  The low field phase of the organic superconductor (TMTSF)2ClO4 is studied by
muon spin rotation. The zero temperature limit of the magnetic penetration
depth within the TMTSF layers is obtained to be lambda_{ab}(0) = 0.86(2) um.
Temperature dependence of the muon spin relaxation shows no indication of gap
nodes on the Fermi surface nor of any spontaneous fields due to
time-reversal-symmetry breaking. The weight of evidence suggests that the
symmetry of this low field phase is odd-frequency p-wave singlet; a novel
example of odd-frequency pairing in a bulk superconductor.
