NASA and ESO announced a system of seven Earth-sized planets around TRAPPIST-1 on February 22, 2017. Their accounts describe the same study led by Michaël Gillon, not separate confirmations. The central reading task is to keep the measurements apart from the conclusions drawn from them: size, mass, density and habitability are different questions. [nasa-telescope-reveals-largest-batch-of-earth-size-habitable-zone-planets-around-single-star][eso1706]

ESO explains the basic observation: a planet passing between its star and Earth blocks some starlight. These events, called transits, produce small dips in the recorded brightness. Repeated crossings provide information about the system. A detected dip is not, by itself, a measurement of everything a planet contains or of conditions on its surface. [eso1706]

NASA reports that Spitzer data yielded sizes for all seven planets and initial mass estimates for six, allowing estimates of density. The density evidence suggested rocky compositions; it did not establish seven fully characterized rocky worlds. Planet h, the most distant member, had no mass estimate, and ESO said its orbital distance remained unconfirmed. [nasa-telescope-reveals-largest-batch-of-earth-size-habitable-zone-planets-around-single-star][eso1706]

ESO placed planets e, f and g in the habitable zone, where surface water could be possible. NASA also stressed the importance of atmospheric conditions. Neither account reported detected oceans or life. Thus a reader can accept the seven-planet finding while leaving composition and surface conditions open: additional observations would have to answer those more demanding questions. [nasa-telescope-reveals-largest-batch-of-earth-size-habitable-zone-planets-around-single-star][eso1706]

Source documents

  1. NASA Telescope Reveals Largest Batch of Earth-Size, Habitable-Zone Planets Around Single Starhttps://science.nasa.gov/missions/hubble/nasa-telescope-reveals-largest-batch-of-earth-size-habitable-zone-planets-around-single-star/
  2. Ultracool Dwarf and the Seven Planetshttps://www.eso.org/public/news/eso1706/