New Mars life detection method strengthens sample return safety protocols

Within the next decade, space agencies plan to bring samples of rock from Mars to Earth for study. Of concern is the possibility these samples contain life, which could have unforeseen consequences. Therefore, researchers in this field strive to create methods to detect life.

For the first time, researchers, including those from the University of Tokyo and NASA, successfully demonstrate a method to detect life in ancient rocks analogous to those found on Mars.

The work is published in the International Journal of Astrobiology.

We've all seen movies in which "scientists bring back something from space, with disastrous consequences," or with some similar premise. The idea makes for a fun story, but the idea of microbial aliens contaminating the Earth is based on genuine concerns, and is also nothing new.

Back in the days of the Apollo program, on their return, the lucky astronauts who stepped foot on lunar soil underwent decontamination procedures and even quarantines, just in case. More recently, all eyes are on Mars, as multiple sample return missions are being planned.

In order to ensure that samples from Mars cannot contaminate Earth life, the international Committee on Space Research (COSPAR) developed the sample safety assessment framework, essentially a set of protocols for those involved in obtaining, transporting and analyzing Mars rocks, to avoid contamination. A key component of this is the ability to detect the presence or absence of life in a sample.

Associate Professor Yohey Suzuki from the Department of Earth and Planetary Science at the University of Tokyo, and his international team, looked at ancient microbe-rich Earth rocks analogous to the kind of Mars rocks we might expect to receive from the red planet in the coming years.

"We first tested conventional analytical instruments, but none could detect microbial cells in the 100-million-year-old basalt rock we use as the Martian analog. So, we had to find an instrument sensitive enough to detect microbial cells, and ideally in a nondestructive way, given the rarity of the samples we may soon see," said Suzuki.

"We came up with optical photothermal infrared (O-PTIR) spectroscopy, which succeeded where other techniques either lacked precision or required too much destruction of the samples."

O-PTIR works by shining infrared light onto prepared samples to analyze; in this case, the rocks had their outer layers removed and were cut into slices. While slightly destructive, it leaves plenty of material intact for other kinds of analyses, or even those we have not come up with.

This essence of preservation for the future also took place with samples from the moon landings. A green laser then picks up signals from the sample where it was exposed to infrared light. With this, researchers can image details as small as half a micrometer, which is enough to discern when a structure is part of something living.

"We demonstrated our new method can detect microbes from 100-million-year-old basalt rock. But we need to extend the validity of the instrument to older basalt rock, around 2 billion years old, similar to those the Perseverance rover on Mars has already sampled," said Suzuki.

"I also need to test other rock types such as carbonates, which are common on Mars and here on Earth often contain life as well. It's an exciting time to work in this field. It might only be a matter of years before we can finally answer one of the greatest questions ever asked."