Eliana Willis

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

Venus has active volcanism. A new analysis of decades-old images reveals the first definitive sign of a volcano erupting on the hellish planet next door.

NASA’s Magellan spacecraft observed the volcano Maat Mons twice between 1990 and 1992. Sometime in the 243 Earth days between each observation, the volcanic vent appears to have morphed from a 2.2-square-kilometer circle to a 4-square-kilometer blob. That change indicates that an eruption had occurred, researchers report online March 15 in Science and at the Lunar and Planetary Science Conference in The Woodlands, Texas.

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“This world is not quiet, not quiescent, not dead,” says planetary scientist Paul Byrne of Washington University in St. Louis who was not involved in the new work.

Venus is about the same size and mass as Earth so it should have a similar amount of internal heat. And that heat must escape somehow. Scientists have long thought that Venus should be volcanically active. “We’ve just never had something we can point to. And now we do,” Byrne says. He’s also confident that volcanoes on Venus can still erupt now.

“There’s no way you have a planet that big that was doing something 30 years ago and stopped,” he says. “It’s definitely still active today.”

Planetary scientist Robert Herrick spotted the change after painstakingly poring through images of the Venusian regions considered most likely to be volcanically active. “This was a needle-in-a-haystack search with no guarantee that the needle exists,” says Herrick, of the University of Alaska Fairbanks.

Several features in these Magellan radar images look like they’ve changed between the first observation (top) and the second (bottom). But most of those differences occurred because the spacecraft was looking in opposite directions, giving different shading and illumination to the surface. Scientists were able to show that one crater’s apparent differences were due to those imaging differences (Unchanged Vent). Another one (Expanded Vent) was due to real changes on Venus’ surface — probably a volcanic eruption.R.R. Herrick and S. Hensley/Science 2023

Much circumstantial evidence for eruptions on Venus has been reported over the decades (SN: 10/22/10; SN: 6/19/15; SN: 10/18/16). But it has been difficult to tell whether any particular change was due to real geology on the ground, or just a mirage. Many reported differences have turned out just to be due to Magellan’s differing viewing angles over successive orbits around Venus.

“Fundamentally, looking at these images is very hard,” says radar scientist Scott Hensley of NASA’s Jet Propulsion Laboratory in Pasadena, Calif. “It’s not like people have not looked [for active volcanism]. People have been looking over the years.”

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Still, the vent’s change in the images alone was not enough to convince Hensley and Herrick that they were seeing evidence for active volcanism. So, Hensley ran more than 100 computer simulations of what Maat Mons would have looked like to Magellan under different imaging conditions. “None of them ever looked like [the 4-square-kilometer blob] on the second cycle,” Hensley says. The change must be real, he concluded.

The volcano’s change in shape suggests that it probably didn’t explosively explode like Washington’s Mount St. Helens did in 1980, Byrne says (SN: 11/1/16). Instead, the eruption was probably more like the long, slow lava drainage from Hawaii’s Kilauea volcano in 2018, only bigger, he says (SN: 1/29/19).

The finding gives scientists an idea of what to expect — and some new ideas for research — when upcoming missions return to Venus (SN: 6/2/21). In the late 2020s or early 2030s, NASA plans to launch VERITAS, a satellite that will map the whole planet from space, and EnVision, which will take high-resolution satellite images of targeted regions.

“The cool part is it means that Venus is volcanically active now. In these upcoming missions, we are going to see things happening,” Herrick said in his March 15 talk. “We already had plans to try and look for new things and changes with time in both of those missions … we now know that that’s a valuable thing to do.”

This work is awe-inspiring, said planetary scientist Darby Dyar of Mount Holyoke College in South Hadley, Ma., who was not involved in the new work. “Everybody in this room should be salivating over the features we’re going to see” in images from future missions. More