Editing Asteroid (section)

== Characteristics ==

=== Size distribution ===
[[File:Asteroids by size and number.svg|thumb|The asteroids of the Solar System, categorized by size and number|300x300px]]
{{image frame
|width=256
 | content = {{Graph:Chart
  | width=75
  | height=75
  | type=pie
  | legend=
  | x=Ceres,Vesta,Pallas,Hygiea,Interamnia,Eunomia,other
  | y1=938,259,204,87,35,30,841<!--total 2394x18kg-->
  | showValues=angle:0,format:.0f
          }}
 | caption = The masses of the largest asteroids in the main belt: [[1 Ceres]] (blue), [[4 Vesta]], [[2 Pallas]], [[10 Hygiea]], [[704 Interamnia]], [[15 Eunomia]] and the remainder of the Main Belt (pink). The unit of mass is {{e|18}} kg.}}
Asteroids vary greatly in size, from almost {{val|1000|u=km}} for the largest down to rocks just 1&nbsp;meter across, below which an object is classified as a [[meteoroid]].{{efn|The definition in the 1995 paper (Beech and Steel) has been updated by a 2010 paper (Rubin and Grossman) and the discovery of 1&nbsp;meter asteroids.}} The three largest are very much like miniature planets: they are roughly spherical, have at least partly differentiated interiors,<ref name=Schmidt2007>{{cite journal |title=Hubble Space Telescope Observations of 2&nbsp;Pallas |journal=Bulletin of the American Astronomical Society |volume=39 |page=485 |date=2007 |display-authors=6 |last1=Schmidt |first1= B. |last2=Russell |first2= C.T. |last3=Bauer |first3= J.M. |last4=Li |first4= J. |last5=McFadden |first5= L.A. |last6=Mutchler |first6= M. |last7=Parker |first7= J.W. |last8=Rivkin |first8= A.S. |last9=Stern |first9= S.A. |author10=Thomas, P.C. |bibcode=2007DPS....39.3519S}}</ref> and are thought to be surviving [[protoplanet]]s. The vast majority, however, are much smaller and are irregularly shaped; they are thought to be either battered [[planetesimal]]s or fragments of larger bodies.

The [[dwarf planet]] [[Ceres (dwarf planet)|Ceres]] is by far the largest asteroid, with a diameter of {{cvt|940|km|-1}}. The next largest are [[4 Vesta]] and [[2 Pallas]], both with diameters of just over {{cvt|500|km|-2}}. Vesta is the brightest of the four main-belt asteroids that can, on occasion, be visible to the naked eye.<ref>{{cite book | title=The Observer's Guide to Astronomy | volume=1 | series=Practical Astronomy Handbooks | editor-first=Patrick | editor-last=Martinez | translator-last1=Dunlop | translator-first1=Storm | publisher=Cambridge University Press | date=1994 | isbn=978-0-521-37945-8 | page=297 | url=https://books.google.com/books?id=k5iUVz7iFTQC&pg=PA297 }}</ref> On some rare occasions, a near-Earth asteroid may briefly become visible without technical aid; see [[99942 Apophis]].

The mass of all the objects of the [[asteroid belt]], lying between the orbits of [[Mars]] and [[Jupiter]], is estimated to be {{val|2394|6|e=18|u=kg}}, ≈&thinsp;3.25% of the mass of the Moon. Of this, [[Ceres (dwarf planet)|Ceres]] comprises {{val|938|e=18|u=kg}}, about 40% of the total. Adding in the next three most massive objects, [[4 Vesta|Vesta]] (11%), [[2 Pallas|Pallas]] (8.5%), and [[10 Hygiea|Hygiea]] (3–4%), brings this figure up to a bit over 60%, whereas the next seven most-massive asteroids bring the total up to 70%.<ref name="Pitjeva2018"/> The number of asteroids increases rapidly as their individual masses decrease.

The number of asteroids decreases markedly with increasing size. Although the size distribution generally follows a [[power law]], there are 'bumps' at about {{val|5|u=km}} and {{val|100|u=km}}, where more asteroids than expected from such a curve are found. Most asteroids larger than approximately 120&nbsp;km in diameter are primordial (surviving from the accretion epoch), whereas most smaller asteroids are products of fragmentation of primordial asteroids. The primordial population of the main belt was probably 200 times what it is today.<ref>{{Cite journal |last1=Bottkejr |first1=W |last2=Durda |first2=D |last3=Nesvorny |first3=D |last4=Jedicke |first4=R |last5=Morbidelli |first5=A |last6=Vokrouhlicky |first6=D |last7=Levison |first7=H |date=May 2005 |title=The fossilized size distribution of the main asteroid belt |url=https://linkinghub.elsevier.com/retrieve/pii/S0019103504003811 |journal=Icarus|volume=175 |issue=1 |pages=111–140 |doi=10.1016/j.icarus.2004.10.026|bibcode=2005Icar..175..111B }}</ref><ref>{{Cite journal |last1=O'Brien |first1=David P. |last2=Sykes |first2=Mark V. |date=December 2011 |title=The Origin and Evolution of the Asteroid Belt{{snd}}Implications for Vesta and Ceres |url=http://link.springer.com/10.1007/s11214-011-9808-6 |journal=Space Science Reviews|volume=163 |issue=1–4 |pages=41–61 |doi=10.1007/s11214-011-9808-6 |bibcode=2011SSRv..163...41O |s2cid=121856071 |issn=0038-6308}}</ref>

====Largest asteroids====
{{See also|Largest asteroids}}

{{Multiple image
| direction         = vertical
| image1            = 42 of the largest objects in the asteroid belt.jpg
| caption1          = 42 of the largest objects in the asteroid belt captured by [[European Southern Observatory|ESO]]'s [[Very Large Telescope]]
| image2            = Eros, Vesta and Ceres size comparison.jpg
| caption2          = Eros, Vesta and Ceres size comparison
| total_width       = 250
}}

Three largest objects in the asteroid belt, [[Ceres (dwarf planet)|Ceres]], [[4 Vesta|Vesta]], and [[2 Pallas|Pallas]], are intact [[protoplanet]]s that share many characteristics common to planets, and are atypical compared to the majority of irregularly shaped asteroids. The fourth-largest asteroid, [[10 Hygiea|Hygiea]], appears nearly spherical although it may have an undifferentiated interior,<ref>{{Cite web|title=Asteroids {{!}} Imaging the Universe|url=http://astro.physics.uiowa.edu/ITU/labs/general-astronomy/asteroids/|access-date=2021-08-31|website=astro.physics.uiowa.edu|archive-date=31 August 2021|archive-url=https://web.archive.org/web/20210831200522/http://astro.physics.uiowa.edu/ITU/labs/general-astronomy/asteroids/|url-status=dead}}</ref> like the majority of asteroids. The four largest asteroids constitute half the mass of the asteroid belt.

Ceres is the only asteroid that appears to have a [[Plasticity (physics)|plastic]] shape under its own gravity and hence the only one that is a [[dwarf planet]].<ref name=IAU-2006/> It has a much higher [[Absolute magnitude#Solar System bodies (H)|absolute magnitude]] than the other asteroids, of around 3.32,<ref name=AstJ-2002-v123-p549/> and may possess a surface layer of ice.<ref name="planetary"/> Like the planets, Ceres is differentiated: it has a crust, a mantle and a core.<ref name="planetary"/> No meteorites from Ceres have been found on Earth.<ref name=satellites/>

Vesta, too, has a differentiated interior, though it formed inside the Solar System's [[Frost line (astrophysics)|frost line]], and so is devoid of water;<ref>{{cite press release |title=Asteroid or mini-planet? Hubble maps the ancient surface of Vesta |date=19 April 1995 |id=STScI-1995-20 |url=http://hubblesite.org/news_release/news/1995-20 |website=Hubble Space Telescope |publisher=Space Telescope Science Institute |access-date=16 December 2017}}<br />{{cite press release |title=Key stages in the evolution of the asteroid Vesta |website=Hubble Space Telescope |publisher=Space Telescope Science Institute |date=19 April 1995 |url=http://hubblesite.org/newscenter/newsdesk/archive/releases/1995/20/image/c |access-date=20 October 2007 |url-status=live |archive-url=https://web.archive.org/web/20080907192327/http://hubblesite.org/newscenter/newsdesk/archive/releases/1995/20/image/c |archive-date=7 September 2008}}</ref><ref>
{{cite journal |last1=Russel |first1=C. |last2=Raymond |first2=C. |last3=Fraschetti |first3=T. |last4=Rayman |first4=M. |last5=Polanskey |first5=C. |last6=Schimmels |first6=K. |last7=Joy |first7=S. |year=2005 |title=Dawn mission and operations |journal=Proceedings of the International Astronomical Union |volume=1 |issue=S229 |pages=97–119 |bibcode=2006IAUS..229...97R |doi=10.1017/S1743921305006691 |doi-access=free }}</ref> its composition is mainly of basaltic rock with minerals such as olivine.<ref>{{cite journal |last=Burbine |first=T.H. |date=July 1994 |title=Where are the olivine asteroids in the main belt? |journal=Meteoritics |volume=29 |issue=4 |page=453 |bibcode-access=free |bibcode=1994Metic..29..453B}}</ref> Aside from the large crater at its southern pole, [[Rheasilvia]], Vesta also has an ellipsoidal shape. Vesta is the parent body of the [[Vestian family]] and other [[V-type asteroid]]s, and is the source of the [[HED meteorite]]s, which constitute 5% of all meteorites on Earth.

Pallas is unusual in that, like [[Uranus]], it rotates on its side, with its axis of rotation tilted at high angles to its orbital plane.<ref name="Torppa1996"/> Its composition is similar to that of Ceres: high in carbon and silicon, and perhaps partially differentiated.<ref name=Icarus-1983-v56-p398/> Pallas is the parent body of the [[Palladian family]] of asteroids.

Hygiea is the largest carbonaceous asteroid<ref name=Icarus-2002-156-p202/> and, unlike the other largest asteroids, lies relatively close to the [[plane of the ecliptic]]. It is the largest member and presumed parent body of the [[Hygiean family]] of asteroids. Because there is no sufficiently large crater on the surface to be the source of that family, as there is on Vesta, it is thought that Hygiea may have been completely disrupted in the collision that formed the Hygiean family and recoalesced after losing a bit less than 2% of its mass. Observations taken with the [[Very Large Telescope]]'s [[VLT-SPHERE|SPHERE]] imager in 2017 and 2018, revealed that Hygiea has a nearly spherical shape, which is consistent both with it being in [[hydrostatic equilibrium]], or formerly being in hydrostatic equilibrium, or with being disrupted and recoalescing.<ref name=NatAstr-2019-10-28/><ref name=Strickland2019/>

Internal differentiation of large asteroids is possibly related to their lack of [[natural satellite]]s, as satellites of main belt asteroids are mostly believed to form from collisional disruption, creating a [[rubble pile]] structure.<ref name=satellites>{{cite journal|title=Dawn mission's search for satellites of Ceres: Intact protoplanets don't have satellites|journal=Icarus|volume=316|date=December 2018|pages=191–204|author1-first=Lucy A.|author1-last=McFadden |author2-first=David R. |author2-last=Skillman |author3-first=N |author3-last=Memarsadeghi |doi=10.1016/j.icarus.2018.02.017|bibcode=2018Icar..316..191M |s2cid=125181684 |quote=Examination of the physical properties of the 41 largest and most massive main belt asteroids suggests that large asteroids without satellites are intact and their interiors have internal strength. This is consistent with results from the Dawn mission at both Vesta and Ceres. Ceres' volatile-rich composition also is a likely contributor to both the absence of satellites at Ceres and of Ceres meteorites at Earth. These results suggest that collisional disruption creating rubble pile structure is a necessary condition for formation of satellites around main belt asteroids.}}</ref>

{| class="wikitable"
|+ Attributes of largest asteroids
|- style="font-size: smaller;"
!Name
!Orbital<br />radius<br />([[Astronomical unit|AU]])
![[Orbital period|Orbital<br />period]]<br />(years)
![[Inclination|Inclination<br />to ecliptic]]
![[Orbital eccentricity|Orbital<br />eccentricity]]
! Diameter<br />(km)
! Diameter<br />(% of [[Moon]])
! Mass<br />({{e|18}} kg)
! Mass<br />(% of Ceres)
! Density<br />(g/cm<sup>3</sup>)
! Rotation<br />period<br />(hr)
|- style="text-align:center;"
! style="text-align:left;"| [[Ceres (dwarf planet)|Ceres]]
| 2.77
| 4.60
| 10.6°
| 0.079
| 964×964×892<br />(mean 939.4)
| 27%
| 938
| 100%
| 2.16±0.01
| 9.07
|- style="text-align:center;"
! style="text-align:left;"| [[4 Vesta|Vesta]]
| 2.36
| 3.63
| 7.1°
| 0.089
| 573×557×446<br />(mean 525.4)
| 15%
| 259
| 28%
| 3.46 ± 0.04
| 5.34
|- style="text-align:center;"
! style="text-align:left;"| [[2 Pallas|Pallas]]
| 2.77
| 4.62
| 34.8°
| 0.231
| 550×516×476<br />(mean 511±4)
| 15%
| 204±3
| 21%
| 2.92±0.08
| 7.81
|- style="text-align:center;"
! style="text-align:left;"| [[10 Hygiea|Hygiea]]
| 3.14
| 5.56
| 3.8°
| 0.117
| 450×430×424<br />(mean 433±8)
| 12%
| 87±7
| 9%
| 2.06±0.20
| 13.8
|}

=== Rotation ===
{{Further|List of fast rotators (minor planets)|List of slow rotators (minor planets)}}
Measurements of the rotation rates of large asteroids in the asteroid belt show that there is an upper limit. Very few asteroids with a diameter larger than 100 meters have a rotation period less than 2.2&nbsp;hours.<ref>{{cite web |title=About Lightcurves |series=Asteroid Lightcurve Photometry Database |website=ALCDEF |date=4 December 2018 |url=http://alcdef.org/ |access-date=27 December 2018}}</ref> For asteroids rotating faster than approximately this rate, the inertial force at the surface is greater than the gravitational force, so any loose surface material would be flung out. However, a solid object should be able to rotate much more rapidly. This suggests that most asteroids with a diameter over 100 meters are [[rubble pile]]s formed through the accumulation of debris after collisions between asteroids.<ref name=Rossi-2004/>

=== Color ===
Asteroids become darker and redder with age due to [[space weathering]].<ref name="UHi2005-05-19" /> However evidence suggests most of the color change occurs rapidly, in the first hundred thousand years, limiting the usefulness of spectral measurement for determining the age of asteroids.<ref name="Courtland-2009" />

=== Surface features ===
[[File:Vesta Cratered terrain with hills and ridges.jpg|thumb|Cratered terrain on 4 Vesta]]

Except for the "[[List of exceptional asteroids#Largest by mass|big four]]" (Ceres, Pallas, Vesta, and Hygiea), asteroids are likely to be broadly similar in appearance, if irregular in shape. {{convert|50|km|mi|abbr=on}} [[253 Mathilde]] is a rubble pile saturated with craters with diameters the size of the asteroid's radius. Earth-based observations of {{convert|300|km|mi|abbr=on}} [[511 Davida]], one of the largest asteroids after the big four, reveal a similarly angular profile, suggesting it is also saturated with radius-size craters.<ref name="Icarus-2007-v191-p616" /> Medium-sized asteroids such as Mathilde and [[243 Ida]], that have been observed up close, also reveal a deep [[regolith]] covering the surface. Of the big four, Pallas and Hygiea are practically unknown. Vesta has compression fractures encircling a radius-size crater at its south pole but is otherwise a [[spheroid]].

''[[Dawn (spacecraft)|Dawn spacecraft]]'' revealed that Ceres has a heavily cratered surface, but with fewer large craters than expected.<ref name="marchi">{{cite journal |last1=Marchi |first1=S. |last2=Ermakov |first2=A. I. |last3=Raymond |first3=C. A. |last4=Fu |first4=R. R. |last5=O'Brien |first5=D. P. |last6=Bland |first6=M. T. |last7=Ammannito |first7=E. |last8=De Sanctis |first8=M. C. |last9=Bowling |first9=T. |last10=Schenk |first10=P. |last11=Scully |first11=J. E. C. |date=26 July 2016 |title=The missing large impact craters on Ceres |journal=[[Nature Communications]] |volume=7 |pages=12257 |bibcode=2016NatCo...712257M |doi=10.1038/ncomms12257 |pmc=4963536 |pmid=27459197 |last12=Buczkowski |first12=D. L. |last13=Williams |first13=D. A. |last14=Hiesinger |first14=H. |last15=Russell |first15=C. T.}}</ref> Models based on the formation of the current asteroid belt had suggested Ceres should possess 10 to 15 craters larger than {{convert|400|km|mi|abbr=on}} in diameter.<ref name="marchi" /> The largest confirmed crater on Ceres, [[Kerwan (crater)|Kerwan Basin]], is {{convert|284|km|mi|abbr=on}} across.<ref>{{cite journal |last=David A. Williams |first= T. Kneiss |date=December 2018 |title=The geology of the Kerwan quadrangle of dwarf planet Ceres: Investigating Ceres' oldest, largest impact basin |url=https://www.sciencedirect.com/science/article/abs/pii/S0019103516305632 |url-status=live |journal=Icarus |volume=316 |pages=99–113 |bibcode=2018Icar..316...99W |doi=10.1016/j.icarus.2017.08.015 |archive-url=https://web.archive.org/web/20210816123323/https://www.sciencedirect.com/science/article/abs/pii/S0019103516305632?via%3Dihub |archive-date=16 August 2021 |access-date=16 August 2021 |s2cid=85539501}}</ref> The most likely reason for this is [[Viscoelasticity|viscous relaxation]] of the crust slowly flattening out larger impacts.<ref name="marchi" />

=== Composition ===
Asteroids are classified by their characteristic [[Emission spectrum|emission spectra]], with the majority falling into three main groups: [[C-type asteroid|C-type]], [[M-type asteroid|M-type]], and [[S-type asteroid|S-type]]. These describe carbonaceous ([[Carbon|carbon-rich]]), [[metal]]lic, and [[silica]]ceous (stony) compositions, respectively. The physical composition of asteroids is varied and in most cases poorly understood. Ceres appears to be composed of a rocky core covered by an icy mantle; Vesta is thought to have a [[nickel-iron]] core, [[olivine]] mantle, and basaltic crust.<ref name="Hubble-Vespa-1995-04-19" /> Thought to be the largest undifferentiated asteroid, [[10 Hygiea]] seems to have a uniformly primitive composition of [[carbonaceous chondrite]], but it may actually be a differentiated asteroid that was globally disrupted by an impact and then reassembled. Other asteroids appear to be the remnant cores or mantles of proto-planets, high in rock and metal. Most small asteroids are believed to be piles of rubble held together loosely by gravity, although the largest are probably solid. Some asteroids have [[Asteroid moon|moons]] or are co-orbiting [[binary asteroid|binaries]]: rubble piles, moons, binaries, and scattered [[asteroid family|asteroid families]] are thought to be the results of collisions that disrupted a parent asteroid, or possibly a [[disrupted planet|planet]].<ref name="ARX-20060816" />

In the main asteroid belt, there appear to be two primary populations of asteroid: a dark, volatile-rich population, consisting of the [[C-type asteroid|C-type]] and [[P-type asteroid|P-type]] asteroids, with albedos less than 0.10 and densities under {{val|2.2|u=g/cm3}}, and a dense, volatile-poor population, consisting of the [[S-type asteroid|S-type]] and [[M-type asteroid|M-type]] asteroids, with albedos over 0.15 and densities greater than 2.7. Within these populations, larger asteroids are denser, presumably due to compression. There appears to be minimal macro-porosity (interstitial vacuum) in the score of asteroids with masses greater than {{val|10|e=18|u=kg}}.<ref name="VLT">P. Vernazza et al. (2021) VLT/SPHERE imaging survey of the largest main-belt asteroids: Final results and synthesis. ''Astronomy & Astrophysics'' 54, A56</ref>

Composition is calculated from three primary sources: [[albedo]], surface spectrum, and density. The last can only be determined accurately by observing the orbits of moons the asteroid might have. So far, every asteroid with moons has turned out to be a rubble pile, a loose conglomeration of rock and metal that may be half empty space by volume. The investigated asteroids are as large as 280&nbsp;km in diameter, and include [[121 Hermione]] (268×186×183&nbsp;km), and [[87 Sylvia]] (384×262×232&nbsp;km). Few asteroids are [[List of notable asteroids#Largest by diameter|larger than 87&nbsp;Sylvia]], none of them have moons. The fact that such large asteroids as Sylvia may be rubble piles, presumably due to disruptive impacts, has important consequences for the formation of the Solar System: computer simulations of collisions involving solid bodies show them destroying each other as often as merging, but colliding rubble piles are more likely to merge. This means that the cores of the planets could have formed relatively quickly.<ref name="Icarus-2011-02-p1022" />

==== Water ====
{{Main|Asteroidal water}}

Scientists hypothesize that some of the first water brought to Earth was delivered by asteroid impacts after the collision that produced the [[Moon]].<ref name="Campins2010" /> In 2009, the presence of [[ice|water ice]] was confirmed on the surface of [[24 Themis]] using NASA's [[Infrared Telescope Facility]]. The surface of the asteroid appears completely covered in ice. As this ice layer is [[Sublimation (phase transition)|sublimating]], it may be getting replenished by a reservoir of ice under the surface. Organic compounds were also detected on the surface.<ref name="Cowen-2009" /><ref name="Atkinson-2009" /><ref name="Campins2010" /><ref name="RivkinEmery2010" /> The presence of ice on 24 Themis makes the initial theory plausible.<ref name="Campins2010" />

In October 2013, water was detected on an extrasolar body for the first time, on an asteroid orbiting the [[white dwarf]] [[GD 61]].<ref>{{Cite web|url=https://keckobservatory.org/watery_asteroid_discovered_in_dying_star_points_to_habitable_exoplanets/|title=Watery Asteroid Discovered in Dying Star Points to Habitable Exoplanets – W. M. Keck Observatory|date=10 October 2013 }}</ref> On 22&nbsp;January 2014, [[European Space Agency]] (ESA) scientists reported the detection, for the first definitive time, of [[water vapor]] on [[Ceres (dwarf planet)|Ceres]], the largest object in the asteroid belt.<ref name="KüppersO'Rourke2014" /> The detection was made by using the [[Far-infrared astronomy|far-infrared abilities]] of the [[Herschel Space Observatory]].<ref name="NASA-20140122" /> The finding is unexpected because comets, not asteroids, are typically considered to "sprout jets and plumes". According to one of the scientists, "The lines are becoming more and more blurred between comets and asteroids."<ref name="NASA-20140122" />

Findings have shown that [[solar wind]]s can react with the oxygen in the upper layer of the asteroids and create water. It has been estimated that "every cubic metre of irradiated rock could contain up to 20 litres"; study was conducted using an atom probe tomography, numbers are given for the Itokawa S-type asteroid.<ref>{{cite journal |last1=Daly |first1=Luke |last2=Lee |first2=Martin R. |last3=Hallis |first3=Lydia J. |last4=Ishii |first4=Hope A. |last5=Bradley |first5=John P. |last6=Bland |first6=Phillip A. |last7=Saxey |first7=David W. |last8=Fougerouse |first8=Denis |last9=Rickard |first9=William D. A. |last10=Forman |first10=Lucy V. |last11=Timms |first11=Nicholas E. |last12=Jourdan |first12=Fred |last13=Reddy |first13=Steven M. |last14=Salge |first14=Tobias |last15=Quadir |first15=Zakaria |last16=Christou |first16=Evangelos |last17=Cox |first17=Morgan A. |last18=Aguiar |first18=Jeffrey A. |last19=Hattar |first19=Khalid |last20=Monterrosa |first20=Anthony |last21=Keller |first21=Lindsay P. |last22=Christoffersen |first22=Roy |last23=Dukes |first23=Catherine A. |last24=Loeffler |first24=Mark J. |last25=Thompson |first25=Michelle S. |title=Solar wind contributions to Earth's oceans |journal=Nature Astronomy |date=December 2021 |volume=5 |issue=12 |pages=1275–1285 |doi=10.1038/s41550-021-01487-w |bibcode=2021NatAs...5.1275D |osti=1834330 |s2cid=244744492 |url=https://www.nature.com/articles/s41550-021-01487-w |access-date=30 March 2022|issn=2397-3366}}</ref><ref>{{cite web |title=Earth's water may have been formed by solar winds |url=https://www.nhm.ac.uk/discover/news/2021/december/earth-s-water-may-have-been-formed-by-solar-winds.html |website=nhm.ac.uk |access-date=30 March 2022}}</ref>

Acfer 049, a meteorite discovered in Algeria in 1990, was shown in 2019 to have an ultraporous lithology (UPL): porous texture that could be formed by removal of ice that filled these pores, this suggests that UPL "represent fossils of primordial ice".<ref>{{cite journal |last1=Matsumoto |first1=Megumi |last2=Tsuchiyama |first2=Akira |last3=Nakato |first3=Aiko |last4=Matsuno |first4=Junya |last5=Miyake |first5=Akira |last6=Kataoka |first6=Akimasa |last7=Ito |first7=Motoo |last8=Tomioka |first8=Naotaka |last9=Kodama |first9=Yu |last10=Uesugi |first10=Kentaro |last11=Takeuchi |first11=Akihisa |last12=Nakano |first12=Tsukasa |last13=Vaccaro |first13=Epifanio |title=Discovery of fossil asteroidal ice in primitive meteorite Acfer 094 |journal=Science Advances |date=November 2019 |volume=5 |issue=11 |pages=eaax5078 |doi=10.1126/sciadv.aax5078|pmid=31799392 |pmc=6867873 |bibcode=2019SciA....5.5078M }}</ref>

==== Organic compounds ====

Asteroids contain traces of [[amino acid]]s and other organic compounds, and some speculate that asteroid impacts may have seeded the early Earth with the chemicals necessary to initiate life, or may have even brought life itself to Earth (an event called "[[panspermia]]").<ref name="SPACE-2001-12-19" /><ref name="Reuell-2019" /> In August&nbsp;2011, a report, based on [[NASA]] studies with [[meteorite]]s found on [[Earth]], was published suggesting [[DNA]] and [[RNA]] components ([[adenine]], [[guanine]] and related [[organic molecules]]) may have been formed on asteroids and [[comet]]s in [[outer space]].<ref name="Callahan" /><ref name="Steigerwald" /><ref name="DNA" />

In November 2019, scientists reported detecting, for the first time, [[Sugar|sugar molecules]], including [[ribose]], in [[meteorite]]s, suggesting that chemical processes on asteroids can produce some fundamentally essential bio-ingredients important to [[life]], and supporting the notion of an [[RNA world]] prior to a DNA-based [[Abiogenesis|origin of life]] on Earth, and possibly, as well, the notion of [[panspermia]].<ref name="NASA-20191118" /><ref name="PNAS-20191118" /><ref>{{Cite web |last=Steigerwald |first=Bill |date=2022-03-31 |title=Could the Blueprint for Life Have Been Generated in Asteroids? |url=http://www.nasa.gov/feature/goddard/2022/life-blueprint-in-asteroids |access-date=2022-07-06 |website=NASA}}</ref>