'Dubbed HD 219134b, this exoplanet, which orbits too close to its star to sustain life, is a mere 21 light-years away.'
There are closer planets, but their composition is unknown:
'For reference, the closest known planet is GJ674b at 14.8
light-years away; its composition is unknown.'
So the main reason why this is exiting:
'Only a small fraction of exoplanets can be detected transiting their stars due to their relative orientation to Earth. When the orientation is just right, the planet’s orbit places it between its star and Earth, dimming the detectable light of its star. It’s this dimming of the star that is actually captured by observatories such as Spitzer, and can reveal not only the size of the planet but also clues about its composition.'
There are closer planets, but their composition is unknown:
'For reference, the closest known planet is GJ674b at 14.8 light-years away; its composition is unknown.'
So the main reason why this is exiting:
'Only a small fraction of exoplanets can be detected transiting their stars due to their relative orientation to Earth. When the orientation is just right, the planet’s orbit places it between its star and Earth, dimming the detectable light of its star. It’s this dimming of the star that is actually captured by observatories such as Spitzer, and can reveal not only the size of the planet but also clues about its composition.'