Until recently, our solar system was thought to be typical.

"Astronomers have been raised since babies on the cosmological principle that our solar system is not a special place in the universe," said Levison. "Now we're finding that that may not be true and we may have to abandon that principle. It may be that only one in a thousand stars may be capable of sustaining solar systems like ours, where Earth-like worlds capable of sustaining complex life are possible."

However, because technology is not yet sufficiently sensitive to detect solar systems like ours around other stars, there is currently no way to determine whether our solar system is common or rare.

If planets form only through core accretion, then our solar system's protoplanetary disk must have been long-lived.

And if long-lived disks are rare, then planets in general must also be rare. If, however, planets can form by another, quicker means -- like disk instability -- then planets could be more common.

Boss views the discovery of these super-Jupiters as strong evidence that disk instability is at work.

"The rate of discovery of extrasolar gas-giant planets seems to show that gas-giant planets are common," he said. "This implies that there must an efficient mechanism for forming gas-giant planets. That seems to point to disk instability. If long-lived disks exist, they are a rarity, whereas disk instability may occur very frequently. A high frequency of extrasolar planets orbiting nearby stars would imply that disk instability must occur."

But "common" is a relative word where the universe is concerned.

"We have only seen planets around 5 percent of the stars studied," Levinson cautioned. "We still don't know what is typical."

Could planets form through a combination of accretion and disk instability?

Boss thinks so, pointing to the existence of planetesimals, tiny bits of rocky or metallic material that would likely have formed in a protoplanetary disk along with or even before a disk instability -- making some sort of coupled planetary evolution inevitable.

"In some cases, the planetesimals would be tossed around or out of the solar system," he explained. Others "would be swallowed by a proto-Jupiter" formed through disk instability.

Boss said such "swallowed" planetesimals could account for the abundance of heavy metals detected in Jupiter's thick outer envelope of molecular hydrogen and helium.

In order for a planet composed of only dense gases and a solid core to acquire these metals in its envelope, Boss thinks some sort of planetesimal accretion and disk instability must have occurred together.

Just as asteroids and comets occasionally bombard Jupiter today, planetesimals would have been gravitationally attracted to the clump of gas that would eventually become Jupiter.

"In that sense," Boss said, "a compromise theory combining disk instability and planetesimal accretion is not just attractive, it may be absolutely necessary."

But Levison doesn't see how both mechanisms could work together to form a planet.

"The time scales for disk instability are very, very short," he said. "So short, in fact, that planetesimals wouldn't even have a chance to form. So I don't think a planet could form through both accretion and disk instability."

Boss disagrees, arguing that disk instabilities might not occur until after some planetesimals had already formed.

Both scientists, however, agree that the same protoplanetary disk can support both processes at once, with disk instability forming some planets and accretion forming others -- if disk instability were responsible for forming Jupiter, our own solar system would be such a hybrid.