Rocks/Rocky objects

A rocky object is any object, including astronomical objects, composed of one or more types of rocks.

This image is of asteroid 2012 LZ1 by the Arecibo Observatory in Puerto Rico using the Arecibo Planetary Radar. Credit: Arecibo Observatory.


This is an image of an olivine rock. Credit: Canica.
Here is mica in a rock. Credit: Rpervinking.
Cristobalite spheres appear within obsidian. Credit: Rob Lavinsky.
Specimen consists of "porcelainite" - a semivitrified chert- or jasper-like rock composed of cordierite, mullite and tridymite, admixture of corundum, and subordinate K-feldspar. Credit: John Krygier.
A feldspar rock is shown. Credit: Dave Dyet.
This is an example of a travertine. Credit: USGS.

Rocks are composed of one or more types of minerals.

Top right is an image of an olivine rock.

Top left is the mineral mica in a rock.

Second on the right is an image of Cristobalite spheres within obsidian.

Second on the left is an image of a specimen that consists of "porcelainite" - a semivitrified chert- or jasper-like rock composed of cordierite, mullite and tridymite, admixture of corundum, and subordinate K-feldspar.

Third on the right is a feldspar rock.

Def. "light, porous form of concretionary limestone (or calcite)"[1] is called a travertine.


This covellite specimen is from the Black Forest of Germany. Credit: .

A mineral is a crystalline solid with a molecular formula. Each unit cell possesses at least one formula unit.

Covellite has been found in veins at depths of 1,150 meters, as the primary mineral. Covellite formed as clusters in these veins reaching one meter across.


Each chemical element can occur as a solitary atom or when possible in a molecule with another atom or many atoms.

Theoretical rocky objectsEdit


1.a: "something that is or is capable of being seen, touched, or otherwise sensed",
1.b: "something physical or mental of which a subject is cognitively aware",
2. "something that arouses an emotion in an observer", or
3. "a thing that forms an element of or constitutes the subject matter of an investigation or science"

is called an object.[2]

Def. full "of, or abounding in, rocks; consisting of rocks... [l]ike a rock"[3] is called rocky.

Dwarf planetsEdit

Ceres as seen by the Dawn spacecraft, 19 February 2015. Credit: NASA, JPL-Caltech, UCLA, MPS, DLR, IDA.

The Gamma Ray and Neutron Detector (GRaND) onboard the Dawn spacecraft is based on similar instruments flown on the Lunar Prospector and Mars Odyssey space missions. It will be used to measure the abundances of the major rock-forming elements (oxygen, magnesium, aluminium, silicon, calcium, titanium, and iron) on Vesta and Ceres, as well as potassium, thorium, uranium, and water (inferred from hydrogen content).[4][5][6][7][8][9]

Def. "a celestial body that

(a) is in orbit around the Sun,

(b) has sufficient mass for its self-gravity to overcome rigid forces so that it assumes a hydrostatic equilibrium (nearly round) shape,

(c) has not cleared the neighbourhood around its orbit, and

(d) is not a satellite" is called a dwarf planet.[10]


This is a fireball meteor trail with some burning still visible above the Urals city of Chelyabinsk, Russia, on February 15, 2013. Credit: Reuters/

Def. any natural object radiating through a portion or all of the Earth's or another natural object's atmosphere is called a meteor.


The Zodiacal Light is over the Faulkes Telescope, Haleakala, Maui. Credit: 808caver.
Mount Redoubt in Alaska erupted on April 21, 1990. The mushroom-shaped plume rose from avalanches of hot debris that cascaded down the north flank. Credit: R. Clucas, USGS.

Def. a "suspension of dry dust ... in the atmosphere"[11] is called a lithometeor.

"A lithometeor consists of solid particles suspended in the air or lifted by the wind from the ground."[12]

"A lithometeor is the general term for particles suspended in a dry atmosphere; these include dry haze, smoke, dust, and sand."[13]

The Zodiacal light is a faint, roughly triangular, diffuse white glow seen in the night sky that appears to extend up from the vicinity of the Sun along the ecliptic or zodiac.[14] It is best seen just after sunset and before sunrise in spring and autumn when the zodiac is at a steep angle to the horizon. Caused by sunlight scattered by space dust in the zodiacal cloud, it is so faint that either moonlight or light pollution renders it invisible. The zodiacal light decreases in intensity with distance from the Sun, but on very dark nights it has been observed in a band completely around the ecliptic. In fact, the zodiacal light covers the entire sky, being responsible for major part[15] of the total skylight on a moonless night. There is also a very faint, but still slightly increased, oval glow directly opposite the Sun which is known as the gegenschein. The dust forms a thick pancake-shaped cloud in the Solar System collectively known as the zodiacal cloud, which occupies the same plane as the ecliptic. The dust particles are between 10 and 300 micrometres in diameter, with most mass around 150 micrometres.[16]


This is a very large hailstone from the NOAA Photo Library. Credit: NOAA Legacy Photo; OAR/ERL/Wave Propagation Laboratory.

A megacryometeor is a very large chunk of ice sometimes called huge hailstones, but do not need to form in thunderstorms.

A megacryometeor is a very large chunk of ice which, despite sharing many textural, hydro-chemical and isotopic features detected in large hailstones, is formed under unusual atmospheric conditions which clearly differ from those of the cumulonimbus cloud scenario (i.e. clear-sky conditions). They are sometimes called huge hailstones, but do not need to form in thunderstorms. Jesus Martinez-Frias, a planetary geologist at the Center for Astrobiology in Madrid, pioneered research into megacryometeors in January 2000 after ice chunks weighing up to 6.6 pounds (3.0 kg) rained on Spain out of cloudless skies for ten days.

Def. "pieces of ice falling as precipitation"[17] are called hail.

Def. a "single ball of hail"[18] is called a hailstone.

Def. water ice crystals falling as light white flakes are called snow.


The volcanic eruption from Mount Pinatubo deposits a snowlike blanket of tephra on June 15, 1991. Credit: R.P. Hoblitt, USGS.

Def. the "solid material thrown into the air by a volcanic eruption that settles on the surrounding areas"[19] is called tephra.

"[T]ephra, is a general term for fragments of volcanic rock and lava that are blasted into the air by volcanic explosions or carried upward in the volcanic plume by hot, hazardous gases. The larger fragments usually fall close to the volcano, but the finer particles can be advected quite some distance. ... [Fine ash] can contain rock, minerals, and volcanic glass fragments smaller than .1 inch in diameter, or slightly larger than the size of a pinhead."[13]


The image contains a 27.70 g fragment of the Carancas meteorite fall. The scale cube is 1 cm3. Credit: Meteorite Recon.

On September 20, the X-Ray Laboratory at the Faculty of Geological Sciences, Mayor de San Andres University, La Paz, Bolivia, published a report of their analysis of a small sample of material recovered from the impact site. They detected iron, nickel, cobalt, and traces of iridium — elements characteristic of the elemental composition of meteorites. The quantitative proportions of silicon, aluminum, potassium, calcium, magnesium, and phosphorus are incompatible with rocks that are normally found at the surface of the Earth.[20]

"In X-ray wavelengths, many scientists are investigating the scattering of X-rays by interstellar dust, and some have suggested that astronomical X-ray sources would possess diffuse haloes, due to the dust.[21]


The image shows the first film ever of a meteor plunging down at terminal velocity. Credit: Anders Helstrup / Dark Flight, montage, Hans Erik Foss Amundsen.

"A skydiver may have captured the first film ever of a meteorite plunging down at terminal velocity, also known as its “dark flight” stage."[22]

"The footage was captured in 2012 by a helmet cam worn by Anders Helstrup as he and other members of the Oslo Parachute Club jumped from a small plane that took off from an airport in Hedmark, Norway."[22]

“It can’t be anything else. The shape is typical of meteorites -- a fresh fracture surface on one side, while the other side is rounded.”[23]

“It has never happened before that a meteorite has been filmed during dark flight; this is the first time in world history.”[23]

"Having the rock in hand would certainly help. But despite triangulations and analyses, Helstrup and his recruits still haven’t found it."[22]


The photograph shows the meteor, afterglow, and wake as distinct components of a meteor during the peak of the 2009 Leonid Meteor Shower. Credit: Navicore.
This picture is of the Alpha-Monocerotid meteor outburst in 1995. It is a timed exposure where the meteors have actually occurred several seconds to several minutes apart. Credit: NASA Ames Research Center/S. Molau and P. Jenniskens.
This image taken October 17, 2012, is prior to the meteorite fall on the same day. Credit: Paola-Castillo; and Petrus M. Jenniskens, SETI Institute/NASA ARC.

The image at the top of the article shows "[t]he trail of a falling object ... seen above the Urals city of Chelyabinsk [on] February 15, 2013".[24]

Meteors become visible between about 75 to 120 kilometers (34 - 70 miles) above the Earth. They disintegrate at altitudes of 50 to 95 kilometers (31-51 miles). Most meteors are observed at night, when darkness allows fainter objects to be recognized. Most meteors glow for about a second.

A fireball is a brighter-than-usual meteor. The International Astronomical Union defines a fireball as "a meteor brighter than any of the planets" (magnitude −4 or greater).[25] The International Meteor Organization (an amateur organization that studies meteors) has a more rigid definition. It defines a fireball as a meteor that would have a magnitude of −3 or brighter if seen at zenith. This definition corrects for the greater distance between an observer and a meteor near the horizon. For example, a meteor of magnitude −1 at 5 degrees above the horizon would be classified as a fireball because if the observer had been directly below the meteor it would have appeared as magnitude −6.[26] For 2011 there are 4589 fireballs records at the American Meteor Society.[27]

Def. a fireball "reaching magnitude −14 or brighter.[28] is called a bolide.

Def. a fireball reaching an magnitude −17 or brighter is called a superbolide.

At left is a cell phone camera image of the green fireball over San Mateo, California, that left meteorite fragments. "The asteroid entered at a speed of 14 km/s, typical but on the slow side of other meteorite falls for which orbits were determined. ... The orbit in space is also rather typical: perihelion distance close to Earth's orbit (q = 0.987 AU) and a low-inclination orbit (about 5 degrees). ... 2012, October 17 - At 7:44:29 pm PDT this evening, a bright fireball was seen in the San Francisco Bay Area."[29]

"The distribution of photographic meteors in iron, stony, and porous meteors is given in this paper".[30] "[A]mong all the 217 meteors for which we know the beginning there are 70 iron meteors, i. e. about 32 p. c., and 147 stony meteors, i. e. 68 p. c."[30] The meteor streams: Perseids, Geminids, Taurids, Lyrids, κ Cygnids and Virginids, are quite stony.[30]

"The dominant group in all cases are stony meteors."[30]


This Sin-Kamen (Blue Rock) near Lake Pleshcheyevo used to be a Meryan shrine Credit: Viktorianec.

"Sin-Kamen (Синь-Камень, in Russian literally – Blue Stone, or Blue Rock) is a type of pagan sacred stones, widespread in Russia, in areas historically inhabited by both Eastern Slavic (Russian), and Uralic tribes (Merya, Muroma[31]).

While in the majority of cases, the stones belonging to the Blue Stones type, have a black, or dark gray color, this particular stone in the image does indeed look dark blue, when wet.[32]


NWA 6963 is an igneous Martian shergottite meteorite found in September 2011 in Morocco. Credit: Steve Jurvetson.

Def. "a meteor that reaches the surface of the Earth without being completely vaporized"[2] is called a meteorite.

Imaged at right is an igneous Martian shergottite meteorite. "The perimeter exhibits a fusion crust from the heat of entry into the Earth’s atmosphere. It is a fresh sample of NWA 6963, an igneous Martian shergottite meteorite found in September 2011 in Morocco. Meteorites are often labeled NWA for North West Africa, not because they land there more often, but because they are easy to spot as peculiar objects in the desert sands. From the geochemistry and presence of various isotopes, the origin and transit time is deduced. The 99 meteorites from Mars exhibit precise elemental and isotopic compositions similar to rocks and atmosphere gases analyzed by spacecraft on Mars, starting with the Viking lander in 1976. Compared to other meteorites, the Martians have younger formation ages, unique oxygen isotopic composition (consistent for Mars and not for Earth), and the presence of aqueous weathering products. A trapped gas analysis concluded that their origin was Mars quite recently, in the year 2000."[33]

"The formation ages of meteorites often come from their cosmic-ray exposure (CRE), measured from the nuclear products of interactions of the meteorite in space with energetic cosmic ray particles. This one is particularly young, having crystallized only 180 million years ago, suggesting that volcanic activity was still present on Mars at that time. Volcanic flows are the youngest part of a planet, and this one happened to be hit by a meteor impact, ejecting" it from the youthful Mars.[33]


This is a micrometeorite collected from the antarctic snow. Credit: NASA.

"[T]he carbonaceous material [is] known from observation to dominate the terrestrial [micrometeorite (MM)] flux."[34] "Ureilites occur about half as often as eucrites (Krot et al. 2003), are relatively friable, have less a wide range of cosmic-ray exposure ages including two less than 1 Myr, and, like the dominant group of MM precursors, contain carbon."[34]

Sun-grazing cometsEdit

"Sun-grazing comets almost never re-emerge, but their sublimative destruction near the sun has only recently been observed directly, while chromospheric impacts have not yet been seen, nor impact theory developed."[35] "[N]uclei are ... destroyed by ablation or explosion ... in the chromosphere, producing flare-like events with cometary abundance spectra."[35]

"The death of a comet at r ~ Rʘ has been seen directly only very recently (Schrijver et al 2011) using the SDO AIA XUV instrument. This recorded sublimative destruction of Comet C/2011 N3 as it crossed the solar disk very near periheloin q = 1.139Rʘ."[35]


To accentuate the geological context of the spectral measurements, the MASCS data have been overlain on the MDIS monochrome mosaic. Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington.

"The [Mercury Atmosphere and Surface Composition Spectrometer] MASCS instrument was designed to study both the exosphere and surface of Mercury. To learn more about the minerals and surface processes on Mercury, the Visual and Infrared Spectrometer (VIRS) [VIRS Color Composite Wavelengths: 575 nm as red, 415 nm/750 nm as green, 310 nm/390 nm as blue] portion of MASCS has been diligently collecting single tracks of spectral surface measurements since MESSENGER entered orbit. The track coverage is now extensive enough that the spectral properties of both broad terrains and small, distinct features such as pyroclastic vents and fresh craters can be studied. To accentuate the geological context of the spectral measurements, the MASCS data have been overlain on the MDIS monochrome mosaic."[36]


Using an imaging radar technique, the Magellan spacecraft was able to lift the veil from the face of Venus and produce this spectacular high resolution image of the planet's surface. Red, in this false-color map, represents mountains, while blue represents valleys. Credit: Magellan Team, JPL, NASA.
This is a false color image of Venus produced from a global radar view of the surface by the Magellan probe while radar imaging between 1990-1994. Credit: NASA.

The first un-ambiguous detection of Venus was made by the Jet Propulsion Laboratory (JPL) on 10 March 1961. A correct measurement of the AU soon followed.

"The advantages of radar in planetary astronomy result from (1) the observer's control of all the attributes of the coherent signal used to illuminate the target, especially the wave form's time/frequency modulation and polarization; (2) the ability of radar to resolve objects spatially via measurements of the distribution of echo power in time delay and Doppler frequency; (3) the pronounced degree to which delay-Doppler measurements constrain orbits and spin vectors; and (4) centimeter-to-meter wavelengths, which easily penetrate optically opaque planetary clouds and cometary comae, permit investigation of near-surface macrostructure and bulk density, and are sensitive to high concentrations of metal or, in certain situations, ice."[37]

When viewed using radio astronomy, the resulting radar image, at left, shows that just beneath the cloud layers is a rocky planet.


This geologic province map depicts features approximately 150 km across and greater due to the fact that the resolution of the maps is consistent with the resolution of the seismic refraction data. Credit: USGS.

Def. the intellectual and practical activity encompassing the systematic study through observation and experiment of naturally occurring astronomical rocky objects, their physical structure and substance, history and origin, and the processes that act on them, especially by examination of their rocks, is called astrogeology.

Identifying the rocks, regoliths, and sediments on the solid surface of the Earth is often best accomplished from above the surface.

Locations on EarthEdit

This is an accretionary lava ball. Credit: J. D. Griggs, USGS HVO.
This is a volcanic bomb found in the Mojave Desert National Preserve by Rob McConnell. Credit: Wilson44691.
This is a picture of a lavabomb at Strohn, Germany. Credit: Jhintzbe.

Def. "distinctively shaped [natural] projectiles ... which acquired their shape essentially before landing"[38] are called bombs.

Def. a bomb "ejected from a volcanic vent"[38] is called a volcanic bomb.

Volcanic bombs can be thrown many kilometres from an erupting vent, and often acquire aerodynamic shapes during their flight.

The image at top right is an "[a]ccretionary lava ball [coming] to rest on the grass after rolling off the top of an ‘a‘a flow in Royal Gardens subdivision. Accretionary lava balls form as viscous lava is molded around a core of already solidified lava."[39]

Volcanic bombs cool into solid fragments before they reach the ground. Because volcanic bombs cool after they leave the volcano, they do not have grains making them extrusive igneous rocks. Volcanic bombs can be thrown many kilometres from an erupting vent, and often acquire aerodynamic shapes during their flight.

Volcanic bombs can be extremely large; the 1935 eruption of Mount Asama in Japan expelled bombs measuring 5–6 m in diameter up to 600 m from the vent. A large volcanic bomb is shown in the third image at right from Strohn, Germany.

Volcanic bombs are known to occasionally explode from internal gas pressure as they cool, but explosions are rare. Bomb explosions are most often observed in 'bread-crust' type bombs.

Ribbon or cylindrical bombs form from highly to moderately fluid magma, ejected as irregular strings and blobs. The strings break up into small segments which fall to the ground intact and look like ribbons. Hence, the name "ribbon bombs". These bombs are circular or flattened in cross section, are fluted along their length, and have tabular vesicles.

Spherical bombs also form from high to moderately fluid magma. In the case of spherical bombs, surface tension plays a major role in pulling the ejecta into spheres.

Spindle, fusiform, or almond/rotational bombs are formed by the same processes as spherical bombs, though the major difference being the partial nature of the spherical shape. Spinning during flight leaves these bombs looking elongated or almond shaped; the spinning theory behind these bombs' development has also given them the name 'fusiform bombs'. Spindle bombs are characterised by longitudinal fluting, one side slightly smoother and broader than the other. This smooth side represents the underside of the bomb as it fell through the air.

Cow pie bombs are formed when highly fluid magma falls from moderate height; so the bombs do not solidify before impact (they are still liquid when they strike the ground). They consequently flatten or splash and form irregular roundish disks, which resemble cow-dung.

Bread-crust bombs are formed if the outside of the lava bombs solidifies during their flights. They may develop cracked outer surfaces as the interiors continue to expand.

Cored bombs are bombs that have rinds of lava enclosing a core of previously consolidated lava. The core consists of accessory fragments of an earlier eruption, accidental fragments of country rock or, in rare cases, bits of lava formed earlier during the same eruption.


The white spot on this image of the Earth side of the Moon is the impact site of a meteor from March 17, 2013. Credit: NASA.
This image shows the lunar meteorite Allan Hills 81005. Credit: NASA.
Composite image of the Moon is taken by the Galileo spacecraft on 7 December 1992. The color is 'enhanced' in the sense that the CCD camera is sensitive to near infrared wavelengths of light beyond human vision. Credit: NASA/JPL/USGS.
This full disk is nearly featureless, a uniform grey surface with almost no dark mare. There are many bright overlapping dots of impact craters. Credit: NASA/GSFC/ASU LRO.

Lunar origin is established by comparing the mineralogy, the chemical composition, and the isotopic composition between meteorites and samples from the Moon collected by Apollo missions.

Cosmic ray exposure history established with noble gas measurements have shown that all lunar meteorites were ejected from the Moon in the past 20 million years. Most left the Moon in the past 100,000 years.

All six of the Apollo missions on which samples were collected landed in the central nearside of the Moon, an area that has subsequently been shown to be geochemically anomalous by the Lunar Prospector mission. In contrast, the numerous lunar meteorites are [likely to be] random samples of the Moon and consequently provide a more representative sampling of the lunar surface than the Apollo samples. Half the lunar meteorites, for example, likely sample material from the farside of the Moon.

At top left is a NASA photograph showing the bright flash of light from a meteor impact that occurred on the Moon on March 17, 2013. According to NASA, a 0.3 m rock slammed into the lunar surface at 90,120 km/h, creating a fresh crater 20 m wide.

"The crash caused the biggest and brightest explosion scientists have seen since they started monitoring lunar meteorite strikes in 2005. ... The lunar blast was the equivalent of 5 tons of TNT going off".[40]

"The flash was so bright it saturated the camera".[41]

"During its flight, the Galileo spacecraft returned images of the Moon. The Galileo spacecraft took these images on December 7, 1992 on its way to explore the Jupiter system in 1995-97. The distinct bright ray crater at the bottom of the image is the Tycho impact basin. The dark areas are lava rock filled impact basins: Oceanus Procellarum (on the left), Mare Imbrium (center left), Mare Serenitatis and Mare Tranquillitatis (center), and Mare Crisium (near the right edge). This picture contains images through the Violet, 756 nm, 968 nm filters. The color is 'enhanced' in the sense that the CCD camera is sensitive to near infrared wavelengths of light beyond human vision."[42]

The Moon has been detected using gamma-ray astronomy. These gamma-rays are produced by cosmic ray bombardment of its rocky surface.

"Four radiometers [aboard Luna 13 ] recorded infrared radiation from the [Moon's] surface.

"Nine out of 10 well-characterized Apollo 17 breccia matrices fall into Group 2, and this includes both the blue-grey breccias which are the dominant rock type at this site".[43]


Mars is imaged from Hubble Space Telescope on October 28, 2005, with dust storm visible. Credit: .

"Mars is the fourth planet from the Sun in the Solar System. Named after the Roman god of war, Mars, it is often described as the "Red Planet" as the [iron(III) oxide] iron oxide prevalent on its surface gives it a reddish appearance.[44] ... The red-orange appearance of the Martian surface is caused by iron(III) oxide, more commonly known as hematite, or rust.[45] ... Much of the surface is deeply covered by finely grained iron(III) oxide dust.[46][47]


Hemispheric topographic maps of Ceres, centered on 60° and 240° east longitude (July 2015). Credit: NASA/JPL-Caltech/UCLA/MPS/DLR/IDA.

"This pair of images shows color-coded maps from NASA's Dawn mission, revealing the highs and lows of topography on the surface of dwarf planet Ceres."[48]

"The map at left is centered on terrain at 60 degrees east longitude; the map at right is centered on 240 degrees east longitude."[48]

"The color scale extends about 5 miles (7.5 kilometers) below the surface in indigo to 5 miles (7.5 kilometers) above the surface in white."[48]

"The topographic map was constructed from analyzing images from Dawn's framing camera taken from varying sun and viewing angles. The map was combined with an image mosaic of Ceres and projected as an orthographic projection."[48]

"The well-known bright spots in the center of Ceres northern hemisphere in the image at right retain their bright appearance, although they are color-coded in the same green elevation of the crater floor in which they sit."[48]

"Note: The elevation scale used for this topographic map product differs slightly from the scale used to create PIA19605."[48]


This is an ultraviolet image of Pallas showing its flattened shape taken by the Hubble Space Telescope. Credit: NASA.

"Pallas, minor-planet designation 2 Pallas, is the second asteroid to have been discovered (after Ceres), and one of the largest in the Solar System. It is estimated to comprise 7% of the mass of the asteroid belt,[49] and its diameter of 544 kilometres (338 mi) is slightly larger than that of 4 Vesta. It is however 10–30% less massive than Vesta,[50] placing it third among the asteroids.


This is a composite Dawn spacecraft image of Vesta.

"The [NASA's Dawn spacecraft] Framing Camera (FC) discovered enigmatic orange material on Vesta. FC images revealed diffuse orange ejecta around two impact craters, 34-km diameter Oppis, and 30-km diameter Octavia, as well as numerous sharp-edge orange units in the equatorial region."[51] The spacecraft "entered orbit around asteroid (4) Vesta in July 2011 for a year-long mapping orbit."[51]

"Using Dawn’s Gamma Ray and Neutron Detector, ... Global Fe/O and Fe/Si ratios are consistent with [howardite, eucrite, and diogenite] HED [meteorite] compositions."[52]


This is a composite image, to scale, of the asteroids which have been imaged at high resolution. As of 2011 they are, from largest to smallest: 4 Vesta, 21 Lutetia, 253 Mathilde, 243 Ida and its moon Dactyl, 433 Eros, 951 Gaspra, 2867 Šteins, 25143 Itokawa. Credit: NASA/JPL-Caltech/JAXA/ESA.
This is an approximately natural color picture of the asteroid 243 Ida on August 28, 1993. Credit: NASA/JPL.

The majority of known asteroids orbit within the asteroid belt between the orbits of Mars and Jupiter. This belt is now estimated to contain between 1.1 and 1.9 million asteroids larger than 1 km in diameter.[53] and millions of smaller ones.[54]

At second right is an approximately natural color image of the asteroid 243 Ida. "There are brighter areas, appearing bluish in the picture, around craters on the upper left end of Ida, around the small bright crater near the center of the asteroid, and near the upper right-hand edge (the limb). This is a combination of more reflected blue light and greater absorption of near infrared light, suggesting a difference in the abundance or composition of iron-bearing minerals in these areas."[55]

"The [Sloan Digital Sky Survey] SDSS “blue” asteroids are related to the C-type (carbonaceous) asteroids, but not all of them are C-type. They are a mixture of C-, E-, M-, and P-types."[56]


This image of Callisto from NASA's Galileo spacecraft, taken in May 2001, is the only complete global color image of Callisto obtained by Galileo. Credit: NASA/JPL/DLR(German Aerospace Center).

It is generally believed that large astronomical objects like Callisto are spheroidal to spherical due to hydrodynamic stability. Another possibility is that relatively random collisions with the initial seed object all around it eventually lead to a spherical or spheroidal object as more material collides and sticks to the seed object. Callisto may be the best example of this growth process.


This is the opposite side of Europa from the usual image. Credit: NOAA.

"The most interesting feature of Europa, Jupiter’s sixth moon, is the incredibly smooth surface with relatively few craters. There are only three craters that have a diameter greater than 3.1 miles. This is an incredibly small amount for the moon which is just slightly less than the size of Earth’s Moon. Scientists believe that the surface of Europa is relatively young because of that fact. Another notable feature is the basically level surface with very little change in altitude across the moon. While there is almost no elevation change on Europa to observe, there are distinct lines which encircle the moon. The latest theory is that these markings are from volcanoes or geysers."[57]

"Europa is one of only five moons in the solar system known to have an atmosphere. This atmosphere is incredibly small with a pressure of only 1 x 10-8 mb compared to the average of approximately 1000 mb on Earth. An ocean that is up to 30 miles deep is thought to exist under the surface layer of Europa. Another theory regarding the distinct markings on Europa is that they are the result of the moon’s crust expanding and fracturing causing the cracks to fill in with water and freeze."[57]

Ganymede ice sheetsEdit

A true color image of Ganymede is acquired by the Galileo spacecraft on June 26, 1996. Credit: NASA/JPL.

"If Ganymede rotated around the Sun rather than around Jupiter, it would be classified as a planet."[58]

The Galilean Moons is a "name given to Jupiter's four largest moons, Io, Europa, Callisto & Ganymede. They were discovered independently by Galileo Galilei and Simon Marius."[59]


Io, the most volcanic body in the solar system, is seen in the highest resolution obtained to date by NASA's Galileo spacecraft. Credit: NASA.

Io "is the innermost of the four Galilean moons of the planet Jupiter and, with a diameter of 3,642 kilometres (2,263 mi), the fourth-largest moon in the Solar System. ... With over 400 active volcanoes, Io is the most geologically active object in the Solar System.[60][61] ... Most of Io's surface is characterized by extensive plains coated with sulfur and sulfur dioxide frost. ... Io's volcanism is responsible for many of the satellite's unique features. Its volcanic plumes and lava flows produce large surface changes and paint the surface in various shades of yellow, red, white, black, and green, largely due to allotropes and compounds of sulfur.

In the image at right, "[t]he smallest features that can be discerned are 2.5 kilometers in size. There are rugged mountains several kilometers high, layered materials forming plateaus, and many irregular depressions called volcanic calderas. Several of the dark, flow-like features correspond to hot spots, and may be active lava flows. There are no landforms resembling impact craters, as the volcanism covers the surface with new deposits much more rapidly than the flux of comets and asteroids can create large impact craters. The picture is centered on the side of Io that always faces away from Jupiter; north is to the top."[62]

"Color images acquired on September 7, 1996 have been merged with higher resolution images acquired on November 6, 1996 by the Solid State Imaging (CCD) system aboard NASA's Galileo spacecraft. The color is composed of data taken, at a range of 487,000 kilometers, in the near-infrared, green, and violet filters and has been enhanced to emphasize the extraordinary variations in color and brightness that characterize Io's face. The high resolution images were obtained at ranges which varied from 245,719 kilometers to 403,100 kilometers."[62]


Unlike most of the dull grey moons in the Solar System, Hyperion's color is a rosy tan, as this view shows. Credit: NASA/JPL/Space Science Institute.

"Unlike most of the dull grey moons in the Solar System, Hyperion's color is a rosy tan, as this view [on the right] shows."[63]

"The origin of the moon's unusual hue is not known. Some scientists suspect the color comes from falling debris from moons further out. A similar origin has been suggested for the dark reddish material on Saturn's moon Iapetus."[63]

"Images taken using red, green and blue spectral filters were combined to create this natural color view. The images were taken in visible light with the Cassini spacecraft narrow-angle camera on June 28, 2006 at a distance of approximately 291,000 kilometers (181,000 miles) from Hyperion. Image scale is 2 kilometers (1 mile) per pixel."[63]


This is an an animation showing Iapetus's surface. Credit: Brandon Amaro.

"Although it is no longer uncharted land, the origin of the dark territory of Cassini Regio on Iapetus remains a mystery. Also puzzling is the equatorial ridge that bisects this terrain, and how it fits into the story of the moon's strange brightness dichotomy."[64]


Enhanced color composite of Saturn's moon Dione is based on infrared, green, ultraviolet, and clear-filter images taken by the Cassini spacecraft December 14, 2004. Credit: Matt McIrvin, Cassini/NASA.
Dione is shown here in a composite of images from Cassini. Credit: NASA, JPL, SSI, ESA.

This at right is an "[e]nhanced color composite of Saturn's moon Dione, based on infrared, green, ultraviolet, and clear-filter images [is] taken by the Cassini spacecraft December 14, 2004."[65]

It shows "the darker, fractured terrain of the trailing hemisphere. The Padua Chasmata trace an arc on the left, interrupted near the top by central peak crater Ascanius. The Janiculum Dorsa extend along the upper right terminator. Near the lower left limb is the small crater Cassandra with its prominent ray system."[65]

At left is another image of Dione partially rotated from the one at right and showing a violet cast on the apparent higher elevation portion toward the terminator. This image is from Cassini "taken 1 August 2005 from 243,000 km away."[66]


This is an enhanced color view of Enceladus. Credit: NASA/JPL/Space Science Institute.

"The south polar terrain is marked by a striking set of 'blue' fractures and encircled by a conspicuous and continuous chain of folds and ridges, testament to the forces within Enceladus that have yet to be silenced."[67]

"The mosaic was created from 21 false-color frames taken during the Cassini spacecraft's close approaches to Enceladus on March 9 and July 14, 2005. Images taken using filters sensitive to ultraviolet, visible and infrared light (spanning wavelengths from 338 to 930 nanometers) were combined to create the individual frames."[67]

"The mosaic is an orthographic projection centered at 46.8 degrees south latitude, 188 degrees west longitude, and has an image scale of 67 meters (220 feet) per pixel. The original images ranged in resolution from 67 meters per pixel to 350 meters (1,150 feet) per pixel and were taken at distances ranging from 11,100 to 61,300 kilometers (6,900 to miles) from Enceladus."[67]


This view from the Cassini orbital mission at Saturn shows the high-resolution color of the leading hemisphere of Tethys. Credit: NASA/JPL/Space Science Institute/Universities Space Research Association/Lunar & Planetary Institute.

At right is the first global high-resolution color image of Tethys.

"The color map shows the prominent dusky bluish band along the equator, first seen by Voyager in 1980, and shown ... to be due to the bombardment and alteration of the surface by high energy electrons traveling slower than the satellite's revolution period."[68]


This is a mosaic of infrared images of Titan with nomenclature. Credit: Hargitai.

Depending on the astronomy technique used to view Titan, it may appear differently.

Titan has a mean radius of 2576 ± 2 km.[69]

Titan is the largest object of any type in orbit around Saturn with an atmospheric pressure on the surface 50% greater than that on Earth.


The complex terrain of Ariel is viewed in this image, the best Voyager 2 color picture of the Uranian moon. Credit: NASA/JPL.

"The complex terrain of Ariel is viewed in [the image at right], the best Voyager 2 color picture of the Uranian moon. The individual photos used to construct this composite were taken Jan. 24, 1986, from a distance of 170,000 kilometers (105,000 miles. Voyager captured this view of Ariel's southern hemisphere through the green, blue and violet filters of the narrow-angle camera; the resolution is about 3 km (2 mi). Most of the visible surface consists of relatively intensely cratered terrain transected by fault scarps and fault-bounded valleys (graben). Some of the largest valleys, which can be seen near the terminator (at right), are partly filled with younger deposits that are less heavily cratered. Bright spots near the limb and toward the left are chiefly the rims of small craters. Most of the brightly rimmed craters are too small to be resolved here, although one about 30 km (20 mi) in diameter can be easily distinguished near the center. These bright-rim craters, though the youngest features on Ariel, probably have formed over a long span of geological time. Although Ariel has a diameter of only about 1,200 km (750 mi), it has clearly experienced a great deal of geological activity in the past."[70]


This color composite of the Uranian satellite Miranda was taken by Voyager 2 on January 24, 1986, from a distance of 147,000 kilometers (91,000 miles). Credit: NASA.

"This color composite [at lower right] of the Uranian satellite Miranda was taken by Voyager 2 on Jan. 24, 1986, from a distance of 147,000 kilometers (91,000 miles). This picture was constructed from images taken through the narrow-angle camera's green, violet and ultraviolet filters. It is the best color view of Miranda returned by Voyager."[71]

"Miranda, just 480 km (300 mi) across, is the smallest of Uranus' five major satellites. Miranda's regional geologic provinces show very well in this view of the southern hemisphere, imaged at a resolution of 2.7 km (1.7 mi). The dark- and bright-banded region with its curvilinear traces covers about half of the image. Higher-resolution pictures taken later show many fault valleys and ridges parallel to these bands. Near the terminator (at right), another system of ridges and valleys abuts the banded terrain; many impact craters pockmark the surface in this region. The largest of these are about 30 km (20 mi) in diameter; many more lie in the range of 5 to 10 km (3 to 6 mi) in diameter."[71]


This false color image of Triton is a composite of images taken through the violet, green and ultraviolet filters. Credit: NASA.

"This false color image of Triton is a composite of images taken through the violet, green and ultraviolet filters. The image was taken early on Aug. 25, 1989 when Voyager 2 was about 190,000 kilometers (118,000 miles) from Triton's surface. The smallest visible features are about 4 kilometers (2.5 miles) across. The image shows a geologic boundary between completely dark materials and patchy light/dark materials. A layer of pinkish material stretches across the center of the image. The pinkish layer must be thin because underlying albedo patterns show through. Several features appear to be affected by the thin atmosphere; the elongated dark streaks may represent particulate materials blown in the same direction by prevailing winds, and the white material may be frost deposits. Other features appear to be volcanic deposits including the smooth, dark materials alongside the long, narrow canyons. The streaks themselves appear to originate from very small circular sources, some of which are white, like the source of the prominent streak near the center of the image. The sources may be small volcanic vents with fumarolic-like activity. The colors may be due to irradiated methane, which is pink to red, and nitrogen, which is white."[72]


Pluto fills the frame in an image from NASA's New Horizons spacecraft taken July 13, when the spacecraft was 476,000 miles from the dwarf planet. Credit: NASA EPA.
A composite image of Pluto from 11 July shows high-resolution black-and-white LORRI images colorized with Ralph data. Credit: NASA-JHUAPL-SWRI.

Pluto is the second largest dwarf planet known (after Eris).


Sweeping slowly through northern skies, the comet PanSTARRS C/2012 K1 posed for this telescopic portrait on June 2nd in the constellation Ursa Major. Credit: Alessandro Falesiedi.

A comet is a small solar system body that has a solid icy nucleus. When near the Sun a comet can also have an extremely tenuous atmosphere called the coma which can grow into a large and bright tail.

On the right is a visual image of comet PanSTARRS C/2012 K1.

"Now within the inner solar system, the icy body from the Oort cloud sports two tails, a lighter broad dust tail and crooked ion tail extending below and right. The comet's condensed greenish coma makes a nice contrast with the spiky yellowish background star above. NGC 3319 appears at the upper left of the frame that spans almost twice the apparent diameter of the full Moon."[73]

Kuiper beltsEdit

The plot displays the known positions of objects in the outer Solar System. Credit: WilyD.
  Jupiter trojans
  Giant planets: J · S · U · N
  Kuiper belt
  Scattered disc
  Neptune trojans
Distances but not sizes are to scale
Source: Minor Planet Center, and others

Occasionally inteferences with the large gas giants of our solar system (Jupiter and Saturn) will further alter their orbit. These comets commonly roam in an area called the Kuiper belt, that surrounds the last planet Neptune. The orbits of these comets vary highly from the diminuitive comet Encke (3 years) to the famed comet Halley seen only once maybe twice a lifetime (76 years).

Oort cloudsEdit

This graphic shows the distance from the Oort cloud to the rest of the Solar System and two of the nearest stars measured in astronomical units (AU). The scale is logarithmic, with each specified distance ten times further out than the previous one.
An artist's rendering of the Oort cloud and the Kuiper belt (inset). Sizes of individual objects have been exaggerated for visibility.

Most of the comets lay at the distant reaches of our system in a hypothesized Oort cloud. At the very edge of the solar these comets orbit in very large loops around the distant reaches of our solar system. The passing of nearby stars, or other objects can alter their orbit, sending them speeding towards the inner reaches of our solar system. these comets typically retain very large orbits such that they will not return (once seen in the inner solar system) for many thousands of years.

Scattered discsEdit

The diagram shows scattered disc objects out to 100 AU. Credit: Eurocommuter.

Scattered Disk Objects (up to 100 AU): Kuiper Belt objects are shown in grey, resonant objects within the Scattered Disk are shown in green.

The position of an object represents

  • its orbit’s semi-major axis a in AU and the orbital period in years (horizontal axis)
  • its orbit’s inclination i in degrees (vertical axis).

The size of the circle illustrates the object’s size relative to others. For a few large objects, the diameter drawn represents the best current estimates. For all others, the circles represent the absolute magnitude of the object.

The eccentricity of the orbit is shown indirectly by a segment extending from the left (perihelion) to the aphelion to the right. In other words, the segment illustrates the variations of the object's distance from the Sun. Objects with nearly circular orbits will show short segments while highly elliptical orbits will be represented by long segments.

Main resonances with Neptune are marked with vertical bars; 1:1 marks the position of Neptune’s orbit (and its Trojan asteroids), 2:3 marks the orbit of Pluto (and plutinos) etc.

Solar nebulasEdit

Artist's concept of a protoplanetary disk, where particles of dust and grit collide and accrete forming planets or asteroids. Credit: NASA.

On the right is one artist's concept of a protoplanetary disk, where particles of dust and grit collide and accrete forming planets or asteroids.


  1. Dusts are rocky objects.

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External linksEdit

{{Radiation astronomy resources}}