After the COVID-19 rules about social distancing went into effect, I developed a morning routine of jogging through the woods near my home. During the first months, I focused on the green branches that stretch upward towards the sky, but recently I started to notice the debris of tree trunks lying on the ground. There are many such remnants, eaten by termites, rotting and ultimately dispersing into the underlying soil. A glimpse at the forest reveals a sequence of evolutionary phases in the history of trees that lived or died at different times.
The phenomenon happens in other contexts. For example, I recently completed a nine-year term as chair of the Astronomy Department at Harvard. And only now have I begun to notice the former chairs scattered around me, just like those tree trunks in the woods.
Entering a new stage of life can be humbling. We acquire a false sense of permanence from reviewing the frozen past, as if it were a statue that will never erode. But this view is shortsighted, since each moment can also be seen a new beginning, shaped by forces beyond our control and swirling on a grander scale.
Old-fashioned astronomy was also permeated by a false sense of permanence. Astronomers collected still images of the universe, creating the impression that nothing really changes under the sun—or above it, either. But just like the revelation from my stroll through the woods, these snapshots showed stars and galaxies of different ages, at various evolutionary phases along their history. Computer simulations helped us patch together the full story by solving the equations of motion for matter, starting from the initial conditions imprinted on the cosmic microwave background at early cosmic times. By generating snapshots of an artificial cosmos similar to those captured by telescopes, these simulations unraveled our cosmic roots. The scientific insight that emerged is that the likely origins for our existence were quantum fluctuations in the early universe. Perhaps we should add “Quantum Mechanics Day” to our annual celebrations of Mother’s Day and Father’s Day.
There are some missing pages in the photo album made up of our observations, however: the period known as the cosmic dawn, for example, when the first stars and galaxies turned on. These missing pages will be filled in the coming decade by the next generation of telescopes, such as the James Webb Space Telescope (JWST), the ground-based “extremely large” telescopes and the Hydrogen Epoch of Reionization Array (HERA).
To reveal a more literal gap in the sky, the Event Horizon Telescope recently captured a still image of the silhouette of the black hole in the giant galaxy M87. The next goal is to obtain a sequence of images or a video, showing the time variability of the accretion flow around the black hole.
The tradition of still images makes sense when dealing with systems like galaxies, which evolve on a timescale of billions of years. But the universe also exhibits transient fireworks that flare up and dim during a human lifetime. Observing them is the motivation behind the Legacy Survey of Space and Time (LSST) on the Vera C. Rubin Observatory, which will have its first light soon. LSST will be a filming project, documenting nearly a thousand deep multicolor images per patch of the southern sky over a decade and recording the most extensive video of the universe ever taken with its plethora of transients in full glory.
Some of the LSST flares are expected to be the counterparts of gravitational wave sources detected by LIGO/Virgo or LISA. Their discovery will usher in multi-messenger astronomy based on both gravitational and electromagnetic waves emitted by the same sources, providing new insights about the central engines that power these transients. The related “standard sirens” could serve as new rulers for measuring precise distances in cosmology.
Within the Milky Way, transient events close to Earth could lead to catastrophe. A supernova explosion, for example, could cause a mass extinction on an unprecedented scale. If a meteor similar to the one that hit the unpopulated regions near Chelyabinsk in 2013 or Tunguska in 1908 hit New York City, it could cause a far larger death toll and economic damage than COVID-19. Or consider the impact of a blob of hot gas from the Sun, a so-called coronal mass ejection of the type that missed the Earth in 2012. Such an event could shut off communication systems, disable satellites and damage power grids. Altogether, astronomical alerts about such celestial threats could be crucial for securing the longevity of our species.
Of greatest relevance for our long-term survival is identifying large objects on a collision course with the Earth, similar to the Chicxulub asteroid that killed the dinosaurs 66 million years ago. In 2005, Congress passed a bill requiring NASA to find and track at least 90 percent of all near-Earth objects larger than 140 meters (enough to cause regional devastation) by 2020. Only a third of these objects have been identified in the sky so far. In a recent paper with my undergraduate student Amir Siraj, we explained some puzzling properties of the Chicxulub asteroid as a tidal breakup of a long-period comet that passed close to the sun. If future sky surveys alert us to another fragment whose apparent size grows rapidly against the sky, we’d better have a contingency plan to deflect its trajectory—or else immediately call our realtor.
Keeping up with the challenge of precision cosmology for the next few decades can demonstrate that the Hubble constant, which describes the expansion rate of the universe, is not really a constant, in accordance with the expected Sandage-Loeb test. In the long run, the only thing that stays constant is change. The accelerated expansion of the universe under the influence of so-called dark energy will be the ultimate manifestation of extragalactic social distancing in the post-COVID-19 era, preventing any future contact between us and civilizations outside our galaxy.
“We are truly living in a time of giants.” Lofty language like this doesn’t happen often in scientific literature. But the person who wrote them, biologist Jeremy Goldbogen, understands: When it comes to writing about whales, the scale and mystery of their lives can be difficult to overstate.
For the past two decades, Goldbogen and his network of collaborators have been piecing together a puzzle: Whales are the largest animals to have ever lived—but why? The puzzle pieces were out of reach until the turn of the current century, and in only the last few years have there been enough in place to grasp the bigger picture.
We now understand that whale gigantism is tied closely to two things: one, their choice of prey, and two, the coincidence of their evolution with a global increase in the upwelling of nutrient-rich water from the depths of the ocean.
The first baleen whales to evolve filter-fed upon plankton—essentially, tiny, drifting sea bugs. But a more recent lineage, known as the rorquals, developed a remarkable new feeding strategy known as “lunge feeding”, which allowed them to access a different type of prey: swarming schools of small fish and krill. The mechanics of this strategy align such that bigger mouths (and hence larger bodies) profit more from lunge feeding than smaller mouths or alternative modes of feeding.
And so the advent of lunge feeding (about seven to 10 million years ago) provided the energetic incentive structure for enormous size, and a sudden rise in ocean upwelling (approximately five million years ago) provided them with ample prey supply: a serendipitous recipe for bigness.
Suddenly, the rorquals had the prey supply they needed to grow. This is why the evolution of the Earth’s largest animals is a remarkably recent event. This truly is a time of giants: The Age of Whales.
But there’s an elephant in the room. Actually, it’s a blue whale.
It may be clear why rorqual whales are so large in general, but of these giants, why are blue whales so much larger than all the others? A blue whale can grow to more than 100 feet long and weigh over 150 tons. Compare this to the fin whale, the second largest animal ever: typically 80 feet long and 60 tons—less than half the blue whale’s weight. What’s going on here? What makes blue whales so special?
Answering this question, I believe, will require a few more puzzle pieces, particularly perspectives from evolutionary ecology. No single species can be understood in isolation; it evolved alongside close relatives in the context of an ever-changing environment.
The rise of lunge feeding in the rorquals was momentous. New varieties of prey were suddenly available to the lineage, and the ocean had never reckoned with a predator quite like them. But rorquals did not feed in a vacuum. Other predators—fish, seabirds and seals—were already working the prey field, and competition was fierce.
The only relief from this pressure was specialization. Not all types of swarming prey were the same, and becoming a specialist of a single kind afforded a crucial competitive edge. Some rorquals learned to target schooling fish. Some doubled-down on plankton. Others became generalists, specializing in dietary flexibility and opportunistic prey switching.
Dozens of rorqual species have arisen and died off since the advent of lunge feeding. The few lineages that persist today are a mere shadow of that old diversity, and they persist only because their specialties allow them to coexist.
And of all present-day rorquals, blue whales are arguably the most specialized. They eat krill and only krill, with very few exceptions. This, as we will see, is the key to their superlative size.
To specialize in krill is no small task. Krill can be superabundant, but only within certain isolated regions of the world ocean, such as upwelling zones and polar oceans. To stumble upon booms of krill yet survive the inevitable busts, blue whales need extreme mobility and large energy reserves. They achieve these with enormous size, sleek bodies, and small, hydrodynamic flippers. Such bodies travel more efficiently through water, and thick stores of energy-rich blubber pile on helpful momentum.
But once found, krill are not so easy to catch. A successful lunge has to be executed at speed and with an element of surprise. Some whales can outmaneuver krill, such as the long-flippered humpback whale, but blue whales have had to sacrifice maneuverability for the sake of long-range efficiency. In the arms race against krill escape, the blue whale’s best option is a larger mouth, which it achieves with a larger body. Yet again, the solution is size.
But ecological specialization is a double-edged sword in a zero-sum world. Investment in one facet of livelihood comes at the cost of others. Specialization offers some security, but it also introduces fragility. Any change to the ecosystem will tend to hurt the specialists first and worst. And the more specialized a predator becomes, the more difficult it is for it to backtrack. Instead the predator is likely to find more success investing in deeper ecological entrenchment. In this way, selection for specialization quickly becomes circular.
Blue whales literally embody this conundrum of specialization. To compete for krill, they have evolved for long-distance efficiency at the cost of maneuverability. Such a body is great for what it does, but it would flounder in vying for any other prey. The other rorquals are just too agile, with far more prey options and fewer energetic needs. And so, the blue whale must consign itself even more resolutely to a dependence upon krill.
There’s another catch to all of this. Bigness is key to the blue whale’s diet, but bigness also adds to the whale’s overall energy budget. A bigger body requires more food, which even fewer portions of the world ocean can support, thus requiring a bigger body that can travel even further with larger energy stores and greater efficiency. But a bigger body requires even more krill … and with each turn of the crank, the blue whale’s precarious life strategy becomes ever more tenuous.
And this is how blue whale has become trapped within a tautological circle of specialization: it needs to be big enough in order to eat enough to be big. The means and the end have become one and the same. Ecological entrenchment has become entrapment. The only way to get out, somehow, is to get bigger. This is why the blue whale has become the largest, by far, of the Earth’s whales.
But enough looking back. If this ecological framework is useful in explaining the blue whale’s past, can it shed any light on its future?
Today’s blue whales find themselves in a whaled and warming ocean. Only a small fraction of blue whales survived the era of commercial whaling. For example, only 0.1 percent were left in the Southern Ocean. In total, 2.9 million great whales were harvested. In some areas, mid-sized predators have increased to fill the ecological vacuum left by whaling, rendering the recovery of large whales even more difficult.
In that same time period, we have also seen long-term declines in phytoplankton production and krill abundance, driven in part by climate change and overfishing—in other words, loss of the very conditions that originally allowed for the evolution of the blue whale’s superlative size. Meanwhile, a growing shipping fleet continues to introduce noise and collide with large whales, persistent pollutants accumulate in the food web, the ocean acidifies, etc.; the list goes on.
Some whale species may readily adapt to these changing conditions—the generalist humpback whale or the small minke whale, for instance—but what about the blue whale, a specialist of cold and productive waters whose only adaptive recourse is to get bigger (and thus needier)?
This is the blue whale’s pickle: a species stuck between two predicaments, one ancient, one modern. On one side, a circular pattern of specialization for enormous size; on the other, the rapidly deteriorating food web of its ocean home. Nowhere to go, and no way to grow.
As Goldbogen and his team have noted, this is no theoretical exercise; it is a matter of conservation and posterity. In a world that increasingly favors the opportunists and generalists of the biosphere, what will happen to specialists like the blue whale? Such record-holders are a testament to the potential of life on Earth. They remind us to be humble before the ecosystems that sustain us. We take these lessons for granted already, but how worse off would we be if they were lost altogether?
Truly, we have been living in a time of giants. Let’s make sure it lasts.
Acknowledgements: The author thanks Lisa Ballance, Jay Barlow, John Calambokidis, and his hero, the late Gretchen Steiger.
Despite freezing temperatures, scores of snakes slithered out of their hibernation dens in the weeks before a magnitude 7.3 earthquake struck the Chinese city of Haicheng on February 4, 1975. The reptiles’ behavior, along with other incidents, helped persuade authorities to evacuate the city hours before the massive quake.
For centuries, people have described unusual animal behavior just ahead of seismic events: dogs barking incessantly, cows halting their milk, toads leaping from ponds. A few researchers have tried to substantiate a link. In a 2013 study, Germany scientists videotaped red wood ants that nested along a fault line and found they changed their usual routine before a quake, becoming more active at night and less active during the day. But most such attempts have relied largely on anecdotal evidence and single observations, according to a 2018 Bulletin of the Seismological Society of America review that examined 180 previous studies.
Now researchers at the Max Planck Institute of Animal Behavior and the University of Konstanz, both in Germany, along with a multinational team of colleagues, say they have managed to precisely measure increased activity in a group of farm animals prior to seismic activity. Though a definitive link has still not been proved, the scientists say their findings are a significant step forward in the search for one. “There are the old tales from Aristotle and Alexander von Humboldt, who saw this behavior,” says study co-author Martin Wikelski, managing director of the Max Planck Institute of Animal Behavior. ”But only now can we do continuous biologging of the activities and the nervousness of animals. The technical possibilities are finally there.”
The researchers used highly sensitive instruments that record accelerated movements—up to 48 each second—in any direction. During separate periods totaling about four months in 2016 and 2017, they attached these biologgers and GPS sensors to six cows, five sheep and two dogs living on a farm in an earthquake-prone area of northern Italy. A total of more than 18,000 tremors occurred during the study periods, with more seismic activity during the first one—when a magnitude 6.6 quake and its aftershocks struck the region. The team’s work was published in July in Ethology.
Earthquake damage to a house in Italy. Credit: Max Planck Institute of Animal Behavior
The paper’s statistical analysis took the animals’ normal daily movements and interactions into account. It showed their activity significantly increased before magnitude 3.8 or greater earthquakes when they were housed together in a stable—but not when they were out to pasture. Wikelski says this difference could be linked to the increased stress some animals feel in confined spaces. Analyzing the increased movements as a whole, the researchers claim, showed a clear signal of anticipatory behavior hours ahead of tremors. “It’s sort of a system of mutual influence,” Wikelski says. “Initially, the cows kind of freeze in place—until the dogs go crazy. And then the cows actually go even crazier. And then that amplifies the sheep’s behavior, and so on.”
Wikelski says this observation is consistent with collective behavior theory. That idea was pioneered, in part, by his Max Planck colleague Iain Couzin, whose lab has reported finding evidence that mammals, birds, insects and fish share information that collectively improves survival skills, such as navigation and predator avoidance. This “swarm intelligence” can happen within or across species, Wikelski says. For example, “we did a study on Galápagos marine iguanas, and we know that they are actually listening in to mockingbirds’ warnings about the Galápagos hawks,” he adds. “These kinds of systems exist all over the place. We’re just not really tuned in to them yet.”
The researchers say the farm animals appeared to anticipate tremors anywhere from one to 20 hours ahead, reacting earlier when they were closer to the origin and later when they were farther away. This finding, the authors contend, is consistent with a hypothesis that animals somehow sense a signal that diffuses outward. It holds that in the days before an earthquake, shifting tectonic plates squeeze rocks along a fault line. This action causes the rocks to release minerals that expel ions into the air, according to a 2010 study. “The animals then react to this novel sensation,” suggested the authors of a 2013 paper.
Wendy Bohon, a geologist at the Incorporated Research Institutions for Seismology in Washington, D.C., who was not involved with the new study, is skeptical of the air ionization idea. Numerous geologists have unsuccessfully tried to find such a precursory signal of impending earthquakes, she notes. Bohon does allow that Wikelski and his co-authors did some “cool things” to explore the possibility of animals predicting earthquakes. But she wonders whether there were instances in which the creatures showed unusual activity and there was no earthquake or did not react before one did occur. “My cat could act crazy before an earthquake,” she says. “But my cat also acts crazy if somebody uses the can opener.” In order to use the animals as prognosticators, it would be imperative to establish that they exhibited unusual behavior only in reaction to upcoming seismic events, Bohon says. “Otherwise,” she adds, “it becomes the ‘Boy Who Cried Wolf’ problem.”
Heiko Woith, a geologist at GFZ German Research Center for Geosciences and a co-author of the 2018 review, praised the authors of the new study for measuring more than a single occasion of abnormal behavior. But he says the time frame was still too short. Woith also points out that many studies claiming to show precursory earthquake signals often rely on too little data collection over time, making it impossible to determine whether a measured signal was related to a quake or was simply noise.
Wikelski and his colleagues say their single study could not differentiate all the potential stimuli the animals might react to. But they still argue that it is a good first step toward more controlled studies in the future. The researchers are setting up a new project in Italy, as well as one in Chile and another on Russia’s Kamchatka Peninsula. They hope to test many more species to see if those animals display sensitivity to earthquake activity. “We’re calling it a biotreasure hunt,” Wikelski says.
The biggest, most complex rover ever sent to Mars is now on its way. NASA’s Perseverance rover launched successfully on 30 July, the third of three Mars missions to launch in the space of just ten days. The rover will be the first mission ever to attempt to collect rock samples for return to Earth; it will also search for signs of ancient alien life, launch the first helicopter on the red planet and use microphones to capture Mars’s sounds for the first time.
The rover blasted into the skies above Cape Canaveral, Florida, aboard an Atlas V rocket at 7.50 a.m. local time. The launch follows the United Arab Emirates’ Mars Hope orbiter, which took off on 20 July, and China’s Tianwen-1 rover, which launched three days after that. All three capitalized on a favourable alignment between the orbits of Earth and Mars for a fuel-efficient journey.
Now, Perseverance will cruise through space for nearly seven months, aiming to land in Mars’s Jezero Crater on 18 February 2021. If it reaches the surface safely, the US$2.7-billion, plutonium-powered, 1,025-kilogram rover will spend at least one Mars year—nearly two Earth years—exploring a landscape where an ancient river flowed into a lake that might have hosted Martian life.
As well as searching the river bed and lake shore for signs of fossilized life, Perseverance will test whether astronauts could produce oxygen from the red planet’s atmosphere. But most importantly, it will fill tubes with Martian rock and soil that a yet-to-be-built spacecraft might one day fly back to Earth—in what would be the first sample return from Mars.
“Perseverance is going to do so much for us,” says Kennda Lynch, an astrobiologist at the Lunar and Planetary Institute in Houston, Texas.
The machine is a beefed-up version of the Curiosity rover, which gripped the world when it landed on Mars 8 years ago in a nail-biting 7-minute manoeuvre. After a journey of roughly 500 million kilometres, Perseverance will hit the Martian atmosphere travelling at around 19,500 kilometres per hour. It will deploy a parachute and then a ‘sky crane’ system—similar to that used by Curiosity—that will fire retrorockets to slow it down as it approaches the planet’s surface. Unlike Curiosity, the spacecraft has an autopiloting system to detect obstacles such as big rocks, and guide it to a safe location.
Once Perseverance touches down, engineers will spend around 90 days remotely checking all of its systems to make sure they’re in working order. The rover probably won’t begin rolling in earnest until May, when it will strike out on its six wheels to explore Jezero Crater, which lies about 3,750 kilometres from Curiosity’s landing site.
Jezero means ‘lake’ in several Slavic languages. More than 3.8 billion years ago, a river flowed into the 45-kilometre-wide crater, and lake waters filled it. Images suggest that along the crater’s rim, carbonate minerals settled out and hardened into rock. That’s exciting because on Earth, ancient carbonate rocks hold some of the oldest known evidence of life, including fossilized bacterial mats known as stromatolites.
If Martian life ever existed, Jezero’s carbonates are a good place to look for it. “We’ve not explored an environment like this before,” says Tanja Bosak, a geobiologist at the Massachusetts Institute of Technology in Cambridge who is working on the mission. Evidence of life could come in the form of actual fossils, or in chemical or geological signatures of organisms that once lived in the rocks.
Tools of the trade
The rover is loaded with instruments that make it a true field geologist—and truly international. They include a pair of zoomable cameras that can spot a fly from the other side of a sports field; a Spanish-built weather station; a Norwegian-built radar to scan layers of soil and rock beneath the planet’s surface; and an advanced version of a laser instrument carried on Curiosity, which will probe rocks to study their chemical make-up. “Who doesn’t love a camera with a laser that zaps rocks?” says John Grunsfeld, a former NASA astronaut who led the development of Perseverance when he ran the agency’s science office from 2012 to 2016.
Perseverance is also pioneering because it carries two microphones, which will not only reveal the winds and other sounds of Mars for the first time, but will also be able to listen for engineering problems in the motors or wheels, Grunsfeld says. And it has a 1.8-kilogram helicopter named Ingenuity, which it can deploy to scout ahead for places where the rover could roll. If the mission is successful, Ingenuity will be the first craft to make a controlled flight on another planet.
But the workhorse of Perseverance is its robotic arm, which can stretch to scrutinize rocks up close, and then drill out samples and store them in tubes in the rover’s belly. The mission will stash these samples until a future spacecraft can retrieve them and bring them back to Earth. Perseverance carries 43 tubes, “and we will use them all in the pursuit of something like 30 or 35 really good samples”, says Ken Farley, a geologist at the California Institute of Technology in Pasadena and the mission’s project scientist. NASA and the European Space Agency plan to bring those rocks back to Earth by 2031 so that scientists can study them in sophisticated laboratories—although only a small part of the funding has yet been committed.
There and back again
“Returning samples will be the first time we will have done a round trip to Mars,” Grunsfeld says. “That’s important because it’s a metaphor for human space flight. Most astronauts who go to Mars are going to want to come back.”
As a step towards that long-term exploration, the rover will use one of its instruments to attempt to produce oxygen from Mars’s carbon dioxide atmosphere. Future human astronauts might be able to do the same, to make oxygen to breathe or produce rocket fuel to get home.
The COVID-19 pandemic hasn’t made Perseverance’s last few months on Earth easy. In March, when the pandemic hit the United States, the spacecraft was in Florida being prepared for launch—but most of its engineers were in California, at the Jet Propulsion Laboratory in Pasadena. When staff needed to travel to Florida to help with final arrangements, NASA used some of its agency aircraft to transport them so they wouldn’t have to risk exposure to the coronavirus by flying commercially.
This article is reproduced with permission and was first published on July 30 2020.
Seen through the eyes of some omnipotent time traveler, our solar system—like any planetary system—is a heaving, pulsing thing. Across millions and billions of years its contents ebb and flow. Planetary orbits shift in shape and orientation, and billions of ancient asteroidal pieces shuffle through the skeletal disk that defines the major architecture of all that surrounds the sun, itself a star that sheds mass and energy as it gradually climbs an-ever brightening staircase of thermonuclear fusion.
But some things are assumed to be comparatively dull and unchanging. Saturn’s largest moon, Titan, for instance, was expected to sit in its orbit with little alteration to that position over the billions of years since its formation. Now a study published in Nature Astronomy by Lainey, et al., has used measurements from the Cassini spacecraft (which orbited Saturn from 2004 to 2017) to determine that Titan has an orbit that grows by an astonishing 11 centimeters each year.
The solution the authors propose to this new mystery rests in an intricate but powerful phenomenon that, if they are correct, could help us understand the grander history of moons around all giant worlds. To understand that, we have to step back and look at the slow changes across our solar system that are due to the complex dissipations of tides—where energy of motion is almost magically transferred into the stretching and grinding of raw materials, from rock and iron, to water and gas. Our own Earth and moon have been doing this for four billion years. The moon’s gravity pulls the spinning Earth into a distorted shape and that movement of mass in turn tugs on the moon, raising its orbit ever higher, at a rate that today amounts to a growth in distance of nearly four centimeters a year, and a corresponding spin-down of Earth’s day length by some 23 microseconds a year.
But those rates of change are intimately connected to Earth’s structure—the location of its continents, the depths and flows of its oceans, and the material composition of its rocky layers. It’s a strange thing, but if all you knew of the Earth and moon was their orbital evolution across the eons you could still learn about Earth’s fundamental construction.
In the outer solar system, the environment for natural satellites gets more complicated and interesting, with families of moons around worlds like Jupiter and Saturn that feel both the tidal interaction with their host worlds and the persistent gravitational tug of their sister moons. But we’ve mostly assumed that it’s very hard for moons to raise significant tides on giant planets, especially when, like Titan, those moons orbit at a considerable distance.
Titan’s 11-centimeter-a-year orbital expansion indicates that Saturn has to be “responding” to Titan’s gravitational pull far, far more than we might have expected. More specifically, the critical measure of how much energy is being dissipated by Titan-Saturn tides is more than 100 times larger than standard theory would predict (and possibly even 1,000 or 10,000 times larger).
So, what’s going on? The answer may be a phenomenon broadly characterized as resonance-locking tidal theory. In essence, if the internals of a planet like Saturn get “strummed” at the right frequency by the gravitational pull of a moon there’s an amplification of the tidal distortion—a kind of natural ringing, or resonance, of the thick gaseous envelope of the planet, and consequently more powerful gravitational interaction with the moon that’s doing the strumming. And because the internal structure of a gas giant evolves over billions of years (because of things like gravitational contraction and helium rain) these resonances will change over time, sometimes “locking” onto different moons’ orbital period and driving unexpectedly fast alterations in their orbits.
Lainey, et al., also follow up earlier studies of other large moons around Saturn, such as Enceladus and Dione, and find that for these too the rate of orbital change is pretty well matched by resonance-locking. The upshot is that all of Saturn’s large moons were likely originally in a much more compact configuration, and they’ve all been driven outwards over the past 4.5 billion years by resonance tides. That includes Titan, which in classical (so-called) equilibrium tidal theory, should have basically not budged from its original orbit. Instead this moon may have drifted outwards from an original formation orbit that was three to four times smaller.
It’s a fantastic reminder that nature is often full of much greater richness than we at first suspect. This result also implies that similar effects might be in play for Jupiter and its major moons—both adding insight to how those moons formed and what we might learn about the inner workings of gas giants in general. Further afield, this discovery has implications for exomoon populations, binary stars and even for cases where close-orbiting planets are raising tides in their parent stars.
For the first century of its existence, Scientific American was primarily a listing of the latest inventions and patents. But in 1948, the magazine was sold and the new owners wanted to reimagine the publication’s mission, hoping to make it more timely and authoritative. As part of this rebranding, they hired freelance artist Stanley Meltzoff to illustrate their covers. A graduate of the Institute of Fine Arts at New York University, Meltzoff had worked as an art director and journalist for an army newspaper during World War II. Afterward he made images for advertising agencies in Manhattan and paperback book covers. His work for Scientific American, a total of 65 covers, launched his career as a magazine illustrator, and he went on to create images for Life, National Geographic and Argosy. Meltzoff died in 2006 at age 89.
Scientific American covers (left to right): Photosynthesis, August 1948; Insect Metamorphosis, April 1950; Fruit Fly and Needle, October 1949. Credit: Scientific American
Meltzoff’s paintings, memorialized in this mesmerizing collection, were all done by hand, mostly as oil on board or canvas. He became an avid scuba diver and painted fish and undersea life, which became his most famous artworks. In the autobiography that accompanies the images, Meltzoff adamantly calls himself simply a “picture maker,” believing that the practical, photorealistic nature of his work did not qualify as the higher-minded creativity of an “artist.” But to examine the images in this collection, it’s hard not to feel that he was mistaken.
Scientific American cover: Bird Flight, April 1952. Credit: © 2020 Silverfish Press
Stanley Meltzoff poses under the sea, 1969. Credit: © 2020 Silverfish Press