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Session 10: Finding Other Worlds

Start thinking: What planets can we see with the naked eye? What about with a telescope?

How do scientists find planets that are much further away - planets outside our solar system?

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Planets we can see with the naked eye:

They look like slightly wandering stars. They are visible because they reflect sunlight and are relatively close.

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Can Earth support life?

Earth can support life.

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Mars cannot support life today, although lower layers (underground water/ice) may contain microbial life.

Can Mars support life?

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Jupiter cannot support life due to extreme gravity and pressure.

Can Jupiter support life?

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Venus cannot support life - the runaway greenhouse

effect turned Venus into a 465°C acid-cloud hothouse.

Can Venus support life?

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Today’s Big Question:

How many planets are there that could harbour life?

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PATHWAY 1

Planet Hunters

Discover the difficulty of spotting distant planets
The wobble method
The transit method

10 mins

PATHWAY 2

Could They Support Life?

The Earth Similarity Index
Detecting gases in distant atmospheres

10 mins

How many planets are there that could harbour life?

Finished? Complete the ‘Hunting for Other Worlds’ Minigame

Before starting the pathways ask: "What does a planet actually need to support life?" Take answers and write them on the board. This naturally leads into liquid water, suitable temperature, atmosphere, energy source, and distance from a star

"Today we are going to find out how scientists even spot a planet that is trillions of kilometres away (by watching stars wobble or dim as planets pass in front of them), and then how they decide whether it could actually support life.

Walk around. If a learner is on Pathway 1, ask them to explain the difference between the wobble method and the transit method in one sentence each. If a learner is on Pathway 2, ask them why a high ESI score is not the same as proof of life. "Which fact surprised you most?" usually brings a disengaged learner back in.

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Your International Planet Search Team has

discovered several planets that might support life!

You have enough money to investigate only ONE planet. Which planet should we choose?

Mars

Kepler-442b

Proxima Centauri b

TRAPPIST-1e

Venus

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Round 1: ESI Scores

Mars

Kepler-442b

Proxima Centauri b

TRAPPIST-1e

Venus

0.64

0.84

0.87

0.85

0.44

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Plot Twist 1 - New Information

Mars

Venus

has evidence of ancient rivers

receives similar energy to Earth

its star produces powerful radiation bursts

may have liquid water

similar in size to Earth

Kepler-442b

Proxima Centauri b

TRAPPIST-1e

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Plot Twist 2 - New Information

Mars

Kepler-442b

Proxima Centauri b

TRAPPIST-1e

Venus

It has a thin atmosphere with no oxygen.

We detected oxygen and methane gas in its atmosphere - two gases that usually only exist together if life is constantly producing them.

Radiation bursts have likely stripped its atmosphere away entirely.

We don't know if it has an atmosphere yet, but scientists are searching for water vapour.

It has a surface temperature is 460°C with an atmosphere of toxic carbon dioxide and sulfuric acid.

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The Final Decision

"We choose ______ because…" Requirements: mention the ESI score mention at least one piece of additional evidence explain why another planet was rejected

Each group has 1 minute to prepare a statement. Requirements: mention the ESI score, mention at least one piece of additional evidence, and explain why another planet was rejected. Take 3–4 quick responses from different groups.

Debrief

Ask: "Which round changed your mind the most: the ESI scores, the first twist, or the second twist? What does that tell us about how scientists should weigh different kinds of evidence?"

The ESI Trap: They should realise that a high Earth Similarity Index (like Proxima Centauri b's 0.87) only measures physical size and temperature, not actual habitability.

The Atmospheric Decider: They should conclude that gas chemistry (like finding oxygen and methane together) is the ultimate evidence for life, while physical size is just a starting point.

The Nature of Science: They should note that scientists must always be willing to change their minds and discard old theories when better data (like telescope spectroscopy) becomes available.

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WE HAVE COVERED:

Why finding planets around distant stars is so difficult
The wobble method and the transit method for detecting exoplanets
What the habitable zone is and why it matters
What the Earth Similarity Index measures
Gases that could be biosignatures

Learner Journal

Part 1: Three Things I Learnt Today

Open your Learner Journal. Write down three things you learnt. These can be facts, ideas, or things that surprised you.

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How many planets are there that could harbour life?

My answer is…

My evidence is…(think about distance, size, and atmospheric gases)

Write your response in your Learner Journal, then ﬁnish sections 3-5.

Learner Journal

Part 2: Reflective Question

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“To know if life can exist on a distant world, we look for atmospheres out of chemical balance. Living things alter their planets - they breathe, produce gases, and leave chemical fingerprints across the light of their star.” Dr. Sara Seager, Astrophysicist & NASA Exoplanet Pioneer (2020)

Real scientific conclusions are built the way your group built its answer today: starting with one piece of evidence, then revising as more arrives.

Lock-In Quote

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Extension Activities

Extension 1

Extension 2

Machines that Think

The Invention That Opened Up the Sky