Translation guide
Refers to species not native to Earth, often in sci-fi or biology contexts. In Japanese, the concept is expressed through compounds combining 'alien' or 'extraterrestrial' with 'species' or 'organism'. The most common term is 宇宙人 (uchūjin), but it primarily means 'alien being' rather than 'species'. For 'species', use 異星生物 (isei seibutsu) or 地球外生物 (chikyūgai seibutsu) in formal contexts.
A species originating from outside Earth, often in science fiction or speculative biology.
Literally 'different star organism'. Common in sci-fi and academic contexts. Neutral and widely understood.
その惑星には異星生物が存在する。
Alien species exist on that planet.
Literally 'extraterrestrial organism'. More formal and scientific. Used in astrobiology and official contexts.
地球外生物の探査が進められている。
The search for alien species is underway.
Literally 'space organism'. Broader term that can include any life in space, not necessarily intelligent. Common in popular science.
宇宙生物の可能性について議論する。
We discuss the possibility of alien species.
A species of intelligent extraterrestrial beings, often humanoid or sentient.
Literally 'space person'. The most common word for 'alien' as a being. Can imply a species when used in plural or with species-related terms.
宇宙人は地球に来たことがあるのだろうか。
I wonder if an alien species has ever visited Earth.
Literally 'different star person'. Similar to 宇宙人 but slightly more formal or literary. Often used in sci-fi to distinguish specific alien races.
Literally 'extraterrestrial intelligent life form'. Very formal and scientific. Used in SETI and academic papers.
地球外知的生命体の探査は続いている。
The search for intelligent alien species continues.
A non-native species introduced to a new environment, often causing harm. This is a distinct biological meaning.
Literally 'foreign species'. The standard term in ecology for invasive or introduced species. Note: this refers to Earth-based non-native species, not extraterrestrial.
外来種が在来種を脅かしている。
Alien species are threatening native species.
Literally 'invasive alien species'. More specific term for harmful invasive species. Used in environmental policy.
侵略的外来種の駆除が行われている。
Eradication of invasive alien species is being carried out.
The English word 'alien' can also mean a foreign national. In Japanese, that is 外国人 (がいこくじん) or 在留外国人 (ざいりゅうがいこくじん). The terms here are only for extraterrestrial or ecological contexts.
Both mean 'alien being'. 宇宙人 is the everyday word, while 異星人 is slightly more formal and often used in fiction to distinguish different alien races. For 'alien species' as a category, use 異星生物 or 地球外生物.
異星人との接触はまだ確認されていない。
Contact with an alien species has not yet been confirmed.