From Arctic Ice to Alien Worlds: Why I'm Betting on Dimethyl Sulfide

Jonathan Durkin
3 days ago
6 min read

A Personal Journey Through Astrobiology

When I first encountered Melosira arctica under a microscope during my NASA Space Grant research, I had no idea this tiny Arctic diatom would eventually lead me to thinking about alien oceans 120 light-years away. But that's exactly what happened. And it's why I believe the scientific community is making a mistake by dismissing dimethyl sulfide (DMS) too quickly in the search for extraterrestrial life.

Let me back up.

It Started With Ice

My research with the NASA Space Grant program focused on Melosira arctica, a remarkable single-celled alga that lives underneath Arctic sea ice. These diatoms form long chains that hang from the ice like microscopic curtains, creating vast underwater forests in one of Earth's most extreme environments. They're photosynthetic powerhouses, incredibly successful at what they do, and—here's the key detail—their close relatives are among Earth's most prolific producers of dimethyl sulfide.

Melosira species and other marine phytoplankton produce massive amounts of a compound called dimethylsulfoniopropionate (DMSP) as a kind of cellular Swiss Army knife: it helps them regulate water balance, protects them in freezing conditions, and shields their cells from oxidative stress. When these cells are damaged, consumed, or die, bacterial and algal enzymes break down DMSP, releasing DMS into the water—and eventually, into the atmosphere.

That distinctive ocean smell you associate with the beach? That's largely DMS and its chemical relatives.

Here's what struck me during my research: Melosira arctica thrives in conditions that most organisms would find impossible. It lives at the ice-ocean interface where temperatures hover near freezing, light is scarce for much of the year, and the environment is in constant flux. Yet it doesn't just survive—it dominates. Massive blooms of Melosira can turn the underside of Arctic ice into a ghostly green forest, producing so much biomass that when the ice melts, the algae sink to the seafloor and feed entire deep-sea ecosystems.

Working with Dr. Suzanne Neuer, I came to appreciate something fundamental about these organisms: they represent exactly the kind of life we should expect to find elsewhere in the universe if life exists at all. They're simple, single-celled, photosynthetic, and chemically-based reproducers. They use basic metabolic processes to harvest energy from sunlight and turn it into biomass. And in doing so, they produce chemical byproducts—like DMS—in quantities large enough to affect their entire planet's atmosphere.

The K2-18b Controversy

Fast forward to September 2023, when astronomers announced a tentative detection of DMS in the atmosphere of K2-18b, an exoplanet orbiting in the habitable zone of a red dwarf star 120 light-years from Earth. On our planet, DMS is produced almost exclusively by life—by organisms like the phytoplankton relatives of Melosira. Finding it on another world seemed like exactly the kind of biosignature we've been searching for.

The scientific community's reaction was electric. Headlines proclaimed "tantalising signs of possible life." But then came the scrutiny. Statistical reanalyses. Questions about the quality of the James Webb Space Telescope data. Discoveries that DMS could form abiotically in comets and interstellar clouds. By mid-2025, the consensus had shifted from excitement to deep skepticism, with multiple papers arguing the detection was either a statistical fluke or an artifact of data processing.

Watching this controversy unfold, I found myself thinking back to those Melosira chains hanging from Arctic ice. And I realized: the scientific community might be missing the point.

Why I'm Still Excited

The debate about whether DMS is actually present on K2-18b is important, and I genuinely believe the signal is likely real—but that's almost beside the point. What matters is this: DMS represents exactly the kind of biosignature we should be looking for, regardless of how the K2-18b story ends.

Think about what my research with Melosira taught me. These organisms are:

Simple: Single-celled, not complex multicellular life
Successful: They achieve global-scale dominance in their niche
Photosynthetic: They harvest energy from starlight
Chemically active: They produce organic molecules that escape into the atmosphere
Environmentally transformative: When they bloom, they change the chemistry of their surroundings

From an astrobiological perspective informed by evolutionary principles, this is exactly what we should expect widespread extraterrestrial life to look like. Not intelligent civilizations broadcasting radio signals, but simple organisms doing what life does: harvesting energy, reproducing, and producing chemical waste products in the process.

The DMS-producing phytoplankton in Earth's oceans release approximately 28 teragrams of DMS into the atmosphere annually. That's enough to affect global cloud formation and climate. These organisms have reshaped our planet's atmosphere through their metabolism alone. This is the kind of large-scale biosignature that might actually be detectable across interstellar distances.

The Water Analogy

We search for water on exoplanets not because water is exclusively biological—water is everywhere in the universe—but because our one example of life (Earth) tells us water is essential. It's a filter that helps us decide which of the thousands of known exoplanets deserve our limited telescope time and attention.

DMS deserves a similar place in our search strategy. On Earth, it's overwhelmingly biological. It's produced by simple, successful organisms in amounts large enough to reach the atmosphere. It's tied to fundamental life processes like photosynthesis in liquid water. And—as the K2-18b detection demonstrated—it's potentially detectable with current technology.

Yes, we now know DMS can form abiotically. We've found it in comets and interstellar clouds. But this is actually a feature, not a bug. It means we can establish baselines. If we find DMS at levels hundreds or thousands of times higher than what abiotic processes can produce—and if we find it alongside other biologically relevant molecules in an atmosphere where liquid water is possible—that cumulative case becomes compelling.

A Research Program, Not a Single Detection

In the op-ed that follows this introduction, I make the case that we need to shift our thinking about DMS from "Is it on K2-18b?" to "What does it mean when we find it, and how do we search more effectively?"

I propose six specific research directions that could strengthen DMS's role in biosignature searches:

Reanalyzing K2-18b with refined atmospheric models to clarify the current controversy
Applying the Sagan test: modeling what Earth's DMS signature would look like from interstellar distances
Machine learning approaches to identify subtle DMS features in spectroscopic data
Statistical frameworks for interpreting ambiguous detections
Marine ecology perspective: using what we know about organisms like Melosira to predict DMS production on exoplanets
Predictive modeling: forecasting expected DMS levels for different classes of worlds

The marine ecology work is where my research comes in. By understanding how Melosira and its relatives produce DMS under different environmental conditions—temperature, light levels, nutrient availability, salinity—we can start to predict what kinds of exoplanet oceans might produce detectable amounts of DMS.

For instance: Melosira arctica produces exceptionally high concentrations of DMSP in cold, low-light environments. What does that tell us about potential life on planets orbiting cooler stars, where less light is available? Could life in those conditions actually produce more detectable biosignatures because the organisms need to synthesize more protective compounds?

These are the questions that connect microscope work in Earth's polar regions to telescopic observations of distant worlds.

The Long View

We live in an extraordinary moment in human history. For the first time, we have the technology to search for signs of life on planets orbiting other stars. The James Webb Space Telescope has given us capabilities that were pure science fiction just decades ago. But with this capability comes a new challenge: deciding what to look for and where to look.

The K2-18b controversy might seem like a setback—an exciting claim that wilted under scrutiny. I see it differently. The debate has shown us that DMS detection is feasible with current technology. It's forced us to develop better analytical methods and more rigorous statistical frameworks. It's prompted discoveries about abiotic DMS production that actually help us establish baselines. And it's opened up interdisciplinary collaborations between astronomers, atmospheric chemists, and marine biologists.

In a universe of potentially billions of habitable worlds, we need breadcrumbs, not just smoking guns. We need reasons to look harder at some planets rather than others. Based on my work with Melosira, my understanding of marine ecology, and my reading of the astrobiological literature, I believe DMS gives us one of those reasons.

The tiny Arctic diatom I studied under a microscope—thriving beneath the ice, producing massive blooms, releasing chemical signatures into the atmosphere—might be our best analog for what life looks like elsewhere. And if similar organisms exist on water-rich worlds orbiting distant stars, DMS might be exactly the breadcrumb that leads us to them.

The excitement was never misplaced. It was, and remains, an invitation to build the research program that could one day answer humanity's oldest question: Are we alone?

Read the Full Op-Ed

What follows is my complete analysis of the K2-18b DMS controversy, from the initial detection through the current scientific debate, followed by my argument for why DMS deserves sustained attention as a biosignature target. I walk through the timeline, explain the technical challenges, address the skeptics' concerns, and lay out a concrete research agenda for moving forward.

Whether you're a professional astronomer, an astrobiology enthusiast, or someone who just thinks the question "Are we alone?" is worth pursuing, I hope this piece gives you a new perspective on how we might answer it.

The search for life beyond Earth isn't just about bigger telescopes and better technology. It's about understanding life on our own planet deeply enough to recognize it when we finally find it somewhere else. That's where Melosira arctica comes in. That's where DMS comes in. And that's where our story begins.