Interstellar comet 'Oumuamua exits the animation)
Discovery [1][2]
Discovered byRobert Weryk using Pan-STARRS 1
Discovery siteHaleakala Obs., Hawaii
Discovery date19 October 2017
MPC designation1I/2017 U1[3]
PronunciationIPA: [ʔouˌmuəˈmuə]
Named after
Hawaiian term for scout[3]
  • 1I
  • 1I/ʻOumuamua
  • 1I/2017 U1 (ʻOumuamua)
  • A/2017 U1[4]
  • C/2017 U1[2]
  • P10Ee5V[5]
interstellar object[3]
hyperbolic asteroid[6]
Orbital characteristics[6]
Epoch 2 November 2017 (JD 2458059.5)
Observation arc34 days
Perihelion0.25534±0.00007 AU
−1.2798±0.0008 AU[Note 1]
26.33±0.01 km/s (interstellar)[7]
0° 40m 48.72s / day
Earth MOID0.0959 AU · 37.3 LD
Jupiter MOID1.455 AU
Physical characteristics
Dimensions230 × 35 × 35 m
(est. at albedo 0.10)[8][9]
Tumbling (non-principal axis rotation)[10]
Reported values include: 8.10±0.02 h[11]
8.10±0.42 h[12]
0.1 (spectral est.)[8]
0.06–0.08 (spectral est.)[12]
B–V = 0.7±0.06[8]
V-R = 0.45±0.05[8]
g-r = 0.47±0.04[12]
r-i = 0.36±0.16[12]
r-J = 1.20±0.11[12]
19.7 to >27.5[7][Note 2][14]

ʻOumuamua (ə/ (About this sound listen)) is a mildly active comet, and the first known interstellar object to pass through the Solar System. Formally designated 1I/2017 U1, it was discovered by Robert Weryk using the Pan-STARRS telescope at Haleakala Observatory, Hawaii, on 19 October 2017, 40 days after it passed its closest point to the Sun. When first seen, it was about 33,000,000 km (21,000,000 mi; 0.22 AU) from Earth (about 85 times as far away as the Moon), and already heading away from the Sun.

ʻOumuamua is a small object, estimated to be about 230 by 35 meters (800 ft × 100 ft) in size. It has a dark red color, similar to objects in the outer Solar System. ʻOumuamua showed no signs of a comet tail despite its close approach to the Sun, but has since undergone non-gravitational acceleration consistent with comet outgassing. It has significant elongation and rotation rate, so it is thought to be metal-rich with a relatively high density. ʻOumuamua is tumbling, rather than smoothly rotating, and is moving so fast relative to the Sun that there is no chance it originated in the Solar System. It also means that ʻOumuamua cannot be captured into a solar orbit, so it will eventually leave the Solar System and resume traveling through interstellar space. ʻOumuamua's system of origin and the amount of time it has spent traveling amongst the stars are unknown.


Hyperbolic trajectory of ʻOumuamua through the inner Solar System with the Sun at the animation)

As the first known object of its type, ʻOumuamua presented a unique case for the International Astronomical Union, which assigns designations for astronomical objects. Originally classified as comet C/2017 U1 it was later reclassified as asteroid A/2017 U1 due to the absence of a coma. Once it was unambiguously identified as coming from outside the Solar System a new designation was created: I, for Interstellar object. ʻOumuamua, as the first object so identified, was designated 1I, with rules on the eligibility of objects for I-numbers and the names to be assigned to these interstellar objects yet to be codified. The object may be referred to as 1I; 1I/2017 U1; 1I/ʻOumuamua; or 1I/2017 U1 (ʻOumuamua).[3] It has since been determined that ʻOumuamua is actually a mildly active comet.[15][16][17][18]

The name comes from Hawaiian ʻoumuamua, meaning 'scout'[19] (from ʻou, meaning 'reach out for', and mua, reduplicated for emphasis, meaning 'first, in advance of'[3]), and reflects the way this object is like a scout or messenger sent from the distant past to reach out to humanity. It roughly translates to "first distant messenger".[3][20] The first character is a Hawaiian ʻokina, not an apostrophe, and is represented by a single quotation mark and pronounced as a glottal stop; the name was chosen by the Pan-STARRS team[21] in consultation with Kaʻiu Kimura and Larry Kimura of the University of Hawaii at Hilo.[22]

Before the official name was decided upon, the name Rama was suggested, the name given to an alien spacecraft discovered under similar circumstances in the 1973 science fiction novel Rendezvous with Rama by Arthur C. Clarke.[23]

Other Languages
العربية: ʻOumuamua
azərbaycanca: 1I/ʻOumuamua
català: 1I/ʻOumuamua
čeština: 1I/ʻOumuamua
Deutsch: 1I/ʻOumuamua
Ελληνικά: Ομούαμούα
español: 1I/ʻOumuamua
euskara: 1I/ʻOumuamua
فارسی: اوموآموا
français: 1I/ʻOumuamua
hrvatski: ʻOumuamua
Bahasa Indonesia: ʻOumuamua
íslenska: ʻOumuamua
italiano: 1I/'Oumuamua
עברית: אומואמואה
Kiswahili: ʻOumuamua
Lëtzebuergesch: 1I/ʻOumuamua
lietuvių: ʻOumuamua
Limburgs: ʻOumuamua
magyar: ’Oumuamua
मराठी: ओमूआमूआ
Bahasa Melayu: ʻOumuamua
မြန်မာဘာသာ: အိုမူအာမူအာ
português: 1I/ʻOumuamua
română: 1I/ʻOumuamua
русский: 1I/Оумуамуа
Scots: ʻOumuamua
suomi: ʻOumuamua
svenska: 1I/ʻOumuamua
Türkçe: ʻOumuamua
українська: 1I/ʻOumuamua
Tiếng Việt: ʻOumuamua
Winaray: ʻOumuamua
中文: 奥陌陌