Making the scale of the solar system easier to understand

01

About PlanetPath

Most people know that planets are far away, but the numbers are hard to picture. Is Jupiter three times farther than Mars, or ten? Would a trip to Neptune take months or decades? PlanetPath exists to answer questions like these quickly, and to show the reasoning behind every answer.

The site is built around one tool, the Planet Path Calculator. It combines a planet distance calculator with a planet travel time calculator: pick a planet, choose which distance to use, enter a spacecraft speed, and see the result alongside facts about the planet you selected.

02

Our purpose

Our purpose is to make planetary distance something you can explore rather than just read about. Numbers like “400 million km” or “4.5 billion km” are easy to quote and hard to feel. Turning them into a travel time at a speed you choose gives them a human scale.

We want PlanetPath to be useful to students checking a homework answer, teachers preparing a lesson, writers researching a story, and anyone who has looked at the night sky and wondered how far away those points of light really are.

03

What the Planet Path Calculator does

Earth is always the starting point. From there, the calculator works as a simple space travel calculator for any of the seven other planets.

• Earth-to-planet distance

  In kilometers, miles and astronomical units (AU).

• Four distance options

  Average, closest, farthest, or the calculated distance on a date you choose.

• Any spacecraft speed

  Enter km/h, km/s or mph, or start from a preset.

• Estimated travel time

  Shown in hours, days, months and years.

• Planet reference facts

  Diameter, gravity, orbital period, rotation, moons and temperature.

• Copy and share

  Copy a clean text summary with a link back to the same result.

04

How our calculations work

Every travel-time result comes from one deliberately simple formula:

1. Find the positions of Earth and the planet

   We use a simplified orbital model based on the approximate orbital elements that NASA’s Jet Propulsion Laboratory publishes for the planets. These published values are intended for the years 1800 to 2050. PlanetPath applies them with its own code; the results are our estimates, not JPL calculations.

2. Measure the Earth-to-planet distance

   For a chosen date, we calculate the straight-line distance between the two planets. For the average, closest and farthest options, we sampled the model twice a day from 1900 to 2050 and recorded the typical, smallest and largest distances.

3. Convert units

   Distances and speeds are converted with standard constants, listed below. Speeds in km/s and mph are converted to km/h before dividing.

4. Divide distance by speed

   The result in hours is converted into days, months and years so it is easy to read. Everything runs in your browser; nothing you enter is sent to us.

1 mile

1.609344 km

1 AU

149,597,870.7 km

1 km/s

3,600 km/h

1 year

365.25 days

05

Understanding planetary distances

There is no single, permanent distance between Earth and another planet. Every planet orbits the Sun at its own speed, on a slightly oval path, so the gap between any two planets is constantly changing. When Earth and another planet are on the same side of the Sun, they can be relatively close. When they are on opposite sides, the Sun sits between them and the planetary distance is far greater.

That is why PlanetPath never presents one fixed number as “the” distance to a planet. You choose which distance to use, and every result tells you which one it is. Our distance table on the calculator page shows the closest, average and farthest values for all seven planets.

Different sources also define “average distance” differently. Some quote the midpoint between the closest and farthest distances; PlanetPath uses the time-averaged distance, meaning the average across every moment in the period we sampled. Both are reasonable, but they give different numbers, which is why we state our definition clearly.

06

Our educational approach

We believe a good estimate you understand is more useful than a precise-looking number you can’t check. So PlanetPath is designed to show its working:

Simple enough to verify. The travel-time formula is one division. You can check any result with a basic calculator and the numbers we display.

Honest about assumptions. Each result states the distance option it used and reminds you that it is a straight-line, constant-speed estimate.

Context, not just answers. Planet facts, light travel times and real mission examples help connect a single result to the bigger picture of how the solar system works.

Open to exploration. Changing the speed, planet or date updates the result instantly, which makes it easy to compare “what if” scenarios in a classroom or on your own.

07

Accuracy and limitations

Calculator results are estimates and reference calculations. They are designed for learning and comparison, and they should not be used for navigation, mission planning, or any purpose where precision matters.

The distance model gives values close to published figures for well-known events, but it is still a simplification, and small differences from other sources are expected. The planet facts are rounded reference values. Some figures, such as the number of known moons, change as new discoveries are confirmed, so they may differ from the latest counts published elsewhere.

08

Why actual space missions differ from simple calculations

A real spacecraft cannot simply aim at a planet and fly there in a straight line at a steady speed. Once its engines stop, it coasts on a curved orbit around the Sun, and mission designers must plan that path so the spacecraft and the planet arrive at the same place at the same time. Several factors shape how long that takes:

• Orbital mechanics

  Spacecraft travel along curved paths shaped by the Sun’s gravity, which are usually longer than a straight line between two planets.

• Changing speed

  A spacecraft speeds up and slows down during a journey, and one that needs to enter orbit or land must lose speed when it arrives.

• Launch windows

  Efficient trips are only possible when the planets are suitably aligned, which can mean waiting months or years to launch.

• Gravity assists

  Flying close to other planets can change a spacecraft’s speed and direction without extra fuel, but often lengthens the route.

This is why some destinations take far longer than their distance suggests. Mercury, for example, is not the farthest planet from Earth, yet reaching orbit around it is especially difficult, because a spacecraft heading toward the Sun gains speed that it must later shed. The calculator page includes a table of real missions for comparison.

09

Our commitment to clear information

Space is full of big numbers, and it is easy to present them with more confidence than they deserve. We aim to do the opposite.

• State our assumptions

  Every result names the distance option it uses and the conditions behind it.

• Label estimates as estimates

  We never present a calculation as an exact or official figure.

• Explain our sources

  We describe where our data comes from and how we use it.

• Correct mistakes

  If you spot an error, tell us. We review reports and update the site when something is wrong or out of date.