An international team of astronomers has put themselves in the shoes of alien life forms light-years away from Earth, asking whether – and how – they would be able to look at Earth through their telescopes and figure out whether our planet indeed supports life.
It's not just a science-fiction question. Researchers are designing new generations of space-based telescopes, and they're trying to figure out exactly what they need to peer at other planets circling distant stars, and answer the same question. To date, our instruments have been good enough to detect huge planets on the scale of Jupiter or beyond, but these are very unlikely to support life.
The team started from the idea that Earth, as seen from that distance would appear at best as just a single pixel of light. To get even enough information to determine which chemicals are in the atmosphere – which could be done by analyzing the spectrum of the light reflected by the pixel-planet – these alien astronomers would have to keep their telescopes trained on Earth for weeks.
But over that time, the brightness would change, as the planet rotated, and as cloud cover shifted. This could be deeply confusing, but could be helpful if the aliens could figure out what our 24-hour rotation period was.
Using a computer model derived from satellite observations of the planet, the astronomers deduced that there is enough regularity in the
Earth's weather patterns (typically cloudy over rain forests, typically clear over arid regions) that smart aliens would in fact be able to puzzle out the length of our Earth day.
Once they had that, they could figure out that the variations in pixel-brightness would likely be the result of fast-changing weather, very likely the result of water-based clouds. (By contrast, Venus'
atmosphere is always cloudy, and Mars' surface almost never covered in clouds.)
If they were really good, the astronomers would even be able to discern the presence of continents and oceans from the changing light pattern.
Not bad for studying a single pixel of light, right? The team of astronomers say they'd need a space-based telescope at least twice as large as the Hubble to do the same kind of analysis on planets circling the stars nearest to our own Sun.
NASA's Kepler telescope, planned for launch in 2009, is expected to be able to find the existence of Earth-like worlds. But finding information on rotation, weather, and atmospheric composition will have to wait for future projects, such as the proposed Terrestrial Planet
Finder.
But the really amazing thing? That it's possible at all.
The team's paper was published this week in the online version of The Astrophysical Journal
To curious aliens, Earth would stand out as living planet[University of Florida]
MIT, others ask 'What would E.T. see?' [MIT]
(Image: Earth, at slightly better than one-pixel resolution. Credit: NASA Goddard Space Flight Center)
