The rediscovery of a lost planet could pave the way for the discovery of a habitable world in the distant solar system. The habitable zone is a conditional area in space, determined from the calculation that the conditions on the surface of the planets in it will be close to those on Earth and will ensure the existence of water in the liquid phase. The planet, the size and mass of Saturn with an orbit of thirty-five days, is one of the hundreds of “lost” worlds. Astronomers at the University of Warwick have unveiled a new method to track them in hopes of finding colder planets like these. The study is published by Astrophysical Journal Letters.

The planet NGTS-11b orbits a star at a distance of 620 light-years and is located five times closer to its star than Earth is to the Sun. NGTS-11b was originally discovered in a 2018 planetary search using data from NASA’s TESS telescope.

This search uses a planetary transit method that scans the sky for a telltale incident of light from a star. Which indicates that the object has passed between the telescope and the star. TESS scans only most areas of the sky for 27 days. This means that many of the longer period planets enter the TESS database only once.

And without a second observation, the planet is actually lost. A team led by the University of Warwick tracked one of these “lost” planets using telescopes at the Next-Generation Transit Survey (NGTS) in Chile and observed the star for seventy-nine nights. In the end, astronomers caught the planet in transit, this happened only a year after the first detection.

As a result, scientists found a planet with a longer period of revolution around its orbit. Such discoveries are rare but important because they enable scientists to study planets with extended orbital periods. These planets are colder and larger than the planets in our solar system. NGTS-11b has a temperature of only 160°C – colder than that of Mercury and Venus. While this is still too high a temperature to support life as we know it, conditions are close to habitable, says Dr. Samuel Gill of the University of Warwick’s physics department. Especially when comparing NGTS-11b to many previously discovered planets. They usually have temperatures above 1000°C.

Habitable zone refers to the range of orbits that would allow a planet or moon to support liquid water: too close to its star and it will be too hot, but too far away and the water will become too cold.

In the future, TESS will detect hundreds of single transits, which scientists will monitor using the new method. This will allow researchers to spot cooler exoplanets of all sizes. Even including planets more similar to those in our own solar system. Some will be small rocky planets in the habitable zone that are cool enough to house liquid oceans and potentially extraterrestrial life.