The Orbit Sandbox
Every planet's year is set by one number — its distance — and the relationship is not a straight line.
Phase 0 · The phenomenon
One number sets the year
A scatter chart: distance from the Sun in astronomical units on the horizontal axis from 0 to 32, orbital period in years on the vertical axis from 0 to 170. Mercury, Venus, Earth and Mars cluster near zero, Jupiter sits at about 5 AU and 12 years, Saturn at about 10 AU and 29 years, Uranus at about 19 AU and 84 years and Neptune at about 30 AU and 165 years, the points bending upward along a curve.
Mercury circles the Sun in 88 days. Earth takes a year. Neptune, about 30 times farther out than Earth, takes not 30 years but 165.
Mass, size and composition of the planets do not matter: tiny Mercury and giant Jupiter both obey the same rule, and so do comets, asteroids and planets around other stars.
In this lab you will find that rule, use it to read orbits, weigh a distant star, and then turn to the cratered surfaces of other worlds to read the solar system's earliest history.
What single rule connects every planet's distance to the length of its year — and what else can that rule, and the craters on other worlds, tell us?
What this lab works toward
HS-ESS1-4Use mathematics or a computer model to predict how objects orbit in the solar system.HS-ESS1-6Use evidence from ancient rocks, meteorites and other planets' surfaces to reconstruct Earth's early history.
Plain-English summaries. The course maps these performance expectations to this lab; the official wording is published at nextgenscience.org.
The stations
- Kepler's Third LawHow does a planet's year grow with its distance from the Sun?
- Ellipse LabHow does an orbit's shape change a body's speed and its distance from the Sun?
- Star ScaleHow does the star's mass change the rule — and how can a planet's year weigh its star?
- Crater ClockHow do crater counts on the Moon date surfaces and reveal the solar system's violent youth?
Each station runs the same loop: predict before you see any data, investigate the model and record runs, reveal what the measurements show, then explain the gap between your prediction and the result. A claim-evidence-reasoning checkpoint and an exit ticket close the lab.
- Orbits are calculated for one planet around one star. Planets also tug on each other, which shifts their orbits slightly over time.
- Kepler's third law in this form assumes the orbiting body's mass is tiny compared with the star's — true for every planet in the solar system.
- The crater clock uses a curve calibrated with Moon rocks returned by the Apollo and Luna missions. Applying it to other planets needs corrections for their different impact rates.
- Crater counts in the model are idealised. Real counts must exclude secondary craters and account for craters erased by later lava flows or erosion.