Saturn’s moon Mimas may be the newest, if not the most unlikely member of the solar system’s family of icy bodies, with internal liquid water oceans according to a new study by Alyssa Rose Rhoden of the Southwest Research Institute and Matthew E. Walker of the Planetary Science Institute. These bodies, which include Europa, Enceladus, and possibly Pluto and Triton, are all considered prime targets for exploration due to their ability to maintain potentially life-sustaining water under their outer ice shells at a wide range of distances from the Sun.
What makes Mimas unusual is what it lacks in comparison with all other known ocean-bearing moons: active geology. Mimas is small (less than 400 kilometers-in-diameter) and heavily cratered, suggesting that it has remained frozen and geologically inactive for many millions of years despite the powerful tidal forces it experiences as it orbits Saturn. Observations made by the Cassini spacecraft of Mimas’ orbital libration, or variation in its tilt over time, suggested that either its core was irregularly shaped or that an internal ocean could exist. For Mimas to maintain an internal ocean, but have an ice shell thick enough to remain frozen, would require a careful balance of tidal heating, as its small size means it would quickly lose any heat that is produced.
Rhodes and Walker used tidal heating models to find the balance between these two constraints and found that an ice shell between 24 and 31 kilometers thick produced a good fit for the data. Because the thickness of the ice shell is related to the surface heat flux, a future mission with an instrument similar to Juno’s microwave radiometer could verify this finding. The confirmation of an ocean on such an unlikely world would greatly expand our understanding of how prevalent these important ocean moons may be in the solar system and beyond. READ MORE
It’s hard to know exactly why the relatives of today’s sockeye went extinct
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Published Apr 24, 2024 • Last updated 17 hours ago • 3 minute read
The artwork and publicity materials showcasing a giant salmon that lived five million years ago were ready to go to promote a new exhibit, when the discovery of two fossilized skulls immediately changed what researchers knew about the fish.
Initial fossil discoveries of the 2.7-metre-long salmon in Oregon in the 1970s were incomplete and had led researchers to mistakenly suggest the fish had fang-like teeth.
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It was dubbed the “sabre-toothed salmon” and became a kind of mascot for the Museum of Natural and Cultural History at the University of Oregon, says researcher Edward Davis.
But then came discovery of two skulls in 2014.
Davis, a member of the team that found the skulls, says it wasn’t until they got back to the lab that he realized the significance of the discovery that has led to the renaming of the fish in a new, peer-reviewed study.
“There were these two skulls staring at me with sideways teeth,” says Davis, an associate professor in the department of earth sciences at the university.
In that position, the tusk-like teeth could not have been used for biting, he says.
“That was definitely a surprising moment,” says Davis, who serves as director of the Condon Fossil Collection at the university’s Museum of Natural and Cultural History.
“I realized that all of the artwork and all of the publicity materials and bumper stickers and buttons and T-shirts we had just made two months prior, for the new exhibit, were all out of date,” he says with a laugh.
Davis is co-author of the new study in the journal PLOS One, which renames the giant fish the “spike-toothed salmon.”
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It says the salmon used the tusk-like spikes for building nests to spawn, and as defence mechanisms against predators and other salmon.
The salmon lived about five million years ago at a time when Earth was transitioning from warmer to relatively cooler conditions, Davis says.
It’s hard to know exactly why the relatives of today’s sockeye went extinct, but Davis says the cooler conditions would have affected the productivity of the Pacific Ocean and the amount of rain feeding rivers that served as their spawning areas.
Another co-author, Brian Sidlauskas, says a fish the size of the spike-toothed salmon must have been targeted by predators such as killer whales or sharks.
“I like to think … it’s almost like a sledgehammer, these salmon swinging their head back and forth in order to fend off things that might want to feast on them,” he says.
Sidlauskas says analysis by the lead author of the paper, Kerin Claeson, found both male and female salmon had the “multi-functional” spike-tooth feature.
“That’s part of our reason for hypothesizing that this tooth is multi-functional … It could easily be for digging out nests,” he says.
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“Think about how big the (nest) would have to be for an animal of this size, and then carving it out in what’s probably pretty shallow water; and so having an extra digging tool attached to your head could be really useful.”
Sidlauskas says the giant salmon help researchers understand the boundaries of what’s possible with the evolution of salmon, but they also capture the human imagination and a sense of wonder about what’s possible on Earth.
“I think it helps us value a little more what we do still have, or I hope that it does. That animal is no longer with us, but it is a product of the same biosphere that sustains us.”
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Arachnophobes need not fear: A new European Space Agency (ESA) image of Martian “spiders” actually shows seasonal eruptions of carbon dioxide gas on the Red Planet.
The dark, spindly formations were spotted in a formation known as Inca City in Mars‘ southern polar region. Images taken by ESA’s Mars Express orbiter and ExoMars Trace Gas Orbiter show dark clusters of dots that appear to have teeny little legs, not unlike baby spiderlings huddling together.
The formations are actually channels of gas measuring 0.03 to 0.6 miles (45 meters to 1 kilometer) across. They originate when the weather starts to warm in the southern hemisphere during Martian spring, melting layers of carbon dioxide ice. The warmth causes the lowest layers of ice to turn to gas, or sublimate.
As the gas expands and rises, it explodes out of the overlying ice layers, carrying with it dark dust from the solid surface. This dust geysers out of the ice before showering down onto the top layer, creating the cracked, spidery pattern seen here. In some places, the geysers burst through ice up to 3.3 feet (1 m) thick, according to ESA.
Related: Single enormous object left 2 billion craters on Mars, scientists discover
Inca City is also known as Angustus Labyrinthus. It’s named for its linear, ruin-like ridgelines, which were once thought to be petrified sand dunes or perhaps remnants of ancient Martian glaciers, which could have left high walls of sediment behind as they retreated.
In 2002, however, the Mars Orbiter revealed that Inca City is part of a circular feature approximately 53 miles (86 km) wide. This feature may be an old impact crater — suggesting that the geometric ridges may be magma intrusions that rose through the cracked, heated crust of Mars after it was hit by a renegade space rock. The crater would have then filled with sediment, which has since eroded, partially revealing the magma formations reminiscent of ancient ruins.
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The Hubble Space Telescope has captured a stunning new image of the glowing gas ejected from a dying star, which in this case happens to resemble a “cosmic dumbbell.”
The portrait may also include evidence that the star gobbled up another star, in a form of stellar cannibalism, before it collapsed.
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