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What are the best conditions for clouds to form on Earth? What about on other planets? In this lesson students will conduct experiments learning how a cloud can be made in a jar. Thanks to this activity, they will make a hypothesis, understand and test which variables will affect the result, coming up with the conditions necessary to form clouds. Students will be introduced to exoplanet science, and why clouds are so important in this field. They will work in groups in a hands-on approach, learning how to present and discuss their findings to their peers.
Experiment equipment:
Digital/printed resources:
Almost everything we know about planets other than our own has been learned through telescope observations. If an alien was living in another solar system and was looking at earth through an alien telescope, a lot of the surface of the earth would be covered by clouds.
Figure 1: Earth as seen from ESA’s Copernicus Sentinel-3 Satellite
This cloud coverage would make it more difficult for the alien astronomers to observe the surface of the earth. By this same reasoning, our observations of other planets are vastly affected by cloud coverage. In order to understand a planet, its atmosphere and the surface that may be underneath the clouds, it is important that we first understand the clouds themselves.
In this set of activities the students will use inquiry learning methods to understand how clouds form on a planet and what conditions are needed on a planet for it to have clouds. Through this, it will not only help students to understand not only the importance of clouds in astronomy, but also help students to understand the cloud formation process on earth.
Through these activities, students will be encouraged to think about the similarities and differences between planets, and will learn about planets outside of our own solar system (exoplanets). Students will also have opportunities to test their scientific skills, and apply their understanding of cloud formation by using deductive skills to determine what clouds can teach us about all forms of planets from our own out to the furthest reaches of our current telescopes.
Background Science
Cloud formation
Cloud formation requires the same set of physics regardless of the planet the clouds are on, however there are vast differences when it comes to the chemicals and compositions involved in the formation.
The conditions that are required for clouds to form are simply:
On earth, the aerosols that clouds form around can come from many different sources. Some examples of these are smoke from volcanoes, pollution from cars, salt from sea spray, or sand in the air from sand storms.
The relative humidity of a pocket of air depends on the content of vapour in the atmosphere and the temperature of the atmosphere. The higher the temperature of the atmosphere, the more vapor that is needed to achieve super saturation, and vice versa. Super saturation for clouds on earth most commonly occurs when water evaporates from the surface of the earth, thus filling a pocket of air with water vapor. This pocket will then rise through the atmosphere where the air is cooler. As the pocket of air and vapor gets colder, the amount of vapor that the pocket can hold decreases until super saturation is reached. If there are aerosol particles in this pocket of air, the vapor will start to condense onto these particles and this will build up to form clouds.
On other planets, super saturation and aerosols are also both required for cloud formation, but different planet atmospheres will have very different chemical compositions, temperatures and pressures. On terrestrial planets, aerosols may be due to events such as dust storms or volcanos on the planet’s surface but the dust and smoke will likely have an entirely different chemical composition.
Solar system clouds
All of the planets in our solar system have clouds, except Mercury. Mercury does not have any clouds as it does not have an atmosphere. The gas giants have a swirling layer of cloud covering almost their entire surface, and terrestrial planets such as Earth and Mars have clouds coverage more closely resembling that seen on Earth: a variety of cloud patterns, usually with more cloud coverage at the poles and some storms across the planet.
As detailed in the accompanying presentation content, the clouds on other planets in our solar system are formed from a wide range of minerals, ices, gases.
Exoplanet Clouds
Clouds plays a crucial role in exoplanet research. Astronomers have found more than five thousand planets outside of our own solar system and the many of these planets are believed to have clouds in their atmospheres. Cloud coverage can greatly affect the light that we see from a planet with telescopes, so it is crucial that we can understand clouds and their processes in order to learn more about exoplanets. Clouds affect both the light being reflected by a planet, and the properties of the planet itself. Clouds are insulating so can affect the temperature of a planet. They also have a higher opacity than atmospheric gas and so absorb light from a planets host star and re-emit it at different wavelengths.
Clouds on exoplanets can look very different to clouds in our atmosphere here on Earth. The wide variety of planet sizes, compositions and temperatures can result in clouds or cloud layers of varying heights and thicknesses, made up of a huge variety of minerals, liquids, gases and solids. This makes it possible to have clouds on exoplanets that are made up of molten rock, glass, iron, rubies, sapphires and more!
Along with different compositions and sizes, clouds locations on a planet can also vary drastically on exoplanets. Some exoplanets are ‘tidally locked’, this means that the same face of the planet is always facing its host star, resulting in one side of the planet being eternally daytime and one side having continuous night with a twilight zone running around the middle. On planets like these, the day side is often too hot for clouds to form, but the night side might have a warmer planet surface, but a very cold atmosphere. This means the conditions on the nightside are much more suited for clouds to form, so may result in a planet that is half cloudy and half with clear skies!
In this activity, students will be introduced to the idea of clouds on other planets. The goal of this activity is to gauge students prior understanding to the topic and to engage them and elicit the students interest. The science behind cloud formation will not be addressed in this activity, instead it will focus on where clouds have been observed, what effects clouds can have, and why it is important for exoplanet scientists and astronomers to understand clouds.
Exercise: Clouds in Space Quiz
Follow the slideshow (see attachments) of quick quiz questions about clouds in space. Students should be given time to discuss each question. If there are many additional and follow up question from the students at this stage, it is suggested to write down these questions so that they can be addressed at the end of the lesson.
Additional Slide Information
Additional information and tips can be found in Attachment 2: Slide Notes. It is recommended to have these notes accessible during your class
Discussion
As seen in the quiz questions, many of the exoplanets we have found so far are believed to have clouds, and clouds can introduce difficulties when observing a planet. Therefore, it is important that exoplanet scientists can understand how and where clouds form in order to help them ‘see through’ the effects of the clouds, and learn more about the planet below. Learning about clouds also helps scientists to understand the chemical composition and dynamics of a planets atmosphere. If we know what conditions are needed for clouds to form, then when we observe a planet with clouds we can deduce that those conditions must be met on that planet.
Exercise
What do you think are the conditions needed for clouds to form?
There is no set answer for this question at this stage. The goal of this question is to peak the students inquiry. The same question will be asked later in the evaluation section (see Teacher Guide) and answers will be provided.
Show a video demonstration of the cloud in a jar experiment (the video can be found at https://vimeo.com/802277701)
During this demonstration it is important that students are only shown the effect and are not given the explanation yet of what is happening. This is to encourage the curiosity of the students and to encourage them to come up with their own hypotheses during the experiment and exploration phase of the lesson.
The students should see the clouds form in the jar. It is encouraged that they question how this is happening, but that answers are not provided by the teacher at this stage. The students will attempt to develop hypothesis themselves and test them in the following phases of the activity.
Students work as a class to determine the variables in this demonstration.
As a class, ask the students which variables are present in this demonstration. These should be written up on a board or screen that all of the students can see. The teacher may guide the students as needed. For each variable, try to match it to what the equivalent would be in an exoplanet’s atmosphere.
Results
With guidance from the teacher where necessary, the following variables should be identified by the class:
The variables with * are suggested to be tested in the next activity, so identification of these is highly recommended. The variables not in bold are useful for context and completeness and the identification of these will aide in class discussion. You class may also identify other variables that are not on this list! Not all variables will have a direct parallel to exoplanet atmospheres. This is because all physical analogies and demonstrations will have limitations, as it is not an exact replica of an exoplanet atmosphere.
In this activity, students will be split into groups and are asked to build the Clouds in a Jar experiment and investigate the effect of a variable on the cloud that is formed in order to try to determine what a planet would need to have clouds.
Building the experiment
The students should be split into groups of 3 to 5 students for this activity and follow the instruction of the video to build a Clouds in a jar experiment.
Exercise: investigating the variables
Each group will then choose one variable to investigate. If the groups have trouble deciding on a variable, you may instead assign them one of the following variables:
Suggested temperatures are: Ice water ( 0 °C) ,Room temperature (~ 20 °C), Hot (75 - 80°C) Suggested aerosols are: No aerosol, water aerosol (from a spray bottle), hairspray
The suggested optimum combination of variables to create a cloud is: V1 = Hot (75 - 80°C), V2 = Ice water (0 °C), V3 (Aerosol) = hairspray
It is suggested to not allow students to choose the quantity of hairspray as their variable, as this will be difficult to control and may cause issues if there is poor ventilation.
If one group finishes testing their initial variable, they may experiment further to learn more about the topic. To allow students to practice their scientific skills, it is suggested that you allow them to come up with their plans for further experimentation and only intervene if their testing is unsafe.
Students can record their results in any way that they see fit. One suggested method for recording their results is as follows:
Students will set up a digital camera or camera phone so that the eye test chart is visible through the glass container. A photograph will be taken of the container with no cloud as a control. Photos/videos/time-lapses will then be taken (with the same lighting and the camera in the same position) to document the thickness of the cloud. You can keep track of conditions by numbering each test and including a piece of paper in the photograph with that number drawn on it.
To conclude this activity the students can have an open discussion where they break down the steps in the experiment to understand what conditions are needed for clouds to form on a planet.
In this activity students are encouraged to think independently and practice their problem solving skills. Students are allowed to come up with their own hypothesis’ and test them using methods that they deem appropriate and helpful. It is important during this activity that the students are documenting their results in an appropriate and accurate manner.
More details can be found in the teacher notes attachment.
As an extension to the practical part of this activity, students can also make a group presentation. See the teacher notes for more details (available in the attachments)
During this activity there are questions list in the Teacher Guide to be asked during and after the activity. See "Teacher Guide" in the attachments section for more information.
NASA Video - Exoplanet Clouds: 'Jewels' of New Knowledge
ESA resources
Extra information
CHAMELEON Marie Curie Exoplanet Research Network
