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NO CAST REQUIRED. A collection of stars and gas clouds jut
awkwardly from the Milky Way’s Sagittarius Arm in this artist’s
concept. The distance and size of the break is shown in the inset.
NASA/JPL-CALTECH
10 ASTRONOMY • DECEMBER 2021
SOMETIMES, THE FAULT IS NOT IN OURSELVES,
BUT IN OUR ROCKS. That’s what happened to the
Perseverance rover during its first attempted sample collection
in Jezero Crater.
NASA’s newest rover is on a mission to not only explore Mars
but also collect samples that can be studied on Earth. Perseverance
is carrying numerous tubes to store small, drilled core samples of
rock for a later mission to retrieve.
But on Aug. 6, NASA announced that the rover’s first collection
attempt had turned up empty. The rover had successfully gone
through the motions — drilling into the rock and attempting to
place the result into a tube. But when the rover stuck a probe inside
the tube to measure the volume of the sample, it found nothing.
Mission controllers were confident the rover’s drill and coring
bit were in good working order. So, they concluded, it was the
rock that had misbehaved. Called Roubion, this first target is what
researchers refer to as a paver stone — f lat, polygonal rocks they
believe are some of the most ancient in the area. But because such
rocks are old and weathered, this one crumbled under the force of
Perseverance’s drill.
To find a better target, controllers next drove to a ridge called
Citadelle, with outcroppings of rocks very different from the paver
stones. And, on Sept. 2, Perseverance successfully completed its
first sample collection. This time, images from the rover showed
the rock core, a bit wider than a pencil, snug in its sample tube.
The team still hopes to sample a paver stone. Next time, though,
they’ll likely target a less weathered type of paver, in the hopes that
such rocks will provide information similar to older, more fragile
examples. — ALISON KLESMAN
Perseverance prevails,
collects first sample
QUANTUM GRAVITY
The Milky Way has
a broken arm
Even though we call it
home, the Milky Way
remains rich with myster-
ies and surprises. Case in
point: Astronomers recently
noticed our galaxy has a
broken arm.
Stretching about 3,
light-years long, this splinter
of stars and gas juts out
from the Sagittarius Arm at a
roughly 45° angle. While it’s
not unusual to spot sharply-
angled spurs (also called
feathers) in other spiral gal-
axies, it’s the first time that
astronomers have noticed a
defect this stark in our own
galaxy’s arms.
From Earth’s position
within the Milky Way, it’s
difficult for scientists to
see the entirety of the
galaxy. Astronomers used
data obtained by the now-
retired NASA Spitzer Space
Telescope and by the
European Space Agency’s
Gaia mapping mission to
confirm they were seeing
a section of the Milky Way
protruding from the rest of
the arm. “It is only the recent,
direct distance measure-
ments from Gaia that make
the geometry of this new
structure so apparent,” said
study co-author Alberto
Krone-Martins, an astro-
physicist at the University
of California, Irvine, in a
statement.
Though this would be a
rather gruesome fracture in
flesh and bone, in cosmic
terms, this area is spectacu-
lar, filled with star-forming
vistas. The analysis shows
that four famous deep-sky
objects — the Eagle Nebula
(M16), the Omega Nebula
(M17), the Trifid Nebula
(M20), and the Lagoon
Nebula (M8) — all lie within
this structure.
Astronomers believe such
spurs are formed by a com-
bination of gravity, rotation,
and shear. Because these
structures bear the imprint
of those forces, finding more
spurs like this one could help
scientists better understand
how spiral galaxies form
their graceful, curving arms.
— HAILEY ROSE MCLAUGHLIN
SECOND TIME’S THE CHARM. The
borehole from Perseverance’s first
sample attempt (above) shows the
target rock’s poor integrity. On its
second attempt at a different rock,
the rover successfully drilled a
sample and stored it in a titanium
tube (left). FROM TOP: ASA/JPL-CALTECH/MSSS;
NASA/JPL-CALTECH/ASU/MSSS