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Magnets and batteries on Mars

Electricity and magnetism · level 1, lesson 6 of 6

A question to start

If you landed on Mars and got lost, could you take out a compass and find north?

The idea

No. A compass points north on Earth because the whole Earth acts like a giant magnet. Mars does not, not any more. Long ago it did, and some of its rocks are still a little magnetic, but there is no planet-wide magnet for a compass to follow.

Magnets Mars Earth
The whole planet acts like a magnet no, not now yes
A compass points north no yes

Mars has a surprise, though: its dust sticks to magnets. The rover Opportunity carried a small magnet, and the red dust that landed on it gathered in a ring. Scientists found that nearly all of the dust in Mars's air is magnetic, because it has iron in it.

And rovers run on batteries, just like a torch. The batteries are charged up again by sunlight on solar panels, or by a nuclear generator that makes electricity from heat.

dust gathers in a ring on the magnet

Worked examples

1. Lost on Mars. A compass needle on Mars would not settle on north. Astronauts would find their way with maps, landmarks and radio signals from satellites in orbit.

2. Magnetic dust. Hold a magnet in a pile of Mars dust and it would come out fuzzy with red grains, like a magnet in iron filings.

3. A rover's batteries. Perseverance has two batteries for the busy moments of its day, charged up by its nuclear generator.

Try it

  1. Why would a compass not point north on Mars?
  2. What did Opportunity's magnet show about Mars dust?
  3. What makes Mars dust stick to magnets?
  4. How are a rover's batteries charged?
Answers
  1. Mars no longer acts like a giant magnet.
  2. Nearly all of the dust in the air is magnetic.
  3. It has iron in it.
  4. By solar panels or by a nuclear generator.

Common mistake

"Mars has no magnets at all." Some of its old rocks and almost all of its dust are magnetic. What Mars lacks is a magnet the size of the whole planet.

Where it leads