Is there a flaw in Mars life detection? The latest research reveals embarrassing possibilities

Produced by: Science Popularization China

Author: Ma Xiaojun

Producer: China Science Expo

Since the launch of the Viking mission in the 1970s, humans have been constantly trying to find signs of life on Mars. However, half a century later, despite the continuous efforts of Mars exploration projects in various countries, only simple organic molecules with extremely low content have been found on Mars. This evidence is far from enough to assert that life on Mars does exist. Last week, a new study published in Nature Communications showed that the limitations of the detection equipment carried on the Mars rover may be the bottleneck that hinders people from finding evidence of life on Mars. In other words, the lack of discovery does not mean that there is no life on Mars, but it may be that the detection equipment is not powerful enough.

Photos of Mars taken by the Rosetta probe

(Image credit: ESA & MPS for OSIRIS Team)

Mars - Earth's sister planet

Mars is the fourth planet in the solar system and the second smallest planet. It is very similar to the Earth in many aspects. Although the average temperature on Mars is -63°C, the local temperature in some seasons can be as high as 20-35°C, which is already within the habitable range for human survival. This red planet has an atmosphere dominated by carbon dioxide, but it is very thin, with an air pressure of only 1% of that on Earth. In addition, Mars stores a large amount of solid water resources, which also makes it a promising place for future human immigration. Many research conclusions show that Mars may have or once had lower life forms such as microorganisms, which is one of the important reasons why countries around the world are keen to explore Mars.

Size comparison between Earth and Mars

(Image source: Wikipedia)

Humans have conducted many Mars exploration missions in the past few decades, including orbiting, flying over, and landing. Detecting whether there is life on Mars is one of the core missions of these missions. The probes launched by humans can conduct detailed observations and analyses of the surface, atmosphere, underground, and hydrological systems of Mars to explore whether Mars has the conditions for the existence of life or evidence of life. The life detectors they carry are mainly based on the following principles.

The relative positions of the landing sites of previous Mars exploration missions

(Image source: Wikipedia)

First, the detection of surface composition , such as the relevant equipment carried by Zhurong, which can analyze the elements, minerals and rock types on the surface of Mars, providing a basis for judging whether Mars is suitable for life; second, the detection of atmospheric composition , such as the solar wind ion analyzer carried by Maven, which can observe the influence of the sun on the Martian atmosphere, and thus explore their possible relationship with life activities. Third, the detection of organic matter , such as the instruments carried by Curiosity and Perseverance, can not only detect minerals, but also find evidence of the existence of organic matter.

A photo of the Zhurong rover and lander on the surface of Mars, taken by a detachable camera released by the rover

(Photo source: China News Service)

In fact, every Mars rover will carry multiple detection equipment at the same time. Take Perseverance as an example. The detection equipment it carries is very rich and diverse.

Mastcam-Z: A zoom panoramic camera located on a mast, capable of producing high-definition panoramic and stereo images;

MEDA: A miniature weather station capable of measuring temperature, wind speed, direction, pressure, humidity and dust particles;

MOXIE: An experimental instrument that can extract oxygen from the Martian atmosphere using carbon dioxide;

PIXL: X-ray fluorescence spectrometer, capable of analyzing the chemical composition of rocks and soils;

RIMFAX: Geological radar, capable of detecting underground structures and layers;

SHERLOC: a laser imaging system capable of detecting organic matter and minerals;

SuperCam: A versatile instrument that uses lasers, infrared light and sound waves to analyze rocks and soil.

Various scientific payloads on the Perseverance Mars Rover

(Image credit: NASA)

So, what are the specific principles of these devices? Let's take the Sample Analyzer for Mars (SAM) on Curiosity as an example. SAM is an instrument used to detect organic matter and other chemical components in Martian soil and rocks . Its principle is to use a micro furnace to heat the sample and analyze the released gas by mass spectrometry, gas chromatography and laser spectroscopy. These analyses can determine the components contained in the rock sample and their existence forms with very high accuracy, such as whether it contains iron? Is the iron present in the form of a single substance or a compound? Is it ferrous oxide or ferroferric oxide? And so on.

Sample Analysis at Mars (SAM)

(Image credit: NASA)

If carbon-based life exists or has existed on Mars, then their bodies, corpses and other remains, as well as various substances released to the outside world during life activities, will leave traces of organic matter. We can then explore the possibility of the existence of life based on these organic molecules.

Microorganisms are one of the possible ways to produce methane on Mars

(Image credit: NASA)

It’s good but not perfect. Does exploring life on Mars still depend on laboratories on Earth?

From the perspective of exploring chemical composition, such equipment is enough to let us understand the properties of Martian soil and rocks. However, the effectiveness of similar equipment in exploring life has been questioned by scientists.

Since humans have not been able to obtain real Martian rock samples except for meteorites, it is not feasible to study Martian life on Earth. In this latest study, scientists tested a series of samples from Earth. However, these samples are not the rocky volcanic soil that we can see everywhere around us. They come from an extremely desolate secret place - the Atacama Desert in the middle of the west coast of South America.

A Martian rock sample collected by Perseverance

(Image credit: NASA)

Here, scientists collected an ideal research object from a place called Red Stone. Red Stone is located in the Atacama Desert. The rock formations are rich in hematite and mudstone, which contain clay minerals such as vermiculite and montmorillonite. Therefore, it is geologically similar to Mars. Even its name, Red Stone, has a strong connection with Mars. The best part is that Red Stone was formed under extremely dry conditions 100-160 million years ago, and has very similar geological features to the Jezero Crater, which is the main research site of Perseverance on Mars. Judging from the video released by the authors of the paper at the same time, the landform of Red Stone is simply a replica of Mars.

Redstone

(Photo credit: Armando Azua-Bustos)

In addition to using rock composition analysis methods similar to those used by Mars exploration equipment, scientists also used a variety of biochemical analysis methods to test samples from red rocks. These technologies can directly extract or culture microbial genetic material from rock samples, such as DNA and RNA. After performing evolutionary analysis on these genetic material fragments, the relationship between these microbial samples and known microorganisms can also be determined.

To the surprise of scientists, there are a large number of microorganisms in the red stone samples, and the genetic material of these microorganisms has mixed characteristics of existing and ancient microorganisms. Moreover, most of these microbial genetic materials have never been recognized and described by humans. Perhaps inspired by the "dark matter" in the universe that cannot be observed for the time being, scientists call this type of microorganism "dark microbial community."

Although there is no analytical equipment on Earth that is exactly the same as that on the Mars rover, scientists still used equipment similar to the SAM on Curiosity to detect traces of life on red stone samples. The results showed that although instruments like SAM can well obtain the mineral composition of red stone samples, they cannot detect very small amounts of microbial organic matter in the samples, let alone genetic material with decisive evidence significance.

Photo of the Jezero crater on Mars

(Image credit: NASA)

Therefore, scientists assert that it is difficult or even impossible for the instruments and technologies currently carried by the Mars rover to detect organic matter with similar content in Martian rocks, let alone to decipher the specific genetic material fragments of microorganisms. In a nutshell, if you want to find out whether there is life on Mars, you still have to bring samples back to Earth. After all, no matter how advanced the Mars rover of each country is, the functions of the equipment it carries cannot be comparable to the various large-scale equipment in laboratories on Earth. Moreover, if you want to make cutting-edge equipment miniaturized, highly reliable, long-life, and maintenance-free, compromises in performance are naturally inevitable. At the same time, it is also difficult to cultivate microorganisms on Mars exploration equipment, and it is the amplification of genetic material brought about by cultivation that makes detection easier.

However, ideals are full and reality is skinny. Although humans have obtained a large number of lunar soil samples from the moon, they have never been able to obtain soil and rocks on Mars. After all, compared with the moon, Mars is far away, and spacecraft will have to go through numerous difficulties when going to Mars. When taking off on the return trip, they will have to overcome greater gravity and atmospheric resistance than on the moon, so humans have not yet achieved this goal. However, around 2030, China, the United States, and Europe all have plans to bring back "fire soil" from Mars. By then, we may have a chance to determine whether life on Mars exists.

The location of the volcanic soil samples collected by the Perseverance Mars rover, which will be brought back to Earth by subsequent probes in the future

(Image credit: NASA)

References:

[1] What are the challenges of detecting life on Mars? International research shows that currently deployed scientific instruments are not sensitive enough

https://baijiahao.baidu.com/s?id=1758537162727420797&wfr=spider&for=pc

[2] Dark microbiome and extremely low organics in Atacama fossil delta unveil Mars life detection limits

https://www.nature.com/articles/s41467-023-36172-1