ʻOumuamua

ʻOumuamua is the first interstellar object detected passing through the Solar System.[23] Formally designated 1I/2017 U1, it was discovered by Robert Weryk using the Pan-STARRS telescope at Haleakalā Observatory, Hawaii, on 19 October 2017, approximately 40 days after it passed its closest point to the Sun on 9 September. When it was first observed, it was about 33 million km (21 million mi; 0.22 AU) from Earth (about 85 times as far away as the Moon) and already heading away from the Sun.

Quick facts: Discovery[2][3], Discovered by, Discover... ▼

ʻOumuamua

ʻOumuamua on 28 October 2017[lower-alpha 1]
Discovery[2][3]
Discovered by	Robert Weryk using Pan-STARRS 1
Discovery site	Haleakalā Obs., Hawaii
Discovery date	19 October 2017
Designations
MPC designation	1I/2017 U1[4]
Pronunciation	/oʊˌmuːəˈmuːə/, Hawaiian: [ʔowˈmuwəˈmuwə] ⓘ
Named after	Hawaiian term for scout[4]
Alternative designations	1I 1I/ʻOumuamua 1I/2017 U1 (ʻOumuamua) A/2017 U1[5] C/2017 U1[3] P10Ee5V[6]
Minor planet category	Interstellar object[4] Hyperbolic asteroid[7][8][9]
Orbital characteristics[7]
Epoch 23 November 2017 (JD 2458080.5)
Observation arc	80 days
Perihelion	0.255916±0.000007 AU
Semi-major axis	−1.2723±0.0001 AU[lower-alpha 2]
Eccentricity	1.20113±0.00002
Average orbital speed	26.33±0.01 km/s (interstellar)[10] 5.55 AU/year
Mean anomaly	51.158°
Mean motion	0° 41m 12.12s / day
Inclination	122.74°
Longitude of ascending node	24.597°
Argument of perihelion	241.811°
Earth MOID	0.0958 AU 37.3 LD
Jupiter MOID	1.454 AU
Physical characteristics
Dimensions	115 m × 111 m × 19 m[11][12] 100–1000 m long[13][14][15] 230 m × 35 m × 35 m[16][17] (est. at albedo 0.10)[16][17]
Synodic rotation period	Tumbling (non-principal axis rotation)[18] Reported values include: 8.10±0.02 h[19] 8.10±0.42 h[20] 6.96+1.45 −0.39 h[21]
Geometric albedo	0.1 (spectral est.)[16] 0.06–0.08 (spectral est.)[20]
Spectral type
Apparent magnitude	19.7 to >27.5[10][22][lower-alpha 3]
Absolute magnitude (H)	22.08±0.45[7]

ʻOumuamua is a small object estimated to be between 100 and 1,000 metres (300 and 3,000 ft) long, with its width and thickness both estimated between 35 and 167 metres (115 and 548 ft).[13] It has a red color, like objects in the outer Solar System. Despite its close approach to the Sun, it showed no signs of having a coma. It exhibited non‑gravitational acceleration, potentially due to outgassing or a push from solar radiation pressure.[24][25] It has a rotation rate similar to that of Solar System asteroids, but many valid models permit it to be more elongated than all but a few other natural bodies. Its light curve, assuming little systematic error, presents its motion as "tumbling" rather than "spinning", and moving sufficiently fast relative to the Sun that it is likely of an extrasolar origin. Extrapolated and without further deceleration, its path cannot be captured into a solar orbit, so it will eventually leave the Solar System and continue into interstellar space. Its planetary system of origin and age are unknown.

ʻOumuamua would be remarkable for its extrasolar origin, high obliqueness, and observed acceleration without an apparent coma. By July 2019, most astronomers concluded that it was a natural object, but its exact characterization is contentious given the limited observation window. While an unconsolidated object (rubble pile) would require ʻOumuamua to be of a density similar to rocky asteroids,[26] a small amount of internal strength similar to icy comets[27] would allow it to have a relatively low density. Proposed explanations of its origin include the remnant of a disintegrated rogue comet,[28][29] or a piece of an exoplanet rich in nitrogen ice, similar to Pluto.[30][31][32] On 22 March 2023, astronomers proposed the observed acceleration was "due to the release of entrapped molecular hydrogen that formed through energetic processing of an H₂O-rich icy body",[33] consistent with 'Oumuamua being an interstellar comet, "originating as a planetesimal relic broadly similar to solar system comets".[34]

Avi Loeb has suggested that it could be a product of extraterrestrial technology,[35] but there is insufficient evidence to support any hypotheses, "despite all [its] strangeness".[36][37][38]^{[self-published source?]} In January 2022, researchers proposed Project Lyra, where a spacecraft launched from Earth could catch up to 'Oumuamua in 26 years for closer studies.[39][40]