The Invisible Danger: Could Undiscovered Asteroids Near Venus Threaten Earth?

Venus shares its orbit with a rare type of asteroid called co-orbitals—space rocks that follow the same average path around the Sun as Venus. Currently, only twenty such asteroids are known, and most have elongated (eccentric) orbits that occasionally bring them near Earth. These close approaches make them easier to discover. But this observed pattern might not reflect reality. In this new study led by Valerio Carruba, researchers explore whether many more co-orbitals exist with rounder (low-eccentricity) orbits—and whether they might pose a hidden threat to Earth.

Why Haven’t We Seen Them?

To determine whether low-eccentricity co-orbitals are simply rare or just hard to detect, the authors used a detailed simulation called NEOMOD3. This model replicates how near-Earth asteroids (NEAs) move through space. The results show that there is no dynamic reason why co-orbitals should avoid low-eccentricity orbits. The real reason we haven’t seen them, the authors argue, is observational bias. These faint objects don’t come close enough to Earth to appear bright and are usually positioned near the Sun in the sky, making them almost impossible to detect using ground-based telescopes.

Modeling Their Paths

To understand the motion of these potential asteroids, the study uses a semi-analytical model to examine the dynamics of the 1:1 resonance—a special gravitational relationship between Venus and its co-orbitals. These models reveal different types of orbital behavior, such as "tadpole" orbits near Venus’s stable points or "horseshoe" shapes. To go beyond short-term predictions, the team also performed long-term numerical simulations of over 3,400 artificial asteroids. These simulations, running over 36,000 years, reveal that even low-eccentricity co-orbitals can eventually cross paths with Earth, especially at certain orbital inclinations.

How Likely Are Earth Encounters?

The researchers focused on calculating how close these objects could come to Earth, using a measure called the Minimum Orbital Intersection Distance (MOID). They found that even some low-eccentricity co-orbitals could get within striking distance. The greatest risks came from objects with eccentricities close to 0.38—the tipping point where an asteroid’s orbit begins to overlap with Earth's. The danger is especially high for asteroids with lower orbital inclinations, meaning they stay close to the plane of the Solar System and are more likely to intersect Earth's path.

Can We See Them from Earth?

The team simulated how easily these hypothetical asteroids could be observed from the Vera C. Rubin Observatory in Chile. They found that even under ideal conditions, many co-orbitals would be visible only briefly, just after sunset or before sunrise, and often too close to the Sun’s glare. The apparent brightness of these objects is generally just at or below the telescope's detection threshold. Interestingly, the study found that higher eccentricity asteroids were much easier to detect—suggesting that current observation methods are biased toward spotting these and overlooking the rounder, more Earth-threatening ones.

Looking from a Better Vantage Point

Given the challenges of spotting these asteroids from Earth, the researchers turned their attention to space-based observation. They explored the possibility of placing telescopes near Venus, in orbit or at stable gravitational points (Lagrange points). From this closer perspective, the sky is darker, and low-eccentricity asteroids appear brighter and more frequently. Several missions—such as NASA’s NEO Surveyor or the proposed CROWN satellite constellation—could take advantage of this vantage point to detect a much larger portion of the co-orbital population and track their paths more precisely.

Why This Matters

This research highlights a potentially serious blind spot in our planetary defense strategy. Although no low-eccentricity Venus co-orbital has yet been confirmed as a threat, simulations show that many could pose significant risks. These hidden objects, if large enough, could cause regional destruction if they impacted Earth. Since they’re difficult to detect with existing Earth-based systems, space missions focused on the inner Solar System may be our best bet for uncovering them before it’s too late.

Final Thoughts

Carruba and his colleagues conclude that a large, undetected population of Venus co-orbitals likely exists—and some may be capable of colliding with Earth. Current ground-based surveys may catch a few during favorable alignments, but only dedicated space-based observations from a location near Venus will allow astronomers to fully map this elusive group. As recent asteroid discoveries have reminded us, even a single missed object could have serious consequences.

Source: Carruba