A Cold, Distant Birth for Jupiter?

[18 Nov 1999] One of the more perplexing things about the large Jupiter-plus sized extrasolar planets discovered thus far is that many of them orbit their sun at very close distances taking only days to complete an orbit – much, much closer than Mercury orbits our sun. Given their composition, and the way solar nebulas are thought to condense into planets, much colder temperatures were needed for their formation. So what are they doing so close to their sun? Did they form further out and move inwards?

A key to this riddle has apparently been uncovered from the analysis of data sent back by the Galileo probe that dove into Jupiter’s atmosphere in 1995. In a paper to be published in the 18 November edition of Nature (“A low-temperature origin for the planetesimals that formed Jupiter“), amounts of Argon, Krypton and Xenon in Jupiter’s atmosphere were found to be several times higher than they’d be had Jupiter formed only from materials in the solar nebula.

Jupiter’s present orbit is too close to the sun to have allowed it to have accumulated these gases in their current quantities – it’s just too warm – at least according to currently accepted models of the temperature of the solar nebula. According to the research team analyzing this data, Jupiter may have been formed in part by cold objects that comprise the Kuiper belt – objects located much further out than the icy planetesimals that have been, up to now, seen as the building blocks for Jupiter. This has led researchers to speculate further that Jupiter may have formed at a much greater distance from the sun, and has moved in closer. Once again studies of our own solar system help us to understand other solar systems – and vice versa.

Press releases from NASA and the University of Michigan provide more detail on this research.