1991 VG is a very small
near-Earth object
A near-Earth object (NEO) is any small Solar System body whose orbit brings it into proximity with Earth. By convention, a Solar System body is a NEO if its closest approach to the Sun (perihelion) is less than 1.3 astronomical units (AU) ...
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.
The company owns and operates several higher-learning institutions, includin ...
, 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, in the United States. The Spa ...
telescope on
Kitt Peak National Observatory
The Kitt Peak National Observatory (KPNO) is a United States 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 more than ...
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, it ...
in May 2017. It was removed from the Sentry Risk Table
Sentry is a highly automated impact prediction system operated by the JPL Center for NEO Studies (CNEOS) since 2002. It continually monitors the most up-to-date asteroid catalog for possibilities of future impact with Earth over the next 100+ y ...
on 1 June 2017.
Earth-like orbit
On 6 November 1991, Scotti discovered a faint object which was designated ''1991 VG'' soon after discovery. The object's heliocentric
Heliocentrism (also known as the Heliocentric model) is the astronomical model in which the Earth and planets revolve around the Sun at the center of the universe. Historically, heliocentrism was opposed to geocentrism, which placed the Earth ...
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
An Earth trojan is an asteroid that orbits the Sun in the vicinity of the Earth–Sun Lagrangian points (leading 60°) or (trailing 60°), thus having an orbit similar to Earth's. Only two Earth trojans have so far been discovered. The name ...
, , 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 of an astronomical body is the region in which it dominates the attraction of satellites. To be retained by a planet, a moon must have an orbit that lies within the planet's Hill sphere. That moon would, in turn, have a Hill sp ...
. 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 of light intensity of a celestial object or region as a function of time, typically with the magnitude of light received on the y axis and with time on the x axis. The light is usually in a particular frequ ...
measured have rotation period
The rotation period of a celestial object (e.g., star, gas giant, planet, moon, asteroid) may refer to its sidereal rotation period, i.e. the time that the object takes to complete a single revolution around its axis of rotation relative to the ...
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 is not a monolith, consisting instead of numerous pieces of rock that have coalesced under the influence of gravity. Rubble piles have low density because there are large cavities between th ...
s.
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, Florida. Commander Charle ...
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 .
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
, owners =
, headquarters = Paris, Île-de-France, France
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, spaceport = Guiana Space Centre
, seal = File:ESA emblem seal.png
, seal_size = 130px
, image = Views in the Main Control Room (1 ...
and ESO
The European Organisation for Astronomical Research in the Southern Hemisphere, commonly referred to as the European Southern Observatory (ESO), is an intergovernmental research organisation made up of 16 member states for ground-based ast ...
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 Sentry Risk Table
Sentry is a highly automated impact prediction system operated by the JPL Center for NEO Studies (CNEOS) since 2002. It continually monitors the most up-to-date asteroid catalog for possibilities of future impact with Earth over the next 100+ y ...
on 1 June 2017.
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 miniaturized satellite based around a form factor consisting of cubes. CubeSats have a mass of no more than per unit, and often use commercial off-the-shelf (COTS) components for their electronics and structure. CubeSat ...
solar sail
Solar sails (also known as light sails and photon sails) are a method of spacecraft propulsion using radiation pressure exerted by sunlight on large mirrors. A number of spaceflight missions to test solar propulsion and navigation have been ...
spacecraft by NASA
The National Aeronautics and Space Administration (NASA ) is an independent agency of the US federal government responsible for the civil space program, aeronautics research, and space research.
NASA was established in 1958, succeedi ...
capable of encountering near-Earth asteroid
A near-Earth object (NEO) is any small Solar System body whose orbit brings it into proximity with Earth. By convention, a Solar System body is a NEO if its closest approach to the Sun (perihelion) is less than 1.3 astronomical units (AU) ...
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
See also
* near-Earth asteroid temporarily captured by Earth in 2022
* another temporary Earth satellite discovered in 2020
* the first temporary Earth satellite discovered ''in situ'' 2006
References
External links
*
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