6 steps · 7 min

Earth or Another World?

Six close views test what terrain, atmosphere and scale can—and cannot—tell you.

1. 01

   Scale is hidden

   Without the caption, what tells you how large this landscape is?

   Andes Altiplano, South America
2. 02

   A polar edge

   Which boundaries look carved, deposited or eroded?

   At the Edge of a Polar Cap
3. 03

   Find the atmosphere

   Where does the solid world end and its atmosphere begin?

   Sunrise, Earth Limb
4. 04

   Texture without scale

   Could these repeated forms belong to Earth? What evidence is missing?

   Southern Dunes
5. 05

   Light above a world

   What makes this glow different from light on the surface?

   STS-45 Earth observation of the Aurora Australis or Southern Lights
6. 06

   Another magnetic sky

   Which familiar pattern appears around a planet unlike Earth?

   Alien aurorae spotted on Uranus by Hubble