The two giant planets indicate the possible presence of a ‘cold Saturn’.

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The two giant planets indicate the possible presence of a 'cold Saturn'.

This illustration captures the hypothetical appearance of TOI-4600 c, a “cold Saturn,” one of two giant planets recently discovered orbiting a star 700 light-years away.

The discovery unveils two massive planets, akin to our own Saturn, orbiting a star approximately 700 light-years away. The outer planet boasts an extraordinary year length of 483 days, a record identified by NASA’s TESS (the Transiting Exoplanet Survey Satellite) and stands out as one of the coldest in the exoplanet catalog.


Key Facts: Named TOI-4600 b and c, these planets hold significance for astronomers probing the formation and evolution of large, gaseous planets. Bridging the knowledge gap between our solar system’s gas giants and the “hot Jupiters” observed elsewhere in the galaxy, these discoveries contribute essential data to our understanding of planetary diversity and evolution.


In the extensive search for exoplanets spanning decades, over 5,500 confirmed planets have been discovered within the Milky Way, a galaxy likely hosting hundreds of billions. However, the prevalent detection method predominantly uncovers “long period” planets, characterized by years lasting 50 days or more. This technique, known as the transit method, focuses on detecting shadows as planets pass in front of their stars, favoring those with shorter orbits. Spaceborne telescopes like TESS, reliant on this method, have spearheaded exoplanet detections, yet the challenge intensifies with longer orbits.


A study from September 2023, utilizing TESS data, identified TOI-4600 b and c with extended orbits of 83 and 483 days, respectively. Though seemingly modest compared to our solar system’s gas giants, Jupiter and Saturn, these planets present a potential wealth of data due to the rarity of detecting long-period exoplanets. Their unique orbits offer a promising opportunity to unveil atmospheric components of “temperate” gas giants, distinct from the scorching atmospheres observed in hot and warm Jupiters.


“Temperate” proves to be a relative term as TOI-4600 b and c, though not suitable vacation destinations, offer intriguing insights. TOI-4600 b, slightly smaller than Saturn and nearly seven times the width of Earth, maintains an estimated atmospheric temperature of 165 degrees Fahrenheit (74 Celsius). In contrast, Planet c, roughly the size of Saturn and over nine times Earth’s width, experiences an estimated temperature of minus 116 Fahrenheit (minus 82 Celsius), ranking among the coldest exoplanets detected by TESS.


The Discoverers: this remarkable find is credited to an international team, led by astronomer Ismael Mireles from the University of New Mexico. Their detailed exploration of TOI-4600 b and c, titled “TOI-4600 b and c: Two Long-period Giant Planets Orbiting an Early K Dwarf,” was published in “The Astrophysical Journal Letters” in September 2023, showcasing the collaborative efforts that unveiled these distant giants.

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