Why it matters that health agencies finally said the coronavirus is airborne

This year, health experts around the world revised their views about how the coronavirus spreads. Aerosol scientists, virologists and other researchers had determined in 2020 that the virus spreads through the air, but it took until 2021 for prominent public health agencies to acknowledge the fact. The admission could have wide-ranging consequences for everything from public health recommendations and building codes to marching band practices (SN: 8/14/21, p. 24).

For decades, doctors and many researchers have thought that respiratory viruses such as cold and flu viruses spread mainly by people touching surfaces contaminated by mucus droplets and then touching their faces. That’s why, in the early days of the pandemic, disinfectant wipes flew off store shelves.

Surface-to-face transfer is still a probable route of infection for some cold-causing viruses, such as respiratory syncytial virus, or RSV. But it turns out that the coronavirus spreads mainly through fine aerosol particles that may hang in the air for hours, particularly indoors.

People spread such aerosols when coughing or sneezing, but also when talking, singing, shouting and even quietly breathing, allowing infected people to spread the disease even before they know they’re sick. Some evidence suggests that the coronavirus may be evolving to spread more easily through the air (SN: 9/25/21, p. 6).

It took collecting reams of data and more than 200 scientists pushing the World Health Organization and other public health agencies to acknowledge airborne spread of the coronavirus. In April 2021, both the WHO and U.S. Centers for Disease Control and Prevention updated their recommendations to note that airborne spread is a major route of infection (SN Online: 5/18/21).

That recognition was vital to public understanding of why wearing well-fitting masks is necessary in public indoor places (SN: 3/13/21, p. 14; SN Online: 7/27/21). Masking, social distancing and other measures to guard against the coronavirus are also credited with nearly wiping out flu last winter (SN Online: 2/2/21). Experts fear a resurgence of cold and flu this winter if those measures aren’t continued (SN Online: 8/12/21).

Knowledge that COVID-19 is an airborne disease has led to such measures as rearranging seating in orchestras (SN Online: 6/23/21) and updating recommendations for proper ventilation and filtration in buildings. Some scientists and activists have also suggested that the safety of indoor air should be regulated to reduce the spread of diseases, much like safety standards for food and drinking water.

Methods of getting results from real-world experiments win 2021 economics Nobel

Some of the most insightful — and now most celebrated — studies of such major social issues as minimum wages and immigration have seized on naturally occurring events. Pioneering efforts by three economists to study the effects of real-life economic events that mimic controlled laboratory investigations have won the Nobel Memorial Prize in Economic Sciences.

David Card of the University of California, Berkeley will receive half of the prize of 10 million Swedish kronor (or half of about $1.14 million). The other half will be split by Joshua Angrist of MIT and Guido Imbens of Stanford University. The Royal Swedish Academy of Sciences announced the prize October 11.

Research by the Nobel Prize winners was instrumental in the development during the 1990s of what are known as natural experiments. These investigations rely on naturally occurring differences between groups or populations that either do or don’t experience specific conditions. In this way, social scientists can study, say, how differences in income affect physical health or how immigration influences employment rates.

Natural experiments are especially important because investigators of key social questions, such as whether pollution slows children’s mental development or whether strong public institutions promote economic growth, often can’t assign people at random to treatment and control conditions. It would be unethical, impractical or both.
“The Nobel winners developed techniques that replicate the idea of truly scientific experiments like you would use to test a vaccine, except [the experiments] occurred in the real world,” says economist Phillip Levine of Wellesley College in Massachusetts. These methods “were at the forefront of a ‘credibility revolution’ in economics” that made the field relevant and understandable to the public, he adds. Levine was a Princeton University graduate student with Angrist, and Card was his thesis adviser.

Natural experiments in economics are related to another influential line of research that examines ways to counteract poverty’s harmful effects using field experiments, work that won the 2019 economics Nobel (SN: 10/14/19).

In a key 1994 paper, Card and the late Princeton economist Alan Krueger challenged conventional wisdom in economics that increases in the minimum wage reduce employment. Card and Krueger surveyed fast-food restaurants in New Jersey and a neighboring section of eastern Pennsylvania before and after a minimum wage hike that was instituted only in the Garden State. Full-time employment slightly increased in New Jersey following wage increases, while it declined in Pennsylvania where wages stayed the same.
Further research addressed the complexities of how the minimum wage interacts with employment rates, but it was clear after Card and Krueger’s report that a simple cause-and-effect relationship didn’t exist.

Card also conducted a natural experiment indicating that a huge influx of Cuban refugees to Miami in 1980 did not result in reduced wages and employment for Miami residents with low education levels. That work led Card and others to further explore how new immigration influences the economic standing of native-born citizens and earlier immigrants.

Angrist and Imbens expanded on such work by devising steps to determine under what conditions a natural experiment, such as being given an opportunity to leave school at age 16, affects later outcomes, such as annual income. For instance, the researchers’ method estimated the effect on later income of an additional year of education, which they put at about 9 percent lower for each year lost after age 16, but only for people who chose to leave school early. The estimate excluded earnings histories of individuals who had planned to go to college all along because those people never considered leaving school early.
Card, Angrist and Imbens “have promoted a type of scholarly investigation that is of practical use outside academic journals,” says economist Melissa Kearney of the University of Maryland in College Park, who has studied and worked with both Card and Angrist. The Nobel Prize winners’ research equipped social scientists with “tools to credibly draw causal conclusions about empirical relationships.”

A new particle accelerator aims to unlock secrets of bizarre atomic nuclei

Inscribed on an Italian family’s 15th century coat of arms and decorating an ancient Japanese shrine, the Borromean rings are symbolically potent. Remove one ring from the trio of linked circles and the other two fall apart. It’s only when all three are entwined that the structure holds. The rings have represented the concepts of unity, the Christian Holy Trinity and even certain exotic atomic nuclei.

A rare variety, or isotope, of lithium has a nucleus that is made of three conjoined parts. Lithium-11’s nucleus is separated into a main cluster of protons and neutrons flanked by two neutrons, which form a halo around the core. Remove any one piece and the trio disbands, much like the Borromean rings.

Not only that, lithium-11’s nucleus is enormous. With its wide halo, it is the same size as a lead nucleus, despite having nearly 200 fewer protons and neutrons. The discovery of lithium-11’s expansive halo in the mid-1980s shocked scientists (SN: 8/20/88, p. 124), as did its Borromean nature. “There wasn’t a prediction of this,” says nuclear theorist Filomena Nunes of Michigan State University in East Lansing. “This was one of those discoveries that was like, ‘What? What’s going on?’ ”
Lithium-11 is just one example of what happens when nuclei get weird. Such nuclei, Nunes says, “have properties that are mind-blowing.” They can become distorted into unusual shapes, such as a pear (SN: 6/15/13, p. 14). Or they can be sheathed in a skin of neutrons — like a peel on an inedible nuclear fruit (SN: 6/5/21, p. 5).

A new tool will soon help scientists pluck these peculiar fruits from the atomic vine. Researchers are queuing up to use a particle accelerator at Michigan State to study some of the rarest atomic nuclei. When it opens in early 2022, the Facility for Rare Isotope Beams, or FRIB (pronounced “eff-rib”), will strip electrons off of atoms to make ions, rev them up to high speeds and then send them crashing into a target to make the special nuclei that scientists want to study.

Experiments at FRIB will probe the limits of nuclei, examining how many neutrons can be crammed into a given nucleus, and studying what happens when nuclei stray far from the stable configurations found in everyday matter. With FRIB data, scientists aim to piece together a theory that explains the properties of all nuclei, even the oddballs. Another central target: pinning down the origin story for chemical elements birthed in the extreme environments of space.

And if scientists are lucky, new mind-blowing nuclear enigmas, perhaps even weirder than lithium-11, will emerge. “We’re going to have a new look into an unexplored territory,” says nuclear physicist Brad Sherrill, scientific director of FRIB. “We think we know what we’ll find, but it’s unlikely that things are going to be as we expect.”
Exploring instability
Atomic nuclei come in a dizzying number of varieties. Scientists have discovered 118 chemical elements, distinguished by the number of protons in their nuclei (SN: 1/19/19, p. 18). Each of those elements has a variety of isotopes, different versions of the element formed by switching up the number of neutrons inside the nucleus. Scientists have predicted the existence of about 8,000 isotopes of known elements, but only about 3,300 have made an appearance in detectors. Researchers expect FRIB will make a sizable dent in the missing isotopes. It may identify 80 percent of possible isotopes for all the elements up through uranium, including many never seen before.

The most familiar nuclei are those of the roughly 250 isotopes that are stable: They don’t decay to other types of atoms. The ranks of stable isotopes include the nitrogen-14 and oxygen-16 in the air we breathe and the carbon-12 found in all known living things. The number following the element’s name indicates the total number of protons and neutrons in the nucleus.

Stable nuclei have just the right combination of protons and neutrons. Too many or too few neutrons causes a nucleus to decay, sometimes slowly over billions of years, other times in mere fractions of a second (SN: 3/2/19, p. 32). To understand what goes on inside these unstable nuclei, scientists study them before they decay. In general, as the proton-neutron balance gets more and more off-kilter, a nucleus gets further from stability, and its properties tend to get stranger.

Such exotic specimens test the limits of scientists’ theories of the atomic nucleus. While a given theory might correctly explain nuclei that are near stability, it may fail for more unusual nuclei. But physicists want a theory that can explain the most unusual to the most banal.

“We would like to understand how the atomic nucleus is built, how it works,” says theoretical nuclear physicist Witold Nazarewicz, FRIB’s chief scientist.
A fast clip
Accelerating beams of ions in FRIB is like herding cats.

In the beginning, “it’s just a gaggle of cats,” says Thomas Glasmacher, FRIB’s laboratory director. The cats meander this way or that, but if you can nudge the unruly bunch in a particular direction — maybe you open a can of cat food — then the cats start moving together, despite their natural tendency to wander. “Pretty soon, it’s a stream of cats,” he says.

In FRIB’s case, the cats are ions — atoms with some or all of their electrons stripped off. And rather than cat food, electromagnetic forces get them moving en masse.

The journey starts in one of FRIB’s two ion sources, where elements are vaporized and ionized. After some initial acceleration to get the ions moving, the beam enters the linear accelerator, which is what sets the particles really cruising. The linear accelerator looks like a scaled-down freight train — a line of 46 boxes the color of pistachio ice cream, each about 2.5 meters tall, of varying lengths. But the accelerator sends the beam moving much faster than a cargo-filled train — up to about half the speed of light.

Within the green boxes, called cryomodules, superconducting cavities are cooled to just a few kelvins, a smidge above absolute zero. At those temperatures, the cavities can accelerate the ions using rapidly oscillating electromagnetic fields. The chain of pistachio modules wends around the facility in the shape of a paper clip, a contortion necessary so that the approximately 450-meter-long accelerator fits in the 150-meter-long tunnel that houses it.

When the beam is fully accelerated, it’s slammed into a graphite target. That hard hit knocks protons and neutrons off the nuclei of the incoming ions, forming new, rarer isotopes. Then, the specific one that a scientist wants to study is separated from the riffraff by magnets that redirect particles based on their mass and electric charge. The particles of interest are then sent to the experimental area, where scientists can use various detectors to study how the particles decay, measure their properties or determine what reactions they undergo.
The energy of FRIB’s beam is carefully selected for producing rare isotopes. Too much energy would blow the nuclei apart when they collide with the target. So FRIB is designed to reach less than a hundredth the energy of the Large Hadron Collider at CERN near Geneva, the world’s most energetic accelerator.

Instead, the new accelerator’s potential rests on its juiced-up intensity: Essentially, it has lots and lots of particles in its beam. For example, FRIB will be able to slam 50 trillion uranium ions per second into its target. As a result, it will produce more intense streams of rare isotopes than its predecessors could.

For isotopes that are relatively easily produced, FRIB will churn out about a trillion per second; plenty to study. That opens prospects for scrutinizing isotopes that are more difficult to make. Those isotopes might pop up once a week in FRIB, but that’s still much more often than in a weaker beam. It’s like a case of low water pressure in the bathroom: “You can’t have a shower if it’s just trickling,” says Nunes, who is one of the leaders of a coalition of theoretical physicists supporting research at FRIB. Now, “FRIB is going to come in with a fire hose.”
Dripping with neutrons
That fire hose will also come in handy for pinpointing a crucial boundary known as the neutron drip line.

Try to stuff too many neutrons in a nucleus, and it will decay almost immediately by spitting out a neutron. Imagine a greedy chipmunk with its cheeks so full of nuts that when it tries to shove in one more, another nut pops right back out. The threshold at which nuclei decay in this way marks the ultimate limits for bound nuclei. On a chart of the known elements and their isotopes, this boundary traces out a line, the neutron drip line. So far, scientists know the location of this crucial demarcation up through, at most, the 10th element on the periodic table, neon.

“FRIB is going to be the only way to go heavier and far enough out to define that drip line,” says nuclear physicist Heather Crawford of Lawrence Berkeley National Laboratory in California. FRIB is expected to determine the neutron drip line up to the 30th element, zinc, and maybe even farther.
Near that drip line, where neutrons greatly outnumber protons, is where nuclei get especially strange. Lithium-11, with its capacious halo, sits right next to the drip line. Crawford focuses on magnesium isotopes that are close to the drip line. The most common stable magnesium isotope has 12 protons and 12 neutrons. Crawford’s main target, magnesium-40, has 12 protons and more than double that number of neutrons — 28 — in its nucleus.

“That’s right out at the limits of existence,” Crawford says. Out there, theories that predict the properties of nuclei are no longer reliable. Theoretical physicists can’t always be sure what size and shape a given nucleus in this realm might be, or even whether it qualifies as a bound nucleus. A given theory might also fall short when predicting how much energy is needed to bump the nucleus into its various energized states. The spacing of these energy levels acts as a kind of fingerprint of an atomic nucleus, one that’s highly sensitive to the details of the nucleus’ shape and other properties.

Sure enough, magnesium-40 behaves unexpectedly, Crawford and colleagues reported in 2019 in Physical Review Letters. While theories predicted its energy levels would match those of magnesium isotopes with slightly fewer neutrons, magnesium-40’s energy levels were significantly lower than its neighbors’.

In August, Crawford learned that she will be one of the first scientists to use FRIB. Two experiments she and colleagues proposed were selected for the first round of about 30 experiments to take place over FRIB’s first two years. She’ll take a closer look at magnesium-40, which, like lithium-11, has a Borromean nucleus. Crawford now aims to determine if her chosen isotope also has a haloed nucleus. That’s one possible explanation for magnesium-40’s oddness. Despite the fact that nuclei with halos have been known for decades, theories still can’t reliably predict which nuclei will be festooned with them. Understanding magnesium-40 could help scientists firm up their accounting of nuclei’s neutron adornments.
Elemental origins
Physicists want to be able to poke around, like mechanics under the hood, to understand the cosmic nuclear reactions that make the universe go. “Nuclear physics is like the engine of a sports car. It’s what happens in the engine that determines how well the car performs,” says nuclear physicist Ani Aprahamian of the University of Notre Dame in Indiana.

The cosmos powered by that engine can be a violent place for nuclei, punctuated with dramatic stellar explosions and extreme conditions, including matter crammed into ultratight quarters by crushing gravity. These environments beget wonders of nuclear physics unlike those normally seen on Earth. FRIB will let scientists get a glimpse at some of those processes.

For example, physicists think that certain neutron-rich environments are the cauldron where many of the universe’s chemical elements are cooked. This cosmic connection allowed nuclear physicist Jolie Cizewski to make good on a childhood dream.

When Cizewski was a little girl, she caught the astronomy bug, she says. “I decided I was going to become an astronomer so I could go into space.” It might seem that she took a left turn from her childhood obsession. She never made it to orbit and she didn’t become an astronomer.

But echoes of that childhood dream now anchor her research. Instead of peering at the stars with a telescope, she’ll soon be using FRIB to reveal secrets of the cosmos.

Cizewski, of Rutgers University in New Brunswick, N.J., is working to unveil details of the cosmic nuclear reactions responsible for the nuclei that surround us. “I’m trying to understand how the elements, in particular those heavier than iron, have been synthesized,” she says.

Many of the elements around us — and in us — formed within stars. As large stars age, they fuse progressively larger atomic nuclei together in their cores, creating elements farther along the periodic table — oxygen, carbon, neon and others. But the process halts at iron. The rest of the elements must be born another way.

A process called the rapid neutron capture process, or r-process, is responsible for many of those other elements found in nature. In the r-process, atomic nuclei quickly soak up neutrons and bulk up to large masses. The neutronfest is interspersed with radioactive decays that form new elements. The sighting of two neutron stars merging in 2017 revealed that such collisions are one place where the r-process occurs (SN: 11/11/17, p. 6). But scientists suspect it might happen in other cosmic locales as well (SN: 6/8/19, p. 10).

Cizewski and colleagues are studying an abbreviated form of the r-process that might thrive in supernovas, which may not have enough oomph for the full r-process. The team has zeroed in on germanium-80, which plays a pivotal role in the weak r-process. Physicists want to know how likely this nucleus is to capture another neutron to become germanium-81. At FRIB, Cizewski will slam a beam of germanium-80 into deuterium, which has one proton and one neutron in its nucleus. Knowing how often germanium-80 captures the neutron will help scientists nail down the neutron-slurping chain of the weak r-process, wherever it might crop up.
A Borromean bent
Like the interlinked Borromean rings, different facets of nuclear physics are closely entwined, from mysteries of the cosmos to the inner workings of nuclei. The exotic nuclei that FRIB cooks up could also allow physicists to tap into the very bedrock of physics by testing certain fundamental laws of nature. And there’s a practical side to the facility as well. Scientists could collect some of the isotopes FRIB produces for use in medical procedures, for example.

Physicists are ready for surprises. “Every time we build such a facility, new discoveries come and breakthroughs in science come,” Nazarewicz says. Like the 1980s discovery of lithium-11’s Borromean nucleus, scientists may find something totally unexpected.

China’s lunar rock samples show lava flowed on the moon 2 billion years ago

Lava oozed across the moon’s surface just 2 billion years ago, bits of lunar rocks retrieved by China’s Chang’e-5 mission reveal.

A chemical analysis of the volcanic rocks confirms that the moon remained volcanically active far longer that its size would suggest possible, researchers report online October 7 in Science.

Chang’e-5 is the first mission to retrieve lunar rocks and return them to Earth in over 40 years (SN: 12/1/20). An international group of researchers found that the rocks formed 2 billion years ago, around when multicellular life first evolved on Earth. That makes them the youngest moon rocks ever collected, says study coauthor Carolyn Crow, a planetary scientist at the University of Colorado Boulder.

The moon formed roughly 4.5 billion years ago. Lunar rocks from the Apollo and Soviet missions of the late 1960s and 70s revealed that volcanism on the moon was commonplace for the first billion or so years of its existence, with flows lasting for millions, if not hundreds of millions, of years.
Given its size, scientists thought that the moon started cooling off around 3 billion years ago, eventually becoming the quiet, inactive neighbor it is today. Yet a dearth of craters in some regions left scientists scratching their heads. Parts of celestial bodies devoid of volcanism accumulate more and more craters over time, in part because there aren’t lava flows depositing new material that hardens into smooth stretches. The moon’s smoother spots seemed to suggest that volcanism had persisted past the moon’s early history.

“Young volcanism on a small body like the moon is challenging to explain, because usually small bodies cool fast,” says Juliane Gross, a planetary scientist at Rutgers University in Piscataway, N.J., not involved in the study.

Scientists had suggested that radioactive elements might offer an explanation for later volcanism. Radioactive decay generates a lot of heat, which is why nuclear reactors are kept in water. Enough radioactive materials in the moon’s mantle, the layer just below the visible crust, would have provided a heat source that could explain younger lava flows.

To test this theory, the Chang’e-5 lander gathered chunks of basalt — a type of rock that forms from volcanic activity — from a previously unexplored part of the moon thought to be younger than 3 billion years old. The team determined that the rocks formed from lava flows 2 billion years ago, but chemical analysis did not yield the concentration of radioactive elements one would expect if radioactive decay were to explain the volcanism.
This finding is compelling scientists to consider what other forces could have maintained volcanic activity on the moon.

One theory, says study coauthor Alexander Nemchin, a planetary scientist at the Beijing SHRIMP Center and Curtin University in Bentley, Australia, is that gravitational forces from the Earth could have liquefied the lunar interior, keeping lunar magma flowing for another billion or so years past when it should have stopped.

“The moon was a lot closer 2 billion years ago,” Nemchin explains. As the moon slowly inched away from the Earth — a slow escape still at work today — these forces would have become less and less powerful until volcanism eventually petered out.
Impacts from asteroids and comets also could have kept the moon’s volcanic juices flowing, but “at this point, any guess is a good guess,” says Jessica Barnes, a planetary scientist at the University of Arizona in Tucson not involved in the study.

“This is a good example of why we need to get to know our closest neighbor,” Barnes says. “A lot of people think we already know what’s going on with the moon, but it’s actually quite mysterious.”

5 cool things to know about NASA’s Lucy mission to the Trojan asteroids

For the first time, a spacecraft is headed to Jupiter’s odd Trojan asteroids. What Lucy finds there could provide a fresh peek into the history of the solar system.

“Lucy will profoundly change our understanding of planetary evolution in our solar system,” Adriana Ocampo, a planetary scientist at NASA Headquarters in Washington, D.C., said at a news briefing October 14.

The mission is set to launch from the Kennedy Space Center at Cape Canaveral, Fla., as early as October 16. Live coverage will air on NASA TV beginning at 5 a.m. EDT, in anticipation of a 5:34 a.m. blast off.

The Trojan asteroids are two groups of space rocks that are gravitationally trapped in the same orbit as Jupiter around the sun. One group of Trojans orbits ahead of Jupiter; the other follows the gas giant around the sun. Planetary scientists think the Trojans could have formed at different distances from the sun before getting mixed together in their current homes. The asteroids could also be some of the oldest and most pristine objects in the solar system.

The mission will mark several other firsts, from the types of objects it will visit to the way it powers its instruments. Here are five cool things to know about our first visit to the Trojans.

  1. The Trojan asteroids are a solar system time capsule.
    The Trojans occupy spots known as Lagrangian points, where the gravity from the sun and from Jupiter effectively cancel each other out. That means their orbits are stable for billions of years.

“They were probably placed in their orbits by the final gasp of the planet formation process,” the mission’s principal investigator Hal Levison, a planetary scientist at Southwest Research Institute in Boulder, Colo., said September 28 in a news briefing.

But that doesn’t mean the asteroids are all alike. Scientists can tell from Earth that some Trojans are gray and some are red, indicating that they might have formed in different places before settling in their current orbits. Maybe the gray ones formed closer to the sun, and the red ones formed farther from the sun, Levison speculated.

Studying the Trojans’ similarities and differences can help planetary scientists tease out whether and when the giant planets moved around before settling into their present positions (SN: 4/20/12). “This is telling us something really fundamental about the formation of the solar system,” Levison said.

  1. The spacecraft will visit more individual objects than any other single spacecraft.
    Lucy will visit eight asteroids, including their moons. Over its 12-year mission, it will visit one asteroid in the main asteroid belt between Mars and Jupiter, and seven Trojans, two of which are binary systems where a pair of asteroids orbit each other.

“We are going to be visiting the most asteroids ever with one mission,” planetary scientist Cathy Olkin, Lucy’s deputy principal investigator, said in the Oct. 14 briefing.

The spacecraft will observe the asteroids’ composition, shape, gravity and geology for clues to where they formed and how they got to the Lagrangian points.

The spacecraft’s first destination, in April 2025, will be an asteroid in the main belt. Next, it will visit five asteroids in the group of Trojans that orbit the sun ahead of Jupiter: Eurybates and its satellite Queta in August 2027; Polymele in September 2027; Leucus in April 2028; and Orus in November 2028. Finally, the spacecraft will shift to Jupiter’s other side and visit the twin asteroids Patroclus and Menoetius in the trailing group of space rocks in March 2033.

The spacecraft won’t land on any of its targets, but it will swoop within 965 kilometers of their surfaces at speeds of 3 to 5 meters per second relative to the asteroids’ speed through space.

There’s no need to worry about collisions while zipping through these asteroid clusters, Levison said. Although there are about 7,000 known Trojans, they’re very far apart. “If you were standing on any one of our targets, you wouldn’t be able to tell you were part of the swarm,” he said.

  1. Lucy will have a weird flight path.
    In order to make so many stops, Lucy will need to take a complex path. First, the spacecraft will swoop past Earth twice to get a gravitational boost from our planet that will help propel it onward to its first asteroid.

The closest Earth flyby, in October 2022, will take it within 300 kilometers of the planet’s surface, closer than the International Space Station, the Hubble Space Telescope and many satellites, Olkin said. Observers on Earth might even be able to see it. “I’m hoping to go near where it flies past and look up and see Lucy flying by a year from now,” she said.

Then in December 2030, after more than a year exploring the “leading” swarm of Trojans, Lucy will come back to the vicinity of Earth for one more boost. That final gravitational slingshot will send the spacecraft to the other side of the sun to visit the “trailing” swarm. This will make Lucy the first spacecraft ever to venture to the outer solar system and come back near Earth again.

  1. Lucy will travel farther from the sun than any other solar-powered craft.
    Another record Lucy will break has to do with its power source: the sun. Lucy will run on solar power out to 850 million kilometers away from the sun, making it the farthest-flung solar powered spacecraft ever.

To accomplish that, Lucy has a pair of enormous solar arrays. Each 10-sided array is more than 7.3 meters across and includes about 4,000 solar cells per panel, Lucy project manager Donya Douglas-Bradshaw said in a news briefing on October 13. Standing on one end, Lucy and its solar panels would be as tall as a five-story building.

“It’s a very intricate, sophisticated design,” she said. The advantage of using solar power is that the team can adjust how much power the spacecraft needs based on how far from the sun it is.

  1. The inspiration for Lucy’s name is decidedly earthbound.
    NASA missions are often named for famous scientists, or with acronyms that describe what the mission will do. Lucy, on the other hand, is named after a fossil.

The idea that the Trojans hold secrets to the history of the solar system is part of how the mission got its unusual name. To understand, go back to 1974, when paleoanthropologist Donald Johanson and a graduate student discovered a fossil of a human ancestor who had lived 3.2 million years ago. After listening to the Beatles song “Lucy in the Sky with Diamonds” at camp that night, Johanson’s team named the fossil hominid “Lucy.” (In a poetic echo, the first asteroid the Lucy spacecraft will visit is named Donaldjohanson.)

Planetary scientists hope the study of the Trojans will revolutionize our understanding of the solar system’s history in the same way that studying Lucy’s fossil revolutionized our understanding of human history.

“We think these asteroids are fossils of solar system formation,” Levison said. So his team named the spacecraft after the fossil.

The spacecraft even carries a diamond in one of its instruments, to help split beams of light. Said planetary scientist Phil Christensen of Arizona State University in Tempe at the Oct. 14 briefing: “We truly are sending a diamond into the sky with Lucy.”

What the Perseverance rover’s quiet landing reveals about meteor strikes on Mars

The lander was listening. On February 18, NASA’s InSight lander on Mars turned its attention to the landing site for another mission, Perseverance, hoping to detect its arrival on the planet.

But InSight heard nothing.

Tungsten blocks ejected by Perseverance during entry landed hard enough to create craters on the Martian surface. Collisions like these — whether from space missions or meteor strikes — send shock waves through the ground. Yet in the first experiment of its kind on another world, InSight failed to pick up any seismic waves from the blocks’ impacts, researchers report October 28 in Nature Communications.

As a result, researchers think that less than 3 percent of the energy from the impacts made its way into the Martian surface. The intensity of impact-generated rumblings varies from planet to planet and is “really important for understanding how the ground will change from a big impact event,” says Ben Fernando, a geophysicist at the University of Oxford.
But getting these measurements is tricky. Scientists need sensitive instruments placed relatively near an impact site. Knowing when and where a meteor will strike is nearly impossible, especially on another world.

Enter Perseverance: a hurtling space object set to hit Mars at an exact time and place (SN: 2/17/21). To help with its entry, Perseverance dropped about 78 kilograms of tungsten as the rover landed about 3,450 kilometers from InSight. The timing and weight of the drop provided a “once-in-a-mission opportunity” to study the immediate seismic effects of an impact from space, Fernando says.

The team had no idea whether InSight would be able to detect the blocks’ impacts or not, but the quiet arrival speaks volumes. “It lets us put an upper limit on how much energy from the tungsten blocks turned into seismic energy,” Fernando says. “We’ve never been able to get that number for Mars before.”