Somewhere between 100-200 times Astronomical Units (AU) from the Sun, planets get COLD enough for hydrogen to begin condensing, as the surface temperature drops below the hydrogen critical point (~33.2 K, 13 atm) and then triple point (~20.6 K, 0.07 atm). Raw hydrogen is unlikely to be present without helium – both were ~99% of the mass of the Solar Nebula that the planets formed out of. Helium, in the form of its stable isotopes helium-4 and helium-3, doesn’t condense until much, much further from the Sun and inside the Galaxy might be too hot for it to condense at all.
The recent study, blogged here, which computed primordial H2/He atmospheres would resist being eroded from Super-Earths by their stars’ early high levels of soft x-rays (“XUV”), also computed significant H2/He atmospheres would be captured by planets from Mars-size and upwards. If such an object was driven out of the Inner System, or from near the Gas Giants, then it might’ve retained its primordial atmosphere and found orbital stability in the region beyond Neptune. Several such objects may exist, for there’s reason to think the Gas Giants formed from Mars-size “planetary embryos”, but such would be undetectable by astronomers due to their slow orbits and dimness… all, except the inner-most, which may explain the curious orbits of objects like Sedna and 2012 VP133, as reported recently:
Of course, being Crowlspace, our take is the implications of a planet with a condense hydrogen surface (oceans?) and an atmosphere of high-purity helium. Helium-3 is an advanced fusion fuel and, once we have reactors up to the task, highly desirable. With a solar abundance of 4E-4 (i.e. 1/2500) relative to Helium-4, that might sound a bit scarce, but it’s immensely more than what we can scrape together here on Earth. A “Super-Mars” (~0.5 Earth masses) with a primordial atmosphere might have captured anything from 4.7 bars to 772 bars of atmosphere according to this reference:
Let’s assume a neat 100 bars. A 0.5 Earth-mass planet, of Earth composition, would have a radius of (0.5)^0.3 ~ 0.81 times Earth and thus a surface gravity of (0.5)^0.4 ~ 0.76 times Earth, with a column mass of ~1,350 tonnes, of which 75% is hydrogen. Thus 336.4 tonnes of helium for every square metre of planet and ~100 kg of that would be helium-3. Total supply would be ~3.8E+16 kg. Interestingly the primordial deuterium/hydrogen ratio is 1/40,000, meaning that the condensed hydrogen would supply 50 kg/square metre of deuterium. A stoichometric mixture of D/He3 for fusion would be 50/75 or 125 kg/square metre of planet – 4.2E+16 kg or 42 trillion tonnes. One could fuel up 840 million “Daedalus” class starships. For the same fuel mass, 50,000 tonnes per ship, one could send 50,000 tonnes of payload (a small space-colony) to the stars at 0.012 c and slow it down at the destination. With a mass allotment of ~50 tonnes per person, the total travelling population would be ~840 billion people…