How Space Samples Changed Our Understanding of Earth’s Water Origins

The Great Water Mystery That Puzzled Scientists for Decades

For years, scientists were stuck on one of the biggest puzzles in planetary science – how did Earth end up being the only known water world in our solar system? Models of Earth's birth suggest that the planet was quite hot after its formation about 4.6 billion years ago, so scientists think it's unlikely that any water currently on Earth's surface dates back to the time of the planet's creation. The young Earth was basically a molten hellscape, far too hot to hold onto water. Yet here we are, on a planet where water covers 70% of the surface. Something had to deliver all that H2O after things cooled down.

Scientists suspected that space rocks – asteroids and comets – were the delivery service that brought water to early Earth during a chaotic period called the Late Heavy Bombardment. Prior studies have hinted that cosmic impacts could have easily brought water later, during a violent era known as the Late Heavy Bombardment, about 800 million years after Earth's formation. But proving this theory required something extraordinary: actual samples from space that could be analyzed in Earth's most sophisticated laboratories.

The challenge was immense. To uncover the source of Earth's water, scientists look for bodies elsewhere in the solar system with similar water. Out of every 10,000 water molecules on Earth, three are not normal water molecules, but instead are so-called heavy water molecules. A normal water molecule is made of two hydrogen atoms and one oxygen atom. Scientists needed to find space water with the same unique fingerprint as Earth's oceans.

When OSIRIS-REx Brought Back Asteroid Gold

The spacecraft delivered the sample to Earth on Sept. 24, 2023 when it released a capsule with grains of Bennu over Earth's atmosphere. The capsule parachuted to the Department of Defense's Utah Test and Training Range, where the OSIRIS-REx team was waiting to retrieve it. This wasn't just any space rock – it was the largest asteroid sample ever collected, weighing in at a whopping 121.6 grams. Scientists were practically trembling with excitement as they cracked open the sample container.

What they found inside completely exceeded their wildest expectations. Initial studies of the 4.5-billion-year-old asteroid Bennu sample collected in space and brought to Earth by NASA show evidence of high-carbon content and water, which together could indicate the building blocks of life on Earth may be found in the rock. But this was just the beginning of what would become one of the most groundbreaking discoveries in space science.

Among the most compelling detections were amino acids – 14 of the 20 that life on Earth uses to make proteins – and all five nucleobases that life on Earth uses to store and transmit genetic instructions in more complex terrestrial biomolecules, such as DNA and RNA, including how to arrange amino acids into proteins. Scientists had literally found the ingredients for life floating around in space for billions of years. Scientists also described exceptionally high abundances of ammonia in the Bennu samples. Ammonia is important to biology because it can react with formaldehyde, which also was detected in the samples, to form complex molecules, such as amino acids – given the right conditions.

The discovery was so significant that it prompted one researcher to exclaim with amazement about finding what essentially amounts to a recipe for life preserved in a 4.5-billion-year-old cosmic time capsule.

The Shocking Discovery of Ancient Saltwater in Space

But OSIRIS-REx had even more surprises in store. Studies of rock and dust from asteroid Bennu delivered to Earth by NASA's OSIRIS-REx spacecraft have revealed molecules that, on our planet, are key to life, as well as a history of saltwater that could have served as the "broth" for these compounds to interact and combine. Scientists found evidence that Bennu once had flowing saltwater – like a cosmic ocean floating through space.

Researchers identified salt minerals in the Bennu samples that were deposited as a result of brine evaporation from the asteroid's parent body. In particular, they found a number of sodium salts, such as the needles of hydrated sodium carbonate highlighted in purple in this false-colored image – salts that could easily have been compromised if the samples had been exposed to water in Earth's atmosphere. This was direct evidence that asteroids weren't just dry rocks – they were remnants of much larger, water-rich worlds.

Think of it like finding salt residue on a dried-up lake bed, except this lake bed had been floating through space for billions of years. It also hints that the asteroid could have been born from a larger, water-rich celestial body. Scientists were looking at fossils of ancient cosmic oceans, preserved in mineral form.

Japan's Hayabusa2 Rewrites the Textbook on Organic Molecules

While NASA was making headlines with Bennu, Japan's Hayabusa2 mission was quietly revolutionizing our understanding of organic chemistry in space. The Hayabusa2 spacecraft visited the carbonaceous asteroid Ryugu and collected samples of its surface materials, which were brought to Earth in December 2020. The samples from Ryugu were like opening a chemistry set that had been sealed for billions of years.

Asteroid Ryugu has a rich complement of organic molecules, according to a NASA and international team's initial analysis of a sample from the asteroid delivered to Earth by Japan's Hayabusa2 spacecraft. The discovery adds support to the idea that organic material from space contributed to the inventory of chemical components necessary for life. But the real bombshell came when scientists found something truly extraordinary.

As a result, we succeeded in detecting uracil, one of the nucleobases in the RNA of all earth life, and vitamin B3 (niacin), one of the coenzymes essential for the metabolism of life. They had found actual building blocks of RNA – the molecule that many scientists believe came before DNA in the story of life on Earth. It was like discovering that space had been cooking up the ingredients for life long before Earth even existed.

Amino acids, aliphatic amines, carboxylic acids, polycyclic aromatic hydrocarbons, and nitrogen-heterocyclic compounds were detected, which had properties consistent with an abiotic origin. These compounds likely arose from an aqueous reaction on Ryugu's parent body and are similar to the organics in Ivuna-type meteorites. The diversity of organic molecules was staggering – more complex than what scientists had ever found in meteorites that crashed into Earth.

The Moon's Surprising Secret Water Reservoirs

Just when scientists thought they had a handle on space water, China's Chang'e 5 mission dropped another bombshell. Here we show the Chang'E-5 in-situ spectral observations of lunar water under Earth's magnetosphere shielding and relatively high temperatures. Our results show the hydroxyl contents of lunar soils in Chang'E-5 landing site are with a mean value of 28.5 ppm, which is on the weak end of lunar hydration features. Scientists had found water on the Moon – not just at the freezing cold poles, but in the middle latitudes where spacecraft had landed.

But the source of this lunar water was the real surprise. Here, we show the prominence of water (OH/H2O) attributed to solar wind implantation on the uppermost surface of olivine, plagioclase, and pyroxene grains from Chang'E-5 samples. The results of spectral and microstructural analyses indicate that solar wind-derived water is affected by exposure time, crystal structure, and mineral composition. The Sun itself was creating water on the Moon's surface!

The H ions in the solar wind bombard the lunar surface at high speed (300–800 m/s), and then are injected into the surface to form OH or H2O with free O bonds created probably by solar wind particle sputtering and implantation, micrometeorite vaporization, solar UV radiation or cosmic and galactic ray spallation and implantation. It's like the solar wind is a cosmic bartender, mixing hydrogen from the Sun with oxygen in lunar rocks to serve up fresh water cocktails. Our estimate of a minimum of 170 ppm water content in lunar soils in the Chang'E-5 region is consistent with that reported by the Moon Minerology Mapper and Chang'E-5 lander.

The Itokawa Revelation That Changed Everything

Even before the big sample return missions made headlines, scientists had their first hint that space rocks could be water factories. In a paper published in Nature Astronomy, a team of researchers, including two from the University of Hawaiʻi at Mānoa School of Ocean and Earth Science and Technology (SOEST), describe how analysis of dust grains from the surface of an ancient asteroid suggests that extraterrestrial dust grains from asteroids and comets carried water to the surface of the early Earth. The water in the grains is produced by space weathering, a process by which charged particles from the Sun, known as solar wind, altered the chemical composition of the grains to produce water molecules.

The samples came from asteroid Itokawa, visited by Japan's first Hayabusa mission. The samples they analysed came from an asteroid called Itokawa, which were collected by the Japanese space probe Hayabusa and returned to Earth in 2010. Scientists used incredibly advanced techniques to peer inside individual dust grains smaller than the width of a human hair.

What they discovered was mind-blowing. Findings have shown that solar winds can react with the oxygen in the upper layer of the asteroids and create water. It has been estimated that "every cubic metre of irradiated rock could contain up to 20 litres"; study was conducted using an atom probe tomography, numbers are given for the Itokawa S-type asteroid. Every cubic meter of space rock could potentially hold 20 liters of water – that's like finding a water cooler in every washing machine-sized chunk of asteroid!

Comets: The Icy Wildcards That Surprised Everyone

While asteroids were stealing the spotlight, comets – those icy wanderers from the outer solar system – threw scientists a curveball. Scientists now think that Earth's water was probably delivered by asteroids, not comets, in the early epochs of the solar system billions of years ago. This was completely opposite to what many scientists had expected for decades.

The European Space Agency's (ESA) Rosetta spacecraft is helping scientists learn more about the role these icy nomads have played in the evolution of the solar system and life on Earth by analyzing the composition of Comet 67P/Churyumov–Gerasimenko. Before Rosetta began orbiting Comet 67P/C-G in August, it was using an instrument known as ROSINA to analyze the chemical fingerprint of gases in the comet's fuzzy envelope. Scientists focused on data from the instrument regarding water to help uncover whether asteroids or comets delivered the water in Earth's oceans.

The results were shocking. Comet water had a different isotopic signature than Earth's oceans. It was like comparing tap water from New York to mineral water from Mars – they just didn't match. Comets and asteroids probably delivered some of the water and other ingredients that allowed the complex chemistry of life to begin on Earth. While comets likely contributed some water and organic materials, they weren't the main delivery service that scientists had long suspected.

The Carbon-Rich Treasure Troves Floating in Space

One of the most stunning revelations from space samples was just how rich in organic compounds these ancient rocks really are. The OSIRIS-REx sample is the biggest carbon-rich asteroid sample ever delivered to Earth and will help scientists investigate the origins of life on our own planet for generations to come. Scientists were dealing with samples that were essentially cosmic coal – packed with the carbon-based molecules that form the backbone of all life.

Organic matter is abundant in the Ryugu grains, distributed as submicrometer-sized organic grains and as organic matter dispersed in matrix. Macromolecular organic matter, a dark, complex acid-insoluble organic matter (IOM), accounts for most carbon in primitive carbonaceous chondrite meteorites. These weren't just traces of organic material – entire grains were packed with complex carbon compounds.

The diversity was staggering. Wide variety of organic molecules such as amino acids, amines, carboxylic acids, aromatic hydrocarbons, and nitrogen-containing cyclic compounds were detected. The diversity of these organic molecules is greater than that of carbonaceous meteorites, suggesting that they formed in a relatively low-temperature environment. Space wasn't just preserving organic molecules – it was creating entirely new varieties that Earth-bound chemists had never seen before.

Meteorites vs. Pristine Samples: Why Fresh Beats Fallen

For decades, scientists had to rely on meteorites that crashed into Earth to study space materials. But these samples were like crime scene evidence that had been contaminated – exposed to Earth's atmosphere, weathering, and potentially millions of years of terrestrial contamination. The new sample return missions changed everything.

Unlike meteorites, the Ryugu samples were collected and delivered for study under controlled conditions, reducing terrestrial contamination and the effects of atmospheric entry. Unlike meteorites, these samples were collected from a specific spot on the surface of a well-characterized asteroid and were retrieved without contamination from the biosphere. Scientists were getting their hands on truly pristine materials for the first time.

The difference was like comparing fresh fruit to fruit that had been sitting in a dusty warehouse for decades. Scientists have previously found nucleobases and vitamins in certain carbon-rich meteorites, but there was always the question of contamination by exposure to the Earth's environment. Since the Hayabusa2 spacecraft collected two samples directly from asteroid Ryugu and delivered them to Earth in sealed capsules, contamination can be ruled out. Finally, scientists could be confident they were studying genuine space chemistry, not Earth contamination.

The Solar Wind's Unexpected Role as Water Maker

One of the most surprising discoveries was that the Sun itself is actively creating water throughout the solar system. The water in the grains is produced by space weathering, a process by which charged particles from the Sun, known as solar wind, altered the chemical composition of the grains to produce water molecules. This process is happening constantly on every airless world in our solar system.

We think it's reasonable to assume that the same space weathering process which created the water on Itokawa will have occurred to one degree or another on many airless worlds like the Moon or the asteroid Vesta. That could mean that space explorers may well be able to process fresh supplies of water straight from the dust on the planet's surface. It's exciting to think that the processes which formed the planets could help to support human life as we reach out beyond Earth.

Imagine that – the very same solar wind that creates the beautiful aurora on Earth is also manufacturing water on countless worlds throughout our solar system. It's like having a cosmic factory running 24/7, powered by our Sun, churning out the most precious resource in the universe. This discovery has massive implications for future space exploration and the possibility of finding water on other worlds.

Ancient Impact Glass: Time Capsules from Space

Among the most fascinating discoveries were tiny glass beads found in lunar samples. A solar wind-derived water reservoir on the Moon hosted by impact glass beads. These weren't just ordinary glass – they were formed by ancient meteorite impacts and had been storing water like tiny time capsules for billions of years.

The U-Pb dating of impact glass beads reveals at least 17 main impact events. New space weathering effects, especially the formation of Fe3+, have been found. Scientists could literally read the history of cosmic bombardment preserved in these microscopic glass spheres. Each bead told the story of a violent impact that happened millions or billions of years ago.

The glass be