# Ask Jimmy and the Bug

Hey, Jimmy!
Brendan R. from Illinois wants to know: “How long does it take to get to Mars?”

It depends on when you go. Earth and Mars zip around the Sun like cars on a funky racetrack. They travel at different speeds and in different-shaped “lanes,” or orbits—with slower Mars on the outside and faster Earth on the inside. The distance between them keeps changing. They can be as close as 34.65 million miles or as far apart as 243 million miles.

Spaceships bound for Mars are launched when the two planets are relatively close together. Otherwise, the trip would take way too long. According to space expert Dr. David Stern, “Only once every 26 months are they in the right position for an Earth-Mars mission, with Mars a little ahead on the ‘racetrack.’”

To make sure the spaceship will meet up with Mars, scientists “aim” it not where Mars is but where it will be when the spaceship reaches the Mars orbit. (This is like the quarterback who throws the football down the field in front of his receiver so the ball will be there when the receiver arrives.)

In July 2003, the timing was right, and NASA launched Spirit and Opportunity into space. After a journey of nearly seven months, these two small robot rovers landed on Mars in January 2004.

## Activity

1. Why are Earth and Mars closer to each other at certain times and farther away at other times?
[anno: Earth and Mars travel at different speeds and in different paths, or orbits, around the Sun. Sometimes their speeds and paths bring them closer together, and sometimes their speeds and paths take them farther away.]
2. How close can Earth and Mars be to each other? How far away? What is the difference in miles between the closest and farthest distances?
[anno: The closest Earth and Mars can be is 34.65 million miles apart. The farthest Earth and Mars can be from each other is 243 million miles. The difference between these two distances is 208,350,000 miles or 208.35 million miles.]
3. It takes about seven months for a spacecraft to reach Mars from Earth when the two planets are as close together as they can be. Approximately how long would it take a spacecraft to reach Mars from Earth when the two planets are as far away from each other as they can be? Explain how you figured out your answer.
[anno: It would take a spacecraft about 49 months or 4 years and one month to reach Mars when Mars and Earth are the farthest away that they can be. To figure out this problem, divide 243 million miles by 34.65 million miles to see how many times the seven-month journey time period should be multiplied.]