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tokens: , will produce a bow shock if their radius is larger than the mean free path of gas molecules (Landau Lifshitz 1959 ). The mean free path for molecular collisions is with being the H 2 cross-section. Thus, for objects larger than km, bow shocks are formed if the gas density . The post-shock gas has a high temperature and can be efficient in thermal sputtering. However, bow shocks are not expected to form for objects of and . 5. Numerical Results 5.1. Destruction in the ISM Assuming that H 2 objects of various sizes are produced in a nearby GMC, we estimate the minimum size of objects that could reach the Earth. The closest GMC, W51, is located at a distance of . Thus, at a speed of , it takes yr for objects to reach the solar system. Figure 1 compares the various destruction times with for different object radii at a typical speed. The sublimation time is obtained using the equilibrium temperature (see Section 2 ). We find that only very large objects of radius could survive thermal sublimation and reach the solar system. The minimum size of the objects that can survive is obtained by setting , yielding Figure 1. Comparison of various destruction timescales (slanted colored lines) as a function of the object radius (in meters) to the travel time from a GMC at a distance of 5.2 kpc, assuming a characteristic speed of 30 km s −1 (horizontal black line). 5.2. Destruction on the Way from the Center of GMCs to the ISM The total gas column density toward the densest GMC amounts to extinction of (see e.g., Mathis et al. 1983 ), which corresponds to a hydrogen column density of based on the scaling with (Draine 2011 ). Assuming a mean GMC density and a GMC radius , the travel time is . Equation ( 22 ) implies a destruction time by gas collisions of , which is longer than the travel time. As shown in Section 2 , collisional heating is important in GMCs because of their high density, . Assuming that a fraction η of the impinging proton’s energy is converted into surface heating to a temperature below , collisional heating raises the temperature of the surface towhich implies effective cooling by evaporation (see Equation ( 9 )). To find the actual equilibrium temperature, we solve Equation ( 12 ) and obtain for , assuming . Substituting this typical temperature into Equation ( 3 ) yields The minimum size of the objects that can survive is obtained by setting , yielding We conclude that H 2 objects cannot survive their journey from their GMC birthplace to the ISM if their radius is below . The actual value would be larger because the surface temperature is higher when objects are moving through the core of GMCs with higher gas density. 5.3. Destruction in the Solar System When ‘Oumuamua entered the solar system, solar radiation heated the frontal surface to an equilibrium. We numerically solve Equation ( 12 ) and obtain the equilibrium temperatures and at heliodistances D = 0.25 and . Substituting these temperatures into Equation ( 4 ), one obtains and