New to Orions Arm

[stevebowers]

Some of the larger superterrestrials could have hydrogen atmospheres - but because hydrogen is so abundant, this is likely to dominate the atmosphere and to form a thick envelope around the planet. But I'm fairly sure there will be a fraction of all superterrestrials which are large enough to retain a hydrogen atmosphere but not quite large enough to become a gas dwarf. As the local star gets more luminous on the Main Sequence some of this hydrogen would be lost, until the atmosphere is relatively sparse and reasonably similar in pressure to other terrestrial worlds. Such a planet could presumably hold a biosphere for a certain, limited amount of time, in the best cases a billion years or more.

There would be helium as well, acting as a buffer gas.
https://en.wikipedia.org/wiki/Buffer_gas