Astronomers warn of invisible asteroid threat to Earth lurking in Venus’s shadow
By isabelle // 2025-09-24
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  • A new study reveals at least 20 undiscovered city-killer asteroids near Venus hidden by the sun’s glare.
  • Current telescopes struggle to detect these unstable space rocks, which could one day threaten Earth.
  • Simulations show some may drift into Earth’s path over millennia, posing a long-term catastrophic risk.
  • NASA’s upcoming NEO Surveyor and China’s CROWN mission could finally expose these hidden dangers.
  • Experts warn planetary defense must address unseen threats before it’s too late.
For decades, astronomers have warned about the dangers of near-Earth asteroids, but a new study reveals a terrifying blind spot: at least 20 massive, undiscovered space rocks lurking near Venus, each capable of wiping out a major city. These "Venus co-orbital" asteroids—some as wide as 390 meters—remain hidden in the sun’s glare, evading detection by Earth’s telescopes. And while they pose no immediate threat, their unstable orbits mean they could one day be flung toward our planet with devastating consequences. The research, published in Astronomy & Astrophysics, confirms what many have feared: our current asteroid surveillance is dangerously incomplete. Led by astronomer Valerio Carruba of São Paulo State University, the study used advanced simulations to track how these asteroids could shift over millennia, potentially crossing Earth’s path. The findings suggest that without space-based telescopes near Venus, we may never see them coming until it’s too late.

The invisible menace: Why these asteroids are so hard to detect

Most asteroid-hunting telescopes scan the night sky, but Venus co-orbitals hide in plain sight, buried in sunlight. Ground-based observatories can only spot them during brief windows at dawn or dusk, and even then, only if they stray far enough from the sun’s blinding glow. The Vera C. Rubin Observatory in Chile, which is set to begin operations soon, may help, but its effectiveness is limited. As Carruba explained, these asteroids "can remain invisible for months or years and appear for only a few days under very specific conditions." Worse yet, the 20 known Venus co-orbitals are just the tip of the iceberg. Computer models suggest many more exist, some with nearly circular orbits that keep them perpetually hidden. These "low-eccentricity" asteroids are the most dangerous because they stay close to Venus, making them nearly impossible to detect from Earth. Simulations show that if one were to strike, it could unleash energy equivalent to 410 megatons of TNT—enough to flatten a metropolis and carve a crater over 3 kilometers wide.

A ticking time bomb? The long-term risk we can’t ignore

While the odds of an impact in our lifetime are slim, the study warns that these asteroids could become a serious threat over thousands of years. Their orbits are unstable, shifting between different configurations in cycles lasting about 12,000 years. During these transitions, some could drift dangerously close to Earth. In fact, the researchers’ simulations found that five test particles came within striking distance of our planet. Statistically, this represents a near-certain impact on a millennial timescale. Carruba emphasized that planetary defense must account for what we can’t see, not just what we can. "These objects enter into 1:1 resonance with Venus, meaning they complete one revolution around the sun in the same time as the planet," he said. "But during transition phases, they can reach extremely small distances from Earth’s orbit." The only real fix? Deploying telescopes near Venus. NASA’s upcoming NEO Surveyor, set to launch after 2027, will help by scanning from a position between Earth and the sun. But even that won’t be enough. The most ambitious proposal, China’s CROWN mission, would place seven telescopes in Venus’s orbit, potentially detecting more than 94% of hidden inner-solar-system threats. Until then, we’re playing a cosmic game of roulette. These asteroids didn’t form overnight; they’re remnants of the early solar system, gradually nudged into Venus’s orbit by Jupiter’s gravity. And while they may not hit tomorrow, the study proves that what we don’t know can hurt us. This isn’t fearmongering; it’s a reality check. The same year astronomers briefly panicked over asteroid 2024 YR4 (later ruled harmless), we’re learning that far greater dangers lurk just out of sight. The good news? We have the technology to find them. The bad news? We’re not using it yet. As Carruba put it, "Planetary defense needs to consider not only what we can see, but also what we can’t yet see." The question isn’t if one of these city-killers will eventually head our way... it’s whether we’ll be ready when it does. Sources for this article include: StudyFinds.org Phys.org USAToday.com
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