Even with a telescope with many times the power of the Hubble Space Telescope, an Earth-sized world would appear as a single pixel in a vast empty space. You wouldn't get any kind of detailed resolution.
Can a single pixel tell you anything about that world? Researchers say, "yes". In a new paper published in the online edition of the Astrophysical Journal, they say that observers looking at the Earth from afar would be able to judge our rotation rate, the probability of oceans, weather, and even if the planet has life.
If distant astronomers were watching Earth, they'd see the brightness change over time as clouds rotated in and out of view. If they could also measure its rotation period, they'd know whether a certain part of the planet was in view, and start to deduce if there are oceans or land masses pointed towards them.
The researchers have created a computer model for the brightness of Earth over time, showing that the global cloud cover is surprisingly constant. There are usually clouds over the rain forests, and arid regions are clear.
We'll see likely planets with life on them long before we try to go there.
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