Every meteorite that falls to Earth has an incredible story to tell about its extraterrestrial origins and interplanetary adventures. That’s particularly true of the 4.5 billion-year-old space rocks known as Monahans and Zag, which respectively landed in Texas and Morocco in 1998. Soon after their recovery, scientists detected microscopic pockets of water and halite (rock salt) crystals in the meteorites—a direct window into an ancient briny world from the solar system’s infancy.
Now, an extensive analysis of the meteorites led by Open University astrobiologist Queenie Chan reveals that these alien salt crystals contain organic matter, or “life’s precursor molecules,” as the team put it. These carbon compounds provide new insights into the distribution of prebiotic materials in the early solar system, while shedding light on the meteorites’ protracted and occasionally bumpy voyage to Earth.
The paper, out Wednesday in Science Advances, also marks the first time scientists have found organics in extraterrestrial samples that still contain liquid water, Chan told me over email. This is significant because water and organic matter are the key ingredients for life as we know it, and the paper suggests they may have been widespread on primitive worlds in the ancient solar system.
“Finding organic compounds in meteorites [and] other extraterrestrial samples is nothing new,” Chan said. “However, this study is unique in the sense that we have studied the organic material contained within the water-bearing salt crystals within the meteorites.”
Identifying these subtle compounds within the millimeter-scale crystals required an exhaustive experimental approach. Chan’s team scrutinized the samples with a wide range of advanced spectrometry, spectroscopy, microscopy, and liquid chromatography techniques to achieve their results. They detected carbon, oxygen, and nitrogen-bearing materials “exhibiting a wide range of structural order,” as well as “aromatic, ketone, imine, and/or imidazole compounds.”
The fact that this organic matter was locked inside these sapphire-colored crystals raises the tantalizing possibility that speculative alien beings, most likely in tiny microbe form, could be preserved the same way. Chan referred me to a 1988 study that described terrestrial bacteria suspended in small liquid inclusions within salt crystals, so it’s not absurd to think extraterrestrial life could be likewise contained.
“If life formed elsewhere, there is such a possibility that it could be trapped in a way similar to that of the terrestrial setting,” Chan told me. “Bear in mind that, while the rich deposits of organic remnants recovered from the meteorites don’t provide any proof of life outside of Earth, finding abundant organic precursors associated with water indicates that complex chemical processes could have occurred.”
“This offers a significant implication for the context for the origin of life,” she added.
These organics also flesh out the backstory of the Zag and Monahans meteorites. The rocks are similar in composition to the carbonaceous surface of Ceres, the largest object in the asteroid belt, suggesting they probably originated on that world. Chan and her colleagues propose that hydrovolcanic activity on young Ceres produced brines, and when the water eventually evaporated, it left behind these salt crystals filled with organic molecules.
At some point, these hydrovolcanic disruptions on Ceres were forceful enough to blast the material into space, where exposure to ionizing radiation caused the crystals to turn that “beautiful blue color,” Chan said, which is “pretty unique in nature.”
The ejected material then impacted with another world, possibly the metal-rich asteroid Hebe, which imprinted its own signature of organics and amino acids into the meteorites. Finally, these intermixed samples were gently “stripped” from this asteroid by natural processes, and ended up on Earth some 20 years ago.
It’s pretty mind-boggling to retread this story of interworld hops, written in the chemical composition of the Zag and Monahans meteorites. What’s even trippier is the notion that these journeys may be quotidian, with similar exchanges likely occurring right now around some of the most promising candidates for life in our solar system.
“In the context of understanding moons such as Enceladus and Europa,” Chan’s team said in the study, “halite crystals formed from cryovolcanism and ejected into space represent an ideal sample to study prebiotic and possibly biotic processes on these bodies.”
It’s impossible to predict what first contact with an alien organism might look like, but with this comprehensive new paper, Chan and her colleagues have distinguished salt crystals embedded in world-hopping rocks as a smart bet.