Hard-to-spot asteroids hiding near Venus could threaten Earth

Astronomers have flagged a stealthy class of space rocks that slip past our telescopes. These asteroids share Venus’s orbital neighborhood, hide in sun-glare most of the time, and can switch onto paths that graze Earth’s orbit.

No asteroid has been spotted yet, but modeling suggests a larger, hard-to-see population could exist – and a few could be trouble on millennial timescales.

An international team led by experts in Brazil used analytical theory and long-term numerical simulations to trace the dynamics of “Venusian co-orbital” asteroids.

The study shows how these bodies can linger near Venus for thousands of years, then transition into configurations that carry them uncomfortably close to Earth.

“There’s a population of potentially dangerous asteroids that we can’t detect with current telescopes,” said Valerio Carruba, a professor at the UNESP School of Engineering at the Guaratinguetá campus (FEG-UNESP) and the paper’s lead author. “These objects orbit the Sun, but aren’t part of the Asteroid Belt, located between Mars and Jupiter.”

“Instead, they’re much closer, in resonance with Venus. But they’re so difficult to observe that they remain invisible, even though they may pose a real risk of collision with our planet in the distant future.”

Hidden asteroids share Venus’s path

The objects circle the Sun, not Venus, but they share the planet’s orbital region and period. “These objects enter into a 1:1 resonance with Venus, which means that they complete one revolution around the Sun in the same time as the planet,” Carruba said.

Unlike the relatively stable Trojan swarms of Jupiter, the known Venus co-orbitals are jumpy. Simulations show they alternate between several orbital modes in cycles averaging about 12,000 years.

“During these transition phases, the asteroids can reach extremely small distances from Earth’s orbit, potentially crossing it,” Carruba warned.

In the safe phases, asteroids loiter near Venus. In the risky phases, they wander outward and inward, where Earth becomes a possible close passer-by – or worse.

Telescope blind spot near Venus

Only 20 Venus co-orbitals are on the books today, and all but one have very elongated paths, with eccentricities above 0.38. The higher the eccentricity, the farther from the Sun the asteroid wanders during part of its loop – into darker skies where ground telescopes can actually point.

The team’s models, however, predict many more with lower eccentricities that keep them snuggled closer to the Sun’s glare and out of view.

“The absence of objects with an eccentricity of less than 0.38 is clearly the result of an observational bias,” Carruba said.

In plain terms: the ones we can see are the outliers. The more circular, centrally tucked-in objects – the ones simulations say can evolve into Earth-crossing configurations – are the very ones we’re least able to detect.

Asteroids with devastating power

The simulations map “risk regions,” places in orbital-element space where Venus co-orbitals are most likely to drift near Earth’s path after a resonance switch.

Some modeled bodies approach Earth’s orbit so closely that, statistically, impacts on a thousand-year timescale become plausible. Size matters, too.

“Asteroids about 300 meters in diameter, which could form craters 3 to 4.5 kilometers (1.9 to 2.8 miles) wide and release energy equivalent to hundreds of megatons, may be hidden in this population,” Carruba said.

“An impact in a densely populated area would cause large-scale devastation.” Such objects are not civilization-enders, but they are city-killers.

Asteroids slip past sky cameras

Could next-generation sky cameras catch these rocks anyway? The team tested detectability with the Vera Rubin Observatory’s wide, deep survey.

The verdict is sobering. For co-orbitals with the right brightness, observing windows appear only when they climb above about 20 degrees on the horizon – often for just a week or two – then vanish for months or years.

“Such asteroids can remain invisible for months or years and appear for only a few days under very specific conditions. This makes them effectively undetectable with Vera Rubin’s regular programs,” Carruba noted.

In other words, you have to look almost into the Sun at just the right times, from just the right place, to snag them.

Eyes in orbit can help

Space-based eyes aimed closer to the Sun offer a way forward. Infrared missions like NASA’s forthcoming NEO Surveyor, and proposed platforms such as China’s Crown, can watch at low solar elongations where ground observatories cannot.

From those vantage points, co-orbitals near Venus become fair game, and coverage can be continuous enough to catch brief apparition windows. “Planetary defense needs to consider not only what we can see, but also what we can’t yet see,” Carruba argued.

Born in the Asteroid Belt

The likely source is not Venus itself, but the Main Asteroid Belt. Over eons, gravitational nudges – especially from Jupiter and Saturn – shake some fragments inward. A few slip into a temporary 1:1 resonance with Venus, hanging there for on-and-off stretches that average about 12,000 years.

“These captures are ephemeral on an astronomical timescale, lasting, on average, about 12,000 years. And the objects may eventually evolve into trajectories close to Earth or be ejected from the Solar System,” Carruba explained.

That ephemerality is the essence of the hazard: the same rock can shift from harmless to hazardous as its resonance state flips.

Next steps in asteroid tracking

The message is not alarm but awareness. Co-orbitals with Venus are a blind spot in today’s planetary defense picture. The models say a hidden population likely exists, with the more circular, harder-to-see members posing the longer-term risk.

A realistic plan includes dedicated space telescopes that can stare near the Sun, targeted follow-ups during short visibility windows from Earth, and dynamical maps that tell observers where and when to look.

We have grown good at finding big, dark-sky asteroids. This study widens the searchlight to a tougher part of the sky – and a class of objects that may spend most of their lives where our instruments rarely glance. If the rocks are there, we need to build the tools to see them.

The research is published in the journal Astronomy & Astrophysics.

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