Pioneer 10 and 11: the first human-made objects to be sent on their way to infinity.

The US American space probe Pioneer 10 was launched on March 3, 1972, toward the planet Jupiter. It passed the planet in December 1973, sending pictures and measurement data back to Earth. Since then it has been on a straight route toward Aldebaran in the constellation Taurus, which it will reach in about 2 million years. Its current speed is 40,000 km/h or 0.00004 light-years per year. Our last contact with the unmanned spacecraft was established on January 22, 2003. At that time it was at a distance of 12 billion kilometers from Earth; due to exhausted batteries, its signals were at the limit of receiver sensitivity. At a later attempt in February 2003, no signals were received from the space probe.

Pioneer 11 was launched on April 6, 1973 on an Atlas Centaur rocket. The space probe passed Jupiter in December 1974 and Saturn five years later. In February 1990, Pioneer 11 crossed Neptune's orbit and reached interstellar space. The last contact was established on November 24, 1995.

The Pioneer Anomaly

Prior to the breakdown of radio contact, the space probes transmitted some data that have become known as "Pioneer anomaly", puzzling the NASA scientists for many decades. The trajectories of both space probes deviated slightly from the calculations. It seemed as if the probes were slowed down by something located outside of the solar system, as if they were immersed in some invisible medium. Furthermore, the strength of their deceleration was roughly equivalent to the product of the speed of light and the Hubble constant. To account for this, all known possible factors — errors in computation or measurement, solar wind, gas leaks, a mass defect in the solar system, a modification of the law of gravity, and many more — have been considered. It was not before 2011 that a convincing explanation could be found, using a computer simulation of the thermal radiation of the spacecraft. The difference of front and back radiation apparently caused a small recoil that was responsible for the deceleration.

The Last Message of Humanity...

Aside from the anomaly, there was another earthly factor that almost prevented the missions from succeeding. Since the spacecraft will continue traveling until they hit on an obstacle, NASA decided to furnish them with a greeting plaque for any extraterrestrials that may encounter them — a last message from our civilization, so to speak, which will presumably be extinct by that time. The gold-anodized 23 x 15 cm aluminum plaque was designed by the astronomer Carl Sagan, his wife Linda, and Frank Drake, who is known for his Drake formula.

Politically incorrect greeting for extraterrestrials (NASA)

The dumbbell-shaped object at the top left symbolizes the hyperfine structure transition of the hydrogen molecule, the most common molecule in the universe. With a wavelength of 21 cm it serves as a standard for the binary figures on the plaque. On the left you'll find the position of our sun in relation to 14 pulsars and to the center of the Milky Way. Next to it stand two people in front of a silhouette of the Pioneer probe. The average female height is indicated on the right in hydrogen units (168 cm). The male demonstrates the anatomic peculiarity of the antidromic thumb. At the very bottom you can see our solar system with the nine planets and the probe launching from the third planet. The planetary distances are represented in binary numbers with a units of 1/10 of Mercury's orbit, so that with some imagination you can figure out that human beings use the decimal system for counting.

...Turns out to be Space Pornography

Once the content of the plaque was revealed to the public (fortunately only after the first probe had been launched), NASA had to weather a storm of protest. Thousands of upright US citizens protested the use of their tax money to send pornography into space. Feminists discovered that the passive posture of the female and its orientation toward the male could only serve to convert extraterrestrials to endorsing male dominance. Representatives of ethnic minorities were enraged about the complete absence of representatives of minority groups in the message. The reactions revealed more about humanity than the entire content of the plaque. NASA nonetheless managed to launch the second Pioneer probe, but has since been more careful to stay politically correct. The later space probes Voyager 1 and 2 contained records with similar images though avoiding all nudity.

Golden record of the Voyager probes [NASA]

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