"It is mere speculation at this stage, but there is a possibility that some [probably not all] of the missing mass in galaxies can be explained by invoking large quantities of cool and/or tenuous molecular hydrogen," Ivison said.

Ivison said much of the missing matter must still be what is known as dark matter, according to current theories, and could not be accounted for by molecular hydrogen.

Details of the studies

Hydrogen is by far the most abundant element in the universe. Hydrogen and helium make up about 98 percent of the mass of our entire solar system. And Jupiter is mostly hydrogen. So in looking for the ingredients to make giant planets, researchers hunt for hydrogen. Specifically, they look for molecular hydrogen, or H₂, which is made of two hydrogen atoms bonded together.

Previous studies of the three nearby stars had measured carbon monoxide, using that as an indicator of how much molecular hydrogen was present. But the new study measured molecular hydrogen directly, using the European Space Agency's Infrared Space Observatory.

In the disk surrounding Beta Pictoris, a Southern Hemisphere star that formed about 20 million years ago approximately 60 light-years from Earth, Blake's team found hydrogen equal to one-fifth the mass of Jupiter -- enough to make four Neptunes. Around 49 Ceti, 10 million years old and 200 light-years away, hydrogen equal to 40 percent of the mass of Jupiter was spotted. And a 10 million-year-old star named HD135344, some 260 light-years away, harbors six Jupiters worth of molecular hydrogen.

"There are over 100 candidate debris disks within about 200 light-years of the Sun," Blake said, "and our work suggests that many of these systems may still be capable of making planets."