Is every hole possible?

Yes. A script fires thousands of shots at every hole and checks that each one can be done at or under par.

Why did my ball roll straight over the cup?

It was going too fast. The cup only catches a slow ball, so on long shots use less power or let a planet slow the ball down first.

How does the gravity work?

Each planet pulls the ball toward its center with a strength that falls off with the square of the distance, as in Newton’s law of universal gravitation.

What is a gravity assist?

A maneuver where a spacecraft flies close to a moving planet to change its speed and direction without using fuel. NASA’s Voyager probes used a series of them to tour the outer planets.

Can I play on a phone?

Yes. On a tall phone screen the course rotates to fit, and you drag with your finger to shoot. Tap the notes tab at the bottom to scroll down to this page.

Gravity Golf

Slingshot your ball around planets. 18 holes across the solar system. Back to the game

How to play

Press anywhere on the course, pull back like a slingshot, and let go. The further you pull, the harder you hit. A red dotted line shows the first second of your shot; after that, gravity takes over. Land the ball in the cup with the red flag. Some cups float in space, others sit on a planet’s surface, where your ball can land, roll and stop for another shot.

The cup only catches a ball that is moving slowly enough. Roll over it too fast and it skips straight past. If a shot flies off into deep space, falls into a black hole or ends up circling forever, it comes back to where you shot from and you take a one-stroke penalty, just like a lost ball in real golf.

On a keyboard, press an arrow key to aim, use up and down for power, and press Space to shoot (Shift with left or right fine-tunes the angle). Press G, or tap “see gravity”, to show which way space pulls at every spot on the course.

The physics is real (mostly)

Every planet pulls your ball with a force that follows Newton’s law of gravitation: the pull gets four times weaker each time you double the distance. That’s why a ball skimming close to a planet whips around sharply while a distant one only bends a little. The bent grid on the paper is a picture of that pull: the lines sag toward each mass, most steeply right next to it.

Close passes bend your path sharply. Real spacecraft use the same pull, plus the planet’s own motion around the Sun, to gain speed in a gravity assist. Voyager 2 did this at Jupiter, Saturn and Uranus on its way to Neptune. In this game the planets stand still, so a fly-by changes your direction but not your speed.

A few other things are game rules rather than physics. Balls bounce off rock instead of cratering it, cups gently catch a ball that drifts close, and wormholes are, as far as anyone knows, science fiction. Black holes, on the other hand, really do have a point of no return called the event horizon.

Strategy tips

Don’t aim at the cup. Aim at the gravity, and let it bend the ball toward the cup.
Soft shots stay near planets and curve more. Hard shots fly straighter and further.
For cups on a planet, come in slowly and nearly sideways, so the ball rolls rather than bounces.
Moving moons change the course over time. Watch one orbit before you shoot.

Scoring

Each hole has a par, the number of strokes a good player needs. One under par is a birdie, two under is an eagle, and one stroke is a hole in one. Your scorecard and progress are saved in your browser, so you can finish the round later. After a full round, tap any hole on your scorecard to practise it and chase your best score there.

Questions people ask

Is every hole possible?: Yes. A script fires thousands of shots at every hole and checks that each one can be done at or under par.
Why did my ball roll straight over the cup?: It was going too fast. The cup only catches a slow ball, so on long shots use less power or let a planet slow the ball down first.
How does the gravity work?: Each planet pulls the ball toward its center with a strength that falls off with the square of the distance, as in Newton’s law of universal gravitation.
What is a gravity assist?: A maneuver where a spacecraft flies close to a moving planet to change its speed and direction without using fuel. NASA’s Voyager probes used a series of them to tour the outer planets.
Can I play on a phone?: Yes. On a tall phone screen the course rotates to fit, and you drag with your finger to shoot. Tap the notes tab at the bottom to scroll down to this page.