Ancient Mars Rock and Jet-Lagged Seabirds · Morning Gist
Sunday, November 15 stories · 15 min
Ancient Mars Rock and Jet-Lagged Seabirds
Several of today's findings overturn earlier assumptions about CTE rates, how the universe cleared and where life's chemistry came from, alongside an ancient Mars rock and jet-lagged seabirds.
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Saharan meteorite Teghaza 001 was altered by Martian water 4.1 billion years ago, a rare sample from Mars's possibly habitable youth. story 1 ↓
Correcting for donation bias, Boston University estimates 74.5% of deceased NFL players had CTE, down from 99% in donated brains. story 2 ↓
Hubble data on six starburst galaxies suggest supernova winds trap, rather than release, the ionizing light that made the universe transparent. story 3 ↓
Comet strikes likely destroyed their hydrogen cyanide on early Earth, a Cambridge simulation finds; Mars received about five times more intact. story 4 ↓
Twenty years of GPS tracks from 1,045 Manx shearwaters show jet lag skews their Sun-compass headings by up to 15 degrees. story 5 ↓
Timekeepers have dropped the leap second, so atomic time will drift from Earth's rotation; a 'leap hour' may eventually be needed instead.
1/5NASA· Amanda Barnett· Oct 29
Rock from the Sahara is a 4.1-billion-year-old piece of Mars
Scientists dated individual mineral grains in an 800-gram meteorite found in Mali in 2022. It turned out to be ancient Martian crust, changed by underground water about 4.1 billion years ago.
Why it matters · Only a handful of Mars samples date from the planet's first few hundred million years. That is the period when it may have been wet enough for life.
Know this first
Context from the editor, not the article · 27 sec
1 · Mars rocks on Earth
Large impacts on Mars throw rock into space, and a few pieces eventually land on Earth. About 435 such meteorites are known. Most are fairly young volcanic rocks, so very old samples are rare.
2 · Ancient, wetter Mars
Mars's heavily cratered southern highlands are its oldest surface. Orbiters and rovers show that liquid water once shaped the planet, mostly more than about 3.5 billion years ago, before Mars lost much of its atmosphere.
3 · Clocks inside minerals
Radiometric dating measures how much of a radioactive parent isotope has turned into its daughter. Rubidium-87 decays very slowly into strontium-87, so their ratio in a mineral shows when it formed or was last reset.
2/5Science News· Aimee Cunningham· Oct 28
About three-quarters of NFL players who died had brain disease CTE
Boston University researchers studied all 2,300-plus former NFL players who died from 2008 to 2023. After correcting for which families choose to donate brains, they estimate 74.5% had the degenerative brain disease CTE.
Why it matters · The study is the first to estimate how common CTE is among all NFL players instead of only donated brains, and it shows how a skewed sample can inflate a statistic.
Know this first
Context from the editor, not the article · 28 sec
1 · What CTE is
Chronic traumatic encephalopathy is a brain disease linked to repeated head blows over years. Clumps of a misfolded protein called tau build up and damage the brain. It can only be confirmed by examining the brain after death.
2 · Why brain banks skew
CTE research depends on brains that families choose to donate. Families who watched a relative struggle with memory loss, depression or impulsive behavior are likelier to donate, so brain-bank samples overrepresent sick players.
3 · The 2017 headline
In 2017, Boston University researchers found CTE in 110 of 111 donated brains of former NFL players, about 99%. Critics and the authors both noted the sample was self-selected, so it couldn't show how common CTE is overall.
3/5Live Science· Ivan Farkas · Oct 31
Supernova winds may have trapped the light that cleared the early universe
Using Hubble, astronomers studied six nearby galaxies that resemble those of the early universe. Ionizing light escaped best from young starbursts and less once supernovas began. Most simulations predict the reverse.
Why it matters · What ended the cosmic "dark age" is a major open question about how the universe became transparent, and this result goes against an assumption built into most simulations.
Know this first
Context from the editor, not the article · 27 sec
1 · The cosmic fog
About 400,000 years after the Big Bang, neutral hydrogen atoms filled space and absorbed ultraviolet light. Later, light from the first stars and galaxies stripped electrons from that hydrogen (reionization), and the universe became transparent.
2 · Escape fraction
Galaxies make plenty of ionizing ultraviolet light, but most of it is absorbed by gas inside the galaxy. The share that gets out, called the escape fraction, decides how much a galaxy contributes to reionization.
3 · Why use local analogues
Ionizing light from galaxies that existed during reionization is absorbed before it reaches us, so it can't be measured directly. Astronomers instead study nearer, compact, fast star-forming galaxies that resemble those early ones.
4/5Universe Today· Evan Gough· Oct 28
Comets probably didn't deliver life's key ingredient intact to early Earth
Cambridge researchers simulated comet impacts on the young Earth. Most cometary hydrogen cyanide, a key starting chemical for life, broke down on the way in, and what survived was too dilute to matter.
Why it matters · It weakens a popular explanation for where life's raw chemistry came from. That points origin-of-life research back toward chemistry made on Earth itself, and possibly toward Mars.
Know this first
Context from the editor, not the article · 32 sec
1 · Prebiotic chemistry
Before life could start, simple molecules had to react and form building blocks like nucleotides and amino acids. Researchers call this prebiotic chemistry. It needs a supply of reactive starting molecules, called feedstocks, at high enough concentrations to react with each other.
2 · Why hydrogen cyanide matters
Hydrogen cyanide, or HCN, is a small, energy-rich molecule. Lab experiments going back to the 1960s show it can be turned into pieces of RNA and proteins. Many origin-of-life schemes therefore treat it as a central feedstock.
3 · Comets as delivery vans
5/5Ars Technica Science·
John Timmer
· Oct 31
Seabirds flying home over the Atlantic get jet lag that bends their Sun compass
Oxford researchers analyzed 20 years of GPS tracks from Manx shearwaters. Birds that flew far east or west in a day veered off course in the way a slightly wrong internal clock would predict.
Why it matters · It is the first clear evidence that wild animals traveling on their own get jet lag, and it shows how animals combine an internal clock, a compass and a map.
Know this first
Context from the editor, not the article · 27 sec
1 · How a Sun compass works
Many birds steer by the Sun. The Sun moves across the sky during the day, so to hold a heading a bird must know the time and adjust its angle to the Sun. That job falls to its internal circadian clock.
2 · Clock-shift experiments
For decades, researchers have tested Sun compasses by shifting a bird's internal clock with artificial light schedules. Clock-shifted homing pigeons fly off in predictably wrong directions, which shows they rely on the Sun and an internal clock.
3 · Longitude and time
Earth turns 360 degrees in 24 hours, or 15 degrees of longitude per hour. Each degree east or west therefore shifts local solar time by four minutes.
Teghaza 001, the rose-colored 800-gram meteorite found on a salt plain in Mali in 2022.1 / 3
A rose-colored, roughly 800-gram rock found in 2022 on a salt plain in Mali has turned out to be one of the oldest pieces of Mars ever found on Earth. In a paper published October 29 in Science, a team led by Yang Liu of NASA's Jet Propulsion Laboratory (JPL) reports that the meteorite, named Teghaza 001, was altered by Martian water about 4.1 billion years ago. That means the rock itself formed even earlier.
From ordinary to unusual
Researchers at the University of New Mexico first identified the rock as Martian from its 1, the mix of oxygen atom types that acts as a chemical fingerprint for each planet. It looked like a 2, the most common and usually young type of Martian meteorite. Liu nearly turned down the chance to study it. Under the microscope, though, it showed odd textures, unfamiliar minerals and 3 crystals, which are durable minerals that can be dated precisely.
Dating single grains
Caltech's Francois Tissot used his lab's 4. Most methods dissolve a whole sample. This one measures single mineral grains on the surface of a chip smaller than a fingernail, so most of the rare rock is left for later work. Tissot says few labs can do this, and his is the first to date such an old Martian meteorite this way.
Why it's unusual
Only two other Martian meteorites are as old, and each reveals less. 5 is of similar age but is made almost entirely of one mineral. "Black Beauty" is a jumble of volcanic fragments that, according to the release, formed about 2.1 billion years ago. Teghaza 001 contains a mix of 6 minerals, meaning minerals that crystallized from cooling magma. That mix records how the crust formed and how underground water later changed it. Its mineralogy matches what NASA's 7 sees in the cratered 8. The team lists 13 places on Mars where it could have come from.
Second author Lee Saper calls it the first sample from a part of Mars never sampled before, one that may even hold "an imprint of the Martian atmosphere as it was losing water." A separate Science Advances paper published in June measured the rock's water content.
Caveats
This is a first description, and the release comes from NASA, which funded the work. It gives no exact formation age, no error bars and no detailed water findings. It says only that the evidence points to a "much more dynamic water cycle" on early Mars. The exact launch site on Mars will never be known.
A rock that sat on a salt plain in Mali has turned out to be one of the oldest pieces of Mars ever found on Earth. In a paper published October 29 in Science, researchers led by Yang Liu of NASA's Jet Propulsion Laboratory (JPL) give a first description of Teghaza 001, an 800-gram (nearly 2-pound) rose-colored meteorite found in the Sahara in 2022. It is named after the Teghaza salt plain where it was found. Its minerals show that Martian water altered it about 4.1 billion years ago, so the rock formed earlier than that. One of the paper's reviewers called it "a Rosetta Stone for Mars."
Why old Mars rocks are scarce
About 435 Martian meteorites are known. Each was blasted off the planet by an impact, drifted through space and eventually fell to Earth. They are usually found in deserts or on snowy plains, where a dark or unusual stone stands out. Scientists confirm a meteorite is Martian by comparing its minerals and chemistry with measurements from Mars missions, including the Viking landers and the Curiosity and Perseverance rovers.
The difficulty is age. Mars's earliest period, before it lost much of its atmosphere and surface water, is the most interesting one for questions about climate and habitability. Rocks from that time are rare in the meteorite collection. Before Teghaza 001, only two ancient Martian meteorites were known, and the release argues that each offers a limited view:
1, found in Antarctica, is about as old as Teghaza 001 but is made almost entirely of one mineral, so it records little variety.
"Black Beauty" is a breccia, a rock made of cemented fragments, here small volcanic pieces. The release says it formed about 2.1 billion years ago.
Teghaza 001 differs because it contains a mix of 2 minerals, meaning minerals that crystallized from cooling magma. Together they record how the crust solidified, and the rock's texture and chemistry also show how subsurface water later changed it.
Nearly passed over
The rock first looked routine. Researchers at the University of New Mexico identified it as Martian from its 3. Oxygen comes in several isotopes, versions of the atom with different masses. Each planetary body has its own characteristic ratio of them, so the ratio works like a fingerprint. Teghaza 001's ratio matched other Martian meteorites. It also looked like a 4, the most common class of Martian meteorite. Shergottites are volcanic rocks and usually geologically young.
Liu, a planetary-sample specialist, had seen many shergottites and almost declined to study it. When she looked, she found textures and minerals she hadn't seen before. She also found 5 crystals. Zircon is a very durable mineral that traps radioactive elements as it grows, which makes it one of geology's best minerals for precise dating.
How the age was measured
Caltech coauthor Francois Tissot applied an 6 method his team developed. The principle is straightforward. Rubidium-87 decays very slowly into strontium-87, with a half-life of about 49 billion years. A mineral that took in rubidium when it crystallized slowly builds up strontium-87. Measure the ratio of the two in several minerals from the same rock and you can calculate when the system was last "set." That moment is either when the rock formed or when an event such as hot-water alteration reset the clock.
The new part is in situ, meaning "in place." Standard bulk analysis dissolves a whole sample and measures the mixture. Tissot's method measures individual mineral grains on the surface of a piece smaller than a fingernail. The release describes three advantages: high precision, speed, and the fact that most of the sample survives for other studies. That matters for a rock that exists only once. The release does not describe the instrument used. Tissot says his lab is one of very few able to do this and the first to date such an ancient Martian meteorite with it. He hopes the method will be used on more Martian meteorites and on samples returned from other planets, moons and asteroids.
When the results came in, the alteration date was about 4.1 billion years ago. Liu says she was shocked. Because water changed the rock at that point, the crust itself must be older.
Where on Mars
No one can say exactly where on Mars the rock came from. Its mineralogy does match what NASA's 7, a spacecraft that maps surface minerals from orbit, has seen in the 8. This heavily cratered terrain is among the oldest on the planet. The team found 13 locations whose mineralogy and chemistry match the meteorite. Second author Lee Saper, who did the work as a JPL postdoc and is now at NASA's Ames Research Center, calls it "our first piece of Martian crust from a part of Mars we've never had a sample of before." He adds that it may preserve "an imprint of the Martian atmosphere as it was losing water."
Water
The team says oxygen-isotope, textural and chemical clues together point to a "much more dynamic water cycle" on early Mars. A separate paper published in Science Advances in June measured the meteorite's water content. The release gives no figures from either paper, so how much water there was, how hot it was and how long it acted are not described here.
What's open
This is a first characterization, published in a peer-reviewed journal and summarized in a NASA press release about NASA-funded work. Several things are missing from the release:
An exact formation age. It gives only "more than 4.1 billion years," with no uncertainties.
The age of the zircons themselves, as distinct from the alteration date.
How the rock relates to the shergottite class, given that it was first taken for one.
The details of the water story and the atmospheric "imprint" Saper mentions.
The authors say they expect the wider community to study the rock further. "We've only scratched the surface," Liu said. The single-grain dating may matter beyond this one meteorite. If it is as precise and sparing as described, it could be used on the small, precious samples that future missions bring back from Mars.
Remember
Water altered Teghaza 001 about 4.1 billion years ago, so its crust formed earlier, in Mars's poorly sampled early era.
The team dated single grains on a chip smaller than a fingernail, leaving most of the rare rock intact.
It nearly went unstudied because it looked like an ordinary shergottite, the most common Martian meteorite type.
NFL players at the line of scrimmage. Repeated hits like these over a career are linked to CTE.
Boston University researchers estimate that 74.5% of former National Football League (NFL) players who died between 2008 and 2023 had 1, or CTE. The study appeared October 28 in the peer-reviewed journal 2. The team calls it the first estimate of CTE's prevalence across the whole population of NFL players.
The disease
CTE is a degenerative brain disease linked to repeated head impacts over years. It shows up in contact-sport athletes, combat veterans and survivors of domestic violence, and most often in American football players. In CTE, 3, a protein that normally helps nerve cells work, forms damaging clumps. Symptoms in life can include memory loss, poor concentration, depression and impulsivity. The diagnosis can only be confirmed at autopsy.
Why the old 99% figure was misleading
Because diagnosis requires a brain, research depends on families donating one. A 2017 analysis of donated brains found CTE in about 99% of former NFL players. But families who saw a relative decline have more reason to donate. That kind of 4 loads brain banks with players who were likely sick already.
How the new estimate works
The team counted every former NFL player who died from January 2008 through December 2023, more than 2,300 men. Almost 400 had brains in the university's 5, a research collection of donated brains. The rest were identified through the U.S. 6, a federal database of death records.
The researchers found that families of players with CTE-related symptoms were five times more likely to donate than families of players without symptoms. They adjusted the brain-bank results for that imbalance, which effectively gives extra weight to the under-donated, symptom-free players. With that correction, they arrived at 74.5%.
As an illustration with made-up numbers: if half of 1,000 players had CTE and their families donated at five times the rate of other families, a brain bank could show about 83% prevalence when the true figure was 50%.
Caveats
Only about 400 brains were examined. The rest of the estimate rests on a statistical model of why families donate.
The players who died in this window mostly played decades ago, so the figure may not apply to current players.
The article doesn't break cases down by severity.
The work comes from the same group behind the 2017 figure and hasn't yet been independently replicated.
The result is lower than 99% but still high: roughly three in four former players who died in this period had the disease.
A Boston University team estimates that 74.5% of former National Football League (NFL) players who died between January 2008 and December 2023 had 1 (CTE), a degenerative brain disease. The result appeared October 28 in 2, a peer-reviewed journal. According to the researchers, it is the first estimate of CTE's prevalence across the whole population of NFL players, not just the players whose brains reached a laboratory.
The disease and how it's diagnosed
CTE is linked to repeated blows to the head over many years. It has been found in contact-sport athletes, military combat veterans and survivors of intimate partner violence. It has been identified most often in American football players. Earlier research on football players suggests that the longer someone takes repeated head impacts, the higher the risk and the more severe the disease.
The disease centers on 3, a protein that normally helps nerve cells function and communicate. In CTE, tau goes wrong and forms irregular, damaging clumps in brain tissue. People later diagnosed with CTE may have had memory problems, trouble concentrating, depression and poor impulse control while alive. But those symptoms aren't specific to CTE. The diagnosis can only be confirmed at autopsy, by looking for the characteristic tau deposits.
Why 99% wasn't the real number
Because diagnosis needs a brain, research depends on donations. In 2017, researchers reported CTE in an estimated 99% of former NFL players whose brains had been donated. That figure was widely quoted, but it described the donated brains, not all players.
The problem is 4. A family that watched a relative lose his memory or change personality has a strong reason to want answers and to donate his brain. A family whose relative aged without obvious problems has less reason. So brain banks fill up with players who were already likely to have the disease.
What the new study did
The team started with every former NFL player who died during the 16-year window, more than 2,300 men. Almost 400 had brains in the university's 5, a collection of donated brains used for research on head trauma. The rest were identified through the U.S. 6, a federal database of death records.
The researchers then measured how strong the donation bias was. Families of players who had CTE-related symptoms in life were five times more likely to donate the brain than families of players without symptoms. After adjusting for that difference, they arrived at 74.5%.
The article doesn't describe the statistical method in detail. A simple illustration (made-up numbers, not from the study) shows how a bias of this size distorts a count, and how a correction works. Picture 1,000 players, half of whom have CTE. Assume for simplicity that everyone with CTE had symptoms and no one else did. If 10% of symptomatic families donate and 2% of the others do, which is the five-to-one ratio, the bank receives 50 diseased brains and 10 healthy ones. The bank then shows 83% prevalence when the true figure is 50%. To correct, each under-donated healthy brain is counted as standing in for five times as many players. In the real study, CTE and symptoms don't line up perfectly, which is why the corrected figure stays high.
How to read 74.5%
The corrected number is lower than 99%, but it still means about three in four players who died in this period had the disease. The researchers argue that knowing the true prevalence matters for understanding CTE's public health impact. A figure drawn from a skewed sample can't measure that.
Some caveats, several of which the article doesn't address:
It's a modeled estimate. Only about 400 of the 2,300-plus players had brains examined. The 74.5% figure depends on how well the correction captures why families donate. If donation is influenced by factors beyond symptoms, the estimate could be off in either direction.
It covers players who died between 2008 and 2023. Most of them played in earlier decades, under different rules and with different equipment. The figure may not apply to today's players or to those still living.
"Having CTE" covers a range. CTE is graded by severity, and the article doesn't say how many cases were mild versus severe. It also doesn't say how the tau findings relate to the symptoms players actually experienced.
This is one research group. Boston University runs the brain bank that produced the 2017 figure. Independent replication would strengthen the result.
What's still open
The study narrows a large uncertainty: CTE in former NFL players looks common, though not nearly universal. Whether it can be diagnosed in living people, how risk scales with years of play and position, and what the figure is for amateur and youth players are questions this study doesn't answer.
Remember
Families of symptomatic players were five times likelier to donate brains, which skewed earlier CTE figures upward.
Only about 400 of 2,300-plus players' brains were examined; the 74.5% rests on a statistical correction.
The players studied died between 2008 and 2023 and mostly played decades ago, so the figure may not apply to today's game.
Timeline from the Big Bang to today, showing the first stars forming out of the hydrogen fog.
Supernovas are often credited with helping the early universe become transparent. A new study suggests they may have done the opposite. Using the Hubble Space Telescope, Cody Carr of the University of Michigan and colleagues found that galaxies with strong supernova-driven winds let out the least ionizing light. The work was published Oct. 15 in the peer-reviewed journal Nature Astronomy.
The problem
After about 400,000 years, the young universe was filled with neutral hydrogen, which absorbs ultraviolet light. Radiation from the first stars and galaxies later ionized that gas, splitting the atoms into protons and electrons, and space became transparent. This was the 1. The light responsible is 2 radiation, ultraviolet photons energetic enough to strip hydrogen's electron.
Galaxies make plenty of LyC light, but their own gas soaks most of it up. The standard idea, built into most simulations, is that supernova blasts drive winds that clear channels for the light to escape.
The test
Early galaxies can't be measured directly, because the fog of that era absorbs their LyC light. So the team studied six nearby stand-ins about 3.5 billion light-years away. These compact 3 are under 6,500 light-years across and form about 10 solar masses of stars a year, several times the Milky Way's rate. Hubble 4, which split each galaxy's light by wavelength, showed the speed, direction and makeup of the outflowing gas. Because the galaxies' starbursts were at different ages, the team could follow how winds and light escape change over time.
Two phases
In the first ~3 million years, winds from newborn massive stars cut through the surrounding gas at nearly 3,000 km/s, and LyC light escaped. After that, the most massive stars began to explode. Their debris added mass to the gas and stirred it up, trapping the light. The galaxies with the fastest supernova winds let out the least LyC light.
"The strongest LyC emitters do not have fast 5," Carr said. He noted that this contradicts simulations in which light escape peaks after supernova winds start. Newborn stars' own light, in the short window before any of them explode, now looks like the main driver of reionization.
Caveats
This rests on six galaxies. They are analogues that are far younger and closer than true reionization-era galaxies, and their timeline comes from comparing snapshots of different galaxies. The authors want larger samples and higher-resolution observations at other wavelengths.
A new study suggests that supernovas, often treated as the force that let starlight clear the early universe's hydrogen fog, may have done the opposite. Cody Carr of the University of Michigan and colleagues used the Hubble Space Telescope to study six nearby galaxies. The ones leaking the most ionizing light had no fast supernova-driven winds. The galaxies with the strongest supernova winds leaked the least. The work was published Oct. 15 in the peer-reviewed journal Nature Astronomy.
The problem: what cleared the fog?
About 400,000 years after the Big Bang, the universe had cooled enough for electrons and protons to combine into neutral atoms, mostly hydrogen. Neutral hydrogen absorbs ultraviolet light strongly, so the cosmos was opaque to it. A few hundred million years later the first stars switched on and gathered into galaxies. Their radiation ionized the hydrogen, splitting it back into protons and electrons, and light could then travel freely. This period is the 1, which the researchers call the "last major phase transition in the universe."
The light that does this work is 2 radiation: ultraviolet photons energetic enough to knock the electron off a hydrogen atom. Every young galaxy makes LyC light. The hard part is getting it out. The gas and dust inside a galaxy absorb most of these photons before they reach intergalactic space. The share that escapes, the 3, is what decides whether a galaxy helps reionize the universe.
"We don't know exactly what objects caused reionization or how it evolved," Carr said. "We know that it took place, but we don't have complete answers to those questions."
The usual answer to how the light gets out has involved supernovas. Stars of roughly 8 to 50 solar masses end in these explosions, and the idea is that their energy drives 4 that blow holes in the surrounding gas, opening channels for LyC photons. Most cosmological simulations build in this sequence: in Carr's words, they "typically show the LyC escape fraction peaking after the launch of supernova-driven winds."
How the team tested it
Ionizing light from galaxies that existed during reionization can't be measured directly, because the neutral hydrogen of that era absorbs it on the way to us. So the team studied stand-ins. They chose six compact 5 galaxies about 3.5 billion light-years away. Each is under about 6,500 light-years across and forms around 10 solar masses of stars per year. The Milky Way is up to 20 times larger, and these galaxies form stars several times faster than it does.
Hubble recorded their 6, which split each galaxy's light by wavelength. Absorption and emission features in a spectrum show where outflowing gas came from, what it is made of, and how fast it is moving and in which direction. Because each galaxy's starburst is at a different age, the team could put together a sequence of how a galaxy's winds change as its stars age, and how much LyC light gets out at each stage.
What they found: two phases
Phase one, the first ~3 million years. Newly formed massive stars drive stellar winds, gas pushed off the stars by their own intense radiation. These winds tore through the surrounding neutral gas and dust at nearly 3,000 kilometers per second (about 2,000 miles per second). They cleared paths, and LyC light escaped into intergalactic space.
Phase two, after ~3 million years. The most massive stars, the hot, blue 7, burn out quickly and explode. Their ejected material added mass to the gas around them and stirred it up, which thickened the barrier instead of clearing it. Winds driven by the supernovas overtook the stellar winds, and LyC light got trapped. (The article's text says this happened "several billion years later." That conflicts with its own 3-million-year timeline and with the short lives of massive stars, which last only a few million years, so it looks like an error.)
One analogy for intuition, not from the study: the first phase is like a fan blowing a clean tunnel through smoke. The second is like dumping more smoke into the tunnel and stirring it. Both push gas outward fast, but only the first leaves a clear path.
The pattern held across the sample. The oldest starbursts had the fastest supernova-driven winds and let out the least ionizing radiation. "The most interesting thing about our paper is the observation that the strongest LyC emitters do not have fast galactic winds," Carr said. "This challenges the notion that galaxies require fast supernova-driven winds to enable LyC escape."
What it implies
If the result holds, supernovas did not drive reionization and may have slowed it. The best candidate becomes the direct light of newborn massive stars in the brief window before any of them explode. That matters for simulations, because it changes when and for how long each galaxy contributes ionizing light. It may also shift which kinds of galaxies dominated reionization.
Caveats and open questions
Six galaxies is a small sample. The two-phase picture rests on a handful of objects, and the authors themselves call for larger samples.
These are analogues, not the real thing. Galaxies 3.5 billion light-years away are much younger than the universe at reionization, which was more than 13 billion years ago. Early galaxies had less heavy-element content and different surroundings, so the resemblance is assumed, not proven.
Inferring age sequences from snapshots. Each galaxy is seen at one moment. The timeline comes from comparing galaxies at different stages, not from watching one galaxy change.
Other wavelengths needed. The team suggests higher-resolution observations at other wavelengths to check the picture.
The article doesn't give measured escape fractions for the six galaxies, and it doesn't say how the team estimated each starburst's age. Those are the details a reader would need to judge how strong the trend is.
Remember
Light escaped most during the first ~3 million years of a starburst, before any supernovas.
Supernova debris adds mass to the surrounding gas and stirs it up, trapping ionizing light instead of clearing a path.
The result rests on six nearby analogue galaxies, so it needs larger samples.
Comets are porous lumps of ice and dust left over from the Solar System's formation. Space missions such as ESA's Rosetta found glycine, phosphorus and HCN on comet 67P. That led to a long-standing idea that comet impacts stocked the early Earth with these molecules.
Rosetta at comet 67P, where glycine, phosphorus and other organics were detected.1 / 3
Comets carry many of the molecules that origin-of-life chemists care about. The European Space Agency's 1 mission found glycine (an amino acid), phosphorus and 2 on comet 67P. That gave rise to a popular idea: comet impacts stocked the young Earth with the raw materials for life.
A new study in Scientific Reports, led by Richard Anslow of the University of Cambridge's Institute of Astronomy, concludes that this delivery was "an exceedingly rare event." "It's kind of a romantic idea," Anslow says, "but our results suggest it's highly unlikely."
The problem: carrying isn't delivering
The team focused on HCN, a small, energy-rich molecule that lab experiments can turn into building blocks of RNA and proteins. HCN is also fragile. A 2020 study found that only the gentlest impacts, slow and small, stay cool enough for it to survive. The new question was how many such impacts Earth actually received.
How they tested it
The researchers ran a 3: they generated many random comet impacts based on models of real comet populations and counted the outcomes. They used 4, which orbit the Sun in about 200 years or less and hit more slowly than long-period ones. This is the best case for HCN surviving. Several steps remove candidates along the way:
Break-up in space. Gas jetting off a comet near the Sun can spin it up until it flies apart. Small comets are hit hardest.
Atmospheric filtering. Comets are porous and weak, so Earth's atmosphere destroys small comets and those arriving at a slant.
A short window. Bombardment fell off sharply after Earth's first 500 million years or so.
The result: only a handful of comets could have delivered HCN at all, and never at concentrations useful for prebiotic chemistry.
A fallback idea holds that impact craters create hot underground water systems where delivered HCN could react. The authors argue that groundwater would rush into the new crater lake and dilute it too much. Anslow calls success "a one-in-a-million occurrence" (a figure of speech, not a computed odds), though "we can't rule out for certain" that it happened.
Mars did better
On Mars, about five times as many comets survived to the surface. Impacts there are slower because of its weaker gravity and wider orbit, and its thin atmosphere filters out less. The authors call this a best case. Anslow notes the "perhaps more likely" alternative: comet delivery didn't happen on either planet.
Caveats
This is a peer-reviewed modelling study of one delivery route, focused mostly on one molecule. The article doesn't give the simulated concentrations or say how sensitive the results are to the model's assumptions.
The claim being tested
Comets carry many of the small organic molecules that origin-of-life chemists care about. The European Space Agency's 1 mission orbited comet 67P/Churyumov–Gerasimenko from 2014, and its Philae lander touched down that year. Together they detected the amino acid glycine, phosphorus (an element in the backbone of DNA and RNA), and 2. Philae's COSAC and Ptolemy instruments, two onboard chemical analysers, picked up sixteen organic compounds on the surface. From finds like these grew a hypothesis: that comet impacts on the young Earth delivered the raw materials for 3, the emergence of life from non-living chemistry.
A new paper in Scientific Reports, led by Richard Anslow of the University of Cambridge's Institute of Astronomy, concludes that this delivery route was "an exceedingly rare event." The title puts it bluntly: "Cometary impacts an unlikely pathway towards the origins of life on Earth." It is a modelling study, not an observation or experiment, so its strength depends on the assumptions fed into the simulations.
Why carrying is not the same as delivering
The authors focus on HCN, which they call "a key feedstock molecule" because it can drive the high-energy reactions behind prebiotic synthesis. HCN is also fragile. A comet hits at hypervelocity, many kilometres per second, and the shock heating can break molecules apart. Earlier work already pointed this way. A 2020 study by Todd and Öberg found that only "the most favorable impacts (low impact angle, low velocity, small radius)" stay below the temperature at which HCN is destroyed. Anslow's team takes that impact-survival physics as given. The question they add is how many such favourable impacts the early Earth actually received.
How the model works
The team ran a 4 of Earth's cometary bombardment. The method draws many random comets from realistic distributions of size, speed and angle, then tallies the outcomes. It combines three kinds of input:
Dynamical models of where 5 come from and how their orbits change over time. Short-period comets orbit the Sun in roughly 200 years or less. The authors chose them because they hit at much lower speeds than long-period comets, which gives HCN its best chance of surviving. In effect, this is the best case for delivery.
Comet break-up before arrival. As a comet nears the Sun, jets of escaping gas push on it unevenly. Like thrusters on a spinning top, they can spin it up until it flies apart. Small comets are most at risk, so fewer of them ever reach Earth.
Atmospheric entry. Comets are porous and mechanically weak. The authors describe the atmosphere as "a filter," one that "preferentially" destroys small comets and those coming in at a slant before they reach the ground.
On top of this, the bombardment dropped off steeply after roughly the planet's first 500 million years, as the young Solar System ran out of loose bodies. Combine a short window, break-up in space, the atmospheric filter and destruction on impact, and the authors find that only a handful of comets could have delivered any HCN at all. Globally, they agree with Todd and Öberg that comets could not supply a "prebiotically relevant concentration."
The crater-lake fallback
One rescue for the idea holds that a large impact also creates a 6: hot water circulating through fractured rock under the crater. Some researchers see this as a promising setting for early chemistry, because cometary HCN would arrive right where it could react. The authors argue against it. A high-speed impact causes "the rapid influx of local groundwater into the newly-formed crater-lake." That water would dilute any surviving HCN below useful levels. Concentration is the point: a few molecules spread through a lake do nothing.
Anslow sums up the chain of requirements: "not only would you need an impact at just the right speed and just the right angle, you would also need everything to happen after that point." He calls it "a one-in-a-million occurrence," which is a figure of speech, not a calculated probability. He adds that "we can't rule out for certain that it happened that way."
Mars comes out ahead
The team ran the same analysis for Mars. Fewer comets hit it, but delivery was "far more effective," with surviving comets about five times as common as on Earth. There are two reasons. First, comets strike Mars more slowly, because the planet has weaker gravity (a lower 7) and sits farther from the Sun (a larger 8, meaning a wider orbit). Second, its thin atmosphere destroys fewer small comets. All else being equal, the authors say, Mars was the better target, and if comet delivery matters at all, that "strengthens the possibility that life could have emerged on Mars."
They call this a best-case scenario that other factors weaken. Anslow frames the logic as a conditional: if comet delivery worked on Earth, it would be odd for it to fail on Mars. "Or the other, perhaps more likely, alternative, is that it didn't happen on either planet."
What this does and doesn't show
The study is about one route, delivery of intact molecules by comets, and mainly about one molecule, HCN. It doesn't rule out other things comets may have contributed, such as impact energy or elements, and it doesn't address meteorites or asteroids. The article doesn't give the simulated HCN concentrations, the threshold counted as "prebiotically relevant," or how sensitive the results are to assumed comet sizes and break-up rates. Those numbers would show how strong the conclusion is. The paper is peer-reviewed, but its conclusion rests on models of a bombardment no one observed. The result moves the burden of proof toward HCN being made on Earth itself, which leaves the origin of life's chemistry an open problem.
Remember
Earth's atmosphere filters comets, destroying small and slanting ones before they reach the ground.
Even surviving HCN would likely be diluted by groundwater flooding into the new crater.
The result rests on simulations of an unobserved bombardment, not on direct evidence from early Earth.
1, long-winged seabirds that breed around the UK and Ireland, get jet lag on their long flights home across the North Atlantic. A study in Science led by Patrick Lewin of the University of Oxford shows that the jet lag leaves a measurable trace: it bends the 2 the birds use to steer.
Why a Sun compass needs a clock
Shearwaters feed up to 1,000+ km out to sea. To get home, they are thought to work out where they are with a "3," possibly based on smell, and then pick a direction using the Sun. The Sun moves across the sky, though. A bird heading south must keep the Sun on its left at dawn, dead ahead at noon and on its right at dusk. That requires knowing the time, which the bird's internal 4 provides.
The shearwater clock resets only at dawn and dusk. Earth turns 15 degrees of longitude per hour, so each degree a bird flies east or west during the day leaves its clock four minutes off local time. A bird flying east thinks it is earlier than it is, misjudges where the Sun should be, and veers clockwise. A bird flying west veers anticlockwise.
Finding a small effect in a large dataset
Clock-shifting had been demonstrated in captive or relocated birds, but never in wild animals traveling on their own, because the effect is small. Oxford researchers have GPS-tagged shearwaters since 2004. They now have 3,688 foraging trips from 1,045 birds. Homeward legs are easy to spot because the birds switch from wiggly foraging to fast, straight flight.
For each flight, the team noted where the bird last saw sunrise and calculated how much its east–west travel since then should have skewed its compass. They then compared that prediction with how the bird actually strayed from a straight line to its burrow.
Results
The clock offsets were usually 10–15 minutes, with about an hour at most. Even so, across 335 homing flights out of sight of land, the birds veered as the Sun-compass model predicted, by up to about 15 degrees. The study is observational, and Lewin urges caution about cause. Still, crosswinds, the 5 (the apparent deflection caused by Earth's rotation) and a magnetic compass all fit the data worse.
The cost is small. A bird flying 1,000 km east in a day would average about a 7-degree error. If it keeps checking its position, that adds only about 5 km to the trip.
Still open
Birds following coastlines also drifted slightly toward or away from shore, which hints that compass and landmark navigation run in parallel. No one yet knows whether shearwaters have other jet-lag symptoms, or whether the effect touches their foraging or breeding. Lewin suspects many fast fliers and polar animals face the same problem.
A study published in Science shows that 1, long-winged seabirds that breed around the UK and Ireland, give themselves jet lag on long flights over the North Atlantic. Because they steer partly by the Sun, the mismatch between their internal clock and local time shows up as a small, predictable error in their heading. The work was led by Patrick Lewin, a behavioral and sensory ecologist at the University of Oxford. It draws on two decades of GPS tracking.
The problem: a compass that moves
Shearwaters nest in burrows on coastal islands, and about half the world's population lives in Wales. To feed, they fly anywhere from a few dozen to more than 1,000 kilometers out into the Atlantic. To get home, they are thought to work out where they are with a "2," possibly based on smell, and then use the Sun as a compass to choose a direction.
The Sun is an awkward compass because it moves. Lewin gives an example: an animal heading south all day must fly 90 degrees clockwise of the Sun at sunrise, straight toward it at midday, and 90 degrees anticlockwise of it at sunset. That only works with an accurate sense of the time of day. Birds, like nearly all animals, have an internal 3 that supplies it.
Why travel throws the clock off
The shearwater clock resets at every dawn and dusk. Between those resets it keeps running on the time where the bird last saw the Sun rise or set. Earth turns 15 degrees of longitude per hour, so every degree a bird travels east or west between sunrise and sunset puts its clock four minutes out of step with local time.
Here is an illustrative example (not from the study). At the latitude of Wales, roughly 52°N, one degree of longitude spans about 70 kilometers. A bird that flies 700 km east during one day covers about 10 degrees, so its clock runs about 40 minutes slow. Local noon arrives while the bird's clock still reads late morning. It expects the Sun to sit further east than it actually is, and so it misreads its heading. The prediction is that eastbound birds veer clockwise and westbound birds veer anticlockwise.
Researchers had already shown this effect artificially. They caught penguins and quickly moved them across lines of longitude, and they shifted pigeons' clocks with light schedules. No one had clearly shown it in wild animals traveling under their own power. The effect is small and gets lost in the noise unless you have a very large dataset.
Twenty years of tracks
The Oxford group had that dataset. In 2004, when GPS tags first became small enough for a pigeon-sized bird, Tim Guilford (Lewin's supervisor) and long-time shearwater researcher Chris Perrins began tagging birds. Since then the team has logged 3,688 foraging trips by 1,045 birds from colonies along Britain's western coasts. Trips last from one day to two weeks.
Homeward legs were easy to pick out. While foraging, shearwaters make short, wiggly flights between dives. When they decide to go home, Lewin says, they switch to flying "as fast as they can in pretty much a straight line" for long stretches.
For each homing flight, the team found where the bird last saw sunrise, the point at which its clock should have matched local time. At every later GPS fix they calculated how far east or west it had traveled since then, and therefore how far its 4 should be bent. They knew the destination, the bird's own burrow, so they could compare that predicted bias with how far the bird actually strayed from a direct course.
What they found
The clock offsets were small. Lewin says about an hour was the most they observed, and most were probably 10 to 15 minutes. Those offsets would be imperceptible to a person, but they still left a detectable mark on the birds' headings. Across 335 homing flights made out of sight of land, the birds veered in the directions the Sun-compass model predicted. Errors reached up to about 15 degrees.
The study is observational, not a controlled experiment, and Lewin cautions against drawing firm conclusions about cause. The team did test other explanations. They calculated the biases expected from crosswinds, from the 5 (the apparent deflection caused by Earth's rotation) and from a magnetic compass, and none fit the data well. "Our observed biases match by far the best to the Sun compass biases that we would expect," Lewin said.
Why the error barely matters
Even a 15-degree error costs the birds little, because the map sense lets them notice drift and correct it. The team calculated a case near the maximum they observed: a shearwater flying 1,000 km east in a day. Its average heading error would be about seven degrees. If it keeps checking its position, that error adds only about five kilometers to the trip.
Two systems running at once
The team found the bias even when birds were following coastlines. Depending on their expected compass error, they drifted slightly closer to or farther from shore. Oxford work about 20 years ago found the same thing in 6 homing pigeons following a familiar road. That led to the hypothesis that birds run two navigation systems in parallel, one based on the compass and one on familiar landmarks, and never rely entirely on either. Lewin offers another possibility: the birds may not know exactly where on the coast they are, and may use the Sun to decide which way to follow it. "We don't quite know," he says. He notes the question matters for engineers designing navigation systems inspired by animals.
Open questions
The study could not tell whether shearwaters have other jet-lag symptoms, such as poor sleep or hunger at odd hours. Lewin says the team hasn't been able to investigate that yet. Next, he wants to know whether the time shifts affect when birds forage, how much food they bring back to chicks, and how well they breed.
Lewin thinks the effect is probably widespread. Any animal with an internal clock that moves far enough east or west in a day should experience it. That mostly means strong fliers and animals near the poles, where lines of longitude bunch together and a short trip crosses many degrees. The long-term question is whether animals that live with constant jet lag have evolved ways to cope with it. In humans, Lewin notes, frequent jet lag has real long-term health costs, so such animals might suggest ways to reduce it in people.
Remember
Each degree of longitude flown between dawn and dusk puts a bird's clock four minutes off local time.
The effect only showed up because the team had 20 years of GPS tracks and 335 usable homing flights.
Map-based course correction keeps the cost tiny: about 5 extra kilometers on a 1,000 km eastward day.
