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tokens: (in agreement with expectations about Gaia for this separation). But they do have very similar parallaxes (the average is 33.82 mas and the difference 0.04 mas) and radial velocities (Simbad gives − 4.6 ± 2.0km s −1 for HD 224636), so they are almost certainly a physical binary. If they were in a common plane perpendicular to the line-of-sight, their physical separation would be 73 au and their relative velocity 4.8 km s −1 . This compares to a relative orbital velocity of two solar-mass stars in a mutual circular orbit of this radius of 4.9 km s −1 (and their period would be 440 yr). As their proper motion difference of 35 mas yr −1 is about a quarter of their absolute proper motions, the velocity of their center-of-mass could differ significantly from that of either component. If we knew the masses of both components of the binary, we could solve for both the center-of-mass and the Keplerian orbital elements (6+6 parameters from the 3D position and 3D velocity for each star). The spectral type of this pair is given by Struve Franklin (1955) as F8+G1, with F8 presumably referring to GJ 4384 because this is slightly brighter and bluer (by 0.3 mag and 0.05 mag respectively in Gaia DR2). This agrees with their T eff and positions in the color-absolute magnitude diagram, as given by Gaia DR2. We adopt a mass of 1 M ⊙ for each component to compute the position and velocity of the center-of-mass. Integrating the center-of-mass’s motion back in time, we find the time, distance, and relative speed of its closest encounter with 2I/Borisov to be −1380 kyr, 3.64 pc, and 20.9 km s −1 respectively. This is considerably more distant than the encounter found when neglecting the binary motion (the second line of Table 2 ). We do not compute the covariance on these parameters due to an inadequately characterized correlation in the Gaia astrometric uncertainties for sources close to one another. The largest uncertainty is the radial velocity of s528. If we change this by ± 2 σ , the encounter distance remains between 3.3 and 4.0 pc. We conclude that the binary motion renders the GJ 4384–HD 224636 system a much more distant encounter than is shown in Table 2 . Although a binary system is an attractive option for ejecting 2I/Borisov, this encounter distance is far larger than the size of the system. We note that GJ 4384 is listed as the second closest encounter to 2I/Borisov as found by Hallatt Wiegert (2019) with similar encounter parameters to ours ( = 0.32 pc) when we neglect binarity. 3.3 Other candidates We note that several of our other close encounters are binary systems. One of these, HD 22781, has a planetary companion ( Díaz et al. 2012 ), but the encounter velocity of 36 km s −1 is rather high for this planet to be plausibly involved in ejecting 2I/Borisov. It is worth examining in addition those encounters beyond 1 pc (not listed in Table 2 ) that are particularly slow. The slowest encounter we find within 5 pc is with Gaia DR2