Precovery
Encyclopedia
Precovery is a term used in astronomy
that describes the process of finding the image of an object in old archived images or photographic plates, for the purpose of calculating a more accurate orbit
. The name is based on pre-discovery recovery; recovery being the process of making new observations of a previously observed object after a period of non-observation. This happens most often with minor planet
s, but sometimes a comet
, a dwarf planet
, or a natural satellite
is found in old archived images; even exoplanet
precovery observations have been obtained.
Calculating the orbit of an astronomical object involves measuring its position on multiple occasions. The more widely separated these are in time, the more accurately the orbit can be calculated. However, for a newly discovered object, only a few days' or weeks' worth of measured positions may be available, which is only sufficient for a preliminary (imprecise) orbit calculation.
When an object is of particular interest (as with asteroid
s with a chance of impacting Earth
), a search for precovery images is made. Using the preliminary orbit calculation to predict where the object might appear on old archival images, those images (sometimes decades old) are searched to see if it had been in fact photographed already. If so, a far more precise orbital calculation can then be made.
Until fast computers were widely available, it was impractical to analyze and measure images for possible minor planet discoveries because this involved a considerable amount of manual labor. Usually, such images were made years or decades earlier for other purposes (studies of galaxies
, etc.), and it was not worth the time it took to look for precovery images of ordinary asteroids. Today, computers can easily analyze digital astronomical images and compare them to star catalogs containing up to a billion
or so star positions to see if one of the "stars" is actually a precovery image of the newly discovered object. This technique has been used since the mid-1990s to determine the orbits of an enormous number of minor planets.
Note: The term "Precovery" refers to a pre-discovery image. "Recovery" refers to imaging of an object which was lost to our view (as behind the sun), but is now visible again.
).
The asteroid 69230 Hermes
was found in 2003 and numbered, but was found to be a discovery from 1937 which had even been named, but subsequently lost. Consequently, its old name "Hermes" has been applied to it. Centaur 2060 Chiron
was discovered in 1977, and precovery images from 1895 have been located.
Another extreme case of precovery concerned Neptune
. Galileo
observed Neptune on both December 28, 1612 and January 27, 1613, when it was in a portion of its orbit where it was nearly directly behind Jupiter as seen from Earth. Because Neptune moves very slowly and is very faint, Galileo mistook Neptune for a fixed star
, leaving Neptune undiscovered until 1846. He did note that the "star" Neptune did seem to move, noting that between his two observations its apparent distance from another star had changed. However, unlike photographic images, drawings such as those Galileo made are usually not precise enough to be of use in refining an object's orbit. In 1795, Lalande
also mistook Neptune for a star. In 1690, John Flamsteed
did the same with Uranus, even cataloging it as "34 Tauri".
s and candidates:
Astronomy
Astronomy is a natural science that deals with the study of celestial objects and phenomena that originate outside the atmosphere of Earth...
that describes the process of finding the image of an object in old archived images or photographic plates, for the purpose of calculating a more accurate orbit
Orbit
In physics, an orbit is the gravitationally curved path of an object around a point in space, for example the orbit of a planet around the center of a star system, such as the Solar System...
. The name is based on pre-discovery recovery; recovery being the process of making new observations of a previously observed object after a period of non-observation. This happens most often with minor planet
Minor planet
An asteroid group or minor-planet group is a population of minor planets that have a share broadly similar orbits. Members are generally unrelated to each other, unlike in an asteroid family, which often results from the break-up of a single asteroid...
s, but sometimes a comet
Comet
A comet is an icy small Solar System body that, when close enough to the Sun, displays a visible coma and sometimes also a tail. These phenomena are both due to the effects of solar radiation and the solar wind upon the nucleus of the comet...
, a dwarf planet
Dwarf planet
A dwarf planet, as defined by the International Astronomical Union , is a celestial body orbiting the Sun that is massive enough to be spherical as a result of its own gravity but has not cleared its neighboring region of planetesimals and is not a satellite...
, or a natural satellite
Natural satellite
A natural satellite or moon is a celestial body that orbits a planet or smaller body, which is called its primary. The two terms are used synonymously for non-artificial satellites of planets, of dwarf planets, and of minor planets....
is found in old archived images; even exoplanet
Extrasolar planet
An extrasolar planet, or exoplanet, is a planet outside the Solar System. A total of such planets have been identified as of . It is now known that a substantial fraction of stars have planets, including perhaps half of all Sun-like stars...
precovery observations have been obtained.
Calculating the orbit of an astronomical object involves measuring its position on multiple occasions. The more widely separated these are in time, the more accurately the orbit can be calculated. However, for a newly discovered object, only a few days' or weeks' worth of measured positions may be available, which is only sufficient for a preliminary (imprecise) orbit calculation.
When an object is of particular interest (as with asteroid
Asteroid
Asteroids are a class of small Solar System bodies in orbit around the Sun. They have also been called planetoids, especially the larger ones...
s with a chance of impacting Earth
Impact event
An impact event is the collision of a large meteorite, asteroid, comet, or other celestial object with the Earth or another planet. Throughout recorded history, hundreds of minor impact events have been reported, with some occurrences causing deaths, injuries, property damage or other significant...
), a search for precovery images is made. Using the preliminary orbit calculation to predict where the object might appear on old archival images, those images (sometimes decades old) are searched to see if it had been in fact photographed already. If so, a far more precise orbital calculation can then be made.
Until fast computers were widely available, it was impractical to analyze and measure images for possible minor planet discoveries because this involved a considerable amount of manual labor. Usually, such images were made years or decades earlier for other purposes (studies of galaxies
Galaxy
A galaxy is a massive, gravitationally bound system that consists of stars and stellar remnants, an interstellar medium of gas and dust, and an important but poorly understood component tentatively dubbed dark matter. The word galaxy is derived from the Greek galaxias , literally "milky", a...
, etc.), and it was not worth the time it took to look for precovery images of ordinary asteroids. Today, computers can easily analyze digital astronomical images and compare them to star catalogs containing up to a billion
1000000000 (number)
1,000,000,000 is the natural number following 999,999,999 and preceding 1,000,000,001.In scientific notation, it is written as 109....
or so star positions to see if one of the "stars" is actually a precovery image of the newly discovered object. This technique has been used since the mid-1990s to determine the orbits of an enormous number of minor planets.
Note: The term "Precovery" refers to a pre-discovery image. "Recovery" refers to imaging of an object which was lost to our view (as behind the sun), but is now visible again.
Examples
In an extreme case of precovery, an object was discovered on December 31, 2000, designated 2000 YK66, and a near-Earth orbit was calculated. Precovery revealed that it had previously been discovered on February 23, 1950 and given the provisional designation 1950 DA, and then been lost for half a century. The exceptionally long observation period allowed an unusually precise orbit calculation, and the asteroid was determined to have a small chance of colliding with the Earth. After an asteroid's orbit is calculated with sufficient precision, it can be assigned a number (in this case, (29075) 1950 DA(29075) 1950 DA
-External links:* from JPL /...
).
The asteroid 69230 Hermes
69230 Hermes
-External links:* * *...
was found in 2003 and numbered, but was found to be a discovery from 1937 which had even been named, but subsequently lost. Consequently, its old name "Hermes" has been applied to it. Centaur 2060 Chiron
2060 Chiron
2060 Chiron is a minor planet in the outer Solar System. Discovered in 1977 by Charles T. Kowal , it was the first-known member of a new class of objects now known as centaurs, with an orbit between Saturn and Uranus.Although it was initially classified as an asteroid, it was later found to...
was discovered in 1977, and precovery images from 1895 have been located.
Another extreme case of precovery concerned Neptune
Neptune
Neptune is the eighth and farthest planet from the Sun in the Solar System. Named for the Roman god of the sea, it is the fourth-largest planet by diameter and the third largest by mass. Neptune is 17 times the mass of Earth and is slightly more massive than its near-twin Uranus, which is 15 times...
. Galileo
Galileo Galilei
Galileo Galilei , was an Italian physicist, mathematician, astronomer, and philosopher who played a major role in the Scientific Revolution. His achievements include improvements to the telescope and consequent astronomical observations and support for Copernicanism...
observed Neptune on both December 28, 1612 and January 27, 1613, when it was in a portion of its orbit where it was nearly directly behind Jupiter as seen from Earth. Because Neptune moves very slowly and is very faint, Galileo mistook Neptune for a fixed star
Fixed star
The fixed stars are celestial objects that do not seem to move in relation to the other stars of the night sky. Hence, a fixed star is any star except for the Sun. A nebula or other starlike object may also be called a fixed star. People in many cultures have imagined that the stars form pictures...
, leaving Neptune undiscovered until 1846. He did note that the "star" Neptune did seem to move, noting that between his two observations its apparent distance from another star had changed. However, unlike photographic images, drawings such as those Galileo made are usually not precise enough to be of use in refining an object's orbit. In 1795, Lalande
Jérôme Lalande
Joseph Jérôme Lefrançois de Lalande was a French astronomer and writer.-Biography:Lalande was born at Bourg-en-Bresse...
also mistook Neptune for a star. In 1690, John Flamsteed
John Flamsteed
Sir John Flamsteed FRS was an English astronomer and the first Astronomer Royal. He catalogued over 3000 stars.- Life :Flamsteed was born in Denby, Derbyshire, England, the only son of Stephen Flamsteed...
did the same with Uranus, even cataloging it as "34 Tauri".
Dwarf planets
Discovery and precovery dates for well known dwarf planetDwarf planet
A dwarf planet, as defined by the International Astronomical Union , is a celestial body orbiting the Sun that is massive enough to be spherical as a result of its own gravity but has not cleared its neighboring region of planetesimals and is not a satellite...
s and candidates:
| Dwarf Planet (or candidate) | Discovery Year | Precovery Year |
|---|---|---|
| Ceres | 1801 | none |
| Pluto Pluto Pluto, formal designation 134340 Pluto, is the second-most-massive known dwarf planet in the Solar System and the tenth-most-massive body observed directly orbiting the Sun... |
1930 | 1914 |
| Huya 38628 Huya 38628 Huya is a trans-Neptunian object . It was discovered in March 2000 by Ignacio Ferrin and announced on 24 October 2000. It is classified as a plutino being in a 2:3 mean motion resonance with Neptune. With a Spitzer size estimate of , this plutino is also a likely dwarf-planet. It is expected... |
2000 | 1996 |
| Ixion 28978 Ixion 28978 Ixion is a Kuiper belt object discovered on May 22, 2001. Ixion is a plutino and a very likely dwarf planet; its diameter of 650 km estimated by Spitzer makes it about the fifth largest plutino. It is named after Ixion, a figure from Greek mythology... |
2001 | 1982 |
| Quaoar 50000 Quaoar 50000 Quaoar is a rocky trans-Neptunian object in the Kuiper belt with one known moon. Discovered on June 4, 2002 by astronomers Chad Trujillo and Michael Brown at the California Institute of Technology from images acquired at the Samuel Oschin Telescope at Palomar Observatory, it is thought by... |
2002 | 1954 |
| Sedna 90377 Sedna 90377 Sedna is a trans-Neptunian object discovered in 2003, which was about three times as far from the Sun as Neptune. For most of its orbit it is even further from the Sun, with its aphelion estimated at 960 astronomical units , making it one of the most distant known objects in the Solar System... |
2003 | 1990 |
| Orcus 90482 Orcus 90482 Orcus is a trans-Neptunian object in the Kuiper belt with a large moon. It was discovered on February 17, 2004 by Michael Brown of Caltech, Chad Trujillo of the Gemini Observatory, and David Rabinowitz of Yale University. Precovery images as early as November 8, 1951 were later identified... |
2004 | 1951 |
| Haumea | 2004? | 1955 |
| Eris Eris (dwarf planet) Eris, formal designation 136199 Eris, is the most massive known dwarf planet in the Solar System and the ninth most massive body known to orbit the Sun directly... |
2005 | 1954 |
| Makemake | 2005 | 1955 |
| 2007 OR10 | 2007 | 1985 |
See also
- Discovery imageDiscovery imageIn astronomy, a discovery image is typically a drawing, film base photograph, photographic plate, or digital image in which a celestial object or phenomenon was first found...
- DANEOPSDANEOPSDANEOPS, the DLR-Archenhold Near Earth Objects Precovery Survey, has been initiated to systematically search existing photographic plate archives for precovery images of known NEOs. It has so far precovered or recovered some 145 objects....
- Potentially Hazardous Asteroids Precovery