Sky & Telescope - January 2023 - 8

NEWS NOTES
The ATLAS project captured stills of the
DART mission's impact on Dimorphos. (See the
animation at https://is.gd/DARTphotos.)
and afterward. It passed about 55 kilometers
(34 miles) away from the moon
165 seconds after the impact.
Meanwhile, observers throughout
SOLAR SYSTEM
NASA's DART Mission
Successfully Impacts
Asteroid
AS EARTH BARRELS along its orbit
around the Sun, it's peppered by
impacts from near-Earth objects. While
large collisions are rare, the fossil record
demonstrates that once in a while, large
asteroids have dug out craters, spawned
tsunamis, caused climate changes, and
wiped out life.
But with enough warning, a small
change in an asteroid's orbital velocity
could turn a certain future impact into
a certain miss. The first test of such a
mechanism happened on September
26th, when NASA's Double Asteroid
Redirection Test (DART) smashed nearly
head-on into Dimorphos, the satellite
of asteroid 65803 Didymos. If the crash
changes the velocity of Dimorphos'
orbit by a detectable amount, the mission
will validate the notion that we
can use a kinetic impactor to nudge a
hazardous asteroid's path, keeping
Earth out of harm's way.
DART streamed photos from its
Didymos Reconnaissance and Asteroid
Camera for Optical navigation
(DRACO) down to Earth in real
time, about one per second. Fed into
an onboard computer with software
descended from anti-missile technology,
those images helped DART autonomously
guide itself to impact. On its
approach, it resolved Dimorphos and its
larger companion Didymos into worlds
with fascinating surfaces covered with
gullies and angular blocks. DART initially
targeted the binary system, then
it differentiated the larger and smaller
member of the binary pair, and finally it
steered toward the smaller Dimorphos.
While the DRACO camera feed
ended upon impact, the Italian-built
minisatellite LICIACube (pronounced
" lee-chee-ah kyoob " ), separated from
DART on September 11th to establish a
viewpoint on the carnage. LICIACube
used two cameras (the high-resolution,
monochrome LEIA and wider-angle,
color LUKE) to shoot photos of Dimorphos
throughout the approach, impact,
space and across Earth watched the
immediate and long-term effects of the
crash. Other in-space observers include
the Lucy spacecraft, currently cruising
toward its Jupiter Trojan asteroid mission,
as well as the Hubble and James
Webb Space Telescopes. Along with
Earth-based observers, the telescopes
saw the plumes of dust that rose off the
surface of Dimorphos in response to
the crash. At least two separate plumes
were visible: One, crescent-shaped,
spread out in the direction opposite the
impact, while another, fainter one jetted
at an angle behind Didymos' apparent
motion across the sky.
The key result from the mission
- detecting a significant decrease in
Dimorphos' orbital period - will take
days to weeks to achieve. Observers
across Earth will look for the telltale
dimming of the Didymos system's light
as the asteroid pair mutually eclipse
each other throughout the rest of 2021.
The period will need to decrease by at
least 70 seconds for the change to be
detectable above the uncertainty in
the orbit. Didymos is fainter than 14th
magnitude, out of reach of typical backyard
scopes, so the mission organized
no formal amateur observing campaign.
¢EMILY LAKDAWALLA
See more impact follow-up observations
at https://is.gd/DARTphotos.
pThe CubeSat LICIACube separated from DART on Sept. 11th to photograph the impact on Sept. 26th from a safe distance. The spacecraft swung
closest to the asteroid 165 seconds after impact (second frame) and captured asymmetric plumes of dust coming from Dimorphos.
8
JANUARY 2023 * SKY & TELESCOPE
DART IMPACT FROM GROUND-BASED TELESCOPE: IMAGES: ATLAS PROJECT (UNIVERSITY OF HAWAI`I /
NASA); IMAGE PROCESSING: EMILY LAKDAWALLA; LICIA CUBESAT PHOTOS OF IMPACT: ASI / NASA (4)

https://www.is.gd/DARTphotos https://www.is.gd/DARTphotos

Sky & Telescope - January 2023

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