Europa is the smallest of Jupiter’s Galilean moons, and while it is only slightly smaller than our own Moon, it is nevertheless the 15th biggest object in the solar system, and more massive than all the other known moons in the solar system that are smaller than it combined.
Europa is also the object with the smoothest surface in the solar system, with there being no mountains, hills, or other noteworthy geologic features on its surface to mention. Although Galileo is recognized as having discovered Europa in January of the year 1610, it may have been discovered independently by the German astronomer Simon Marius a few days earlier. Below are some more interesting facts about Europa:
Europa is named after a Phoenician noblewoman
Europa was yet another of Zeus’ paramours, and in this case, she was a Phoenician noblewoman who was abducted by Zeus after he had transformed himself into a bull. Rather fittingly, Zeus established Europa on the island of Crete as its queen, where he had several children with her, including Minos, the legendary king of Crete. In later ages, the continent of Europe would be named after Europa.
Europa’s surface is younger than the moon itself
Although Europa is as old as the rest of the solar system, its surface is only between 40 and 90 million years old, due to tidal flexing of the crust that maintains tectonic activity that in turn, recycles the surface in much the same way that tectonic activity on Earth continually recycles the Earth’s surface.
Unprotected humans on Europa would die within a day
Solar radiation and energetic particles produced by Jupiter’s powerful magnetic field combine to deliver a dose of radiation to Europa’s surface of about 5,400 millisieverts (mSv) which is strong enough to kill an unprotected human in less than 24 hours. By way of comparison, an ordinary medical CT scan produces only 6 to 20 millisieverts, depending on the type and duration of the scan.
Europa has a liquid ocean under its crust
Like some other moons in the solar system, Europa is known to have a liquid saltwater ocean under its icy crust, which is suspected to be about 100 km deep. Studies have revealed that this ocean directly supports the ice crust as it rotates around the moon’s core once every 12,000 years or so.
Europa may have twice as much water as Earth’s oceans
If current theories and models turn out to be accurate, the total volume of water in Europa’s subsurface ocean is about 3 × 1018 cubic meters, which is just more than twice the volume of all the water in Earth’s oceans.
Europa is tidally locked to Jupiter
Europa orbits Jupiter in 3.5 days, which is the same time it takes to complete one revolution around its own axis. Because the moon is tidally locked to Jupiter, there is a sub-Jovian point on the moon from which an observer would always see Jupiter directly overhead. Europa’s orbit is also nearly circular, with an eccentricity of only 0.009, and an orbital inclination relative to Jupiter’s equatorial plane of less than 0.5 degree.
Europa has an oxygen based atmosphere
Although Europa has a predominantly molecular oxygen atmosphere, the atmospheric pressure is only 0.1 µPa (micropascal), which is 10-12 lower than on Earth. The oxygen does not derive from biological processes but from solar radiation that breaks up hydrogen atoms into water and oxygen.
Europa has water volcanoes
Although “volcanoes” might not be the most accurate word to describe the phenomenon, the Hubble telescope has captured images of a 120-mile-high plume of water being ejected from Europa. It is thought that these jets erupt from the moon during times when tidal flexing is “squeezing” the ice crust, much like water might be squirted from a flexible container such as a soda bottle if it is squeezed.
Europa is among the brightest moons in the solar system
The moon’s icy surface gives it an albedo of 0.64, which places it among the brightest of all the known solar system moons. By way of comparison, our Moon has an albedo of only 0.12, which means it reflects only about 7% of the light that falls onto it, as opposed to Europa that reflects more than 90% of light. Note that in the case of our moon, the albedo value excludes a phenomenon known as the “opposition surge” that can increase perceived visual brightness by up to 50%.
The lines on Europa are cracks in its surface
The lines on Europa’s surface, called lineae, are taken as evidence that tidal flexing periodically distorts the ice crust. Since the moon’s orbit is not perfectly circular, the higher gravitational forces that are obtained when the moon is closest to Jupiter compress the crust and stretch the crust when the moon is furthest away. The top layer of the crust reacts to these changing forces by splitting or cracking, which then freezes over when liquid water from below the crust fills the cracks.
However, only the youngest of the cracks conform to the predicted pattern, which suggests that the changing pattern of cracks, which is directly related to the age of individual cracks, is evidence of the fact that the moon’s solid crust is indeed rotating at a different speed than the core.