Robert McNees
The Pioneer 10 spacecraft launched #OTD in 1972.
It was a mission of firsts: passing through the asteroid belt, visiting Jupiter, crossing the orbits of Neptune and then Pluto. We detected a last, faint signal on January 23, 2003. Now it belongs to the cosmos.
Images: NASA
Robert McNees
Pioneer 10 was also the first human-made object to achieve the escape velocity needed to carry it outside of our solar system. But that won’t happen until the late 2050s, and there won’t be a signal to notify us.
(Despite being first to achieve this escape velocity, Pioneer 10’s trajectory has it leaving the solar system well after the Voyager probes.)
Robert McNees
The Pioneer 10 spacecraft, launched #OTD in 1972, famously carries a gold-anodized aluminum plaque that encodes its origins. The plaque was suggested by science journalist Eric Burgess, designed by Carl Sagan and Frank Drake, and illustrated by Linda Salzman Sagan.
Robert McNees
The plaque is decoded via its depiction, in the upper-left corner, of the hyperfine transition in neutral hydrogen.
The hyperfine transition emits a photon with a characteristic wavelength of 21cm and frequency of 1,420 MHz. Distances and frequencies shown on the plaque use these as base units.
Robert McNees
The diagram on the left-hand side of the plaque, which also appears on the Voyager Golden Records, indicates the position of Earth relative to 14 pulsars.
The period of each pulsar, in units of the inverse hyperfine frequency, is indicated in binary along its line.
Robert McNees
The plaque also shows the probe’s path through our solar system, with binary depictions of each planet’s distance from the sun in multiples of 1/10 the orbital radius of Mercury.
At the time of launch the solar system comprised nine planets — poor Pluto was still in the club.
Robert McNees
👽 1: Is this the right solar system
👽 2: Idk, their transmissions refer to only 8 planets
👽 1: [counting] But the plaque shows 9 planets
👽 2: We should visit them and ask-
👽 1: Negative, no one just changes the number of planets, let's try the next system
Robert McNees
👽 1: We have deciphered the plaque. The location of the probe’s home planet is known to us. We should visit.
👽 2: Query. What is their technology level?
👽 1: Difficult to assess. Development of rudimentary spacecraft. But no evidence of pants.
👽 2: Okay let’s hold off on that visit.
Robert McNees
👽 1: Jumpsuits?
👽 2: Scanning...Negative.
Alec Perkins
@mcnees seems kind of threatening when put like that: we used to have 9 planets, now we have 8.
Robert McNees
@alec Nice nonet…be a real shame if it became an octet.
dominic 🌱
@mcnees we have adults rompers. Does that count?
Robert McNees
@dominicvfx Negative.
Michael Busch
@Kencf618033 @mcnees The original "A Message From Earth" paper gives the list of pulsars on the plaque: https://astro.swarthmore.edu/astro61_spring2014/papers/sagan_science_1972.pdf .
The spin periods and relative directions of the pulsars are intended to specify both the Sun's position and the time the plaque was made.
However, some of the pulsar periods were not well known then and all of them have some random variation. So eventually the map will become useless.
:tor: Kenneth Freeman
@mcnees
Which pulsars? And is there a calendar?
Dorothy Bishop
@mcnees what's the London Underground doing on it?
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