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Solar System Exploration

New Horizons passed Pluto on Bastille Day, July 14 2015!

July 14 2015: Flyby of Pluto, Charon, Hydra, Nix, Kerberos and Styx. The closest approach to Pluto was 13,695 km, at which point New Horizons was cruising at 13.78 km/s (49,600 km/h).

NASA probe New Horizons was launched on January 19, 2006, and flew by Jupiter, with nearest approach on February 28, 2007. With this slingshot assist, it passed Saturn's orbit (but Saturn was not at home) on June 8, 2008, and has taken another 7 years to reach Pluto, at 32.9 AU (an AU is the distance from the Earth to the Sun) from the Sun. (March 18, 2011: passed Neptune's orbit; August 25, 2014: passed Neptune's orbit).

The probe has been sending images of Pluto and its companion Charon, but it was not until May 15, 2015 that its images exceeded the resolution of the Hubble telescope's best efforts (which is testament to the excellence of Hubble, rather than a detraction from NASA's probe specs).

The probe will continue towards the outer reaches of the solar system, passing into the Kuiper Belt by 2020, where it will attempt to answer questions about the mysterious bodies which inhabit it, about their surface geologies, interior structures and any atmospheres.

It will then continue on to enter the Heliosphere, where Voyager 1 is now, only around 2040!

Deep Space Probes

There have been two series of missions to the outer planets, which have successfully sent probes towards interstellar space. Testaments to the brilliance of human engineering and pioneering skill, scientific curiosity, and an enduring legacy affirming human existence.


Pioneer plaque
Pioneer 10 and 11 deep-space probes are carrying this plaque beyond our solar system's furthest reaches. Who knows who may one day find them....?

The Pioneer Program was a series of unmanned space probes, launched between 1958 and 1978.

Proposed by Carl Sagan, both Pioneer X and Pioneer XI are carrying gold-anodized aluminum plaques (15.2 x 22.9 cm), with images of male and female humans, and a pictographic map of the origin of the spacecraft. Top left is an illustration of the sub-atomic structure of hydrogen, the most abundant element in the universe, and the principle component of stars.

Pioneer X

Pioneer XI
Pioneer space probe: artist's impression, courtesy of NASA Ames Research Center

Launch: 3 March, 1972

Weight: 258 kg

Power source: Pu-238 (plutonium radioactive isotope 238, half-life 88 years).

Planets visited: Jupiter, closest approach 3 December, 1973 (132,000 km).

Mission objectives:

First spacecraft to enter and transverse asteroid belt between Mars and Jupiter.

Imaging and polarimetry (measurements of magnetic fields, cosmic rays and charged particles) of the environment of Jupiter and satellites. In particular, its approach to within 3 radii of the planet would supply information concerning the radiation emitted by Jupiter, which could damage probe equipment - information vital for planning future missions.

Pioneer X was the first human artifact to pass beyond the orbit of the outermost planet, Neptune, on June 13, 1983. Although at the time Pluto was still considered a planet, Neptune was further from the Sun in 1983.

Current status: Out of contact. On January 23, 2003 Pioneer X had reached a distance of 12 billion kilometers (80 AU) from Earth, or 2.67 times the distance to Neptune, and sent its final signal. Beyond this point the spacecraft had insufficient power remaining to transmit, and the mission was finally closed down. This plucky little ambassador from Earth will however continue its journey into interstellar space, reaching the distance of other stars around 40,000 years from now.

Pioneer XI

Saturn's rings
Saturn's rings photographed by Pioneer XI, August 1979

Launch: 6 April, 1973

Planets visited: Jupiter (closest approach 3 December 1974), Saturn (closest approach 1 September, 1979)

Weight: 258 kg

Power source: 4 Pu-238 (plutonium radioactive isotope 238, half-life 88 years) radioisotope thermoelectric generators (RTGs), to provide 155W power for 12 scientific instruments and communications.

Current status: out of contact. Final transmission on 24 November, 1995.


First images of polar regions of Jupiter, detailed imagery of Great Red Spot.

Determined mass of Callisto.

First use of gravity slingshot to accelerate probe to Saturn.

Pioneer was used to test the route through the Sturn ring plane prior to the arrival of the Voyager probes.

Pioneer nearly collided with a previously undetected small moon of Saturn (Epimetheus), and went on to discover another moon and additional ring, and mapped Saturn's magnetic field. It also revealed that the largest moon, Titan, was too cold to host life.

Pioneer Anomaly

The Pioneer spacecraft both displayed an initially inexplicable phenomenon. Precise measurements of the position revealed they were decelerating slightly (of the order of a tenth of a billionth of g, the gravitational acceleration experienced near the Earth's surface). Slava Turyshev et al. proposes that the phenomenon is due to a thermal recoil force due to asymmetric thermal radiation.


Ed Stone
Ed Stone, project scientist for NASA’s Voyager missions. Dr. Stone has been with the Voyager programme since the start.

Powered by plutonium-238 radioisotope thermoelectric generators, the two Voyager probes have both had stunning successes in their different missions. Both have now left the solar system, Voyager 1 'straight up' after Saturn, and Voyager 2 'along the length' of the solar plane, and are still sending back valuable data, four decades after launch!

Voyager disk
Both Voyager probes carry missives from Earth in the form of an analogue recording of sounds from Earth. Golden disk and cover.

Each of the Voyager craft bears a disk, an analogue recording of sounds of 55 Earth languages, natural sounds (nature, weather and animal and bird sounds), music and other information.

Voyager 1

Launch: 5 September, 1977 (Cape Canaveral, Titan-Centaur rocket)

Voyager 2

Planets visited: Jupiter (1979), Saturn (1980)

Voyager was sent to examine Titan, the largest moon of Saturn. After this encounter, it was slingshot into a trajectory which has been taking it perpendicularly away from the plane of the solar system. Its cameras were turned to take a 'snapshot' of the solar system from 'above', giving rise to the famous 'blue dot' image of the Earth.

On 25 August, 2012, Voyager 1 became the first spacecraft to enter the threshold to deep space, passing into the heliopause, which is the boundary between the solar system's furthest sphere of influence. By 15 December, 2014, the wave of solar particles receded, confirming the craft's probable passage into interstellar space, beyond the Sun's effects. Current projections are for the craft to continue sending data until around 2015, when the electrical power will no longer be sufficient for operations.

A volcano on Io, the innermost moon of Jupiter, spewing a cloud 270 km into space

The giant spot of Jupiter was revealed to be a 300-year-old storm. The very active cloud system and Coriolis effect was observed in detail.

These meteorological effects were being driven by a high-pressure core of metallic hydrogen, which gave rise to a powerful magnetic field, generating lethal levels of radiation in belts around the planet.

Dr. Linda Hyder discovered the first active non-terrestrial volcano on Io, the innermost moon of Jupiter. In total, 8 active volcanoes were discovered in Io, dispelling the myth that the distance from the sun made the outer planetary bodies geologically inert.


Dr. Carolyn Porco discovered that Saturn's rings had 'spokes' with a regular period of occurrence, which coincided with the magnetic field rotating with the planet. Edward Stone has been a project scientist for this mission since launch.

There were rings in what had previously been assumed to be gaps between the more visible rings, which would have been hazardous to the spacecraft had the attempt been made to fly through, as had been proposed. Some rings had 'shepherd' moons keeping them in place.

Saturn's largest moon, Titan, touted as a 'twin' of Earth, and a candidate for extra-terrestrial life, was a disappointment, the atmosphere being too dense for useful observation.

Voyager 2

Voyager 2 team
Voyager 2 team of scientists at the Jet Propulsion Laboratory, California, excited as they receive data from the Saturn flyby on 25 August 1981

Launch: 20 August, 1977 (Cape Canaveral, Titan-Centaur rocket)

Planets visited: Jupiter and moons, Saturn (rings and moons), Uranus and moon Miranda (closest approach 24 January, 1986), and Neptune and moon Tritan (closest approach 25 August, 1989).

On the 5-year journey to Uranus, there was a scare when the scanning system for the camera jammed. It was determined that the cause was redistributed lubricant, which was resolved by slow manipulation.

Currently, Voyager 2 is on a new mission: the Voyager Interstellar Mission (VIM), sending unique and invaluable data concerning the heliosheath, the region of space where the last influence of the Sun, the solar wind, encounters resistance from the pressure of interstellar medium.


Uranus has a net negative energy emission. As opposed to the other planets, Uranus has little internal heat generation, making the planet's atmosphere 'bland'.

The moon, Miranda, was discovered to be a recomposition of fragments of debris.

Neptune photographed during the Voyager 2 fly-by, August 1989

Passing with pin-point precision 4,800 km above the north pole, Neptune was revealed to be blue with white clouds in the atmosphere. At just 40K (-233 °C) the surface is frozen nitrogen.

The atmosphere was revealed to be active, with clouds, storms, and active geysers of nitrogen.

Slingshot to the Stars

Michael Minovitch slingshot
Michael Minovitch's original slingshot proposal paper

In 1961, Michael Minovitch, a brilliant mathematician at California UCLA, set about to use the latest computer technology to solve the 3-body problem. The three bodies in question were the Sun, a planet, and a spacecraft.

The solution was the slingshot method used by NASA to accelerate its Voyager 1 and 2 spacecraft to the speeds necessary to reach the outermost planets within a lifetime of the scientists who launched the missions. The 'sling' was the gravity well of a large mass, such as Jupiter and Saturn, and the 'shot' was a close encounter fly-by and an acceleration towards the next target.

It was Dr. Gary Flandro who realised that a special window of opportunity existed in the late 1970s was available for a mission to take in all four large outer planets. And so, Voyager was born.

Deep Space Network (DSN)

DSN control center
Deep Space Network Operations Center, JPL, Pasadena, California

US global network of communication antennas, located in California, Spain and Australia, to ensure 24-hour contact with interplanetary spacecraft. The DSN is operated by NASA's Jet Propulsion Laboratory (JPL), which controlled the Voyager missions.

Content © All rights reserved. Created : January 2, 2015 Last updated :January 17, 2016

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