Sky & Telescope - March 2023 - 12

COSMIC RELIEF by David Grinspoon
Nudging a Space Rock
That's one small change in an asteroid's orbit, one giant leap for humanity.
ON SEPTEMBER 26, 2022, the Double
Asteroid Redirection Test (DART) spacecraft
ended its existence in spectacular
fashion by smashing into the asteroid
Dimorphos (S&T: Jan. 2023, p. 8). Many
of us watched spellbound as DART's
cameras fixed upon the approaching
target. At first, we saw only Dimorphos's
larger orbital companion, 65803
Didymos, as a bright pixel, but soon it
resolved into two objects. In the final
minutes, the target suddenly loomed,
filling the screen with a final, brief, fantastically
detailed glimpse of its surface
(see video at https://is.gd/DARTsmash).
The approach reminded me of my
student days witnessing the Voyager
encounters. The monitors at JPL would
show a distant target growing gradually
for days, followed by a few hours of
quickening expansion to a differentiated
object that filled the screen. I'd
pretend the monitors were windows and
we were flying past newly seen worlds.
I had that sensation again with the
New Horizons spacecraft at Pluto in
2015, and now again with DART. Except
that those other encounters were flybys,
not crash-intos. And instead of days,
this event took place within an hour.
You could almost hear the swooping
Star Trek alert sirens and the command
to " Brace for impact! "
12 MARCH 2023 * SKY & TELESCOPE
The asteroid moonlet Dimorphos, roughly
160 meters (525 feet) long, appears 2.5 minutes,
11 seconds, and 2 seconds before the
DART spacecraft intentionally crashed into it.
The impact shortened the roughly
12-hour orbit of Dimorphos around
Didymos by about 32 minutes (S&T:
Feb. 2023, p. 9). Such a small change
might sound inconsequential. But arguably
it represents a significant turning
point in the history of our planet, our
biosphere, and our solar system. The
influence of the Anthropocene Epoch,
marked by humans as a geological force,
has begun to extend off-planet.
I don't know who first said that the
difference between us and the dinosaurs
is that they lacked a space program, but
this joke is both funny and profound.
Our solar system now has a new kind of
planet - one that can begin to defend
itself. The knowledge gained will help us
forestall dangerous cosmic impacts that,
if we waited long enough and did nothing,
would inevitably cause regional
destruction and, eventually, new mass
extinctions on Earth. We're no longer
helpless against this threat, and so,
assuming we keep our act together
and retain a technologically advancing
global civilization, our biosphere and
our planet need never again suffer such
catastrophes.
Before we get too cocky, though,
remember that dinosaurs walked the
planet for 180 million years. Humans
have been here for a few percent of that.
And our burst of technical ingenuity
has created new, self-imposed threats.
Need I enumerate them? We certainly
are gaining skills that could allow us to
survive while the big lizards perished.
But whether our wisdom keeps pace
with our prowess and allows us to create
the kind of global society that can
harness that cleverness in the service of
dinosaur-scale longevity is still TBD.
Back in the 1990s, Carl Sagan
warned against messing with asteroids,
lest someone get the crazy idea to direct
one towards Earth. But in a world armed
with thousands of nuclear weapons,
that's the least of our worries. At least
now we're taking baby steps toward
protecting ourselves against a truly
long-term, planetary-scale threat.
We, the adolescent technological
species from Earth, have started, ever so
slightly, to rearrange the solar system.
Hopefully this is part of growing up. If
so, then someday we may save not just
our species but our biosphere.
¢ Contributing Editor DAVID GRINSPOON
is author of Earth in Human
Hands: Shaping Our Planet's Future.
NASA / JOHNS HOPKINS APL (3)
https://www.is.gd/DARTsmash
Sky & Telescope - March 2023

Table of Contents for the Digital Edition of Sky & Telescope - March 2023
