Findings in title quoted from the linked paper^1 and a summary^2 from the University of Tokyo.

From the linked paper:^1

>We do not need living organisms, but the existence of life in exoplanets can be probed by remains of microbes, microfossils, minerals produced by biological activities (biominerals), or any other signatures of past biological activities (e.g. concentration of biological molecules or isotopic ratios) (Cavalazzi and Westall 2018).

From the summary:^2

>“I propose we study well-preserved grains ejected from other worlds for potential signs of life,” said Totani [of the University of Tokyo’s Department of Astronomy].

>“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.

>There may be such grains already on Earth, and in plentiful amounts, preserved in places such as the Antarctic ice, or under the seafloor.

^1 Tomonori Totani (2023) Solid grains ejected from terrestrial exoplanets as a probe of the abundance of life in the Milky Way. International Journal of Astrobiology, https://doi.org/10.1017/S147355042300006X

^2 Searching for life with space dust, 22 Mar. 2023, https://www.u-tokyo.ac.jp/focus/en/press/z0508_00283.html