  A new all-sky visible and Near-InfraRed (NIR) space astrometry mission with a
wavelength cutoff in the K-band is not just focused on a single or small number
of key science cases. Instead, it is extremely broad, answering key science
questions in nearly every branch of astronomy while also providing a dense and
accurate visible-NIR reference frame needed for future astronomy facilities.
For almost 2 billion common stars the combination of Gaia and a new all-sky NIR
astrometry mission would provide much improved proper motions, answering key
science questions -- from the solar system and stellar systems, including
exoplanet systems, to compact galaxies, quasars, neutron stars, binaries and
dark matter substructures. The addition of NIR will result in up to 8 billion
newly measured stars in some of the most obscured parts of our Galaxy, and
crucially reveal the very heart of the Galactic bulge region. In this white
paper we argue that rather than improving on the accuracy, a greater overall
science return can be achieved by going deeper than Gaia and by expanding the
wavelength range to the NIR.
