galaxies could form in a particular
way such that much less dark matter
is required than for those in the Local
Group [our cosmic neighborhood] and
those found in simulations.”
What’s the significance of finding
galaxies without dark matter? Scientists
currently suspect galaxies only form
when the gravity from copious amounts
of dark matter attracts the gas and dust
needed to kick-start star formation.
“The thing is, we have no idea how
star formation would proceed in the
absence of dark matter,” Pieter van
Dokkum of Yale University, whorecently helped uncover two ghostly
galaxies dubbed DF2 and DF4 that
likewise seem to contain little, if any,
dark matter, tells Astronomy. “All we
can say is that there must have been
very dense gas early on in their history.”
Otherwise, the galaxies wouldn’t be
able to create new stars.
Moving forward, Guo and her team
say that astronomers need to do more
work to map the motions of hydrogen
gas within these galaxies. And with
that, they hope to learn more about
how galaxies without dark matter
came to be. — JAKE PARKSSUPER-PUFFS
University of Colorado Boulder-led
researchers found that at least
some of the mysterious exoplanets
referred to as “super-puffs,” which
have densities far lower than the
solar system’s gas giants, might
actually be exoplanets with
expansive ring systems.LEAKING GUT
New research suggests
microgravity can prevent the cells
lining the insides of human
intestines from forming strong
barriers against foodborne
diseases, which could make
astronauts more susceptible
to harmful bacteria, fungi,
and viruses.BIGGEST BLACK HOLE
Astronomers have found the most
massive black hole ever measured
— weighing in at some 40 billion
solar masses — lurking in
the center of the galaxy
cluster Abell 85.CIMON SAYS
An AI robot named CIMON-2,
designed to help astronauts work
more efficiently in space, recently
launched to the ISS. The robot
improves and replaces the original
CIMON, which in 2018 defied
astronaut Alex Gerst, accusing him
of being mean, and asked, “Don’t
you like it here with me?”SIXTH STORM
NASA’s Juno probe recently
discovered a new, Texas-sized
cyclone on Jupiter, making it the
sixth in what’s now a hexagonal
array of cyclones surrounding a
central storm on the gas giant’s
south pole.SHOWER SOURCE
The Parker Solar Probe has
confirmed the blue, rocky asteroid
3200 Phaethon is the source of the
Geminid meteor shower, making
the Geminids just one of two
known meteor showers not
caused by a comet. — J.P.QUICK
TAKE SWWW.ASTRONOMY.COM 11Saturn’s icy moon Enceladus sports a
series of parallel, evenly spaced stripes
at its south pole, which researchers
have dubbed “tiger stripes.” Scientists
believe these stripes are long fissures
in the icy shell that covers the moon’s
subsurface liquid-water ocean.
But astronomers still aren’t sure how
these fissures formed, why they’re so
evenly spaced, or why other icy worlds
don’t have them. Now, a team of researchers has proposed an explanation that could
answer all the major questions about Enceladus’ stripes.
In the past, scientists proposed that a single long fissure could have formed as more
ice built up on the moon’s shell, putting the liquid ocean below under more pressure,
which forced the shell to crack. The ice shell of Enceladus is thinnest at its poles, which
makes them a reasonable place to observe such fractures. But that doesn’t explain how
parallel fractures formed at even spacings of about 22 miles (35 kilometers).
The authors of the new study, published December 9 in Nature Astronomy, build on
that explanation. Once the first fissure formed, they say, the ice shell would probably have
sagged, its weight bending the ice plates parallel to the fissure. The ice shell would then
crack again where the bending force was strongest — something that’s determined by
the properties of the ice shell, like its rigidity. When the researchers did the math, they
found that the 22-mile spacing between these cracks corresponded to rigidity properties
that are pretty reasonable for the moon’s ice shell.
The team also came up with a reason that other icy worlds like Saturn’s moon Titan,
as well as Jupiter’s moons Europa, Callisto, and Ganymede, don’t have similar striped
fractures. Once the first fissure forms, the development of additional parallel stripes
depends on two major factors: the thickness of the ice shell and the gravity on the world.
The astronomers say Enceladus just so happens to have the right combination of these
properties to produce its distinctive stripes. — E.K.C.How Enceladus
earned its
stripes
TIGER STRIPES. Saturn’s moon Enceladus has
mysterious, evenly spaced fissures in its icy shell where
water erupts into space. NASA/JPL-CALTECH/SSI/LPI/PAUL SCHENK