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Following enormous collisions, such as asteroid impacts, some amount of material from an impacted world may be ejected into space. This matter can travel vast distances and for extremely long periods of time. In theory, this substance could contain direct or indirect signs of life from the host world, such as fossils of microorganisms. Such material could also be detectable by humans in the near future, or even now.

When you hear the words “vacuum” and “dust” in a sentence, you may groan at the thought of having to do housework. But in astronomy, these words have different connotations. Vacuum, of course, refers to the void of space. Dust, however, means diffuse solid material floating through space. It can be an annoyance to some astronomers, as it may hinder their views of some distant object.

Conversely, dust can be a useful tool to help other astronomers learn about something distant without having to leave the safety of our own planet. Professor Tomonori Totani from the University of Tokyo’s Department of Astronomy offers an idea for space dust that might sound like science fiction, but actually warrants serious consideration.

“I propose we study well-preserved grains ejected from other worlds for potential signs of life,” said Totani. “The search for life outside our solar system typically means a search for signs of communication, which would indicate intelligent life but precludes any pre-technological life. Or the search is for atmospheric signatures that might hint at life, but without direct confirmation there could always be an explanation that does not require life. However, if there are signs of life in dust grains, not only could we be certain, but we could also find out soon.”

The basic idea is that large asteroid strikes can eject ground material into space. There is a chance that recently deceased or even fossilized microorganisms could be contained in some rocky material in this ejecta. This material will vary in size greatly, with different-sized pieces behaving differently once in space. Some larger pieces might fall back down or enter permanent orbits around a local planet or star, and some much smaller pieces might be too small to contain any verifiable signs of life. But grains in the region of 1 micrometer (one-thousandth of a millimeter) could not only host a specimen of a single-celled organism, but they could also potentially escape their host solar system altogether, and under the right circumstances, maybe even venture to ours.

“My paper explores this idea using available data on the different aspects of this scenario,” said Totani. “The distances and times involved can be vast, and both reduce the chance any ejecta containing life signs from another world could even reach us. Add to that the number of phenomena in space that can destroy small objects due to heat or radiation, and the chances get even lower. Despite that, I calculate around 100,000 such grains could be landing on Earth every year. Given there are many unknowns involved, this estimate could be too high or too low, but the means to explore it already exist so it seems like a worthwhile pursuit.”

There may be such grains already on Earth, and in plentiful amounts, preserved in places such as the Antarctic ice, or under the sea floor. Space dust in these places could be retrieved relatively easily, but discerning extrasolar material from material originating in our own solar system is still a complex matter. If the search is extended to space itself; however, there are already missions that capture dust in the vacuum using ultralight materials called aerogels.

“I hope that researchers in different fields are interested in this idea and start to examine the feasibility of this new search for extrasolar life in more detail,” said Totani.

The study will be published in the International Journal of Astrobiology.

Researchers have analyzed samples of the asteroid Ryugu collected by the Japanese Space Agency’s Hayabusa2 spacecraft and found uracil, one of the informational units that make up RNA, the molecules that contain the instructions for how to build and operate living organisms. Nicotinic acid, also known as Vitamin B₃ or niacin, which is an important cofactor for metabolism in living organisms, was also detected in the same samples.

This discovery by an international team, led by Associate Professor Yasuhiro Oba at Hokkaido University, adds to the evidence that important building blocks for life are created in space and could have been delivered to Earth by meteorites. The findings were published in the journal Nature Communications.

“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,” Oba explained. “Since the Hayabusa2 spacecraft collected two samples directly from asteroid Ryugu and delivered them to Earth in sealed capsules, contamination can be ruled out.”

The researchers extracted these molecules by soaking the Ryugu particles in hot water, followed by analyses using liquid chromatography coupled with high-resolution mass spectrometry. This revealed the presence of uracil and nicotinic acid, as well as other nitrogen-containing organic compounds.

“We found uracil in the samples in small amounts, in the range of 6–32 parts per billion (ppb), while vitamin B₃ was more abundant, in the range of 49–99 ppb,” Oba elaborated. “Other biological molecules were found in the sample as well, including a selection of amino acids, amines and carboxylic acids, which are found in proteins and metabolism, respectively.” The compounds detected are similar but not identical to those previously discovered in carbon-rich meteorites.

The team hypothesizes that the difference in concentrations in the two samples, collected from different locations on Ryugu, is likely due to the exposure to the extreme environments of space. They also hypothesized that the nitrogen-containing compounds were, at least in part, formed from the simpler molecules such as ammonia, formaldehyde and hydrogen cyanide. While these were not detected in the Ryugu samples, they are known to be present in cometary ice—and Ryugu could have originated as a comet or another parent body that had been present in low temperature environments.

“The discovery of uracil in the samples from Ryugu lends strength to current theories regarding the source of nucleobases in the early Earth,” Oba concludes. “The OSIRIS-REx mission by NASA will be returning samples from asteroid Bennu this year, and a comparative study of the composition of these asteroids will provide further data to build on these theories.”

A team of geochemists from the Chinese Academy of Sciences, working with colleagues from the University of Hong Kong, Tianjin University and the University of California, has found evidence that suggests much of the oxygen in early Earth’s early atmosphere may have come from rocks. In their study, reported in Proceedings of the National Academy of Sciences, the group conducted lab experiments involving crushing rocks, exposing the results to water and measuring reactive oxygen species that were emitted.

Prior research has shown that Earth experienced what has been called the Great Oxidation Event approximately 2.3 to 2.4 billion years ago. During this time, microbe numbers increased dramatically, as they released oxygen during photosynthesis. But prior research has also suggested that a common life ancestor existed before the Great Oxidation Event, which further suggests that there was some amount of oxygen exposure. In this new effort, the researchers suggest that such oxygen could have come from rocks interacting with water.

The work involved crushing samples of quartz and then exposing them to water, which replicates some of the conditions that existed on early Earth prior to the rise of high levels of oxygen in the atmosphere. Adding water to freshly crushed quartz, the researchers found, led to reactions between the water and newly broken crystals. This resulted it the formation of molecular oxygen along with other reactive oxygen species like hydrogen peroxide. Such species are also known as free radicals and they would have played an important role in the evolution of early life. This is because by damaging DNA and other cell components, the free radicals would have pressured early life to adapt.

The researchers suggest a variety of events could have led to the release of such materials, such as earthquakes, erosion or the movement of glaciers. They further suggest that similar processes could be happening on other planets right now—with Mars sandstorms, for example, or fluctuating tides on moons that have water. Such processes, they point out, could produce oxygen, which could be play a role in the development of life.

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