Changes

== Observation and Exploration ==

== Observation and Exploration ==

Until the advent of space flight, observations of Io were perforce limited to those by Earth-based telescopes. Galileo Galilei had shown that Io was present, of course, but only in the late 19th and 20th centuries did telescope technology allow for any resolution of surface features on Io. Astronomers like [[Edward E. Bernard]] noted the differing brightness between Io's equatorial and polar regions and finally determined that they were strictly due to differences in color and albedo (a measure of surface reflectivity), and not because Io had an odd shape and not because Io was in fact two companion objects.<ref name=Dobbins>Dobbins, T., and Sheehan, W. "The Story of Jupiter's Egg Moons". ''Sky & Telescope'' 107 (1):114–120, 2004.</ref><ref name=Barnard1>Barnard, Edward E. "[http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1894MNRAS..54..134B&db_key=AST&data_type=HTML&format=&high=45f9f8ee3007558 On the dark poles and bright equatorial belt of the first satellite of Jupiter]." ''Monthly Notices of the Royal Astronomical Society'', 54:134, January 1894. Accessed February 18, 2008.</ref><ref name=Barnard2>Barnard, Edwin E. "[http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1891MNRAS..51..543B&db_key=AST&data_type=HTML&format=&high=45f9f8ee3010624 Observations of the Planet Jupiter and his Satellites during 1890 with the 12-inch Equatoreal of the Lick Observatory]." ''Monthly Notices of the Royal Astronomical Society'', 51:543, June 1890. Accessed February 18, 2008.</ref> More detailed observations followed, as recently (to the Voyager missions) as 1973.<ref name=Minton>Minton, R. B. "[http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1973CoLPL..10...35M&db_key=AST&data_type=HTML&format=&high=45f9f8ee3013123 The Polar Caps of Io]." ''Communications of the Lunar and Planetary Laboratory'', 10:35-39, 1973. Accessed February 18, 2008.</ref>

Until the advent of space flight, observations of Io were perforce limited to those by Earth-based telescopes. Galileo Galilei had shown that Io was present, of course, but only in the late 19th and 20th centuries did telescope technology allow for any resolution of surface features on Io. Astronomers like [[Edward E. Bernard]] noted the differing brightness between Io's equatorial and polar regions and finally determined that they were strictly due to differences in color and albedo (a measure of surface reflectivity), and not because Io had an odd shape and not because Io was in fact two companion objects.<ref name=Dobbins>Dobbins, T., and Sheehan, W. "The Story of Jupiter's Egg Moons". ''Sky & Telescope'' 107 (1):114–120, 2004.</ref><ref name=Barnard1>Barnard, Edward E. "[http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1894MNRAS..54..134B&db_key=AST&data_type=HTML&format=&high=45f9f8ee3007558 On the dark poles and bright equatorial belt of the first satellite of Jupiter]." ''Monthly Notices of the Royal Astronomical Society'', 54:134, January 1894. Accessed February 18, 2008.</ref><ref name=Barnard2>Barnard, Edward E. "[http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1891MNRAS..51..543B&db_key=AST&data_type=HTML&format=&high=45f9f8ee3010624 Observations of the Planet Jupiter and his Satellites during 1890 with the 12-inch Equatoreal of the Lick Observatory]." ''Monthly Notices of the Royal Astronomical Society'', 51:543, June 1890. Accessed February 18, 2008.</ref> More detailed observations followed, as recently (to the Voyager missions) as 1973.<ref name=Minton>Minton, R. B. "[http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1973CoLPL..10...35M&db_key=AST&data_type=HTML&format=&high=45f9f8ee3013123 The Polar Caps of Io]." ''Communications of the Lunar and Planetary Laboratory'', 10:35-39, 1973. Accessed February 18, 2008.</ref>

The Pioneer missions 10 and 11 flew by Io in 1973 and 1974. They revealed little beyond a better estimate of Io's mass, and one good image from Pioneer 11. The heavy radiation in the torus of radioactive particles that surrounds Io compromised Pioneer's instruments, and all its observations were lost.

The Pioneer missions 10 and 11 flew by Io in 1973 and 1974. They revealed little beyond a better estimate of Io's mass, and one good image from Pioneer 11. The heavy radiation in the torus of radioactive particles that surrounds Io compromised Pioneer's instruments, and all its observations were lost.