Heliocodex

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Other worlds and life

Planets round other stars, the places nearer home where there may be water, and the oldest question of all.

11 lessons in 3 parts. Every one can be read again at a deeper level.

Begin with lesson 1

A dark picture crossed by faint bands of light, with one tiny pale speck in the right-hand band.
A photograph. The only world known to have life, from 6 billion km away: the pale speck in the right-hand band of light. Voyager 1, 14 February 1990. Credit: NASA/JPL-Caltech.

Part 1

Worlds round other stars

How they are found, and one system with seven of them.

  1. 1
    Planets round other stars

    More than 6,000 planets are now known round other stars. Almost none has been seen directly. Here is how they are found.

  2. 2
    How planets are found

    Four ways of finding a planet round another star: the star's wobble, its dimming, a direct picture, and a flicker of bent light. Each finds a different kind.

    With moving pictures and photographs

  3. 3
    The kinds of planet out there

    More than 6,000 planets are known round other stars, and most are nothing like ours. The commonest kind found so far is one the Solar System does not have.

    With moving pictures and photographs

  4. 4
    TRAPPIST-1

    Seven planets the size of the Earth circle one small red star, all of them closer in than Mercury is to the Sun.

Part 2

What makes a world fit to live on

Air, warmth and water, here and on the moons of the giant planets.

  1. 5
    Air and the greenhouse: Venus, Earth and Mars

    Three rocky planets began much alike and ended as a furnace, a home and a frozen desert. The difference is their air.

  2. 6
    The habitable zone

    The band round a star where a planet could keep liquid water on its surface. It is a useful first guide, and our own Solar System shows how much it leaves out.

    With moving pictures and photographs

  3. 7
    Moons with oceans

    Several icy moons hide seas of liquid water under their crusts, kept warm by tides. They are the likeliest places to look for life.

Part 3

The question

What is known, what is not, and how people are looking.

  1. 8
    Are we alone?

    Life is known on one planet only. Where else might it be, how would we recognise it, and what has the search found so far?

  2. 9
    What life needs

    Life on Earth needs liquid water, a few common elements and a supply of energy. Given those, it turns up in boiling springs and in the dark of the sea floor.

    With moving pictures and photographs

  3. 10
    Looking for life in the Solar System

    Four places near home might hold life or the remains of it: Mars, Europa, Enceladus and Titan. Spacecraft have been to all four, and more are on the way.

    With moving pictures and photographs

  4. 11
    Listening for someone else

    Since 1960 radio telescopes have listened for a signal from another civilisation. Nothing confirmed has been heard. That silence is itself a puzzle.

    With moving pictures and photographs

Go and look