Why “organics on Mars” is meaningless for life

Mars is the closest compelling candidate for life beyond Earth.

On Mars, bare-rock structures hold onto heat far better than sand-like structures do, meaning they will appear brighter at night, when viewed in the infrared. A variety of rock types and colors can be seen, as dust clings to some surfaces much better than others. From up close, it’s very clear that Mars is not a uniform planet, and the rock structure definitely indicates a watery past. Could life have once been present, too?

For ~1.5 billion years, the planet seemed Earth-like.

While Mars is known as a frozen, red planet today, it has all the evidence we could ask for of a watery past, lasting for approximately the first 1.5 billion years of the Solar System. Could it have been Earth-like, even to the point of having had life on it, for the first third of our Solar System’s history?

With plentiful surface liquid water having flowed, Mars may have developed life.

Oxbow bends only occur in the final stages of a slowly flowing river’s life, and this one is found on Mars. While many of Mars’s channel-like features originate from a glacial past, there is ample evidence of a history of liquid water on the surface, such as this dried-up riverbed: Nanedi Vallis.

But finding “organics” in Martian soil isn’t even a useful clue.

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

Yes, the Perseverance rover found them, as did Curiosity previously.

NASA’s Curiosity rover found a number of fascinating properties throughout its (still ongoing) mission, and that includes a number of organic molecules, including seasonally-varying methane and sulfur-containing organic molecules.

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

The way that atoms link up to form molecules, including organic molecules and biological processes, is only possible because of the Pauli exclusion rule that governs electrons, forbidding any two of them from occupying the same quantum state.

Most organic molecules are prebiotic: formed through inorganic chemical processes.

The raw ingredients that we believe are necessary for life, including a wide variety of carbon-based molecules, are found not only on Earth and other rocky bodies in our Solar System, but in interstellar space, such as in the Orion Nebula: the nearest large star-forming region to Earth.

Presently, 256 unique organic species are known within interstellar dust clouds.

Dust grains come in a variety of sizes and compositions, and can form in the aftermath of an energetic collision. As the material expands and cools, dust forms, gets heated, and re-radiates that heat in the infrared, enabling telescopes like JWST to detect its presence. But we must be careful; other, more distant features can mimic dust in this regard.

Alcohols, acids, aldehydes, amines, and hydrocarbons all number among these compounds.

As spectroscopic imaging with JWST reveals, chemicals like atomic hydrogen, molecular hydrogen, and hydrocarbon compounds occupy different locations in space within the Tarantula Nebula, showcasing how varied even a single star-forming region can be. Atoms, ions, and molecules all exist throughout the cosmos.

So do various cyanides and ethyl formate: found copiously 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 to the James Webb Space Telescope. Carbon-rich molecules, known as polycyclic aromatic hydrocarbons, show up in green, while stars and warm dust are also visible. A glow where our supermassive black hole sits is identifiable as well. The presence of ethyl formate was found in the gas cloud Sagittarius B2: the same molecule that gives raspberries their characteristic scent.

Wherever new stars form, additional variants of organic molecules abiotically emerge.

Ultra-hot, young stars can sometimes form jets, like this Herbig-Haro object in the Orion Nebula, just 1,500 light years away from our position in the galaxy. The radiation and winds from young, massive stars can impart enormous kicks to the surrounding matter, where we find organic molecules as well. These hot regions of space emit much greater amounts of energy than our Sun does, heating up objects in their vicinity to greater temperatures than the Sun can.

Complex carbon-ringed molecules — polycyclic aromatic hydrocarbons — form ubiquitously.

The existence of complex, carbon-based molecules in star forming regions is interesting, but isn’t anthropically demanded. Here, glycoaldehydes, an example of simple sugars, are illustrated in a location corresponding to where they were detected in an interstellar gas cloud: offset from the region presently forming new stars the fastest. Interstellar molecules are common, with many of them being complex and long-chained.

Protoplanetary disks around newborn stars contain formaldehyde and methanol.

This artist’s illustration shows a young protoplanetary disk around a young star, like V883 Ori. The outer part of the disk is cold and dust particles are covered with ice, while various organic molecules are found closer in: toward the water frost line. We do not yet know what a “typical” protoplanetary disk or a typical planetary system looks like.

As stellar systems evolve, dense bodies form, concentrating simple molecules and enabling synthesizing reactions.

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

Leftover protoplanetary material persists as asteroids and Kuiper belt objects.

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

The organics inside them are staggering.

This diagram shows a number of new amino acids that were identified in the Murchison Meteorite, which fell in 1969, as recently as 2017. That later analysis not only discovered a number of novel amino acids, but an entire new family of such molecules in the Murchison meteorite.

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

This image shows a fragment of the Murchison Meteorite, which fell in Australia in 1969. The Murchison Meteorite is particularly rich in amino acids, as analysis of the material inside has revealed approximately 80 amino acids so far, with left-handed and right-handed amino acids both represented abundantly. By comparison, only 22 amino acids participate in life processes on Earth, all of which are right-handed.

It would’ve been shocking if such compounds were absent on Mars.

The hematite spheres (or ‘Martian blueberries’) as imaged by the Mars Exploration Rover. These are almost certainly evidence of past liquid water on Mars, and possibly of past life. NASA scientists must be certain that every site we examine on the Red Planet is not contaminated by the very act of our observing and landing spacecraft there. As of yet, there is no surefire evidence for either past or present Martian life.

Sample return missions could reveal Martian life.

An Atlas V rocket with 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 of 2021, where it seeks signs of ancient life and is collecting rock and soil samples for possible return to Earth. The sample-return mission was recently designated a “highest-priority” mission by the National Academies of Sciences’ decadal review.

These discovered “organics,” however, provide insufficient evidence.

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

Mostly Mute Monday tells an astronomical story in images, visuals, and no more than 200 words. Talk less; smile more.