44 Nysa

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Template:Short description Template:Use dmy dates Template:Infobox planet

44 Nysa is an asteroid located in the inner region of the main asteroid belt. It is the largest, brightest, and first confirmed E-type asteroid,Template:Efn a rare type of asteroid with a highly reflective surface rich in enstatite. It was discovered by Hermann Goldschmidt in Paris, France on 27 May 1857 and was named after the nymph who raised the god Dionysus in Greek mythology.Template:Efn Nysa has one small moon which was discovered in 2026 and has not yet been named.

High-resolution imaging in 2026 revealed that Nysa has a highly concave and irregular shape, with three apparent lobes carved by several massive valleys and craters. Astronomers believe that it most likely resulted from the slow agglomeration of three asteroids—making Nysa a contact trinary. The asteroid has a uniform surface color and rotates with a period of 6.42 hours.

The origin of Nysa is uncertain. It probably did not experience any destructive collision events, as it is not known to host a family of asteroids sharing similar orbits and compositions. However, some small near-Earth asteroids including Template:Mpl and Template:Mpl have been suspected of being escaped fragments of Nysa. The asteroid orbits the Sun in the same region as the Nysa–Polana complex, a group of overlapping asteroid families. Despite the Nysa–Polana complex's name, researchers generally do not consider it related to Nysa due to their different compositions.

History

Discovery and naming

Nysa was discovered by German–French astronomer[1] Hermann Goldschmidt in Paris, France on the night of 27 May 1857.[2] He made the discovery using a Template:Convert telescope, which was usually stationed at the upper floor of either his apartment or studio.[3][4] Goldschmidt spotted the asteroid as a star-like object in the constellation Libra,[5]Template:Efn at an apparent magnitude of 10.1.[6][2] Although the weather became poor afterwards, Goldschmidt was able to reobserve Nysa on 1 June.[7] He reported his discovery to the Astronomische Nachrichten via telegram and announced it as the 44th planetTemplate:Efn on the next day.[7] It was his sixth asteroid discovery.[2]Template:Efn

Over the next few weeks, Goldschmidt[8] and other astronomers took additional observations of Nysa, allowing for the calculation of the asteroid's orbit and ephemerides.[9][10] In the meantime, Goldschmidt continued discovering new asteroids, beginning with 45 Eugenia on 27 June 1857.[11] Earlier that month, he had asked German polymath Alexander von Humboldt to suggest a name for the 44th asteroid.[5] Humboldt chose the name Nysa,Template:Efn after the nymph and daughter of Aristaeus who raised the god Dionysus (also known as Bacchus) in Greek mythology.Template:Efn In a letter responding to Goldschmidt, Humboldt expressed his honor of naming Nysa and praised Goldschmidt's discovery on behalf of astronomers Johann Franz Encke, Karl Christian Bruhns, Heinrich Louis d'Arrest, and Franz Brünnow.[12] Humboldt's choice of name was announced to Goldschmidt in a separate letter by Encke.[13]

Nysa never received a planetary symbol, as their use had fallen out of favor due to the increasing rate of asteroid discoveries in the 1850s.[14] Nysa was instead represented by its minor planet number 44 (enclosed in parentheses),[8][9] which historically meant it was the 44th asteroid discovered.[14] This became the modern minor-planet designation scheme where the asteroid's number is prefixed to its name,[14] as in (44) Nysa[15] or 44 Nysa.[16]

Observational characterization

In terms of apparent magnitude from Earth, Nysa ranks among the top 40 brightest main-belt asteroids.[17][18] Its apparent magnitude ranges from 9 to 12 depending on its phase angle and distance from Earth.[15][17] Although Nysa is too faint to be seen with the naked eye, it could be observed with a pair of binoculars[1] or through a telescope with a moderate aperture size (at least Template:Convert[19]).[20] Because of its brightness, Nysa has attracted numerous observational studies.[21][22]

In 1913, astronomers began suspecting that Nysa exhibits brightness variations over short periods.[23]Template:Rp This was confirmed by Template:Ill and E. Padova in 1920,[24] who plotted Nysa's light curve for the first time and measured a period of 3.2 hours.[23][25] By the 1950s, astronomers recognized that the 3.2-hour period is actually half of Nysa's rotation period.[24] The direction of Nysa's rotation axis was determined by 1962.[24]

During the 1970s, astronomers began measuring the diameters of asteroids for the first time via infrared radiometry.[26] This led to the first measurement of Nysa's diameter and albedo, revealing it to be a small and highly reflective object.[27] In 1975, polarimetry and color measurements revealed that Nysa had an enstatite-rich surface unlike any previously observed asteroid.[28][29]Template:Rp Two more asteroids—64 Angelina and 434 Hungaria—were later found to share similar compositions as Nysa, which led astronomers to introduce the E-type asteroid classification for these objects in 1977.[29]Template:Rp

In 1979, astronomers pointed out that Nysa's light curve resembles that of the contact binary star W Ursae Majoris, which raised suspicions that the asteroid might be a binary or contact binary.[30][31] This prompted an international campaign for observing Nysa later that year.[31] Although the 1979 campaign was unable to confirm Nysa's binarity, it provided more accurate measurements of the asteroid's rotation period and axis direction.[31] Subsequent studies using light curves, radar observations, interferometric imaging, and stellar occultations all hinted that Nysa's shape must be elongated, lopsided,Template:Efn and concave, but could not conclude whether it is a contact binary.[21]

Nysa was first imaged in detail in 2026, through the use of large ground-based telescopes (Large Binocular Telescope and Very Large Telescope) equipped with adaptive optics.[21] The images revealed that Nysa has a three-lobed shape and a tiny moon; the shape was reported by a team of astronomers led by Kate Minker in February 2026,[32] while the moon's discovery was reported later by a team led by Anthony Berdeu in May 2026.[33] The finalized results were later announced in an August 2026 press release by the Lowell Observatory.[22][34]

Orbit

Diagram showing the orbits of Nysa and the inner Solar System planets

Nysa is located in the main asteroid belt between the orbits of Mars and Jupiter. Specifically, it is in the inner region of the main belt, where the outer edge is cut off by the 3:1 mean-motion orbital resonance with Jupiter.[35][36] Nysa follows an elliptical orbit around the Sun with a semi-major axis of 2.42 astronomical units (AU) and an orbital period of 3.77 Earth years.[16] Its current orbit brings it within Template:Val of Sun at perihelion to Template:Val at aphelion, with an eccentricity of 0.15 and a low[36] inclination of 3.7° with respect to the ecliptic.[16] Over millions of years, Nysa's orbital elements vary[35] and average out with a proper eccentricity of 0.17 and a proper inclination of 3.1°.[37]

Nysa orbits within a densely populated region of the inner main belt, where several asteroid families including the Nysa–Polana complex and Massalia family can be found.[38] Nysa occasionally passes close enough to other asteroids to show noticeable gravitational perturbations.[39] For example, in April 1988, astronomers observed Nysa pass within Template:Convert of 20 Massalia.[39]

Physical characteristics

Size and shape

Surface features of NysaTemplate:Efn
Label Type Width
(km) 		Depth
(km)
A Crater/secondary basin 38 6
B Crater 20
C Crater 35
D Crater 21
E Southern cavity 53 17
F Northern cavity 44 5
G Crater 17
H Crater 8
I Collum/Valley
J Collum/Valley

Template:Multiple image

Nysa is an elongated object with dimensions of Template:Cvt (15% uncertainty for each axis).[40] When treated as a sphere, Nysa's has a volume equivalent diameter of Template:Val (Template:Val).[21] Long-term measurements of perturbations in the trajectories of other asteroids indicate that Nysa has a mass of Template:Val.Template:Efn The asteroid is expected to have a bulk density of at least Template:Val, similar to other asteroids and meteorites that share Nysa's composition.Template:Efn This density is higher than that of a typical main-belt asteroid, which may indicate an internal structure consisting of compact (low porosity) rock or a metal-rich core.[21]

Nysa's shape is extremely irregular and more concave than any previously observed asteroid.[21] High-resolution imaging by telescopes has shown that Nysa is carved by ten major indentations, which researchers have alphabetically labeled A to J.[21] These include two deep valleys (labeled I and J), which divide the asteroid into three distinct lobes.[21] These valleys wrap around the asteroid's circumference and make the lobes appear connected by narrow necks, called "colli".[21][22] At least five craters have been identified on Nysa, with diameters ranging from Template:Cvt.[21] Nysa additionally has two major cavities at its south and north poles (labeled E and F, respectively), with E being Template:Cvt wide and Template:Cvt deep and F being Template:Cvt wide and Template:Cvt deep.[21] A possible crater or secondary basin, labeled A, lies next to F between Nysa's smallest lobes with a width of Template:Cvt and a depth of Template:Cvt.[21]

The origin of Nysa's shape is uncertain; it could either be the result of multiple large asteroid impacts or the slow agglomeration of three asteroids Template:Cvt in size.[21][41] The latter scenario would suggest that Nysa is a contact trinary—making it the first such object discovered.[22][41] Astronomers believe that this is the most likely case, since impacts alone could not explain the asteroid's valleys.[21] Nevertheless, impacts still play a role in reshaping Nysa, particularly in the creation of impact craters which appear as small concavities.[21]

  • Resolved images of Nysa, with concavities labeled A to J. Valleys are labeled I and J, while non-crater cavities are labeled E and F.
    Resolved images of Nysa, with concavities labeled A to J. Valleys are labeled I and J, while non-crater cavities are labeled E and F.
  • Shape model of Nysa as seen from three different views. In the tip and side views, the rotational north pole points up. This model was constructed from imaging during 2026.
    Shape model of Nysa as seen from three different views. In the tip and side views, the rotational north pole points up. This model was constructed from imaging during 2026.

Rotation

Nysa spins around a fixed axis with a rotation period of approximately 6.42 hours.[21] Its rotation axis crosses through its shortest dimension, with its north pole pointing toward the ecliptic coordinates (λ, β) = (Template:Val, +Template:Val).[21] The asteroid's rotation is prograde[42] with an axial tilt of Template:Val with respect to the ecliptic.Template:Efn Because of its elongated shape, Nysa's brightness periodically varies as it rotates.[21] Astronomers have exploited this phenomenon to measure Nysa's rotation period since the 1920s.[21] When plotted as a light curve, Nysa's brightness exhibits two rounded peaks and two sharp minima per rotation.[43]Template:Rp

Surface and composition

Visible and near-infrared reflectance spectra of Nysa (light blue), the E(III)-type near-Earth asteroid Template:Mpl (black), and different-sized samples of an aubrite from Rantila (navy and orchid). All objects share the Template:Val absorption feature due to pyroxene.[44]

Nysa has a bright, colorlessTemplate:Efn surface rich in enstatite, a reflective silicate mineral that is generally poor in iron.[41][34] This makes Nysa an E-type asteroid, a relatively rare type of asteroid[45] typically found in the inner main asteroid belt.[46]Template:Rp It is the prototype of the E-type asteroids,[29]Template:Rp[29]Template:Rp being the largest, brightest, and first confirmed member of this group.[24]Template:Efn Nysa and the E-type asteroids are believed to be the parent bodies of enstatite-rich meteorites, which include aubrites and enstatite chondrites.[21]

Estimates of Nysa's visible geometric albedo range from 0.41 to 0.55,[21] with the average being 0.48.[45] Resolved imaging of Nysa has shown that its surface is uniform, with no albedo and color variations greater than 5%.[21] Nysa is thought to have a dense surface regolith like other E-type asteroids due to its high radar albedo and polarization ratio—meaning it reflects and polarizes radar waves in large amounts.[40][21] As Nysa comes to opposition (phase angle less than 5°), the asteroid's brightness in visible light sharply peaks by about 0.3 magnitudes.[47][24] Nysa's sharp opposition surge is thought to be caused by coherent backscattering due to fine, submicron-sized particles composing much of its surface.[24]

In visible light, Nysa exhibits a mostly flat reflectance spectrum that slightly increases reflectance at longer (redder) wavelengths.[48][49] In near-infrared, Nysa absorbs light at wavelengths of 0.9 and Template:Val, indicating that its surface contains iron-bearing pyroxene such as orthopyroxene or forsterite.[48]Template:Rp This makes Nysa a member of the E(III) subclass of E-type asteroids, which are thought to be fragments of an igneous parent body that underwent extensive reduction.[49][48]Template:Rp[46]Template:Rp Nysa and other E-type asteroids are also classified as X-type asteroids, because their visible reflectance spectra are indistinguishable from those of metallic M-type and organic-rich P-type asteroids.[40]Template:Rp[44]Template:Rp In the Bus–DeMeo classification system, Nysa is further classified an Xn-type asteroid because its spectrum exhibits a sharp absorption feature at Template:Val.[50]Template:Rp[44]Template:RpTemplate:Efn

Satellite

Nysa and its moon (arrow) photographed by the Large Binocular Telescope on 15 February 2026. A low-exposure photo of Nysa is superimposed on top of a grainy long-exposure photo of the moon.

Nysa is classified as a binary asteroid because it has one known moon.[21] The moon of Nysa is unnamed with the informal designation Template:Mp.[21][22] It was discovered in 2026 by a team of astronomers led by Anthony Berdeu,Template:Efn during analyses of Large Binocular Telescope images of Nysa taken on 15 February and 21 March 2026.[33][21] The discovery was announced by the Central Bureau of Astronomical Telegrams on 26 May 2026.[33]

Template:Nowrap is significantly fainter than Nysa, having an apparent magnitude difference of about 9.[21] Because of this, the moon is hidden within Nysa's glare, which necessitates the use of advanced image processing techniques to detect it.[21][22] Assuming the moon has the same albedo as Nysa, its diameter is estimated to be Template:Cvt.[21] Template:Nowrap has not been observed long enough to have its orbit determined, though the moon's observed projected separation from Nysa suggests that it orbits at least Template:Cvt away.[21]

Origin and family

Template:See also

Many details about Nysa's origin and collisional history are uncertain, and studies of its shape, composition, and surroundings in the asteroid belt have produced different interpretations.[21][45]

A 2026 study by Kate Minker and colleagues proposed that Nysa could either be a contact trinary of slowly-merged asteroids or a coherent single body deformed by several large impacts.[21] Of these scenarios, Minker et al. considered the former more likely.[21] In the contact trinary scenario, the three constituent asteroids most likely had a common composition and origin, since Nysa has a uniform present-day surface.[21] However, the origin of these asteroids is unclear: if they are reaccumulated fragments from a destructive collision event, then there should also be many smaller fragments on similar orbits around the Sun, forming an asteroid family.[21] However, no such family sharing Nysa's orbit and composition has been found.[21][46]Template:Rp

Proper orbital elements (inclination vs. eccentricity) of the Nysa–Polana complex, with each asteroid represented as a circle scaled by diameter and color-coded by albedo. Low-albedo (C-type) asteroids are clustered near 142 Polana, while moderate-albedo (S-type) asteroids are clustered near 135 Hertha. Nysa does not have a cluster of high-albedo asteroids.

Some E-type near-Earth asteroids have been suggested to be escaped fragments of Nysa, due to their similar orbital inclinations and E(III) classification.[46][45] These include Template:Mpl and Template:Mpl, both of which are only a few meters in diameter.[46][45] These asteroids are thought to have migrated from the inner main belt to the near-Earth region via the Yarkovsky effect and ν6 secular resonance, which are caused by sunlight and Saturn's apsidal precession, respectively.[46][45]

Nysa orbits within a region of the asteroid belt populated by multiple overlapping asteroid families, collectively known as the Nysa–Polana complex.[36] The Nysa–Polana complex includes the Hertha family of S-type asteroids, which was historically named the "Nysa family".[51] Despite their names, the Nysa–Polana complex and its "Nysa family" are likely not physically related to Nysa because they have completely different compositions.[52][53][51] For this reason, researchers generally consider Nysa an interloper of the Nysa–Polana complex.[36][53][51] Nevertheless, some studies have attempted to link Nysa to the complex by proposing that the two originated from compositionally different layers of a collisionally destroyed parent body.[36][45]

See also

Notes

Template:Notelist

References

  1. ↑ Template:Cite web Ephemeris Type: Observer and Center: 500@399 (geocentric). In the URL, quantity "1" gives RA/Dec coordinates and quantity "29" gives the abbreviation for the constellation. Cite error: <ref> tag with name "discovery-loc" defined in <references> is not used in prior text.
  2. ↑ Template:Cite journal Cite error: <ref> tag with name "Metzger2019" defined in <references> is not used in prior text.
  3. ↑ Template:Cite book Cite error: <ref> tag with name "MP-dict" defined in <references> is not used in prior text.
  4. ↑ Template:Cite book Cite error: <ref> tag with name "NuO-384" defined in <references> is not used in prior text.
  5. ↑ Template:Cite book Cite error: <ref> tag with name "Cosmos" defined in <references> is not used in prior text.
  6. ↑ Template:Cite book Cite error: <ref> tag with name "Littre" defined in <references> is not used in prior text.
  7. ↑ Template:Cite journal Cite error: <ref> tag with name "Binzel2019" defined in <references> is not used in prior text.
  8. ↑ Template:Cite journal GM of Nysa is shown in Table 5 of the Appendix (A.1. List of Perturber Asteroids). Cite error: <ref> tag with name "FM-2025" defined in <references> is not used in prior text.
  9. ↑ Template:Cite news Cite error: <ref> tag with name "ESO-2026" defined in <references> is not used in prior text.
  10. ↑ 1.0 1.1 Template:Cite news
  11. ↑ 2.0 2.1 2.2 Template:Cite journal
  12. ↑ Template:Cite book
  13. ↑ Template:Cite journal
  14. ↑ 5.0 5.1 Template:Cite book
  15. ↑ Template:Cite journal
  16. ↑ 7.0 7.1 Template:Cite journal
  17. ↑ 8.0 8.1 Template:Cite journal
  18. ↑ 9.0 9.1 Template:Cite journal
  19. ↑ Template:Cite journal
  20. ↑ Template:Cite book
  21. ↑ Template:Cite book
  22. ↑ Template:Cite book
  23. ↑ 14.0 14.1 14.2 Template:Cite web
  24. ↑ 15.0 15.1 Template:Cite web
  25. ↑ 16.0 16.1 16.2 Template:Cite web
  26. ↑ 17.0 17.1 Template:Cite web
  27. ↑ Template:Cite web
  28. ↑ Template:Cite web
  29. ↑ Template:Cite web
  30. ↑ 21.00 21.01 21.02 21.03 21.04 21.05 21.06 21.07 21.08 21.09 21.10 21.11 21.12 21.13 21.14 21.15 21.16 21.17 21.18 21.19 21.20 21.21 21.22 21.23 21.24 21.25 21.26 21.27 21.28 21.29 21.30 21.31 21.32 21.33 21.34 21.35 Template:Cite journal
  31. ↑ 22.0 22.1 22.2 22.3 22.4 22.5 Template:Cite news
  32. ↑ 23.0 23.1 Template:Cite journal
  33. ↑ 24.0 24.1 24.2 24.3 24.4 24.5 Template:Cite journal
  34. ↑ Template:Cite journal
  35. ↑ Template:Cite conference (A full PDF for the conference can be found here)
  36. ↑ Template:Cite journal
  37. ↑ Template:Cite journal
  38. ↑ 29.0 29.1 29.2 29.3 Template:Cite journal
  39. ↑ Template:Cite journal
  40. ↑ 31.0 31.1 31.2 Template:Cite journal
  41. ↑ Template:Cite journal
  42. ↑ 33.0 33.1 33.2 Template:Cite journal
  43. ↑ 34.0 34.1 Template:Cite news
  44. ↑ 35.0 35.1 Template:Cite journal
  45. ↑ 36.0 36.1 36.2 36.3 36.4 Template:Cite journal
  46. ↑ Template:Cite web For more information about proper orbital elements, go to the "Proper Elements" tab and then click "[Help]" at the upper right corner. The synthetic proper orbital elements shown come from simulations over a 2-million-year integration time span (ITS). To convert sin(i) into degrees, use the arcsine function (arcsin(0.0533592) ≈ 3.0587°).
  47. ↑ Template:Cite journal
  48. ↑ 39.0 39.1 Template:Cite journal In Table 2, Nysa's closest encounter was with 20 Massalia on the date JD 2447262.5, which translates to 11 April 1988 UT (use the Julian date converter).
  49. ↑ 40.0 40.1 40.2 Template:Cite journal
  50. ↑ 41.0 41.1 41.2 Template:Cite news
  51. ↑ Template:Cite journal
  52. ↑ Template:Cite journal
  53. ↑ 44.0 44.1 44.2 Template:Cite journal
  54. ↑ 45.0 45.1 45.2 45.3 45.4 45.5 45.6 45.7 Template:Cite journal
  55. ↑ 46.0 46.1 46.2 46.3 46.4 46.5 Template:Cite journal
  56. ↑ Template:Cite journal
  57. ↑ 48.0 48.1 48.2 Template:Cite journal
  58. ↑ 49.0 49.1 Template:Cite conference
  59. ↑ Template:Cite journal
  60. ↑ 51.0 51.1 51.2 Template:Cite journal
  61. ↑ Template:Cite book
  62. ↑ 53.0 53.1 Template:Cite journal

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