Web tool calculates your age on every Solar System planet

A free website now lets you find out how old you are on Mars, Venus, Mercury and beyond. You enter only your name and date of birth, and the tool returns your age on each planet of the Solar System, on selected asteroids and comets, on some exoplanets and even on the Sun.

The results can be striking. A person who is 37.5 years old on Earth turns out to be 19.9 on Mars, 60.9 on Venus and 155.7 on Mercury. In that case, the next birthday falls on Venus, on Halloween.

How the numbers are produced

The method is simple. The site counts the days since you were born and divides them by the length of a year on each object. For planets and dwarf planets, the year lengths come from NASA's planetary data sheets. For asteroids and comets, it uses figures from NASA JPL's Horizons system. Exoplanet data comes from the NASA Exoplanet Archive. Because most of those worlds have very short years, the site only counts "round" birthdays there: every 10, 100 or 1,000.

The Sun is a special case. It defines the year for every other object, so it has no year of its own. The site instead uses its rotation: the equator turns once every 25.05 days, and each turn counts as a "solar day". The person in the example has lived 547 of them.

Birthday map and calendar

The site also draws a map of your birthdays around the Sun. The Sun sits at the center, surrounded by one ring per planet, and a more intensely colored arc on each ring shows how far that planet has travelled since your last birthday. It also lists the date of your birthday on each world, how long until it arrives and which one comes next.

From 4 November the site opens an online shop selling a calendar with your space birthdays and those of your family. Shipping is limited to the United States, so a printable version will be sold as well. The calculations themselves are free and available now.