Context : Planets orbiting low-mass stars such as M dwarfs are now considered a cornerstone in the search for life-harbouring planets .
GJ 273 is a planetary system orbiting an M dwarf only 3.75 pc away , composed of two confirmed planets , GJ 273b and GJ 273c , and two promising candidates , GJ 273d and GJ 273e .
Planet GJ 273b resides in the habitable zone .
Currently , due to a lack of observed planetary transits , only the minimum masses of the planets are known : M _ { b } \sin i _ { b } =2.89 M { { } _ { \oplus } } , M _ { c } \sin i _ { c } =1.18 M { { } _ { \oplus } } , M _ { d } \sin i _ { d } =10.80 M { { } _ { \oplus } } , and M _ { e } \sin i _ { e } =9.30 M _ { \oplus } .
Despite being an interesting system , the GJ 273 planetary system is still poorly studied .

Aims : We aim at precisely determine the physical parameters of the individual planets , in particular to break the mass–inclination degeneracy to accurately determine the mass of the planets .
Moreover , we present thorough characterisation of planet GJ 273b in terms of its potential habitability .

Methods : First , we explored the planetary formation and hydration phases of GJ 273 during the first 100 \mathrm { Myr } .
Secondly , we analysed the stability of the system by considering both the two- and four-planet configurations .
We then performed a comparative analysis between GJ 273 and the Solar System , and searched for regions in GJ 273 which may harbour minor bodies in stable orbits , i.e .
main asteroid belt and Kuiper belt analogues .

Results : From our set of dynamical studies , we obtain that the four-planet configuration of the system allows us to break the mass–inclination degeneracy .
From our modelling results , the masses of the planets are unveiled as : 2.89 \leq M _ { \mathrm { b } } \leq 3.03 \mathrm { M } _ { \oplus } , 1.18 \leq M _ { \mathrm { c } } \leq 1.24 \mathrm { M } _ { \oplus } , 10.80 \leq M _ { \mathrm { d } } \leq 11.35 \mathrm { M } _ { \oplus } and 9.30 \leq M _ { \mathrm { e } } \leq 9.70 \mathrm { M } _ { \oplus } .
These results point to a system likely composed of an Earth-mass planet , a super-Earth and two mini-Neptunes .
From planetary formation models , we determine that GJ 273b was likely an efficient water captor while GJ 273c is probably a dry planet .
We found that the system may have several stable regions where minor bodies might reside .
Collectively , these results are used to comprehensively discuss the habitability of GJ 273b .

Conclusions :