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Bending the Path: Gravity Checks for a Space Game

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Bending the Path: Gravity Checks for a Space Game

Use flyby simulator runs to model how a planet's gravity bends the paths of probes and comets.

Part 1: The flyby runs

Read the passage and Table 1, then answer questions 1–7.

The Game That Forgot Gravity

1The game design club at Juniper Hill Middle School is building a space game in which players steer robot probes through the solar system. When eighth grader Thiago Marchetti tested the first version, he noticed a problem: probes flew straight past giant planets as if nothing were there. The club's advisor, Ms. Wanjiru Castellane, used to plan spacecraft paths for a living. She gave the club a teaching simulator that includes the gravity of each planet, so they could check what real flybys look like.

2In each run, the simulator sends a probe toward a planet from very far away with its engine off. It records the probe's speed while it is still far from the planet, its closest distance from the planet's center, and how many degrees its path has turned by the time it is far away again. A bend of 0° means the path stayed a straight line. Jupiter has about 318 times Earth's mass, and Saturn has about 95 times Earth's mass. For Run 6, Thiago switched off Jupiter's gravity in the simulator. Table 1 shows his runs.

3Thiago also noticed that in every run the probe sped up as it came toward the planet and slowed down again as it moved away, leaving the planet at the same speed it arrived with. Ms. Castellane explained that a real probe that is meant to stay at Jupiter cannot just coast past. It fires its engine near its closest point to the planet.

4For the game's last level, the club added a comet. Before it met Jupiter, the comet traveled on a long orbit around the Sun that took about 200 years. In the simulator it passed about 1,000,000 km from Jupiter's center. Afterward the comet was on a much smaller orbit around the Sun, one that takes about 7 years and never carries it far beyond Jupiter's orbit.

5The final screen zooms out to the whole Milky Way, a disk of hundreds of billions of stars plus huge amounts of gas and dust. The Sun, carrying its planets along, travels around the center of the galaxy at about 230 km/s and takes about 230 million years for one trip. Thiago wondered why the Sun's path keeps curving into a loop instead of bending once, the way a probe's path does.

Table 1: Flyby Simulator Runs (closest distance is from the planet's center)
RunPlanetClosest distance (km)Arrival speed (km/s)Path bends by
1Jupiter1,000,0001068°
2Jupiter2,000,0001046°
3Jupiter1,000,0002028°
4Jupiter1,000,0005113°
5Saturn1,000,0001032°
6Jupiter, gravity off1,000,000100°
1.
Compare Runs 1 and 2. Which statement fits these two runs best?
Question 1 options
2.
Thiago wants to show how a planet's mass alone changes the bend. Which two runs should he compare?
Question 2 options
3.
Use Table 1. Round to the nearest whole number.

The path in Run 4 bent about times as much as the path in Run 3.

4.
Runs 3 and 4 pass at the same distance from Jupiter. Why did the slower probe's path bend so much more?
Question 4 options
5.
Use the patterns in Table 1. Sort each new flyby by how its bend would most likely compare with Run 1 (Jupiter, 1,000,000 km, 10 km/s). Everything not named stays the same as in Run 1.
6.
Use Runs 1 and 6 and paragraph 3. Which statement best describes what Jupiter's gravity does during a flyby?
Question 6 options
7.
Use Table 1 and paragraph 3. A mission team wants its probe to go into orbit around Jupiter instead of flying past. Which plan fits the simulator results best?
Question 7 options

Part 2: Comets and the galaxy

Use paragraphs 4 and 5 and what you learned in Part 1 to answer questions 8–10.

8.
Use paragraph 4. What best explains why the comet ended up on a 7-year orbit?
Question 8 options
9.
Use paragraph 5. Why does the Sun's path keep curving into a loop around the galaxy instead of bending once like a probe's path?
Question 9 options
10.
A club member says, "Gravity only matters for things in orbit. A probe that flies past a planet just keeps going straight, so the game can leave gravity out of flybys." Make a claim about this idea. Use data from at least three runs in Table 1 as evidence, and explain your reasoning about how gravity controls motion in the solar system.