The Earth 2.0 (ET) space mission: science objectives, survey design, and development progress

Abstract

The Earth 2.0 (ET) mission is a dedicated space observatory designed to discover Earth-sized planets over a broad range of orbital separations and to measure the occurrence rates of terrestrial planets, including Earth 2.0s and free-floating Earth-mass planets. The observatory combines six 28-cm wide-field transit telescopes with one 35-cm microlensing telescope in a Sun–Earth L2 halo orbit. The transit telescope array will monitor more than three million FGKM dwarfs in and around the original Kepler field for four years, extending the effective time baseline to approximately eight years for stars observed by both missions. The microlensing telescope will monitor more than 30 million stars toward the Galactic bulge, coordinated with ground-based surveys to improve sensitivity to cold and unbound planets. ET employs large- format 9k×9k backside-illuminated CMOS detector mosaics and stringent thermal and pointing control. Current simulations predict a total noise of about 27 ppm over 6.5 h for an E=12.5 solar-type star and recovery of an approximately 84-ppm Earth-analog transit. The mission is expected to identify about 70,000 exoplanet candidates, including roughly 8,000 Earth-sized candidates, approximately 20 Earth 2.0 candidates, and about 25 free-floating Earth-mass planets. This paper summarizes the scientific rationale, survey strategy, payload design, laboratory validation, science preparation, expected yields, development status, and follow-up framework of ET.