Which exoplanet orbits farthest from its star?
The widest orbit known belongs to UCAC4 328-061594 b, which circles its star at about 19,000 AU, roughly 633 times Neptune's distance from the Sun. Everything about UCAC4 328-061594 b →
| # | World | Orbit radius | Distance |
|---|---|---|---|
| ★ 1 | UCAC4 328-061594 b | 19,000 AU | 130 ly |
| 2 | GJ 900 b | 12,000 AU | 67.9 ly |
| 3 | COCONUTS-2 b | 7,506 AU | 35.5 ly |
| 4 | 2MASS J21252752-8138278 b | 7,493 AU | 111 ly |
| 5 | UCAC3 113-933 b | 6,100 AU | 172 ly |
| 6 | USco1556 b | 3,500 AU | 459 ly |
| 7 | HIP 77900 b | 3,319 AU | 492 ly |
| 8 | USco1621 b | 2,880 AU | 450 ly |
| 9 | WD 0806-661 b | 2,500 AU | 62.8 ly |
| 10 | GU Psc b | 2,000 AU | 155 ly |
| 11 | 2MASS J0249-0557 c | 1,950 AU | 215 ly |
| 12 | BD+60 1417 b | 1,662 AU | 147 ly |
| 13 | Ross 458 c | 1,100 AU | 37.5 ly |
| 14 | WISPIT 1 c | 840 AU | 750 ly |
| 15 | FU Tau b | 800 AU | 435 ly |
| 16 | HN Peg b | 773 AU | 59.1 ly |
| 17 | HIP 78530 b | 740 AU | 446 ly |
| 18 | KOINTREAU-1 b | 690 AU | 517 ly |
| 19 | USco CTIO 108 b | 670 AU | 470 ly |
| 20 | HD 106906 b | 650 AU | 336 ly |
| 21 | 2MASS J11550485-7919108 b | 587 AU | 329 ly |
| 22 | 2MASS J03590986+2009361 b | 572 AU | 383 ly |
| 23 | b Cen AB b | 556 AU | 320 ly |
| 24 | 2MASS J22501512+2325342 b | 518 AU | 187 ly |
| 25 | HD 203030 b | 487 AU | 128 ly |
Showing the top 25 of 5,885 that qualify.
One astronomical unit is the Earth-Sun distance. Neptune orbits at 30, and the outer edge of the Kuiper Belt is around 50, so the worlds at the top of this table sit hundreds or thousands of times further from their star than any planet in our own system. From that distance their star would be a bright point, not a disc.
Every one of them was found by direct imaging, because that is the only method that works far from a star: a transit needs the planet to pass in front, and a wobble takes one full orbit to measure, which here would be tens of thousands of years. The consequence is that these orbits are not measured so much as estimated from a single snapshot of the separation we see today, and whether such wide companions formed as planets at all is an open question.
Which exoplanet orbits farthest from its star?
The widest orbit known belongs to UCAC4 328-061594 b, which circles its star at about 19,000 AU, roughly 633 times Neptune's distance from the Sun.
How long is a year on the widest orbit?
Longer than recorded human history. A planet a few thousand astronomical units out takes on the order of a hundred thousand years to go round once, so nobody has watched one of these worlds move a meaningful fraction of its orbit.
Is a planet that far out still bound to its star?
Loosely. At thousands of astronomical units the gravitational grip is weak enough that a passing star can strip the planet away, so wide companions like these are thought to be a temporary arrangement on galactic timescales.
How did a planet get so far from its star?
Probably not by forming there: there is too little material that far out to build a planet from. The leading explanations are that UCAC4 328-061594 b was flung outward after a close encounter with another giant, or that it formed the way a star does, by collapsing directly out of a cloud of gas alongside its host.
Keep exploring: all records · the longest year known · planets photographed directly