Vulcanoid
The vulcanoids are a hypothetical population of asteroids that orbit the Sun in a dynamically stable zone inside the orbit of the planet Mercury. They are named after the hypothetical planet Vulcan, which was proposed on the basis of irregularities in Mercury's orbit that were later found to be explained by general relativity. So far, no vulcanoids have been discovered, and it is not yet clear whether any exist.
If they do exist, the vulcanoids could easily evade detection because they would be very small and near the bright glare of the Sun. Due to their proximity to the Sun, searches from the ground can only be carried out during twilight or solar eclipses. Any vulcanoids must be between about 100 metres (330 ft) and 6 kilometres (3.7 mi) in diameter and are probably located in nearly circular orbits near the outer edge of the gravitationally stable zone between the Sun and Mercury. These should be distinguished from
The vulcanoids, should they be found, may provide scientists with material from the first period of
History and observation
Celestial bodies interior to the orbit of Mercury have been hypothesized, and searched for, for centuries. The German astronomer
Vulcanoids, should they exist, would be difficult to detect due to the strong glare of the nearby Sun,[4] and ground-based searches can only be carried out during twilight or during solar eclipses.[5] Several searches during eclipses were conducted in the early 1900s,[6] which did not reveal any vulcanoids, and observations during eclipses remain a common search method.[7] Conventional telescopes cannot be used to search for them because the nearby Sun could damage their optics.[8]
In 1998, astronomers analysed data from the
Later attempts to detect the vulcanoids involved taking astronomical equipment above the interference of
Even at these heights the atmosphere is still present and can interfere with searches for vulcanoids. In 2004, a sub-orbital spaceflight was attempted in order to get a camera above Earth's atmosphere. A Black Brant rocket was launched from White Sands, New Mexico, on January 16, carrying a powerful camera named VulCam,[13] on a ten-minute flight.[4] This flight reached an altitude of 274,000 metres (899,000 ft)[13] and took over 50,000 images. None of the images revealed any vulcanoids, but there were technical problems.[4]
Searches of NASA's two STEREO spacecraft data have failed to detect any vulcanoid asteroids.[14] It is doubtful that there are any vulcanoids larger than 5.7 kilometres (3.5 mi) in diameter.[14]
The Before its demise in 2015, however, the craft failed to produce substantial evidence on vulcanoids.
On August 13, 2021, an asteroid, 2021 PH27, was discovered with a perihelion well within the orbit of Mercury. At its minimum distance to the Sun of 0.1331 AU, it comes more than twice as close to the Sun as Mercury's perihelion at 0.307499 AU. This puts its nearest approach well within the hypothesized Vulcanoid Zone.
Orbit
A vulcanoid is an asteroid in a stable orbit with a
The vulcanoids are thought to exist in a gravitationally stable band inside the orbit of Mercury, at distances of 0.06–0.21 AU from the
The outer edge of the vulcanoid zone is approximately 0.21 AU from the Sun. Objects more distant than this are unstable due to interactions with Mercury and would be perturbed into Mercury-crossing orbits on timescales of the order of 100 million years.[18] (Some definitions would nonetheless include such unstable objects as vulcanoids as long as their orbits lie completely interior to that of Mercury.)[21] The inner edge is not sharply defined: objects closer than 0.06 AU are particularly susceptible to Poynting–Robertson drag and the Yarkovsky effect,[18] and even out to 0.09 AU vulcanoids would have temperatures of 1,000 K or more, which is hot enough for evaporation of rocks to become the limiting factor in their lifetime.[22]
The maximum possible volume of the vulcanoid zone is very small compared to that of the
Physical characteristics
Any vulcanoids that exist must be relatively small. Previous searches, particularly from the STEREO spacecraft, rule out asteroids larger than 6 kilometres (3.7 mi) in diameter.[14] The minimum size is about 100 metres (330 ft);[18] particles smaller than 0.2 μm are strongly repulsed by radiation pressure, and objects smaller than 70 m would be drawn into the Sun by Poynting–Robertson drag.[9] Between these upper and lower limits, a population of asteroids between 1 kilometre (0.62 mi) and 6 kilometres (3.7 mi) in diameter is thought to be possible.[10] They would be almost hot enough to glow red hot.[17]
It is thought that the vulcanoids would be very rich in elements with a high melting point, such as iron and nickel. They are unlikely to possess a regolith because such fragmented material heats and cools more rapidly, and is affected more strongly by the Yarkovsky effect, than solid rock.[5] Vulcanoids are probably similar to Mercury in colour and albedo,[7] and may contain material left over from the earliest stages of the Solar System's formation.[12]
There is evidence that Mercury was struck by a large object relatively late in its development,[5] a collision which stripped away much of Mercury's crust and mantle,[16] and explaining the thinness of Mercury's mantle compared to the mantles of the other terrestrial planets. If such an impact occurred, much of the resulting debris might still be orbiting the Sun in the vulcanoid zone.[13]
Significance
Vulcanoids, being an entirely new class of celestial bodies, would be interesting in their own right,
See also
- 594913 ꞌAylóꞌchaxnim (the only known asteroid always within Venus' orbit)
- 2021 PH27, an asteroid in the Atira group with the smallest semi-major axis among asteroids
- Atira asteroid (asteroids always within Earth's orbit)
- Groups of minor planets
- Kreutz sungrazer
- List of hypothetical Solar System objects
- List of Mercury-crossing minor planets
- Vulcan (hypothetical planet)
References
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- ^ a b c "Vulcanoids". The Planetary Society. Archived from the original on 2009-01-08. Retrieved 2008-12-25.
- ^ a b c d Roach, John (2002). "Fighter Jet Hunts for "Vulcanoid" Asteroids". National Geographic News. Archived from the original on May 8, 2002. Retrieved 2008-12-24.
- S2CID 122872992.
- ^ a b c d e "FAQ: Vulcanoid Asteroids". vulcanoid.org. 2005. Archived from the original on July 24, 2008. Retrieved 2008-12-27.
- ^ a b Britt, Robert Roy (2004). "Vulcanoid search reaches new heights". Space.com. Retrieved 2008-12-25.
- ^ .
- ^ a b Whitehouse, David (2002-06-27). "Vulcan in the Twilight Zone". BBC News. Retrieved 2008-12-25.
- ^ David, Leonard (2000). "Astronomers Eye 'Twilight Zone' Search for Vulcanoids". Space.com. Archived from the original on July 24, 2008. Retrieved 2008-12-25.
- ^ a b c "NASA Dryden, Southwest Research Institute Search for Vulcanoids". NASA. 2002. Archived from the original on 2019-05-03. Retrieved 2008-12-25.
- ^ a b c Alexander, Amir (2004). "Small, Faint, and Elusive: The Search for Vulcanoids". The Planetary Society. Archived from the original on 2008-10-11. Retrieved 2008-12-25.
- ^ S2CID 118612132.
- ^ Choi, Charles Q. (2008). "The Enduring Mysteries of Mercury". Space.com. Retrieved 2008-12-25.
- ^ a b c Chapman, C.R.; Merline, W.J.; Solomon, S.C.; Head, J.W. III; Strom, R.G. (2008). "First MESSENGER Insights Concerning the Early Cratering History of Mercury" (PDF). Lunar and Planetary Institute. Retrieved 2008-12-26.
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(help) - ^ a b Noll, Landon Curt (2007). "Vulcanoid Search during a Solar eclipse". Retrieved 2008-12-24.
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The existence of a non-negligible population of Venus-decoupled Vatiras thus begs the question as to whether any objects reach orbits entirely interior to that of Mercury. Accepted convention would likely to be to call such an object a Vulcanoid, although the term is usually intended to mean an object which has been resident inside Mercury for the entire lifetime of the Solar System.
- ^ ISBN 978-0-12-446744-6.
- S2CID 11176435.
- ^ Bibcode:1996ASPC..107...85C.