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Context. The orientation of the spin axis of a comet is defined by the valuesof its equatorial obliquity and its cometocentric longitude of the Sun. Theseparameters can be computed from the components of the nongravitational forcecaused by outgassing, if the cometary activity is well characterized. Thetrajectories of known interstellar bodies passing through the Solar System shownongravitational accelerations.  Aims. The spin-axis orientation of 1I/2017 U1 (`Oumuamua) remains to bedetermined; for 2I/Borisov, the already released results are mutuallyexclusive. Here, we investigate the orientation of the spin axes of `Oumuamuaand 2I/Borisov using public orbit determinations that consider outgassing.  Methods. We applied a Monte Carlo simulation using the covariance matrixmethod together with Monte Carlo random search techniques to compute thedistributions of equatorial obliquities and cometocentric longitudes of the Sunat perihelion of `Oumuamua and 2I/Borisov from the values of thenongravitational parameters.  Results. We find that the equatorial obliquity of `Oumuamua could be about 93deg, if it has a very prolate (fusiform) shape, or close to 16 deg, if it isvery oblate (disk-like). Different orbit determinations of 2I/Borisov gaveobliquity values of 59 deg and 90 deg. The distributions of cometocentriclongitudes were in general multimodal.  Conclusions. The most probable spin-axis direction of `Oumuamua in equatorialcoordinates is (280 degrees, +46 degrees) if very prolate or (312 deg, -50 deg)if very oblate. For the orbit determinations of 2I/Borisov used here, we findmost probable poles pointing near (275 deg, +65 deg) and (231 deg, +30 deg),respectively. Although our analysis favors an oblate shape for 2I/Borisov, aprolate one cannot be ruled out.

Constraining the orientation of the spin axes of extrasolar minor bodies 1I/2017 U1 (`Oumuamua) and 2I/Borisov