Imperial College London scientists say organic material found on asteroid rocks collected during Japan’s Hayabusa 2 mission only proves that Earth microbes can thrive on extraterrestrial material, not that alien life has finally landed.
For decades, astrobiologists have debated whether organic samples found in space rocks are evidence of extraterrestrial life or merely contamination from indigenous life on Earth. In their new study, which appears in Meteoritics & Planetary Science, the Imperial College team has now proven that a sample recently returned from asteroid 162173 Ryugu is not the smoking gun for ET.
Hayabusa 2
The Japanese Aerospace Exploration Agency (JAXA) arose from the merger of three prior entities in 2003. Their Hayabusa 2 mission launched on December 3, 2014, before intercepting the 162173 Ryugu asteroid on June 27, 2018. For a year and a half, the probe surveyed and took samples of the asteroid before ejecting the Sample Return Capsule, which landed safely back on Earth on December 5, 2020. Hayabusa 2 continued on its asteroid observation mission.
JAXA targeted the near-Earth asteroid 162173 Ryugu for clues about the origin of life. As a carbonaceous asteroid, it potentially contained minerals, ice, and organic compounds that were among the most pristine in the universe.
In addition to providing information about planetary origins, JAXA hoped 162173 Ryugu would provide them with important information about the origin of water and life on Earth. Evidence of microbes on the asteroid would have been revolutionary in that it would finally confirm the existence of simple life forms from space, but also because it could provide crucial evidence for the controversial panspermia hypothesis.
Panspermia
Panspermia is the theory that life exists elsewhere and potentially arrived on Earth through unintentional or directed contamination by extraterrestrial lifeforms. Such an event could include everything from a microorganism hitching a ride on a meteoroid to aliens intentionally introducing life on a planet.
The concept is broadly plausible, but most scientists are skeptical. The idea doesn’t explain how life arose; it simply changes the story of its origins. Biologists have never discovered direct evidence pointing to a scenario where life did not arise on Earth. Still, a few tantalizing discoveries hint at the possibility of spacefaring microbes; the European Space Agency’s (ESA) EXPOSE-R-2 platform demonstrated that some of Earth’s extremophiles, organisms that can thrive in harsh environments, can survive in raw space conditions, lending some weight to the idea for panspermia proponents.
A Careful Journey
The Imperial College team was among several groups to receive a piece of the precious 162173 Ryugu sample. The sample’s handlers meticulously followed strict transportation and containment procedures involving hermetically sealed containers and nitrogen storage. At the National History Museum London, scientists took X-ray scans of the samples and further scans with an electron microscope.
While studying this scan, scientists found something extraordinary: filaments and rods suggesting the presence of microbial life.
“When we first looked at the sample, we were excited to see there were small rods and filaments of organic matter present on the surface,” said lead author Dr. Matthew Genge. “They were tiny structures, around one millionth of a metre in width – like microbes!”
Life On A Space Rock
The microscopic lifeforms began to spread and take over the rock, which continued for 19 days until the population eventually declined. Such a spike, followed by over-expansion and drop-off, indicated that the scientists had observed an Earthly organism colonizing the organic material on an extraterrestrial rock instead of a dormant organism springing back to life. Due to complications with the small number of bacteria on the rock and the procedures the sample had undergone to protect it, the team did not attempt to remove any organisms for direct study.
Lacking DNA identification of the microorganism, the team’s best guess was that it was a variety of Bacillus, widespread on Earth and known to colonize new environments aggressively. Following a repolish with ethanediol, the team detected no more filaments on the sample. Ultimately, the observation highlighted the vulnerabilities of containment procedures instead of providing evidence of panspermia.
“These findings suggest what we found were terrestrial microbes that found a new home on an extraterrestrial rock full of organic materials they could take advantage of. Ryugu was literally ‘munchies from space’ for Earth microbes,” Genge concluded.
The paper “Rapid Colonization of a space-Returned Ryugu sample by Terrestrial Microorganisms” appeared on November 13, 2024 in the Meteoritics & Planetary Science.
Ryan Whalen covers science and technology for The Debrief. He holds a BA in History and a Master of Library and Information Science with a certificate in Data Science. He can be contacted at ryan@thedebrief.org, and follow him on Twitter @mdntwvlf.