That Mars was the focus of the space program of the United States and the Soviet Union did not automatically mean that there was no interest in the other planets. In a sense it was quite the opposite.
If Mars had a civilization on it, or even just its ruins, what surprises might be hidden on the other planets and moons of the solar system?
Venus might have been the other main candidate for alien life, but any hopes on that faded after Venera 4 of the Soviet Union had sent a probe descending into the Veneran atmosphere in 1967 and its data had shown that the temperature and the pressure had been too high to allow any life as humanity knew it. The flyby of NASA’s Mariner 5 confirmed the measurements shortly after, with its flyby.
Yet the Soviet’s interest for Venus remained. More probes were sent to Venus, to orbit the planet and land more probes. To NPO Energia and the Academy of Science it was the challenge of landing on Venus and find out more that allowed them to do so. The shorter intervals between launch windows to Venus allowed them test some of the hardware intended for use on the Mars probes.
This time it was it was Venera 10 in 1975, that returned a surprise for the Soviet Union. The cameras of the Venera 10 orbiter captured an image of something orbiting Venus. The anomaly was captured three more times on various orbits around the planet, allowing the Academy of Sciences to calculate a set of preliminary orbital data for the object.
Subsequently it was tried to contact the object with radio transmissions, much like it had happened on Mars, in this case there was no answer.
While the Soviet Union was quick to label the discovery as top secret, a CIA agent within the Academy of Sciences was able to get the information into the United States. Langley however was less inclined to believe in an object orbiting Venus. The orbital data suggested a highly eccentric orbit and the images themselves were not as good as they should have been to suggest that there actually was an object.
That the CIA agent in question was disappeared by the KGB after the information reached the United States, only reinforced the suggestion that the information had been used to find and eliminate the agent.
To the Soviet Union, the unwillingness of the United States to confirm the information only made them more eager to confirm it themselves. The planning of the upcoming Venera missions was accelerated and Venera 11 and 12 first priority , while equipped with landers that would be the first to try and take color images of the Veneran surface, would be able to try and rendezvous with the unknown object.
In 1978 the probes reached Venus and the landers touched down on Venus, operating for more than an hour each. The orbiters on the other hand, while first being used as relay for the landers, started their moves to try and rendezvous with the object.
Venera 11 entered an uncontrollable spin as its reaction control system failed to respond correctly. The probe entered the Veneran atmosphere and was destroyed.
Venera 12 was able to do the required maneuvers to rendezvous with the object, but only for a short while. During two hours of a close flyby of the object the orbiter took thirty images of the object. Due to a construction error of the optics, none of them were detailed enough to allow actual identification. It could have been a captured asteroid, but just as well an alien spacecraft. For the remainder of Venera 12’s lifetime, the probe was responsible for highly detailed readings of the Veneran upper atmosphere, as the probe was unable to meet up with the object again.
Venera 13, 14 and 15 were the next to be launched in 1981. Where Venera 13 and 14 also carried landers, Venera 15 carried the first Synthetic Aperture Radar system used for an interplanetary mission. While Venera 15 was officially launched to take surface images with the SAR system, the actual mission was to use the system to take high quality images of the unknown object, while Venera 13 and 14 would launch their landers and, like Venera 12, then rendezvous with it.
The analysis of the SAR data from Venera 15 needed several months, but together with the images of Venera 13 and 14, it was possible to finally identify the object as artificial and confirm it to be a spacecraft of some sort.
The following probes confirmed the findings of Venera 13 through 15 and while the information managed to get into the hands of the CIA again, the loss of their first agent in the wake of the initial discovery only made them dismiss the claims as another attempt to find their agents.
Venus officially remained interesting from a scientific point of view for NASA. In 1978 they launched two probes to Venus, the Pioneer Venus dual probe. One was designed as orbiter to map the surface with a radar altimeter, and one designed to carry several smaller probes for atmospheric entry. None of these probes detected the alien spacecraft in orbit around Venus as their orbits never intersected at a time that would have made a detection possible.
Mercury was of little consequence to either the Soviets or the United States. The only probes that made its way to Mercury were Mariner 10 and 11 in 1974. Both were the first to use a gravitational assist of Venus to send them on a trajectory to Mercury, which they encountered three times, returning a multitude of images, but nothing that would indicate any signs of habitation or other artificial objects.
The outer planets on the other hand were more obvious targets for NASA.
Pioneer 10 was the first probe to Jupiter, in 1972. It passed the planet in a close trajectory in January 1974, with the gravity of the planet ejecting it from the solar system.
Pioneer 11 followed in 1973, going on a ‘miniature Grand Tour’ and visit Jupiter and Saturn. It passed Jupiter in December 1974, much closer than Pioneer 10, using the gravity of the planet to push it out towards Saturn. In September 1979, the probe passed Saturn, discovered a new moon of the ‘Lord of the Rings’, as well as several new rings and took images of Saturn and Titan.
While Pioneer 10 and 11 were on their way, several people within NASA, among them Carl Sagan, lobbied for the ‘Grand Tour’, using the unique alignment of the four gas giants in combination with gravity assists to visit each of the planets. While, to Sagan, the scientific knowledge gained from such a mission was the most important thing, he wasn’t above using the potential discovery of aliens or alien artifacts at Jupiter and Saturn to gain support for the ‘Grand Tour’.
In 1973, NASA gave in and four ‘Grand Tour’ probes were approved. Two sets of two probes were projected, two for a visit of Jupiter, Saturn and Pluto, and two for a visit of Jupiter, Uranus and Neptune. Mariner JSP 1 and Mariner JSP 2 were launched in 1977, while Mariner JUN 1 and Mariner JUN 2 were launched in 1979.
Mariner JSP 1 and 2 arrived at Jupiter in late 1979, and took pictures of all Jovian moons, discovering the volcanic activity on Io and the ice shields of Europa, Ganymede and Callisto. Anomalies were found on all images made from the jovian satellites. While at first NASA suspected to have found more alien impact á la Mars, soon researchers came up with a legitimate explanation in the form of the enormous radiation emitting from Jupiter itself.
Mariner JSP 1 reached Saturn in November 1980 and during its flyby at Titan made images that made the JPL and NASA do a double take. Two objects were visible on the series of five images, that first grew larger, before growing smaller again. The third of these images captured the objects only a few kilometers distant. Had Mariner JSP 1 been on a slightly different trajectory, it could have collided with either of them. The additional infrared images of the objects showed that they were slightly warmer than they should have been and allowed to identify areas that were warmer than the rest of the objects.
Theories that these objects were spacecraft were quick to appear, but NASA decided that they would try to adjust the trajectory of Mariner JSP 2 slightly to get another set of images, at the cost of the Pluto encounter.
The importance of the discovery of Titan possessing an atmosphere made up of nitrogen and methane was secondary to these new possible alien artifacts.
As Mariner JSP 2 arrived at Saturn, it passed Titan a little closer than its sister probe did, but none of the new images taken showed any of the two anomalies.
However, Saturn and Titan were far away and the only thing that could visit the planet and its moon at that moment were probes. NASA went ahead and planned for a probe that would enter Saturn’s gravitational system and eventually move into an orbit around Titan to actively look for the two unknown objects.
Mariner JUN 1 and 2 were launched in 1979 and passed Jupiter in 1981, discovering a number of new, smaller moons and a ring system around the largest planet of the solar system. Both probes would need until 1987 to arrive at Uranus.
The revelation of the two alien artifacts in orbit around Titan was made by the Washington Post in 1981, after the journalist Carl Bernstein was tipped by a JPL scientist and given evidence, as NASA tried to keep it secret. Pressure from other newspapers as well as TV channels, made NASA admit the issue, diminishing their image in the public eye.
Not much later President Reagan publicly praised NASA and noted the existence of standing orders of the government to keep this kind of information away from undesirable eyes, likes those of the Soviets. He commented that, while personal freedom and freedom of information are basic rights, there exists a responsibility of every free man and woman to make sure that those freedoms are kept. And by releasing these informations the JPL scientist did endanger the American Freedom.
In the aftermath of the entire affair, the scientist who released the information was fired and the Washington Post released a statement where they understood their responsibility very well and noted that they would think twice before releasing similar information in the future.
With this the Academy of Sciences in Moscow finally began to consider that the outer planets might indeed harbour some alien artifacts as well, but compared to their discovery at Venus, which was much closer, Saturn was too far away to realistically plan a manned mission to it.
In reality it was too late to plan an unmanned mission, that used a gravity assist. The only way would be the direct way, if they were to keep up with the United States. NPO Energia took over the planning and by 1981, they were ready to launch Saturn 1 and Saturn 2, a pair of identical probes that used a highly experimental nuclear electric propulsion system to propel them to Titan, with a nuclear reactor feeding an array of Hall Effect thruster with 10 N thrust. The same SAR system that had already imaged the Veneran spacecraft was installed in both probes to search for the two new deviations.
By 1984 the two Soviet probes reached Saturn and, using a complicated series of maneuvers and the use of gravity assists to slow down, entered the orbit of Titan in December 1984. The two objects were finally located in April 1985, allowing to measure their orbital data.
This time the CIA was interested in the information provided by their agents in the Academy of Sciences and NASA used the info to design the Prometheus probe.
The Prometheus probe took advantage of the common modules of the Cislunar Infrastructure Development Plan, cutting down the development time by quite a bit. A single Advanced Propulsion Unit, combined with an Advanced Power Module, an Automated Command Mission Module and a number of specially designed modules. The launch was slated for August 1986.