Dark Companions

The first clear proof of the existence of a planet outside the solar system has now been accepted by astronomers. The proof consists of the mathematical evidence of the presence of a dark companion revolving around one of the stars in Cygnus (the Swan). The presence of this body was first reported last autumn by Swarthmore's Astronomer K. Aa. Strand.

No less an authority than Princeton's grey, gentle Henry Norris Russell, whom many consider the greatest living astronomer, now goes even further: he declares that the Strand discovery should settle the centuries-old argument over whether there are inhabited planets besides the Earth. Dr. Russell asserts confidently that there are -- probably thousands of them.

Swarthmore's Strand picked up the new planet while measuring the orbits of a double star in the constellation Cygnus. He found that in their circlings around each other the two stars deviated from the expected path in regular "oscillations" which could be explained only by the gravitational pull of a third body on them (as the Earth's orbit around the Sun is affected by the Moon). By measuring these deviations, he determined that their unseen companion was a body with about 16 times the mass of Jupiter (largest solar planet), that it revolved around one of the stars in a cycle of 4.9 years. Prodded by Strand's finding, astronomers soon located dark companions of other stars.

How Big? How Hot? Russell tried to determine whether Strand's discovery was a true planet by two tests: 1) "How big is its body?" 2) "How hot is its surface?" (A stable planet must be smaller than its star, cool enough so that it shines only by reflected light.) From calculations based on the body's known mass* and probable compositions (mainly hydrogen and helium), Russell concludes that 1) its diameter is perhaps 216,000 miles, or 40% that of its star--"big for a planet, but passable"; 2) its surface temperature is probably somewhere between 50 and minus 168 degrees Centigrade (122 to minus 272 degrees Fahrenheit).

Dr. Russell has no idea whether Strand's planet is habitable, but he believes it is now clear that among the billions of stars there must be countless dark companions capable of supporting life. Reporting his conclusions in July's Scientific American, he observes:

"If, as appears to be probable, vegetation exists on Mars, life has developed on two out of the three planets in our system where it has any chance to do so. With this as a guide, it appears now to be probable that the whole number of inhabited worlds within the Galaxy is considerable . . . thousands, or even more. . . .

"Though the belief that our world was the material center of the Universe has long been dead, the supposition that it was . . . unique in being the abode of creatures who could study the Universe has lingered long. Now this last stronghold of the old way of thinking has fallen, and there is no longer a basis for supposing that either this world or its inhabitants are unique, or in any way the 'first, last and best of things.' The realization of this should be good for us."

* Not to be confused with weight. Mass is measured by the force required to change its motion (i.e., inertia). Weight is the pull of gravity on a given body.

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