Astronomy: passion for collecting in space | nd-aktuell.de

It’s not exactly as if we on Earth don’t receive plenty of extraterrestrial gifts: every year, more than 5,000 tons of “micrometeorites” fall on Earth, fragments of objects in the solar system that are so tiny that most of them can’t even be seen didn’t notice anything. At most in the form of shooting stars or the brighter fireballs, whose slightly larger original bodies sometimes fall to earth as pebble-sized meteorites. Exceptions are rare. For example, the Chelyabinsk meteor, which made a remarkable appearance in the Russian Urals in 2013 with a blindingly bright tracer, loud thunder, pressure waves and the fall of numerous fragments and, with an initial weight of 12,000 tons, was the largest meteor in over 100 years.

Meteorites or their cosmic parent bodies, the meteoroids, as well as the larger asteroids, are among the most original bodies in the solar system. Unchanged by geological processes, they have been orbiting the sun for billions of years. By studying them, it is possible to study processes and environmental parameters from the early days of the solar system and thus better understand the history of planet formation.

Access to uncontaminated rock

But no matter how original the extraterrestrial fragments once were, they melt as they fly through the earth’s atmosphere and end up in the dust of deserts or in the snow of icy deserts. Both are excellent locations for meteorites, as newly fallen objects are particularly noticeable in the barren landscape. When meteorites land on Earth, they are contaminated with all kinds of terrestrial material.

And so the idea came up to access where no earthly dust should be found: on the moon.

With Apollo 11 on July 20, 1969, two people landed on our satellite for the first time: Neil Armstrong and Edwin “Buzz” Aldrin. In addition to the famous “small step,” the astronauts set up numerous instruments, such as those for measuring the solar wind or seismometers, and then took out their toolbox. They worked on the surface with hammers, shovels and drills and collected – in the classic way by hand – a total of 21 kilograms of moon rock, which was examined shortly afterwards in laboratories around the world. The dusty, dark chunks didn’t look particularly spectacular at first glance, but the analyzes quickly produced some unexpected results – for example, that the moon had to be almost as old as the Earth and showed numerous geological similarities.

The lunar material they brought with them quickly became very earthy again shortly after landing: The astronauts had to fill out a normal customs declaration for this. This included a precise statement of their route and a description of the cargo, neatly signed by the responsible customs inspector at Honolulu Airport.

In total, the Apollo missions between 1961 and 1972 brought around 380 kilograms of moon rock to Earth, divided into just over 2,400 samples. The lunar chunk “Big Muley” at 11.7 kilograms is the heaviest object.

The Soviet unmanned probe “Luna 16” collected significantly less in 1970 – it only carried 101 grams of moon rock with it on its way back to Earth. But the mission was a scientific heavyweight for another reason: With Luna 16, it was possible for the first time to take a lunar sample fully automatically, i.e. only with the use of robots, and bring it back to Earth intact.

The sun in focus

The scientists were beaming – and so was the auction house Sotheby’s: in 2018, 0.2 grams of Luna’s rock was sold for $855,000. With the successful mission, another bright target became the focus of interest: the sun. Now, even with the best gloves, it is not possible to reach into the 5,500 degree Celsius hot surface. But the “Genesis” space probe mission (launched in 2001), the first return mission since Apollo and Luna, was intended to investigate the so-called solar wind. The stream of charged particles is constantly blown away from the sun and allows – at a safe distance – to determine the exact composition of our central star very precisely. For this purpose, highly pure collectors made of gold, sapphire, diamond and silicon were exposed to various solar wind regimes and then brought back to Earth in a sample capsule. A failed landing parachute put a damper on the mission, but despite an impact speed of more than 300 kilometers per hour, some collectors remained intact and could be examined.

It was also planned to create some of the samples as a reserve of solar matter for future scientists – this is also a great incentive for extraterrestrial “hunting and gathering”. Once the material has been archived on Earth, it can be examined at a later date using improved or even new techniques. For example, a working group network was recently founded with the NASA program ANGSA (Apollo Next Generation Sample Analysis Program) to examine selected samples from the Apollo program using the latest technological methods.

A few years later, a Japanese “peregrine falcon” (the translation of the Japanese mission name “Hayabusa”) began its first approach to the near-Earth asteroid Itokawa. For the first time, samples were to be taken from such a small astronomical body and brought to Earth. Since the gravity of the approximately 330 meter long, peanut-shaped object (more of a dense agglomeration of rock than a compact block) was not sufficient to keep the probe in an orbit, “Hayabusa” parked at a distance of around seven kilometers in an orbit accompanying the asteroid around the sun.

Violent solar storms and technical difficulties made sampling difficult, but in November 2005 “Hayabusa” took action. To do this, the probe briefly approached the asteroid and deposited a kind of “dust funnel” on the surface. Attached to the side of the funnel was a firing device that fired a small ball into the surface at 300 meters per second, stirring up dust that could then be “sucked out.” The maneuver was successful and the sample capsule returned to Earth intact. Analysis showed that Itokawa was probably made up of fragments of a much larger asteroid that broke apart. The surface of the fragments was then exposed to space for eight million years.

Traces of amino acids and water

A few years later, the Japanese space agency carried out another successful sample return mission to the asteroid Ryugu with “Hayabusa 2”: The capsule successfully landed back on Earth on December 5, 2020. Initial analyzes of the samples not only revealed more than ten different types of amino acids, the basic building blocks of life, but also evidence of the early presence of water, which helped shape the asteroid’s complex chemistry millions of years ago.

The type of “carbonaceous chondrites”, a rare type of stony meteorite, to which Ryugu would also belong, rarely survives the flight to the earth’s surface intact. The untouched sample thus provided an extraordinary insight into this type of rock – and may provide answers to the question of how the young Earth once accumulated its considerable water reserves.

And with “Wild 2,” a comet also received a visit from Earth as part of NASA’s Stardust Mission, just in time for the start of the new millennium. The probe flew through the coma (the bowl-shaped cloud of matter that forms around the comet’s nucleus as it approaches the sun) in two collection phases and collected comet particles in the “sponge-like” airgel collectors. Since the airgel is an extremely porous solid whose volume consists largely of cavities, the fast particles do not smash the collector – but simply get stuck “at some point”.

And now “Osiris-Rex”, the NASA mission that set off to the asteroid Bennu in 2016. During the observation phase, the surface was searched for a suitable sampling location and the probe was gradually lowered to an orbit just 374 meters above the surface. In October 2020, “Osiris-Rex” approached the asteroid within a few meters and deployed a robotic arm that used a nitrogen fan to stir up sample material and grab it courageously. The sampling instrument penetrated around 50 centimeters into the surface of the asteroid.

Around six months later, the probe, now in an orbit almost four kilometers above the surface, flew over the sample collection site again and took high-resolution images of the site, dubbed the “Nightingale,” in order to document the effects of the sampling procedure. In May 2021, the sample capsule with around 250 grams of material began its journey back to Earth – and in September 2023 it landed gently using a parachute in the Great Salt Desert of Utah in the USA.

A still unopened sample capsule

And the samples are actually guaranteed to be uncontaminated: two of the 35 cover screws have so far stubbornly resisted all attempts to open them. Now specially newly designed screwdrivers should help open the Bennu’s box. However, some asteroid dust, which was found on the outer skin of the sample container and showed an unexpected composition in initial analyses, caused some anticipation. But familiar things, such as hydrocarbons, carbonates and sulfide minerals, were also found in the samples and give hope for further significant discoveries.

Let’s keep our fingers crossed for the NASA scientists that they will soon have the two missing screws loosened and that the new year will bring many more exciting insights into the early days of our solar system – with all its rocky and gas planets, the meteorite confetti and that one huge sparkler in the middle.

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