A few months ago, a new paper was published in Publications of the National Academy of Sciences (PNAS) regarding a population of near-Earth objects (NEOs) that exhibit non-gravitational accelerations with no coma. These objects were assigned the label “dark comets,” an oxymoron since comets are routinely identified by their visible cometary tail.
Shortly after reading the paper, I asked my excellent postdoc, Richard Cloete, to find the timing of the closest approach for these NEOs relative to Earth over the past century. Once Richard sent me the results, I searched archival records of spacecraft launched during the space age following Sputnik 1 in 1957.
Within minutes, I found that one of these objects, 2005 VL1, was at closest approach to Earth in November 1965 when the Venera 2 spacecraft was launched by the Soviet Union to explore the planet Venus. The observed brightness of 2005 VL1 is indeed consistent with a high reflectance from the full surface of Venera 2 including its solar panels.
As known for Venera 2, the orbit of 2005 VL1 implies that it arrived within a short distance from Venus on February 27, 1966, a highly improbable coincidence for the orbital phase of a natural comet that was not designed for a close encounter with Venus. Since the orbital period of Venus is 225 days, the chance of a random encounter of an NEO with the precise orbital phase of Venus on the right date is less than one percent. 2005 VL1’s orbital parameters are very similar to the reported values for Venera 2. Given the area-to-mass ratio of Venera 2, I calculated that 2005 VL1’s non-gravitational acceleration and negligible transverse acceleration match the values expected from solar radiation pressure.
Following the Luna 1 spacecraft to the Moon in 1959, the Solar System was polluted with upper stages of human-made rockets, which appear today as NEOs. For example, 2020 SO was identified as the Centaur upper stage used to launch the 1966 Surveyor 2 spacecraft. This NEO was found to be pushed by solar radiation pressure upon its discovery by the Pan-STARRS observatory on September 17, 2020, nearly three years after the same observatory discovered 1I/‘Oumuamua — which also featured an anomalous non-gravitational acceleration. Other examples for human-made technological objects include XL8D89E, 2018 AV2, and 2023 NM. The NEO J002E3 is thought to be the third-stage Saturn S-IVB booster from Apollo 12 and was identified in an almost identical orbit.
On January 2, 2025, the Minor Planet Center at the Harvard-Smithsonian Center for Astrophysics announced a new asteroid labeled 2018 CN41 with an orbital period of 1.53 years. The “asteroid” was discovered by the amateur astronomer H. A. Guler as a NEO since it arrived within 240,000 kilometers from Earth. Within less than 17 hours, the Minor Planet Center issued an editorial notice on the deletion of 2018 CN41 from its database since the object was the Tesla Roadster car, launched on February 6, 2018, as a dummy payload on the Falcon Heavy first flight. This car is known to be orbiting the Sun on the same eccentric orbit reported for 2018 CN41.
The recent PNAS paper listed data on NEOs that were labeled as “dark comets” because they showed non-gravitational acceleration with no sign of coma around them. In the new paper with Richard, I suggested that 2005 VL1 might be the Soviet Venera 2 spacecraft, launched to explore Venus on November 12, 1965. Radio communication with Venera 2 was lost at closest approach to Venus in February 1966, and its whereabouts were subsequently unknown.
We used the parameters of 2005 VL1 and integrated the orbit back in time. Remarkably, 2005 VL1 was at closest approach to Earth and Venus at the same times as Venera 2. The inferred perihelion of 2005 VL1 is 69% of the Earth-Sun separation, similar to the 72% associated with the orbital radius of Venus. The eccentricity of 2005 VL1’s orbit also agreed with the eccentricity of Venera 2.
The Venera 2 spacecraft can be approximated as a cylinder plus rectangular solar panels with a total mass of about a ton, a length of about 3.3 meters and a width of about 4.4 meters. Adopting the associated cross-sectional area to reflect sunlight, I derived the resulting non-gravitational acceleration away from the Sun. This non-gravitational push away from the Sun declines inversely with heliocentric distance squared like the Sun’s gravity. It amounts to a small reduction in the Sun’s gravitational acceleration. We used this simple reduction in the Sun’s gravity when calculating the shifts relative to the expected gravitational trajectory of 2005 VL1.
The only statistically significant component of the reported non-gravitational acceleration of 2005 VL1 is out of the ecliptic plane. Given 2005 VL1’s orbital inclination we predicted the out-of-plane component of the solar radiation acceleration for Venera 2. For high reflectance, this expected result for Venera 2 is comparable to the inferred value for 2005 VL1. The transverse acceleration is consistent with zero, as expected for solar radiation pressure. The radial acceleration in the ecliptic plane is consistent with the reported value.
To demonstrate consistency of the expected radiation pressure on Venera 2 with the non-gravitational residuals of 2005 VL1, we compared the expected astrometric shifts from radiation pressure directly to the reported data. We integrated the orbit of 2005 VL1 based on the reported orbital parameters and calculated the residual Right Ascension (RA) and Declination (DEC) for an orbit influenced by radiation pressure on Venera 2 in which the Sun’s gravity was reduced by a small fraction compared to an orbit with the full Sun’s gravity.
The approximate agreement between the observed and expected data for the DEC and RA shifts implies that 2005 VL1’s non-gravitational acceleration is consistent with the expected solar radiation pressure on Venera 2. Since the Venera 2 spacecraft is not spherically symmetric, the solar radiation force perpendicular to any reflecting surface could also have a non-radial component. This additional component is difficult to model, as it requires knowledge of the orientation of the spacecraft and its rotation rate.
It is conceivable that other “dark comets” are technological space debris similar to 2005 VL1, in which case their inferred non-gravitational acceleration is not the result of invisible cometary evaporation. For example, 2016 GW221 shares nearly identical inclination, perihelion and aphelion and closest distance from Earth on April 2, 1964, as the Zond 1 spacecraft to Venus. To accommodate such objects, the label “dark comets” should be replaced by the more appropriate label “objects with anomalous non-gravitational acceleration (OANGAs),” because their nature may be different from that of the familiar class of comets. For the same reason that elephants are not classified as “zebras without stripes,” spacecraft should not be classified as “comets without a visible tail”.
Some OANGAs could be either the products of human technologies over the past 66-year history of the modern space age or products of extraterrestrial civilizations over the past billions of years. Interstellar objects in the latter category could have been either trapped by gravitational interactions with massive planets like Jupiter or designed to settle in the inner Solar System.
In summary, our paper shows that 2005 VL1, originally classified as a “dark comet”, may in fact be the Venera 2 spacecraft, illustrating how some NEOs may be remnants of past space missions. Identifying such space debris among NEOs has key implications for planetary defense, mission planning, and the interpretation of small Solar System bodies. This finding underscores the challenge of distinguishing real comets or asteroids from unrecognized technological fragments, highlighting the need for continued observational and orbital analyses. By demonstrating that technological space debris contributes to newly discovered objects, this work broadens our understanding of both NEOs and human-made debris in the inner Solar System, with important implications for the upcoming Legacy Survey of Space and Time (LSST) of the new Vera C. Rubin Observatory in Chile. Future data would help to validate our association of 2005 VL1 with Venera 2 and measure any unmodeled force components.
This identification is important, as some scientists proposed in a 2018 paper to capture 2005 VL1 for the benefit of mineral mining. Imagine a scenario where entrepreneurs or astronomers would invest a major effort and a large sum of money in capturing 2005 VL1, only to find out that it is a failed Soviet spacecraft from 1965.
[For the related scientific paper, click here]
ABOUT THE AUTHOR
Avi Loeb is the head of the Galileo Project, founding director of Harvard University’s — Black Hole Initiative, director of the Institute for Theory and Computation at the Harvard-Smithsonian Center for Astrophysics, and the former chair of the astronomy department at Harvard University (2011–2020). He is a former member of the President’s Council of Advisors on Science and Technology and a former chair of the Board on Physics and Astronomy of the National Academies. He is the bestselling author of “Extraterrestrial: The First Sign of Intelligent Life Beyond Earth” and a co-author of the textbook “Life in the Cosmos”, both published in 2021. The paperback edition of his new book, titled “Interstellar”, was published in August 2024.
