Space Age2026-04-03

My Solution: Exercism Space Age solution

Instructions

Calculate a person's age on different planets given their age in Earth seconds.

Constraints: One Earth year is 31,557,600 seconds. Return the final number rounded to two decimal places.

Planet	Orbital period in Earth Years
Mercury	0.2408467
Venus	0.61519726
Earth	1.0
Mars	1.8808158
Jupiter	11.862615
Saturn	29.447498
Uranus	84.016846
Neptune	164.79132

Solution

const ORBITAL_PERIODS: Record<string, number> = {
  mercury: 0.2408467,
  venus: 0.61519726,
  earth: 1.0,
  mars: 1.8808158,
  jupiter: 11.862615,
  saturn: 29.447498,
  uranus: 84.016846,
  neptune: 164.79132
};

export function age(planet: string, seconds: number): number {
  const SECONDS_IN_YEAR_ON_EARTH = 31557600;

  return Number((seconds / SECONDS_IN_YEAR_ON_EARTH / ORBITAL_PERIODS[planet]).toFixed(2));
}

Test Cases

expect(age('earth', 1000000000)).toEqual(31.69);
expect(age('mercury', 2134835688)).toEqual(280.88);
expect(age('venus', 189839836)).toEqual(9.78);
expect(age('mars', 2129871239)).toEqual(35.88);

Mental Model

Treat Earth years as the base unit.

The Math: Convert the total seconds to Earth years first. Then, normalize that number by dividing it by the target planet's specific orbital period. Round to two decimal places at the very end to pass the strict tests.

The TS Architecture (Record): Instead of using a quirky TypeScript enum, I used a standard JavaScript object and wrapped it in the Record<string, number> utility type. This is a cleaner pattern that guarantees every planet key maps strictly to a numerical multiplier, preventing runtime lookup errors.