History of Jupiter

History of Jupiter

The star that failed

As the solar system condensed out of interstellar gas and dust, Jupiter acquired most of the matter that was not ejected into interstellar space and did not fall inward to from the Sun. Had Jupiter been several dozen times more massive, the matter in its interior would have undergone thermonuclear reactions, and Jupiter would have begun to shine by its own light.

The largest planet is a star that failed. Even so, its interior temperatures are sufficiently high that it gives off about twice as much energy as it receives from the Sun. In the infrared part of the spectrum, it might even be correct to consider Jupiter a star. Had it become a star in visible light, we would today inhabit a binary or double-star system, with two suns in our sky, and the nights would come more rarely – a commonplace, we are almost sure, in countless solar systems throughout the Milky Way Galaxy. We would doubtless think the circumstances natural and lovely.

That Jupiter is a source of radio emission was discovered accidentally in the 1950’s, the early days of radio astronomy. Two young Americans, Bernard Burke and Kenneth Franklin, were examining the sky with a newly constructed and for that time very sensitive radio telescope. They were searching the cosmic radio background – that is, radio sources far beyond our solar system. To their surprise, they found an intense and previously unreported source that seemed to correspond to no prominent star, nebula or galaxy. What is more, it gradually moved, with respect to the distant stars, much faster than any remote objet could (because the speed of light is finite, of course). After finding no likely explanation of all this in their charts of the distant Cosmos, they one day stepped outside the observatory and looked up in the sky with the naked eye to see if anything interesting happened to be there. Bemusedly they noted an exceptionally bright object in the right place, which they soon identified as the planet Jupiter. This accidental discovery is, incidentally, entirely typical of the history of science.

Every evening before Voyager I’s encounter with Jupiter, scientists could see that giant planet twinkling in the sky, a sight our ancestors have enjoyed and wondered at for a million years. And on the evening of Encounter, on his way to study the Voyager data arriving at JPL, Carl Sagan thought that Jupiter would never be the same, never again just a point of light in the night sky, but would forever after be a place to be explored and known. Jupiter and its moons are a kind of miniature solar system and exquisite world with much to teach us.

Jupiter, the largest planet, is a star that failed. Illustration: © Megan Jorgensen