Extrasolar planets (“exoplanets”) are planets around stars other than our own Sun. As of the summer of 2026 over 6435 planets and 4827 planetary systems (!!) have been detected, and most of these are confirmed and have some of the properties measured. Most of them (3884 are more than twice as massive as the Earth and most of these are more massive than Jupiter. But although they orbit some of the nearest stars to the Sun, nearly all of them are too far away and too small to be discovered in pictures. Almost all of them were discovered in one of five ways: (1) by measuring the wobble in the star’s motion as the planet orbits around the star; (2) if the orbit fortuitously crosses our line-of-sight to the star, by spotting the faint dimming of the star’s light as the planet passes between it and the view from Earth; (3), when a star and its planet are fortuitously reimaged by a gravitational lens (a star nearer to Earth whose gravity bends light like a lens — see Chapter 3) — by finding a characteristic spike in the star’s re-imaged light as the lensing star moves through space (only three examples of this so far); (4) direct imaging by using a mask to block out the star’s light, or my identifying gaps the planets create in the dusty disks around the stars; (5) inferring their presence by detecting how their gravity influences other planets in the system.
Five exoplanets are known that are about 10% of the Earth’s mass, and there is every reason to think that more Earth-sized planets will be found before long, as new instruments become more and more capable of discovering smaller planets. If an Earth-like planet orbits its star at a safe and comfortable distance where water can be liquid rather than frozen or gaseous (the “habitable zone”), perhaps in time life can form on it. Perhaps that life can evolve and become intelligent. Perhaps we are not alone in the Universe.
The implications for religious believers need not be threatening. Many theologians have accepted that an omnipotent God could have created more than one world; in 1277, the Bishop of Paris, Étienne Tempier, declared just that. In his commentary to the biblical Song of Deborah (Judges 5:23), the medieval commentator Rashi remarks that the inhabitants of a place named in the Song, “Meroz,” actually live around another star.
Let There Be Light, Chapter 6, talks about the Anthropic Principle (the amazing, contingent circumstances that make life possible), and revisits the idea in Chapter 8 in the context of intelligent life on Earth. In Secrets of Creation a more updated discussion of these principles, including results from JWST, is found in Chapters 7, 8 and 10. My opinion is that, despite the increasingly long list of extrasolar planets, we will not know for a very long time, if ever, whether intelligent life exists elsewhere in the Universe. It is rare at best. Nevertheless there is no convincing reason why the human task of tikkun olam, repairing the world by good deeds, could not be seen as a goal for all intelligent beings, everywhere.