Sky & Telescope - March 2025 - 11

SOLAR SYSTEM
200 km
Oldest and Largest Impact
Crater Found on Venus
SCIENTISTS HAVE FOUND what might
be the oldest and largest crater on Venus
- and it's like none ever seen on our
sister planet.
Radar has previously enabled scientists
to identify some 1,000 impact
craters on Venus's surface. Dating
only as far back as 1 billion years, and
with sizes of at most 300 kilometers
(190 miles) across, they're far younger
and smaller than craters found on
the Moon, Mercury, and Mars. Those
worlds still have records of impacts
from the solar system's first 2.5 billion
years, when large chunks of planetforming
material still roamed around.
Now, a new discovery published
in the October Journal of Geophysical
Research: Planets might record an earlier
impact on Venus. Vicki Hansen (University
of Minnesota, Duluth) found
the possible crater while mapping the
oldest and most highly disrupted type of
terrain on Venus: tesserae.
The team was surprised that one of
these regions, the Haasttse-baad Tessera,
contains a circular, multi-ringed
structure 1,500 km wide. " The beautiful
IN BRIEF
Radio Burst from a
" Dead " Galaxy
For the first time ever, astronomers have
detected a fast radio burst (FRB) in a large
elliptical galaxy. The discovery, announced by
Tarraneh Eftekhari (Northwestern University)
at a conference in Khao Lak, Thailand, supports
earlier indications that there are various
ways to form the extreme objects that produce
these ultra-brief flashes of radio waves.
Most FRBs for which accurate sky positions
are known can be traced to galaxies with a
high rate of star formation. That's one of the
reasons why scientists think that the bursts
occur on magnetars - young and strongly
magnetized neutron stars left behind when
massive stars end their short lives in supernova
explosions. However, FRB 20240209A
doesn't fit this picture. Between February
and July, the Canadian Hydrogen Intensity
Mapping Experiment (CHIME) radio obserconcentric
structures were very different
from the rest of the tesserae, "
Hansen says.
When Hansen and fellow mapper
Ivan López (Rey Juan Carlos University,
Spain) went looking for solar system
analogs to help explain the rings' origins,
they had to go as far afield as the
icy moons of Jupiter. Callisto's Valhalla
Crater and Europa's Tyre Crater both
sport multiple rings, probably formed
after something big punched through
an icy shell floating on liquid water.
While Venus wouldn't have had
water, it did have lava. Team member
Evan Bjonnes (Lawrence Livermore
National Laboratory) used computer
simulations to show that a single, large
object hitting a crust a few kilometers
thick could have melted the underlyvatory
detected 22 bursts. Thanks to the
repeated bursts and the recent addition of a
smaller outrigger telescope, CHIME pinpointed
the burst's origins to the outskirts of
an old, massive, and luminous elliptical galaxy
almost 2 billion light-years away that doesn't
show any signs of recent star formation. If
FRB 20240209A occurred on a magnetar, the
object may have resulted from some other
process than a core-collapse supernova.
¢GOVERT SCHILLING
Read more at https://is.gd/FRB0209.
New Views of Vega's
Dusty Disk
Astronomers have used the Hubble and
James Webb space telescopes to gain an
unprecedented view of the vast disk of gas
and dust surrounding the star Vega - and it's
exceedingly smooth. Schuyler Wolff (University
of Arizona) led an effort using Hubble
to peer at the outer, cooler part of the disk,
where small, smoke-size particles glint in
pOn a geologic map of Haasttse-baad Tessera,
black lines depict the concentric rings of an
ancient impact crater.
ing layer, leaving a thin crust over a hot
lava pond. A second impact hitting the
same spot could then have splattered
ejecta in multi-ringed fashion. (The lava
pond likely remained hot for millions of
years, making a double-impact scenario
less unlikely.)
Venus researcher Anna Gülcher
(Caltech) says she is " quite excited "
about the new insight the impact scenario
offers for tesserae. Understanding
this odd terrain type, unique to Venus,
has become one of the highest priorities
for future missions to this planet, and
studies like this one lay the groundwork
for explaining its origin.
¢JEFF HECHT
Vega's light. Meanwhile, team member Kate
Su (also at University of Arizona) led an accompanying
analysis of Webb data, revealing
sand-size particles in the hotter, inner part
of the disk. The disk's smooth gradient is
marred only by a subtle gap located about
twice as far from Vega as Neptune circles the
Sun. The results will appear in the Astrophysical
Journal. While other stars' disks exhibit
distinct gaps that might have been cleared
out by giant planets, the absence of such
planets around Vega could explain its disk's
smoothness. According to René Oudmaijer
(Royal Observatory of Belgium), who wasn't
involved in these studies, " it is becoming
more established that more massive stars are
less likely to be accompanied by planets than
lower mass stars such as our Sun. " Or, if Vega
does have planets, they might be smaller than
these new observations can pick up; the data
can only rule out planets bigger than Neptune
in large orbits.
¢COLIN STUART
sk yand tele scope .o r g * MARCH 2025
11
LOPEZ ET AL. / JOURNAL OF GEOPHYSICAL RESEARCH: PLANETS 2024
https://www.is.gd/FRB0209 http://skyandtelescope.org
Sky & Telescope - March 2025

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