SPACE ASTRONOMY AND PLANET EARTH
Stellar systems emit strongly in the infrared during their birth. If we wish to know about the formation of the solar system the investigation of new stars with the aid of satellites such as IRAS, the Shuttle Infrared Telescope Facility (SIRTF), their successors, and the new generation of ground infrared interferometers and high-altitude balloon telescopes, is paramount (the SIRTF is 1000 times more sensitive than any other infrared system previously used in the atmosphere). And so is the search for already established planetary systems. Infrared astronomy is particularly useful in this last regard because a star's radiation is so strong relative to that of its planets, and the arc between the planets and the star so small, that the star simply does not let us see the planets in orbit around it, if any exist. At the infrared level, however, the contrast between star and planets is not quite so large, which makes this range of wavelength promising, if not for this generation of space telescopes at least for the next. Infrared observations have already identified dense disks of matter around Vega and other stars, perhaps planets in formation. The grains of dust around newly born stars are smaller than those around stars hundreds of millions of years older, in accordance with the predictions of the planetesimals theory of the formation of planets. We have by now obtained infrared pictures of such disks “from above” and have noticed circular strings clear of dust, just what a planet would do as it clears the region of space in its path. Most importantly, we have discovered hundreds of Jupiter-size planets and a few terrestrial-size planets around several stars (by using spectral analysis of those stars, so as to determine by Doppler shifts in the starlight frequency whether a large planetary body influences the motion of the star).
The next few decades of exploration will give us the opportunity of testing our most cherished theories about the formation of our own planetary system, and to settle such issues as the temperature of the newly born planets. This last issue has much to do with the story of life on our own planet. Eventually we may even test our ideas about the composition of the primordial atmospheres. As we saw in Chapter 4, to know about the Earth we needed to examine other planets. To know about our planetary system we need to examine other planetary systems, for very much the same sorts of reasons. And surely, in this task it is crucial to determine the role of the star or stars of the system.
Apart from the Earth itself no other object rivals the sun in importance for us. Life depends on it; the Earth depends on it. Thus to know what to expect from the sun has obvious benefits. For example, a variety of solar cycles seem to affect the Earth's climate. In the 17th and 18th century the famous sun spots disappeared for a period of about 70 years. As Science describes it, "Europe became so cold at that time that the Thames froze regularly and Louis XIV had the beautiful, but chill, marble floors of Versailles covered with wood parquet to keep his feet warm."
Understanding the sun better, however, requires a variety of investigations.
(1) The sun is a very complex body. Its surface temperature is 6,000 degrees, but the corona around it is about a million degrees, and in the heart of solar flares the temperature goes up to about 100 million degrees. To understand this range of temperatures, to understand the sun's magnetism (which apparently has much to do with the sun spots), we need to look at all the wavelengths in which the sun radiates energy. And in particular we need to look at it in the ultraviolet and X-ray bands of the spectrum. The plasmas, the magnetic and nuclear properties, and the structure of the sun are beginning to be explained by solar physics, some of which must unavoidably be done in space.
(2) To understand the internal environment of the sun it pays to try to understand the sun as a star. We can use vibrations on the sun’s surface as evidence of waves that travel through the interior of the sun, and which in turn give us evidence about that interior. But these observations need to be interpreted in light of our theories of the nature of stars. To calibrate these theories properly we need to study many other stars. And this in turn requires, in part, the help of telescopes placed in orbit. For the variations in the behavior of stars can be determined only by observing the full spectrum of their radiation.
(3) To know what a star may do, we need to have some inkling of its evolution, just as it was the case for planets as well. In this regard it becomes extremely helpful to look at many stars in different stages of evolution. But this evolution must be seen in the context of the galactic environment in which it takes place. We want to know the chemical composition and distribution of the gas and dust in the galaxy, how they form proto-stellar clouds, how those clouds collapse, how is the collapse affected by the other events (e.g., supernovas), and why the gas between stars is so hot (the solar system seems to be engulfed by a gas hot enough to emit X-rays: one million degrees!). As it turns out, most of the mass in the galaxy and many of the most telling events are invisible. We need unusual detectors in some cases (e.g., neutrino detectors in the middle of gold mines), but most often we require the space telescopes, and their complementary high-tech new ground telescopes, that can give us a reading of the full spectrum of electromagnetic radiation.
In these three respects space physics and space astronomy complete the task of comparative planetology that we discussed in Chapter 4. It is fair, then, to extend the same sort of justification to them. We have thus one more illustration of my thesis that serendipity is a natural consequence of science.
Space physics and space astronomy have thus been shown not to be exceptions about the theses on the nature of science that I advanced in Chapter 3. Some of their activity completes the task that justified comparative planetology (e.g., solar physics and the astronomical efforts to put it in the proper context). And other was shown, against the objection, to be fundamental science, and therefore it should be presumed to exhibit the natural connection with serendipity used to justify scientific exploration in general.
I cannot deny that much of what space science proposes to do sounds very esoteric. But so have sounded nearly all the revolutionary advances in the history of science. In some instances the masses and energies that we wish to study with the aid of space are as large as the effects that we wish to measure are small in other instances. How could they be of practical relevance? Equivalent questions to those we ask now about the relevance of general relativity, for example, could have been asked earlier of the special theory as well. Relativistic effects become pronounced only at extraordinary velocities (close to the velocity of light, 300,000 Km per second). But what regular person is ever going to travel at that velocity? Someday we might, actually, but the point is that those strange effects do show up in particle accelerators and make their way into our contemporary physics. Indeed much of contemporary physics is based on the study of phenomena so small as to be beyond the conscious experience of any regular person. The grand man of atomic physics himself, Niels Bohr, often remarked that it was pointless even to ask questions about the reality of the processes of micro-physics. Nevertheless, the study of the remotely small and the remotely fast has produced surgical lasers and many other beneficial wonders in our time. We have no reason to expect fewer rewards as our playful science moves into the cosmos.