"Even the closest exoplanets are more than 4 light years away (36 trillion miles), which makes it doubtful that we'll ever visit one-so why bother? The reason is, it helps us answer an age-old question: Are we alone in the universe? As far as we understand, you need a planet to have life, and the race is on to locate one with Earth-like qualities."
"The problem is, you can't just take your best telescope and start looking around the sky. Telescopes have a limited resolving power-the smallest angular size they can "see." For the Hubble Space Telescope that's 0.05 arc second, which is incredibly tiny-about 1/72,000th of a degree. The HST could make out a giant, Jupiter-size planet at a distance of 590 billion kilometers. That's amazing, but it's just 0.06 light year, and the nearest star, Proxima Centauri, is 4.25 light years away."
Clyde W. Tombaugh discovered Pluto nearly a century ago; no new planets were found until 1992 when the first exoplanet orbiting another star was detected. More than 6,000 exoplanets have since been cataloged, including extreme worlds like HD 189733b. Even the nearest exoplanets lie over four light years away, making travel unlikely and motivating searches for Earth-like planets to address the question of life elsewhere. Direct imaging is limited by telescope angular resolution and the faintness of reflected planetary light compared with stellar brightness. Detection relies on indirect techniques such as monitoring stellar wobble, Doppler blue shifts, and transits.
Read at WIRED
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