The mix of gases that make up Jupiter’s atmosphere has long puzzled astronomers, but now it seems that the giant planet’s shadowy birthplace may be responsible.
Jupiter has a high proportion of nitrogen and noble gases in its atmosphere compared to the sun, but theories of how the solar system formed suggest they should be similar, because the solar system started out as a dense cloud of dust and gas which collapsed to form the sun and then the planets. Gases in Jupiter’s atmosphere would once have been frozen inside small pebbles, but this can only occur at -240°C – much colder than the current average temperature in Jupiter’s clouds, which is around -150°C.
So the mystery is how these gases ever survived to make it into Jupiter’s atmosphere. Previous ideas have suggested that Jupiter formed further out in the solar system and then moved to its current location, but that doesn’t fit with our understanding of how planets migrate, says at the University of California, Santa Cruz.
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Now, Ohno and at the National Astronomical Observatory of Japan say that Jupiter may have formed in a shadow created by dust in the protoplanetary disc surrounding our young star.
This would provide the cold environment required to create large amounts of nitrogen and noble gases while also allowing Jupiter to have formed near to where it currently orbits.
The researchers say that the dust will have built up in a region of the disc where ice sublimates from solid to gas, creating a “traffic jam” of rocky grains when the dust passes through the water vapour. We have seen similar shadows in other star systems, says Ueda. “Recent observations have shown that more than 80 per cent of protoplanetary discs have shadow-like structures on their surface.”
Robin Wordsworth at Harvard University says the issue of Jupiter’s atmosphere has long been a “vexing problem” in planetary science. “The solution that the authors have proposed is very creative,” he says. “However, further research will be required to determine whether a dust shadow of sufficient opacity could be maintained in the dynamic environment of the protosolar disc.”
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