OUR Solar System may not have had the unusually sheltered upbringing that scientists thought, meaning many others like it could be dotted throughout the Galaxy.
Astronomers had believed that huge gas planets like Jupiter couldn鈥檛 form in the intense bath of ultraviolet radiation that鈥檚 common to most star systems, so they assumed our Solar System must have formed in a region of particularly low UV. Now a US researcher says giant planets could have formed under harsh UV conditions and that Uranus and Neptune even show signs of surviving such a blasting.
The conventional theory of planet formation says that dust particles orbiting a newly formed star collide and stick together over time. It would take around 10 million years to build a planet as large as Jupiter this way. But we know from looking at stars in the nearby Orion Nebula that the dust gets blown away by the radiation from nearby stars before that can happen, within just a few million years.
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So how did the larger planets in our Solar System arise? Alan Boss of the Carnegie Institution in Washington DC says there鈥檚 no need to assume our Sun was especially sheltered. He thinks giants such as Jupiter and Saturn formed in a much faster way. Rather than starting with particles sticking together, he suggests gas clumps formed first. The clumps had enough gravity to trap dust particles, and eventually collapsed to form planets.
Boss鈥檚 simulations, which he has submitted to the journal Icarus, show that this process would take just a thousand years or so, fast enough for giant planets to form before they are blasted by radiation. The UV bombardment would have blown much of the gas envelopes off the outer planets Neptune and Uranus, explaining their relatively small size.