An artist's conception shows an alien planet orbiting star HD 209458.
According to NASA, "Astronomers using ground-based telescopes to hunt for planets outside our solar system, dubbed extrasolar planets, have nabbed more than a hundred alien worlds. But they needed the keen 'eye' of Hubble to make the first direct measurement of the chemical makeup of an extrasolar planet's atmosphere. The telescope detected the elements sodium, hydrogen, carbon, and oxygen in the atmosphere of a Jupiter-size planet. The unique observation demonstrates that Hubble and other telescopes can sample the chemical makeup of the atmospheres of alien worlds."