  Large potentially hazardous asteroids (PHAs) are capable of causing a global
catastrophe in the event of a planetary collision. Thus, rapid assessment of
such an object's physical characteristics is crucial for determining its
potential risk scale. We treated the near-Earth asteroid (99942) Apophis as a
newly discovered object during its 2020-2021 close-approach as part of a mock
planetary defense exercise. The object was detected by the Near-Earth Object
Wide-field Infrared Survey Explorer (NEOWISE), and data collected by the two
active bands (3.4 ${\mu}$m and 4.6 ${\mu}$m) were analyzed using thermal and
thermophysical modeling. Our results indicate that Apophis is an elongated
object with an effective spherical diameter D$_{eff}$ = 340 $\pm$ 70 m, a
geometric visual albedo p$_{V}$ = 0.31 $\pm$ 0.09, and a thermal inertia
$\Gamma$ $\sim$ 150 - 2850 Jm$^{-2}$s$^{-0.5}$K$^{-1}$ with a best-fit value of
550 Jm$^{-2}$s$^{-0.5}$K$^{-1}$. NEOWISE "discovery" observations reveal that
(99942) Apophis is a potentially hazardous asteroid that would likely cause
damage at a regional level and not a global one.
