快猫短视频

ARE Jupiter and Saturn, the gas giants of the Solar System, Earth鈥檚 larger
siblings or could they be interlopers that drifted in from deep space billions
of years ago? For the first time astronomers have analysed the light spectra
from planet-sized balls of gas floating free in space, and found them remarkably
similar to that of a primordial Jupiter.

Earlier this year, Rafael Rebolo and his colleagues at the Institute of
Astrophysics in the Canary Islands managed to identify 18 dim objects in the
constellation Orion which they estimate are just a few times more massive than
Jupiter but are far from the nearest star鈥攁t least 7500 billion
kilometres away. The area is filled with a dense molecular cloud that is
continually collapsing to form young stars and brown dwarfs
(快猫短视频, 1 April, p 14).

Now the team has obtained enough light from three of them to analyse their
spectra, revealing their composition鈥攚hich includes water鈥攁nd
temperature. 鈥淪o we know they will contract and cool over the next 100 million
years until they are about the same temperature and size as Jupiter,鈥� says
Rebolo.

It鈥檚 possible that such free-floating objects could be captured by one of the
nearby stars peppering their neighbourhood. Most astronomers believe that
planets take shape from a spinning disc of matter around a young star as it
forms. 鈥淢aybe star systems are made up of some planets which formed in discs and
others further out which were captured from the interstellar medium.鈥�

But Alan Boss of the Carnegie Institution in Washington DC thinks this idea
is unlikely to apply to our Solar System. 鈥淭he planets all orbit in the same
plane, which suggests they formed from the same disc, whereas with capture you
would expect all kinds of eccentric orbits.鈥� Rebolo hopes further study will
reveal if the objects have dust discs, or even moons, of their own.