A billion miles from the Sun a tiny moon, Enceladus, orbits Saturn.

Transcription

1 Life on Enceladus?

2 A billion miles from the Sun a tiny moon, Enceladus, orbits Saturn. Enceladus is one of the brightest objects in the solar system. 2 Starter Main Plenary

3 Enceladus is covered in clean white ice. Its surface temperature is 200 ºC. Yet scientists say it has oceans of hot liquid water. Is this true? Where could the liquid water be? 3 Starter Main Plenary

4 On Earth, life may have started in the oceans. Lava, hot water and sulfur compounds burst into the ocean from seafloor hydrothermal vents. Chemical reactions around these vents formed the molecules of the first living things. If Enceladus has oceans, could it be home to alien life? 4 Starter Main Plenary

5 In this activity, you will Decide whether the evidence supports the conclusion that there is hot liquid water on Enceladus: Matter: How particle arrangements explain the properties of liquid water and ice Consider conclusions: Assess the strength of evidence for a conclusion Big Idea Working Scientifically 5

6 Scientists have made two conclusions: 2 Enceladus could be 1 There is hot liquid water on Enceladus home to alien life. Does the evidence support the first conclusion? robot spacecraft Cassini If so, is it worth sending another spacecraft to look for alien life? 6 Starter Main Plenary

7 SS1-2 Does the evidence support the conclusion that there is hot liquid water on Enceladus? 1 2 Read the evidence cards and look at the images. For each evidence card: Decide which box on SS2 you think it should go in. Write the title of the evidence card in this box. 3 In your group, weigh up all the evidence and decide on an answer to the question above. 4 Work alone to write down your own answer to the question above. Explain your decision. 7 Starter Main Plenary

8 SS1-2 Is it worth sending a spacecraft to look for alien life? What else do you want to know before you decide? 8 Starter Main Plenary

9 Evidence card A SS1a Geysers Cassini detected more than100 geysers erupting from cracks in the surface of Enceladus. The geysers blow out 200 kg of water every second, as water vapour and tiny ice crystals. Some scientists think that the source of water for the geysers may be a buried sea of liquid water. Student sheets

10 Evidence card B Solid and liquid SS1b Particles in solid water (ice) Most substances have a higher density as a solid than as a liquid. This is because particles are more closely packed in the solid. But water is different. At 0 C particles are more closely packed in the liquid. This means that liquid water has a higher density than ice. So any liquid water on Enceladus is probably under the ice. Particles in liquid water Student sheets

11 SS1c Evidence card C Gravity As Cassini flew past Enceladus, it changed direction. Scientists monitored the change of direction. They said it was caused by the gravitational field of Enceladus. Scientists calculated that Enceladus has more mass at its south pole than you would expect if the moon was ice all the way down to its rocky core. Liquid water at 0 C has a greater density than ice, and so more mass for a given volume. An ocean under the ice could explain the extra mass at the south pole. liquid water ice rocky core Student sheets

12 Evidence card D SS1d Cyanide Cassini observed samples of the mixture that comes out of the geysers on Enceladus. geysers mass spectrometer An instrument called a mass spectrometer identified one substance in the mixture as hydrogen cyanide. Hydrogen cyanide reacts with other substances dissolved in liquid water to make new ones. Cassini has not detected these new substances in the geysers. Student sheets

13 SS1e Evidence card E Rocky grains Cassini took samples of substances that come out of the geysers on Enceladus. The mixture includes tiny grains of rock. The rock is mainly silicon dioxide. Scientists suggest that the rock grains form like this: Hot water moves upwards. It contains dissolved substances from the rocky core. The concentrated solution is slightly alkaline. The hot solution comes into contact with cold water. It cools quickly. Tiny rock grains come out of solution. Much of the sand on Earth is silicon dioxide. Student sheets

14 Evidence card F SS1f Hot core Cassini measured the temperature at the south pole of Enceladus as 116 ºC. This is warmer than the temperature of other bodies at the same distance from the Sun. Scientists suggest that the high temperature is evidence that Enceladus has a hot core. Energy from the core might raise the temperature enough to melt some of the ice under the south pole. This could create underground seas of liquid water. Student sheets

15 Evidence card G SS1g Sublimation Geysers erupt from Enceladus. The geysers give out water vapour and tiny ice crystals. Sublimation is the change from the solid state to the gas state, without going through the liquid state. Some scientists say that the water vapour forms when ice under the surface sublimes. This picture shows solid carbon dioxide subliming. Student sheets

16 Evidence card H SS1h Surface Some areas of Enceladus have big craters in its surface. The surface of Enceladus is not smooth. Other areas have no craters. Scientists say that this is evidence that the surface recently changed. The different features on the surface of Enceladus suggest that it may have been active with water volcanoes which have changed its surface over time. Student sheets

17 SS2 Organising evidence Conclusion There is liquid water on Enceladus. Strong evidence for the conclusion Strong evidence against the conclusion Weak evidence for the conclusion Weak evidence against the conclusion Student sheets

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