Habitable Zones and the Number of Gaia's Sisters Franck, S. ; von Bloh, W. ; Bounama, C. ; Steffen, M. ; Schönberner, D. ; Schellnhuber, H. -J. Abstract Publication: The Evolving Sun and its Influence on Planetary Environments Pub Date: 2002 Bibcode: 2002ASPC..269..261F