After more than a decade in space, Pioneer 10, the world’s
first outer-planetary probe, left the outer limits of the known
solar system by crossing the orbit of Neptune, the system’s
then farthest planet.

The following day, it radioed back its first scientific data on
interstellar space.

Galileo di Vincenzo Bonaiuti de’ Galilei
(15 February 1564 – 8 January 1642)

With eight planets in our solar system, more than 200 moons
surround those natural satellites.

Jupiter, one of the most recognizable planets, has 80 of those
moons.

On this day in history, Jan. 7, 1610, Galileo discovered the
moons of Jupiter — making it the first observation of this
planet. 

The astronomer discovered the moons with a homemade
telescope.

Tomb of Galileo, Santa Croce, Florence.

German astronomer Johann Gottfried Galle (below) 
discovered the planet Neptune at the Berlin
Observatory.

Johann Gottfried Galle
(9 June 1812 – 10 July 1910)

The the Berlin Observatory. 

The 1829 9"/24cm refractor telescope of New Berlin
Observatory that discovered Neptune.

Artist’s impression of the planet Neptune.

The blue gas giant, which has a diameter four
times that of Earth, was named for the Roman
god of the sea. It has eight known moons, of
which Triton is the largest, and a ring system
containing three bright and two dim rings.

It completes an orbit of the sun once every
165 years. In 1989, the U.S. planetary
spacecraft Voyager 2 was the first human
spacecraft to visit Neptune.

MIKE GRACIA

Richard Benjamin Speck
(December 6, 1941 – December 5, 1991)

Pioneer 10, the world’s first outer-planetary probe,was
launched from Cape Canaveral, Florida, on a mission to
Jupiter, the solar system’s largest planet, on this day
in 1972.

In December 1973, after successfully negotiating the
asteroid belt and a distance of 620 million miles,
Pioneer 10 reached Jupiter and sent back to Earth
the first close-up images of the spectacular gas giant.

In June 1983, the NASA spacecraft left the solar system
and the next day radioed back the first scientific data on
interstellar space. NASA officially ended the Pioneer 10
project on March 31, 1997, with the spacecraft having
traveled a distance of some six billion miles.