Venus co-orbital asteroids are celestial bodies that share Venus's orbital path around the Sun, locked in a 1:1 mean-motion resonance. Currently, 20 such asteroids are known, but only one has an orbital eccentricity below 0.38, likely due to observational biases favouring the detection of asteroids with higher eccentricities (meaning how much the orbit deviates from a perfect circle) that approach Earth more closely. These asteroids are classified as Potentially Hazardous Asteroids (PHAs) if they have a diameter of at least 140 metres and come within 0.05 astronomical units (au, approximately 7.5 million kilometers) of Earth's orbit.

Research by Valerio Carruba and colleagues indicates that a significant population of undetected Venus co-orbital asteroids with low eccentricities (e < 0.38) and lower inclinations could pose a collisional risk to Earth. Simulations over 36,000 years, using a grid of 26 cloned asteroids with varying orbital characteristics, show that some of these objects could have minimum orbital intersection distances (MOIDs) as low as 0.0005 au (74,800 km), placing them in the same risk category as known PHAs like 2020 SB, 524522 (Zoozve), and 2020 CL1. An asteroid of 150 metres in diameter could release energy equivalent to hundreds of megatons of TNT upon impact, thousands of times more potent than the Hiroshima bomb, potentially causing city-wide destruction or tsunamis if it strikes an ocean.

Detecting these asteroids is difficult due to:

  • Solar Glare: Their proximity to the Sun creates a blind spot, limiting observation windows to brief periods just before sunrise or after sunset when solar elongation (the angular distance from the Sun) is favourable.
  • Low Eccentricity: Asteroids with nearly circular orbits (low eccentricity) remain closer to Venus and are fainter, with absolute magnitudes often exceeding 19, making them detectable only by large telescopes at high azimuth angles.
  • Chaotic Orbits: These asteroids have Lyapunov times (time scale for which a system is chaotic) of about 150 years, meaning their orbits become unpredictable after this period due to chaotic dynamics, complicating long-term tracking.

The Vera C. Rubin Observatory, set to begin operations in July 2025 in Chile, is expected to detect some of these asteroids during favourable conditions using its advanced wide-field survey telescope. However, its "low-SE twilight survey" program, designed to capture short exposures closer to the Sun, may still miss low-eccentricity objects due to limited observation windows and solar elongation constraints.

The study emphasises that ground-based observatories alone are insufficient. A dedicated space-based mission near Venus, positioned to face away from the Sun (e.g., at Sun-Venus L1 or L2 Lagrange points), could provide continuous monitoring and map the full population of these "invisible" PHAs. Such a mission would overcome visibility issues and improve orbital predictions, critical for early warning and mitigation. Proposed missions like NEO Surveyor, potentially launching after 2027, could orbit the Sun-Earth or Sun-Venus L1 point to enhance detection capabilities.

While the probability of a Venus co-orbital asteroid striking Earth in the near term is low, the potential consequences are catastrophic. An impact from a 150-metre asteroid could release 1.5 to 4.1 × 10² megatons of TNT, creating craters 2–3 km in diameter and qualifying as a level 8 event on the Torino impact hazard scale. Even a single event could devastate cities, trigger fires, or cause tsunamis, with economic and human costs in the billions or trillions. From a utility perspective (probability × cost), the high cost of such an event justifies significant investment in detection and mitigation, despite the low probability. For instance, the recent discovery of 2024 YR4, a potential "city-killer" with a high impact probability, underscores the urgency of addressing these threats.

Beyond Venus co-orbital asteroids, other hidden threats from outer space warrant attention:

Near-Earth Asteroids (NEAs)

  • Scale: Over 2,350 PHAs have been identified, but an estimated 3,000+ remain undetected. These include asteroids larger than 140 metres that come within 0.05 au of Earth's orbit.
  • Impact Potential: A 600-foot asteroid like 2022 SF289, discovered by the HelioLinc3D algorithm, demonstrates the potential for undetected NEAs to approach within 140,000 miles of Earth. While not an immediate threat, such objects highlight gaps in current detection systems.
  • Detection Efforts: NASA's mandate to identify 90% of NEAs larger than 1 km has been expanded to include smaller PHAs (down to 100 metres). The Vera C. Rubin Observatory is expected to detect 60–90% of PHAs larger than 140 metres, but smaller objects (45 metres) may only be detected 1–3 months before impact, leaving limited time for deflection.

Comets

  • Unpredictability: Comets like C/1996 B2 Hyakutake, which passed within 0.10 au of Earth in 1996, can appear with little warning due to their long orbital periods. A 3-km comet could cause global devastation, and the Rubin Observatory could provide up to 8 years of warning with over 500 observations.
  • Challenges: Comets are harder to track than asteroids due to their volatile nature and outgassing, which can alter their orbits unexpectedly.

Interstellar Objects

  • Rare but Dangerous: Objects like 'Oumuamua (1I/2017 U1) and 2I/Borisov, which originate outside our solar system, are rare but could pose a threat if on a collision course. Their high velocities and unpredictable trajectories make detection and deflection challenging.
  • Detection: Current surveys are not optimised for interstellar objects, which may only be spotted when already close to Earth.

Mitigation Strategies

  • Ground-Based Observatories: The Vera C. Rubin Observatory, with its 8.4-metre mirror and 3,200-megapixel camera, will enhance PHA detection starting in 2025. Its HelioLinc3D algorithm can identify asteroids with fewer observations, as demonstrated by the discovery of 2022 SF289. However, it is less effective for Venus co-orbitals due to solar glare.
  • Space-Based Missions: Missions like NEO Surveyor or a proposed Venus-orbiting observatory could provide comprehensive coverage of inner solar system threats. A constellation of surveyors in Venus-like orbits, as proposed in the CROWN concept, could optimise detection by focusing on sunward regions.
  • Deflection Techniques: Methods like kinetic impactors (e.g., NASA's DART mission) or nuclear deflection could mitigate threats if detected early. However, the short warning time for Venus co-orbitals (potentially weeks) underscores the need for proactive surveillance.
  • International Collaboration: Global cooperation, as seen in efforts involving NASA, ESA, and observatories worldwide, is crucial for sharing data and resources to refine orbital predictions and develop defense strategies.

Recent posts on X and some media outlets have exaggerated claims, suggesting three Venus co-orbital asteroids (2020 SB, 524522, and 2020 CL1) could strike Earth within weeks. These claims lack credible evidence, as NASA's Sentry Risk Table and ESA's risk assessments indicate no imminent collision risk. However, these asteroids are noted for their long-term potential hazard due to close approaches (within 74,800 km) and sizes (300–400 metres). The focus should remain on improving detection to address long-term risks rather than fuelling panic.

In conclusion: the hidden threat of Venus co-orbital asteroids, combined with other cosmic hazards like NEAs, comets, and interstellar objects, underscores the need for enhanced detection and mitigation strategies. While the probability of an impact is low, the catastrophic consequences, city-wide destruction, tsunamis, or even global effects, justify significant investment from a utility perspective. The Vera C. Rubin Observatory will improve detection capabilities, but only a dedicated space-based mission near Venus can fully map these elusive PHAs. By prioritising international collaboration and innovative technologies, humanity can better prepare for these improbable but high-stakes threats from outer space.

https://www.sciencealert.com/a-serious-threat-may-be-lurking-in-the-orbit-of-venus-says-study

Twenty years ago, the US Congress instructed NASA to find 90 percent of near-Earth asteroids threatening Earth. They've made progress finding these asteroids that orbit the Sun and come to within 1.3 astronomical units of Earth.

However, they may have to expand their search since astronomers are now finding asteroids co-orbiting Venus that could pose a threat.

New research tries to understand how many more may co-orbit Venus and how we can detect them. They can be hidden in the Sun's glare and resist our efforts to find them. It comes down to observability windows and how the asteroids' brightness changes.

The research is titled "The invisible threat: assessing the collisional hazard posed by the undiscovered Venus co-orbital asteroids," and has been submitted to the journal Astronomy and Astrophysics. The lead author is Valerio Carruba, an assistant professor at São Paolo University in Brazil. The paper is currently available at arxiv.org.

"Twenty co-orbital asteroids of Venus are currently known," the authors write. "Co-orbital status protects these asteroids from close approaches to Venus, but it does not protect them from encountering Earth."

Venus's co-orbital asteroids are considered potentially hazardous asteroids (PHA) if they have "a minimum diameter of about 140 meters and come within 0.05 astronomical units (au) of Earth's orbit," they explain.

The big question is, do these pose a collisional threat to Earth?

"We aim to assess the possible threat that the yet undetected population of Venus co-orbiters may pose to Earth, and to investigate their detectability from Earth and space observatories," the authors write.

Only one of the 20 known asteroids has an orbital eccentricity below 0.38. This makes sense since asteroids with wider orbits come closer to Earth and are easier to detect. So its detection is likely the result of an observational bias. Unfortunately, it also means there could be many more of them with minor orbital eccentricities that are very difficult to detect.

Most of the Solar System's asteroids are in the main belt between Mars and Jupiter. However, others are co-orbital with planets, like the Jupiter Trojans, which form two groups: one behind and one ahead of Jupiter. Astronomers are finding more asteroids co-orbiting with Venus, posing a threat to Earth. (NASA/LPI)

One problem in determining their danger is that co-orbitals have unpredictable orbits.

"The co-orbital asteroids of Venus are highly chaotic, with Lyapunov times of the order of 150 years," the authors explain. The Lyapunov time refers to how long an object's orbit takes to become unpredictable because of chaotic dynamics.

This means that studying a single orbit of an object doesn't tell us much about what its orbit will evolve into in more than about 150 years. The authors write that a statistical study of 'clone' asteroids provides a clearer picture.

The researchers created a grid with different orbital inclinations and populated it with 26 cloned asteroids with different orbital characteristics. They then integrated them with the orbits of the Solar System's planets for 36,000 simulated years. Then they checked to see if any cloned asteroids had a close encounter with Earth.

"There is a range of orbits with eccentricity < 0.38, larger at lower inclinations, for which Venus' co-orbitals can pose a collisional hazard to Earth," the authors write.

Then they checked to see if they are observable from Earth with the upcoming Vera Rubin Observatory. They found that these objects are only observable periodically due to the Sun's glare. These observational windows mostly occur when the objects are near their closest approach to Earth.

"The combination of elevation constraints and solar elongation limitations restricts our observations to specific periods throughout the year," the authors write. Solar elongation means the angular distance between one of these asteroids and the Sun, as measured from Earth's perspective.

The study shows how difficult it can be to detect these dangerous asteroids from Earth. One solution might be to send a spacecraft to Venus' orbit.

"However, observations conducted from Venus' orbit, positioned facing away from the Sun, may enhance the detection of these bodies," the researchers explain. Several missions have been proposed, including to the Sun-Earth or Sun-Venus L1 or L2 halo orbit.

We know there are asteroids out there with considerable chances to strike Earth. Some of them are large enough to destroy entire cities. Even a relatively small asteroid 150 meters in diameter can strike Earth with a force equal to hundreds of megatons of TNT.

That's thousands of times more potent than the atomic bombs dropped in World War 2.

"Among these, low-e Venus co-orbitals pose a unique challenge, because of the difficulties in detecting and following these objects from Earth," the authors write in their conclusion.

The Vera Rubin Observatory should detect many asteroids during its regular survey operations. However, finding potentially dangerous asteroids co-orbiting with Venus might take a special effort.

"While surveys like those from the Rubin Observatory may be able to detect some of these asteroids in the near future, we believe that only a dedicated observational campaign from a space-based mission near Venus could potentially map and discover all the still "invisible" PHA among Venus' co-orbital asteroids," the researchers conclude.