3.6 Flying Out of the Solar System
179
Los Angeles Herald-Examiner, and both agreed enthusiastically. As a result, Burgess
and Hoagland approached Carl E. Sagan (1934−1996), Director of the Laboratory of
Planetary Studies at Cornell University, who was then visiting the JPL in the city of
Pasadena, California, in connection with Mariner-9. Carl Sagan, together with Frank
D. Drake (1930−) who was Director of the National Astronomy and Ionosphere
Center at Cornell University, had ever designed a type of message that might be used
to communicate with an alien intelligence, and a short while earlier, also been invited
to attend a conference in the Crimea devoted to the problem of communicating with
extraterrestrial intelligences. Sagan was enthusiastic about the idea of a message
carried with the Pioneers, and invited Drake to take part in designing the plaque
with the mankind’s message patterns. Sagan’s second wife, L. Salzman Sagan who
was an American artist and writer, was in charge of the pattern drawing and artistic
processing. The design pattern was presented to the NASA and soon approved,
and etched into a 6061-T6 gold-anodized aluminum plate, with a size of 15.2 cm
by 22.9 cm, a thickness of 0.127 cm and a weight of 0.12 kg. Its mean depth of
engraving is 0.0381 cm to ensure that the pattern will still be legible after millions of
years of space flight. The gold-anodized aluminum plate took only three weeks from
design to completion, and was attached to the spacecraft’s antenna support struts in a
position to help shield from erosion by interstellar dust. The detailed design pattern
of the Pioneer plaque is shown in Fig. 3.6, which mainly includes the following four
aspects.
(1) Hyperfine Transition of the Neutral Hydrogen
The neutral hydrogen is a normal hydrogen atom composed of one proton and one
electron orbiting the proton, while the proton and the electron also make the spin
motion respectively. Generally, the corresponding energies of the electrons moving
around the nuclei in different orbits are discontinuous values, which are called the
energy levels of atoms. When an electron is in the orbit closest to the nucleus, the
atomic state is the most stable, which is called ground state of the atom. When an
electron is in the high-energy level of other orbits and has the tendency of returning
to the ground state, the atomic state is unstable, which is called excited state of the
atom. The spin motion of the hydrogen atom in the ground state forms two hyperfine
structures of the atomic energy levels. One is that when the spin directions of the
electron with the proton are same, the hydrogen atom is in hyperfine high energy
state. The other is that when the spin directions of the electron with the proton
are opposite, the hydrogen atom is in hyperfine low energy state. In the quantum
mechanics, the process that an atom jumps from one energy level state to another
is usually called transition. Transiting from the hyperfine high energy state to the
hyperfine low energy state, the neutral atomic hydrogen will release the energy in the
form of stable electromagnetic radiation, with a frequency of 1420.40575177 MHz
and a wavelength of 21.10611405413 cm, which is the so-called 21-centimeter line,
also known as hydrogen line.
The neutral hydrogen is the most abundant element in the universe. The proton
and electron usually have their axes aligned and spin in the same direction, giving the
179
Los Angeles Herald-Examiner, and both agreed enthusiastically. As a result, Burgess
and Hoagland approached Carl E. Sagan (1934−1996), Director of the Laboratory of
Planetary Studies at Cornell University, who was then visiting the JPL in the city of
Pasadena, California, in connection with Mariner-9. Carl Sagan, together with Frank
D. Drake (1930−) who was Director of the National Astronomy and Ionosphere
Center at Cornell University, had ever designed a type of message that might be used
to communicate with an alien intelligence, and a short while earlier, also been invited
to attend a conference in the Crimea devoted to the problem of communicating with
extraterrestrial intelligences. Sagan was enthusiastic about the idea of a message
carried with the Pioneers, and invited Drake to take part in designing the plaque
with the mankind’s message patterns. Sagan’s second wife, L. Salzman Sagan who
was an American artist and writer, was in charge of the pattern drawing and artistic
processing. The design pattern was presented to the NASA and soon approved,
and etched into a 6061-T6 gold-anodized aluminum plate, with a size of 15.2 cm
by 22.9 cm, a thickness of 0.127 cm and a weight of 0.12 kg. Its mean depth of
engraving is 0.0381 cm to ensure that the pattern will still be legible after millions of
years of space flight. The gold-anodized aluminum plate took only three weeks from
design to completion, and was attached to the spacecraft’s antenna support struts in a
position to help shield from erosion by interstellar dust. The detailed design pattern
of the Pioneer plaque is shown in Fig. 3.6, which mainly includes the following four
aspects.
(1) Hyperfine Transition of the Neutral Hydrogen
The neutral hydrogen is a normal hydrogen atom composed of one proton and one
electron orbiting the proton, while the proton and the electron also make the spin
motion respectively. Generally, the corresponding energies of the electrons moving
around the nuclei in different orbits are discontinuous values, which are called the
energy levels of atoms. When an electron is in the orbit closest to the nucleus, the
atomic state is the most stable, which is called ground state of the atom. When an
electron is in the high-energy level of other orbits and has the tendency of returning
to the ground state, the atomic state is unstable, which is called excited state of the
atom. The spin motion of the hydrogen atom in the ground state forms two hyperfine
structures of the atomic energy levels. One is that when the spin directions of the
electron with the proton are same, the hydrogen atom is in hyperfine high energy
state. The other is that when the spin directions of the electron with the proton
are opposite, the hydrogen atom is in hyperfine low energy state. In the quantum
mechanics, the process that an atom jumps from one energy level state to another
is usually called transition. Transiting from the hyperfine high energy state to the
hyperfine low energy state, the neutral atomic hydrogen will release the energy in the
form of stable electromagnetic radiation, with a frequency of 1420.40575177 MHz
and a wavelength of 21.10611405413 cm, which is the so-called 21-centimeter line,
also known as hydrogen line.
The neutral hydrogen is the most abundant element in the universe. The proton
and electron usually have their axes aligned and spin in the same direction, giving the