Saturn’s moon Mimas may have ocean under its crust
- February 20, 2024
- Posted by: OptimizeIAS Team
- Category: DPN Topics
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Saturn’s moon Mimas may have ocean under its crust
Subject: Science and tech
Section: Space tech
What is Mima?
- Mimas is the smallest of the major moons of Saturn-known as the “big seven” or the “inner moons”.
- Nicknamed “Death Star” for the resemblance of its cratered surface to a space station in the Star Warsfranchise.
Presence of ocean under crust:
- Mimas was an unlikely candidate to host an ocean because the presence of these water bodies is generally marked by modifications of the surface by internal dynamics.
- Scientists analysed Mimas’s orbital motion based on data from NASA’s Cassini spacecraft and determined that the moon’s liberations — or oscillations — indicate it either has an elongated silicate core or a global ocean.
Possibility 1:
- If Mimas were solid, its librations would depend on gravity coefficient and changes in orbit on this and another factor called J2.
- By measuring its librations and orbital changes, scientists could determine the values for these numbers if Mimas is entirely solid.
- But calculations reached a dead end. Possibility of being elongated silicate layer is thus omitted.
Possibility 2: Mimas hosting a subsurface ocean.
- They used a theoretical approach to understand how an underground ocean would affect the moon’s movement, depending on the shape of three deformed layers, the gravity coefficients, and the number of liberations.
- The outer Icy layer is considered viscoelastic (i.e. both viscous and elastic) in the liberational model.
- And the interior interfaces are assumed to be hydrostatic (i.e. at rest).
- The resulting calculations suggested the ice sheet would have to be 20-30 km thick to match observations.
- These figures agreed closely with the findings of a 2022 study as well.
- Further, the amount of heat released at the surface of Mimas was estimated to be around 25milliwattper sq. m, which should reduce the moon’s eccentricity — a measure of the extent to which its orbit’s shape deviates from a perfect circle — by a factor of two in 4-5 million years.
- Based on these values, the scientists ran simulations and found that its ocean may have formed 2-25 million years ago.
- The predicted surface heat also matched observations of Enceladus — a Saturn moon that has a global ocean beneath its crust — indicating Mimas may have a hydrothermally active core even if surface activity doesn’t indicate that.
Conclusion:
Mimas may have a liquid ocean around 20-30 km under its heavily cratered ice shell.