Tag Archives: #earth

Earth and Venus Grew up as Rambunctious Planets (Planetary Science)

What doesn’t stick comes around: Using machine learning and simulations of giant impacts, researchers at the Lunar and Planetary Laboratory found that the planets residing in the inner solar system were likely born from repeated hit-and-run collisions, challenging conventional models of planet formation. 

Planet formation – the process by which neat, round, distinct planets form from a roiling, swirling cloud of rugged asteroids and mini planets – was likely even messier and more complicated than most scientists would care to admit, according to new research led by researchers at the University of Arizona Lunar and Planetary Laboratory.

The findings challenge the conventional view, in which collisions between smaller building blocks cause them to stick together and, over time, repeated collisions accrete new material to the growing baby planet.

Instead, the authors propose and demonstrate evidence for a novel “hit-and-run-return” scenario, in which pre-planetary bodies spent a good part of their journey through the inner solar system crashing into and ricocheting off of each other, before running into each other again at a later time. Having been slowed down by their first collision, they would be more likely to stick together the next time. Picture a game of billiards, with the balls coming to rest, as opposed to pelting a snowman with snowballs, and you get the idea.

The research is published in two reports appearing in the Sept. 23 issue of The Planetary Science Journal, with one focusing on Venus and Earth, and the other on Earth’s moon. Central to both publications, according to the author team, which was led by planetary sciences and LPL professor Erik Asphaug, is the largely unrecognized point that giant impacts are not the efficient mergers scientists believed them to be.

“We find that most giant impacts, even relatively ‘slow’ ones, are hit-and-runs. This means that for two planets to merge, you usually first have to slow them down in a hit-and-run collision,” Asphaug said. “To think of giant impacts, for instance the formation of the moon, as a singular event is probably wrong. More likely it took two collisions in a row.”

The inner planets: Mercury, Venus, Earth and Mars
The terrestrial planets of the inner solar system, shown to scale. According to ‘late stage accretion’ theory, Mars and Mercury (front left and right) are what’s left of an original population of colliding embryos, and Venus and Earth grew in a series of giant impacts. New research focuses on the preponderance of hit-and-run collisions in giant impacts, and shows that proto-Earth would have served as a ‘vanguard’, slowing down planet-sized bodies in hit-and-runs. But it is proto-Venus, more often than not, that ultimately accretes them, meaning it was easier for Venus to acquire bodies from the outer solar system. Lsmpascal – Wikimedia commons

One implication is that Venus and Earth would have had very different experiences in their growth as planets, despite being immediate neighbors in the inner solar system. In this paper, led by Alexandre Emsenhuber, who did this work during a postdoctoral fellowship in Asphaug’s lab and is now at Ludwig Maximilian University in Munich, the young Earth would have served to slow down interloping planetary bodies, making them ultimately more likely to collide with and stick to Venus.

“We think that during solar system formation, the early Earth acted like a vanguard for Venus,” Emsenhuber said.

The solar system is what scientists call a gravity well, the concept behind a popular attraction at science exhibits. Visitors toss a coin into a funnel-shaped gravity well, and then watch their cash complete several orbits before it drops into the center hole. The closer a planet is to the sun, the stronger the gravitation experienced by planets. That’s why the inner planets of the solar system on which these studies were focused – Mercury, Venus, Earth and Mars – orbit the sun faster than, say, Jupiter, Saturn and Neptune. As a result, the closer an object ventures to the sun, the more likely it is to stay there.

So when an interloping planet hit the Earth, it was less likely to stick to Earth, and instead more likely to end up at Venus, Asphaug explained.

“The Earth acts as a shield, providing a first stop against these impacting planets,” he said. “More likely than not, a planet that bounces off of Earth is going to hit Venus and merge with it.”

Emsenhuber uses the analogy of a ball bouncing down a staircase to illustrate the idea of what drives the vanguard effect: A body coming in from the outer solar system is like a ball bouncing down a set of stairs, with each bounce representing a collision with another body.

“Along the way, the ball loses energy, and you’ll find it will always bounce downstairs, never upstairs,” he said. “Because of that, the body cannot leave the inner solar system anymore. You generally only go downstairs, toward Venus, and an impactor that collides with Venus is pretty happy staying in the inner solar system, so at some point it is going to hit Venus again.”

Earth has no such vanguard to slow down its interloping planets. This leads to a difference between the two similar-sized planets that conventional theories cannot explain, the authors argue.

“The prevailing idea has been that it doesn’t really matter if planets collide and don’t merge right away, because they are going to run into each other again at some point and merge then,” Emsenhuber said. “But that is not what we find. We find they end up more frequently becoming part of Venus, instead of returning back to Earth. It’s easier to go from Earth to Venus than the other way around.”

Simulated aftermath of a hit-and-run collisions between the young Earth and  another planetary body
The moon is thought to be the aftermath of a giant impact. According to a new theory, there were two giant impacts in a row, separated by about 1 million years, involving a Mars-sized ‘Theia’ and proto-Earth. In this image, the proposed hit-and-run collision is simulated in 3D, shown about an hour after impact. A cut-away view shows the iron cores. Theia (or most of it) barely escapes, so a follow-on collision is likely.A. Emsenhuber/University of Bern/University of Munich

To track all these planetary orbits and collisions, and ultimately their mergers, the team used machine learning to obtain predictive models from 3D simulations of giant impacts. The team then used these data to rapidly compute the orbital evolution, including hit-and-run and merging collisions, to simulate terrestrial planet formation over the course of 100 million years. In the second paper, the authors propose and demonstrate their hit-and-run-return scenario for the moon’s formation, recognizing the primary problems with the standard giant impact model.

“The standard model for the moon requires a very slow collision, relatively speaking,” Asphaug said, “and it creates a moon that is composed mostly of the impacting planet, not the proto-Earth, which is a major problem since the moon has an isotopic chemistry almost identical to Earth.”

In the team’s new scenario, a roughly Mars-sized protoplanet hits the Earth, as in the standard model, but is a bit faster so it keeps going. It returns in about 1 million years for a giant impact that looks a lot like the standard model.

“The double impact mixes things up much more than a single event,” Asphaug said, “which could explain the isotopic similarity of Earth and moon, and also how the second, slow, merging collision would have happened in the first place.”

The researchers think the resulting asymmetry in how the planets were put together points the way to future studies addressing the diversity of terrestrial planets. For example, we don’t understand how Earth ended up with a magnetic field that is much stronger than that of Venus, or why Venus has no moon.

Their research indicates systematic differences in dynamics and composition, according to Asphaug.

“In our view, Earth would have accreted most of its material from collisions that were head-on hits, or else slower than those experienced by Venus,” he said. “Collisions into the Earth that were more oblique and higher velocity would have preferentially ended up on Venus.”

This would create a bias in which, for example, protoplanets from the outer solar system, at higher velocity, would have preferentially accreted to Venus instead of Earth. In short, Venus could be composed of material that was harder for the Earth to get ahold of.

“You would think that Earth is made up more of material from the outer system because it is closer to the outer solar system than Venus. But actually, with Earth in this vanguard role, it makes it actually more likely for Venus to accrete outer solar system material,” Asphaug said.

The co-authors on the two papers are Saverio Cambioni and Stephen R. Schwartz at the Lunar and Planetary Laboratory and Travis S. J. Gabriel at Arizona State University in Tempe, Arizona.

Featured image: Artist’s illustration of two massive objects colliding.NASA/JPL-Caltech

Provided by University of Arizona

Earthly Rocks Point Way To Water Hidden on Mars (Planetary Science)

 A combination of a once-debunked 19th-century identification of a water-carrying iron mineral and the fact that these rocks are extremely common on Earth, suggests the existence of a substantial water reservoir on Mars, according to a team of geoscientists.

“One of my student’s experiments was to crystalize hematite,” said Peter J. Heaney, professor of geosciences, Penn State. “She came up with an iron-poor compound, so I went to Google Scholar and found two papers from the 1840s where German mineralogists, using wet chemistry, proposed iron-poor versions of hematite that contained water.”

In 1844, Rudolf Hermann named his mineral turgite and in 1847 August Breithaupt named his hydrohematite. According to Heaney, in 1920, other mineralogists, using the then newly developed X-ray diffraction technique, declared these two papers incorrect. But the nascent technique was too primitive to see the difference between hematite and hydrohematite.

Video: Hydrohematite: Water containing hydrohematite on Earth and on Mars EARTH & MINERAL SCIENCES, PENN STATE

Si Athena Chen, Heaney’s doctoral student in geosciences, began by acquiring a variety of old samples of what had been labeled as containing water. Heaney and Chen obtained a small piece of Breithaupt’s original sample, a sample labeled as turgite from the Smithsonian Institution, and, surprisingly, five samples that were in Penn State’s own Frederick Augustus Genth collection.

After multiple examinations using a variety of instruments including infrared spectroscopy and synchrotron X-ray diffraction, a more sensitive, refined method than used in the mid-19th century, Chen showed that these minerals were indeed light on iron and had hydroxyl — a hydrogen and oxygen group — substituted for some of the iron atoms. The hydroxyl in the mineral is stored water.

The researchers recently proposed in the journal Geology “that hydrohematite is common in low-temperature occurrences of iron oxide on Earth, and by extension it may inventory large quantities of water in apparently arid planetary environments, such as the surface of Mars.”

lump of rock with dark red streaks and the original German label
The specimen of hydrohematite discovered by German mineralogist August Breithaupt in 1843 with its original label. IMAGE: ANDREAS MASSANEK, TU BERGAKADEMIE, FREIBERG, GERMANY

“I was trying to see what were the natural conditions to form iron oxides,” said Chen. “What were the necessary temperatures and pH to crystallize these hydrous phases and could I figure out a way to synthesize them.”

She found that at temperatures lower than 300 degrees Fahrenheit, in a watery, alkaline environment the hydrohematite can precipitate out, forming sedimentary layers.

“Much of Mars’ surface apparently originated when the surface was wetter and iron oxides precipitated from that water,” said Heaney. “But the existence of hydrohematite on Mars is still speculative.”

The “blueberries” found in 2004 by NASA’s Opportunity rover are hematite. Although the latest Mars rovers do have X-ray diffraction devices to identify hematite, they are not sophisticated enough to differentiate between hematite and hydrohematite.

“On Earth, these spherical structures are hydrohematite, so it seems reasonable to me to speculate that the bright red pebbles on Mars are hydrohematite,” said Heaney.

The researchers note that anhydrous hematite — lacking water — and hydrohematite — containing water — are two different colors, with hydrohematite being redder or containing dark red streaks.

Chen’s experiments found that naturally occurring hydrohematite contained 3.6% to 7.8% by weight of water and that goethite contained about 10% by weight of water. Depending on the amount of hydrated iron minerals found on Mars, the researchers believe there could be a substantial water reserve there.

Mars is called the red planet because of its color, which comes from iron compounds in the Martian dirt. According to the researchers, the presence of hydrohematite on Mars would provide additional evidence that Mars was once a watery planet, and water is the one compound necessary for all life forms on Earth.

view of Martian landscape, redish brown dirt with occasional rocks showing the tire tracks from the rover
The Red Planet as photographed by the Martian rover Curiosity.  IMAGE: NASA/JPL-CALTECH/MSSS

Other researchers involved in this project include Jeffrey E. Post, mineralogist and curator in charge of gems and minerals, Smithsonian Institution; Timothy B. Fischer, Chevron, Houston; Peter J. Eng, research professor, Consortium for Advanced Radiation Sources and the James Franck Institute, University of Chicago; and Joanne E. Stubbs, research associate professor, Consortium for Advanced Radiation Sources, University of Chicago.

The National Science Foundation and the U.S. Department of Energy supported this research.

Featured image: Hydrohematite (right) is a brighter red than anhydrous hematite (left).Image: Si Athena Chen, Penn State

Reference: Si Athena Chen et al, Superhydrous hematite and goethite: A potential water reservoir in the red dust of Mars?, Geology (2021). DOI: 10.1130/G48929.1

Provided by Penn State

Astronomers Discover Trio Of Planets Orbiting An M-Dwarf Star (Planetary Science)

A team of international astronomers reported on the discovery of one super-Earth- (TOI-1749b) and two sub-Neptune-sized planets (TOI1749c and TOI-1749d) transiting an early M dwarf TOI-1749 at a distance of 100 pc. Their study recently appeared in Arxiv.

Astronomers first identified these systems as planetary candidates using data from the TESS photometric survey. Later, they have followed up this system from the ground by means of multiband transit photometry, adaptive-optics imaging, and low-resolution spectroscopy, from which they have validated the planetary nature of the candidates.

They found that TOI-1749 b, c, and d have orbital periods of 2.39, 4.49, and 9.05 days, and radii of 1.4, 2.1, and 2.5 R, respectively. (More derived parameters are given in Table 1 below)

Table 1: Derived parameters from the results of photodynamical analysis. © Fukui et al.

In addition, using photodynamical models they have been able to place 95% confidence level upper limits on the masses of TOI-1749b, TOI-1749c, and TOI-1749d of 57, 14, and 15 M, respectively.

Figure 1: Period and radius diagram for planets around M dwarfs. The gray dots are known planets around M dwarfs taken from the NASA Exoplanet Archive. The magenta squares and black dots are for planets in the TOI-1749 and TOI-270 systems, respectively. The orange dashed line indicates the location of the proposed radius valley for M dwarf planets by Van Eylen et al. (2021). © Fukui et al.

The periods, sizes, and tentative masses of these planets are in line with a scenario in which all three planets initially had a hydrogen envelope on top of a rocky core, and only the envelope of the innermost planet has been stripped away by photoevaporation and/or core-powered mass loss mechanisms.

“The compositions of the innermost planet and the outer two planets can be explained by a bare rocky core and a rocky core + thin hydrogen envelope respectively.”

In addition, they have confirmed that the system is dynamically stable for at least 109 orbits of the innermost planet.

Figure 2. Period ratios of planetary trios including a near 2:1 commensurability pair. P1, P2, and P3 denote the orbital period of the inner planet in a near 2:1 commensurability pair, that of the outer planet in the same pair, and that of another planet inside (left panels) or outside (right panels) of the near 2:1 commensurability pair, respectively. Top and bottom panels show planetary trios around M dwarfs (Teff ≤ 4000K) and FGK dwarfs (Teff > 4000K), respectively. The gray dashed, dash-dotted, and dotted lines indicate the locations of the exact 2:1, 2:3, and 3:5 commensurabilities, respectively. This figure shows that additional planets to planetary pairs near 2:1 commensurability around M (FGK) dwarfs tend to have an inside (outside) orbit. Note that the TOI-178 system shows an opposite property; the host star however has an effective temperature that is close to the boundary (Teff = 4316K) © Fukui et al.

The outer planetary pair has a period ratio very close to the 2:1 commensurability (2.015), sharing the orbital architecture with the other M dwarf systems TOI-270 and TOI-175. This characteristic architecture might be a consequence of common planetary formation and migration processes in these systems.

“Further follow-up observations of this system would be worth pursuing to characterize the system in more detail.”

— concluded authors of the study

Featured image credit: Getty Images

Reference: A. Fukui, J. Korth, J. H. Livingston, J. D. Twicken, M. R. Zapatero Osorio, J. M. Jenkins, M. Mori, F. Murgas, M. Ogihara, N. Narita, E. Pallé, K. G. Stassun, G. Nowak, D. R. Ciardi, L. Alvarez-Hernandez, V. J. S. Béjar, N. Casasayas-Barris, N. Crouzet, J. P. de Leon, E. Esparza-Borges, D. Hidalgo Soto, K. Isogai, K. Kawauchi, P. Klagyivik, T. Kodama, S. Kurita, N. Kusakabe, R. Luque, A. Madrigal-Aguado, P. Montanes Rodriguez, G. Morello, T. Nishiumi, J. Orell-Miquel, M. Oshagh, H. Parviainen, M. Sánchez-Benavente, M. Stangret, N. Watanabe, G. Chen, M. Tamura, P. Bosch-Cabot, M. Bowen, K. Eastridge, L. Freour, E. Gonzales, P. Guerra, Y. Jundiyeh, T. K. Kim, L. V. Kroer, A. M. Levine, E. H. Morgan, M. Reefe, R. Tronsgaard, C. K. Wedderkopp, J. Wittrock, K. A. Collins, K. Hesse, D. W. Latham, G. R. Ricker, S. Seager, R. Vanderspek, J. Winn, E. Bachelet, M. Bowman, C. McCully, M. Daily, D. Harbeck, N. H. Volgenau, “TOI-1749: an M dwarf with a Trio of Planets including a Near-Resonant Pair”, Arxiv, pp. 1-30, 2021. https://arxiv.org/abs/2107.05430

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Changes in Earth’s Orbit Enabled the Emergence of Complex Life (Earth Science)

Scientists at the University of Southampton have discovered that changes in Earth’s orbit may have allowed complex life to emerge and thrive during the most hostile climate episode the planet has ever experienced.

The researchers – working with colleagues in the Chinese Academy of Sciences, Curtin University, University of Hong Kong, and the University of Tübingen – studied a succession of rocks laid down when most of Earth’s surface was covered in ice during a severe glaciation, dubbed ‘Snowball Earth’, that lasted over 50 million years. Their findings are published in the journal Nature Communications.

“One of the most fundamental challenges to the Snowball Earth theory is that life seems to have survived,” says Dr Thomas Gernon, Associate Professor in Earth Science at the University of Southampton, and co-author of the study. “So, either it didn’t happen, or life somehow avoided a bottleneck during the severe glaciation.”

The research team ventured into the South Australian outback where they targeted kilometre-thick units of glacial rocks formed about 700 million years ago. At this time, Australia was located closer to the equator, known today for its tropical climates. The rocks they studied, however, show unequivocal evidence that ice sheets extended as far as the equator at this time, providing compelling evidence that Earth was completely covered in an icy shell.

Thick Snowball Earth glacial deposits exposed in Tillite Gorge, Arkaroola, South Australia © University of Southampton

The team focused their attention on “Banded Iron Formations”, sedimentary rocks consisting of alternating layers of iron-rich and silica-rich material. These rocks were deposited in the ice-covered ocean near colossal ice sheets.

During the snowball glaciation, the frozen ocean would have been entirely cut off from the atmosphere. Without the normal exchange between the sea and air, many variations in climate that normally occur simply wouldn’t have.

“This was called the ‘sedimentary challenge’ to the Snowball hypothesis,” says Professor Ross Mitchell, professor at the Chinese Academy of Sciences in Beijing, China and the lead author. “The highly variable rock layers appeared to show cycles that looked a lot like climate cycles associated with the advance and retreat of ice sheets.” Such variability was thought to be at odds with a static Snowball Earth entombing the whole ocean in ice.

“The iron comes from hydrothermal vents on the seafloor,” added Gernon. “Normally, the atmosphere oxidizes any iron immediately, so Banded Iron Formations typically do not accumulate. But during the Snowball, with the ocean cut off from the air, iron was able to accumulate enough for them to form.”

Using magnetic susceptibility – a measure of the extent to which the rocks become magnetised when exposed to a magnetic field – the team made the discovery that the layered rock archives preserve evidence for nearly all orbital cycles.

Earth’s orbit around the sun changes its shape and the tilt and wobble of Earth’s spin axis also undergo cyclic changes. These astronomical cycles change the amount of incoming solar radiation that reaches Earth’s surface and, in doing so, they control climate.

Banded iron formations studied by the authors showing the alternation between iron-rich (red) and silica-rick (white) layers. © University of Southampton

“Even though Earth’s climate system behaved very differently during the Snowball, Earth’s orbital variations would have been blissfully unaware and just continued to do their thing,” explains Professor Mitchell.

The researchers concluded that changes in Earth’s orbit allowed the waxing and waning of ice sheets, enabling periodic ice-free regions to develop on snowball Earth.

Professor Mitchell explained, “This finding resolves one of the major contentions with the snowball Earth hypothesis: the long-standing observation of significant sedimentary variability during the snowball Earth glaciations appeared at odds with such an extreme reduction of the hydrological cycle”.

The team’s results help explain the enigmatic presence of sedimentary rocks of this age that show evidence for flowing water at Earth’s surface when this water should have been locked up in ice sheets. Dr. Gernon states: “This observation is important, because complex multicellular life is now known to have originated during this period of climate crisis, but previously we could not explain why”.

“Our study points to the existence of ice-free ‘oases’ in the snowball ocean that provided a sanctuary for animal life to survive arguably the most extreme climate event in Earth history,” Dr Gernon concluded.

Featured image: Glacial “dropstone” from the deposits showing a scratched surface (also called) striations linked to the movement of ice. © University of Southampton

Reference: Mitchell, R.N., Gernon, T.M., Cox, G.M. et al. Orbital forcing of ice sheets during snowball Earth. Nat Commun 12, 4187 (2021). https://doi.org/10.1038/s41467-021-24439-4

Provided by University of Southampton

CARMENES Instrument Finds Two New Planetary Systems Formed by Earths and Super-Earths (Planetary Science)

The Institute of Astrophysics of Andalusia (IAA-CSIC) leads the detection of what, according to the data, is the most common type of planetary systems around dwarf stars, the most common in the Milky Way

The era of the detection of planets outside our Solar System, which began less than three decades ago, has so far yielded more than four thousand detected planets. Their astonishing variety has shown that the structure of our Solar System, with rocky planets in the inner regions and gaseous icy planets in the outer regions, is not as typical as previously thought, and that other configurations appear more common, such as gas giant planets very close to their stars or systems with several super-Earths around dwarf stars. In this context, a new detection of two planetary systems by the CARMENES instrument, operating at Calar Alto Observatory (CAHA, Almería), reinforces the idea that dwarf stars tend to harbour rocky planets.

The 3.5-metre telescope at Calar Alto Observatory, where the CARMENES instrument operates. © IAA CSIC

“Our current understanding of the formation of low-mass planets in orbits very close to small stars suggests that they are very abundant, with an average of at least one planet per star. Despite this abundance, we hardly have any data on the density of these planets that would allow us to deduce their composition,” says Pedro J. Amado, a researcher at the Institute of Astrophysics of Andalusia (IAA-CSIC) who heads the study.

In our Solar System, Earth, Mars, Mercury and Venus are categorised as terrestrial or rocky planets. For extrasolar planets, those between half and twice the size of Earth are considered to be terrestrial, while those up to ten times the mass of Earth are classified as super-Earths, terms that have no implications for surface conditions or habitability. In fact, while the composition of Earth-like exoplanets may be similar to that of the rocky planets in the Solar System, the composition of super-Earths may also include other combinations of gas, rock, ice or water. 

The newly detected systems are found around the red dwarf (or M-dwarf) stars G 264-012 and Gl 393. Two planets with a minimum mass of 2.5 and 3.8 times that of the Earth have been found around the former, orbiting their star every 2.3 and 8.1 days. The planet in Gl 393 has a minimum mass of 1.7 Earth masses and orbits its star every seven days. All three planets fall into the category of hot earths and super-earths, and reach temperatures that preclude the presence of liquid water on the surface.

“To understand how the different planetary systems we are observing form and evolve, we need robust statistics on the number of planets that exist, as well as information on the architecture of the systems and the density of the planets. This will allow us to explain those that do not fit the known mechanisms, such as the GJ 3512 system that we also found with CARMENES, which has a giant planet around a dwarf star, or to confirm the tendency of dwarf stars to host multiple systems,” says Pedro J. Amado (IAA-CSIC).

In this sense, this work has also made it possible to detect a new factor that seems to influence the detections, since the planet around the star Gl 393 had gone unnoticed in previous campaigns with highly efficient planet-hunting instruments. Red dwarf stars show intense activity in the form of flares that can mask the signal from potential planets, and the research team noted that the non-detection of Gl 393’s planet could be due to the fact that previous observations were carried out during a peak of activity. They concluded that planets can most easily be detected in dwarf stars with moderate activity or outside the peaks of the star’s activity cycle.

“The CARMENES work is focused on extending the available data to compose a global picture of the planetary systems. The three planets in these two systems are among the smallest in mass, and therefore in the amplitude of the radial velocity they instill in their stars, which accounts for the quality of the instrument,” concludes Pedro J. Amado (IAA-CSIC).

Reference: P. J. Amado et al. “The CARMENES search for exoplanets around M dwarfs. Two terrestrial planets orbiting G264-012 and one terrestrial planet orbiting Gl393”. Astronomy & Astrophysics, https://doi.org/10.1051/0004-6361/202140633, June 2021

Provided by IAA CSIC

Are We Missing Other Earths? (Planetary Science)

Astronomers studying stellar pairs uncover evidence that there could be many more Earth-sized planets than previously thought

Some exoplanet searches could be missing nearly half of the Earth-sized planets around other stars. New findings from a team using the international Gemini Observatory and the WIYN 3.5-meter Telescope at Kitt Peak National Observatory suggest that Earth-sized worlds could be lurking undiscovered in binary star systems, hidden in the glare of their parent stars. As roughly half of all stars are in binary systems, this means that astronomers could be missing many Earth-sized worlds.

Earth-sized planets may be much more common than previously realized. Astronomers working at NASA Ames Research Center have used the twin telescopes of the international Gemini Observatory, a Program of NSF’s NOIRLab, to determine that many planet-hosting stars identified by NASA’s TESS exoplanet-hunting mission [1] are actually pairs of stars — known as binary stars — where the planets orbit one of the stars in the pair. After examining these binary stars, the team has concluded that Earth-sized planets in many two-star systems might be going unnoticed by transit searches like TESS’s, which look for changes in the light from a star when a planet passes in front of it [2]. The light from the second star makes it more difficult to detect the changes in the host star’s light when the planet transits.

The team started out by trying to determine whether some of the exoplanet host stars identified with TESS were actually unknown binary stars. Physical pairs of stars that are close together can be mistaken for single stars unless they are observed at extremely high resolution. So the team turned to both Gemini telescopes to inspect a sample of exoplanet host stars in painstaking detail. Using a technique called speckle imaging [3], the astronomers set out to see whether they could spot undiscovered stellar companions.

Using the `Alopeke and Zorro instruments on the Gemini North and South telescopes in Chile and Hawai‘i, respectively, [4] the team observed hundreds of nearby stars that TESS had identified as potential exoplanet hosts. They discovered that 73 of these stars are really binary star systems that had appeared as single points of light until observed at higher resolution with Gemini. “With the Gemini Observatory’s 8.1-meter telescopes, we obtained extremely high-resolution images of exoplanet host stars and detected stellar companions at very small separations,” said Katie Lester of NASA’s Ames Research Center, who led this work.

Lester’s team also studied an additional 18 binary stars previously found among the TESS exoplanet hosts using the NN-EXPLORE Exoplanet and Stellar Speckle Imager (NESSI) on the WIYN 3.5-meter Telescope at Kitt Peak National Observatory, also a Program of NSF’s NOIRLab. 

After identifying the binary stars, the team compared the sizes of the detected planets in the binary star systems to those in single-star systems. They realized that the TESS spacecraft found both large and small exoplanets orbiting single stars, but only large planets in binary systems. 

These results imply that a population of Earth-sized planets could be lurking in binary systems and going undetected using the transit method employed by TESS and many other planet-hunting telescopes. Some scientists had suspected that transit searches might be missing small planets in binary systems, but the new study provides observational support to back it up and shows which sizes of exoplanets are affected [5]

We have shown that it is more difficult to find Earth-sized planets in binary systems because small planets get lost in the glare of their two parent stars,” Lester stated. “Their transits are ‘filled in’ by the light from the companion star,” added Steve Howell of NASA’s Ames Research Center, who leads the speckle imaging effort and was involved in this research.

Since roughly 50% of stars are in binary systems, we could be missing the discovery of — and the chance to study — a lot of Earth-like planets,” Lester concluded.

The possibility of these missing worlds means that astronomers will need to use a variety of observational techniques before concluding that a given binary star system has no Earth-like planets. “Astronomers need to know whether a star is single or binary before they claim that no small planets exist in that system,” explained Lester. “If it’s single, then you could say that no small planets exist. But if the host is in a binary, you wouldn’t know whether a small planet is hidden by the companion star or does not exist at all. You would need more observations with a different technique to figure that out.

As part of their study, Lester and her colleagues also analyzed how far apart the stars are in the binary systems where TESS had detected large planets. The team found that the stars in the exoplanet-hosting pairs were typically farther apart than binary stars not known to have planets [6]. This could suggest that planets do not form around stars that have close stellar companions.

This speckle imaging survey illustrates the critical need for NSF telescope facilities to characterize newly discovered planetary systems and develop our understanding of planetary populations,” said National Science Foundation Division of Astronomical Sciences Program Officer Martin Still.

This is a major finding in exoplanet work,” Howell commented. “The results will help theorists create their models for how planets form and evolve in double-star systems.


[1] TESS is the Transiting Exoplanet Survey Satellite, a NASA mission designed to search for planets orbiting other stars in a survey of around 75% of the entire night sky. The mission launched in 2018 and has detected more than 3500 candidate exoplanets, of which more than 130 have been confirmed. The satellite looks for exoplanets by observing their host stars; a transiting exoplanet causes a subtle but measurable dip in the brightness of its host star as it crosses in front of the star and blocks some of its light.

[2] The transit technique is one way of discovering exoplanets. It involves looking for regular decreases in the light of a star that could be caused by a planet passing in front of or “transiting” the star and blocking some of the starlight.

[3] Speckle imaging is an astronomical technique that allows astronomers to see past the blur of the atmosphere by taking many quick observations in rapid succession. By combining these observations, it is possible to cancel out the blurring effect of the atmosphere, which affects ground-based astronomy by causing stars in the night sky to twinkle.

[4] `Alopeke & Zorro are identical imaging instruments permanently mounted on the Gemini North and South telescopes. Their names mean “fox” in Hawaiian and Spanish, respectively, reflecting their respective locations on Maunakea in Hawaiʻi and on Cerro Pachón in Chile.

[5] The team found that planets twice the size of Earth or smaller could not be detected using the transit method when observing binary systems.

[6] Lester’s team found that the exoplanet-hosting binary stars they identified had average separations of about 100 astronomical units. (An astronomical unit is the average distance between the Sun and Earth.) Binary stars that are not known to host planets are typically separated by around 40 astronomical units.

More information

This research is presented in the paper “Speckle Observations of TESS Exoplanet Host Stars. II. Stellar Companions at 1-1000 AU and Implications for Small Planet Detection” to appear in the Astronomical Journal.

The team is composed of Kathryn V. Lester (NASA Ames Research Center), Rachel A. Matson (US Naval Observatory), Steve B. Howell (NASA Ames Research Center), Elise Furlan (Exoplanet Science Institute, Caltech), Crystal L. Gnilka (NASA Ames Research Center), Nicholas J. Scott (NASA Ames Research Center), David R. Ciardi (Exoplanet Science Institute, Caltech), Mark E. Everett (NSF’s NOIRLab), Zachary D. Hartman (Lowell Observatory & Department of Physics & Astronomy, Georgia State University), and Lea A. Hirsch (Kavli Institute for Particle Astrophysics and Cosmology, Stanford University).

NSF’s NOIRLab (National Optical-Infrared Astronomy Research Laboratory), the US center for ground-based optical-infrared astronomy, operates the international Gemini Observatory (a facility of NSFNRC–CanadaANID–ChileMCTIC–BrazilMINCyT–Argentina, and KASI–Republic of Korea), Kitt Peak National Observatory (KPNO), Cerro Tololo Inter-American Observatory (CTIO), the Community Science and Data Center (CSDC), and Vera C. Rubin Observatory (operated in cooperation with the Department of Energy’s SLAC National Accelerator Laboratory). It is managed by the Association of Universities for Research in Astronomy (AURA) under a cooperative agreement with NSF and is headquartered in Tucson, Arizona. The astronomical community is honored to have the opportunity to conduct astronomical research on Iolkam Du’ag (Kitt Peak) in Arizona, on Maunakea in Hawai‘i, and on Cerro Tololo and Cerro Pachón in Chile. We recognize and acknowledge the very significant cultural role and reverence that these sites have to the Tohono O’odham Nation, to the Native Hawaiian community, and to the local communities in Chile, respectively.

Featured image: This illustration depicts a planet partially hidden in the glare of its host star and a nearby companion star. After examining a number of binary stars, astronomers have concluded that Earth-sized planets in many two-star systems might be going unnoticed by transit searches, which look for changes in the light from a star when a planet passes in front of it. The light from the second star makes it more difficult to detect the changes in the host star’s light when the planet passes in front of it. Credit: International Gemini Observatory/NOIRLab/NSF/AURA/J. da Silva


Provided by NOIRLab

Life in These Star-systems Could Have Spotted Earth (Planetary Science)

Scientists at Cornell University and the American Museum of Natural History have identified 2,034 nearby star-systems – within the small cosmic distance of 326 light-years – that could find Earth merely by watching our pale blue dot cross our sun.

That’s 1,715 star-systems that could have spotted Earth since human civilization blossomed about 5,000 years ago, and 319 more star-systems that will be added over the next 5,000 years.

Exoplanets around these nearby stars have a cosmic front-row seat to see if Earth holds life, the scientists said in research published June 23 in Nature.

“From the exoplanets’ point-of-view, we are the aliens,” said Lisa Kaltenegger, professor of astronomy and director of Cornell’s Carl Sagan Institute, in the College of Arts and Sciences.

“We wanted to know which stars have the right vantage point to see Earth, as it blocks the Sun’s light,” she said. “And because stars move in our dynamic cosmos, this vantage point is gained and lost.”

Kaltenegger and astrophysicist Jackie Faherty, a senior scientist at the American Museum of Natural History and co-author of “Past, Present and Future Stars That Can See Earth As A Transiting Exoplanet,” used positions and motions from the European Space Agency’s Gaia eDR3 catalog to determine which stars enter and exit the Earth Transit Zone – and for how long.

“Gaia has provided us with a precise map of the Milky Way galaxy,” Faherty said, “allowing us to look backward and forward in time, and to see where stars had been located and where they are going.”

Of the 2,034 star-systems passing through the Earth Transit Zone over the 10,000-year period examined, 117 objects lie within about 100 light-years of the sun and 75 of these objects have been in the Earth Transit Zone since commercial radio stations on Earth began broadcasting into space about a century ago.

“Our solar neighborhood is a dynamic place where stars enter and exit that perfect vantage point to see Earth transit the Sun at a rapid pace,” Faherty said.

Included in the catalog of 2,034 star-systems are seven known to host exoplanets. Each one of these worlds has had or will have an opportunity to detect Earth, just as Earth’s scientists have found thousands of worlds orbiting other stars through the transit technique.

By watching distant exoplanets transit – or cross – their own sun, Earth’s astronomers can interpret the atmospheres backlit by that sun. If exoplanets hold intelligent life, they can observe Earth backlit by the sun and see our atmosphere’s chemical signatures of life.

The Ross 128 system, with a red dwarf host star located in the Virgo constellation, is about 11 light-years away and is the second-closest system with an Earth-size exoplanet (about 1.8 times the size of our planet). Any inhabitants of this exoworld could have seen Earth transit our own sun for 2,158 years, starting about 3,057 years ago; they lost their vantage point about 900 years ago.

The Trappist-1 system, at 45 light-years from Earth, hosts seven transiting Earth-size planets – four of them in the temperate, habitable zone of that star. While we have discovered the exoplanets around Trappist-1, they won’t be able to spot us until their motion takes them into the Earth Transit Zone in 1,642 years. Potential Trappist-1 system observers will remain in the cosmic Earth transit stadium seats for 2,371 years.

“Our analysis shows that even the closest stars generally spend more than 1,000 years at a vantage point where they can see Earth transit,” Kaltenegger said. “If we assume the reverse to be true, that provides a healthy timeline for nominal civilizations to identify Earth as an interesting planet.”

The James Webb Space telescope – expected to launch later this year — is set to take a detailed look at several transiting worlds to characterize their atmospheres and ultimately search for signs of life.

The Breakthrough Starshot initiative is an ambitious project underway that is looking to launch a nano-sized spacecraft toward the closest exoplanet detected around Proxima Centauri – 4.2 light-years from us – and fully characterize that world.

“One might imagine that worlds beyond Earth that have already detected us, are making the same plans for our planet and solar system,” said Faherty. “This catalog is an intriguing thought experiment for which one of our neighbors might be able to find us.”

The Carl Sagan Institute, the Heising Simons Foundation and the Breakthrough Initiatives program supported this research.

Reference: Kaltenegger, L., Faherty, J.K. Past, present and future stars that can see Earth as a transiting exoplanet. Nature 594, 505–507 (2021). https://doi.org/10.1038/s41586-021-03596-y

Provided by Cornell University

The Earth Has A Pulse — A 27.5-million-year Cycle Of Geological Activity (Geology)

Analysis of 260 million years of major geological events finds recurring clusters 27.5 million years apart

Geologic activity on Earth appears to follow a 27.5-million-year cycle, giving the planet a “pulse,” according to a new study published in the journal Geoscience Frontiers.

“Many geologists believe that geological events are random over time. But our study provides statistical evidence for a common cycle, suggesting that these geologic events are correlated and not random,” said Michael Rampino, a geologist and professor in New York University’s Department of Biology, as well as the study’s lead author.

Over the past five decades, researchers have proposed cycles of major geological events–including volcanic activity and mass extinctions on land and sea–ranging from roughly 26 to 36 million years. But early work on these correlations in the geological record was hampered by limitations in the age-dating of geologic events, which prevented scientists from conducting quantitative investigations.

However, there have been significant improvements in radio-isotopic dating techniques and changes in the geologic timescale, leading to new data on the timing of past events. Using the latest age-dating data available, Rampino and his colleagues compiled updated records of major geological events over the last 260 million years and conducted new analyses.

The team analyzed the ages of 89 well-dated major geological events of the last 260 million years. These events include marine and land extinctions, major volcanic outpourings of lava called flood-basalt eruptions, events when oceans were depleted of oxygen, sea-level fluctuations, and changes or reorganization in the Earth’s tectonic plates.

They found that these global geologic events are generally clustered at 10 different timepoints over the 260 million years, grouped in peaks or pulses of roughly 27.5 million years apart. The most recent cluster of geological events was approximately 7 million years ago, suggesting that the next pulse of major geological activity is more than 20 million years in the future.

The researchers posit that these pulses may be a function of cycles of activity in the Earth’s interior–geophysical processes related to the dynamics of plate tectonics and climate. However, similar cycles in the Earth’s orbit in space might also be pacing these events.

“Whatever the origins of these cyclical episodes, our findings support the case for a largely periodic, coordinated, and intermittently catastrophic geologic record, which is a departure from the views held by many geologists,” explained Rampino.

In addition to Rampino, study authors include Yuhong Zhu of NYU’s Center for Data Science and Ken Caldeira of the Carnegie Institution for Science.

Featured image: NYU researchers found that global geologic events are generally clustered at 10 different timepoints over the 260 million years, grouped in peaks or pulses of roughly 27.5 million years apart. © Rampino et al., Geoscience Frontiers

Reference: Michael R. Rampino, Ken Caldeira, Yuhong Zhu, A pulse of the Earth: A 27.5-Myr underlying cycle in coordinated geological events over the last 260 Myr, Geoscience Frontiers, Volume 12, Issue 6, 2021, 101245, ISSN 1674-9871, https://doi.org/10.1016/j.gsf.2021.101245. (https://www.sciencedirect.com/science/article/pii/S1674987121001092)

Provided by New York University

Scientists Create Unique Instrument To Probe The Most Extreme Matter On Earth (Physics)

Laser-produced high energy density plasmas(link is external), akin to those found in stars, nuclear explosions, and the core of giant planets, may be the most extreme state of matter created on Earth. Now scientists at the U.S. Department of Energy’s (DOE) Princeton Plasma Physics Laboratory (PPPL), building on nearly a decade of collaboration with the National Ignition Facility (NIF) at the DOE’s Lawrence Livermore National Laboratory (LLNL), have designed a novel X-ray crystal spectrometer to provide high-resolution measurements of a challenging feature of NIF-produced HED plasmas.

Most powerful lasers

The collaboration with NIF, home to the world’s largest and most powerful lasers, represents a major expansion for PPPL’s X-ray crystal spectrometer designs, which are used by fusion laboratories(link is external) around the world to record on detectors the spectrum of X-rays from the plasma – gases of electrons and atomic nuclei, or ions — that fuel fusion reactions. These PPPL instruments measure profiles of key parameters such as the ion and electron temperatures in large volumes of hot plasmas that are magnetically confined in doughnut-shaped  tokamak(link is external) fusion devices  to facilitate fusion reactions. By contrast, NIF laser-produced HED plasmas are tiny, point-like substances that require differently designed spectrometers for high-resolution studies.

“We previously built a spectrometer for the NIF that has been quite successful,” said physicist Manfred Bitter, a long-time member of the PPPL design team. That spectrometer, delivered in 2017, provides high-resolution measurements of the temperature and density of NIF extreme plasmas for inertial confinement fusion experiments, and the data obtained have been presented in invited talks and peer-reviewed publications.

The HED experiments differ from the magnetically confined experiments that PPPL conducts in many respects. A major difference that affects the design of  spectrometers is the small size of laser-produced HED plasmas, whose volumes are typically on the order of a cubic millimeter and can be considered as point-like X-ray sources. This small size compares with extended tokamak plasmas, which have volumes of several cubic meters and require very different diagnostic designs.

New design challenges

PPPL’s new spectrometer for the NIF responds to new design challenges. They call for measuring a fine structure in the X-ray spectra of HED plasmas that reveals their state of matter under extreme conditions. Such measurements can show whether the ions in the highly-compressed plasma are in a random, or fluid-like arrangement, or in a more ordered lattice-like arrangement that is typical for a solid.

This critical state of matter can be detected in what is called the Extended X-ray Absorption Fine-Structure (EXAFS) —  the technical term for the tiny intensity variations, or wiggles, in the X-ray energy spectrum recorded by crystal spectrometers. “The standard crystal forms which have been used for the diagnosis of HED plasmas, so far, cannot be used in this case,” said Bitter, lead author of a paper(link is external) in the Review of Scientific Instruments that describes the PPPL spectrometer being fabricated for the NIF. “Their resolution and photon throughput are not high enough and they introduce imaging and other errors.”

These are the challenges the new crystal spectrometer must meet, Bitter said:

• To reduce statistical errors, the design must be adapted to a high throughput of photons, the particles of light that X-ray sources and all other light sources emit. The X-ray reflecting crystal must therefore have a large area without introducing any of the imaging errors that large standard crystals tend to produce.  

• The crystal must reflect the wide range of X-ray energies over which the fine structure is observed.

• Finally, the crystal and detector arrangements must minimize the effects of what is called source-size broadening. This problem results from the tiny, but not negligible, size of a laser-produced HED plasma that deteriorates, or muddles, the spectral resolution. The standard crystal forms that have been used until now cannot fully eliminate or minimize these broadening effects. 

Bitter and PPPL physicist Novimir Pablant worked together to design the new spectrometer. Bitter came up with the idea of shaping the crystal that mirrors the spectrum in the form of what is called a sinusoidal spiral. These spirals denote a family of curves whose shapes can be determined to assume any real value, making it possible to select a special shape of crystal. Pablant, who co-authored the Review of Scientific Instruments paper, created a computer code to design the sinusoidal crystal in a process that he outlines in a recently submitted companion paper to the same journal.

“I developed a code that would allow me to model the complicated 3-D shape of the crystal and simulate the performance of this new spectrometer design,” Pablant said. The simulations showed that the performance of the crystal marked “a five-times improvement in energy resolution for this NIF project compared to their previous spectrometer design.” 

The collaboration will move to NIF in October when the new spectrometer is scheduled for  testing there, with researchers at both laboratories eagerly awaiting the results. “Experiments at the NIF that measure the EXFAS spectrum at high X-ray energies have had low signals,” said Marilyn Schneider, leader of the Radiative Properties Group at the Physics and Life Sciences Directorate of LLNL and a co-author of the paper. “The spectrometer design described in the paper concentrates the low signal and increases the signal-to-noise ratio while maintaining the high resolution required for observing EXAFS,” she said.

Experimental verification is the next step required. “We arrived at this design after several attempts and are confident that it will work,” said Bitter. “But we have not yet tested the design at NIF and must see how it performs in the fall.” 

PPPL co-authors of the paper include physicists Ken Hill, Lan Gao, Luis Delgado-Aparicio, Brent Stratton, and Brian Kraus. Philip Efthimion, who heads the PPPL Plasma Science & Technology Department that oversaw this work, was also a co-author.  Co-authors at NIF include physicists Federica Coppari, Robert Kauffman, Michael MacDonald, Andrew MacPhee, Yuan Ping, Stanislav Stoupin, and Daniel Thorn. The DOE Office of Science supported this research.

Featured image: Physicists Manfred Bitter, upper right, and Novimir Pablant, lower left, with figures from spectrometer design poster. Sketches include target chamber for laser-produced plasmas, upper center, and a crystal spectrometer, lower right. (Photos and collage by Elle Starkman/PPPL Office of Communications.)

Reference: M. Bitter, N. Pablant, K. W. Hill, Lan Gao, B. Kraus, P. C. Efthimion, L. Delgado-Apericio, B. Stratton, M. Schneider, F. Coppari, R. Kauffman, M. J. MacDonald, A. MacPhee, Y. Ping, S. Stoupin, and D. Thorn , “A new class of focusing crystal shapes for Bragg spectroscopy of small, point-like, x-ray sources in laser produced plasmas”, Review of Scientific Instruments 92, 043531 (2021) https://doi.org/10.1063/5.0043599

Provided by PPPL