We analytically and numerically investigate the possibility that a still undiscovered body X , moving along an unbound hyperbolic path from outside the solar system , may penetrate its inner regions in the next few years posing a threat to the Earth .
By conservatively using as initial position the lower bounds on the present-day distance d _ { X } of X dynamically inferred from the gravitational perturbations induced by it on the orbital motions of the planets of the solar system , both the analyses show that , in order to reach the Earth ’ s orbit in the next 2 yr , X should move at a highly unrealistic speed v , whatever its mass M _ { X } is .
For example , by assuming for it a solar ( M _ { X } = M _ { \odot } ) or brown dwarf mass ( M _ { X } = 80 m _ { Jup } ) , now at not less than d _ { X } = 11 - 6 kau ( 1 kau=1000 astronomical units ) , v would be of the order of 6 - 10 \% and 3 - 5 \% of the speed of light c , respectively .
By assuming larger present-day distances for X , on the basis of the lacking of direct observational evidences of electromagnetic origin for it , its speed would be even higher .
Instead , the fastest solitary massive objects known so far , like hypervelocity stars ( HVSs ) and supernova remnants ( SRs ) , travel at v \approx 0.002 - 0.005 c , having acquired so huge velocities in some of the most violent astrophysical phenomena like interactions with supermassive galactic black holes and supernova explosions .
It turns out that the orbit of the Earth would not be macroscopically altered by a close ( 0.2 au ) passage of such an ultrafast body X in the next 2 yr. On the contrary , our planet would be hurled into the space if a Sun-sized body X would encounter it by moving at v / c = 10 ^ { -4 } .
On the other hand , this would imply that such a X should be now at just 20 - 30 au , contrary to all direct observational and indirect dynamical evidences .