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For decades, astronomers have looked into dark clouds where stars are born and come up short on sulfur. A new lab study points to a hidden stash locked in icy grains as complex sulfur molecules that telescopes have struggled to see.

The so-called sulfur shortfall is not small. In dense clouds, measured sulfur can be down by about a factor of 1,000 compared with what models predict for the gas, a gap that has puzzled researchers across multiple surveys. 

“The observed amount of sulfur in dense molecular clouds is less, compared to predicted gas-phase abundances, by three orders of magnitude,” said Ralf Kaiser, professor of chemistry at the University of Hawaii at Manoa.

The research team includes Ryan Fortenberry of the University of Mississippi, Ralf Kaiser, and Samer Gozem of Georgia State University.

Sulfur trapped in icy space dust

The study shows how hydrogen sulfide on icy dust can transform at frigid temperatures into two families of molecules, polysulfanes and octasulfur, using lab conditions that mimic space.

The work points to sulfur being present mostly as chains and eight-atom rings rather than as simple gas molecules that are easy to spot.

The experiments report that a sizable fraction of hydrogen sulfide converts into higher-mass sulfur species over cloud lifetimes, including a measurable yield of S8 rings (molecules made up of eight sulfur atoms arranged in a closed loop) in the thermodynamically stable crown shape.

Warming matters because ices do not release everything at once. As clouds evolve into star-forming regions, different sulfur compounds let go over a broad, molecule-specific temperature range, so astronomers should look in zones where those temperatures are reached.

Why telescopes miss sulfur

In ice surveys, carbonyl sulfide (OCS) has been the most reliable sulfur marker.

In fact, OCS is currently the only securely detected sulfur-bearing species in interstellar ices, which underscores why much of the sulfur budget has stayed off the books.

Early James Webb Space Telescope (JWST) spectra toward the background stars NIR38 and J110621 revealed solid OCS and even hints of sulfur dioxide, but not the bulk of the missing sulfur.

That leaves a lot of sulfur unaccounted for when observers tally up ices and gases along the same lines of sight. At this point, JWST can now resolve faint ice features with sensitivity that older missions could not match.

“If you use, for instance, the James Webb Space Telescope, you get a specific signature at specific wavelengths for oxygen and carbon and nitrogen and so forth. But when you do that for sulfur, it’s out of whack, and we don’t know why there isn’t enough molecular sulfur,” said Fortenberry. 

How sulfur changes in space

The team built its case with photoionization reflectron time-of-flight mass spectrometry and careful control of ionization energy to pinpoint which isomers of sulfur compounds were present.

That approach allowed them to identify chains up to H₂S₁₁ (one of the largest sulfur chain molecules detected in laboratory simulations of interstellar ice chemistry) and to confirm that only the crown form of octasulfur emerged under the ice-processing conditions.

“Laboratory simulations of interstellar conditions such as this study discover possible inventories of sulfur, containing molecules that can be formed on interstellar ices.

Astronomers can then utilize the results and look for these polysulfane molecules in the interstellar medium via radio telescopes once sublimed into the gas-phase in star forming regions,” said Kaiser.

When those ices warm, the lab data indicate that polysulfanes should enter the gas at distinct temperatures, making them promising targets for radio searches. 

Asteroid clue to sulfur

There is a tantalizing link between cold clouds and nearby rocks. Analyses of samples from the asteroid Ryugu reported elemental sulfur rings among the extracted compounds, consistent with S8 showing up beyond Earth.

The new study goes further by estimating that the Taurus Molecular Cloud could accumulate an amount of octasulfur equivalent to hundreds of Earth masses when integrated over cloud lifetimes, if similar chemistry operates at scale.

That perspective connects interstellar ices to the inventory of material that young planetary systems can inherit.

Why sulfur in space matters on Earth

Sulfur chemistry is not just an astrophysical curiosity. Hydrogen sulfide arises from natural and industrial sources and interacts with air and water systems that people care about, so basic knowledge feeds practical understanding.

“Hydrogen sulfide is everywhere: it’s a product of coal-fired power plants, it has an effect on acid rain, it changes the pH levels of oceans and it comes out of volcanoes,” Fortenberry concluded.

“If we gain a better understanding of what the chemistry of sulfur can do, the technological commercialization that can come from that can only be realized with a foundation of fundamental knowledge.”

The study is published in Nature Communications.

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Tiny robots often struggle with batteries, sensors, and navigation, yet a common fruit fly already packs all three in a two and a half millimeter body. Researchers at Harvard’s Rowland Institute have now learned to steer those insects as if they were remote controlled microrobots, trading silicon for living tissue.

The team reports that it can point Drosophila melanogaster along preset routes, flip its heading on command, and even choreograph a swarm that traces the phrase “HELLO WORLD” across a floor.

Lead author Kenichi Iwasaki of the Rowland Institute explained that the work shows how biology can solve problems that stump microengineering.

Turning live flies into microrobots

The first trick relied on the fly’s optomotor response, an ancient reflex that keeps moving patterns stable on the retina.

By projecting a rotating blue and black pinwheel, the scientists nudged the insect to veer right or left, achieving 94 percent waypoint accuracy in a five inch corridor.

Visual cues were only half the story. The group also used optogenetics to plant light sensitive channels in each antenna, letting red or blue flashes mimic odor plumes and pull the fly toward a target with 95 percent fidelity after a brief neural tune up.

Building a miniature autopilot

To keep left and right commands separate, one antenna was coated with blue blocking dye and its twin with red blocking dye, creating a simple “two bit” control channel.

Because the fly supplied its own muscles and metabolism, the external hardware shrank to an overhead projector, a camera, and a computer smaller than a lunchbox.

When tested side by side, light steered flies covered the thirteen inch track four times faster than untreated controls and wandered half as far off course, performance that held steady for hours without food rewards.

That durability hints that the reflexes sit below the insect’s motivational circuitry, so guidance does not need constant recalibration.

From scribbles to “HELLO WORLD”

After mapping simple lines, the researchers strung thirty one checkpoints into the outline of ten letters, guiding a single fly to walk each stroke until the phrase appeared on screen.

The insect finished the “writing” in just under seventeen minutes, confirming that the closed loop system can handle complex sequences.

In parallel trials three separate flies played the role of independent pens, each assigned a subset of strokes, and still reproduced the message legibly.

The multi-pen demonstration shows that guidance commands can be broadcast in parallel without mixing up which insect receives which cue.

Microrobots haul loads and walk mazes

Size does not equal weakness. A fly weighing a single milligram hauled an extra milligram of brass, roughly 0.000035 ounces, back and forth between two points more than six hundred times before tiring.

When the arena was replaced with a seventeen inch square maze lined by dead end branches, the pinwheel guidance still kept insects on the main loop for hundreds of laps.

Those trials show that the method works even when walls block direct sightlines and cast confusing shadows.

Borrowing nature for microrobotics

Conventional microrobots often stall once they leave the lab, because dust, humidity, and radio interference swamp their fragile circuits.

A living fly reared for pennies in a jar brings built in power, stereo smell, and a flight computer honed by evolution, delivering fault tolerance that engineers currently pay for in weight and expense.

Swarms of such “biobots” could sniff hazardous leaks, map collapsed buildings, or pollinate rows of strawberries without the carbon footprint or price tag of disposable electronics.

Soft robotics specialists say biological carriers could also ferry sensors deep into rubble that wheeled machines cannot enter.

“Fruit flies have evolved for millions of years to handle tight spaces and unpredictable environments,” said Sasha Rayshubskiy, Rowland Fellow at Harvard University.

His group believes that modest on board gadgets will be enough to steer the insects outdoors once proof of concept backpacks now tested on cockroaches move below the one milligram threshold.

From lab to field tests

Solar powered “circuit saddles” only four hundredths of an ounce have already helped cyborg beetles right themselves after falls, suggesting similar packs could drive flies for days without human input.

A recent study showed that a swarm of such cyborgs can navigate dunes without bunching up, thanks to simple neighbor to neighbor rules.

Transplanting that algorithm onto fruit flies could let hundreds sweep a greenhouse for pests, each insect sharing only local information yet covering acres faster than a single drone.

Because the guidance signals piggyback on reflexes rather than override them, the team predicts that the insects will still sleep, eat, and mate on schedule, reducing welfare concerns.

Hurdles remain for living microrobots

Engineers still need to miniaturize guidance hardware to under one milligram, the payload limit seen in weight tests.

They must also ensure that artificial cues do not block essential behaviors such as feeding, which would shorten any field deployment.

Ethicists will ask how much autonomy a sentient agent should sacrifice for human benefit.

The Harvard group argues that the flies already use the same reflexes in nature, so the intervention resembles turning up the volume rather than rewriting the score.

A glimpse at future swarms

Because each insect costs pennies to rear and requires minutes to train, fleets numbering in the thousands are plausible.

Machine vision algorithms could direct those swarms to converge on odor plumes, forming a living, distributed sensor that highlights pollutant hotspots in real time.

Meanwhile laboratory neuroscientists gain a bonus tool, a way to hold a moving fly at any coordinate, then record how specific brain cells behave when the animal chooses, or refuses, to follow orders.

That feedback loop could clarify decision making at a resolution unseen in larger animals.

The study is published in Proceedings of the National Academy of Sciences.

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