Originally termed planetoids, they are now preferably called as minor planets or asteroids. Most of the asteroids are much small objects compared with the planets. Typically most are irregularly shaped bodies about one kilometre or less in diameter. Several are hundreds of kilometres across, with Ceres being the largest at just under 1 000 kilometres. Of all these planetary objects, we can see only Vesta near its favourable oppositions with the naked-eye.
First of these objects to be discovered was Ceres by the Sicilian observer Giuseppe Piazzi on 1st January 1801. Second was Pallas in March 1802, followed in succession by, Juno in 1804 and Vesta in 1807. Yet nearly forty years were to pass when the fifth minor planet, Astraea, was discovered in 1845. After 1846, there was a litany of new discoveries. Three were then found in 1847, being Hebe, Iris and Flora; Metis in 1848 and Hygeia in 1849.
In the 1850s, fifty new ones were added — eight in 1852 alone! By 1860, sixty bodies were list, and one hundred with 100 Hekate in 1868. (See Table at the end of this page.) By the 1891, the listed ended with 322 Phaeo, and at the end of the 19th Century the last was 452 Hamiltonia. After this period of fever-pitched telescopic observation, astronomers began instead to discover many new asteroids photographically. Some were just found accidentally during several important whole sky-surveys of the heavens.
In another fifty years, the first one found in 1950, was 1612 Hirose – 1160 new asteroids. By 1991 more than 4,500 were catalogued, with 4,200 having identified and accurate enough orbital parameters to predicting future positions. In 2000 A.D., the number of bodies reached 38,679 asteroids. By October 2006, some 13,500 having proper or given names, with about 125 000 having been numbered of an estimated 360 000 — increasing by between 4,000 to 7,000 per month! In quite recent years with improved instrumentation and far more sensitive CCD cameras, the numbers of objects have exploded. Sometime in 2009 or 2010, the numbered asteroids will surpass the 100,000 mark!!
Mostly for the majority of them, we have little information on their own physical characteristics, such as their general size and shape — though in recent years this has improved significantly in our knowledge.
Naming of all minor planets began by using the adopted traditional method of using the plethora of Greek and Roman gods. The first several hundred asteroids discovered were all given female names. For example, Ceres as named after the Sicilian goddess of grain and agriculture. Juno and Vesta were named after Ceres’ two sisters, who were also sisters to Jupiter, with Juno being his wife as well. Pallas name is derived the alternative name for the goddess Athena, daughter of Jupiter, and therefore the niece of Ceres. Hebe is the cup bearer of the gods, while Iris is the messenger of the various Muses, Graces, Horae, nymphs, etc.
After the 1860s this system became quite impracticable due to the vast number of new discoveries. Today, several hundred are discovered annually, all requiring designated names. Presently, the I.A.U. officially decides the naming of newly discovered asteroids, which are announced in a new list each year.
Many of them have been named after famous
people;
I.e. 1677 Tycho Brahe, 8000 Isaac Newton /
1986 RL5, 1134 Kepler / 1929 SA,
4000 Hipparchus / 1989 AV and 238
Hypatia;
Continents;
2404 Antarctica (1980 TE), 1193 Africa/ 1931
HB, 8088 Australia / 1990 SL27.
Others are small states within
countries.
I.e. 439 Ohio, 793 Arizona / 1907 AD and
48575 Hawaii / 1994 NN.
Chemicals; I.e. 308 Polyxo
Variations on common names.
I.e. 114 Kassandra, 354 Eleonora and 537
Pauly.
Each asteroid is listed in order of discovery with the temporary designation, Ie. 1982 FA (F=June; A=First one discovered in that month.)
If an orbit is ascertained, then numbers are assigned, given in the order of their discovery of the orbital elements. I.e. 43 Ariadne or 2101 Adonis.
Many asteroids orbit the Sun roughly between the orbits of Mars and Jupiter averaging distances of between 2.0 and 2.5 Astronomical Units or 300 to 375 million kilometres.) There are perhaps millions of fragments orbiting the Sun at similar distances. Science once popularly described for many years the theory of the destruction of some large Moon or Mars-sized planet, but among astronomers holding this once prominent theory has generally been in slow decline. We now believe the origin of these objects is some incomplete remnant from the very beginning of the Solar System, which never properly formed into a small planet.
Some asteroids have highly elliptical orbits that sometimes cross the path of the Earth’s orbit. Several hundred of these are known and described as Apollos or Apollo-type asteroids. Examples include, the first discovered, Apollo, followed by others like; Eros, Icarus, Hermes and Geographos. Asteroids do also exist inside the Earth’s orbit and are placed in the sub-group known as Atens. Those crossing either Mars orbit, or those with similar terrestrial-like orbits, are often alternatively called Amors.
Other similar asteroid groups also do exist, like the those that precede and follow the orbit of Jupiter. These are believed to be naturally captured minor planets by Jupiter’s own powerful gravitational field.
The Achilles group lie 60º ahead, while the Patroclus group follows some 60º behind. Technically these places are called the Lagrangian Points; specifically being L4 and L5. They have named both groups of asteroids after the major combatants in the classical story of Trojan War as told in the Iliad and Odyssey as written by Homer. For reasons, which we do not really know, there are about 40% more asteroids in the trailing Patroclus group.
Closest known asteroid in approach the Sun is 3200 Phaethon / 1983 TB, being 5.1 km across whose solar distance varies between 2.403 AU down to 0.140 AU. At perihelion its closest approach is 0.15 A.U. or merely 10 million kilometres! Furthest from the Sun of the inner asteroids is 944 Hidalgo / 1920 HZ averages some 5.5 A.U, but whose eccentric orbit (e=0.660) finds the range anywhere between 1.95 AU to 9.54 AU during the 13.77 year period — being longer than even Jupiter. The orbit itself is highly inclined to the ecliptic at 42.6º !
Sometimes close approaches of asteroids to the Earth do occur. For example, on 30th October 1937 the Apollo-type 300 metre equally massed binary asteroid 69230 Hermes / 1937 UB, came within 700 000 km or 2.0 times the lunar distance from Earth. During WWII in 1942, Hermes made an even closer approach of 1.7 the Moon’s distance but was not observed. Next approach will be in There is no chance of a direct impact of the Earth in the foreseeable future.
On 22nd March 1989 another even closer approach of 600 000 km (1.8 lunar distances) was made by 300 metre diameter 4581 Asclepius, whose diameter is estimated to be about 150 metres across.
Yet another in January 1991, the tiny asteroid designated 1991 BA streaked past the Earth. Although only reaching a very faint 17th magnitude, the object passed within 130 000 km, only half the distance from the Moon! The object was calculated to be 5 to 10 metres in diameter, and so far the closest approach to date (2003).
All these Earth-crossing asteroids hold great interest (and some fear), as one of these bodies could crash into the planet, creating mass destruction. Some scientists believe that the dinosaur extinction some sixty-five million years ago was caused by an asteroid or comet, hitting the Earth and causing the so-called nuclear winter. The effect of any one kilometre or larger sized object would throw enormous amounts of dust into the atmosphere. This dust would block out the Sun for month or so — similar to the sight of burning of the oil-wells in Kuwait during the first Iraqi war. Under such conditions, temperatures on our planet could fall by an average by 60ºC. Most living creatures and people would probably just die from malnutrition due to all plants being unable to grow. This effect of nuclear winter could be expected to last six to twelve months — at least till most of the dust had settled.
Such collisions with asteroid sized objects are fortunately rare — happening once perhaps every two-hundred million years or so.
The majority of the asteriods have very dark surfaces, perhaps dark as lumps of coal. Others have highly reflectivities or albedos — the latter being the measured proportion of the amount of received light against the reflected light. I.e. Earth has an albedo of 0.39.
All asteroids are generally classified into a number of different types that are decided by observing the spectra displayed by them and the value of the albedo. Such important signatures tell us much about the composition of the asteroids themselves, and in some instances correspond to similar meteorites. Some of the major types include;
C-type: This class is typical of more than three-quarters of all known asteroids they are extremely dark, having typical albedos around 0.03. They are very similar to the carbonaceous chondrite meteorites, whose chemical constitution are mainly lighter than typical rock and contain many complex hydrocarbons. Most seem devoid of water ices like the comets.
S-type: These asteroids comprise 17% to 18% of all these three main types. They are relatively bright objects, whose albedos are brighter than C-types - typically between 0.10 and 0.22. Most are more metallic objects often with either mixtures of nickel-iron, iron or magnesium-silicates.
M-type. These asteroid types comprise of the remaining 7% to 8%, and are typically bright with albedos between 0.10 and 0.18. There composition are almost pure nickel-iron, and can have mean densities similar to the Earth.
Other than these main classes, there are also about another dozen rare types. I.e. K-class. Most today are placed in a variety of different classification systems, which is confusing to the average observerbut important for specialists in the field. Several problems also exist when placing objects within some category, as some minor planets can display multiple characteristics. Really, the types are related to their densities, but knowledge of this for the vast majority have not yet accurately determined. Some asteroids are astonishingly light — about the density of water — clearly suggesting they are in many cases just a conglomerate of rocks gathered together gravitationally.
The S-Type can be measured spectroscopically to determine their compositions, with most seemingly being silicate type rocks mixed with dark organic molecules. since the fly-by mission of Halley’s Comet in 1986, the very similar spectroscopic analysis obtained between comet and asteroid surfaces, have many planetary astronomers now believing there is real connection between comets and asteriods.
Of the bright C-type reflected asteroids, most are thought to be composed of ices such as water, ammonia or carbon dioxide scattered across their surfaces. In October 1991, the Galileo spacecraft had a fly-by of 951 Gaspra discovering some details about of its nature, followed in August 1993 by 243 Ida, and its moon Dactyl. On August and September 2005, the Japanese Hayabusa spacecraft, was placed into orbit around the 600-metre long potato-shaped asteroid, 25143 Itokawa (1998 SF36).
Several asteroids diameters have been determined by rare stellar occultations — when time when faint stars disappears behind their tiny disks. Stellar positions are usually well known, but predicting any minor planet’ position is never approaching near this precision. Asteroidal occultations can only be exactly predicted by photographing the position several days before the event. The possible error in position is still large, with the path being several thousands of kilometers wide, even though the true path can only be as large as the asteroid. If several observers fall inside the path the rough shape of the asteroid can be determined. To see one of these events is often more like simply good luck than any real planning.
Asteroid shapes that have so far been determined do indicate only a very few of them are even close to spherical. Even Ceres, now formally classed as a dwarf planet is slightly oblate. Most are very odd cigar or irregular shapes. For example, 624 Hektor, is twice as long as it is wide!
In 1977, observations of the 225-kilometre 532 Herculina was found to have two separate pairs of occultations, indicating a ‘double-asteroid’ merely 0.9 arc seconds away! Calculations revealed that this was actually possible. These two asteriods were found to be tens of kilometres across and are believed to be gently touching or nudging each other, or more correctly actually sitting together. Others subsequently have also been discovered, so that planetary observers now believe that multiple or double asteriods are rather commonplace, and are no longer deemed as unusual.
Several in recent years have been found to have no one but two companions, such as 87 Sylvia, which have been called after the mythology of the ancient Roman founders Romulus and Remus (or Sylvia I and II). Sylvia was the mother of these two brothers, who were taken from her when they were very young, and in legend were suckled to maturity by wolves. Sylvia was discovered by Norman Pogson on morning of 17th May 1866 in India. When found the magnitude of the body was 11.7v magnitude in northern Scorpius, and slowly fading, whose brightness was at the limits of the charts that were available to Pogson at the time. Its size is about 385×265×230 kilometres (c.±0.5), whose mean distance from the Sun is 3.49 AU or 522 million kilometres. The orbit itself is fairly circular, with an eccentricity of 0.080, whose period is roughly 6.52 years or 2381.68 days. As such, favourable oppositions are fairly rare when compared to the the four major asteroids. This dark asteroid is fairly faint because of it low reflective albedo, and some believe that it is not a solid object, but is merely just a gravitational collection of rubble of low density material. The highly elongated body has been found to have the rotational period of 5.18 hours, based on the light-curve, whose axis is tilted at 29.1º to the ecliptic.
Romulus was discovered on 16th February 2001 and seems quite sizeable compared to Sylvia itself, being about 18 kilometres acoss, along with an orbital period of 87.59 hours or 3.6496 days, moving at the mean distance of 1356±0.5 kilometres. His brother Remus, was found on the 9th August 2004, being roughly half the diameter of Romulus or 7 kilometres across and also half the distance at 706±5 km. An orbital period of 33.09 hours or 1.3788 days has been calculated, but presently, little is known about the long term stability of the orbits of these moons.
Another established triple asteroid is 45 Eugenia, whose second little companion was found in 2004. Eugenia was discovered in Paris by Herman Goldschmidt in 27th June 1857, exactly one month after his discovery of 44 Nysa. The name is not from classical mythology, but is named after the last Empress Consort of France, Her Imperial Majesty, Empress Eugénie de Montijo (1826-1920) who was the wife of Napoleon III.
Its diameter is some 305×220×145 kilometres, and like Sylvia, is thought to be composed of very dark material probably made of collection of rubble-like material. A mean distance 406.897 million km. or 2.720 AU, the orbital period 4.49 years or 1638.46 days.
During 1998, observers at Mauna Kea found a small moon which was later named Petit-Prince, who was born to Empress Eugénie on the 16th March 1856. With an orbital period of about five days, the estimated size is about 15 kilometres across, and is much like many other double asteroids. The second moon, called S/2004 (45) 1, was found by Franck Marchis as announced in the IAUC 8817 Circular on 7th March 2007, even though the observations were made in February 2004 by the 8.2m telescope at Cerro Paranal owned by the European Southern Observatory (ESO). Presently the estimated diameter is merely 6 km. as it orbits closer to Eugenia to the asteroid than Petit-Prince.
Several other minor planets also display significant axial rotations, found more usually by observing the slow fluctuations in the observed magnitude. Many have periods ranging between 1 and 40 days. The dog-boned shaped asteroid 216 Kleopatra (217±94 km.) and the K-type 104 kilometre diameter — 221 Eos vary by as much as 1.5 magnitudes.
Binary Asteroids : 22 Kalliope, 41 Daphne, 45 Eugenia, 87 Sylvia, 90 Antiope, 107 Camilla, 121 Hermione, 130 Elecktra, 243 Ida, 283 Emma, 379 Huenna, 69230 Hermes.
(1) C E R E S |
(2) P A L L A S |
(3) J U N O |
(4) V E S T A |
(5) A S T R A E A |
(6) H E B E |
(7) I R I S |
(8) F L O R A |
(9) M E T I S |
(10) H Y G I E A |
P L U T O |
E R I S |
(20000) V A R U N A |
(50000) Q U A O A R |
(90377) S E D N A |
(90482) O R C U S |
(136108) 2003 EL 61 |
(136472) 2005 FY 9 |
(28978) I X I O N |
(2060) C H I R O N |
************************************************************************************
No. Name Period Dia. Opp. Disc | No. Name Period Dia. Opp. Disc
(yr.) (km.) Mag. Year | (yr.) (km.) Mag. Year
************************************************************************************
1 Ceres 4.599 848.4 06.8 1801 | 51 Nemausa 3.639 147.9 09.9* 1858
2 Pallas 4.619 498.1 08.3 1802 | 52 Europa 5.461 305 10.1* 1858
3 Juno 4.362 233.9 10.1 1804 | 53 Kalypso 4.244 115.4 11.1* 1858
4 Vesta 3.627 468.3 05.9 1807 | 54 Alexandra 4.457 165.8 10.1* 1858
5 Astraea 4.136 119.1 09.8 1845 | 55 Pandora 4.585 66.7 10.6* 1858
*****************************************|******************************************
6 Hebe 3.777 185.2 08.6 1847 | 56 Melete 4.187 113.2 10.3* 1859
7 Iris 2.686 199.8 09.0 1847 | 57 Mnemosyne 3.149 112.6 10.7* 1859
8 Flora 3.266 135.9 09.2 1847 | 58 Concordia 4.434 93.4 12.1* 1860
9 Metis 3.686 151 09.6 1848 | 59 Elpis 4.667 164.8 10.8* 1860
10 Hygeia 5.589 407.1 10.0 1849 | 60 Echo 3.703 60.2 10.2* 1860
*****************************************|******************************************
11 Partherope 3.841 150 09.5 1850 | 61 Danae 2.982 82.0 11.0* 1860
12 Victoria 5.587 126 09.6 1850 | 62 Erato 3.122 95.4 12.1* 1860
13 Egeria 4.133 224 09.9 1851 | 63 Ausonia 2.395 103.1 09.7* 1861
14 Irene 4.167 158 09.1 1851 | 64 Angelina 2.684 50.5 10.2* 1861
15 Enunomia 4.297 272 09.1 1851 | 65 Cybele 3.433 237.3 10.9* 1861
*****************************************|******************************************
16 Psyche 5.006 250 10.1 1852 | 66 Maja 2.645 72.8 11.7* 1861
17 Thetis 3.882 109 10.0 1852 | 67 Asia 2.421 58.1 10.2* 1861
18 Melpomena 3.479 150 09.5 1852 | 68 Leto 2.783 122.6 09.6* 1861
19 Fortuna 3.815 215 09.7 1852 | 69 Hesperia 2.979 138.1 10.3* 1861
20 Massalia 3.737 230 09.3 1852 | 70 Panopaea 2.616 122.2 10.8* 1861
*****************************************|******************************************
21 Lutetia 3.081 115 10.5 1852 | 71 Niobe 2.755 83.4 10.4* 1861
22 Calliope 4.962 177 10.0 1852 | 72 Feronia 2.266 86.1 10.9* 1861
23 Thalia 4.293 111 11.5 1852 | 73 Klytia 2.665 44.4 12.2* 1862
24 Themis 5.57 177 11.0 1853 | 74 Galatea 2.778 118.7 10.6* 1862
25 Phocaea 3.723 249 10.6 1853 | 75 Eurydike 2.674 55.7 10.6* 1862
*****************************************|******************************************
26 Proserpine 4.329 80 09.7 1853 | 76 Freia 3.418 183.7 11.8* 1862
27 Euterpe 3.596 108 09.7 1853 | 77 Frigga 2.666 69.2 11.2* 1862
28 Bellora 4.631 126 10.1 1853 | 78 Diana 2.620 120.6 10.2* 1865?
29 Amphitrate 4.087 195 09.1 1854 | 79 Eurynome 2.444 66.5 09.6* 1863
30 Urania 3.655 91 10.0 1854 | 80 Sappho 2.297 78.4 09.8* 1864
************************************************************************************
31 Euphrosyne 5.590 255.9 10.2* 1854 | 81 Terpsichore 2.855 119.1 11.2* 1864
32 Pomona 4.163 80.8 10.6* 1854 | 82 Alkmene 2.760 61.0 10.6* 1864
33 Polyhymnia 4.851 65 09.9 1854 | 83 Beatrix 2.432 81.4 11.0* 1865
34 Circe 4.400 113.5 11.2* 1855 | 84 Klio 2.362 79.2 10.8* 1865
35 Leukothea 5.169 103.1 11.7* 1855 | 85 Io 2.654 154.8 10.1* 1865
*****************************************|******************************************
36 Atalante 4.552 105.6 10.4* 1855 | 86 Semele 3.114 120.6 11.6* 1866
37 Fides 4.292 108.3 09.6* 1855 | 87 Sylvia 3.489 260.9 11.5* 1866
38 Leda 4.544 115.9 11.2* 1856 | 88 Thisbe 2.766 200.6 09.7* 1866
39 Laetitia 4.607 149.5 09.1* 1856 | 89 Julia 2.550 151.5 08.9* 1866
40 Harmonia 3.415 107.6 09.3* 1856 | 90 Antiope 3.157 120.1 11.6* 1866
*****************************************|******************************************
41 Daphne 4.590 174.0 09.6* 1856 | 91 Aegina 2.591 109.8 11.5* 1866
42 Isis 3.813 100.2 09.4* 1856 | 92 Undina 3.190 126.4 10.5* 1867
43 Ariadne 3.270 68 08.8 1857 | 93 Minerva 2.754 141.0 10.7* 1867
44 Nysa 3.769 65 08.5* 1857 | 94 Aurora 3.159 204.9 11.5* 1867
45 Eugenia 4.489 107.3 10.8* 1857 | 95 Arethusa 3.068 136.0 11.2* 1867
*****************************************|******************************************
46 Hestia 4.018 124.1 10.6* 1857 | 96 Aegle 3.057 169.9 11.0* 1868
47 Aglaja 4.891 127.0 11.0* 1857 | 97 Klotho 2.668 82.8 09.0* 1868
48 Doris 5.488 221.8 10.9* 1857 | 98 Ianthe 2.685 104.5 11.3* 1868
49 Pales 5.412 149.8 10.7* 1857 | 99 Dike 2.663 71.9 11.7* 1868
50 Virginia 4.314 99.8 11.8* 1857 |100 Hekate 3.093 88.7 10.7* 1868
************************************************************************************
* Maximum Opposition Magnitude till 2025
Binary Asteroids : 22 Kalliope, 41 Daphe, 45 Eugenia, 87 Sylvia, 90 Antiope.
The user applying this data for any purpose forgoes any liability against the author. None of the information should be used for regarding either legal or medical purposes. Although the data is accurate as possible some errors might be present. The onus of its use is place solely with the user.
