44 Nysa · Lablypedia

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 2015 TC25 and 1998 KY26 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 Hermann Goldschmidt in Paris, France on the night of 27 May 1857. He made the discovery using a 4-inch (10 cm) telescope, which was usually stationed at the upper floor of either his apartment or studio. Goldschmidt spotted the asteroid as a star-like object in the constellation Libra, at an apparent magnitude of 10.1. Although the weather became poor afterwards, Goldschmidt was able to reobserve Nysa on 1 June. He reported his discovery to the Astronomische Nachrichten via telegram and announced it as the 44th planet on the next day. It was his sixth asteroid discovery.

Over the next few weeks, Goldschmidt and other astronomers took additional observations of Nysa, allowing for the calculation of the asteroid's orbit and ephemerides. In the meantime, Goldschmidt continued discovering new asteroids, beginning with 45 Eugenia on 27 June 1857. Earlier that month, he had asked German polymath Alexander von Humboldt to suggest a name for the 44th asteroid. Humboldt chose the name Nysa, after the nymph and daughter of Aristaeus who raised the god Dionysus (also known as Bacchus) in Greek mythology. 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. Humboldt's choice of name was announced to Goldschmidt in a separate letter by Encke.

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. Nysa was instead represented by its minor planet number 44 (enclosed in parentheses), which historically meant it was the 44th asteroid discovered. This became the modern minor-planet designation scheme where the asteroid's number is prefixed to its name, as in (44) Nysa or 44 Nysa.

Observational characterization

In terms of apparent magnitude from Earth, Nysa ranks among the top 40 brightest main-belt asteroids. Its apparent magnitude ranges from 9 to 12 depending on its phase angle and distance from Earth. Although Nysa is too faint to be seen with the naked eye, it could be observed with a pair of binoculars or through a telescope with a moderate aperture size (at least 3 to 6 inches or 8 to 15 cm). Because of its brightness, Nysa has attracted numerous observational studies.

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

During the 1970s, astronomers began measuring the diameters of asteroids for the first time via infrared radiometry. This led to the first measurement of Nysa's diameter and albedo, revealing it to be a small and highly reflective object. In 1975, polarimetry and color measurements revealed that Nysa had an enstatite-rich surface unlike any previously observed asteroid. 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.

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. This prompted an international campaign for observing Nysa later that year. 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. Subsequent studies using light curves, radar observations, interferometric imaging, and stellar occultations all hinted that Nysa's shape must be elongated, lopsided, and concave, but could not conclude whether it is a contact binary.

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. 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, while the moon's discovery was reported later by a team led by Anthony Berdeu in May 2026. The finalized results were later announced in an August 2026 press release by the Lowell Observatory.

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Orbit

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. 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. Its current orbit brings it within 2.1 AU of Sun at perihelion to 2.8 AU at aphelion, with an eccentricity of 0.15 and a low inclination of 3.7° with respect to the ecliptic. Over millions of years, Nysa's orbital elements vary and average out with a proper eccentricity of 0.17 and a proper inclination of 3.1°.

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. Nysa occasionally passes close enough to other asteroids to show noticeable gravitational perturbations. For example, in April 1988, astronomers observed Nysa pass within 0.037 AU (5.5 million km; 3.4 million mi) of 20 Massalia.

Physical characteristics

Size and shape

Nysa is an elongated object with dimensions of 113 km × 67 km × 65 km (70 mi × 42 mi × 40 mi) (15% uncertainty for each axis). When treated as a sphere, Nysa's has a volume equivalent diameter of 75+3
−1 km (47+2
−1 mi). Long-term measurements of perturbations in the trajectories of other asteroids indicate that Nysa has a mass of (5.76±1.43)×10¹⁷ kg. The asteroid is expected to have a bulk density of at least 3 g/cm³, similar to other asteroids and meteorites that share Nysa's composition. 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.

Nysa's shape is extremely irregular and more concave than any previously observed asteroid. High-resolution imaging by telescopes has shown that Nysa is carved by ten major indentations, which researchers have alphabetically labeled A to J. These include two deep valleys (labeled I and J), which divide the asteroid into three distinct lobes. These valleys wrap around the asteroid's circumference and make the lobes appear connected by narrow necks, called "colli". At least five craters have been identified on Nysa, with diameters ranging from 8 to 35 km (5.0 to 21.7 mi). Nysa additionally has two major cavities at its south and north poles (labeled E and F, respectively), with E being 53 km (33 mi) wide and 17 km (11 mi) deep and F being 44 km (27 mi) wide and 5 km (3.1 mi) deep. A possible crater or secondary basin, labeled A, lies next to F between Nysa's smallest lobes with a width of 38 km (24 mi) and a depth of 6 km (3.7 mi).

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 20 to 60 km (12 to 37 mi) in size. The latter scenario would suggest that Nysa is a contact trinary—making it the first such object discovered. Astronomers believe that this is the most likely case, since impacts alone could not explain the asteroid's valleys. Nevertheless, impacts still play a role in reshaping Nysa, particularly in the creation of impact craters which appear as small concavities.

Rotation

Nysa spins around a fixed axis with a rotation period of approximately 6.42 hours. Its rotation axis crosses through its shortest dimension, with its north pole pointing toward the ecliptic coordinates (λ, β) = (102.7°±0.5°, +55.3°±0.5°). The asteroid's rotation is prograde with an axial tilt of 34.7°±0.5° with respect to the ecliptic. Because of its elongated shape, Nysa's brightness periodically varies as it rotates. Astronomers have exploited this phenomenon to measure Nysa's rotation period since the 1920s. When plotted as a light curve, Nysa's brightness exhibits two rounded peaks and two sharp minima per rotation.

Surface and composition

Nysa has a bright, colorless surface rich in enstatite, a reflective silicate mineral that is generally poor in iron. This makes Nysa an E-type asteroid, a relatively rare type of asteroid typically found in the inner main asteroid belt. It is the prototype of the E-type asteroids, being the largest, brightest, and first confirmed member of this group. Nysa and the E-type asteroids are believed to be the parent bodies of enstatite-rich meteorites, which include aubrites and enstatite chondrites.

Estimates of Nysa's visible geometric albedo range from 0.41 to 0.55, with the average being 0.48. Resolved imaging of Nysa has shown that its surface is uniform, with no albedo and color variations greater than 5%. 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. As Nysa comes to opposition (phase angle less than 5°), the asteroid's brightness in visible light sharply peaks by about 0.3 magnitudes. Nysa's sharp opposition surge is thought to be caused by coherent backscattering due to fine, submicron-sized particles composing much of its surface.

In visible light, Nysa exhibits a mostly flat reflectance spectrum that slightly increases reflectance at longer (redder) wavelengths. In near-infrared, Nysa absorbs light at wavelengths of 0.9 and 1.8 μm, indicating that its surface contains iron-bearing pyroxene such as orthopyroxene or forsterite. 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. 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. In the Bus–DeMeo classification system, Nysa is further classified an Xn-type asteroid because its spectrum exhibits a sharp absorption feature at 0.9 μm.

Satellite

Nysa is classified as a binary asteroid because it has one known moon. The moon of Nysa is unnamed with the informal designation S/2026 (44) 1. It was discovered in 2026 by a team of astronomers led by Anthony Berdeu, during analyses of Large Binocular Telescope images of Nysa taken on 15 February and 21 March 2026. The discovery was announced by the Central Bureau of Astronomical Telegrams on 26 May 2026.

S/2026 (44) 1 is significantly fainter than Nysa, having an apparent magnitude difference of about 9. Because of this, the moon is hidden within Nysa's glare, which necessitates the use of advanced image processing techniques to detect it. Assuming the moon has the same albedo as Nysa, its diameter is estimated to be 1.0 ± 0.5 km (0.6 ± 0.3 mi). S/2026 (44) 1 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 180 km (110 mi) away.

Origin and family

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.

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. Of these scenarios, Minker et al. considered the former more likely. 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. 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. However, no such family sharing Nysa's orbit and composition has been found.

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. These include 2015 TC25 and 1998 KY26, both of which are only a few meters in diameter. 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.

Nysa orbits within a region of the asteroid belt populated by multiple overlapping asteroid families, collectively known as the Nysa–Polana complex. The Nysa–Polana complex includes the Hertha family of S-type asteroids, which was historically named the "Nysa family". Despite their names, the Nysa–Polana complex and its "Nysa family" are likely not physically related to Nysa because they have completely different compositions. For this reason, researchers generally consider Nysa an interloper of the Nysa–Polana complex. 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.