What is the largest star with a known planet?
The largest star known to hold a planet is HD 18438, with a radius about 88 times the Sun's: put it where the Sun is and its surface would swallow the orbit of Mercury. Everything about HD 18438 →
| # | Star | Radius | Distance |
|---|---|---|---|
| ★ 1 | HD 18438 | 88.5× the Sun's radius | 731 ly |
| 2 | Mirach | 86.4× the Sun's radius | 199 ly |
| 3 | HD 81817 | 83.8× the Sun's radius | 878 ly |
| 4 | HD 240237 | 71.2× the Sun's radius | 3,044 ly |
| 5 | HD 112300 | 65.8× the Sun's radius | 202 ly |
| 6 | HD 220074 | 54.9× the Sun's radius | 1,059 ly |
| 7 | HD 208527 | 51.1× the Sun's radius | 1,018 ly |
| 8 | HD 158996 | 50.3× the Sun's radius | 925 ly |
| 9 | BD+37 3172 | 50.2× the Sun's radius | 1,482 ly |
| 10 | BD+20 2457 | 49.0× the Sun's radius | 5,022 ly |
| 11 | bet Cnc | 47.2× the Sun's radius | 290 ly |
| 12 | HD 4760 | 42.4× the Sun's radius | 1,754 ly |
| 13 | HD 95127 | 41.0× the Sun's radius | 2,207 ly |
| 14 | HD 24064 | 40.0× the Sun's radius | 979 ly |
| 15 | HD 112640 | 39.0× the Sun's radius | 1,055 ly |
| 16 | HD 13189 | 38.4× the Sun's radius | 1,624 ly |
| 17 | HD 36384 | 38.4× the Sun's radius | 683 ly |
| 18 | Kochab | 38.3× the Sun's radius | 126 ly |
| 19 | HD 96127 | 35.0× the Sun's radius | 1,917 ly |
| 20 | BD+03 2562 | 32.4× the Sun's radius | 3,492 ly |
| 21 | HD 19615 | 32.3× the Sun's radius | 865 ly |
| 22 | Algieba | 31.9× the Sun's radius | 130 ly |
| 23 | 11 UMi | 29.8× the Sun's radius | 409 ly |
| 24 | HD 60292 | 27.0× the Sun's radius | 1,028 ly |
| 25 | tau Gem | 26.8× the Sun's radius | 367 ly |
Showing the top 25 of 4,431 that qualify.
Every star at the top of this table is a giant, and every one of them was once an ordinary star like the Sun. When a star exhausts the hydrogen in its core it swells enormously, and any close-in planet is swallowed in the process. The planets that remain are the ones that were far enough out to survive, which is why giant-star systems tend to hold worlds on wide orbits.
Radii here are measured values from the NASA Exoplanet Archive rather than estimates from colour and brightness, and the ranking requires an undisputed planet. Our own Sun will do this in about five billion years, expanding past the orbit of Mercury and probably Venus. Whether it reaches Earth is still argued over.
What is the largest star with a known planet?
The largest star known to hold a planet is HD 18438, with a radius about 88 times the Sun's: put it where the Sun is and its surface would swallow the orbit of Mercury.
How big is the largest star with a planet?
HD 18438 is about 88 times the Sun's radius. Placed at the centre of our solar system, a star that size would swallow the innermost orbit entirely.
What happens to a planet when its star becomes a giant?
Close-in planets are engulfed and destroyed. Planets further out are spared the surface but not the consequences: the star's output climbs, the habitable zone sweeps outward past them, and much of the outer atmosphere is eventually shed as a planetary nebula.
Will the Sun swallow the Earth?
In roughly five billion years the Sun will expand into a red giant that certainly reaches Mercury and Venus. Earth's fate is genuinely uncertain: the Sun loses mass as it expands, which widens Earth's orbit, and the two effects nearly cancel.
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