Sky & Telescope - September 2022 - 15

NASA / JHU APL
F
or all its destructiveness, smashing stuff together tells
us a great deal about the universe. Colliding suspended
balls demonstrated conservation of momentum and
energy in the 17th century and led to every 1980s executive's
favorite desk decoration, Newton's cradle. Atom smashers
like the Large Hadron Collider have revealed the tiniest
constituents of reality. And observing two distant black holes
violently merge has offered us a new window into extreme
gravity at work in the cosmos.
Our exploration of the solar system has been no different.
Sending multi-million-dollar probes into fatal nose-dives has
a rich past. After the USSR's Luna 2 made history with the
first impact on another world in 1959, the NASA Ranger 7-9
probes followed, smashing into the Moon's surface in 1964
and 1965 in order to take detailed images that would inform
the design of Apollo. More recently, NASA's Deep Impact shot
a projectile into Comet Tempel 1 at the end of its primary
mission in 2005, revealing surprising details about the
comet's composition.
Most impactor missions in the last couple of decades have
udge
This year, the DART mission will
make humanity's first perceptible
impact on the motion of a celestial
body. The result might help us
someday avert our potential
annihilation by asteroid.
been designed to expose the makeup of the body into which
they collide. But the latest project has a different aim. NASA's
Double Asteroid Redirection Test (DART) mission is traveling
to Dimorphos, a companion moonlet of asteroid 65803
Didymos, in order to bump it off course in its orbit.
NASA is not doing this because the binary asteroid is a
threat to us: " It's always good to state clearly that we are
not in danger - we are not doing this because we have to.
It's a test, " emphasizes DART program scientist Tom Statler
(NASA). Moreover, the change won't push the asteroids onto
a dangerous path toward Earth - Dimorphos won't leave its
orbit around Didymos, and the asteroids will continue on
their current trajectory around the Sun.
Instead, scientists hope that DART will show us whether
crashing a probe into an asteroid actually changes its motion,
knowledge we must have in case we ever need to nudge an
asteroid away from Earth to avert annihilation.
Don't Look Up
Planetary defense against asteroid impacts can be boiled
down to two tasks: finding threats and removing them.
Responsibility for the former rests on the International
Astronomical Union's Minor Planet Center (MPC) and the
Jet Propulsion Laboratory's Center for Near-Earth Object
Studies (CNEOS).
The MPC is the internationally recognized clearinghouse
for small-body position measurements, including near-Earth
objects. Data fed into the MPC come from observatories
around the world and include valuable contributions from
amateur astronomers. CNEOS in turn plugs MPC data into
its recently updated Sentry-II impact-monitoring system,
which continuously performs long-term analyses of the
INCOMING The DART spacecraft will slam into Didymos' moon,
Dimorphos, in an attempt to change the size of the moon's orbit around
the larger asteroid.
sk yand tele scope .o r g * SEPTEMBER 2022 15
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Sky & Telescope - September 2022

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