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In the last few years, multiwavelength observations have revealed theubiquity of gaps/rings in circumstellar discs. Here we report the first ALMAobservations of HD 92945 at 0.86 mm, that reveal a gap at about 73$\pm$3 auwithin a broad disc of planetesimals that extends from 50 to 140 au. We findthat the gap is $20^{+10}_{-8}$ au wide. If cleared by a planet in situ, thisplanet must be less massive than 0.6 $M_\mathrm{Jup}$, or even lower if the gapwas cleared by a planet that formed early in the protoplanetary disc andprevented planetesimal formation at that radius. By comparing opposite sides ofthe disc we also find that the disc could be asymmetric. Motivated by theasymmetry and the fact that planets might be more frequent closer to the starin exoplanetary systems, we show that the gap and asymmetry could be producedby two planets interior to the disc through secular resonances. These planetsexcite the eccentricity of bodies at specific disc locations, opening radialgaps in the planetesimal distribution. New observations are necessary toconfirm if the disc is truly asymmetric, thus favouring the secular resonancemodel, or if the apparent asymmetry is due to a background galaxy, favouringthe in-situ planet scenario. Finally, we also report the non-detection of COand HCN gas confirming that no primordial gas is present. The CO and HCNnon-detections are consistent with the destruction of volatile-rich SolarSystem-like comets.

A gap in HD 92945's broad planetesimal disc revealed by ALMA