There are many celestial bodies in the solar system that are predicted to have oceans larger than Earth beneath their thick ice. Such an environment suggests the existence of life, but if the existence of liquid water is “guaranteed”, can we really think that life may exist?
A research team led by Catherine Neish of the University of Western Ontario has discovered that Saturn’s moons have abundant organic compounds on their surfaces and are thought to have an underground ocean.titan”, we estimated the amount of organic compounds transported from the surface to the underground. As a result, it was estimated that the amount of organic compounds transported was less than 7,500 kg/year in terms of glycine, which is far from sufficient to sustain life.
This study shows that even Titan, which is rich in organic compounds, has difficulty supporting life, suggesting that conditions may be worse on other celestial bodies.
[▲Figure 1: An imaginary diagram of Titan’s internal structure. There is a prediction that there is a thick ocean beneath the icy crust (Credit: NASA)]
■Is there an “underground ocean” beneath frozen celestial bodies?
So far, we have only discovered life on Earth. Life has been found in a wide variety of environments, including the deep sea, glaciers, and volcanoes, but it has been found that life cannot survive in any place without liquid water. For this reason, the presence of liquid water is considered a prerequisite for searching for life on celestial bodies other than Earth.
Earth is currently the only celestial body that has been confirmed to have abundant liquid water, but even within the solar system there are several strong candidates. All of these celestial bodies are located far from the Sun, and most of their surfaces are covered with thick ice. However, there is an abundance of liquid water beneath it.Underground sea (internal sea)” is thought to form.
As the surface is covered with ice, the solar energy reaching these objects is not strong enough to melt the ice. However, it is thought that tidal forces generated by the gravity of other celestial bodies and the decay heat of radioactive materials contained in rocks may melt the ice as geothermal heat. The candidates for underground oceans are all much smaller than Earth, butThe volume of the underground ocean is several to several dozen times larger than the volume of the Earth’s oceans.It is thought that this may be the case.
Life has been discovered on Earth that relies on geothermal energy to survive in the deep ocean, where no light penetrates, so it is easy to imagine a biosphere spreading on the ocean floor. There are many celestial bodies that are thought to have underground oceans, including the dwarf planets Pluto and Haumea, Jupiter’s moons Europa and Ganymede, and Saturn’s moons Enceladus and Titan, and like Enceladus and Europa, the existence of underground oceans is almost certain. There are also celestial bodies that have In order to avoid contaminating these celestial bodies, precautions are taken to prevent planetary probes from crashing after they have finished operating.
■Titan has abundant organic compounds on its surface
[▲Figure2:Titan’ssurfaceiscoveredwithathickatmosphereandthegroundsurfacecannotbeseenThisyellowishhazethatobstructsvisibilityiscomposedofhigh-molecularorganiccompounds(Credit:NASAJPL&SpaceScienceInstitute)
However, life cannot survive on water alone. Organic compounds are needed as an energy source for life activities or to create our own bodies. Although signs of the existence of organic compounds in the underground ocean have already been observed, it is not known whether there are enough organic compounds to support life, and this research has not been as intensely studied compared to studies that demonstrate the existence of an underground ocean. It’s hard to say that we are doing so.
A clue to this question may be found in Saturn’s largest satellite,titan“is. Titan’s surface is known to be rich in organic compounds. Most of them are very simple molecules such as methane and ethane, but larger molecules are also known to exist. The thick atmosphere surrounding Titan looks hazy because light is scattered by the high molecular weight organic compounds contained in the atmosphere.
The amount of organic compounds on Titan’s surface is the largest in the solar system other than Earth. In addition, although there are many lakes of liquid methane on the surface, it is thought that deep underground there is 14 times more liquid water than the Earth’s oceans. If the rich organic compounds on the surface are supplied to the underground ocean, it would not be surprising if a unique life form is nurtured, but for this to happen, organic compounds must be supplied several kilometers underground.
Neish and his colleagues estimated the amount of organic compounds transported to the subsurface ocean on Titan. Titan is thought to lack plate tectonics like Earth, so there are limited means of transporting surface material to the underground ocean. Neish et al. hypothesized that celestial bodies collide with each other for material transport. When a celestial body collides, the energy melts ice on the surface, mixing liquid water and organic compounds. Water is denser than ice, and because it “sinks” against ice, it is thought to reach the underground ocean.
■Titan’s underground ocean is an “extremely thin soup”
Neish and his colleagues used glycine, one of the simplest amino acids, to estimate the rate at which glycine is produced and degraded in Titan’s environment. They then estimated the amount of glycine that would be supplied to the underground ocean based on estimates of the collision rate of celestial bodies with Titan.
Surprisingly,The amount of glycine supplied to the underground ocean is less than 7,500 kg per year.It was estimated that Even if you put the same amount of glycine as one African elephant into an ocean 14 times the size of Earth, it would only produce an “extremely thin soup” of organic compounds, which would be far from enough to sustain life. .
This result, which shows that even an object as rich in organic compounds as Titan has a poor supply of organic compounds, is bad news when considering life in the subsurface ocean. Other candidate objects, such as Europa and Enceladus, are thought to have even fewer organic compounds than Titan. This research is attracting attention as to whether this research will have an impact on other celestial bodies.
Source
- Catherine Neish, et al. “Organic Input to Titan’s Subsurface Ocean Through Impact Cratering”. (Astrobiology)
- Jeff Renaud. “Saturn’s largest moon most likely non-habitable: Western study”. (Western University)
Written by Riri Aya
