3, crashed down in the Nubian desert in Sudan in 2008, and its recovered batch of meteorites, called Almahata Sitta, are mostly composed of ureilites with a variety of chondrites. Ureilite fragments are coarse-grained rocks that are primarily made up of olivine and pyroxene that originated from the mantle of the ureilite parent body (UPB), that has experienced a disruption resulting from a catastrophic impact that occurred early in our Solar System’s existence. High concentrations of carbon distinguishes ureilites from all other achondrite meteorites, with graphite and diamond nestled between grains of silicate.

Shooting GalleryWhen our Solar System was first forming, strange things were occurring. Primordial planetary building blocks, called planetesimals, traveled away from where they had been born, and violently crashed into one another as a result. Sometimes these wandering planetsimals merged, but quite frequently they collided, leaving only the wreckage of both bodies behind to tell the tragic story of their ancient, deadly collision.

The history of our Solar System is one of turmoil, and this is also the case with distant planetary systems around other stars beyond our Sun. Stars are born surrounded by a whirling disk made up of gas and dust, termed a protoplanetary accretion disk. These swirling disks form at about the same time that the baby star, called a protostar, is born within its blanketing, obscuring natal cloud.

Protoplanetary accretion disks contain large quantities of gas and dust that feed growing, voracious protoplanets. Our own Solar System, as well as other planetary systems, form when a relatively small and very dense blob, embedded within the billowing, undulating swirls of a cold, dark, giant molecular cloud, collapses under the merciless influence of its own gravity. Floating throughout our Milky Way Galaxy in huge numbers, these phantom-like, beautiful clouds, serve as the bizarre nurseries of fiery baby stars. These gigantic, frigid clouds are mostly composed of gas, but they also harbor smaller quantities of very fine dust. Although it seems counterintuitive, things have to get cold in order for a hot baby star to be born.

Most of the collapsing blob collects at the center, and ultimately ignites with a brilliant stellar fire as a result of the process of nuclear fusion–thus forming a new stellar infant (protostar). The remaining gas and dust eventually evolves into the protoplanetary accretion disk from which planets, their moons, and other smaller objects are born. In its earliest stages, a protoplanetary accretion disk is both very massive and searing-hot–and it can circle its host star for as long as ten million years.

By the time a brilliant star, that is about the same mass as our Sun, reaches what is termed the T Tauri phase of its development, the very hot, massive surrounding accretion disk has become considerably cooler–and thinner. A T Tauri is a stellar tot–a very young, variable star that is similar to our Sun, and is quite active at the age of a mere 10 million years. These fiery stellar toddlers sport large diameters that are several times greater than that of our own Star at present. However, T Tauris are still in the process of shrinking. Unlike human babies, Sun-like stellar tots shrink as they grow up. By the time the stellar toddler has reached this stage, less volatile materials have started to condense close to the center of the surrounding accretion disk, thus creating very fine and extremely sticky motes of dust. The delicate dust particles carry within them crystalline silicates.

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