"Are we alone?" has been a fundamental question since the dawn of civilization, and we have always been curious about the possibility of extraterrestrial life. Since the discovery of the first giant exoplanet orbiting a sun-like star named 51 Peg in 1995, over 5000 exoplanets have been discovered, with diverse properties and characteristics that are often different from our own planets. However, despite these great advancements, we have yet to discover another habitable Earth-like planet orbiting a sun-like star - an Earth 2.0. This forum will discuss key scientific issues such as “are we alone?”, “How common are Earth-like planets in the universe?” “How do terrestrial planets form?”, review status on searching of terrestrial-like planets and understanding their formation and discuss future plans for follow-up studies of Earth-like planet candidates detected by the ET space mission. 

ET will deploy a space observatory consisting of six wide-field transit telescopes and one microlensing telescope on a halo orbit around the Sun-Earth Lagrange L2 point. It will be the first combined effort to utilize the transit method and the microlensing method, employing space-based ultra-wide field and high-precision optical photometric observations. Its primary objective is to search for as yet undiscovered ‘Earth 2.0s’ and determine their occurrence rates, conducting the first large-scale survey of terrestrial planets and free-floating planets that are currently poorly understood. It aims to make the first discovery of free-floating Earths and determine their occurrence rates, thereby unraveling the origins of terrestrial and free-floating planets, and providing candidates and new directions for the search for extraterrestrial life.