Like a shelf in an old house, the Earth collects a lot of dust from its surroundings. This “space dust” is mostly made up of micrometeorites that survive atmospheric entry and provides researchers with a cheap and easy way to obtain samples to study our cosmic neighbors. However, it can be difficult to determine which objects certain samples originated from if their parent bodies aren’t already in available catalogs. A recent study, published in Science Advances, describes a new subset of space dust with such mysterious origins and how researchers are tracking down potential sources.
The study of ‘space dust’
Some micrometeorites, called cosmic spherules, melt upon entry, resulting in a spherical shape. These cosmic spherules lose their original mineral structure during entry heating, making their parent bodies hard to identify. In some cases, oxygen isotopes act like a chemical fingerprint, helping researchers determine where this dust came from. Yet about 10% of cosmic spherules have unusually small oxygen-16 isotope signatures that don’t match any previously identified meteorite group. Researchers refer to these as the “Group 4” cosmic spherules.
The team involved in the new study says orbital parameters could also prove useful for source identification. They write, “In one particular case, however, the mineralogical and textural properties of a subset of cosmic spherules do provide information on the orbital parameters of their precursors, including eccentricity and encounter velocity. This subset is termed CumPo after its characteristic cumulate olivine porphyritic texture, characterized by clustered olivine phenocrysts that increase in size from one side of the spherule to the other.”
The features associated with CumPo spherules suggest unusual orbital parameters that may point to atypical parent bodies, according to the researchers. In particular, prior research on these textures suggested some spherules may have experienced unusually high entry speeds, which can hint at the orbital eccentricity of the parent body.
A new category of cosmic spherules
To try to learn more about their origins, the researchers examined 10 CumPo cosmic spherules from Antarctica and a more modern collection found on urban rooftops. They used electron microscopy and microprobe chemistry to analyze textures and key minerals and chemistry. They also measured oxygen isotopes with SIMS and NanoSIMS to fingerprint sources.
The team found many similarities between the two collections and defined them as a new subset of sulfur-rich cumulate olivine cosmic spherules, which they call “SCumPo.” The subset is strongly tied to the oxygen-16-poor Group 4 signature. The group shares a set of features that imply extremely reducing conditions during atmospheric entry. This includes an uncommon near-absence of magnetite, frequent iron-nickel-sulfur droplets, consistently low nickel in olivine crystals, and unusually sulfur-rich glass.
Some spots within a single spherule showed both oxygen-16-poor and oxygen-16-rich signatures, implying the original dust was likely a mixture of at least two components because this does not happen naturally.
The study authors explain, “We interpret this as strong evidence that the SCumPo precursors were composite materials containing at least two different components: one component carrying a 16O-rich signature (relatively low δ18O and negative Δ17O, typical of carbonaceous chondrite anhydrous phases) and another carrying a 16O-poor signature (high δ18O and positive Δ17O not matched to known meteorites but akin to Group 4 fine-grained material).”
A search for SCumPo parent bodies
The team then ran numerical simulations of crystal settling during atmospheric deceleration to determine likely entry speeds and orbital eccentricities. The results showed that olivine “settling” will most likely occur with high encounter speeds of roughly 14–17 km/s. The team says this points to eccentric orbits (around e > 0.2), and this eccentricity is more consistent with near-Earth objects than typical main-belt asteroid sources.
They say this parent body seems to be a previously unsampled, primitive, sulfide-rich carbonaceous asteroid related to a group of carbonaceous meteorites called the CM–CO–CY chondrite clan.
The study authors write, “Given that we have linked their composition to the CM-CO-CY clan of carbonaceous chondrites, it is plausible that their parent body was a primitive carbonaceous asteroid that migrated onto an Earth-crossing orbit—attaining comet-like orbital parameters. For instance, one might consider the disrupted fragments of a thermally altered but water-bearing asteroid (like the CY group) that evolved into near-Earth space.”
The researchers note that this hypothetical parent body represents a “missing” meteorite type. The micrometeorite samples exist, but no meteorite like it exists in current collections. They say that future identification through asteroid missions or meteorite finds would be considered “a pivotal discovery.”
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Publication details
Matthias Van Ginneken et al, 16 O poor cosmic spherules from near-Earth CY chondrite asteroids, Science Advances (2026). DOI: 10.1126/sciadv.aed6340
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Much of Earth’s ‘space dust’ may come from unidentified near-Earth asteroids (2026, July 7)
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