2_Pallas - Wikiparency

# 2 Pallas  **Microsim — three.js (Wikitube framework):** *2 Pallas in the Solar System explorer* <div class="wt-sim" data-src="https://wikitube-3d-microsims.netlify.app/solar/Solar_System.html?obj=Pallas&embed=1" data-title="2 Pallas in the Solar System explorer"></div> *The Solar System explorer locked on this article's state (`?obj=Pallas`); every object and population of the [[PORTAL_Solar_System|Solar System portal]] has its own state in the same scene.*  *Try: drag the view round until the belt is seen edge-on and watch Pallas climb far above and dive far below the thin band where Ceres and Vesta travel, the effect of its 34.9° tilt; set the speed to 1 year/s to see it cross the plane twice on each lap of about four and a half seconds; press o to hide the orbits and follow Pallas against the belt alone.* **Pallas** (minor-planet designation **2 Pallas**) is the third-largest body in the [[Asteroid_belt|asteroid belt]], about 513 km across, after [[Ceres_(dwarf_planet)|Ceres]] and [[4_Vesta|Vesta]].[^marsset2020][^russell2012] Heinrich Olbers found it on 28 March 1802, fifteen months after Ceres, and like the other early [[Asteroid|asteroids]] it was listed for decades as a planet.[^hilton2001][^dawn-serendipity] It holds about 79% of Vesta's mass and 22% of Ceres's, roughly 8% of the belt in all (derived from the cited masses), and is thought to be one of the few protoplanets from the era of planet formation that survived intact.[^mccord2006][^pitjeva2018] What sets Pallas apart is its orbit. Although its average distance from the [[Sun]] is typical of the middle of the belt, the orbit is tilted about 35° to the [[Ecliptic|ecliptic]] and is markedly eccentric, so collisions on Pallas are unusually violent and the body is hard to reach by spacecraft.[^jpl-pallas][^marsset2020] Its surface resembles primitive carbonaceous chondrite meteorites that have been altered less by water than those matching Ceres, and high-resolution imaging shows it to be covered in large craters.[^carry2010][^marsset2020] No spacecraft has visited it.[^eso2020] The explorer at the top of this page is locked on Pallas, drawn on its catalogued orbit with its tilt of 34.9° to the ecliptic; its disc, 511 km across in the explorer's data, is enlarged by the log size law.[^jpl-pallas][^jpl-sbdb] ## History ### Discovery Pallas had been seen before it was recognised. On 5 April 1779 Charles Messier, following the comet now designated C/1779 A1 (Bode), marked it on his chart as an ordinary star.[^bourtembourg2012] The real discovery followed from the hunt for Ceres. After Giuseppe Piazzi's object was lost in the Sun's glare, Carl Friedrich Gauss computed its orbit and Franz Xaver von Zach and Olbers recovered it at the end of 1801.[^hoskin1992][^forbes1971] Olbers was still following Ceres in March 1802 when he noticed a second moving object nearby; the two happened to be passing close together in the sky.[^dawn-serendipity] Gauss determined its orbit too and found a period of about 4.6 years, much like Ceres's, but on a far steeper plane.[^dawn-serendipity] A second body where a single missing planet had been expected was a surprise. It led William Herschel to propose the category "asteroid" and Olbers to suggest that both objects were fragments of a destroyed planet, an idea that did not survive.[^herschel1802][^mccord2006] The size was badly overestimated at first; some early values were as high as 3,380 km, and as recently as 1979 Pallas was put at 673 km, about 26% more than today's figure.[^hilton2001][^hilton2002] ### Later observations In 1917 Kiyotsugu Hirayama began grouping asteroids by their orbital elements, and he later identified three that were associated with Pallas, the start of the Pallas family.[^kozai1994] More members have been found since the 1990s, with semi-major axes of 2.50–2.82 AU and inclinations of 33–38°, and their shared spectra support a common origin.[^foglia1999] Stellar occultations fixed its size and shape. The event of 29 May 1983, timed by some 140 observers as Pallas passed in front of the star 1 Vulpeculae, is among the best-observed asteroid occultations and gave the first accurate diameter.[^dunham1990][^drummond1989] Its mass has been estimated from its pull on other asteroids and on the motion of [[Mars]], tracked by spacecraft in orbit and on the surface.[^pitjeva2004][^baer2011] In September 2007 the Dawn team used the Hubble Space Telescope during a close approach of Pallas to [[Earth]] that recurs only about every twenty years, to obtain comparison data for Ceres and Vesta.[^schmidt2008][^jpl2007] ### Name and symbol The name is one of the epithets of Athena, the Greek goddess of wisdom.[^james2006] The adjective is Palladian. Palladium, discovered in 1803, was named after the asteroid; the stony-iron pallasite meteorites, by contrast, are named after the naturalist Peter Simon Pallas.[^lanl-pd] Its traditional symbol is a spear or lance, one of Athena's emblems. As with the other early asteroids, it gave way after 1852 to the generic numbered disc.[^forbes1971][^gould1852] ## Orbit and rotation Pallas has a semi-major axis of about 2.77 AU, almost the same as Ceres's, and an orbital period of about 4.6 years, but its orbit is inclined 34.9° to the ecliptic and has an eccentricity of about 0.23, nearly as large as [[Pluto]]'s.[^jpl-pallas][^planetary-soc] Its distance from the Sun therefore ranges from about 2.13 to 3.41 AU (derived from a and e). The steep tilt carries it far above and below the rest of the belt, and at the points where it crosses the belt's plane it meets other asteroids at roughly twice the average impact speed on Ceres or Vesta.[^marsset2020] Its high inclination also brings it close in the sky to stars that other bodies never approach: on 9 October 2022 it passed only 8.5 arcminutes from Sirius, a star no planet can come within 30° of.[^lutz2021] The spin axis is almost as extreme. Carry and colleagues found an axial tilt of about 84°, with the north pole pointing to ecliptic latitude 30° and longitude −16° (±5°).[^carry2010] Pallas rotates in about 7.8 hours, so its day is ordinary, but with the axis lying close to its orbital plane much of each hemisphere spends months in unbroken sunlight or darkness, and regions near the poles can stay sunlit for as long as two years.[^carry2010] ### Near resonances Pallas is close to a 1:1 resonance with [[Ceres_(dwarf_planet)|Ceres]], a near-match in orbital period that is probably coincidental and has no significant long-term effect.[^goffin2001] It also lies near an 18:7 resonance with [[Jupiter]], with a period of about 91,000 years, and approximately near a 5:2 resonance with an 83-year period.[^taylor1982] ### Transits of planets from Pallas Seen from Pallas, [[Mercury_(planet)|Mercury]], [[Venus]], Mars and Earth can occasionally cross the face of the Sun. Earth did so in 1968 and 1998 and will next in 2224; Mercury did so in October 2009; the last and next transits of Venus are in 1677 and 2123, and those of Mars in 1597 and 2759.[^solex] ## Physical characteristics Vesta and Pallas have traded the title of second-largest asteroid over the years.[^planetary-soc] With a volume-equivalent diameter of about 513 km, Pallas is now known to be slightly smaller than Vesta, at 525.4 km, and it is less massive, with under 0.3% of the mass of the [[Moon]] (derived).[^marsset2020][^russell2012] Its bulk density, about 2.89 g/cm³, matches that of CM carbonaceous chondrites.[^marsset2020] At the resulting mass of about 2.0 × 10²⁰ kg its surface [[Gravity|gravity]] is roughly 0.2 m/s² (derived from G, M and R).[^openstax] Pallas is fainter from [[Earth]] than [[4_Vesta|Vesta]] because it is farther away and much darker. Its mean opposition magnitude is +8.0, easily within reach of binoculars, and at rare perihelic oppositions it can reach +6.4, at the limit of naked-eye visibility; at small elongations it falls as low as +10.6.[^menzel1983][^odeh] The small asteroid 7 Iris is marginally brighter on average at opposition.[^odeh] Spectrally Pallas is a B type, with an almost flat, slightly bluish visible and near-infrared spectrum and a single clear absorption near 3 micrometres.[^carry2010] The surface is dominated by iron-poor silicates with little water, similar to the material of CM chondrules, and the closest meteorite match is the Renazzo (CR) carbonaceous chondrites, which contain even fewer hydrated minerals than CM types.[^feierberg1982][^sato1997] Pallas is therefore interpreted as a body of broadly Ceres-like, primitive composition that was altered by water far less than Ceres.[^marsset2020] Imaging with SPHERE, the adaptive-optics imager on the European Southern Observatory's Very Large Telescope, shows a surface saturated with craters. Because impacts on Pallas are on average about twice as fast as on Ceres or Vesta, smaller and more common impactors dig craters of a given size, and craters larger than 40 km cover at least 9% of the surface.[^marsset2020] Pallas is not in hydrostatic equilibrium, so it does not qualify as a [[Dwarf_planet|dwarf planet]].[^carry2010] Marsset and colleagues identify a probable large basin near the south pole whose formation removed about 6% of the body's volume, roughly twice the volume excavated by Rheasilvia on Vesta; without it Pallas would be close to the equilibrium shape for a 6.2-hour spin, and the impact may have slowed its rotation and raised its inclination. A smaller crater near the equator is linked to the Pallas family.[^marsset2020] The interior is probably fairly uniform. The close match to CM chondrites suggests that Pallas never reached the roughly 820 K needed to dehydrate its silicates and form a dry core beneath a wet mantle. Some water may nonetheless have migrated outward, and salt deposits left behind could explain a bright spot in the southern hemisphere reminiscent of those on Ceres. If the near-Earth asteroid 3200 Phaethon is a fragment of Pallas, as has been proposed, a salt-rich surface would also account for the sodium seen in the Geminid [[Meteor_shower|meteor shower]] that Phaethon produces.[^marsset2020] ### Surface features Apart from that bright spot, the only features identified on Pallas are craters. By 2020, 36 had been catalogued, 34 of them larger than 40 km, and provisional names drawn from ancient weapons, such as Xiphos (a sword), Doru (a spear) and Sarissa (a pike), were given to some of them.[^marsset2020] ## Satellites No moon of Pallas has been confirmed. An occultation in May 1978 prompted a suggestion that a satellite about 1 km across accompanied it. In 1980 speckle interferometry suggested a much larger companion, but later occultation data ruled that out.[^johnston2007] Johnston's catalogue of reported asteroid companions lists both claims as unconfirmed, whereas moons have been securely detected around a number of smaller main-belt [[Asteroid|asteroids]]. Later high-resolution imaging of Pallas has not revealed any satellite.[^johnston2007][^marsset2020] ## Exploration No spacecraft has visited Pallas. Its steep orbit is the main obstacle: reaching it requires a large change in the plane of a spacecraft's [[Orbit|orbit]] as well as in its distance from the [[Sun]], and plane changes are among the most expensive manoeuvres in propellant.[^eso2020][^perozzi2001] A flyby of Pallas was considered for the Dawn mission, which visited [[4_Vesta|Vesta]] and [[Ceres_(dwarf_planet)|Ceres]] with ion propulsion, but it was not feasible because of this inclination.[^rayman2014] The most developed proposal was Athena, a small spacecraft that would have launched in 2022 as a secondary payload with NASA's Psyche mission and then flown past Pallas on its own trajectory.[^orourke2019][^dorminey2019] Its proposers described Pallas as the largest unexplored protoplanet in the main belt. Athena was proposed to NASA's SIMPLEx small-mission programme but was not among the concepts selected as finalists in 2019.[^lpi2019] Pallas thus remains the largest main-belt body known only from telescopes; the best views come from adaptive-optics imaging from the ground.[^marsset2020][^vernazza2021] ## Gallery All images of Pallas come from telescopes, since no spacecraft has approached it. The first well-resolved images come from the Hubble Space Telescope, which in 2007 recorded Pallas during its close approach to [[Earth]] and was used to measure its shape, size and surface brightness for comparison with Ceres and Vesta.[^schmidt2008][^jpl2007] Adaptive-optics observations with the Keck telescopes and others were combined with occultation timings to build the first detailed three-dimensional shape model and to measure its spin axis.[^carry2010] The sharpest images are those taken in 2019–2020 with SPHERE on the Very Large Telescope as part of a survey of the largest main-belt asteroids; released by ESO under the title "Golf Ball World", they show a surface pocked with large craters and a bright southern spot.[^eso2020][^vernazza2021] Orbit diagrams showing the steep inclination of Pallas's path relative to the planets and the other large asteroids are also commonly used; the explorer above gives the same comparison in three dimensions.[^jpl-pallas] ## See also - [[Asteroid_belt]] · [[Asteroid]] - [[Ceres_(dwarf_planet)]] · [[4_Vesta]] · [[10_Hygiea]] - [[Meteor_shower]] - 881 Athene, another asteroid named after Athena - Pallas family ## Notes The masses as fractions of Vesta, Ceres, the belt and the Moon, the perihelion and aphelion, and the surface gravity are derived from the cited values and rounded. ## References [^marsset2020]: Marsset, M.; Brož, M.; Vernazza, P.; et al. (2020). "The violent collisional history of aqueously evolved (2) Pallas". *Nature Astronomy* 4: 569–576. https://doi.org/10.1038/s41550-019-1007-5 [^russell2012]: Russell, C. T.; Raymond, C. A.; Coradini, A.; et al. (2012). "Dawn at Vesta: testing the protoplanetary paradigm". *Science* 336: 684–686. https://doi.org/10.1126/science.1219381 [^hilton2001]: Hilton, J. L. (2001, revised 2007). "When did the asteroids become minor planets?". US Naval Observatory. https://aa.usno.navy.mil/faq/minorplanets [^dawn-serendipity]: NASA Jet Propulsion Laboratory (2002). "Astronomical serendipity". Dawn mission. http://dawn.jpl.nasa.gov/DawnCommunity/flashbacks/fb_06.asp [^mccord2006]: McCord, T. B.; McFadden, L. A.; Russell, C. T.; Sotin, C.; Thomas, P. C. (2006). "Ceres, Vesta, and Pallas: protoplanets, not asteroids". *Eos* 87: 105. https://doi.org/10.1029/2006EO100002 [^pitjeva2018]: Pitjeva, E. V.; Pitjev, N. P. (2018). "Masses of the main asteroid belt and the Kuiper belt from the motions of planets and spacecraft". *Astronomy Letters* 44: 554–566. https://doi.org/10.1134/S1063773718090050 [^jpl-pallas]: JPL Solar System Dynamics. "Small-Body Database Lookup: 2 Pallas" (elements fetched 2026-09-18). https://ssd.jpl.nasa.gov/tools/sbdb_lookup.html#/?sstr=2 [^carry2010]: Carry, B.; Dumas, C.; Kaasalainen, M.; et al. (2010). "Physical properties of (2) Pallas". *Icarus* 205: 460–472. https://doi.org/10.1016/j.icarus.2009.08.007 [^eso2020]: European Southern Observatory (24 February 2020). "Golf ball world" (picture of the week potw2008a). https://www.eso.org/public/images/potw2008a/ [^jpl-sbdb]: JPL Solar System Dynamics. "Small-Body Database Lookup" (elements fetched 2026-09-18). https://ssd.jpl.nasa.gov/tools/sbdb_lookup.html [^bourtembourg2012]: Bourtembourg, R. (2012). "Messier's missed discovery of Pallas in April 1779". *Journal for the History of Astronomy* 43: 209–214. https://doi.org/10.1177/002182861204300205 [^hoskin1992]: Hoskin, M. (26 June 1992). "Bode's law and the discovery of Ceres". Osservatorio Astronomico di Palermo "Giuseppe S. Vaiana". http://www.astropa.unipa.it/HISTORY/hoskin.html [^forbes1971]: Forbes, E. G. (1971). "Gauss and the discovery of Ceres". *Journal for the History of Astronomy* 2: 195–199. https://doi.org/10.1177/002182867100200305 [^herschel1802]: Herschel, W. (1802). "Observations on the two lately discovered celestial bodies". *Philosophical Transactions of the Royal Society of London* 92: 213–232. https://doi.org/10.1098/rstl.1802.0010 [^hilton2002]: Hilton, J. L. (2002). "Asteroid masses and densities". In Bottke, W. F.; et al. (eds.), *Asteroids III*. University of Arizona Press, pp. 103–112. http://www.lpi.usra.edu/books/AsteroidsIII/pdf/3008.pdf [^kozai1994]: Kozai, Y. (1994). "Kiyotsugu Hirayama and his families of asteroids". In *Seventy-five Years of Hirayama Asteroid Families*, ASP Conference Series 63, p. 1. Bibcode 1994ASPC...63....1K. [^foglia1999]: Foglia, S.; Masi, G. (2004). "New clusters for highly inclined main-belt asteroids". *The Minor Planet Bulletin* 31: 100–102. http://asteroidi.uai.it/family/ [^dunham1990]: Dunham, D. W.; Dunham, J. B.; Binzel, R. P.; et al. (1990). "The size and shape of (2) Pallas from the 1983 occultation of 1 Vulpeculae". *The Astronomical Journal* 99: 1636–1662. https://doi.org/10.1086/115446 [^drummond1989]: Drummond, J. D.; Cocke, W. J. (1989). "Triaxial ellipsoid dimensions and rotational pole of 2 Pallas from two stellar occultations". *Icarus* 78: 323–329. https://doi.org/10.1016/0019-1035(89)90180-2 [^pitjeva2004]: Pitjeva, E. V. (2004). "Estimations of masses of the largest asteroids and the main asteroid belt from ranging to planets, Mars orbiters and landers". *35th COSPAR Scientific Assembly*, abstract 2014. Bibcode 2004cosp...35.2014P. [^baer2011]: Baer, J.; Chesley, S. R.; Matson, R. D. (2011). "Astrometric masses of 26 asteroids and observations on asteroid porosity". *The Astronomical Journal* 141: 143. https://doi.org/10.1088/0004-6256/141/5/143 [^schmidt2008]: Schmidt, B. E.; Thomas, P. C.; Bauer, J. M.; et al. (2008). "Hubble takes a look at Pallas: shape, size, and surface". *39th Lunar and Planetary Science Conference*, abstract 2502. http://www.lpi.usra.edu/meetings/lpsc2008/pdf/2502.pdf [^jpl2007]: NASA Jet Propulsion Laboratory (24 October 2007). "Hubble images of asteroids help astronomers prepare for spacecraft visit". http://dawn.jpl.nasa.gov/science/index.asp [^james2006]: James, A. (1 September 2006). "Pallas". *Southern Astronomical Delights*. http://www.southastrodel.com/PagePallas000.htm [^lanl-pd]: Los Alamos National Laboratory. "Palladium". Periodic Table of Elements. http://periodic.lanl.gov/elements/46.html [^gould1852]: Gould, B. A. (1852). "On the symbolic notation of the asteroids". *The Astronomical Journal* 2: 80. https://doi.org/10.1086/100212 [^planetary-soc]: The Planetary Society (2007). "Notable asteroids". http://www.planetary.org/explore/topics/near_earth_objects/asteroids_and_comets/asteroids.html [^lutz2021]: Lutz, H. (2021). *Astrolutz 2022*. Books on Demand. ISBN 978-3-7534-7124-2. [^goffin2001]: Goffin, E. (2001). "New determination of the mass of Pallas". *Astronomy & Astrophysics* 365: 627–630. https://doi.org/10.1051/0004-6361:20000023 [^taylor1982]: Taylor, D. B. (1982). "The secular motion of Pallas". *Monthly Notices of the Royal Astronomical Society* 199: 255–265. https://doi.org/10.1093/mnras/199.2.255 [^solex]: Vitagliano, A. "Solex" (orbital integration software). Università di Napoli Federico II. http://chemistry.unina.it/~alvitagl/solex/ [^openstax]: Ling, S. J.; Sanny, J.; Moebs, W. (2016). *University Physics Volume 1*, ch. 13 "Gravitation". OpenStax. https://open.umn.edu/opentextbooks/textbooks/university-physics-volume-1 [^menzel1983]: Menzel, D. H.; Pasachoff, J. M. (1983). *A Field Guide to the Stars and Planets*. Houghton Mifflin, p. 391. ISBN 978-0-395-34835-2. [^odeh]: Odeh, M. "The brightest asteroids". Jordanian Astronomical Society. http://jas.org.jo/ast.html [^feierberg1982]: Feierberg, M. A.; Larson, H. P.; Lebofsky, L. A. (1982). "The 3 micron spectrum of asteroid 2 Pallas". *Bulletin of the American Astronomical Society* 14: 719. Bibcode 1982BAAS...14..719F. [^sato1997]: Sato, K.; Miyamoto, M.; Zolensky, M. E. (1997). "Absorption bands near three micrometers in diffuse reflectance spectra of carbonaceous chondrites: comparison with asteroids". *Meteoritics & Planetary Science* 32: 503–507. https://doi.org/10.1111/j.1945-5100.1997.tb01295.x [^johnston2007]: Johnston, W. R. (5 March 2007). "Other reports of asteroid/TNO companions". Johnston's Archive. http://www.johnstonsarchive.net/astro/asteroidmoonsq.html [^perozzi2001]: Perozzi, E.; Rossi, A.; Valsecchi, G. B. (2001). "Basic targeting strategies for rendezvous and flyby missions to the near-Earth asteroids". *Planetary and Space Science* 49: 3–22. https://doi.org/10.1016/S0032-0633(00)00124-0 [^rayman2014]: Rayman, M. (29 December 2014). "Ceres' curiosities: the mysterious world comes into view". NASA Jet Propulsion Laboratory. https://www.jpl.nasa.gov/blog/2014/12/ceres-curiosities-the-mysterious-world-comes-into-view/ [^orourke2019]: O'Rourke, J. G.; Castillo-Rogez, J.; Elkins-Tanton, L. T.; et al. (2019). "Athena: the first-ever encounter of (2) Pallas with a SmallSat". *50th Lunar and Planetary Science Conference*, LPI Contribution 2132. [^dorminey2019]: Dorminey, B. (10 March 2019). "Proposed NASA SmallSat mission could be first to visit Pallas, our third largest asteroid". *Forbes*. https://www.forbes.com/sites/brucedorminey/2019/03/10/proposed-nasa-smallsat-mission-could-be-first-to-visit-pallas-our-third-largest-asteroid [^lpi2019]: Lunar and Planetary Institute (24 June 2019). "Finalists selected for NASA's SIMPLEx program". Planetary News. https://www.lpi.usra.edu/planetary_news/2019/06/24/finalists-selected-for-nasas-simplex-program/ [^vernazza2021]: Vernazza, P.; Ferrais, M.; Jorda, L.; et al. (2021). "VLT/SPHERE imaging survey of the largest main-belt asteroids: final results and synthesis". *Astronomy & Astrophysics* 654: A56. https://doi.org/10.1051/0004-6361/202141781 ## External links - NASA Science. "Asteroids". https://science.nasa.gov/solar-system/asteroids/ - ESO. "Golf ball world": VLT/SPHERE image of Pallas. https://www.eso.org/public/images/potw2008a/ - JPL Small-Body Database. "2 Pallas". https://ssd.jpl.nasa.gov/tools/sbdb_lookup.html#/?sstr=2 ## Wikipedia : Wikitube **Strict pair:** [Wikipedia](https://en.wikipedia.org/wiki/2_Pallas) : [Wikitube](https://en.wikitube.io/wiki/2_Pallas) · pinned revision [1373230982](https://en.wikipedia.org/w/index.php?oldid=1373230982) · 2026-09-18 ## Previous hub tags Hubs: `Life_Physics`. Portals: [[PORTAL_Solar_System]]. --- *Solar System portal child articles, wave 1 · 2026-09-18 · drafted · row SOL-050 · explorer state `?obj=Pallas`.*