  Near-Earth objects (NEOs) moving in resonant, Earth-like orbits are
potentially important. On the positive side, they are the ideal targets for
robotic and human low-cost sample return missions and a much cheaper
alternative to using the Moon as an astronomical observatory. On the negative
side and even if small in size (2-50 m), they have an enhanced probability of
colliding with the Earth causing local but still significant property damage
and loss of life. Here, we show that the recently discovered asteroid 2013 BS45
is an Earth co-orbital, the sixth horseshoe librator to our planet. In contrast
with other Earth's co-orbitals, its orbit is strikingly similar to that of the
Earth yet at an absolute magnitude of 25.8, an artificial origin seems
implausible. The study of the dynamics of 2013 BS45 coupled with the analysis
of NEO data show that it is one of the largest and most stable members of a
previously undiscussed dynamically cold group of small NEOs experiencing
repeated trappings in the 1:1 commensurability with the Earth. This new
resonant family is well constrained in orbital parameter space and it includes
at least 10 other transient members: 2003 YN107, 2006 JY26, 2009 SH2 and 2012
FC71 among them. 2012 FC71 represents the best of both worlds as it is locked
in a Kozai resonance and is unlikely to impact the Earth. Objects in this group
could be responsible for the production of Earth's transient irregular natural
satellites.
