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This week’s new questions

How big would a planet have to be before its gravity made space travel impossible for the inhabitants? How do fish recognise others of their own species?

D73X1R An colorful adult midnight snapper swims over the reef

The positions of most fishes’ eyes mean they cannot see their own body. So, how do they recognise others of their own species?

Bill Dixon
Brisbane, Australia

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3D Illustration of an alien planet with amazing atmosphere; Shutterstock ID 1233283387; purchase_order: -; job: -; client: -; other:

How big would a planet have to be before its gravity made space travel impossible for the inhabitants?

Goronwy Humphreys
Wallasey, Merseyside, UK

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Last Word is Âé¶¹´«Ã½â€™s long-running series in which readers give scientific answers to each other’s questions, ranging from the minutiae of everyday life to absurd astronomical hypotheticals. To answer a question or ask a new one, email lastword@newscientist.comTo answer this question – or ask a new one – email lastword@newscientist.com.

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