Red star or planet partially shaded by smaller dark star or planet.

Scientists aren’t sure how such a big planet formed around such a tiny star!

Image: Katherine Cain, courtesy of the Carnegie Institution for Science

Scientists thought they knew how gas giants like Jupiter were made. Now a newly spotted planet in a faraway solar system is challenging the recipe.

Planets are made from dust, rocks and gas left over after a star is formed. Early in a star’s life, this leftover rock and gas swirls around the star in a disk – a bit like the rings of Saturn but the size of a solar system. Over time, the heavier materials collide to form rocky planets, like Mercury, Venus, Earth, and Mars. If a rocky planet grows very big, about to 5 to 15 times the size of Earth, it attracts more and more gas until it becomes a gas giant like Jupiter.

This “recipe” for gas giants calls for the right amount of “ingredients” in the disk and the right amount of time for the giant planet to “cook.” Using this recipe (called Core Accretion Theory), astronomers predicted that tiny, red dwarf stars wouldn’t have Jupiter-sized planets. They reasoned that these smaller, lighter stars could not provide the right ingredients in the right amount of time.

Surprise! Astronomers just discovered a Jupiter-sized planet orbiting a tiny red dwarf star. Lead scientist Shubham Kanodia explains, “The host star, TOI-5205, is just about four times the size of Jupiter, yet it has somehow managed to form a Jupiter-sized planet, which is quite surprising!” According to the current rules, this planet should be forbidden!

One rule-breaking planet suggests our gas giant recipe needs tweaking. But this isn’t bad news. This is one important way science improves! “Forbidden” rule-breakers like TOI-5205 let us know that our rules are wrong. And it’s hard to fix a mistake if you don’t know you’ve made one!

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