Read Online Billions & Billions by Carl Sagan - Free Book Online Page A
Authors: Carl Sagan
Ads: Link
revelations in all four of these areas can be expected in the next decade or two. Again, there are many other questions in modern astronomy that I could have substituted, but the prediction I can make with the highest confidence is that the most amazing discoveries will be ones we are not today wise enough to foresee.
* “Enuma elish” are the first words of the myth, as if the Book of Genesis were called “In the Beginning”—which is in fact nearly the meaning of the Greek word “genesis.”
* A fifth is described in the following chapter.
CHAPTER 6
SO MANY SUNS,
SO MANY WORLDS
What a wonderful and amazing scheme have we here of the magnificent vastness of the Universe! So many Suns, so many Earths …!
CHRISTIAN HUYGEVS ,
New Conjectures Concerning the Planetary Worlds
,
Their Inhabitants and Productions
(ca. 1670)
I n December 1995, an entry probe, detached from the
Galileo
Jupiter orbiter, entered the turbulent, roiling atmosphere of Jupiter and sank to a fiery death. Along the way it radioed back information on what it found. Four previous spacecraft had examined Jupiter as they raced by. The planet has also been studied by ground-based and space telescopes. Unlike the Earth, which is made mainly of rock and metal, Jupiter is made mostly of hydrogen and helium. It is so big that a thousand Earths could fit inside. At depth, its atmospheric pressure gets so large that electrons are squeezed off atoms and the hydrogen becomes a hotmetal. This state of affairs is thought to be the reason that twice as much energy comes pouring out of Jupiter than Jupiter gets from the Sun. The winds that buffeted the
Galileo
probe at its deepest entry point probably arise not from sunlight but from the energy originating in the deep interior. At the very core of Jupiter there seems to be a rocky and iron world many times the mass of the Earth, surmounted by the immense ocean of hydrogen and helium. Visiting the metallic hydrogen—much less the rocky core—is beyond human abilities for at least centuries or millennia to come.
The pressures are so great in the interior of Jupiter that it is hard to imagine life there—even life very different from our own. A few scientists, myself among them, have tried, just for fun, to imagine an ecology that might evolve in the atmosphere of a Jupiter-like planet, somewhat like the microbes and fish in the Earth’s oceans. The origin of life might be difficult in such an environment, but we now know that asteroidal and cometary impacts transfer surface material from world to world, and it is even possible that impacts in the early history of the Earth transferred primitive life from our planet to Jupiter. This, though, is the merest speculation.
Jupiter is about 5 astronomical units from the Sun. An astronomical unit (abbreviated AU) is the distance of the Earth from the Sun, about 93 million miles, or 150 million kilometers. If not for the interior heat and the greenhouse effect in Jupiter’s immense atmosphere, the temperatures there would be about 160 degrees below zero Celsius. That’s roughly the temperature on the surface of Jupiter’s moons—much too cold for life.
Jupiter and most of the other planets in our Solar System orbit the Sun in the same plane, as if they were confined to separate grooves on a phonograph record or a compact disc. Why should this be? Why shouldn’t the orbital planes be tilted at allangles? Isaac Newton, the mathematical genius who first understood how gravity makes the planets move, was puzzled by the absence of much tilt in the orbital planes of the planets, and deduced that, at the beginning of the Solar System, God must have started the planets out all orbiting in the same plane.
But the mathematician Pierre Simon, the Marquis de Laplace, and later the celebrated philosopher Immanuel Kant, discovered how it could have happened without recourse to divine intervention. Ironically, they relied on the very laws of physics that Newton had
* “Enuma elish” are the first words of the myth, as if the Book of Genesis were called “In the Beginning”—which is in fact nearly the meaning of the Greek word “genesis.”
* A fifth is described in the following chapter.
CHAPTER 6
SO MANY SUNS,
SO MANY WORLDS
What a wonderful and amazing scheme have we here of the magnificent vastness of the Universe! So many Suns, so many Earths …!
CHRISTIAN HUYGEVS ,
New Conjectures Concerning the Planetary Worlds
,
Their Inhabitants and Productions
(ca. 1670)
I n December 1995, an entry probe, detached from the
Galileo
Jupiter orbiter, entered the turbulent, roiling atmosphere of Jupiter and sank to a fiery death. Along the way it radioed back information on what it found. Four previous spacecraft had examined Jupiter as they raced by. The planet has also been studied by ground-based and space telescopes. Unlike the Earth, which is made mainly of rock and metal, Jupiter is made mostly of hydrogen and helium. It is so big that a thousand Earths could fit inside. At depth, its atmospheric pressure gets so large that electrons are squeezed off atoms and the hydrogen becomes a hotmetal. This state of affairs is thought to be the reason that twice as much energy comes pouring out of Jupiter than Jupiter gets from the Sun. The winds that buffeted the
Galileo
probe at its deepest entry point probably arise not from sunlight but from the energy originating in the deep interior. At the very core of Jupiter there seems to be a rocky and iron world many times the mass of the Earth, surmounted by the immense ocean of hydrogen and helium. Visiting the metallic hydrogen—much less the rocky core—is beyond human abilities for at least centuries or millennia to come.
The pressures are so great in the interior of Jupiter that it is hard to imagine life there—even life very different from our own. A few scientists, myself among them, have tried, just for fun, to imagine an ecology that might evolve in the atmosphere of a Jupiter-like planet, somewhat like the microbes and fish in the Earth’s oceans. The origin of life might be difficult in such an environment, but we now know that asteroidal and cometary impacts transfer surface material from world to world, and it is even possible that impacts in the early history of the Earth transferred primitive life from our planet to Jupiter. This, though, is the merest speculation.
Jupiter is about 5 astronomical units from the Sun. An astronomical unit (abbreviated AU) is the distance of the Earth from the Sun, about 93 million miles, or 150 million kilometers. If not for the interior heat and the greenhouse effect in Jupiter’s immense atmosphere, the temperatures there would be about 160 degrees below zero Celsius. That’s roughly the temperature on the surface of Jupiter’s moons—much too cold for life.
Jupiter and most of the other planets in our Solar System orbit the Sun in the same plane, as if they were confined to separate grooves on a phonograph record or a compact disc. Why should this be? Why shouldn’t the orbital planes be tilted at allangles? Isaac Newton, the mathematical genius who first understood how gravity makes the planets move, was puzzled by the absence of much tilt in the orbital planes of the planets, and deduced that, at the beginning of the Solar System, God must have started the planets out all orbiting in the same plane.
But the mathematician Pierre Simon, the Marquis de Laplace, and later the celebrated philosopher Immanuel Kant, discovered how it could have happened without recourse to divine intervention. Ironically, they relied on the very laws of physics that Newton had
Similar Books
