For the first time, scientists may have detected hints of the universe’s primordial sunrise, when the first twinkles of starlight appeared in the cosmos.

Stars began illuminating the heavens by about 180 million years after the universe was born, researchers report in the March 1 Nature. This “cosmic dawn” left its mark on the hydrogen gas that surrounded the stars (SN: 6/8/02, p. 362). Now, a radio antenna has reportedly picked up that resulting signature.
“It’s a tremendously exciting result. It’s the first time we’ve possibly had a glimpse of this era of cosmic history,” says observational cosmologist H. Cynthia Chiang of the University of KwaZulu-Natal in Durban, South Africa, who was not involved in the research.

The oldest galaxies seen directly with telescopes sent their starlight from significantly later: several hundreds of millions of years after the Big Bang, which occurred about 13.8 billion years ago. The new observation used a technique, over a decade in the making, that relies on probing the hydrogen gas that filled the early universe. That approach holds promise for the future of cosmology: More advanced measurements may eventually reveal details of the early universe throughout its most difficult-to-observe eras.

But experts say the result needs additional confirmation, in particular because the signature doesn’t fully agree with theoretical predictions. The signal — a dip in the intensity of radio waves across certain frequencies — was more than twice as strong as expected.

The unexpectedly large observed signal suggests that the hydrogen gas was colder than predicted. If confirmed, this observation might hint at a new phenomenon taking place in the early universe. One possibility, suggested in a companion paper in Nature by theoretical astrophysicist Rennan Barkana of Tel Aviv University, is that the hydrogen was cooled due to new types of interactions between the hydrogen and particles of dark matter, a mysterious substance that makes up most of the matter in the universe.
If the interpretation is correct, “it’s quite possible that this is worth two Nobel Prizes,” says theoretical astrophysicist Avi Loeb of Harvard University, who was not involved with the work. One prize could be given for detecting the signature of the cosmic dawn, and another for the dark matter implications. But Loeb expresses reservations about the result: “What makes me a bit nervous is the fact that the [signal] that they see doesn’t look like what we expected.”

To increase scientists’ confidence, the result must be verified by other experiments and additional tests, says theoretical cosmologist Matias Zaldarriaga of the Institute for Advanced Study in Princeton, N.J. Several other efforts to detect the signal are already under way.

Experimental cosmologist Judd Bowman of Arizona State University in Tempe and colleagues teased out their evidence for the first stars from the impact the light had on hydrogen gas. “We don’t see the starlight itself. We see indirectly the effect that the starlight would have had” on the cosmic environment, says Bowman, a collaborator on the Experiment to Detect the Global Epoch of Reionization Signature, EDGES, which detected the stars’ traces.
Collapsing out of dense pockets of hydrogen gas early in the universe’s history, the first stars flickered on, emitting ultraviolet light that interacted with the surrounding hydrogen. The starlight altered the proportion of hydrogen atoms found in different energy levels. That change caused the gas to absorb light of a particular wavelength, about 21 centimeters, from the cosmic microwave background — the glow left over from around 380,000 years after the Big Bang (SN: 3/21/15, p. 7). A distinctive dip in the intensity of the light at that wavelength appeared as a result.

Over time, that light’s wavelength was stretched to several meters by the expansion of the universe, before being detected on Earth as radio waves. Observing the amount of stretching that had taken place in the light allowed the researchers to pinpoint how long after the Big Bang the light was absorbed, revealing when the first stars turned on.

Still, detecting the faint dip was a challenge: Other cosmic sources, such as the Milky Way, emit radio waves at much higher levels, which must be accounted for. And to avoid interference from sources on Earth — like FM radio stations — Bowman and colleagues set up their table-sized antenna far from civilization, at the Murchison Radio-astronomy Observatory in the western Australian outback.

Scientists hope to use similar techniques with future, more advanced instruments to map out where in the sky stars first started forming, and to reveal other periods early in the universe’s history. “This is really the first step in what’s going to become a new and exciting field,” Bowman says.

A new molecule that reveals active tuberculosis bacteria in coughed-up mucus and saliva could simplify TB diagnoses and speed up tests for detecting strains of the disease that are resistant to drugs.

This synthetic molecule is a modified version of a sugar that TB bacteria consume to help build their cell walls. The sugar is tagged with a dye that lights up under a fluorescent microscope — but only if the dye isn’t surrounded by water. Dubbed DMN-Tre, the hybrid molecule stays dark until it enters a fatty, water-repellant layer in a TB bacterium’s cell wall, where it starts to glow, researchers report online February 28 in Science Translational Medicine.
Standard tests use dyes that stain a bunch of different bacteria, so technicians have to bleach the dye off everything except the TB cells, says Sumona Datta, a tuberculosis researcher at Imperial College London not involved in the work. But that chemical washing is time-consuming and prone to error. Since DMN-Tre only glows when it’s gobbled up by TB or one of its close relatives, the molecule could offer a simpler, more reliable diagnosis, she says.
Tuberculosis killed 1.7 million people worldwide in 2016, according to the World Health Organization. And rampant resistance to drugs is making the disease harder to fight.
Chemical biologist Carolyn Bertozzi, a Howard Hughes Medical Institute investigator at Stanford University, and colleagues tested the new molecule on mucus-saliva mixtures hacked up by 16 people with tuberculosis. The molecule flagged TB microbes in the samples after a couple of hours, and it revealed similar amounts of bacteria as the standard staining technique — without the hassle of post-dye chemical washing.

“That’s pretty impressive,” says Jianghong Rao, a chemist and radiologist at Stanford not involved in the work. But DMN-Tre needs to be tested in a larger clinical trial before being ready for prime time, he says.

The new TB screening technique may also have an edge in checking whether patients respond to treatment, says Eric Rubin, a microbiologist at Harvard University. Because the molecule only lights up when eaten by healthy, hungry TB bacteria, it won’t flag microbes that have been crippled or killed by antibiotics as typical tests do. So if there are still lots of glowing microbes in phlegm from patients treated with an antibiotic, a doctor knows to try a different drug.

While current drug-resistance tests can take weeks or months, DMN-Tre reveals how drug-treated bacteria are faring within a few hours. “That’s tremendously exciting,” says Carlton Evans, also a tuberculosis researcher at Imperial College London not involved in the study. Speedy drug-resistance tests (SN Online: 12/7/14) could help researchers predict sooner which antibiotics stand the best chance of taking down TB bacteria.

LOS ANGELES — In the search for new superconductors, scientists are leaving no stone — and no meteorite — unturned. A team of physicists has now found the unusual materials, famous for their ability to conduct electricity without resistance, within two space rocks.

The discovery implies that small amounts of superconducting materials might be relatively common in meteorites, James Wampler of the University of California, San Diego, said March 6 at a meeting of the American Physical Society. While the superconducting materials found weren’t new to science, additional interplanetary interlopers might harbor new, more technologically appealing varieties of superconductors, the researchers suggest.
Superconductors could potentially beget new, energy-saving technologies, but they have one fatal flaw: They require very cold temperatures to function, making them impractical for most uses. So scientists are on the hunt for new types of superconductors that work at room temperature (SN: 12/26/15, p. 25). If found, such a substance could lead to dramatic improvements in power transmission, computing and high-speed magnetically levitated trains, among other things.

Space rocks are a good avenue to explore in the search for new, exotic materials, says Wampler. “Meteorites are formed under these really unique, really extreme conditions,” such as high temperatures and pressures.

What makes the meteorite superconductors special, the researchers say, is that they occurred naturally, instead of being fabricated in a lab, as most known superconductors are. In fact, says physicist Ivan Schuller, also of University of California, San Diego, these are the highest temperature naturally occurring superconductors known — although they still have to be superchilled to about 5 kelvins (–268.15° C) to work. They are also the first known to have formed extraterrestrially.

“At this point, it’s a novelty,” says chemist Robert Cava of Princeton University. Although Cava is skeptical that scrutinizing meteorites will lead to new, useful superconductors, he says, it’s “kinda cool” that superconductors show up in meteorites.
Wampler, Schuller and colleagues bombarded bits of powdered meteorite with microwaves and looked for changes in how those waves were absorbed as the temperature changed. The sensitive technique can pick out minute traces of superconducting material within a sample.

Analysis of powdered scrapings from more than a dozen meteorites showed that two meteorites contained superconducting material. However, the superconductors found within the meteorites were run-of-the-mill varieties, made from alloys of metals including indium, tin and lead, which are already known to superconduct.

“The idea is, try to look for something that is very unusual,” such as a room temperature superconductor, says Schuller, who led the research. So far, that hope hasn’t been realized — but that hasn’t deterred the search for something more exotic. For a previous study, Wampler, Schuller and colleagues scanned 65 tiny micrometeorites, but found no superconductors at all.

Since parts of space are colder than 5 kelvins, some meteorites may even contain materials that were once superconducting in their chilly natural habitat. That’s an interesting idea, Wampler says, although it’s too early to say whether that possibility might have any astronomical implications for how the objects behave out in space.

Bit by bit, Jupiter is revealing its deepest, darkest secrets.

The latest findings are in from the Juno spacecraft. And they unveil the roots of the planet’s storms, what lies beneath the opaque atmosphere and a striking geometric layout of cyclones parked around the gas giant’s north and south poles.

“We’re at the beginning of dissecting Jupiter,” says Juno mission leader Scott Bolton of the Southwest Research Institute in San Antonio. And the picture that’s emerging — still just a sketch — topples many preconceived notions. The results appear in four papers in the March 8 Nature.
Juno has been orbiting Jupiter since July 4, 2016, on a mission to map the planet’s interior (SN: 6/25/16, p. 16). The probe loops around once every 53 days, traveling on an elongated orbit that takes the spacecraft from pole to pole and as close as about 4,000 kilometers above the cloud tops.

As it plows through Jupiter’s gravity field, Juno speeds up and slows down in response to shifting masses inside the planet. By measuring these minute accelerations and decelerations, scientists can calculate subtle variations in Jupiter’s gravity and deduce how its mass is distributed. That lets researchers build up a three-dimensional map of the planet’s internal structure. At the same time, Juno snaps pictures in visible and infrared light. While other probes have extensively photographed much of the planet, Juno is the first to get an intimate look at the north and south poles.

“The whole thing is really intriguing, especially when you compare [Jupiter] to other giant planets,” says Imke de Pater, a planetary scientist at the University of California, Berkeley. “They are all unique, it looks like.”
Check out these four surprising new things we’ve learned that make Jupiter one of a kind:

1. Rings of cyclones
   Parked at each pole is a cyclone several thousand kilometers wide. That part isn’t surprising. But each of those cyclones is encircled by a polygonal arrangement of similarly sized storms — eight in the north and five in the south. The patterns have persisted throughout Juno’s visit.

“We don’t really understand why that would happen, and why they would collect up there in such a geometric fashion,” Bolton says. “That’s pretty amazing that nature is capable of something like that.”

2. More than skin deep
   Researchers have long debated whether the photogenic bands of clouds that wrap around Jupiter have deep roots or just skim the top of the atmosphere. Juno’s new look shows that the bands penetrate roughly 3,000 kilometers below the cloud tops. That’s 30 times as thick as the bulk of Earth’s atmosphere. While just a tiny fraction of Jupiter’s diameter, that’s deeper than previously thought, Bolton says.
3. Weighty weather
   Within those 3,000 kilometers lies what passes for an atmosphere on Jupiter. It’s the stage on which Jupiter’s turbulent weather plays out. The atmosphere alone is about three times as massive as our planet, or 1 percent of Jupiter’s entire mass, researchers estimate.
4. Stuck together
   Below the atmosphere, Jupiter is fluid. But unlike most fluids, the planet rotates as if it’s a solid mass. Like kids playing crack-the-whip, atoms of hydrogen and helium figuratively link arms and spin around the planet in unison, scientists report. Earlier results from Juno also indicate there’s no solid core lurking beneath this fluid (SN: 6/24/17, p. 14), so anyone dropped into the planet can expect a terribly long fall.

Many of these results are preliminary, and it’s unclear what it all means for how Jupiter operates. But what’s been learned so far, Bolton says, “is quite different than anybody anticipated.”

LOS ANGELES — In the search for new superconductors, scientists are leaving no stone — and no meteorite — unturned. A team of physicists has now found the unusual materials, famous for their ability to conduct electricity without resistance, within two space rocks.

The discovery implies that small amounts of superconducting materials might be relatively common in meteorites, James Wampler of the University of California, San Diego, said March 6 at a meeting of the American Physical Society. While the superconducting materials found weren’t new to science, additional interplanetary interlopers might harbor new, more technologically appealing varieties of superconductors, the researchers suggest.
Superconductors could potentially beget new, energy-saving technologies, but they have one fatal flaw: They require very cold temperatures to function, making them impractical for most uses. So scientists are on the hunt for new types of superconductors that work at room temperature (SN: 12/26/15, p. 25). If found, such a substance could lead to dramatic improvements in power transmission, computing and high-speed magnetically levitated trains, among other things.

Space rocks are a good avenue to explore in the search for new, exotic materials, says Wampler. “Meteorites are formed under these really unique, really extreme conditions,” such as high temperatures and pressures.

What makes the meteorite superconductors special, the researchers say, is that they occurred naturally, instead of being fabricated in a lab, as most known superconductors are. In fact, says physicist Ivan Schuller, also of University of California, San Diego, these are the highest temperature naturally occurring superconductors known — although they still have to be superchilled to about 5 kelvins (–268.15° C) to work. They are also the first known to have formed extraterrestrially.

“At this point, it’s a novelty,” says chemist Robert Cava of Princeton University. Although Cava is skeptical that scrutinizing meteorites will lead to new, useful superconductors, he says, it’s “kinda cool” that superconductors show up in meteorites.
Wampler, Schuller and colleagues bombarded bits of powdered meteorite with microwaves and looked for changes in how those waves were absorbed as the temperature changed. The sensitive technique can pick out minute traces of superconducting material within a sample.

Analysis of powdered scrapings from more than a dozen meteorites showed that two meteorites contained superconducting material. However, the superconductors found within the meteorites were run-of-the-mill varieties, made from alloys of metals including indium, tin and lead, which are already known to superconduct.

“The idea is, try to look for something that is very unusual,” such as a room temperature superconductor, says Schuller, who led the research. So far, that hope hasn’t been realized — but that hasn’t deterred the search for something more exotic. For a previous study, Wampler, Schuller and colleagues scanned 65 tiny micrometeorites, but found no superconductors at all.

Since parts of space are colder than 5 kelvins, some meteorites may even contain materials that were once superconducting in their chilly natural habitat. That’s an interesting idea, Wampler says, although it’s too early to say whether that possibility might have any astronomical implications for how the objects behave out in space.

Adult mice and other rodents sprout new nerve cells in memory-related parts of their brains. People, not so much. That’s the surprising conclusion of a series of experiments on human brains of various ages first described at a meeting in November (SN: 12/9/17, p. 10). A more complete description of the finding, published online March 7 in Nature, gives heft to the controversial result, as well as ammo to researchers looking for reasons to be skeptical of the findings.

In contrast to earlier prominent studies, Shawn Sorrells of the University of California, San Francisco and his colleagues failed to find newborn nerve cells in the memory-related hippocampi of adult brains. The team looked for these cells in nonliving brain samples in two ways: molecular markers that tag dividing cells and young nerve cells, and telltale shapes of newborn cells. Using these metrics, the researchers saw signs of newborn nerve cells in fetal brains and brains from the first year of life, but they became rarer in older children. And the brains of adults had none.

There is no surefire way to spot new nerve cells, particularly in live brains; each way comes with caveats. “These findings are certain to stir up controversy,” neuroscientist Jason Snyder of the University of British Columbia writes in an accompanying commentary in the same issue of Nature.

Zeptonewton
ZEP-toe-new-ton n.
A unit of force equal to one billionth of a trillionth of a newton.

An itty-bitty object can be used to suss out teeny-weeny forces.

Scientists used an atom of the element ytterbium to sense an electromagnetic force smaller than 100 zeptonewtons, researchers report online March 23 in Science Advances. That’s less than 0.0000000000000000001 newtons — with, count ‘em, 18 zeroes after the decimal. At about the same strength as the gravitational pull between a person in Dallas and another in Washington, D.C., that’s downright feeble.
After removing one of the atom’s electrons, researchers trapped the atom using electric fields and cooled it to less than a thousandth of a degree above absolute zero (–273.15° Celsius) by hitting it with laser light. That light, counterintuitively, can cause an atom to chill out. The laser also makes the atom glow, and scientists focused that light into an image with a miniature Fresnel lens, a segmented lens like those used to focus lighthouse beams.

Monitoring the motion of the atom’s image allowed the researchers to study how the atom responded to electric fields, and to measure the minuscule force caused by particles of light scattering off the atom, a measly 95 zeptonewtons.

“Pop” goes the knuckle — but why?

Scientists disagree over why cracking your knuckles makes noise. Now, a new mathematical explanation suggests the sound results from the partial collapse of tiny gas bubbles in the joints’ fluid.

Most explanations of knuckle noise involve bubbles, which form under the low pressures induced by finger manipulations that separate the joint. While some studies pinpoint a bubble’s implosion as the sound’s source, a paper in 2015 showed that the bubbles don’t fully implode. Instead, they persist in the joints up to 20 minutes after cracking, suggesting it’s not the bubble’s collapse that creates noise, but its formation (SN: 5/16/15, p. 16).
But it wasn’t clear how a bubble’s debut could make sounds that are audible across a room. So two engineers from Stanford University and École Polytechnique in Palaiseau, France, took another crack at solving the mystery.

The sound may come from bubbles that collapse only partway, the two researchers report March 29 in Scientific Reports. A mathematical simulation of a partial bubble collapse explained both the dominant frequency of the sound and its volume. That finding would also explain why bubbles have been observed sticking around in the fluid.

Shimmering, gelatinous comb jellies wouldn’t appear to have much to hide. But their mostly see-through bodies cloak a nervous system unlike that of any other known animal, researchers report in the April 21 Science.

In the nervous systems of everything from anemones to aardvarks, electrical impulses pass between nerve cells, allowing for signals to move from one cell to the next. But the ctenophores’ cobweb of neurons, called a nerve net, is missing these distinct connection spots, or synapses. Instead, the nerve net is fused together, with long, stringy neurons sharing a cell membrane, a new 3-D map of its structure shows.
While the nerve net has been described before, no one had generated a high-resolution, detailed picture of it.

It’s possible the bizarre tissue represents a second, independent evolutionary origin of a nervous system, say Pawel Burkhardt, a comparative neurobiologist at the University of Bergen in Norway, and colleagues.

Superficially similar to jellyfish, ctenophores are often called comb jellies because they swim using rows of beating, hairlike combs. The enigmatic phylum is considered one of the earliest to branch off the animal tree of life. So ctenophores’ possession of a simple nervous system has been of particular interest to scientists interested in how such systems evolved.

Previous genetics research had hinted at the strangeness of the ctenophore nervous system. For instance, a 2018 study couldn’t find a cell type in ctenophores with a genetic signature that corresponded to recognizable neurons, Burkhardt says.

Burkhardt, along with neurobiologist Maike Kittelmann of Oxford Brookes University in England and colleagues, examined young sea walnuts (Mnemiopsis leidyi) using electron microscopes, compiling many images to reconstruct the entire net structure. Their 3-D map of a 1-day-old sea walnut revealed the funky synapse-free fusion between the five sprawling neurons that made up the tiny ctenophore’s net.
The conventional view is that neurons and the rest of the nervous system evolved once in animal evolutionary history. But given this “unique architecture” and ctenophores’ ancient position in the animal kingdom, it raises the possibility that nerve cells actually evolved twice, Burkhardt says. “I think that’s exciting.”

But he adds that further work — especially on the development of these neurons — is needed to help verify their evolutionary origin.

The origins of the animal nervous system is a murky area of research. Sponges — the traditional competitors for the title of most ancient animal — don’t have a nervous system, or muscles or fundamental vision proteins called opsins, for that matter. But there’s been mounting evidence to suggest that ctenophores are actually the most ancient animal group, older even than sponges (SN: 12/12/13).

If ctenophores arose first, it “implies that either sponges have lost a massive number of features, or that the ctenophores effectively evolved them all independently,” says Graham Budd, a paleobiologist at Uppsala University in Sweden who was not involved in the research.

If sponges emerged first, it’s still possible that ctenophores evolved their nerve net independently rather than inheriting it from a neuron-bearing ancestor, Burkhardt says. Ctenophores have other neurons outside the nerve net, such as mesogleal neurons embedded in a ctenophore’s gelatinous body layer and sensory cells, the latter of which may communicate with the nerve net to adjust the beating of the combs. So, it’s possible they’re a mosaic of two nervous systems of differing evolutionary origins.

But Joseph Ryan, a bioinformatician at the University of Florida in Gainesville, doesn’t think the results necessarily point to the parallel evolution of a nervous system. Given how long ctenophores have been around — especially if they are older than sponges — the ancestral nervous system may have had plenty of time to evolve into something weird and highly-specialized, says Ryan, who was not part of the study. “We’re dealing with close to a billion years of evolution. We’re going to expect strange things to happen.”

The findings are “one more bit of the jigsaw puzzle,” Budd says. “There’s a whole bunch we don’t know about these rather common and rather well-known animals.”

For instance, it’s unclear how the nerve net works. Our neurons use rapid changes in voltage across their cell membranes to send signals, but the nerve net might work quite differently, Burkhardt says.

There are reports of potentially similar systems in other animals, such as by-the-wind-sailor jellies (Velella velella). Studying them in detail, along with nerve nets in other ctenophore species, could determine just how unusual this synapse-less nervous system is.

Northern elephant seals are the true masters of the power nap.

On long trips out to sea, the seals snooze less than 20 minutes at a time, researchers report in the April 21 Science. The animals average just two hours of shut-eye per day while swimming offshore for months — rivaling African elephants for the least sleep measured among mammals (SN: 3/1/17).

“It’s important to map these extremes of [sleep behavior] across the animal kingdom to get a better sense of the evolution and the function of sleep for all mammals, including humans,” says Jessica Kendall-Bar, an ecophysiologist at the University of California, San Diego. Knowing how seals catch their z’s could also guide conservation efforts to protect places where they sleep.
Northern elephant seals (Mirounga angustirostris) spend most of the year out in the Pacific Ocean. On these odysseys, the animals forage around the clock for fish, squid and other food to sustain their enormous bodies, which can be as hefty as a car (SN: 2/4/22). Because northern elephant seals are most vulnerable to sharks and killer whales at the surface, they come up for air only a couple minutes at a time between 10- to 30-minute deep dives (SN: 9/28/02).

“People had known that these seals dive almost all the time when they’re out in the ocean, but it wasn’t known if and how they sleep,” says Niels Rattenborg, a neurobiologist at the Max Planck Institute for Biological Intelligence in Seewiesen, Germany, who was not involved in the study.

To find out if the seals sleep while diving, Kendall-Bar and her colleagues developed a watertight EEG cap for the animals. Using the cap and other sensors, the team tracked the brain waves, heart rates and 3-D motion of 13 young female seals, including five at a lab and six hanging out at coastal Año Nuevo State Park north of Santa Cruz, Calif. EEG data recorded while seals were slumbering revealed what the animals’ naptime brain waves looked like.

Kendall-Bar’s team also took two sensor-strapped seals from Año Nuevo and released them at another beach about 60 kilometers south. To swim home, the seals had to cross the deep Monterey Canyon — a locale similar to the deep, predator-fraught waters frequented by seals on months-long foraging trips. Matching the seals’ EEG readings to their diving motions on this journey showed how northern elephant seals sleep on long voyages.

The animals first swim 60 to 100 meters below the surface, then relax into a glide, Kendall-Bar says. As they nod off into slow-wave sleep, the animals keep holding themselves upright for several minutes. But as REM sleep sets in, so does sleep paralysis. The animals flip upside-down and drift in gentle spirals toward the seafloor. Seals can descend hundreds of meters deep during these naps — far below where their predators normally prowl. When the seals wake after five to 10 minutes of sleep, they swim up to the surface. The whole routine takes about 20 minutes.

Looking for that distinct sleep dive motion, the researchers could pick out naps in the dive records of 334 adult seals that had been outfitted with tracking tags from 2004 to 2019. Those sleep patterns revealed that northern elephant seals conk out, on average, around two hours per day while on months-long foraging missions. But the seals sleep nearly 11 hours per day while on land to mate and molt, where they can indulge in long, beachside siestas without worrying about predators.
“What the seals are doing might be something like what we do when we sleep in on the weekend, but it’s on a much longer timescale,” Rattenborg says. He and his colleagues have found a similar feast-and-famine style of sleep in great frigate birds, which fly over the ocean (SN: 6/30/16). “Although they can sleep while they’re flying,” he says, “they sleep less than an hour a day for up to a week at a time, and once back on land, they sleep over 12 hours a day.”

Curiously, northern elephant seals’ sleep habits are quite different from how other marine mammals have been seen sleeping in labs. “Many of them … sleep in just half of their brain at a time,” Kendall-Bar says. That half-awake state allows dolphins, fur seals and sea lions to practice constant vigilance, literally sleeping with one eye open.

“I think it’s pretty cool that elephant seals are doing this without [one-sided] sleep,” Kendall-Bar says. “They’re shutting off both halves of their brain completely and leaving themselves vulnerable.” It seems the key to enjoying such deep sleep is sleeping deep in the sea.