How could there be an element lighter than hydrogen? Elements are atoms -- nuclei of protons and neutrons orbited by electrons. A hydrogen nucleus is... one proton. Period. Since there are no free quarks...
There wouldn't need to be. Theoretically, quark matter (which is very bizzare and highly unstable) would be intrinsically lighter than hydrogen since particles composed of quark matter would lack protons or neutrons and would instead consist of electrons bound to positively-charged quarks.
It would have some INCREDIBLY bizzare properties, which would depend on its condition, structure and stability. On the scifi side, Mass Effect's "Element Zero" is basically this, a substance that has the odd property of waring space when subjected to an electrical charge; on the alarmist side, there are some theories going around that quark matter is "metastable" such that ordinary matter that comes into contact with quark matter will immediately be converted into quark matter, and then immediately disintegrate (in some cases, deflagrate
) since quark matter cannot sustain alot of the more complex chemical structures found in ordinary matter.
BTW here is another photon torpedo case for you.
In terms of Quark Matter: http://smu.edu/newsinfo/releases/01342.html
In their new paper, the SMU researchers describe two seismic events with the linear pattern they were looking for. One event occurred on Oct. 22, 1993, when something entered the Earth off Antarctica and left it south of India .73 of a second later. The other occurred on Nov. 24, 1993, when an object entered south of Australia and exited the Earth near Antarctica .15 of a second later. The first event was recorded at seven monitoring stations in India, Australia, Bolivia and Turkey, and the second event was recorded at nine monitoring stations in Australia and Bolivia.
“We can’t prove that this was strange quark matter, but that is the only explanation that has been offered so far,” Herrin said.
Then too, there is the tetraneutron
That's about as simple as it gets.