At least 20 km thick ice on the surface of Jupiter's moon Europa estimated from the impact topography Space Portal Website

Moons of JupiterEuropeIt is believed that there is a vast ocean within it, but it has not been possible to confirm this directly because its surface is covered with thick ice. So, how thick is this ice crust?

A research team led by Shigeru Wakita of Purdue University conducted an operation conducted by the National Astronomical Observatory of Japan on the hypothesis that the topography of the basin, which consists of layered ring structures formed as a result of collisions with celestial bodies, is related to the thickness and solidity of celestial bodies. Ice crust, we ran a simulation on the Compute Server. Results,Multicyclic basins in Europe can only be explained if the ice crust is at least 20 km thick.I understand that. The results of this study are important because they provide fundamental information about the structure of Europa, which is still not well understood.

■ How thick is Europe's ice?

So far, only one celestial body, Earth, has been found to have a significant amount of liquid water on its surface. Underground, in icy bodies whose surfaces are covered with ice, the ice melts and turns into liquid water.Inland seaIt is widely believed to be widespread. It is said to be several to ten times larger than the Earth's oceans.

There are several candidate celestial bodies that are thought to have an inner ocean, including Jupiter's moons.EuropeAnd Saturn's moon Enceladus, there are some celestial bodies that almost certainly have inner oceans. However, since the surfaces of these orbs are covered in ice, no confirmed examples have been found.

Not much is clearly known about this question: How thick is the ice crust? There have been a number of attempts to estimate the thickness using observational data obtained during close exploration by spacecraft and simulations using computer models, but preliminary research suggests that if it is thin, it will be several hundred meters thick, and if it is thick, it will be several Hundreds of metres. It would be thicker, and it was extremely wide, several hundred kilometers across.

This situation is improving as research progresses, for example, for Europe, by incorporating small craters that are thought to be affected by the thickness of the ice crust into the calculation model, the thickness has been narrowed from several kilometers to about 10-10 km. Strange kilometres. However, with previous models, it was difficult to distinguish between a “thin ice crust that is difficult to break” and a “thick ice crust that is brittle and easy to break,” making it difficult to clearly identify. Thickness.

■Estimation of ice thickness from multi-ring basins

In order to improve this situation, Dr. Wakita and his research team are trying to improve this situation by:Multiple ring basinWe performed a simulation using a terrain with a diameter of about 100 km called “. A polycyclic basin is a landform in which ring-shaped terrain forms concentrically, and is thought to have been created by a collision with a large-scale celestial body that was large enough to penetrate the icy crust.

The thickness and hardness of the ice crust are expected to have a significant impact on the conditions for the formation of multi-ring basins, but it is difficult to simulate the topography formed by the participation of hard and soft materials. In fact, it initially took up to a month to run a single simulation, but with subsequent innovations we were able to improve the system to the point that more than 100 calculations could be performed within a realistic period of time.

In this research we will use “Account server“The numerical collision calculation code that simulates celestial collisions.”I sell“To find the thickness and hardness of the ice crust that best reproduces the polycyclic basins found over Europa.

Results,Multicyclic basins can only form if the ice is at least 20 km thick.This has been shown. We also found that ice consists of layers that are hard and difficult to break, and layers that are brittle and easy to break, and that if the brittle parts were too brittle, multi-ring basins would not form. This structure of the ice crust is consistent with the assumption of an internal ocean, so the multi-ring basin indirectly indicates the existence of an internal ocean.

It is not known when the polycyclic basins formed in Europe, and it is possible that the thickness of the ice crust was different between the time the polycyclic basins formed and in modern times. However, the surface of Europa is constantly being updated, and it is believed that the craters will disappear after 20 to 200 million years. This is a fairly short time period in geological terms, and shows that the estimated thickness of the ice crust at the time of the formation of the polycyclic basin is likely to apply to modern Europe.

■ The thickness of the ice also affects its life.

The reason celestial bodies like Europa, which are thought to have inner oceans, are attracting interest is that they are expected to harbor unique life forms. So, even if unique life forms exist, in what way are the different elements and molecules that make up life forms provided? The source could be material coming from outside, such as comets, or ice crust decay products, but the amount supplied also depends on the thickness of the ice crust.

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In this study, we were able to establish a lower limit on the thickness of Europe's ice crust, which is at least 20 km, but no upper limit has been determined. Data for estimating Europe's ice crust are mainly based on observational results from the Jupiter Galileo probe launched by NASA (National Aeronautics and Space Administration) in 1989. The reason is that there is a general lack of data, and there is also… NASA plans to launch a new spacecraft, Europa Clipper, in October 2024, so more observational data may improve this situation.

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Text / Riri Ayaka Editing / sorae editorial department