In Cassini’s Final Days, It Is Sweeping Through Dramatic, Close Flybys Of Saturn’s Rings

Galilean moons

The Galilean moons are the four largest moons of Jupiter — Io, Europa, Ganymede, and Callisto. They were first seen by Galileo Galilei in January 1610, and recognized by him as satellites of Jupiter in March 1610. They are the first objects found to orbit another planet. Their names derive from the lovers of Zeus. They are the first objects found to orbit another planet. Their names derive from the lovers of Zeus. They are among the largest objects in the Solar System with the exception of the Sun and the eight planets, with a radius larger than any of the dwarf planets. 

Io is the fourth largest moon in the Solar System. With over 400 active volcanos, Io is the most geologically active object in the Solar System. Its surface is dotted with more than 100 mountains, some of which are taller than Earth’s Mount Everest. Unlike most satellites in the outer Solar System (which have a thick coating of ice), Io is primarily composed of silicate rock surrounding a molten iron or iron sulfide core. Although not proven, recent data from the Galileo orbiter indicate that Io might have its own magnetic field.

Europa the second of the four Galilean moons, is the second closest to Jupiter and the smallest at 3121.6 kilometers in diameter, which is slightly smaller than the Moon. The name comes from a mythical Phoenician noblewoman, Europa, who was courted by Zeus and became the queen of Crete, though the name did not become widely used until the mid-20th century.  It has a smooth and bright surface, with a layer of water surrounding the mantle of the planet, thought to be 100 kilometers thick. The smooth surface includes a layer of ice, while the bottom of the ice is theorized to be liquid water. The apparent youth and smoothness of the surface have led to the hypothesis that a water ocean exists beneath it, which could conceivably serve as an abode for extraterrestrial life. 

Ganymede is the largest moon in the Solar System, and is even bigger than the planet Mercury. It is the only satellite in the Solar System known to possess a magnetosphere, likely created through convection within the liquid iron core. 

Callisto  is the fourth and last Galilean moon, and is the second largest of the four, and at 4820.6 kilometers in diameter, it is the third largest moon in the Solar System, and barely smaller than Mercury, though only a third of the latter’s mass. It is named after the Greek mythological nymph Callisto, a lover of Zeus who was a daughter of the Arkadian King Lykaon and a hunting companion of the goddess Artemis. It is one of the most heavily cratered satellites in the Solar System, and one major feature is a basin around 3000 km wide called Valhalla. 

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image credit: NASA/JPL

Earth images photographed by satellites and the International Space Station

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Arthur Strengthens, Moves Northward by NASA Goddard Photo and Video

Blue Marble, Eastern Hemisphere March 2014 by NASA Goddard Photo and Video

Landing Day for InSight by NASA’s Marshall Space Flight Center

Should NASA Send New Horizons To A Nearby Star For Its Final Mission?

“Over the next million years, the Voyagers and Pioneers will approach numerous stars, but only at relatively large separations. The closest will be Pioneer 10, encountering HIP 1177795 in ~90,000 years from 0.75 light-years away. But New Horizons, unlike the others, still has significant fuel remaining. After encountering Pluto and Arrokoth, it may yet target another object in the outer Kuiper belt. Subsequently, it will eventually enter interstellar space, but can be boosted to approach future stellar targets.”

In the 1970s, four spacecraft were launched with speeds large enough that they would eventually escape the Solar System: Pioneer 10 and 11 and Voyager 1 and 2. In the 2000s, New Horizons became the fifth spacecraft that will leave the Solar System and enter interstellar space. But unlike the other four, it still has fuel remaining and could boost itself to alter its trajectory. In the aftermath of the ESA’s Gaia mission, we now can predict where more than a billion stars in the Milky Way will be located up to a million years in the future, raising the possibility that we could alter New Horizon’s trajectory to encounter another solar system in the distant future.

Should we do it? Of course we should! Come learn about this fascinating possibility today.

Our Amazing Solar System

Our Amazing Solar System!

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