The mix of gases that make up Jupiter鈥檚 atmosphere has long puzzled astronomers, but now it seems that the giant planet鈥檚 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鈥檚 atmosphere would once have been frozen inside small pebbles, but this can only occur at -240掳C 鈥� much colder than the current average temperature in Jupiter鈥檚 clouds, which is around -150掳C.
So the mystery is how these gases ever survived to make it into Jupiter鈥檚 atmosphere. Previous ideas have suggested that Jupiter formed further out in the solar system and then moved to its current location, but that doesn鈥檛 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 鈥渢raffic jam鈥� of rocky grains when the dust passes through the water vapour. We have seen similar shadows in other star systems, says Ueda. 鈥淩ecent observations have shown that more than 80 per cent of protoplanetary discs have shadow-like structures on their surface.鈥�
Robin Wordsworth at Harvard University says the issue of Jupiter鈥檚 atmosphere has long been a 鈥渧exing problem鈥� in planetary science. 鈥淭he solution that the authors have proposed is very creative,鈥� he says. 鈥淗owever, 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.鈥�
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