Hidden asteroids in Venus’ orbit pose impact risk to Earth

A new study from São Paulo State University, published in the journal Astronomy and Astrophysics, suggests we have been underestimating the number of asteroids orbiting the Sun on paths similar to that of Venus.

Venus co-orbitals are asteroids that travel around the Sun at nearly the same average distance as Venus, essentially sharing the planet’s orbit but not remaining at a fixed point relative to the planet. Their orbital alignment with Venus and the interaction of their trajectories with those of Venus and Earth make them difficult to detect with current ground-based observatories. Their positions relative to the Sun often keep them hidden from view.

In the new study, researchers used a combination of semi-analytical models, long-term orbital simulations, and observational visibility tests to re-examine the potential risk these concealed asteroids could pose to Earth.

So far, only 20 Venus co-orbitals have been confirmed, and most of them have high-eccentricity orbits with values above 0.38. This threshold is significant because it indicates when an asteroid’s farthest distance from the Sun can overlap with Earth’s closest approach, increasing the potential for close encounters.

The fact that so few low-eccentricity co-orbitals have been found begs the question of whether they’re actually missing from the population or if we’re just not detecting them because of how and where we’re looking.

To dig into this, Valerio Carruba and his team used the Near-Earth Object Model version 3 (NEOMOD3) dynamical model to simulate how near-Earth asteroids behave around Venus’s orbit. Their results showed a fairly even spread of orbital eccentricities, including many with values below 0.38. This suggests that the lack of observed objects isn’t because they don’t exist, but because they’re hard to spot with current observation methods.

Since these objects stick close to Venus’s orbit, they rarely come near enough to Earth to reflect enough sunlight to be picked up by ground-based telescopes.

The researchers used a semi-analytical Hamiltonian model to map out the resonance structure and set up starting points for long-term simulations. This method captures different orbital patterns like tadpole, horseshoe, and retrograde satellite paths. These setups are usually stable for thousands of years, but shifts between them can sometimes push an object into an Earth-crossing orbit.

To estimate the impact risk, Carruba and his team created a grid of synthetic Venus co-orbitals with eccentricities between 0.24 and 0.38 and inclinations up to 60 degrees. They ran each of these setups through 36 000 year simulations, covering three full co-orbital cycles.

The simulations showed that many of these objects experience minimum orbital intersection distances (MOIDs) with Earth well below the 0.05 au threshold used to define Potentially Hazardous Asteroids (PHAs). Some even had MOIDs under 0.0005 au, putting them in the same risk category as known high-risk objects like 2020 SB and 524522 Zoozve.

Assuming diameters of 300–400 m (985–1 300 feet), typical albedos, and impact velocities near Earth’s escape velocity, such objects would release impact energies between 1.5 and 4.1 × 10² megatons of Trinitrotoluene (TNT).

To draw an analogy for better comprehension and understanding, that is enough energy to create craters of 2 to 3 km (1.2–1.9 miles) in diameter and qualifies as a level 8 threat on the Torino impact hazard scale.

Even though the dynamics clearly suggest these objects exist, detecting them is still a challenge. To see how likely (or difficult) they are to be observed, the researchers ran visibility simulations using the Vera C. Rubin Observatory, testing both real and synthetic co-orbitals. They focused on factors like solar elongation, elevation in the sky, and how bright the objects appear.

The simulations show that although the observatory can spot some of these objects, the opportunities are limited and depend a lot on their inclination and eccentricity. Objects with eccentricities near 0.38 are much more likely to be seen, which suggests that the available data is biased toward detecting those with higher eccentricity orbits.

The study also looks at what detection would be like from a platform near Venus. Compared to telescopes on Earth, an observer closer to Venus would get longer viewing periods, better angles, and more favorable lighting conditions. Simulations from this position show more consistent brightness and improved visibility across a broader range of orbits. This makes a strong case for placing future space-based missions near Venus to help uncover this hard-to-detect group of asteroids.

To expand detection efforts, the paper looks at several mission proposals like the Near-Earth Object (NEO) Surveyor and the Corona Borealis constellation. These missions would operate in heliocentric orbits inside Earth’s or near Venus’s Lagrange points, giving them the extended coverage and observation time needed to spot low-eccentricity co-orbitals.

References:

¹ Assessing the collisional hazard posed by the undiscovered Venus co-orbital asteroids – V. Carruba, R. Sfair, R. A. Araujo, O. C. Winter, D. C. Mourão, S. Di Ruzza, S. Aljbaae, G. Caritá, R. C. Domingos, A. A. Alves – Astronomy & Astrophysics – May 23, 2025 – DOI https://doi.org/10.48550/arXiv.2505.15968 – OPEN ACCESS