enceladus? life on - do...
TRANSCRIPT
Life on Enceladus?
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Plenary
A billion miles from the Sun a tiny moon, Enceladus, orbits Saturn.
Enceladus is one of the
brightest objects in
the solar system.
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MainStarter
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Enceladus is covered in clean white ice.
Main PlenaryStarter
Is this true? Where could the liquid water be?
Yet scientists say it has oceans of hot liquid water.
Its surface temperature is −200 ºC.
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Main PlenaryStarter
On Earth, life may have started in the oceans.
If Enceladus has oceans, could it be home to alien life?
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.
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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
Working ScientificallyBig Idea
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Scientists have made two conclusions:
Does the evidence support the first conclusion?
If so, is it worth sending another spacecraft to
look for alien life?
1 There is hot liquid water on Enceladus
robot spacecraft Cassini
Starter PlenaryMain6
2 Enceladus could be home to alien life.
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SS1-2
Does the evidence support the conclusion that there is hot liquid water on Enceladus?
Starter PlenaryMain
1 Read the evidence cards and look at the images.
2 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.
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Starter Main Plenary
Is it worth sending a spacecraft to look
for alien life?
What else do you want to know before you decide?
SS1-2
Student sheets
Evidence card ASS1a
Cassini detected more than100 geysers erupting from cracks in the surface of Enceladus.
Geysers
Some scientists think that the source of water for the geysers may be a buried sea of liquid water.
The geysers blow out 200 kg of water every second, as water vapour and tiny ice crystals.
Student sheets
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.
SS1b
Most substances have a higher density as a solid than as a liquid. This is because particles are more closely packed in the solid.
Solid and liquid
Particles in liquid water
Particles in solid water (ice)
So any liquid water on Enceladus is probably under the ice.
Evidence card B
Student sheets
SS1c
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.
Gravity
liquid water
rocky coreice
Evidence card C
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.
Student sheets
SS1d
Cyanide
Cassini observed samples of the mixture that comes out of the geysers on Enceladus.
geysers
Evidence card D
Cassini has not detected these new substances in the geysers.
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.
mass spectrometer
Student sheets
SS1e
Cassini took samples of substances that come out of the geysers on Enceladus.
Rocky grains
Evidence card E
The mixture includes tiny grains of rock. The rock is mainly silicon dioxide.
■ 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.
Scientists suggest that the rock grains form like this:
Much of the sand on Earth is silicon dioxide.
Student sheets
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.
Evidence card F
Energy from the core might raise the temperature enough to melt some of the ice under the south pole.
Scientists suggest that the high temperature is evidence that Enceladus’ has a hot core.
This could create underground seas of liquid water.
Student sheets
SS1g
Sublimation
Geysers erupt from Enceladus. The geysers give out water vapour and tiny ice crystals.
This picture shows solid carbon dioxide
subliming.
Evidence card G
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.
Student sheets
SS1h
Surface
Evidence card H
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.
Some areas of Enceladus have big craters in its surface.
Other areas have no craters. Scientists say that this is evidence that the surface recently changed.
The surface of Enceladus is not smooth.
Student sheets
Organising evidenceSS2
Conclusion There is liquid water on Enceladus.
Strong evidence for the conclusion
Weak evidence for the conclusion
Strong evidence against the conclusion
Weak evidence against the conclusion
http://thedayusa.com/brhttp://thedayusa.com/briefing/cassini-s-grand-finaleiefing/cassini-s-grand-finale
