Astronomers have discovered giant planets, called planemos, roaming free through space unbound by any star. Moreover, they have moons orbiting around them - or should we call them planets rather than moons?

"Now that we know of these planetary mass objects with their own little infant planetary systems, the definition of the word 'planet' has blurred even more", says Ray Jayawardhana, an associate professor of astronomy and astrophysics at the University of Toronto. "In a way, the new discoveries are not too surprising - after all, Jupiter must have been born with its own disk, out of which its bigger moons formed."

These planemos can be 100 times less massive than our sun and only a few times more massive than Jupiter and thus their gravity isn't capable of igniting them - they cannot become stars. But the new findings show that these objects are also born with disks of dust and gas, the raw material for planet (or moon) making. (Research done by Jayawardhana's group and others in recent years had shown that such disks are common around failed stars known as "brown dwarfs".)

The planemos can be seen because they emit infrared light from the dusty disks that will eventually evolve into miniature planetary systems. Jayawardhana discovered two planemos wandering by themselves, each having 10 to 15 times Jupiter's mass, and one 8 Jupiter-mass planemo orbiting together with a brown dwarf 25 times heftier than Jupiter. Researchers think this pair probably formed together, just like a binary star system, instead of the companion forming in a disk around the brown dwarf.

Both sets of discoveries point to objects not much more massive than Jupiter forming the same way as stars like the sun, and perhaps being accompanied by their own retinues of small planets. "The diversity of worlds out there is truly remarkable", Jayawardhana adds. "Nature often seems more prolific than our imagination."

"Any kind of planet that forms around them is committed to an eternal freeze", he added.