AUTHOR=Kanik Isik, Paul de Vera Jean-Pierre TITLE=Editorial: Astrobiology of Mars, Europa, Titan and Enceladus - Most Likely Places for Alien Life JOURNAL=Frontiers in Astronomy and Space Sciences VOLUME=8 YEAR=2021 URL=https://www.frontiersin.org/articles/10.3389/fspas.2021.643268 DOI=10.3389/fspas.2021.643268 ISSN=2296-987X