Astronomers discover giant planet that takes 483 days to orbit its star

An international team led by astronomer Ismael Mireles of the University of New Mexico have discovered two Saturn-like giant planets, TOI-4600 b and c, that orbit their star some 700 light-years away. The outer planet takes 483 days to orbit its star - the longest of any found so far by NASA's TESS (Transiting Exoplanet Survey Satellite) mission - while TOI-4600 b takes 83 days.

The two exoplanets could provide insights into how large, gaseous planets form and evolve. So far, few exoplanets with long periods have been detected and this is why TOI-4600 b and c could prove to be a gold mine of data for astronomers. The two planets offer the rarer prospect of revealing the atmospheric ingredients of temperate gas giants - those without scorching atmospheres.

TOI-4600 c is also one of the coldest exoplanets discovered by TESS to date. It has an estimated temperature of minus 116 Fahrenheit (minus 82 Celsius). TOI-4600 b, on the other hand, has a temperature of 165 degrees Fahrenheit (74 Celsius).

📣Discovery Alert! 📣 It's a long year for a cold Saturn. TOI-4600 c, a bit smaller than our Saturn, rounds its star in 483 days. Companion exoplanet TOI-4600 b orbits in 83 days. Planet b averages 165° F (74 C); planet c averages -116° F (-82 C). 🥶 https://t.co/pu5TjKwoOI pic.twitter.com/TaeBkIJQNd

— NASA Exoplanets (@NASAExoplanets) March 7, 2024

Now in an extended mission, NASA's TESS is designed to discover thousands of exoplanets - planets outside our solar system - in orbit around the brightest dwarf stars in the sky.

Spaceborne telescopes like TESS rely on the transit method which captures the tiny dip in starlight as an orbiting planet crosses the face of its star. But the longer a planet's orbit, the harder it is for TESS to catch it transiting its star.