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Some animals keep track of where they are by continuously adding up their own movements from a known starting point. Mammals can use signals from balance, body movement, and what they see moving around them. This allows navigation even without familiar landmarks.

Compared with many known planetary systems, ours has no planets closer to the Sun than Mercury and no super-Earths—planets larger than Earth but smaller than Neptune. Super-Earths are the most common type of planet in the Milky Way, making their absence unusual.