How Long Would It Take to Reach the Nearest Earth Like Planet?
The short answer
About 75,000 years, if you flew at the speed of Voyager 1. The nearest planet that might be like Earth is Proxima b. It circles Proxima Centauri, the closest star to the Sun, about 4.2 light years away. Voyager 1 moves at about 17 km per second (38,000 mph).
Proxima b is at least as heavy as Earth and sits where liquid water could exist. But its star flares, and its air could be long gone.
Where the 75,000 years comes from
NASA puts Proxima Centauri 40,208,000,000,000 km away, about 4.25 light years. Voyager 1 moves at about 17.0 km per second (38,000 mph) relative to the Sun. Divide the distance by that speed and you get close to 75,000 years. NASA's own page uses an older speed, 17.3 km per second, and says over 73,000 years. Either way, it's tens of thousands of years.
Voyager 1 isn't actually heading to Proxima. It's flying in a different direction. The number is how long the trip would take at its speed. Even light needs a bit over four years to get there. A message sent in late 2026 would arrive in early 2031.
A trip that long outlasts everyone on board. Over the past 250,000 years, human generations have averaged about 26.9 years. 75,000 divided by 26.9 is about 2,790. So whoever lands would be nearly 3,000 generations after whoever left.
Why it might not be a second Earth
Proxima is a red dwarf, too faint to see from Earth without a telescope. Because it's so dim, the zone where water could stay liquid sits close in. Proxima b orbits at about 5% of the Earth to Sun distance, so its year lasts 11.2 days. Its minimum mass is about 1.07 times Earth's. It's only a minimum because the planet was found by the wobble it gives its star.
The problem is flares. Proxima b gets up to about 400 times the X rays Earth does, and about 100 times by a more typical estimate. In 2019 a single flare made Proxima more than 14,000 times brighter in ultraviolet. A NASA model found that the star's radiation could strip an Earth like atmosphere. In the fastest case, the planet could lose the equivalent of Earth's whole atmosphere in about 100 million years. Nobody knows yet whether Proxima b has air or water at all.
Key numbers
| What | Number | Source |
|---|---|---|
| Travel time to Proxima at Voyager 1's speed | about 75,000 years | Our arithmetic from NASA Imagine the Universe and NASA, Voyager 1 |
| NASA's figure, using 17.3 km/s | over 73,000 years | NASA Imagine the Universe |
| Distance to Proxima Centauri | 40,208,000,000,000 km, about 4.25 light years | NASA Imagine the Universe |
| Voyager 1's speed relative to the Sun | 17.0 km/s (about 38,000 mph) | NASA, Voyager 1 |
| Proxima b's minimum mass | about 1.07 Earths | NASA Exoplanet Catalog |
| Proxima b's distance from its star | about 0.0485 AU, about 5% of the Earth to Sun distance | NASA Exoplanet Catalog |
| A year on Proxima b | 11.2 days | ESO, 2016 (Anglada-Escudé et al.) |
| Proxima's brightness seen from Earth | about magnitude 11, too faint for the naked eye | Space.com |
| X rays Proxima b gets compared with Earth | up to about 400 times, about 100 times by a more typical estimate | Eos (AGU) |
| Ultraviolet brightening in Proxima's 2019 flare | more than 14,000 times | MacGregor et al. 2021, via AAS Nova |
| Time to lose the equivalent of Earth's whole atmosphere, fastest case | about 100 million years | NASA Goddard, 2017 |
| Generations on a 75,000 year trip | about 2,790, at 26.9 years each | Our arithmetic from Wang et al. 2023, Science Advances |
What the film simplifies
- "Hundreds of times Earth's X rays" is the top of the published range: up to about 400 times, with about 100 times as a more typical estimate.
- The 75,000 years uses Voyager 1's current speed. NASA's page uses an older, faster figure and says over 73,000. Voyager 1 isn't headed for Proxima, so the film draws it beside the rocket, never on the path.
- "At least as heavy as Earth" means a minimum mass of about 1.07 Earths. The real mass is likely a bit more.
- The star answering "No." right away is a cartoon joke. At light speed, a reply would take more than 8 years to come back.
- "Nearly three thousand generations" is about 2,790 at 26.9 years each. The on screen label rounds it to about 2,800.
- The talking rocket, the grumpy star with crossed arms, her eye glaring back through the telescope and the kid stepping onto the planet are cartoon. The line about needing a telescope is about seeing Proxima from Earth.
For teachers
Runtime 1 minute 6 seconds · Topics: Exoplanets, Space travel, Red dwarf stars, Light years · Full script below
Ask your class
Light reaches Proxima in a bit over four years. Why would Voyager 1 need about 75,000?
Answer
Voyager 1 moves at about 17 km per second, far slower than light. Crossing about 40 trillion km at that speed takes about 75,000 years.
A year on Proxima b lasts only 11.2 days. How can a planet that close to its star still have temperatures that allow liquid water?
Answer
Proxima is a dim red dwarf, so the zone where water could stay liquid sits very close to it, about 5% of the Earth to Sun distance.
If a human generation lasts about 27 years, roughly how many generations would pass on a 75,000 year trip?
Answer
About 2,800. 75,000 divided by 26.9 is about 2,790.
The script
Host: Seventy five thousand years. That's your flight time to the nearest planet that might be like Earth.
Rocket: Hop in! I'll have you there by Friday!
Host: It's called Proxima b. It circles the very next star, four point two light years away.
Host: It's at least as heavy as Earth, and just warm enough for oceans. Maybe.
Rocket: Hey, neighbor! Can we come over?
Host: Even at the speed of light, that message takes over four years to get there.
Proxima (the star): No.
Host: Meet Proxima. A red dwarf so dim, you need a telescope to see it.
Proxima (the star): Dim?! Watch this!
Host: Red dwarfs flare. Its planet takes hundreds of times Earth's X rays. Its air could be long gone.
Host: And we fly way slower than light. Even Voyager one would need the full seventy five thousand.
Rocket: I never said which Friday!
Host: So whoever lands won't be you. It'll be a grandkid, nearly three thousand generations later.
Rocket: Great, great, great, great, great grandkid!
Proxima (the star): Took you long enough.
Host: Soon: one long video, from Earth's core to the end of the universe. Follow!
Sources
- At Voyager's speed, reaching Proxima would take over 73,000 years.NASA Imagine the Universe
- Proxima b is 4.2 light years away, at least Earth's mass.NASA Exoplanet Catalog
- Proxima b orbits where liquid water could exist on its surface.ESO, 2016 (Anglada-Escudé et al.)
- Proxima is too faint to see with the naked eye.Space.com
- Proxima b gets hundreds of times Earth's X ray dose.Eos (AGU)
- Proxima b could lose an Earth like atmosphere.NASA Goddard, 2017
- Voyager 1 travels about 17 km per second.NASA, Voyager 1
- The average human generation lasts about 27 years.Wang et al. 2023, Science Advances
- A 2019 flare made Proxima Centauri more than 14,000 times brighter in ultraviolet.MacGregor et al. 2021, via AAS Nova
- Over the past 250,000 years, the average age at which humans had children is 26.9 years (Wang et al. 2023).Indiana University, 2023