Galilean satellites

(gal-ă-lee -ăn) The satellites Io, Europa, Ganymede, and Callisto of Jupiter, discovered in 1610 by Galileo Galilei and, independently, by the German astronomer Simon Marius. They are bright enough to be seen with the aid of binoculars and have been studied in detail by Pioneer and Voyager spacecraft and the Galileo spaceprobe. The Galilean satellites are Jupiter's largest satellites by far, comparable in size with the small planets. Ganymede, the largest satellite in the Solar System, is slighter bigger than Mercury in diameter, and all of them except Europa are larger than the Moon. Each is in synchronous rotation, keeping one face permanently turned toward Jupiter. Their maximum surface temperatures vary between the 120 K of Io to 155 K for Callisto, probably as a result of differences in albedo; the albedo of Io is 0.61, of Europa 0.64, of Ganymede 0.42, and of Callisto as low as 0.20. They show a progressive decrease in bulk density from Io, the closest (3.57 times that of water) through Europa (2.97) and Ganymede (1.94) to Callisto, the farthest (1.86), indicating that the proportion of rocky material to ice is greater for the denser satellites. Ganymede and Callisto, unlike Io and Europa, are both heavily cratered bodies. The three Galilean satellites closest to Jupiter in order of distance – Io, Europa, and Ganymede – follow paths that are locked in to each other by orbital resonance. Thus for every single orbit completed by Ganymede, Europa completes two and Io four. One consequence of this orbital resonance takes the form of gravitational effects. Europa's gravitational influence on Io has perturbed it into a more eccentric orbit around Jupiter, taking it both closer to and farther away from the giant planet and exposing it to the tidal stresses that produce the active volcanoes observed by the Voyager and Galileo spacecraft. Europa in its turn is acted upon by Ganymede and as a result its geology may have been subject to the effects of tidal friction and heating. It has been suggested that as Callisto's distance from Jupiter increases owing to the tidal exchange of angular momentum between it and the giant planet, it too will eventually reach a 2:1 resonance with Ganymede. See also Jupiter's satellites; Table 2, backmatter.

Collins Dictionary of Astronomy © Market House Books Ltd, 2006

Galilean satellites

[‚gal·ə¦lē·ən ′sad·əl‚īts]

(astronomy)

The four largest and brightest satellites of Jupiter (Io, Europa, Ganymede, and Callisto).

Mentioned in

References in periodicals archive

The stately world reaches east quadrature, 90[degrees] east of the Sun, on August 6th, permitting improved views of eclipses of the Galilean satellites (see page 51 for a listing of specific events).

And Then There Were Five: Four bright planets grace the skies, and tiny Mercury appears at the end of the month

These so-called Galilean satellites, named after the 17th century scientist Galileo Galilei, who discovered them with a telescope, complete orbits around Jupiter with durations ranging from 2 days to 17 days.

Hubble Captures Rare Triple-Moon Conjunction

Your telescope becomes a super-long, super-aperturt telephoto lens, enabling you to take wonderfully detailed close-ups of the Moon's surface or show Jupiter as a disk with two dark bands accompanied by its four bright Galilean satellites.

Capturing the night sky: it keeps getting easier to take I great images of things in space

Europa is one of the four largest moons of Jupiter, which collectively are known as Galilean satellites. They were discovered by Galileo in 1610.

Space odyssey

While at Durham, Prof Sampson's research included studying the motions of Jupiter''s four Galilean satellites, work for which he later won the Gold Medal of the Royal Astronomical Society in 1928.

SEALED BIDS FOR SALE OF TV PERSONALITY'S LISTED OBSERVATORY HOME

The arrangement of the Galilean satellites around Jupiter is governed by the same regularity as the arrangement of planets around the Sun, i.e., the closer they are to the planet, the higher their densities are.

Origin of planetary systems due to dichotomous division of the ejected superheat mass

The orbital periods of the Galilean satellites of Jupiter, many asteroids' orbits, Jupiter's orbit, and Pluto's orbit with Neptune are some examples.

All together now

In particular, it provided strong evidence of a subsurface ocean on Europa, one of the four largest moons known as the Galilean satellites.

Galileo's Jupiter mission reaches dramatic end

This large moon is the least active--and most ordinary looking--of the four Galilean satellites. This geologically dead world shows the scars of innumerable meteoric impacts, though with no trace of major internal wrenchings.

THE MYSTERIOUS MOONS OF JUPITER