The three previously discovered planets around the pulsar have their orbits in almost exact proportion to the spacings among Mercury, Venus, and Earth. Wolszczan says the whole planetary system looks like a scaled-down copy of our own inner solar system.
Astronomers are increasingly using bigger and better telescopes to look beyond the brightest objects in the cosmos, such as supernova explosions and giant galaxies. Now they're focusing on exotic planets that could harbor life.
Scientists using NASA's Spitzer Space Telescope recently discovered a dusty disk around a so-called brown dwarfa star that failed to grow big enough to ignite and burn hydrogen, as our sun does. The finding suggests that there may be mini-solar systems in which planets orbit objects that are barely bigger than a planet itself.
The failed star, known as OTS 44, is about 500 light-years away. It is among the smallest known brown dwarfsjust 15 times the mass of Jupiter. It is also the smallest object yet found with a disk of material around it.
A disk of such material once surrounded our sun, and the Earth is believed to have formed from it. The presence of a disk around brown dwarfs suggests that terrestrial planets could form around an object that is too small to shine via nuclear fusion, as our sun does.
"We have identified the smallest body that is known to have the building blocks around it for making planets," said Kevin Luhman, lead author of a study by the Harvard-Smithsonian Center for Astrophysics in Cambridge, Massachusetts.
Meanwhile, another team of scientists theorized that some faraway planets could be mostly carbon, with a thick layer of diamonds hiding under the surface.
Earth, Mars, and Venus are "silicate planets," consisting mostly of silicon-oxygen compounds condensed from a disk of gas orbiting the sun. Carbon planets, though, might form more differently, the scientists said.
In gas with extra carbon or too little oxygen, carbon compounds like carbides and graphite could form instead of silicates, said Marc Kuchner, an astronomer at Princeton University in New Jersey.
Any condensed graphite would then change into diamond under high pressure and potentially form diamond layers. Inside the planets such layers could be several miles thick.
Kuchner said the galaxy is becoming richer in carbon as it gets older. "It may become so carbon rich that all planets formed in the future may be carbon planets," he said. "Just wait a couple of billion years."
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