Tiny Black Holes May Cross the Solar System—Mars Still Hasn’t Revealed Them

Tiny primordial black holes have not been discovered passing through the Solar System. The much-discussed estimate—at least one inner-system crossing per decade—comes from a conditional model: it applies if black holes in a particular asteroid-mass range constitute all of the local dark matter.

The practical outlook has also become less optimistic since that proposal appeared in 2024. A more detailed study published in 2025 concluded that the accumulated disturbance in the Earth–Mars distance would remain below present measurement uncertainties, while another team developed a different, radiation-based search that has not yet produced a detection.

Where the once-per-decade claim comes from

Primordial black holes are hypothetical relics that could have formed when unusually dense regions of the early universe collapsed. Unlike ordinary black holes created by dying stars, their possible masses span a much broader range. The objects relevant here would combine an asteroid-like mass with an extremely compact, optically dark form.

The central claim is a population estimate, not evidence that astronomers have identified such an object nearby. In the scenario examined by the original flyby study, asteroid-mass primordial black holes supply all dark matter; their inferred local number density and speed then imply at least one passage through the inner Solar System per decade. The authors simulated brief, one-time encounters on hyperbolic paths and proposed looking for their gravitational imprint in decades of planetary-position data.

“Could pass regularly” and “has been observed” are therefore very different statements. If primordial black holes provide only a fraction of dark matter, their expected crossing rate falls. The estimate also describes passages through a large region containing the inner planets, not collisions with Earth, Mars or the Sun.

Why Mars appeared to be a promising detector

A passing compact mass would gravitationally tug on every nearby body. Because Earth and a planet such as Mars would experience slightly different accelerations, the encounter could alter their measured separation. The proposed signal is not a planet visibly lurching in the sky, but a small residual left after researchers fit observations with a detailed model of Solar System motion.

Mars is useful because spacecraft ranging has supplied a long record of its distance from Earth. A flyby would act as a relatively short impulse, followed by an oscillating displacement tied to the planet’s orbit. In principle, that time pattern could help distinguish a fast, unseen interloper from a poorly modeled mass or the gradual influence of known Solar System bodies.

That distinction is a formidable analysis problem. Modern ephemerides already account for the Sun, planets, moons, numerous asteroids, relativistic effects and measurement-system errors. A simulated displacement larger than a quoted ranging precision does not automatically become a detectable signal after all those parameters are fitted together.

Later simulations found the Mars signal below current uncertainty

A separate team subsequently modeled a Solar System embedded in a full population of asteroid-mass primordial black holes rather than concentrating only on selected singular encounters. The independent Earth–Mars analysis, published in The Astrophysical Journal in February 2025, found that the closest encounter usually dominates the disturbance but that the resulting perturbations remain smaller than current ranging uncertainties. Its authors estimated that detecting the cumulative gravitational effect would require more than an order-of-magnitude improvement in measurement accuracy, or a method capable of extracting a signal well below the existing noise level.

This result does not demonstrate that primordial black holes are absent. It says the presently modeled Earth–Mars record does not directly constrain the all-dark-matter scenario through this particular effect. The two studies used different simulation strategies and detection assumptions, which explains why an initially plausible observable can look insufficient in a more complete treatment.

It also clarifies what a future candidate would need. Researchers would require a coherent signature across multiple observations, a trajectory compatible with a rapid unbound flyby, and evidence that uncertainties in asteroid masses and planetary modeling could not reproduce it. A lone unexplained residual would not establish that the perturber was a black hole.

A second search route looks for particles instead of a wobble

Low-mass black holes should emit Hawking radiation, so a nearby passage might create a time-dependent excess of particles rather than only a gravitational displacement. A published positron-signal study, revised in January 2026 to match its Physical Review D version, simulated flybys as they might appear to the Alpha Magnetic Spectrometer in low-Earth orbit. The authors found that existing AMS characteristics provide sensitivity only to present-day black holes below about 2 × 10¹⁴ grams, but modeled daily positron measurements from 5 to 500 MeV could probe extended mass distributions whose peaks lie in the asteroid-mass window.

The study’s order-of-one detectable transit per year is also conditional. It emerges across portions of the tested mass-function parameter space and assumes a suitable daily, lower-energy dataset; it is not a count of events already recorded by AMS. The approach targets the lighter tail of an evolving population, so its rate should not be treated as a correction to the gravitational study’s once-per-decade estimate.

Radiation and orbital searches have complementary weaknesses. The former depends on the black holes’ mass distribution, evaporation history and detector coverage; the latter depends on exceptionally precise dynamical modeling. Agreement between independent signatures would be far more persuasive than either an isolated particle excess or a small orbital anomaly.

What the current evidence actually permits

As of August 2026, the responsible conclusion is narrower than the idea of black holes “cruising” through the Solar System suggests. Regular passages are a calculated consequence of one still-allowed dark-matter hypothesis, not an observed feature of our planetary neighborhood. The studies examined here report predicted signals and detection prospects, not a confirmed flyby.

Mars remains scientifically useful because planetary ranging can test gravitational effects that telescopes cannot see directly. For now, however, detailed simulations indicate that its orbit has not supplied a decisive test. The newest value lies in the expanding search strategy: researchers can compare planetary residuals with time-dependent positron, gamma-ray or X-ray signatures instead of relying on a single hypothetical wobble.

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