1991 VG is a very small

near-Earth object A near-Earth object (NEO) is any small Solar System body orbiting the Sun whose closest approach to the Sun ( perihelion) is less than 1.3 times the Earth–Sun distance (astronomical unit, AU). This definition applies to the object's orbit a ...

of the

Apollo group Apollo Education Group, Inc. is an American corporation based in the South Phoenix area of Phoenix, Arizona, with an additional corporate office in Chicago, Illinois. It is privately-owned by a consortium of investors including The Vistria Grou ...

, approximately in diameter. It was first observed by American astronomer

James Scotti James Vernon Scotti (born 1960) is an American astronomer. He was born in Bandon, Oregon, and graduated from Edmonds Woodway High School in Edmonds, Washington in 1978. He received his B.Sc. in Astronomy from the University of Arizona in Tucson, ...

on 6 November 1991, using the

Spacewatch The Spacewatch Project is an astronomical survey that specializes in the study of minor planets, including various types of asteroids and comets at University of Arizona telescopes on Kitt Peak near Tucson, Arizona. The Spacewatch Project has be ...

telescope on

Kitt Peak National Observatory The Kitt Peak National Observatory (KPNO) is a United States astronomy, astronomical observatory located on Kitt Peak of the Quinlan Mountains in the Arizona-Sonoran Desert on the Tohono Oʼodham Nation, west-southwest of Tucson, Arizona. With ...

near Tucson, Arizona, in the United States. On 6 December 1991 it passed about from the Moon. The asteroid then went unobserved from April 1992 until it was recovered by

Paranal Observatory Paranal Observatory is an astronomical observatory operated by the European Southern Observatory (ESO). It is located in the Atacama Desert of Northern Chile on Cerro Paranal at altitude, south of Antofagasta. By total light-collecting area, ...

in May 2017. It was removed from the

Sentry Risk Table Sentry is an automated impact prediction system started in 2002 and operated by the Center for Near Earth Object Studies (CNEOS) at NASA's Jet Propulsion Laboratory. It continually monitors the most up-to-date asteroid catalog for possibilities ...

on 1 June 2017.

Discovery and observations

On 6 November 1991, Scotti discovered a faint object which was designated 1991 VG soon after discovery.

Recovery

1991 VG was not observed between 1992 and 2017. But after 26 years, 1991 VG had returned to the vicinity of Earth. As part of a program by

ESA The European Space Agency (ESA) is a 23-member international organization devoted to space exploration. With its headquarters in Paris and a staff of around 2,547 people globally as of 2023, ESA was founded in 1975 in the context of European ...

and

ESO The European Southern Observatory is an astronomical research organisation. ESO may also refer to: *Employee stock option (also: executive stock option) *'' Ether Saga Odyssey'', a fantasy massively multiplayer online role-playing game *''The Elde ...

to secure the orbit of faint but potentially threatening Near-Earth Objects, 1991 VG was recovered by the ESO VLT on 30 May 2017, at magnitude 25. With this recovery, the orbit of 1991 VG is now determined with a high precision. It was removed from the

on 1 June 2017.

Orbit

Soon after 1991 VG's discovery, its

heliocentric Heliocentrism (also known as the heliocentric model) is a Superseded theories in science#Astronomy and cosmology, superseded astronomical model in which the Earth and Solar System, planets orbit around the Sun at the center of the universe. His ...

orbit was found to be very similar to Earth's orbit and it was calculated that it would make a close approach to Earth in the month after discovery at 1.2 lunar distances or on 5 December 1991. 1991 VG also passed 0.0568 AU from Earth on 7 August 2017 and 0.0472 AU on 11 February 2018. Given such an Earth-like orbit, the dynamical lifetime of such an object is relatively short with the object quickly either impacting Earth or being perturbed by Earth onto a different orbit. The similarity of its orbit with Earth was also very difficult to explain from natural sources, with ejecta from a recent Lunar impact or non-gravitational perturbations such as the

Yarkovsky effect The Yarkovsky effect is a force acting on a rotating body in space caused by the anisotropic emission of thermal photons, which carry momentum. It is usually considered in relation to meteoroids or small asteroids (about 10 cm to 10 km ...

having been suggested. The first Earth Trojan asteroid, , was later identified and such objects could well be a source for objects like 1991 VG. 1991 VG has been a transient co-orbital of the horseshoe type in the past (for example between AD 1382 and 1667) and it will return to such in the future. In 1991–1992 it looped around the Earth in a retrograde manner (east to west) with closest approach at 0.00306 AU on 5 December 1991. It had an eccentricity of less than 1 with respect to the Earth from 23 February to 21 March 1992, but was outside of Earth's

Hill sphere The Hill sphere is a common model for the calculation of a Sphere of influence (astrodynamics), gravitational sphere of influence. It is the most commonly used model to calculate the spatial extent of gravitational influence of an astronomical ...

. This temporary capture has taken place multiple times in the past and it is expected to repeat again in the future. Currently, it is falling behind Earth as it orbits the Sun along with Earth. The two will again be on the same side of the Sun in November 2038. Simulation has been performed for 5000 years into the future without detecting an impact on Earth. Around 400 BC there was an approach to a distance of around 0.001 AU, closer than the Moon (see Figure 1 in the paper by Carlos and Raúl de la Fuente Marcos).

Possible monolithic structure

Since the discovery of 1991 VG, about 80% of small asteroids with absolute magnitudes fainter than 22.0 (corresponding to sizes smaller than about 200 meters) which have had their

lightcurve In astronomy, a light curve is a graph (discrete mathematics), graph of the Radiance, light intensity of a celestial object or region as a function of time, typically with the magnitude (astronomy), magnitude of light received on the ''y''-axis ...

measured have

rotation period In astronomy, the rotation period or spin period of a celestial object (e.g., star, planet, moon, asteroid) has two definitions. The first one corresponds to the '' sidereal rotation period'' (or ''sidereal day''), i.e., the time that the objec ...

s under 2 hours. The so-called fast rotators are typically monolithic bodies or, alternatively, welded conglomerates with a sufficient intrinsic strength to counteract centrifugal forces. More slowly rotating asteroids are sometimes gravitationally bound aggregates or

rubble pile In astronomy, a rubble pile is a celestial body that consists of numerous pieces of debris that have coalesced under the influence of gravity. Rubble piles have low density because there are large cavities between the various chunks that make the ...

Possible artificial origin

The uncertainty of the object's origin, combined with rapid variation in the object's brightness in images obtained during its close passage with Earth in early December 1991, led to some speculation that 1991 VG might be a spent rocket fuel tank. There was speculation that it could be a rocket body from a satellite launched in the early 1970s, or from the

Apollo 12 Apollo 12 (November 14–24, 1969) was the sixth crewed flight in the United States Apollo program and the second to land on the Moon. It was launched on November 14, 1969, by NASA from the Kennedy Space Center in Florida. Commander Charles ...

mission. A detailed analysis of the available evidence confirms that there is no compelling reason to believe that 1991 VG is not natural. The natural versus artificial issue also emerged in the case of the temporary capture episode experienced by near-Earth asteroid .

Exploration

The

Near-Earth Asteroid Scout The Near-Earth Asteroid Scout (NEA Scout) was a mission by NASA to develop a controllable low-cost CubeSat solar sail spacecraft capable of encountering near-Earth asteroids (NEA). NEA Scout was one of ten CubeSats launched into a heliocentri ...

is a low-cost

CubeSat A CubeSat is a class of small satellite with a form factor of cubes. CubeSats have a mass of no more than per unit,, url=https://static1.squarespace.com/static/5418c831e4b0fa4ecac1bacd/t/5f24997b6deea10cc52bb016/1596234122437/CDS+REV14+2020-07-3 ...

solar sail Solar sails (also known as lightsails, light sails, and photon sails) are a method of spacecraft propulsion using radiation pressure exerted by sunlight on large surfaces. A number of spaceflight missions to test solar propulsion and navigati ...

spacecraft by

NASA The National Aeronautics and Space Administration (NASA ) is an independent agencies of the United States government, independent agency of the federal government of the United States, US federal government responsible for the United States ...

capable of encountering

near-Earth asteroid A near-Earth object (NEO) is any small Solar System body orbiting the Sun whose closest approach to the Sun (perihelion) is less than 1.3 times the Earth–Sun distance (astronomical unit, AU). This definition applies to the object's orbit aro ...

s and taking high resolution images and 1991 VG was the planned target before 2020 GE became the new target. The spacecraft was successfully launched into heliocentric orbit on 16 November 2022, however contact with the spacecraft was not successfully established and it is considered lost.

Notes

References

External links

* * {{DEFAULTSORT:1991 VG # Minor planet object articles (unnumbered) # Claimed moons of Earth # # 19911205 # 19911106