In the 1960s a GRAND PLANETARY TOUR to study the outer planets was proposed. It was an
ambitious plan to send unmanned probes to the outer planets of the outer solar system.
The Grand Tour could exploit a rare, unusual and favorable alignment of the planets Jupiter,
Saturn, Uranus, Neptune and Pluto. This planetary alignment would occur in the late 1970s and
would not occur again for 175 years. This special alignment of these planets, could
allow a probe to be sent to Jupiter and use that planet as a gravitational slingshot to
extend its trajectory to the other planets further out in the Solar System. Gravity assist
would enable a single probe to visit the four gas giantsÖ.Jupiter, Saturn, Uranus, and
NeptuneÖ.while requiring a minimal amount of propellant and a shorter travel time between
planets. The NASA space probes Voyager 1 and Voyager
2 have been exploring our solar system to the outer planets for more than 34 years.
Many of the scientists now working on the Voyager project werenít even born when the
probes were launched in the 1970s. Originally, the Voyager probes were designed
as part of the Mariner program. Voyager 1 was called Mariner 11 and Voyager 2 was called
Mariner 12. The program progressed, however, and the name was changed to Voyager. Voyager
2 was actually launched first on August 20, 1977 and Voyager 1 followed 2 weeks later
on September 5, 1977 and was sent on a faster, longer, and more circular trajectory.
Remote control programming was used to endow the Voyagers with greater capabilities than
they had when they left the earth, enabling their 2 planet mission to become a 4 planet
mission. Voyager 1 could have been sent to Pluto after Saturn, but instead was sent on
a trajectory which brought it close to Titan, Saturnís planet sized moon, eliminating the
Pluto flyby. Voyager 2ís trajectory could not be bent to bring the probe by Pluto after
the Neptune flyby in 1989. Eventually, Voyager 1 and Voyager 2 explored all the giant outer
planets of our solar system, 48 of their moons, and the unique systems of rings and magnetic
fields that those planets possess. On December 19, 1977 Voyager 2 entered the
asteroid belt. Nine days later, Voyager 1 (traveling at a greater speed) overtook Voyager
2. In June of 1977, the primary radio receiver
failed on Voyager 2 and the mission since then on has been flown using the backup receiver.
September 5 1977: Voyager 1 sent the first spacecraft photo of Earth and the Moon.
March 5 1979: Voyager 1 flew past Jupiter in its closest approach to that planet.
July 9: Voyager 2 made its closest fly-by of Jupiter.
Jupiter is the largest planet in the solar system. Colorful latitudinal bands and atmospheric
clouds and storms illustrate Jupiterís dynamic weather system. The giant planet was then
known to possess 16 moons. Although astronomers have studied Jupiter through telescopes on
Earth for centuries, scientists were surprised by many of the Voyager findings.
The Great Red Spot was revealed by Voyager as a complex storm moving in a counterclockwise
direction, and an array of other smaller storms and eddies were found throughout the clouds.
Discovery of active volcanism on the moon IO was easily the greatest unexpected discovery
at Jupiter. It was the first time active volcanoes had been seen on another body in the solar
system. Together, the Voyagers observed the eruption of nine volcanoes on IO. Plumes from
the volcanoes extend to more than 190 miles above the surface. The Voyagers observed material
being ejected at velocities up to a kilometer per second.
The moon Europa displayed a large number of intersecting linear features in the low-resolution
photos from Voyager 1. Higher resolution photos from Voyager 2, however, left scientists puzzled
as to what the lines were or how they formed. Voyager showed the moon Ganymede to be the
largest moon in the solar system. It showed 2 distinct types of terrain ñ cratered and
grooved ñ suggesting to scientists that Ganymedeís entire icy crust has been under tension from
global tectonic processes. Voyager showed the moon Callisto to be a very
old, heavily cratered moon whose crust showed remnant rings of enormous impact craters.
Voyager found a faint, dusty ring of material circling around Jupiter.
2 new, small satellites, Adrastea and Metis, were found orbiting just outside the ring.
A 3rd new satellite, Thebe, was discovered between the orbits of Amathea and Io.
Voyager found that as Jupiterís magnetosphere rotates, it sweeps past Io and strips away
about one ton of material off the moon every second. The material forms a torus, or a doughnut-shaped
cloud of ions that glow in the ultraviolet, resulting in auroras.
November 12 1980: Voyager 1ís trajectory sent it in a close fly-by of the planet Saturn
within 40,000 miles of the cloud tops, then closely past Saturnís large moon Titan and
behind Saturnís rings. Perhaps the greatest surprises and the most
puzzles were found by the Voyagers in Saturnís rings. It was thought that the rings formed
from larger moons that were shattered by impacts of comets and meteoroids. The resulting dust
and boulder-to house-size particles have accumulated in a broad plane around the planet varying
in density and forming Saturnís famous rings. Unexpected structures such as kinks and spokes
were found in addition to thin rings and broad, diffuse rings not observed from Earth.
Radial, spoke-like features in the broad B-ring were found by the Voyagers.
Winds blow at extremely high speeds on Saturn ñ up to 1,100 miles per hour.
Saturn holds a wide assortment of satellites in its orbit, ranging from Phoebe (a small
moon that travels in a retrograde orbit) to Titan, the planet-sized moon with a thick
nitrogen-methane atmosphere. Voyager showed the chemistry in Titanís atmosphere
to strongly resemble that which occurred on Earth before life evolved.
The most active of any moon seen by the Voyagers in the Saturn system was that of Enceladus.
Voyager 1 found the moon Mimas scarred with a crater so huge that the impact that caused
it nearly broke the satellite apart. The spacecraftís path northward was bent
out of the ecliptic plane ñ the plane in which most of our planets orbit the Sun. Since
this was its last scheduled fly-by, Voyager 1 began its trip out of the Solar System.
August 25 1981: Voyager 2 also successfully flew close by Saturn, within 26,000 miles,
and it was shown that Voyager 2 would likely be able to continue on to Uranus with all
instruments operating. The next year NASA upgraded two of its antennas
so they could pick up weak radio signals from the Voyager space crafts.
January 24 1986: Voyager 2 completed the first-ever spacecraft encounter with the planet Uranus
ñ a close fly-by that brought the space craft to within 50,600 miles from the planetís
cloud tops and returned detailed photos and other data on the planet, its moons, magnetic
field and dark rings. Uranus is distinguished by the fact that it is tipped on its side
exposing its poles to the sun. Its unusual position is thought to be the result of a
collision with a planet-sized body early in the solar systemís history. Scientists were
not sure what to expect at Uranus. Voyager 2 found that this sideways position
of the planet caused its magnetic field to be tilted 60 degrees. The magnetotail was
shown to be twisted by the planetís rotation into a long corkscrew shape behind the planet.
The presence of a magnetic field at Uranus was not even known until Voyagerís arrival.
Voyager detected a high layer of haze around the sunlit pole.
Voyager found 10 new moons, bringing the total number of moons known around Uranus to 15.
Five large moons appeared to be ice-rock conglomerates like the satellites of Saturn.
The moon Miranda, innermost of the five large moons, was shown to be one of the strangest
bodies yet seen in the solar system. Detailed images from Voyagerís flyby of the moon showed
huge fault canyons as deep as 12 miles, terraced layers, and a mixture of old and young surfaces.
Voyager showed that the moon Titania was marked by huge fault systems and canyons indicating
some degree of geologic, probably tectonic, activity in its history.
Voyager showed the moon Ariel to be the brightest and possibly youngest surface of all the Uranian
moons. All nine previously known rings were studied
by the spacecraft and showed the Uranian rings to be distinctly different from those at Jupiter
and Saturn. Uranusí rings appeared to be relatively young
and probably did not form at the same time as the planet.
There was no indication that geologic activity had occurred on the moons Umbriel or Oberon
judging by their old and dark surfaces. NASAís Deep Space Network once again expanded
two antennas for better reception of the even weaker signals from the now very distant Voyager
spacecraft. Meanwhile, Voyager 1 continued to press outward,
conducting studies of interplanetary space. In 1987 Voyager 2 observed a faraway stellar
explosion known as Supernova 1987A. On August 25 1989 Voyager 2 was the first
spacecraft to observe the planet Neptune up close.
When Voyager 2 flew within 3,000 miles of Neptune, the planet was the most distant member
of the solar system from the Sun. It is the smallest of our Solar Systemís gas giants.
Thanks to Voyager, Neptune is now known to have 8 moons, six of which were found by Voyager.
Even though Neptune receives only 3 percent as much sunlight as Jupiter does, it is a
dynamic planet and surprisingly showed several large, dark spots similar to Jupiterís hurricane-like
storms. The Great Dark Spot on Neptune was about the size of earth and was similar to
the Great Red Spot on Jupiter. The strongest winds on any planet were measured
on Neptune. Most of the winds blow westward, or opposite to the rotation of the planet.
Near the Great Dark Spot, winds speeds reached 1,200 miles per hour.
Triton, the largest of the moons of Neptune, was shown to be not only the most intriguing
satellite of the Neptunian system, but one of the most interesting in all the solar system.
Voyager 2 images showed active geyser-like eruptions spewing invisible nitrogen gas and
dark dust particles several kilometers into the atmosphere.
The new moons found at Neptune by Voyager are all small and remain close to Neptuneís
equatorial plane. Names for the new moons were selected from mythologyís water dieties.
They include Naiad, Thalassa, Despina, Galatea, Larissa, and Proteus.
Voyager 2 solved many of the questions scientists had about Neptuneís rings.
With no more planet fly-bys in its plan, Voyager 2 began its trip out of the Solar System.
In 1989 Voyager 2 used the gravity of Neptune to sling shot itself like Voyager 1, out of
the solar system. Both probes set sail into the void. Voyager 2 is still the only probe
ever to visit Uranus and Neptune. During both Voyagers tours of Jupiter, Saturn,
Uranus, and Neptune, the space crafts sent home nearly 80 thousand images and more than
5 trillion bits of data. January 1 1990: With Voyagerís new interplanetary
destinations, the projectís designation was changed to Voyager Interstellar Mission.
Voyager 1ís cameras had been dormant since it left the vicinity of Saturn. But, on Valentineís
Day, 1990, before beginning its journey out of our Solar System, NASA turned the cameras
back on to look back to where the spacecraft had come from and transmit its last imagesÖ..the
Earth and our Solar System. By 1998, both spacecraft had shown signs of
a lessening power supply. Voyagerís signals are transmitted by a 20-watt radio transmitter
and are so faint that the amount of power reaching NASAís antennas is 20 billion times
smaller than the power of a digital watch battery.
February 17 1998: Voyager 1 passed Pioneer 10 to become the most distant human-made object
in outer space. In 2002, the then 25-year-old Voyager 1 was
more than 8 billion miles away from Earth. Radio signals required 12 hours to reach the
probe. NASA sent commands to activate a spare sun sensor and star tracker to help the craft
locate its position. Voyager 1 was leaving the Solar System, rising above the ecliptic
plane at an angle of about 35 degrees, at a speed of 39,000 per hour. Voyager 2 was
also leaving the Solar System diving below the ecliptic plane at an angle of about 48
degrees at a speed of 35,000 per hour. Both spacecraft continue to study ultraviolet sources
among the stars, and the fields and particles instruments aboard the Voyagers will continue
to search for the boundary between the Sunís influence and interstellar space. The Voyager
spacecraft are expected to return valuable data for two or three more decades. Communications
will be maintained until the Voyagersí nuclear power sources can no longer supply enough
electrical energy to power critical subsystemsÖestimated to be sometime in 2020.
August 1 2002: Voyager 1 reported that the solar wind speed appeared to slow down. Voyager
may have crossed the Solar System ìtermination shock.î
April 15 2004: Voyager 2 detected a shock wave from the October 2003 solar storms, experienced
here on Earth. Voyager 2 measured its speed, composition, temperature and magnetism.
January 5 2005: After 10,000 days and 7 billion miles away from Earth, Voyager 2 held and
still holds the record of travelling to more planets than any other man-made object in
history. January 21: Also after 10,000 days and 9 billion
miles from Earth, in a dark and cold area at the very edge of our Solar System, Voyager
1 held and still holds the record as the explorer from Earth that has traveled farthest from
home. It was more than 100 times farther from the Sun than the Earth.
The Infrared Spectrometer and Radiometer heater was turned off to save power on Voyager 1
on December 7, 2011. The heater was used to keep the UVS (or Ultra Violet Spectrometer)
warm. The UVS temperature has dropped to below the measurement limits of the sensor; however,
UVS is still operating. Scientists expect to continue to receive data from the UVS until
mid-2013, at which time the instrument will be turned off to save power. There are several
other instruments that continue to work. So where are the Voyagers now?
Our entire solar system ñ every planet, asteroid, spacecraft, and life form belonging to our
solar system ñ sits inside a gargantuan bubble of gas about four times wider than the orbit
of Neptune..Ö and our sun is responsible for this. The sun blows the bubble by means
of the solar wind. Astronomers call the bubble itself the Heliosphere and its outer membrane
is the Heliosheath. The Heliosheath is important to humans because
it helps protect us from galactic cosmic rays. Galactic cosmic rays are subatomic particles
accelerated to nearly light speed by supernovas and black holes. Cosmic rays can penetrate
flesh and damage DNA, so scientists need to learn as much as possible about the Heliosheath.
Voyager 1 is currently located about 12 billion miles from Earth. It has crossed the Termination
Shock, and is now inside the Heliosheath. Voyager tells us that we are in a stagnation
region where the wind of charged particles streaming out from our sun has calmed. It
is showing that what is outside this region is pushing back. The Heliosheath is 3 to 4
billion miles thick, so the Voyagers will be inside it for another 10 years or more
before crossing the Heliopause and into inter stellar space.
Voyager 2 is currently located about 10 billion miles from Earth also in the Heliosheath.
Voyager 1 will be the first to pass through the HELIOPAUSE, which is the boundary area
between the solar and the interstellar wind. Recent data from Voyager has shown this boundary
is NOT smooth but frothy and bubbly..and the bubbles are GIGANTIC.
Both Voyagers continue exploring where nothing from Earth has flown before. In the more than
34 years since their launch, they each are much farther away from Earth and the Sun than
Pluto. Each of the Voyager probes is famously equipped
with a Golden Record, literally, a gold-coated copper phonograph record containing photographs,
sounds, and salutations from the Earth. Said Carl Sagan at the time. A billion years
from now, when everything on Earth weíve ever made has crumbled into dust, when the
continents have changed beyond recognition and our species is unimaginably altered or
extinct, the Voyager record will speak for us. The discs will be there in the event
that sometime in the distant future, Voyager encounters alien life or some future human
life. Barring any serious spacecraft subsystem failures,
or they crash into something we cannot yet calculate, the Voyagers may survive until
the early twenty-first century, about 2025, when diminishing power and hydrazine levels
will prevent further operation. Were it not for these dwindling consumables and the possibility
of losing lock on the faint Sun, our tracking antennas could continue to "talk" with the
Voyagers for another century or two!