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The Pioneer Interstellar Mission and Beyond

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National Aeronautics and Space Administration (NASA) of the United States launched Pioneer 10 and Pioneer 11 spacecraft in 1972 and 1973 respectively, with the aim of travelling through the asteroid belt to obtain pictures of Jupiter and Saturn, as well as studying the solar wind, cosmic rays and heliosphere, etc. After safe passage through the asteroid belt between Mars and Jupiter, the two Pioneers carried out their missions of exploring Jupiter and Saturn. With respect to the technology at that time, the Pioneers were equipped with innovative scientific instruments, such as photopolarimeter for taking planetary images, and radioisotope thermoelectric generator for electrical power supply. The "exclusive" information obtained by the Pioneers was valuable, such as the earliest close-up images of Jupiter and Saturn, first-time confirmation of Jupiter's intense magnetic field and discovery of Saturn's new ring. Pioneers 10 and 11 lost contact with NASA in 2003 and 1995 respectively. Nevertheless, they are still carrying, beyond the Solar System, a "message in a bottle" that represents all humans on Earth.

Today, 50 years later, let us review the technology, journey and discoveries of the Pioneers and their implications to future space exploration in this exhibition.

Venue: Foyer, Hong Kong Space Museum
Exhibition period: 26 October 2022 - 29 May 2023
Free admission

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References

Solar wind is a stream of charged particles emitted by the Sun. Solar wind blows against the interstellar medium (mostly neutral gases and dust) along its path and wipes out a bubble-like asymmetric region surrounding the Solar System, which is called the heliosphere. Solar wind flows unimpeded through the Solar System far beyond even the region of Pluto, until its motion slows abruptly by the outside pressure of the interstellar medium in termination shock. Solar wind continues to slow down as it passes through the heliosheath. Going further, solar wind arrives at the heliopause, and is halted by the pressure from interstellar gases. Beyond the heliopause is interstellar space.

Pioneer 10 is heading towards the heliotail direction while Pioneer 11 is heading towards the "nose" of the heliosphere. During their outbound journeys, both Pioneer 10 and 11 will find respectively the "downwind" and "upwind" boundaries of the heliosphere where the solar wind slows down and forms a termination shock, beyond which there would be the heliopause and finally the bow shock of the interstellar medium.

Interactive exhibit Termination Shock
Visitors can use the interactive exhibit "Termination Shock" when visiting the exhibition or try the following activity at home to simulate the formation of the "heliosphere".

  1. Print the image of the heliosphere on an A4-sized paper (image of the heliosphere can be downloaded here);
  2. Attach the paper onto a stiff surface such as cardboard or plastic board;
  3. Wrap the cardboard from Step 2 with plastic wrap or plastic folders and try to avoid wrinkles or air bubbles on the side with the printed image;
  4. Place the plastic wrapped image under the stream of water in the kitchen sink and move the image so that the water hits the location of the Sun;
  5. Tilt the image slightly to let water flow away from the "bow wave" side;
  6. Adjust the position of the image up and down and the amount of water coming out of the tap so that water clears out a bubble-shaped area that matches up the termination shock on the image.

The water flows quickly away from where it hits the image and clears out a bubble-shaped area. This is analogous to the solar wind from the Sun which blows away the interstellar medium and eventually subsides, resulting in a bubble we called "heliosphere".

Activity credit: NASA/IBEX

 

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