In the search for our origins, old witnesses are not always easy to find: Only the oldest chunks of the solar system complete the once upon a time of our young planetary system. Eventually even the most frugal astronomer gets greedy - he wants something he can touch. Because if there is a theory, let's take the current one about the formation of the solar system, then nothing is more exciting than to practically understand the predictions that can be derived from the theory on the object and possibly find them confirmed. Incidentally, it's no big deal if a result doesn't really match the theories - they can also be changed from time to time. So it's almost even more exciting when the collision between practice and reality opens up a few highly interesting new gaps to fill.
A research team led by Philip Bland from Imperial College London is dealing with a particularly obstinate and nebulous gap in knowledge: that of the theoretically inadequately supported, very different composition of "volatile" and "moderately volatile elements" in the sun and earth. "Volatile" is relatively relative here: what is meant are elements that condense into something solid at temperatures below the comparatively cool 650 Kelvin. These include zinc, lead and sodium - they occur on the sun in rather large amounts, but in the sum of terrestrial rocks and the other inner rocky planets, obviously in hardly any significant amounts.
Strange, because the building material that the sun and planets are made of is actually pretty much identical - after all, everything comes from one and the same pile of rubble, the primeval solar nebula, which began to form the bodies of the to condense the solar system. At some point these volatile elements must have made themselves out of the dust of the earth: the great volatile depletion, one of the inexplicable mysteries on the way from the original material grit to the finished planet.
Now wondering where, when and why it took place - and this is where explorer greed comes into play. After examining typical Terrestrial old rock in a comparatively simple manner, researchers were keen to examine non-Terrestrial chunks to question the absence of the missing elements on more than one class of objects. And since, apart from a few chunks of lunar debris, no soil sample has yet been taken from extraterrestrial celestial bodies, the scientists are concentrating on stones that reach Earth from space by themselves: meteorites.
The so-called chondrite meteorites are the coveted old stars, the oldest witnesses of matter on earth from the primeval times of the solar system, which condensed fairly soon from the solar primeval nebula and much later apparently remained almost unchanged over time fell to the ground. If one examines the meteorites as freshly as possible after the impact, one finds an original mixture of crumbly baked carbon compounds and larger iron and magnesium-containing fused globules of silicates, the chondrules that give the meteorite its name. It also contains preserved, unchanged traces of the solar primordial matter from the beginning of all times in the solar system. And what proportion of the mysterious volatile elements?
Bland's group looked for the answer by looking at a few typical representatives of the 45 primitive meteorites that have been found so far around the world and analyzed the distribution of element traces in them. Some samples had already been taken from them and it was found that only the most primitive of all meteorites, the so-called CI chondrites, actually contain the same composition of elements as our sun.
But the researchers have now shown that it is worth taking a closer look: it is complicated to analyze only the really oldest building blocks of the somewhat younger meteorites. All other parts of the object may have changed over time under various influences. This precise proof has only been achieved now, indirectly and with the help of a few calculation and analysis tricks by Bland and colleagues. Result of their efforts: In fact, not only the CI variety, but all meteorites were originally formed from matter already robbed of its volatile elements. The solar primeval nebula was therefore apparently poor in these element representatives very early on. Whatever process is responsible for this, it must have taken place in the earliest infancy of the planetary system - and could well be very typical for the formation of planetary systems at all.
This, Bland reassures, "answers one of the many questions" that could still be asked about the formation of planets from the primordial solar nebula. Luckily only one - it would also be a pity if another exciting knowledge gap were to remain closed for good.