The universe is an interesting mix of different objects. There are huge, heavy black holes and galaxy superclusters, and then there are tiny, invisible quarks and electrons that make up most matter. Objects like stars radiate energy, while planets and moons rely on them to become worlds of their own – just like our Earth.
Even in our solar system, not all planets are the same – the four closest to the sun, with iron and stones on their surfaces, are rocky planets, while the other four are massive gas giants with swirling gases and no hard surfaces.
Although Earth is the only planet among the eight to host life, rocky, Earth-like planets are of particular interest to scientists. They believe that if there is life elsewhere in the universe, it must be on one of the 10 billion rocky planets thought to exist.
It is estimated that half of the stars with Sun-like temperatures have a rocky planet with liquid water on their surface, and over 300 million exist in the Milky Way. Outside our solar system, scientists have studied over 5,000 exoplanets, 187 of which are rocky Earth-like planets that could potentially be habitable. A major breakthrough came in 2017 when NASA astronomers discovered a planetary system around a star called TRAPPIST-1. Much cooler and redder than our Sun, this ultra-cool dwarf star is located 39 light-years away in the constellation of Aquarius. It’s named after NASA’s ground-based TRAPPIST (TRAnsiting Planets and PlanetesImals Small Telescope) telescope, which helped with the discovery.
TRAPPIST-1 is orbited by seven Earth-sized terrestrial planets, and scientists think each of them may have liquid water on the surface. These planets, named TRAPPIST-1a through TRAPPIST-1g, are believed to be between 5.4 and 9.8 billion years old, or twice the age of our solar system. The planets are likely tidally dependent and only one side of each planet faces the star at all times, creating perpetual day and night sides on them. Using the data from the telescopes, scientists have deciphered that TRAPPIST-1b and c are the warmest of the group, receiving most of the light from the star, and TRAPPIST-1e, f and g are more likely to have surface water. Although there are no signs of life yet, TRAPPIST-1 could be a flashy new address if we are looking for habitable worlds of the future!