Planets' Atmosphere Analysis and Atmosphere’s Protection

Introduction

The name atmosphere name means vapour (atmos) and sphere (sphaira) coming from the Greek language. The atmosphere is a layer which consists out of other layers of gasses surrounding a planet, the atmosphere is held in place by the gravity of a planet. On earth we also have different layers in the atmosphere: troposphere, stratosphere, mesosphere, thermosphere and the exosphere. Beyond the exosphere is outer space. The atmosphere has differences in pressure due to the layers of gasses. An increase in altitude means a decrease in pressure due to having less layers of gasses pressing.

The atmosphere on earth is formed by gases which volcanoes spew around 4.6 billion years ago. This atmosphere would have 200 times as much carbon dioxide as today’s atmosphere and almost have no oxygen in the air, the oxygen in the atmosphere took millions of years to accumulate. This was probably done by primitive organisms, bacteria and plants (photosynthesis).

The atmosphere we have on earth protects us from many things making it suitable for human life, but does Kepler-186f have an atmosphere which is suitable for human life?

Analysing an Atmosphere

To determine a planet’s atmospheric composition is done by using spectrometers and telescopes. Certain elements absorb different parts of the light spectrum, using this we can generate a light signature. This light signature can be used to determine the elements in the atmosphere of a planet. The planet Kepler-186f is too distant for us to analyse the atmosphere with our existing telescopes. Our next generation telescope (James Webb Space Telescope) will be launched in 2021 and will only have a range of 1,5 million kilometres, thus making it impossible to determine the atmospheric composition of Kepler-186f as the planet is 550 light years away from us. However models do suggest that there is a great chance that Kepler-186f has an atmosphere which is suitable for humans.

Atmosphere’s Protection

The atmosphere is a vital part for all organisms on the earth, as the atmosphere protects us from dangerous radiation from the sun. The light of the sun gives off ultraviolet radiation which can destroy living cells and can cause for example skin cancer. The ultraviolet radiation is filtered out by the atmosphere, it acts as a radiation shield. The atmosphere holds the surface heat on the earth and prevents it from radiating out into space which we call the greenhouse effect. Without this effect the earth would be very cold and many organisms would not survive on earth, it also decreases extreme temperature differences between day and night time. Without an atmosphere a planet would have a terrain that is covered in craters because the planet has no protection from meteoroids. On earth we are protected from meteoroids as most meteoroids burn up into meteorites in the atmosphere which are much smaller.

Atmospheric Composition

Life would not be possible without the right chemical ingredients in the atmosphere, the most important chemical ingredients are: hydrogen, oxygen, nitrogen and carbon dioxide. These should also be balanced, the atmosphere cannot be too thick or too thin. Planets like Jupiter, Saturn, Uranus and Neptune have an atmosphere which consists of mostly hydrogen and helium. Mercury and Mars have the right ingredients but they are not balanced which means the atmosphere is too thin or too thick to support life.

The atmosphere on the earth consists of 78.09% nitrogen, 20.95% oxygen, 0.93% argon, 0.04% carbon dioxide and a very small amount consists of neon, helium, methane, krypton and hydrogen, as well as water vapor. In table 5 we can see the requirements for a planet to be habitable. The atmospheres were assumed to be composed of CO2, N2, and H2O only. N2 and CO2 are assumed to be well-mixed throughout the atmosphere. H2O concentrations are calculated following the temperature. Calculations were done on gravity and insolation, as well as N2 and CO2 partial pressures. The assumed range of CO2 and N2 partial pressures is only realistic if Kepler-186f is a rocky planet.

Surface temperature as a function of CO2 partial pressure for different N2 partial pressures. Water triple-point temperature of 273 K indicated by horizontal dashed line. Top to bottom rows: decreasing insolation. Left to right columns: increasing gravity. The calculated surface temperatures as a function of CO2 partial pressure for different N2 partial pressures. Most of the temperatures are above freezing levels and under burning levels, but not all of them. These results do suggest that Kepler-186f is a potentially habitable planet if it is a rocky planet and Earth-like in the atmospheric composition. The calculated surface temperature rise up to 350–370 K (77 - 97°C) for high-pressure atmospheres. Such high temperatures are not ideal for most organisms. Another potential challenge for life forms might be the increased pH value of rain due to high amounts of atmospheric CO2.

The Earth’s Atmosphere

As stated in the introduction, the earth has many layers in the atmosphere. One of them is the troposphere which is the lowest atmospheric layer. On average the troposphere is about 10 kilometres high. The weather develops in the troposphere because is it contains almost all of the atmosphere’s water vapour. The troposphere also contains the clouds, air masses and high-pressure and low-pressure systems. It also has a decrease of oxygen compared to the surface because of the thin air as the altitude increases, there are simply less oxygen molecules in the air. Because of the thin air, the temperature also decreases.

The next layer above troposphere is the stratosphere. Here we can find a strong horizontal wind, almost no clouds and water vapour. In this layer we will also find airplanes as there is almost no turbulence in this layer. We also find the ozone layer in the stratosphere which absorbs most of the sun ultraviolet radiation. Temperatures actually increases higher in the stratosphere.

At an average of 85 kilometres altitude we can find the mesosphere, the mesosphere has the lowest temperature of the layers and lays around -120°C (150 K). The mesosphere is the most difficult layer in the atmosphere to explore because it is too high for aircraft and weather balloons, but too low for spacecraft.
Then we have the ionosphere, the ionosphere conducts electricity. This happens with ions which are created by energetic particles from sunlight and outer space.
Next we have the thermosphere which is the thickest layer in the atmosphere, the lightest gasses (oxygen, helium and hydrogen) can be found here. Temperatures can rise to 1500°C (1733 K) in the thermosphere. The ISS (International Space Station) and the Hubble Space Telescope (NASA telescope) can be found in this layer.
And last is the exosphere, in the exosphere we can find solar storms. We find mostly hydrogen in the exosphere as it is the lightest element. Also weather satellites can be found in the exosphere.

Comparable Planets

There have been a small number of earth-sized planets discovered such as Kepler-20e. However, these all orbit too close to their star, making them too hot and therefore not habitable for life forms. Lots of other planets have been found outside of the star’s zone but are larger than earth. Many are thought to have a thick atmosphere like Jupiter and Neptune rather than a solid surface. Kepler-186f is one of the first planets which could be habitable because of the right size and orbits at the right distance. If Kepler-186f is rocky like earth and has a suitable atmosphere, any water at the surface of Kepler-186f could be in liquid form, making it possible to be habitable for life forms.

Sources:

1. https://www.solarsystemquick.com/universe/kepler-186f.htm
2. https://www.space.com/25541-alien-planet-kepler-186f-facts.html
3. https://en.wikipedia.org/wiki/Kepler-186f
4. https://apod.nasa.gov/apod/ap140419.html
5. https://www.nationalgeographic.org/encyclopedia/atmosphere/
6. https://www.space.com/17683-earth-atmosphere.html
7. http://iopscience.iop.org/article/10.1088/0004-637X/793/1/3/meta
8. https://en.wikipedia.org/wiki/Atmosphere_of_Earth
9. http://www.scienceterrific.com/atmosphere_function.php
10. https://curiosity.com/topics/how-to-analyze-the-atmosphere-of-another-planet-curiosity/
11. https://www.scienceabc.com/nature/universe/scientists-determine-atmosphere-planets.html
12. https://jwst.nasa.gov/comparison_about.html

Date
What did I do?
Time

2 July 2018
Sub-question + task division
2 hours

3 July 2018
Searched information
4 hours

4 July 2018
Searched information
2,5 hours

5 July 2018
Searched information and worked a bit on text
2,5 hours

6 July 2018
Searched information and worked a bit on text
2 hours

27 September
Worked on text
2 hours

14 November
Went to Leiden University and did some research on the transit method
6 hours

25 November
Worked on text
3 hours

2 January
Worked on the presentation + PowerPoint design
5 hours

3 January
Wrote text for the presentation
1,5 hours

4 January
Learned for the presentation
0,5 hours

5 January
Improved PowerPoint and learned for the presentation
1,5 hours

6 January
Learned for the presentation
0,5 hours

7 January
Learned for the presentation & worked on text
2,5 hours

8 January
Learned for the presentation
0,5 hours

19 January
Worked on text and improved layout
5 hours

Total: 41 hours