Why “organics on Mars” is meaningless for life

Mars is the next compelling candidate for life beyond Earth.

On Mars, bare rock structures retain heat much better than sand-like structures, meaning they appear brighter at night when viewed in infrared. A variety of rock types and colors are seen, as dust adheres much better to some surfaces than others. Up close, it is clear that Mars is not a uniform planet and the rock structure clearly indicates a watery past. Could there once have been life?

(Source: NASA/JPL-Caltech/MSSS, Mars Curiosity Rover)

For about 1.5 billion years, the planet appeared to be Earth-like.

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life mars

While Mars is now known as the frozen, red planet, it has all the evidence we could ask for of a watery past that lasted roughly the first 1.5 billion years of the solar system. Could it have been Earth-like for the first third of our solar system’s history, even to the point where there was life on it?

(Image credit: Kevin M. Gil/flickr)

Because copious amounts of liquid surface water have flowed, Mars may have evolved life.

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Backwaters appear only in the final stages of life of a slow-moving river, and this one is found on Mars. While many of Mars’ channel-like features date from a glacial past, there is ample evidence of a history of liquid water on the surface, such as this dry riverbed: Nanedi Vallis.

(Source: ESA/DLR/FU Berlin (G. Neukum))

But finding “organic matter” in the Martian soil isn’t even a useful clue.

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NASA’s Perseverance rover has its robotic arm working around a rocky outcrop called “Skinner Ridge” in Mars’ Jezero Crater. Numerous organic compounds have already been identified by Perseverance in the Martian soils present at this location, but “organics,” despite the implications of the word, usually have nothing to do with life at all.

(Source: NASA/JPL-Caltech/ASU/MSSS)

Yes, the Perseverance rover found them, just like Curiosity did before them.

NASA’s Curiosity rover found a number of intriguing features during its (still ongoing) mission, including a range of organic molecules including seasonally variable methane and sulfur-containing organic molecules.

(Source: NASA/GSFC)

However, “organic molecules” simply mean “molecules containing carbon plus hydrogen.”

life beyond earth

The way atoms combine to form molecules, including organic molecules and biological processes, is only possible because the Pauli exclusion rule applies to electrons and prohibits two of them from occupying the same quantum state.

(Image credit: NASA/Jenny Mottar)

Most organic molecules are prebiotic: they are formed by inorganic chemical processes.

The raw materials we believe are necessary for life, including a variety of carbon-based molecules, are found not only on Earth and other rocky bodies in our solar system, but also in interstellar space, as in the Orion Nebula: the closest one large star-forming region to earth.

(Source: ESA, HEXOS and the HIFI consortium)

There are currently 256 unique organic species known to reside in interstellar dust clouds.

This scanning electron microscope image shows an interplanetary dust particle at a scale of just over ~1 micron. In interstellar space, we only have inferences about dust distribution in terms of size and composition, particularly at the low-mass, small-size end of the spectrum. However, these particles, which are abundant not only in interstellar space but also in stellar systems, including our own solar system, notoriously contain organic compounds.

(Source: EK Jessberger et al., in Interplanetary Dust, 2001)

These compounds include alcohols, acids, aldehydes, amines and hydrocarbons.

As shown by spectroscopic imaging with JWST, chemicals such as atomic hydrogen, molecular hydrogen and hydrocarbon compounds occupy different locations in space within the Tarantula Nebula, showing how diverse even a single star-forming region can be.

(Image Credits: NASA, ESA, CSA, STScI, Webb ERO Production Team)

So also various cyanides and ethyl formate: found in abundance in the galactic center.

This three-color composite shows the galactic center as imaged in three different wavelength bands by NASA’s Spitzer, the predecessor of the James Webb Space Telescope. Carbon-rich molecules, known as polycyclic aromatic hydrocarbons, appear green, while stars and warm dust are also visible. Ethyl formate was found in the gas cloud Sagittarius B2: the same molecule that gives raspberries their characteristic scent.

(Source: NASA/JPL-Caltech)

Wherever new stars form, further variants of organic molecules arise abiotically.

Ultra-hot, young stars can sometimes form jets, like this Herbig-Haro object in the Orion Nebula, just 1,500 light-years from our position in the galaxy. The radiation and wind from young, massive stars can impart enormous jolts to the surrounding matter, where we also find organic molecules. These hot regions of space give off much more energy than our sun, and heat nearby objects to higher temperatures than the sun can.

(Source: NASA, ESA, Hubble Heritage (STScI/AURA)/Hubble-Europe Collaboration; Credits: D. Padgett (NASA’s GSFC), T. Megeath (U. Toledo), B. Reipurth (U. Hawaii))

Complex molecules with carbon rings – polycyclic aromatic hydrocarbons – form ubiquitously.

The existence of complex, carbon-based molecules in star-forming regions is interesting but not required by humans. Here, glycoaldehydes, an example of simple sugars, are shown in a location consistent with where they have been detected in an interstellar gas cloud: offset from the region where new stars are currently forming most rapidly.

(Source: ALMA (ESO/NAOJ/NRAO)/L. Calçada (ESO) & NASA/JPL-Caltech/WISE team)

Protoplanetary disks around newborn stars contain formaldehyde and methanol.

Artist’s rendering of the protoplanetary disk around young star V883 Ori. The outer part of the disk is cold and dust particles are covered with ice. ALMA detected various complex organic molecules around the water frost line in the disk.

(Image credit: NAOJ)

As stellar systems evolve, dense bodies form that concentrate simple molecules and allow for synthetic reactions.


This image shows the Orion molecular clouds, the target of the VANDAM survey. Yellow dots are the positions of the observed protostars on a blue Herschel background image. The side panels show nine young protostars imaged by ALMA (blue) and the VLA (orange). Protoplanetary disks are not only rich in organic molecules, but also contain species not often seen in typical interstellar dust clouds.

(Source: ALMA (ESO/NAOJ/NRAO), J. Tobin; NRAO/AUI/NSF, S. Dagnello; Herschel/ESA)

Remaining protoplanetary material persists as asteroids and Kuiper Belt objects.

Concept image of meteoroids delivering nucleobases to old earth. All five nucleobases used in life processes, A, C, G, T, and U, have now been found in meteorites. Meteorites are also known to contain more than 80 amino acids: far more than are known to be used in life processes here on Earth.

(Credit: NASA Goddard/CI Lab/Dan Gallagher)

The organics in them are stunning.

This diagram shows a series of new amino acids identified as recently as 2017 in the Murchison meteorite that fell in 1969. This later analysis not only discovered a series of new amino acids, but a whole new family of such molecules in the Murchison meteorite.

(Source: T. Koga and H. Naraoka, Nature Scientific Reports, 2017)

These include fullerenes, alkanes and over 70 types of amino acids.

This image shows a fragment of the Murchison meteorite that fell in Australia in 1969. The Murchison meteorite is particularly rich in amino acids, as analysis of the material inside has so far identified about 80 amino acids, with left- and right-handed amino acids both abundant. For comparison: only 22 amino acids are involved in life processes on earth, all of which are right-handed.

(Source: Basilicofresco/Wikimedia Commons)

It would have been shocking if such connections did not exist on Mars.

The hematite spheres (or “Martian blueberries”) as imaged by the Mars Exploration Rover. This is almost certainly evidence of past liquid water on Mars and possibly past life. NASA scientists must be sure that any location we study on the Red Planet is not contaminated by the mere act of our observation and spacecraft landing there. As of now, there is no solid evidence of past or present life on Mars.

(Source: NASA/JPL-Caltech/Cornell University)

Sample return missions could reveal Martian life.

An Atlas V rocket carrying NASA’s Perseverance Mars rover launches from Pad 41 at Cape Canaveral Air Force Station. The Mars 2020 mission landed the Perseverance rover on the red planet in February 2021, where it will search for signs of ancient life and collect rock and soil samples for a possible return to Earth. The sample return mission was recently named a “top priority” mission by the National Academies of Sciences Decade Review.

(Credit: NASA/Joel Kowsky)

However, these discovered “organics” do not provide sufficient evidence.

This mosaic from NASA’s Perseverance rover shows a rocky outcrop called “Wildcat Ridge” at the foot of an ancient delta: where a Martian river once flowed into a lake. Two rock cores have been extracted and are currently being stored by the rover, which could eventually be returned to Earth by a future sample-return mission.

(Source: NASA/JPL-Caltech/ASU/MSSS)

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