# Our Nearest Exoplanet: How Long Is the Trip?

## Result

The NASA Exoplanet Archive data downloaded on **23 September 2026** place
**Proxima Centauri b and d** at the same nearest-host distance: **1.301190 pc**, or
**4.243914 light-years**. NASA reports an asymmetric distance uncertainty of
**+0.000340 / -0.000350 pc** (approximately +0.001109 / -0.001142 light-years).

| Cruise speed | Earth-frame time | Time onboard |
|---|---:|---:|
| 17 km/s | 74,840.79 years | 74,840.79 years |
| 1% c | 424.391 years | 424.370 years |
| 10% c | 42.439 years | 42.226 years |
| 90% c | 4.715 years | 2.055 years |

At 17 km/s, time dilation changes the traveler's elapsed time by only about
1.05 hours. At 90% of light speed, Earth observers measure 4.72 years while
travelers experience about 2.06 years.

The distance uncertainty contributes approximately 0.027% uncertainty to every
time: about +19.6/-20.1 years at 17 km/s, +0.111/-0.114 years at 1% c,
+0.0111/-0.0114 years at 10% c, and +0.00123/-0.00127 years at 90% c in the
Earth frame. Onboard uncertainties are smaller by the Lorentz factor.

![Earth-frame and onboard travel times](travel_time_comparison.png)

## Method

The live NASA `pscomppars` table was queried through its synchronous TAP service.
All rows with a non-null system distance were retained, then sorted locally.
The minimum-distance rows were Proxima Cen b and Proxima Cen d. For distance
`D`, speed `v`, and `gamma = 1/sqrt(1-v^2/c^2)`, the calculations use
`t_Earth = D/v` and `t_onboard = t_Earth/gamma`. The supplied upper and lower
distance errors were propagated linearly.

## Scope and limitations

These are one-way, constant-speed cruise calculations, not mission designs.
They omit acceleration and braking, propulsion energy and reaction mass,
collisions with interstellar dust and gas, radiation shielding, navigation and
target motion, arrival-orbit insertion, communications delay, and the life
support and reliability requirements of decades-to-millennia-long flight.
At relativistic speeds, the energy and shielding requirements are especially
severe. The spacecraft and Proxima system are also treated as inertial for the
simple special-relativistic comparison.

## Provenance

Data source: NASA Exoplanet Archive, Planetary Systems Composite Parameters
(`pscomppars`), downloaded 2026-09-23. The exact query and constants are recorded
in `README.md` and `reproduce.py`; the original CSV is included unchanged.
