Dubbed Voyager 1 and Voyager 2, they were designed by NASA to photograph Jupiter and Saturn.
In the early 1970s Pioneer 10 and Pioneer 11 were sent to fly past Jupiter and Saturn.
These momentarily warmer periods coincided with times when orbital positions of Jupiter and Saturn were relatively close to the Sun and Earth.
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The laurels for that probably belong to the rescuers of Voyager 2, the second of two probes launched towards Jupiter and Saturn in 1977.
But what we think is that the really big guys, Jupiter and Saturn, had it relatively easy and they didn't suffer so much at this.
"First, this icy 'super-Earth' dominates the region around its star that in our Solar System is populated by the gas-giant planets, Jupiter and Saturn, " he said.
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And once the planets lined up in their orbits, Earth would "overtake" the others, meaning that Jupiter and Saturn would appear to change direction in the night sky.
These upheavals will, supposedly, be the result of a planetary alignment, as the combined gravitational influences of the moon, Mercury, Venus, Mars, Jupiter and Saturn wreak havoc on the earth.
But computer modelling revealed that most of the asteroids ejected by Jupiter and Saturn quickly dive into the sun, and thus cannot account for the large number of known Earth-crossers.
And then we started, you know, scientists, astronomers started to wonder, well, why is it that Jupiter and Saturn seem to be pretty much where we expect them to have been born?
Just over 50 extrasolar planetary systems have so far been discovered and analysis of them shows just how unusual our local system is with its giant planets (Jupiter and Saturn) positioned well away from the Sun.
To cap that, having looked at Jupiter and Saturn, Voyager 2's controllers decided to extend the mission by taking pictures of Uranus and Neptune as the craft continued on its journey out of the solar system.
Hughes's best explanation for this series of events is something known as a triple conjunction between Jupiter and Saturn - with the two planets coming close together in the sky three times over a short period.
Scafetta believes that a natural 60-year climate cycle associated with astronomical cycles may also explain calendars adopted in traditional Chinese, Tamil and Tibetan civilizations, since all major ancient civilizations knew about 20-year and 60-year Jupiter and Saturn cycles.
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Dr. THOMMES: Well, what we think happened in our solar system is that we are an example of a system that was sort of near the boundary between something that actually formed gas giants, formed, well, the Jupiter and Saturn that we see today, and something that if conditions had been a little bit different wouldn't have really formed any gas giants at all.
The probes' initial goal was to survey the outer planets Jupiter, Saturn, Uranus and Neptune - a task they completed in 1989.
In a lot of ways, the weather of the four giant planets (Jupiter, Saturn, Uranus and Neptune) should be easier to understand than that of the earth, because there are no oceans and continents to complicate matters.
If the question is life - and that's one of the most profound questions we can ask, he says - the answer is almost certainly not Mars or an asteroid, but rather the icy moons orbiting distant planets like Saturn and Jupiter.
Europa, a satellite of Jupiter, and Enceladus, which orbits Saturn, both have large volumes of liquid water buried beneath their icy crusts.
Several panel members have favored dividing planets into categories: terrestrial planets (Mercury, Venus, Earth, Mars), giant planets (Jupiter, Saturn, Uranus, Neptune) and a third class that would include Pluto.
Two further sine waves emerged in 2002, corresponding to one planet that has the mass of Saturn and is also orbiting more closely than Mercury, and another with four times the mass of Jupiter that is located in what would be Jupiter's orbit.
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