Artist's impression of ʻOumuamua, the first confirmed interstellar asteroid [1]
Discovery  [2] [3]
Discovered by Robert Weryk using Pan-STARRS 1
Discovery site Haleakala Obs., Hawaii
Discovery date 19 October 2017
MPC designation 1I/2017 U1 [4]
Pronunciation ə/ ( About this sound  listen)
Named after
( Hawaiian name) [4]
1I · 1I/ʻOumuamua · 1I/2017 U1 (ʻOumuamua) · A/2017 U1 [5] · C/2017 U1 [3] · P10Ee5V [6]
Interstellar object [4]
hyperbolic asteroid (JPL) [7]
Orbital characteristics [7]
Epoch 2017-Oct-31 ( JD 2458057.5)
Observation arc 34 days
Aphelion N/A
Perihelion 0.25534±0.00007 AU
−1.2799±0.0009 AU [n 1]
Eccentricity 1.19949±0.00019
26.33±0.01  km/s (interstellar) [8]
35.060 °
0° 40m 48.72s / day
Inclination 122.69°
Earth  MOID 0.0958 AU · 37.3 LD
Jupiter  MOID 1.455 AU
Physical characteristics
Dimensions 180 × 30 × 30 m (est. at albedo 0.10) [9] [10]
200  m (est. at albedo 0.06–0.08) [11]
Tumbling (non-principal axis rotation). [12]. Reported values include: 8.10±0.02 h [13]
8.10±0.42 h [11] 6.96+1.45
0.1 (spectral est.) [9]
0.06–0.08 (spectral est.) [11]
RR (red, featureless) [15]
D? [9]
P? [11]
B–V = 0.7±0.06 [9]
V-R = 0.45±0.05 [9]
g-r = 0.47±0.04 [11]
r-i = 0.36±0.16 [11]
r-J = 1.20±0.11 [11]
19.7 to >27.5 [8] [n 2] [16]
22.08±0.45 [7]

ʻOumuamua ( ə/ ( About this sound  listen); formally designated 1I/2017 U1) is the first known interstellar object to pass through the Solar System. It was discovered by Robert Weryk using the Pan-STARRS telescope 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. Initially assumed to be a comet, it was reclassified as an asteroid a week later, then the first of a new class of interstellar objects.

ʻOumuamua is a relatively small object, estimated to be 30-180 meters in size. It is dark and very red, similar to objects in the outer Solar System. It is moving so fast relative to the Sun that there is no chance it originated in the Solar System, nor can it be captured into orbit, so it will eventually leave the Solar System and resume traveling in interstellar space. ʻOumuamua's system of origin, and the amount of time the object has been traveling among the stars in the galactic disc, remain unknown.


As the first known object of its type, ʻOumuamua presented a unique case for the International Astronomical Union, which assigns designations for astronomical objects. Before its true nature was known it was classified as comet C/2017 U1 and later as asteroid A/2017 U1. Once it was known as an unambiguous interstellar object, a new designation was created, I, with ʻOumuamua being 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. [4] Correct forms for referring to this object are: 1I; 1I/2017 U1; 1I/ʻOumuamua; and 1I/2017 U1 (ʻOumuamua). [4]

The name comes from Hawaiian ʻou.mua.mua, meaning "scout", [17] (from ʻou, meaning "reach out for", and mua, reduplicated for emphasis, meaning "first, in advance of" [4]) and reflects the way this object is like a scout or messenger sent from the distant past to reach out to us. [4] [18] 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 [19] in consultation with Kaʻiu Kimura and Larry Kimura of the University of Hawaii at Hilo. [20]

Before the official name was decided upon a popular choice was Rama, the name of a similar object discovered under similar circumstances in the science fiction novel Rendezvous with Rama by Arthur C. Clarke. [21] [22] Adding to the coincidence, both the real and the fictional objects are unusually elongated.

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
italiano: 1I/'Oumuamua
עברית: אומואמואה
Lëtzebuergesch: 1I/ʻOumuamua
Limburgs: ʻOumuamua
magyar: 'Oumuamua
Bahasa Melayu: ʻOumuamua
português: 1I/ʻOumuamua
română: 1I/ʻOumuamua
русский: 1I/Оумуамуа
Scots: ʻOumuamua
suomi: ʻOumuamua
svenska: 1I/ʻOumuamua
Türkçe: ʻOumuamua
українська: 1I/ʻOumuamua
Tiếng Việt: ʻOumuamua
中文: 奥陌陌