So Long Old Friend
January 23, 2003: Last Contact With Pioneer 10
So long old friend. On this day in 2003 we had our last contact with Pioneer 10 which was heading in the direction of the star Aldebaran* in the constellation Taurus. At current speed it should arrive there in about 2 million years. Pioneer 10 is the most distant man-made object in the universe (not to be compared to alien made).
Pioneer 10, after completing its mission to Jupiter, became the first spacecraft to escape our solar system. Launched on March 3, 1972 from Cape Canaveral, Pioneer 10 began photographing Jupiter November 15, 1973 transmitting about 500 images.
At the behest of Carl Sagan, Pioneer 10 and Pioneer 11 carry a 152 by 229 mm gold-anodized aluminum plaque in case either spacecraft is ever found by intelligent life-forms. The plaques feature the figures of a human male and female along with several symbols that are designed to provide information about the origin of the spacecraft.
At the top left of the plate is a schematic representation of the hyperfine transition of hydrogen, which is the most abundant element in the universe. Below this symbol is a small vertical line to represent the binary digit 1.
On the right side of the plaque, a man and a woman are shown in front of the spacecraft. Between the brackets that indicate the height of the woman, the binary representation of the number 8 can be seen. The right hand of the man is raised as a sign of good will. Although this gesture may not be understood, it offers a way to show the opposable thumb and how the limbs can be moved.
Originally Sagan intended for the humans holding hands, but soon realized that an extraterrestrial might perceive the figure as a single creature rather than two organisms. Behind the figures of the human beings, the silhouette of the Pioneer spacecraft is shown in the same scale so that the size of the human beings can be deduced by measuring the spacecraft.
The radial pattern on the left of the plaque shows 15 lines emanating from the same origin. Fourteen of the lines have corresponding long binary numbers, which stand for the periods of pulsars, using the hydrogen spin-flip transition frequency as the unit. Since these periods will change over time, the epoch of the launch can be calculated from these values.
If the plaque is found, only some of the pulsars may be visible from the location of its discovery. Showing the location with as many as 14 pulsars provides redundancy so that the location of the origin can be triangulated even if only some of the pulsars are recognized.
At the bottom of the plaque is a schematic diagram of the Solar System. A small picture of the spacecraft is shown, and the trajectory shows its way past Jupiter and out of the solar system. Saturn’s rings could give a further hint to identifying the Solar System. The binary numbers above and below the planets show the relative distance to the sun.
*Aldebaran or Alpha Tauri is the brightest naked eye star in the constellation Taurus and is the 14th brightest star in the entire sky. Aldebaran has a luminosity 425 times the Sun. Its diameter is 44.2 times that of the Sun. The image below shows the uncropped view of Aldebaran (North is up).
Aldebaran is one of the easiest stars to find in the night sky, partly due to its brightness and partly due to its spatial relation to one of the more noticeable asterisms in the sky. If one follows the three stars of Orion’s belt from left to right (in the Northern Hemisphere) or right to left (in the Southern), the first bright star found by continuing that line is Aldebaran.