Separating space dust: a micrometeorite hunt with sieves, magnets and filters
Pupils plan and carry out the separation of a model roof-dust mixture of gravel, sand, salt and iron filings, recover the salt by evaporation, and find out how scientists search for real micrometeorites and why a magnet alone is not proof.
- Choose a method to separate each part of a mixture: sieving, a magnet, dissolving and filtering, and evaporating.
- Recover a dissolved substance from a solution, and explain that dissolving is a reversible change.
- Explain how scientists collect micrometeorites, and why most magnetic specks in towns are not from space.
National Curriculum links
- Year 5, Properties and changes of materials: use knowledge of solids, liquids and gases to decide how mixtures might be separated, including through filtering, sieving and evaporating.
- Year 5, Properties and changes of materials: know that some materials will dissolve in liquid to form a solution, and describe how to recover a substance from a solution.
- Year 5, Properties and changes of materials: compare and group together everyday materials on the basis of their properties, including their response to magnets; demonstrate that dissolving and mixing are reversible changes.
- Upper Key Stage 2, working scientifically: planning different types of scientific enquiry; reporting and presenting findings, including conclusions and explanations.
Key vocabulary
- mixture
- sieve
- magnetic
- dissolve
- solution
- filter
- residue
- filtrate
- evaporate
- micrometeorite
Resources
- For each group, a cup of "roof dust" made up by the teacher: two tablespoons of dry sand, one tablespoon of small gravel, one teaspoon of table salt and a small pinch of iron filings.
- A tea strainer or kitchen sieve, a magnet sealed inside a plastic food bag, and two sheets of white paper.
- A jar of warm tap water, a spoon, a funnel with filter paper or a coffee filter, and a beaker to catch the liquid.
- A saucer or evaporating dish for each group, and a sunny windowsill or warm place.
- Hand lenses, trays and eye protection.
- The worksheet, one per pupil.
Background for the teacher
Every day, space dust lands all over the Earth. Particles smaller than about 2 mm that survive the fall are called micrometeorites, and most are only a tenth to a few tenths of a millimetre across. Several thousand tonnes of them reach the ground each year. Many melted on the way down into tiny balls called cosmic spherules, and because many contain the magnetic iron oxide magnetite, scientists use magnets to help pick them out of Antarctic snow, deep-sea mud and desert sand. Since 2016 they have also been found in dust swept from city roofs.
A magnet is only the first step. In towns, nearly all magnetic specks come from human activity, such as vehicles, building work and industry. A real micrometeorite is confirmed under a microscope by its shape and the crystal patterns on its surface, and then by measuring what it is made of.
The classroom mixture practises the same thinking. A sieve separates by grain size, so gravel stays behind. A magnet picks out the iron filings; with the magnet inside a bag, taking the magnet out lets the filings drop neatly off. Salt dissolves in water to form a solution, but sand does not, so filtering leaves the sand on the paper as residue and lets the salty water through as filtrate. Leaving the filtrate in a warm place evaporates the water and the salt reappears as crystals, which shows that dissolving is reversible. Order matters: pull the iron out before adding water, or it will start to rust.
Lesson plan
Starter 10 minutes
Tell the class that space dust lands on the school roof every day. How could scientists ever find it among all the other dirt? Show a cup of the model roof dust and list what is in it and one property of each part: gravel is big, sand is small, salt dissolves, iron is magnetic.
Groups put the method cards (sieve, magnet, dissolve and filter, evaporate) in the order they think will work best.
Main 35 minutes
Groups carry out their plan, wearing eye protection and working over a tray.
1. Sieve the mixture over white paper. The gravel stays in the sieve. 2. Move the bagged magnet slowly over the fine powder. Hold it over the second sheet of paper and pull the magnet out of the bag: the iron filings drop off. 3. Stir what is left into the warm water for one minute. Pupils describe what happens to the salt. 4. Pour the mixture through the filter paper. Sand stays on the paper; the clear salty water drips through. 5. Pour the filtrate onto a saucer and leave it in a warm place. Over the next few days the water evaporates and salt crystals form.
Pupils record each step and what it separated on the worksheet flow chart.
Plenary 15 minutes
Ask: why did we use the magnet before the water? Agree that iron rusts in water, and that the magnet works best on a dry powder.
Then show how real micrometeorite hunters work: a magnet, then sieves, then a microscope. Ask: if you found a tiny magnetic ball in gutter dust, could you be sure it came from space? Agree that most are made by people, and only a close look under a microscope by an expert can tell.
Differentiation
Use picture method cards in a fixed order, and work with an adult on the filtering step.
Plan the order, carry it out and complete the flow chart with what each method separated.
Explain why the magnet must be used before the water, and explain why salt and sugar mixed together could not be separated by filtering.
Safety and risk assessment
Check these points against your employer's risk assessment and your school's policies before the lesson.
| Hazard | How to control it |
|---|---|
| Iron filings in eyes or skin | Wear eye protection, keep filings in a tray, use the magnet inside a bag, do not rub eyes, and wash hands afterwards. |
| Small, strong magnets can pinch or be swallowed | Use ordinary classroom magnets, not small round magnets, and count them back in. |
| Scalds from hot water | Use warm tap water only, no hotter than a warm bath. |
| Spitting if the salt solution is heated | Leave the water to evaporate in a warm place; if speeding it up with heat, only an adult heats it, with eye protection. |
| Falls from collecting real roof or gutter dust | Pupils never climb. Real dust is collected by an adult from ground level, such as the bottom of a downpipe. |
Assessment questions with answers
- Which method separates the gravel from the sand?Answer: Sieving: the gravel is too big to pass through the holes.
- How did you get the iron filings out of the mixture?Answer: With a magnet inside a bag. Taking the magnet out of the bag let the filings drop off.
- When you stirred the mixture into water, the salt seemed to disappear. Where did it go, and how can you get it back?Answer: It dissolved to make a solution. Evaporating the water leaves the salt behind as crystals.
- Why does filtering separate sand from salty water?Answer: Sand grains are too big to pass through the tiny holes in the filter paper, but water with the salt dissolved in it passes through.
- A pupil finds a tiny magnetic ball in dust from a drain. Is it definitely a micrometeorite? Explain.Answer: No. Most magnetic particles in towns are made by human activity. It would need to be examined under a microscope, and its make-up measured, before anyone could say it came from space.
Homework
Write numbered instructions for separating a mixture of rice, salt and steel paperclips. For each step, say which property of the materials you are using.
Answer guidance: One good order: pick out the paperclips with a magnet (they are magnetic); sieve so that the rice stays behind and the finer salt passes through (grain size); or dissolve the salt in water, pour through a sieve to keep the rice, and evaporate the water to get the salt back (salt dissolves, rice does not).
Use with these pages
- What are micrometeorites?
- Micrometeorites in towns and cities
- Recognising a micrometeorite, and telling it from industrial spherules
- How to search for micrometeorites yourself, safely
- Micrometeorite
- Meteorites and magnets
These eight lessons are a free starter pack, written specially for this site. The full set of 25 lesson plans, with worksheets, end-of-unit tests and mark schemes, is in the Corvanelle book Teaching Meteorites. The lessons in the book are different lessons, so the starter pack and the book work together rather than repeating each other.