VOCABULARY:
atmosphere
carbon dioxide
helium
hydrogen
Solar System
BACKGROUND:
An atmosphere is the layer of gases that envelop a planet. On the Earth, it is this envelope that allows organisms to live. Atmospheric ozone protects us from ultraviolet radiation. CO2 and other gases trap heat and keep the surface warm enough for life to thrive. Oxygen has allowed life to evolve.
Each of the planets has a different atmosphere, although there are clear similarities between the atmospheres of the four terrestrial planets and the four gas giant planets. The terrestrial planets are rich in heavier gases and gaseous compounds, such as carbon dioxide, nitrogen, oxygen, ozone, and argon. In contrast, the gas giant atmospheres are composed mostly of hydrogen and helium.
The atmospheres of at least the inner planets has evolved since they formed. This is clearest for the Earth. The Earth’s original atmosphere was probably similar to Venus in composition, consisting of carbon dioxide and nitrogen. The evolution of photosynthesis converted carbon dioxide in the Earth’s atmosphere to oxygen, increasing the amount of O2 in it from an initial 0.01% to its current 22% level.
Mercury has a very thin, almost undetectable atmosphere composed of sodium and potassium gas. These elements were likely blown from the surface of Mercury by the solar wind.
The atmosphere of Venus is composed mainly of carbon dioxide with minor amounts of nitrogen and trace amounts of nitrogen, helium, neon, and argon.
The Earth's atmosphere primarily composed of nitrogen and oxygen. Minor gases include and carbon dioxide, ozone, argon, and helium.
Mars' atmosphere is a thin layer composed mainly of carbon dioxide. Nitrogen, argon, and small traces of oxygen and water vapor are also present.
Jupiter's atmosphere contains mainly helium and hydrogen with trace amounts of water, ammonia, methane, and other carbon compounds. Three layers of clouds may exist in Jupiter’s outermost atmosphere. The lowest are made of water ice or droplets, the next are crystals of a compound of ammonia and hydrogen sulfide, and the highest clouds are ammonia ice. There seems to be no solid surface under the atmosphere, only a transition from gas to liquid metallic hydrogen. In the top one-fourth of the planet, the pressure and temperature are so high that the hydrogen atoms are stripped of their outer electrons, forming a liquid metal.
Like Jupiter, Saturn has a thick atmosphere composed of hydrogen and helium. The ratio of hydrogen to helium ratio decreases with depth. Methane and ammonia are also present. The atmosphere of Saturn envelops a thick layer of metallic hydrogen.
Uranus' atmosphere is composed mainly of hydrogen and minor amounts of helium Methane is present in minor amounts, and probably forms most of the clouds seen by space probes and telescopes. Uranus and Neptune both appear blue because methane strongly absorbs light of other wavelengths.
The atmosphere of Neptune consists mainly of hydrogen and helium, but about 2.5-3% of the atmosphere is methane. Like Uranus, clouds in Neptune's atmosphere are composed of crystals of methane.
Pluto's atmosphere seems to be very thin, and is likely composed of nitrogen and carbon dioxide.
Note that none of the other planets or moons in the Solar System have atmospheres similar to the Earth. This means that if humans travel to other bodies, they will have to bring their own atmosphere in order to survive.
PROCEDURE:
Present the information on planetary atmospheres discussed in the Background with your students.
After the children discuss this information, have them compare and contrast the different atmospheres. They should observe that the inner planets all have nitrogen and carbon dioxide, except for Mercury. They should note that the gas giant planets have abundant helium, hydrogen and methane. You may wish to explain that planetary atmospheres have changed through time, using the Earth as an example.
In a first, atmosphere found around Earth-like planet Updated April 7, 2017
GJ 1132b, just 39 light years away, raises the tantalising possibility of life beyond our solar system.
Astronomers have, for the first time, detected an atmosphere around an Earth-like planet just 39 light years away, a significant step towards the detection of life beyond our solar system.
Scientists, including those from Max Planck Institute for Astronomy in Germany, studied the planet known as GJ 1132b, which is 1.4 times the size of our planet.
They imaged the planet’s host star, GJ 1132, and measured the slight decrease in brightness as the planet and its atmosphere absorbed some of the starlight while passing directly in front of their host star.
Too much like our Earth
The detection of an atmosphere around super Earth GJ 1132b marks for the first time the detection of an atmosphere around a planet with a mass and radius close to the Earth’s mass and radius (1.6 Earth masses, 1.4 Earth radii), researchers said.
“With the present observation, we have taken the first tentative steps into analysing the atmosphere of smaller, lower mass planets that are much more Earth-like in size and mass,” researchers said.
GJ 1132b orbits the red dwarf star GJ 1132 in the southern constellation Vela, at a distance of 39 light years from us.
The team used the GROND imager at the 2.2-m ESO/MPG telescope of the European Southern Observatory in Chile to observe the planet simultaneously in seven different wavelength bands.
Transiting planet
GJ 1132b is a transiting planet: From the perspective of an observer on the Earth, it passes directly in front of its star every 1.6 days, blocking some of the star’s light.
The size of stars like GJ 1132 is well-known from stellar models. From the fraction of starlight blocked by the planet, astronomers can deduce the planet’s size — in this case around 1.4 times the size of the Earth.
The new observations showed the planet to be larger at one of the infrared wavelengths than at the others.
This suggests the presence of an atmosphere that is opaque to this specific infrared light (making the planet appear larger) but transparent at all the others.
Different possible versions of the atmosphere were then simulated by team members at the University of Cambridge and the Max Planck Institute for Astronomy.
Methane-rich, a ‘water world’
According to those models, an atmosphere rich in water and methane would explain the observations very well.
Observations to date do not provide sufficient data to decide how similar or dissimilar GJ 1132b is to Earth.
Possibilities include a “water world” with an atmosphere of hot steam, researchers said.
“GJ 1132b provides a hopeful counterexample of an atmosphere that has endured for billion of years. Given the great number of M dwarf stars, such atmospheres could mean that the preconditions for life are quite common in the universe,” they said.
The research was published in the Astronomical Journal.
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