How Old Would I Be on Mars?

How old would I be if I lived on another planet?

On Earth, a "year" is the time our planet takes to complete one orbit around the Sun — about 365.25 days. But every planet orbits at a different speed and distance. Mars takes 686.97 Earth days per orbit, so a Martian year is nearly twice as long. If you were born on Mars, you'd have accumulated roughly half as many birthdays as you have on Earth. Mercury, meanwhile, races around the Sun in just 88 Earth days — you'd be celebrating a new birthday almost every three months.

A planet's "day" is the time it takes to complete one full rotation on its axis. Mars rotates at nearly the same rate as Earth — a Martian day (called a "sol") is just 24 hours and 37 minutes. Jupiter spins so fast that a Jovian day is under 10 Earth hours, meaning you'd rack up local days almost 2.5 times faster than on Earth. Out at Neptune, days are about 16 hours long, even though a Neptunian year spans 165 Earth years.

Halley's Comet is a special case: it follows a highly elliptical orbit and swings past the Sun roughly every 75 years. Most people alive today have experienced at most one appearance. It last visited in 1986 and isn't expected back until 2061.

Fun facts to explore

• Mars: At 1.88 Earth years per orbit, you're just over half your Earth age in Mars years. A 30-year-old is only about 16 on Mars.
• Mercury: One Mercury year is only 88 Earth days — birthdays come fast, but so does the radiation.
• Jupiter: A Jovian year is 11.86 Earth years. A 40-year-old has lived through fewer than 4 Jupiter years.
• Saturn: One Saturn year takes nearly 29.5 Earth years. If you're under 30, you haven't lived through a full Saturnian year.
• Neptune: Neptune completed its first full orbit since discovery in 2011, 165 years after being found in 1846. No living person will ever see two Neptune years.
• Pluto: A Plutonian year lasts 248 Earth years. No one born today will live to see Pluto finish a single orbit.
• Local days: Fast-spinning gas giants let you pile up local days quickly — Jupiter gives you about 2.4 local days per 1 Earth day.