Geologists determine early Earth was a 'water world' by studying exposed ocean crust

Ocean panorama (stock image).

The Earth of 3.2 billion years ago was a "water world" of submerged continents, geologists say after analyzing oxygen isotope data from ancient ocean crust that's now exposed on land in Australia.

And that could have major implications on the origin of life.

"An early Earth without emergent continents may have resembled a 'water world,' providing an important environmental constraint on the origin and evolution of life on Earth as well as its possible existence elsewhere," geologists Benjamin Johnson and Boswell Wing wrote in a paper just published online by the journal Nature Geoscience.

Johnson is an assistant professor of geological and atmospheric sciences at Iowa State University and a recent postdoctoral research associate at the University of Colorado Boulder. Wing is an associate professor of geological sciences at Colorado. Grants from the National Science Foundation supported their study and a Lewis and Clark Grant from the American Philosophical Society supported Johnson's fieldwork in Australia.

Johnson said his work on the project started when he talked with Wing at conferences and learned about the well-preserved, 3.2-billion-year-old ocean crust from the Archaean eon (4 billion to 2.5 billion years ago) in a remote part of the state of Western Australia. Previous studies meant there was already a big library of geochemical data from the site.

Johnson joined Wing's research group and went to see ocean crust for himself -- a 2018 trip involving a flight to Perth and a 17-hour drive north to the coastal region near Port Hedland.

After taking his own rock samples and digging into the library of existing data, Johnson created a cross-section grid of the oxygen isotope and temperature values found in the rock.

(Isotopes are atoms of a chemical element with the same number of protons within the nucleus, but differing numbers of neutrons. In this case, differences in oxygen isotopes preserved with the ancient rock provide clues about the interaction of rock and water billions of years ago.)

Once he had two-dimensional grids based on whole-rock data, Johnson created an inverse model to come up with estimates of the oxygen isotopes within the ancient oceans. The result: Ancient seawater was enriched with about 4 parts per thousand more of a heavy isotope of oxygen (oxygen with eight protons and 10 neutrons, written as 18O) than an ice-free ocean of today.

How to explain that decrease in heavy isotopes over time?

Johnson and Wing suggest two possible ways: Water cycling through the ancient ocean crust was different than today's seawater with a lot more high-temperature interactions that could have enriched the ocean with the heavy isotopes of oxygen. Or, water cycling from continental rock could have reduced the percentage of heavy isotopes in ocean water.

"Our preferred hypothesis -- and in some ways the simplest -- is that continental weathering from land began sometime after 3.2 billion years ago and began to draw down the amount of heavy isotopes in the ocean," Johnson said.

The idea that water cycling through ocean crust in a way distinct from how it happens today, causing the difference in isotope composition "is not supported by the rocks," Johnson said. "The 3.2-billion-year-old section of ocean crust we studied looks exactly like much, much younger ocean crust."

Johnson said the study demonstrates that geologists can build models and find new, quantitative ways to solve a problem -- even when that problem involves seawater from 3.2 billion years ago that they'll never see or sample.

And, Johnson said these models inform us about the environment where life originated and evolved: "Without continents and land above sea level, the only place for the very first ecosystems to evolve would have been in the ocean."

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Materials provided by Iowa State University. Note: Content may be edited for style and length.

Geologists determine early Earth was a 'water world' by studying exposed ocean crust

Ocean panorama (stock image).

The Earth of 3.2 billion years ago was a "water world" of submerged continents, geologists say after analyzing oxygen isotope data from ancient ocean crust that's now exposed on land in Australia.

And that could have major implications on the origin of life.

"An early Earth without emergent continents may have resembled a 'water world,' providing an important environmental constraint on the origin and evolution of life on Earth as well as its possible existence elsewhere," geologists Benjamin Johnson and Boswell Wing wrote in a paper just published online by the journal Nature Geoscience.

Johnson is an assistant professor of geological and atmospheric sciences at Iowa State University and a recent postdoctoral research associate at the University of Colorado Boulder. Wing is an associate professor of geological sciences at Colorado. Grants from the National Science Foundation supported their study and a Lewis and Clark Grant from the American Philosophical Society supported Johnson's fieldwork in Australia.

Johnson said his work on the project started when he talked with Wing at conferences and learned about the well-preserved, 3.2-billion-year-old ocean crust from the Archaean eon (4 billion to 2.5 billion years ago) in a remote part of the state of Western Australia. Previous studies meant there was already a big library of geochemical data from the site.

Johnson joined Wing's research group and went to see ocean crust for himself -- a 2018 trip involving a flight to Perth and a 17-hour drive north to the coastal region near Port Hedland.

After taking his own rock samples and digging into the library of existing data, Johnson created a cross-section grid of the oxygen isotope and temperature values found in the rock.

(Isotopes are atoms of a chemical element with the same number of protons within the nucleus, but differing numbers of neutrons. In this case, differences in oxygen isotopes preserved with the ancient rock provide clues about the interaction of rock and water billions of years ago.)

Once he had two-dimensional grids based on whole-rock data, Johnson created an inverse model to come up with estimates of the oxygen isotopes within the ancient oceans. The result: Ancient seawater was enriched with about 4 parts per thousand more of a heavy isotope of oxygen (oxygen with eight protons and 10 neutrons, written as 18O) than an ice-free ocean of today.

How to explain that decrease in heavy isotopes over time?

Johnson and Wing suggest two possible ways: Water cycling through the ancient ocean crust was different than today's seawater with a lot more high-temperature interactions that could have enriched the ocean with the heavy isotopes of oxygen. Or, water cycling from continental rock could have reduced the percentage of heavy isotopes in ocean water.

"Our preferred hypothesis -- and in some ways the simplest -- is that continental weathering from land began sometime after 3.2 billion years ago and began to draw down the amount of heavy isotopes in the ocean," Johnson said.

The idea that water cycling through ocean crust in a way distinct from how it happens today, causing the difference in isotope composition "is not supported by the rocks," Johnson said. "The 3.2-billion-year-old section of ocean crust we studied looks exactly like much, much younger ocean crust."

Johnson said the study demonstrates that geologists can build models and find new, quantitative ways to solve a problem -- even when that problem involves seawater from 3.2 billion years ago that they'll never see or sample.

And, Johnson said these models inform us about the environment where life originated and evolved: "Without continents and land above sea level, the only place for the very first ecosystems to evolve would have been in the ocean."

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Story Source:

Materials provided by Iowa State University. Note: Content may be edited for style and length.

Low-energy solar particles from beyond Earth found near the Sun

Sun (stock image; elements furnished by NASA).

Using data from NASA's Parker Solar Probe (PSP), a team led by Southwest Research Institute identified low-energy particles lurking near the Sun that likely originated from solar wind interactions well beyond Earth orbit. PSP is venturing closer to the Sun than any previous probe, carrying hardware SwRI helped develop. Scientists are probing the enigmatic features of the Sun to answer many questions, including how to protect space travelers and technology from the radiation associated with solar events.

"Our main goal is to determine the acceleration mechanisms that create and transport dangerous high-energy particles from the solar atmosphere into the solar system, including the near-Earth environment," said Dr. Mihir Desai, a mission co-investigator on the Integrated Science Investigation of the Sun (IS?IS) instrument suite, a multi-institutional project led by Principal Investigator Prof. Dave McComas of Princeton University.. IS?IS consists of two instruments, Energetic Particle Instrument-High (EPI-Hi) and Energetic Particle Instrument-Low (EPI-Lo). "With EPI-Lo, we were able to measure extremely low-energy particles unexpectedly close to the solar environment. We considered many explanations for their presence, but ultimately determined they are the smoking gun pointing to interactions between slow- and fast-moving regions of the solar wind that accelerate high-energy particles from beyond the orbit of Earth. Some of those travel back toward the Sun, slowing against the tide of the outpouring solar wind but still retaining surprisingly high energies."

PSP, which will travel within 4 million miles of the Sun's surface, is collecting new solar data to help scientists understand how solar events, such as coronal mass ejections, impact life on Earth. During the rising portion of the Sun's activity cycle, our star releases huge quantities of energized matter, magnetic fields and electromagnetic radiation in the form of coronal mass ejections (CMEs). This material is integrated into the solar wind, the steady stream of charged particles released from the Sun's upper atmosphere. The high-energy solar energetic particles (SEPs) present a serious radiation threat to human explorers living and working outside low-Earth orbit and to technological assets such as communications and scientific satellites in space. The mission is making the first-ever direct measurements of both the low-energy source populations as well as the more hazardous, higher-energy particles in the near-Sun environment, where the acceleration takes place.

When the Sun's activity reaches a lull, roughly about every 11 years, solar equatorial regions emit slower solar wind streams, traveling around 1 million miles per hour, while the poles spew faster streams, traveling twice as fast at 2 million miles per hour. Stream Interaction Regions (SIRs) are created by interactions at boundaries between the fast and slow solar wind. Fast-moving streams tend to overtake slower streams that originate westward of them on the Sun, forming turbulent corotating interaction regions (CIRs) that produce shock waves and accelerated particles, not unlike those produced by CMEs.

"For the first time, we observed low-energy particles from these CIRs near the orbit of Mercury," Desai said. "We also compared the PSP data with data from STEREO, another solar energy probe. By measuring the full range of energetic populations and correlating the data with other measurements, we hope to get a clear picture of the origin and the processes that accelerate these particles. Our next step is to integrate the data into models to better understand the origin of SEPs and other materials. Parker Solar Probe will solve many puzzling scientific questions -- and is guaranteed to generate new ones as well."

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Materials provided by Southwest Research Institute. Note: Content may be edited for style and length.

NASA planet hunter finds Earth-size habitable-zone world

This illustration of TOI 700 d is based on several simulated environments for an ocean-covered version of the planet.

NASA's Transiting Exoplanet Survey Satellite (TESS) has discovered its first Earth-size planet in its star's habitable zone, the range of distances where conditions may be just right to allow the presence of liquid water on the surface. Scientists confirmed the find, called TOI 700 d, using NASA's Spitzer Space Telescope and have modeled the planet's potential environments to help inform future observations.

TOI 700 d is one of only a few Earth-size planets discovered in a star's habitable zone so far. Others include several planets in the TRAPPIST-1 system and other worlds discovered by NASA's Kepler Space Telescope.

"TESS was designed and launched specifically to find Earth-sized planets orbiting nearby stars," said Paul Hertz, astrophysics division director at NASA Headquarters in Washington. "Planets around nearby stars are easiest to follow-up with larger telescopes in space and on Earth. Discovering TOI 700 d is a key science finding for TESS. Confirming the planet's size and habitable zone status with Spitzer is another win for Spitzer as it approaches the end of science operations this January."

TESS monitors large swaths of the sky, called sectors, for 27 days at a time. This long stare allows the satellite to track changes in stellar brightness caused by an orbiting planet crossing in front of its star from our perspective, an event called a transit.

TOI 700 is a small, cool M dwarf star located just over 100 light-years away in the southern constellation Dorado. It's roughly 40% of the Sun's mass and size and about half its surface temperature. The star appears in 11 of the 13 sectors TESS observed during the mission's first year, and scientists caught multiple transits by its three planets.

The star was originally misclassified in the TESS database as being more similar to our Sun, which meant the planets appeared larger and hotter than they really are. Several researchers, including Alton Spencer, a high school student working with members of the TESS team, identified the error.

"When we corrected the star's parameters, the sizes of its planets dropped, and we realized the outermost one was about the size of Earth and in the habitable zone," said Emily Gilbert, a graduate student at the University of Chicago. "Additionally, in 11 months of data we saw no flares from the star, which improves the chances TOI 700 d is habitable and makes it easier to model its atmospheric and surface conditions."

Gilbert and other researchers presented the findings at the 235th meeting of the American Astronomical Societyin Honolulu, and three papers -- one of which Gilbert led -- have been submitted to scientific journals.

The innermost planet, called TOI 700 b, is almost exactly Earth-size, is probably rocky and completes an orbit every 10 days. The middle planet, TOI 700 c, is 2.6 times larger than Earth -- between the sizes of Earth and Neptune -- orbits every 16 days and is likely a gas-dominated world. TOI 700 d, the outermost known planet in the system and the only one in the habitable zone, measures 20% larger than Earth, orbits every 37 days and receives from its star 86% of the energy that the Sun provides to Earth. All of the planets are thought to be tidally locked to their star, which means they rotate once per orbit so that one side is constantly bathed in daylight.

A team of scientists led by Joseph Rodriguez, an astronomer at the Center for Astrophysics | Harvard & Smithsonian in Cambridge, Massachusetts, requested follow-up observations with Spitzer to confirm TOI 700 d.

"Given the impact of this discovery -- that it is TESS's first habitable-zone Earth-size planet -- we really wanted our understanding of this system to be as concrete as possible," Rodriguez said. "Spitzer saw TOI 700 d transit exactly when we expected it to. It's a great addition to the legacy of a mission that helped confirm two of the TRAPPIST-1 planets and identify five more."

The Spitzer data increased scientists' confidence that TOI 700 d is a real planet and sharpened their measurements of its orbital period by 56% and its size by 38%. It also ruled out other possible astrophysical causes of the transit signal, such as the presence of a smaller, dimmer companion star in the system.

Rodriguez and his colleagues also used follow-up observations from a 1-meter ground-based telescope in the global Las Cumbres Observatory network to improve scientists' confidence in the orbital period and size of TOI 700 c by 30% and 36%, respectively.

Because TOI 700 is bright, nearby, and shows no sign of stellar flares, the system is a prime candidate for precise mass measurements by current ground-based observatories. These measurements could confirm scientists' estimates that the inner and outer planets are rocky and the middle planet is made of gas.

Future missions may be able to identify whether the planets have atmospheres and, if so, even determine their compositions.

While the exact conditions on TOI 700 d are unknown, scientists can use current information, like the planet's size and the type of star it orbits, to generate computer models and make predictions. Researchers at NASA's Goddard Space Flight Center in Greenbelt, Maryland, modeled 20 potential environments of TOI 700 d to gauge if any version would result in surface temperatures and pressures suitable for habitability.

Their 3D climate models examined a variety of surface types and atmospheric compositions typically associated with what scientists regard to be potentially habitable worlds. Because TOI 700 d is tidally locked to its star, the planet's cloud formations and wind patterns may be strikingly different from Earth's.

One simulation included an ocean-covered TOI 700 d with a dense, carbon-dioxide-dominated atmosphere similar to what scientists suspect surrounded Mars when it was young. The model atmosphere contains a deep layer of clouds on the star-facing side. Another model depicts TOI 700 d as a cloudless, all-land version of modern Earth, where winds flow away from the night side of the planet and converge on the point directly facing the star.

When starlight passes through a planet's atmosphere, it interacts with molecules like carbon dioxide and nitrogen to produce distinct signals, called spectral lines. The modeling team, led by Gabrielle Englemann-Suissa, a Universities Space Research Association visiting research assistant at Goddard, produced simulated spectra for the 20 modeled versions of TOI 700 d.

"Someday, when we have real spectra from TOI 700 d, we can backtrack, match them to the closest simulated spectrum, and then match that to a model," Englemann-Suissa said. "It's exciting because no matter what we find out about the planet, it's going to look completely different from what we have here on Earth."

TESS is a NASA Astrophysics Explorer mission led and operated by MIT in Cambridge, Massachusetts, and managed by NASA's Goddard Space Flight Center. Additional partners include Northrop Grumman, based in Falls Church, Virginia; NASA's Ames Research Center in California's Silicon Valley; the Harvard-Smithsonian Center for Astrophysics in Cambridge, Massachusetts; MIT's Lincoln Laboratory; and the Space Telescope Science Institute in Baltimore. More than a dozen universities, research institutes and observatories worldwide are participants in the mission.

The Jet Propulsion Laboratory in Pasadena, California, manages the Spitzer Space Telescope mission for NASA's Science Mission Directorate in Washington. Science operations are conducted at the Spitzer Science Center at Caltech in Pasadena. Space operations are based at Lockheed Martin Space in Littleton, Colorado. Data are archived at the Infrared Science Archive housed at IPAC at Caltech. Caltech manages JPL for NASA.

The modeling work was funded through the Sellers Exoplanet Environments Collaboration at Goddard, a multidisciplinary collaboration that brings together experts to build comprehensive and sophisticated computer models to better analyze current and future exoplanet observations.

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Materials provided by NASA/Jet Propulsion Laboratory. Original written by Jeanette Kazmierczak, NASA's Goddard Space Flight Center, Greenbelt, Md.. Note: Content may be edited for style and length.

How the solar system got its 'Great Divide,' and why it matters for life on Earth

Illustration of inner solar system (stock image).

Scientists, including those from the University of Colorado Boulder, have finally scaled the solar system's equivalent of the Rocky Mountain range.

In a study published today in Nature Astronomy, researchers from the United States and Japan unveil the possible origins of our cosmic neighborhood's "Great Divide." This well-known schism may have separated the solar system just after the sun first formed.

The phenomenon is a bit like how the Rocky Mountains divide North America into east and west. On the one side are "terrestrial" planet, such as Earth and Mars. They are made up of fundamentally different types of materials than the more distant "jovians," such as Jupiter and Saturn.

"The question is: How do you create this compositional dichotomy?" said lead author Ramon Brasser, a researcher at the Earth-Life Science Institute (ELSI) at the Tokyo Institute of Technology in Japan. "How do you ensure that material from the inner and outer solar system didn't mix from very early on in its history?"

Brasser and coauthor Stephen Mojzsis, a professor in CU Boulder's Department of Geological Sciences, think they have the answer, and it may just shed new light on how life originated on Earth.

A sun disk holds vital clues

The duo suggests that the early solar system was partitioned into at least two regions by a ring-like structure that formed a disk around the young sun. This disk might have held major implications for the evolution of planets and asteroids, and even the history of life on Earth.

"The most likely explanation for that compositional difference is that it emerged from an intrinsic structure of this disk of gas and dust," Mojzsis said.

Mojzsis noted that the Great Divide, a term that he and Brasser coined, does not look like much today. It is a relatively empty stretch of space that sits near Jupiter, just beyond what astronomers call the asteroid belt.

But you can still detect its presence throughout the solar system. Move sunward from that line, and most planets and asteroids tend to carry relatively low abundances of organic molecules. Go the other direction toward Jupiter and beyond, however, and a different picture emerges: Almost everything in this distant part of the solar system is made up of materials that are rich in carbon.

This dichotomy "was really a surprise when it was first found," Mojzsis said.

Many scientists assumed that Jupiter was the agent responsible for that surprise. The thinking went that the planet is so massive that it may have acted as a gravitational barrier, preventing pebbles and dust from the outer solar system from spiraling toward the sun.

But Mojzsis and Brasser were not convinced. The scientists used a series of computer simulations to explore Jupiter's role in the evolving solar system. They found that while Jupiter is big, it was probably never big enough early in its formation to entirely block the flow of rocky material from moving sunward.

"We banged our head against the wall," Brasser said. "If Jupiter wasn't the agent responsible for creating and maintaining that compositional dichotomy, what else could be?"

A solution in plain sight

For years, scientists operating an observatory in Chile called the Atacama Large Millimeter/submillimeter Array (ALMA) had noticed something unusual around distant stars: Young stellar systems were often surrounded by disks of gas and dust that, in infrared light, looked a bit like a tiger's eye.

If a similar ring existed in our own solar system billions of years ago, Brasser and Mojzsis reasoned, it could theoretically be responsible for the Great Divide.

That's because such a ring would create alternating bands of high- and low-pressure gas and dust. Those bands, in turn, might pull the solar system's earliest building blocks into several distinct sinks -- one that would have given rise to Jupiter and Saturn, and another Earth and Mars.

In the mountains, "the Great Divide causes water to drain one way or another," Mojzsis said. "It's similar to how this pressure bump would have divided material" in the solar system.

But, he added, there's a caveat: That barrier in space likely was not perfect. Some outer solar system material may still have climbed across the divide. And those fugitives could have been important for the evolution of our own world.

"Those materials that might go to the Earth would be those volatile, carbon-rich materials," Mojzsis said. "And that gives you water. It gives you organics."

The rest is Earth history.

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Materials provided by University of Colorado at Boulder. Original written by Daniel Strain. Note: Content may be edited for style and length.

Meteorite contains the oldest material on Earth: 7-billion-year-old stardust

Illustration of meteor entering Earth's atmosphere (stock image).

Stars have life cycles. They're born when bits of dust and gas floating through space find each other and collapse in on each other and heat up. They burn for millions to billions of years, and then they die. When they die, they pitch the particles that formed in their winds out into space, and those bits of stardust eventually form new stars, along with new planets and moons and meteorites. And in a meteorite that fell fifty years ago in Australia, scientists have now discovered stardust that formed 5 to 7 billion years ago -- the oldest solid material ever found on Earth.

"This is one of the most exciting studies I've worked on," says Philipp Heck, a curator at the Field Museum, associate professor at the University of Chicago, and lead author of a paper describing the findings in the Proceedings of the National Academy of Sciences. "These are the oldest solid materials ever found, and they tell us about how stars formed in our galaxy."

The materials Heck and his colleagues examined are called presolar grains-minerals formed before the Sun was born. "They're solid samples of stars, real stardust," says Heck. These bits of stardust became trapped in meteorites where they remained unchanged for billions of years, making them time capsules of the time before the solar system..

But presolar grains are hard to come by. They're rare, found only in about five percent of meteorites that have fallen to Earth, and they're tiny-a hundred of the biggest ones would fit on the period at the end of this sentence. But the Field Museum has the largest portion of the Murchison meteorite, a treasure trove of presolar grains that fell in Australia in 1969 and that the people of Murchison, Victoria, made available to science. Presolar grains for this study were isolated from the Murchison meteorite for this study about 30 years ago at the University of Chicago.

"It starts with crushing fragments of the meteorite down into a powder ," explains Jennika Greer, a graduate student at the Field Museum and the University of Chicago and co-author of the study. "Once all the pieces are segregated, it's a kind of paste, and it has a pungent characteristic-it smells like rotten peanut butter."

This "rotten-peanut-butter-meteorite paste" was then dissolved with acid, until only the presolar grains remained. "It's like burning down the haystack to find the needle," says Heck.

Once the presolar grains were isolated, the researchers figured out from what types of stars they came and how old they were. "We used exposure age data, which basically measures their exposure to cosmic rays, which are high-energy particles that fly through our galaxy and penetrate solid matter," explains Heck. "Some of these cosmic rays interact with the matter and form new elements. And the longer they get exposed, the more those elements form.

"I compare this with putting out a bucket in a rainstorm. Assuming the rainfall is constant, the amount of water that accumulates in the bucket tells you how long it was exposed," he adds. By measuring how many of these new cosmic-ray produced elements are present in a presolar grain, we can tell how long it was exposed to cosmic rays, which tells us how old it is.

The researchers learned that some of the presolar grains in their sample were the oldest ever discovered-based on how many cosmic rays they'd soaked up, most of the grains had to be 4.6 to 4.9 billion years old, and some grains were even older than 5.5 billion years. For context, our Sun is 4.6 billion years old, and Earth is 4.5 billion.

But the age of the presolar grains wasn't the end of the discovery. Since presolar grains are formed when a star dies, they can tell us about the history of stars. And 7 billion years ago, there was apparently a bumper crop of new stars forming-a sort of astral baby boom.

"We have more young grains that we expected," says Heck. "Our hypothesis is that the majority of those grains, which are 4.9 to 4.6 billion years old, formed in an episode of enhanced star formation. There was a time before the start of the Solar System when more stars formed than normal."

This finding is ammo in a debate between scientists about whether or not new stars form at a steady rate, or if there are highs and lows in the number of new stars over time. "Some people think that the star formation rate of the galaxy is constant," says Heck. "But thanks to these grains, we now have direct evidence for a period of enhanced star formation in our galaxy seven billion years ago with samples from meteorites. This is one of the key findings of our study."

Heck notes that this isn't the only unexpected thing his team found. As almost a side note to the main research questions, in examining the way that the minerals in the grains interacted with cosmic rays, the researchers also learned that presolar grains often float through space stuck together in large clusters, "like granola," says Heck. "No one thought this was possible at that scale."

Heck and his colleagues look forward to all of these discoveries furthering our knowledge of our galaxy. "With this study, we have directly determined the lifetimes of stardust. We hope this will be picked up and studied so that people can use this as input for models of the whole galactic life cycle," he says.

Heck notes that there are lifetimes' worth of questions left to answer about presolar grains and the early Solar System. "I wish we had more people working on it to learn more about our home galaxy, the Milky Way," he says.

"Once learning about this, how do you want to study anything else?" says Greer. "It's awesome, it's the most interesting thing in the world."

"I always wanted to do astronomy with geological samples I can hold in my hand," says Heck. "It's so exciting to look at the history of our galaxy. Stardust is the oldest material to reach Earth, and from it, we can learn about our parent stars, the origin of the carbon in our bodies, the origin of the oxygen we breathe. With stardust, we can trace that material back to the time before the Sun."

"It's the next best thing to being able to take a sample directly from a star," says Greer.

This study was contributed to by researchers from the Field Museum, University of Chicago, Lawrence Livermore National Laboratory, Washington University, Harvard Medical School, ETH Zurich, and the Australian National University. Funding was provided by NASA, the TAWANI Foundation, the National Science Foundation, the Department of Energy, the Swiss National Science Foundation, the Brazilian National Council for Scientific and Technological Development and the Field Museum's Science and Scholarship Funding Committee.

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Materials provided by Field Museum. Note: Content may be edited for style and length.

NASA planet hunter finds Earth-size habitable-zone world

This illustration of TOI 700 d is based on several simulated environments for an ocean-covered version of the planet.

Credit: NASA's Goddard Space Flight Center

NASA's Transiting Exoplanet Survey Satellite (TESS) has discovered its first Earth-size planet in its star's habitable zone, the range of distances where conditions may be just right to allow the presence of liquid water on the surface. Scientists confirmed the find, called TOI 700 d, using NASA's Spitzer Space Telescope and have modeled the planet's potential environments to help inform future observations.

TOI 700 d is one of only a few Earth-size planets discovered in a star's habitable zone so far. Others include several planets in the TRAPPIST-1 system and other worlds discovered by NASA's Kepler Space Telescope.

"TESS was designed and launched specifically to find Earth-sized planets orbiting nearby stars," said Paul Hertz, astrophysics division director at NASA Headquarters in Washington. "Planets around nearby stars are easiest to follow-up with larger telescopes in space and on Earth. Discovering TOI 700 d is a key science finding for TESS. Confirming the planet's size and habitable zone status with Spitzer is another win for Spitzer as it approaches the end of science operations this January."

TESS monitors large swaths of the sky, called sectors, for 27 days at a time. This long stare allows the satellite to track changes in stellar brightness caused by an orbiting planet crossing in front of its star from our perspective, an event called a transit.

TOI 700 is a small, cool M dwarf star located just over 100 light-years away in the southern constellation Dorado. It's roughly 40% of the Sun's mass and size and about half its surface temperature. The star appears in 11 of the 13 sectors TESS observed during the mission's first year, and scientists caught multiple transits by its three planets.

The star was originally misclassified in the TESS database as being more similar to our Sun, which meant the planets appeared larger and hotter than they really are. Several researchers, including Alton Spencer, a high school student working with members of the TESS team, identified the error.

"When we corrected the star's parameters, the sizes of its planets dropped, and we realized the outermost one was about the size of Earth and in the habitable zone," said Emily Gilbert, a graduate student at the University of Chicago. "Additionally, in 11 months of data we saw no flares from the star, which improves the chances TOI 700 d is habitable and makes it easier to model its atmospheric and surface conditions."

Gilbert and other researchers presented the findings at the 235th meeting of the American Astronomical Societyin Honolulu, and three papers -- one of which Gilbert led -- have been submitted to scientific journals.

The innermost planet, called TOI 700 b, is almost exactly Earth-size, is probably rocky and completes an orbit every 10 days. The middle planet, TOI 700 c, is 2.6 times larger than Earth -- between the sizes of Earth and Neptune -- orbits every 16 days and is likely a gas-dominated world. TOI 700 d, the outermost known planet in the system and the only one in the habitable zone, measures 20% larger than Earth, orbits every 37 days and receives from its star 86% of the energy that the Sun provides to Earth. All of the planets are thought to be tidally locked to their star, which means they rotate once per orbit so that one side is constantly bathed in daylight.

A team of scientists led by Joseph Rodriguez, an astronomer at the Center for Astrophysics | Harvard & Smithsonian in Cambridge, Massachusetts, requested follow-up observations with Spitzer to confirm TOI 700 d.

"Given the impact of this discovery -- that it is TESS's first habitable-zone Earth-size planet -- we really wanted our understanding of this system to be as concrete as possible," Rodriguez said. "Spitzer saw TOI 700 d transit exactly when we expected it to. It's a great addition to the legacy of a mission that helped confirm two of the TRAPPIST-1 planets and identify five more."

The Spitzer data increased scientists' confidence that TOI 700 d is a real planet and sharpened their measurements of its orbital period by 56% and its size by 38%. It also ruled out other possible astrophysical causes of the transit signal, such as the presence of a smaller, dimmer companion star in the system.

Rodriguez and his colleagues also used follow-up observations from a 1-meter ground-based telescope in the global Las Cumbres Observatory network to improve scientists' confidence in the orbital period and size of TOI 700 c by 30% and 36%, respectively.

Because TOI 700 is bright, nearby, and shows no sign of stellar flares, the system is a prime candidate for precise mass measurements by current ground-based observatories. These measurements could confirm scientists' estimates that the inner and outer planets are rocky and the middle planet is made of gas.

Future missions may be able to identify whether the planets have atmospheres and, if so, even determine their compositions.

While the exact conditions on TOI 700 d are unknown, scientists can use current information, like the planet's size and the type of star it orbits, to generate computer models and make predictions. Researchers at NASA's Goddard Space Flight Center in Greenbelt, Maryland, modeled 20 potential environments of TOI 700 d to gauge if any version would result in surface temperatures and pressures suitable for habitability.

Their 3D climate models examined a variety of surface types and atmospheric compositions typically associated with what scientists regard to be potentially habitable worlds. Because TOI 700 d is tidally locked to its star, the planet's cloud formations and wind patterns may be strikingly different from Earth's.

One simulation included an ocean-covered TOI 700 d with a dense, carbon-dioxide-dominated atmosphere similar to what scientists suspect surrounded Mars when it was young. The model atmosphere contains a deep layer of clouds on the star-facing side. Another model depicts TOI 700 d as a cloudless, all-land version of modern Earth, where winds flow away from the night side of the planet and converge on the point directly facing the star.

When starlight passes through a planet's atmosphere, it interacts with molecules like carbon dioxide and nitrogen to produce distinct signals, called spectral lines. The modeling team, led by Gabrielle Englemann-Suissa, a Universities Space Research Association visiting research assistant at Goddard, produced simulated spectra for the 20 modeled versions of TOI 700 d.

"Someday, when we have real spectra from TOI 700 d, we can backtrack, match them to the closest simulated spectrum, and then match that to a model," Englemann-Suissa said. "It's exciting because no matter what we find out about the planet, it's going to look completely different from what we have here on Earth."

TESS is a NASA Astrophysics Explorer mission led and operated by MIT in Cambridge, Massachusetts, and managed by NASA's Goddard Space Flight Center. Additional partners include Northrop Grumman, based in Falls Church, Virginia; NASA's Ames Research Center in California's Silicon Valley; the Harvard-Smithsonian Center for Astrophysics in Cambridge, Massachusetts; MIT's Lincoln Laboratory; and the Space Telescope Science Institute in Baltimore. More than a dozen universities, research institutes and observatories worldwide are participants in the mission.

The Jet Propulsion Laboratory in Pasadena, California, manages the Spitzer Space Telescope mission for NASA's Science Mission Directorate in Washington. Science operations are conducted at the Spitzer Science Center at Caltech in Pasadena. Space operations are based at Lockheed Martin Space in Littleton, Colorado. Data are archived at the Infrared Science Archive housed at IPAC at Caltech. Caltech manages JPL for NASA.

The modeling work was funded through the Sellers Exoplanet Environments Collaboration at Goddard, a multidisciplinary collaboration that brings together experts to build comprehensive and sophisticated computer models to better analyze current and future exoplanet observations.

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Materials provided by NASA/Jet Propulsion Laboratory. Original written by Jeanette Kazmierczak, NASA's Goddard Space Flight Center, Greenbelt, Md.. Note: Content may be edited for style and length.

Earth was stressed before dinosaur extinction

New evidence gleaned from Antarctic seashells confirms that Earth was already unstable before the asteroid impact that wiped out the dinosaurs.

The study, led by researchers at Northwestern University, is the first to measure the calcium isotope composition of fossilized clam and snail shells, which date back to the Cretaceous-Paleogene mass extinction event. The researchers found that -- in the run-up to the extinction event -- the shells' chemistry shifted in response to a surge of carbon in the oceans.

This carbon influx was likely due to long-term eruptions from the Deccan Traps, a 200,000-square-mile volcanic province located in modern India. During the years leading up to the asteroid impact, the Deccan Traps spewed massive amounts of carbon dioxide (CO2) into the atmosphere. The concentration of CO2 acidified the oceans, directly affecting the organisms living there.

"Our data suggest that the environment was changing before the asteroid impact," said Benjamin Linzmeier, the study's first author. "Those changes appear to correlate with the eruption of the Deccan Traps."

"The Earth was clearly under stress before the major mass extinction event," said Andrew D. Jacobson, a senior author of the paper. "The asteroid impact coincides with pre-existing carbon cycle instability. But that doesn't mean we have answers to what actually caused the extinction."

The study will be published in the January 2020 issue of the journal Geology, which comes out later this month.

Jacobson is a professor of Earth and planetary sciences in Northwestern's Weinberg College of Arts and Sciences. Linzmeier was a postdoctoral researcher with the Ubben Program for Climate and Carbon Science at the Institute for Sustainability and Energy at Northwestern when the research was conducted. He is now a postdoctoral fellow at the University of Wisconsin-Madison in the Department of Geoscience.

'Each shell is a snapshot'

Previous studies have explored the potential effects of the Deccan Traps eruptions on the mass extinction event, but many have examined bulk sediments and used different chemical tracers. By focusing on a specific organism, the researchers gained a more precise, higher-resolution record of the ocean's chemistry.

"Shells grow quickly and change with water chemistry," Linzmeier said. "Because they live for such a short period of time, each shell is a short, preserved snapshot of the ocean's chemistry."

Seashells mostly are composed of calcium carbonate, the same mineral found in chalk, limestone and some antacid tablets. Carbon dioxide in water dissolves calcium carbonate. During the formation of the shells, CO2 likely affects shell composition even without dissolving them.

For this study, the researchers examined shells collected from the Lopez de Bertodano Formation, a well-preserved, fossil-rich area on the west side of Seymour Island in Antarctica. They analyzed the shells' calcium isotope compositions using a state-of-the-art technique developed in Jacobson's laboratory at Northwestern. The method involves dissolving shell samples to separate calcium from various other elements, followed by analysis with a mass spectrometer.

"We can measure calcium isotope variations with high precision," Jacobson said. "And those isotope variations are like fingerprints to help us understand what happened."

Using this method, the team found surprising information.

"We expected to see some changes in the shells' composition, but we were surprised by how quickly the changes occurred," Linzmeier said. "We also were surprised that we didn't see more change associated with the extinction horizon itself."

A future warning

The researchers said that understanding how the Earth responded to past extreme warming and CO2 input can help us prepare for how the planet will respond to current, human-caused climate change.

"To some degree, we think that ancient ocean acidification events are good analogs for what's happening now with anthropogenic CO2 emissions," Jacobson said. "Perhaps we can use this work as a tool to better predict what might happen in the future. We can't ignore the rock record. The Earth system is sensitive to large and rapid additions of CO2. Current emissions will have environmental consequences."

Brad Sageman and Matthew Hurtgen, both professors of Earth and planetary sciences at Northwestern, are co-senior authors of the paper.

The study, "Calcium isotope evidence for environmental variability before and across the Cretaceous-Paleogene mass extinction," was supported by the Ubben Program for Climate and Carbon Science at Northwestern University, the David and Lucile Packard Foundation (award number 2007-31757) and the National Science Foundation (award numbers EAR-0723151, ANT-1341729, ANT-0739541 and ANT-0739432.

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Materials provided by Northwestern University. Original written by Amanda Morris. Note: Content may be edited for style and length.

Mars once had salt lakes similar to those on Earth

Salt flat in Bolivia

Mars once had salt lakes that are similar to those on Earth and has gone through wet and dry periods, according to an international team of scientists that includes a Texas A&M University College of Geosciences researcher.

Marion Nachon, a postdoctoral research associate in the Department of Geology and Geophysics at Texas A&M, and colleagues have had their work published in the current issue of Nature Geoscience.

The team examined Mars' geological terrains from Gale Crater, an immense 95-mile-wide rocky basin that is being explored with the NASA Curiosity rover since 2012 as part of the MSL (Mars Science Laboratory) mission.

The results show that the lake that was present in Gale Crater over 3 billion years ago underwent a drying episode, potentially linked to the global drying of Mars.

Gale Crater formed about 3.6 billion years ago when a meteor hit Mars and created its large impact crater.

"Since then, its geological terrains have recorded the history of Mars, and studies have shown Gale Crater reveals signs that liquid water was present over its history, which is a key ingredient of microbial life as we know it," Nachon said. "During these drying periods, salt ponds eventually formed. It is difficult to say exactly how large these ponds were, but the lake in Gale Crater was present for long periods of time -- from at least hundreds of years to perhaps tens of thousands of years," Nachon said.

So what happened to these salt lakes?

Nachon said that Mars probably became dryer over time, and the planet lost its planetary magnetic field, which left the atmosphere exposed to be stripped by solar wind and radiation over millions of years.

"With an atmosphere becoming thinner, the pressure at the surface became lesser, and the conditions for liquid water to be stable at the surface were not fulfilled anymore," Nachon said. "So liquid water became unsustainable and evaporated."

The salt ponds on Mars are believed to be similar to some found on Earth, especially those in a region called Altiplano, which is near the Bolivia-Peru border.

Nachon said the Altiplano is an arid, high-altitude plateau where rivers and streams from mountain ranges "do not flow to the sea but lead to closed basins, similar to what used to happen at Gale Crater on Mars," she said. "This hydrology creates lakes with water levels heavily influenced by climate. During the arid periods Altiplano lakes become shallow due to evaporation, and some even dry up entirely. The fact that the Atliplano is mostly vegetation free makes the region look even more like Mars," she said."

Nachon added that the study shows that the ancient lake in Gale Crater underwent at least one episode of drying before "recovering." It's also possible that the lake was segmented into separate ponds, where some of the ponds could have undergone more evaporation.

Because up to now only one location along the rover's path shows such a drying history, Nachon said it might give clues about how many drying episodes the lake underwent before Mars's climate became as dry as it is currently.

"It could indicate that Mars's climate 'dried out' over the long term, on a way that still allowed for the cyclical presence of a lake," Nachon said. "These results indicate a past Mars climate that fluctuated between wetter and drier periods. They also tell us about the types of chemical elements (in this case sulphur, a key ingredient for life) that were available in the liquid water present at the surface at the time, and about the type of environmental fluctuations Mars life would have had to cope with, if it ever existed."

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Materials provided by Texas A&M University. Original written by Keith Randall. Note: Content may be edited for style and length.

Distant worlds under many suns

Is Earth the only habitable planet in the universe or are there more worlds somewhere out there that are capable of supporting life? And if there are, what might they look like? In a bid to answer these fundamental questions, scientists are searching space for exoplanets: distant worlds that orbit other stars outside our solar system.

More than 4,000 exoplanets are known to date, most of them orbiting single stars like our Sun. Now astrophysicist Dr Markus Mugrauer of Friedrich Schiller University Jena, Germany, has discovered and characterised many new multiple star systems that contain exoplanets. The findings confirm assumptions that the existence of several stars influences the process by which planets are formed and develop. The study by Mugrauer, of the Astrophysical Institute and University Observatory of the University of Jena, has now been published in the specialist journal Monthly Notices of the Royal Astronomical Society.

Space telescope provides precise data

"Multiple star systems are very common in our Milky Way," explains Mugrauer. "If such systems include planets, they are of particular interest to Astrophysics, because the planetary systems in them can differ from our solar system in fundamental ways." To find out more about these differences, Mugrauer searched more than 1,300 exoplanet host stars with exoplanets orbiting them to see whether they have companion stars. To this end, he accessed the precise observation data of the Gaia space telescope, which is operated by the European Space Agency (ESA).

In this way, he succeeded in demonstrating the existence of around 200 companion stars to planetary host stars that are up to 1,600 light years away from the Sun. With the help of the data, Mugrauer was also able to characterise the companion stars and their systems in more detail. He found that there are both tight systems with distances of only 20 astronomical units (au) -- which in our solar system corresponds approximately to the distance between the Sun and Uranus -- as well as systems with stars that are over 9,000 au from each other.

Red and white dwarfs

The companion stars also vary as to their mass, temperature and stage of evolution. The heaviest among them weigh 1.4 times more than our Sun, while the lightest have only 8 per cent of the Sun's mass. Most of the companion stars are low-mass, cool dwarf stars that glow faintly red. However, eight white dwarfs were also identified among the faint stellar companions. A white dwarf is the burnt-out core of a sun-like star, which is only about as big as our Earth, but half as heavy as our Sun. These observations show that exoplanets can indeed survive the final evolutionary stage of a nearby sun-like star.

Double, triple and quadruple star systems with exoplanets

The majority of the star systems with exoplanets identified in the study have two stars. However, some two dozen hierarchical triple star systems and even a quadruple star system were detected. In the range of distances investigated, of between approximately 20 and 10,000 astronomical units, a total of 15 per cent of the stars studied have at least one companion star. This is only about half the frequency expected in general for solar-like stars. In addition, the companion stars detected show distances about five times greater than in ordinary systems.

"These two factors taken together could indicate that the influence of several stars in a star system disrupts the process of planet formation as well as the further development of their orbits," says Mugrauer. The cause of this could be first the gravitational impact of a stellar companion on the gas and dust disc in which planets form around their host star. Later, the gravitation of the stellar companion influences the motion of the planets around their host star.

Markus Mugrauer would like to pursue the project further. In the future, too, the multiplicity of newly discovered planetary host stars would be studied using data from the Gaia mission and any companion stars detected would be precisely characterised. "In addition, we will combine the results with those of an international observational campaign, which we are currently conducting on the same topic at the Paranal Observatory of the European Southern Observatory in Chile," added Mugrauer. "We will then be able to investigate the precise influence of stellar multiplicity on the formation and development of planets."