Eliana Willis

Saturn’s rings might have formed while trilobites scuttled about on Earth. Space dust has been accumulating on the icy halos for no more than 400 million years, researchers report in the May 12 Science Advances.

The 4.5-billion-year-old planet appears to have acquired its iconic ornamentation relatively recently, says physicist Sascha Kempf of the University of Colorado Boulder. “We’re quite lucky to see a ring in the first place.”

The rings of Saturn are made of countless icy particles, which become covered with dust as tiny meteoroids strike them. These dustings darken the rings’ complexion, like mud sullies snow on roads in winter.

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This cosmic staining was key to the new analysis, as was the now-defunct Cassini spacecraft’s Cosmic Dust Analyzer. From 2004 to 2017, the instrument caught dust-sized micrometeoroids moving around Saturn, measuring their velocity, mass, charge and composition.

Kempf and colleagues identified about 160 particles — out of millions — that could have hailed from beyond the Saturn system. The researchers estimated the rate at which the incoming dust accumulates on Saturn’s rings, and calculated how long it would have taken to darken the rings to their observed color. The planet’s hoops might have materialized more than 100 million years after trilobites — mysterious, extinct invertebrates — appeared on Earth, the team found (SN: 8/30/19).

The age of the rings has been debated for decades (SN: 10/20/16). Even after the new study, there’s still disagreement.

If the rings are somehow losing dust over time, they could be ancient, says planetary scientist Aurélien Crida of Université Côte d’Azur in Nice, France, who was not involved in the study. “Possibly as old as Saturn.”

It seems clear that the rings have been exposed to micrometeoroid impacts for at least a hundred million years, Crida says. But simulations of the rings’ formation from the gravitational shredding of an early moon suggest their size is consistent with an age of billions of years, he says. And researchers have reported silicate grains falling from the rings into Saturn’s atmosphere (SN: 10/4/18). Some unidentified process might be cleaning the rings of the micrometeoroid dust, making them appear younger than they are, Crida says.

Alternatively, the previously reported falling dust might come from meteoroid impacts that shatter ring ice, Kempf says.

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Experiments that smash micrometeoroids into ice particles could help resolve the discrepancy, Crida says. For now, the debate over the age of the rings lives on. More

It’s time to drop the magnets, meteorite hunters. The commonly used method for identifying space rocks can destroy scientific information.

Touching even a small magnet to a meteorite can erase any record the rock might have retained about the magnetic field of its parent body, researchers report in the April Journal of Geophysical Research: Planets. And the concern isn’t theoretical: a subset of the oldest known Martian meteorites appear to have already had their magnetic memories wiped, the team showed. 

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Scientists often turn to meteorites to get a closeup look at other worlds, as well as understand our own. The space rocks can contain traces of planetary atmospheres, the chemical building blocks for life and more (SN: 1/26/21; SN: 4/26/22).

Planetary scientist Foteini Vervelidou uses meteorites from Mars — chunks of the planet that were blasted into space by an impact and later captured by Earth’s gravity — to study its ancient past. Just a few hundred are known to exist. Rarer still are specimens that contain minerals carrying imprints of the Red Planet’s magnetic field, which collapsed about 3.7 billion years ago (SN: 9/7/15). The oldest known Martian meteorites, which date to roughly 4.4 billion years ago, therefore present an “amazing chance to study the magnetic field,” says Vervelidou, of MIT and the Institute of Earth Physics of Paris. 

But such opportunities can be readily squandered, Vervelidou and colleagues have shown. The team’s numerical calculations and experiments with earthly rocks — stand-ins for meteorites — confirmed that bringing a hand magnet close to a rock can rearrange the spins of the rock’s electrons. That rearrangement overwrites the imprint of a previous magnetic field, a process called remagnetization.What’s more, the process appears to happen frequently. The team examined nine meteorites found at different times and places on Earth. All of them are thought to have originated from the same oldest known chunk of Mars, which most likely broke up when it entered Earth’s atmosphere. All had been remagnetized.  

The finding is unfortunate, but it’s not surprising, says Melinda Hutson, a meteoriticist at Portland State University in Oregon and the curator of the Cascadia Meteorite Laboratory who was not involved in the research. “Just about everyone wants to stick a magnet on the side of a potential meteorite.”

It is possible to evaluate a meteorite without destroying its magnetic properties. Vervelidou uses a lab instrument called a susceptibility meter, which measures how an object would respond to a magnetic field. And portable versions exist: She and a team of meteorite researchers used one to find nearly 1,000 meteorites on a recent expedition in Chile. Hopefully, Vervelidou says, some of those space rocks will shed light on Mars’ magnetic past. More

The hellscape of Venus is riddled with even more volcanoes than scientists thought.

Using radar images taken by NASA’s Magellan spacecraft in the 1990s, researchers cataloged about 85,000 volcanoes strewn across the Venusian surface. That’s nearly 50 times as many volcanoes as past surveys counted. Planetary scientists Rebecca Hahn and Paul Byrne of Washington University in St. Louis debuted the map in the April JGR Planets.

Such a thorough inventory of volcanism on Venus could offer clues about the planet’s interior, such as hot spots of magma production, Byrne says. And with the recent discovery that Venus is volcanically active, the map could also help pinpoint places to look for new eruptions (SN: 3/15/23).

Almost all the volcanoes that Hahn and Byrne found are less than 5 kilometers wide. About 700 are 5 to 100 kilometers across, and about 100 are wider than 100 kilometers. The team also found many tight clusters of small volcanoes called volcanic fields.

“We have a better handle of how many volcanoes are on Venus than are on Earth,” where most volcanoes are probably hidden beneath the oceans, Byrne says. But he doesn’t think the Magellan data tell the whole story of Venus’ volcanism. That spacecraft could see features as small as about 1 kilometer in diameter. Earth has “lots and lots of volcanoes that are far smaller than a kilometer across,” Byrne says. “That’s probably the case with Venus, too.”

We may soon find out. NASA’s VERITAS spacecraft and the European Space Agency’s EnVision mission are slated to turn their much sharper eyes on Venus’ infernal surface within the next decade or so (SN: 6/2/21).    More

NOORDWIJK, THE NETHERLANDS — Life might arise in the darkest of places: the moon of a planet wandering the galaxy without a star.

The gravitational tug-of-war between a moon and its planet can keep certain satellites toasty enough for liquid water to exist there — a condition widely considered crucial for life. Now computer simulations suggest that, given the right orbit and atmosphere, some moons orbiting rogue planets can stay warm for over a billion years, astrophysicist Giulia Roccetti reported March 23 at the PLANET-ESLAB 2023 Symposium. She and her colleagues also report their findings March 20 in the International Journal of Astrobiology.

“There might be many places in the universe where habitable conditions can be present,” says Roccetti, of the European Southern Observatory in Garching, Germany. But life presumably also needs long-term stability. “What we are looking for is places where these habitable conditions can be sustained for hundreds of millions, or billions, of years.”

Habitability and stability don’t necessarily need to come from a nearby sun. Astronomers have spotted about 100 starless planets, some possibly formed from gas and dust clouds the way stars form, others probably ejected from their home solar systems (SN: 7/24/17). Computer simulations suggest that there may be as many of these free-floating planets as there are stars in the galaxy.

Such orphaned planets might also have moons — and in 2021, researchers calculated that these moons need not be cold and barren places.

Unless a moon’s orbit is a perfect circle, the gravitational pull of its planet continually deforms it. Resulting friction inside the moon generates heat. In our own solar system, this process plays out on moons such as Saturn’s Enceladus and Jupiter’s Europa (SN: 11/6/17; SN: 8/6/20). A sufficiently thick, heat-trapping atmosphere, likely one dominated by carbon dioxide, might then keep the surface warm enough for water to remain liquid. That water could come from chemical reactions with the carbon dioxide and hydrogen in the atmosphere, initiated by the impact of high-speed charged particles from space.

But such a moon won’t stay warm forever. The same gravitational forces that heat it up also mold its orbit into a circle. Gradually, the ebb and flow of gravity felt by the moon deforms it less and less, and the supply of frictional heat dwindles.

In the new study, Roccetti and her colleagues ran 8,000 computer simulations of a sunlike star with three Jupiter-sized planets. These simulations showed that planets that are ejected from their solar system will often sail off into space with their moons in tow.

The team then ran simulations of those moons, assumed to be the size of Earth, whizzing around their planets along the orbit they ended up with during the ejection. The goal was to see if gravitational heating occurred and if it lasted long enough for life to potentially originate there. Earth may have become habitable within a few hundred million years, although the earliest evidence of living organisms here date to about 1 billion years after the planet formed (SN: 1/26/18).

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Because an atmosphere is crucial to heat retention, the team did their calculations with three alternatives. For moons with an atmosphere the same pressure as Earth’s, the period of potential habitability lasted at most about 50 million years, the team found. But it can last nearly 300 million years if the atmospheric pressure is 10 times that of Earth, and for about 1.6 billion years at pressures 10 times greater still. That amount of pressure may sound extreme, but it’s close to conditions on the similarly sized Venus.

Warmth and water might not be enough to let living organisms appear, though. Moons of free-floating planets “will not be the most favorable places for life to arise,” says astrophysicist Alex Teachey, of the Academia Sinica Institute of Astronomy & Astrophysics in Taipei, Taiwan.

“I think stars, due to their incredible power output and their longevity, are going to be far better sources of energy for life,” says Teachey, who studies the moons of exoplanets. “A big open question … is whether you can even start life in a place like Europa or Enceladus, even if the conditions are right to sustain life, because you don’t have, for example, solar radiation that can help along the process of mutation for evolution.”

But Roccetti — although not an astrobiologist herself — thinks moons of orphan planets have a few  important advantages. They will have some, but not too much, water, which many astrobiologists think is a better starting point for life than, say, an ocean world. And not having a star nearby means there are no solar flares, which in many cases will destroy the atmosphere of an otherwise promising planet.

“There are many environments in our universe which are very different from what we have here on Earth,” she says, “and it is important to investigate all of them.” More

THE WOODLANDS, TEXAS — A young, ultrabright Jupiter may have desiccated its now hellish moon Io. The planet’s bygone brilliance could have also vaporized water on Europa and Ganymede, planetary scientist Carver Bierson reported March 17 at the Lunar and Planetary Science Conference. If true, the findings could help researchers narrow the search for icy exomoons by eliminating unlikely orbits.

Jupiter is among the brightest specks in our night sky. But past studies have indicated that during its infancy, Jupiter was far more luminous. “About 10 thousand times more luminous,” said Bierson, of Arizona State University in Tempe.

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That radiance would have been inescapable for the giant planet’s moons, the largest of which are volcanic Io, ice-shelled Europa, aurora-cowled Ganymede and crater-laden Callisto (SN: 12/22/22, SN: 4/19/22, SN: 3/12/15). The constitutions of these four bodies obey a trend: The more distant the moon from Jupiter, the more ice-rich its body is.

Bierson and his colleagues hypothesized this pattern was a legacy of Jupiter’s past radiance. The team used computers to simulate how an infant Jupiter may have warmed its moons, starting with Io, the closest of the four. During its first few million years, Io’s surface temperature may have exceeded 26° Celsius under Jupiter’s glow, Bierson said. “That’s Earthlike temperatures.”

Any ice present on Io at that time, roughly 4.5 billion years ago, probably would have melted into an ocean. That water would have progressively evaporated into an atmosphere. And that atmosphere, hardly restrained by the moon’s weak gravity, would have readily escaped into space. In just a few million years, Io could have lost as much water as Ganymede may hold today, which may be more than 25 times the amount in Earth’s oceans.

A coruscant Jupiter probably didn’t remove significant amounts of ice from Europa or Ganymede, the researchers found, unless Jupiter was brighter than simulated or the moons orbited closer than they do today.

The findings suggest that icy exomoons probably don’t orbit all that close to massive planets. More