Terraforming of Europa
||This article possibly contains original research. (July 2011)|
The terraforming of Europa is the hypothetical process of boosting the global environment of Europa, changing its climate, surface and other properties to make it habitable for human colonization without the use of a spacesuit. Although recent astronomical studies indicate that it has the greatest potential to sustain life, out of all bodies in the Solar System (including planets Mars and Venus), its terraformation presents a challenge: it is near a huge radiation belt around Jupiter, but it is claimed that through the usage of human-made space technology, this radiation could be overcome. There are two major changes required:
- The establishment of a magnetic field at least half as strong as Earth's, through convection that usually results in the setting up of a dynamo in the core.
- An ozone layer that absorbs ultraviolet radiation and decreases the total amount of harmful radiation reaching the surface, allowing life on land.
- There would need to be a considerable percentage of oxygen in the atmosphere (at least Earth's amount, about 21%) (see atmosphere of Earth).
- The moon would have to be heated to sustain a warm and suitable temperature.
- The atmospheric pressure would need to be increased.
- Removal of surplus surface water or water ice.
- 1 Reasons for terraforming
- 2 Background
- 3 Alterations required
- 4 Magnetic field and Jupiter radiation belts
- 5 References
- 6 Bibliography
Reasons for terraforming
In the future, population growth and demand for resources may create pressure for humans to colonize new habitats such as Mars, the Moon, and nearby planets, as well as harvesting the Solar System's energy and material resources.
In about 5.6 billion years, the Sun is forecasted to move off the main sequence and become a red giant, as the hydrogen fuel in the core is completely consumed, causing the Sun's core to contract and the outer layers to expand. At this point, the Sun's upper atmosphere will extend as far as 1.2 astronomical units (AU), out past the present orbit of the Earth. This expansion will likely destabilize the orbits of the inner planets, causing them to spiral in towards the Sun and be destroyed. The Sun will lose a significant fraction of its mass in the process of becoming a red giant, and this may cause a widening of the orbits of the other planets. Earth could theoretically achieve a widening of its orbit and could potentially maintain a sufficiently high angular velocity to keep it from being engulfed. In order to do so, its orbit would need to increase to between 1.3 AU and 1.7 AU.
Although Mars is the most popular candidate for terraforming, even if human colonization of Mars lasts for billions of years, the habitable zone will eventually move beyond Mars, towards Jupiter and its system.
It is theorized that Earth will be outside the habitable zone before the Sun enters its red-giant phase. Astronomers estimate that the Sun will be 33% more luminous three billion years from now. The warming Sun and increased solar radiation would cause the Earth's oceans to evaporate, and the Earth eventually to melt. The habitable zone would move farther out from the Sun.
It has been hypothesized that a subsurface water ocean may exist under Europa. If water does indeed exist under the surface, life could thrive in this environment, although it may only be microbial and simple. This may be assumed because on Earth, sponges, crinoids, scallops, snails, fish and many microorganisms thrive under the ice in the Antarctic, despite the frigid conditions.
Europa has no strong magnetic field to protect it from the Jupiter radiation belt, to which it is near. It is suggested that an internal dynamo can be produced through convection (even if Europa is already internally active), though the magnetic field would not need to be stronger than Earth's, for the measurable radiation on Europa is much less than previously predicted (although terraforming the moon would still prove a challenge). An ozone layer would also be necessary.
|Pressure||0.1 μPa (10−12 bar)||101.325 kPa (14.6959 psi)|
|Carbon dioxide (CO2)||0%||0.04%|
Terraforming Europa would entail three major alterations: building up the atmosphere, keeping it warm, and keeping the atmosphere from escaping away into space. The atmosphere of Europa is extremely thin and thus has a very low surface pressure of 0.1 micropascals (1.5×10−11 psi); compared to Earth with 101 kilopascals (15 psi) at sea level and 0.86 kilopascals (0.12 psi) at an altitude of 32 kilometres (20 mi). The atmosphere of Europa consists of mostly molecular oxygen (O2), though not of biological origin, with no other constituents found. Although there was once molecular hydrogen (H2) in the atmosphere, it escaped into space to leave behind oxygen. By comparison, Earth's atmosphere is 78% nitrogen, 21% oxygen, 0.93% argon, 0.04% carbon dioxide, and other constituents.
Building the atmosphere
Although Europa has an atmosphere (revealed by the Hubble Space Telescope in 1995), it is a relatively surface bounded exosphere and totally unbreathable. A minimum 0.2 bar partial pressure of oxygen is required for human breathing, though in practice higher total pressure is needed. This could be supplied by breaking the surface ice into its component hydrogen and oxygen, though a suitable sink for the hydrogen will be required.
Introduction of ammonia to the atmosphere
Another intricate method of terraforming Europa is importing ammonia (NH3) to the atmosphere. Ammonia not only acts as a powerful greenhouse gas that heats the planet for water-based temperatures, but also has high levels of nitrogen, which takes care of the need for a buffer gas in the atmosphere. Part of the ammonia might be imported from Jupiter, Europa's host planet (containing at least 0.026% of ammonia), along with Saturn (0.01% ammonia), Uranus and Neptune (trace amounts of ammonia). It might also be technologically achievable to import ammonia from comets (as they did to Earth) in the asteroid belt, including blowing them up with very large nuclear bombs.
The challenge facing atmosphere builders is the need for a buffer gas. On Earth, nitrogen levels are around 78.08% in the atmosphere, the gas that is the most abundant on Earth. Europa would require a similar buffer gas component to pressurize the surface and regularize cell temperatures. Several inert gases, such as nitrogen, argon or neon, could be utilized as buffer gases, although obtaining sufficient quantities would be difficult.
Introduction of methane to the atmosphere
Sources of methane in the Solar System include Saturn's moon Titan's lakes and atmosphere, as well as trace amounts from the atmosphere of Mars. Or hydrogen could be converted into methane (because methane is four atoms of hydrogen bound to a carbon atom). In this way, methane is used as a boost for a potent greenhouse effect. Methane, and other hydrocarbons, also can be utilized in the increase for the insufficient Europan atmospheric pressure. These gases also can be used for production of water and CO2 for Europa's atmosphere, to initiate plants' photosynthetic processes.
Heating the satellite
After building the atmosphere, heating the satellite would be an important requirement of terraforming Europa, as heat from the Sun is the primary driver of planetary climate. As the satellite becomes warmer, the CO2 that is frozen into solid form in the Europan north and south poles would sublime into gas and further contribute to a potent greenhouse effect. Heating the satellite would also melt the ice on the surface into liquid form.
Asteroids could be directed onto the Europan surface for their composition, including ammonia (which is a greenhouse gas, as aforementioned, and may have seeded Earth), and because the impacting energy could release heat into the atmosphere. Impacting asteroids on these nitrate beds would release additional nitrogen and thicker oxygen into the satellite's tenuous atmosphere.
Magnetic field and Jupiter radiation belts
Earth is covered with water (about 70% of Earth's surface) because the ionosphere is permeated with a strong magnetic field. The hydrogen ions present in its ionosphere move very fast due to their small mass, but they cannot escape to outer space because their trajectories are deflected by the magnetic field. Venus has a dense atmosphere, but only traces of water vapor (20 ppm) because it lacks a magnetosphere. The Europan atmosphere also does occasionally lose molecular oxygen (O2) to space.
Earth is provided extra protection from ultraviolet radiation by its ozone layer, which is in the stratosphere. Ultraviolet light is blocked before it can dissociate water into hydrogen and oxygen. Since little water vapor rises above the troposphere and the ozone layer is in the upper stratosphere, little water is dissociated into hydrogen and oxygen.
Europa receives about 5.40 Sv of radiation per day. (5.0 Sv is already considered lethal acute dose) from Jupiter's large radiation belts (10 times stronger than Earth's Van Allen radiation belts), and is a severe health threat to colonists without adequate radiation shielding. The satellite has only a very weak magnetosphere, which leaves it exposed to radiation by Jupiter and also the solar wind.
Despite this, an atmosphere engineered to be much denser than Earth's can provide protection from cosmic radiation and Jupiter's radiation, and carefully selected upper-atmospheric components may block UV radiation before it can ionize water.
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