ST/ Could more of Earth’s surface host life?

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Paradigm

30 min readSep 14, 2022

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Space biweekly vol.60, 31st August — 14th September

TL;DR

Of all known planets, Earth is as friendly to life as any planet could possibly be — or is it? If Jupiter’s orbit changes, a new study shows Earth could be more hospitable than it is today.
Astronomers have just announced the discovery of two ‘super-Earth’ planets orbiting LP 890–9, a small, cool star located about 100 light-years from Earth.
A new simulation conducted on the world’s most powerful supercomputer dedicated to astronomy has produced a testable scenario to explain the appearance of the bar of the Milky Way. Comparing this scenario to data from current and future space telescopes will help clarify the evolution of our home Galaxy.
To understand the frenzied ‘baby boom’ of star birth that occurred early in the universe’s history, researchers turned to the Small Magellanic Cloud, a satellite galaxy of the Milky Way. The teams’ results show that the process of star formation in the Small Magellanic Cloud is similar to that in our own Milky Way.
A new study suggests that many more planets may have large amounts of water than previously thought — as much as half water and half rock. All that water is probably embedded in the rock, rather than flowing as oceans or rivers on the surface.
Jupiter-sized planets can be stolen or captured by massive stars in the densely populated stellar nurseries where most stars are born, a new study has found.
Physicists and astronomers have studied gamma rays caused by the Sagittarius Dwarf, a small neighboring galaxy of our Milky Way. They showed that all the observed gamma radiation can be explained by millisecond pulsars, and can therefore not be interpreted as a smoking gun signature for the presence of dark matter.
Astronomers using the VLBA have produced a full, 3-D view of a binary star system with a planet orbiting one of the stars. Their achievement promises important new insights into the process of planet formation.
NASA’s MAVEN and the United Arab Emirates’ EMM missions have released joint observations of dynamic proton aurora events at Mars. By combining the observations, scientists determined that what they were seeing was essentially a map of where the solar wind was raining down onto the planet, opening new avenues for understanding the Martian atmosphere.
With an eye toward a possible return mission years in the future, Cornell University astronomers have shown how smooth terrains — a good place to land a spacecraft and to scoop up samples — evolve on the icy world of comets.
Upcoming industry events. And more!

Space industry in numbers

The global smart space market size is projected to grow from USD 9.4 billion in 2020 to USD 15.3 billion by 2025, at a Compound Annual Growth Rate (CAGR) of 10.2% during the forecast period. The increasing venture capital funding and growing investments in smart space technology to drive market growth.

Analysts at Morgan Stanley and Goldman Sachs have predicted that economic activity in space will become a multi-trillion-dollar market in the coming decades. Morgan Stanley’s Space Team estimates that the roughly USD 350 billion global space industry could surge to over USD 1 trillion by 2040.

Source: Satellite Industry Association, Morgan Stanley Research, Thomson Reuters. *2040 estimates

Space industry news

Latest research

System Architecture and Planetary Obliquity: Implications for Long-term Habitability

by Pam Vervoort, Jonathan Horner, Stephen R. Kane, Sandra Kirtland Turner, James B. Gilmore in The Astronomical Journal

Of all known planets, Earth is as friendly to life as any planet could possibly be — or is it? If Jupiter’s orbit changes, a new study shows Earth could be more hospitable than it is today.

When a planet has a perfectly circular orbit around its star, the distance between the star and the planet never changes. Most planets, however, have “eccentric” orbits around their stars, meaning the orbit is oval-shaped. When the planet gets closer to its star, it receives more heat, affecting the climate. Using detailed models based on data from the solar system as it is known today, UC Riverside researchers created an alternative solar system. In this theoretical system, they found that if gigantic Jupiter’s orbit were to become more eccentric, it would in turn induce big changes in the shape of Earth’s orbit.

Schematic depiction of the impact of nodal precession Ω on the obliquity of a planet. (a) The orbit is tilted i° relative to the reference plane with orbital normal n. The northern hemisphere of the planet is tilted away during a given time of year with an angle between the rotational axis and the orbit normal. (b) The nodal precession has rotated the orbital plane by 180° and the orbit is tilted −i° relative to the reference plane. If the rotational axis would remain fixed relative to the fixed background stars, the new obliquity is− 2i. (c)However, solar and lunar torques pull the equatorial bulge toward the solar and lunar planes, driving precession of the rotational axis while affecting the obliquity.

“If Jupiter’s position remained the same, but the shape of its orbit changed, it could actually increase this planet’s habitability,” said Pam Vervoort, UCR Earth and planetary scientist and lead study author.

Between zero and 100 degrees Celsius, the Earth’s surface is habitable for multiple known life forms. If Jupiter pushed Earth’s orbit to become more eccentric, parts of the Earth would sometimes get closer to the sun. Parts of the Earth’s surface that are now sub-freezing would get warmer, increasing temperatures in the habitable range.

A habitable zone, shown in green here, is defined as the region around a star where liquid water, an essential ingredient for life as we know it, could potentially be present. (NASA-JPL/Caltech)

“Many are convinced that Earth is the epitome of a habitable planet and that any change in Jupiter’s orbit, being the massive planet it is, could only be bad for Earth,” Vervoort said. “We show that both assumptions are wrong.”

The researchers are interested in applying this finding to the search for habitable planets around other stars, called exoplanets.

“The first thing people look for in an exoplanet search is the habitable zone, the distance between a star and a planet to see if there’s enough energy for liquid water on the planet’s surface,” said Stephen Kane, UCR astrophysicist and study co-author.

During its orbit, different parts of a planet receive more or fewer direct rays, resulting in the planet having seasons. Parts of the planet may be pleasant during one season, and extremely hot or cold in another.

“Having water on its surface a very simple first metric, and it doesn’t account for the shape of a planet’s orbit, or seasonal variations a planet might experience,” Kane said.

Maximum eccentricity and mean angular momentum deficit. (a) The maximum eccentricity of an Earth-like planet under different planetary architectures, i.e., with a Jupiter-like planet having different initial semimajor axes and eccentricities. (b) The percentage of deviation in the angular momentum (AMD) relative to that of a circular orbit, calculated as the mean deviation across the 10 Myr integration time. Blue colors indicate AMDs less than the modern Earth, below 0.0477%. The red circle is the current position of Jupiter in our solar system.

Existing telescopes are capable of measuring a planet’s orbit. However, there are additional factors that could affect habitability, such as the degree to which a planet is tilted toward or away from a star. The part of the planet tilted away from the star would get less energy, causing it to be colder. This same study found that if Jupiter were positioned much closer to the sun, it would induce extreme tilting on Earth, which would make large sections of the Earth’s surface sub-freezing. It is more difficult to measure tilt, or a planet’s mass, so the researchers would like to work toward methods that help them estimate those factors as well. Ultimately, the movement of a giant planet is important in the quest to make predictions about the habitability of planets in other systems as well as the quest to understand its influence in this solar system.

Duration of the climatic precession (left panel) and obliquity (right panel) cycles as a function of the dynamical ellipticity scaling factor, following Laskar et al. (1993a), for a simulation where Jupiter is located at it is current position with an eccentricity of 0.05. A scaling factor of 1.0 equates to a dynamical ellipticity of 0.00328 equal to the value for the modern Earth.

“It’s important to understand the impact that Jupiter has had on Earth’s climate through time, how its effect on our orbit has changed us in the past, and how it might change us once again in the future,” Kane said.

Two temperate super-Earths transiting a nearby late-type M dwarf

by L. Delrez, C.A. Murray, F.J. Pozuelos, N. Narita, E. Ducrot, M. Timmermans, N. Watanabe, A.J. Burgasser, T. Hirano, B.V. Rackham, K.G. Stassun, V. Van Grootel, C. Aganze, M. Cointepas, S. Howell, L. Kaltenegger, P. Niraula, D. Sebastian in Astronomy & Astrophysics

An international research team including astronomers at the University of Birmingham, has just announced the discovery of two “super-Earth” planets orbiting LP 890–9, a small, cool star located about 100 light-years from Earth. The star, also called TOI-4306 or SPECULOOS-2, is the second-coolest star found to host planets, after the famous TRAPPIST-1.

The system’s inner planet, called LP 890–9b, is about 30% larger than Earth and completes an orbit around the star in just 2.7 days. This first planet was initially identified as a possible planet candidate by NASA’s Transiting Exoplanet Survey Satellite (TESS), a space mission searching for exoplanets orbiting nearby stars. This candidate was confirmed and characterized by the SPECULOOS telescopes (Search for habitable Planets EClipsing ULtra-cOOl Stars), one of which is operated by the University of Birmingham. SPECULOOS researchers then used their telescopes to seek additional transiting planets in the system that would have been missed by TESS.

“TESS searches for exoplanets using the transit method, by monitoring the brightness of thousands of stars simultaneously, looking for slight dimmings that might be caused by planets passing in front of their stars,” explains Laetitia Delrez, a postdoctoral researcher at the University of Liège, and the lead author of the article.
“However, a follow-up with ground-based telescopes is often necessary to confirm the planetary nature of the detected candidates and to refine the measurements of their sizes and orbital properties.”

TESS target pixel files of LP 890–9 for sectors 4 (upper left), 5 (upper right), 31 (lower left), and 32 (lower right).

This follow-up is particularly important in the case of very cold stars, such as LP 890–9, which emit most of their light in the near-infrared and for which TESS has a rather limited sensitivity. The telescopes of the SPECULOOS project, installed at ESO’s Paranal Observatory in Chile and on the island of Tenerife, are optimised to observe this type of star with high precision, thanks to cameras that are very sensitive in the near-infrared.

“The goal of SPECULOOS is to search for potentially habitable terrestrial planets transiting some of the smallest and coolest stars in the solar neighbourhood, such as the TRAPPIST-1 planetary system, which we discovered in 2016,” recalls Michaël Gillon, from the University of Liège, and the principal investigator of the SPECULOOS project. “This strategy is motivated by the fact that such planets are particularly well suited to detailed studies of their atmospheres and to the search for possible chemical traces of life with large observatories, such as the James Webb Space Telescope (JWST).”

Imaging of the present-day position of LP 890–9 over 64 years, to assess for a current blend with an unresolved background object.

The observations of LP 890–9 gathered by SPECULOOS proved fruitful as they not only confirmed the first planet, but they were critical for the detection of a second, previously unknown planet. This second planet, LP 890–9c (renamed SPECULOOS-2c by the SPECULOOS researchers), is similar in size to the first (about 40% larger than Earth) but has a longer orbital period of about 8.5 days. This orbital period, later confirmed with the MuSCAT3 instrument in Hawaii, places the planet in the so-called “habitable zone” around its star.

“The habitable zone is a concept under which a planet with similar geological and atmospheric conditions as Earth, would have a surface temperature allowing water to remain liquid for billions of years” explains Amaury Triaud, a professor of Exoplanetology at University Birmingham and the leader of the SPECULOOS working group that scheduled the observations leading to the discovery of the second planet. “This gives us a license to observe more and find out whether the planet has an atmosphere, and if so, to study its content and assess its habitability.”

The next step will be to study the atmosphere of this planet, for example with the JWST, for which LP 890–9c appears to be the second-most favourable target among the potentially habitable terrestrial planets known so far, surpassed only by the TRAPPIST-1 planets (for which Professor Triaud was also co-discoverer).

“It is important to detect as many temperate terrestrial worlds as possible to study the diversity of exoplanet climates, and eventually to be in a position to measure how frequently biology has emerged in the Cosmos,” added Professor Triaud.

Age distribution of stars in boxy/peanut/X-shaped bulges formed without bar buckling

by Junichi Baba, Daisuke Kawata, Ralph Schönrich in Monthly Notices of the Royal Astronomical Society

A new simulation conducted on the world’s most powerful supercomputer dedicated to astronomy has produced a testable scenario to explain the appearance of the bar of the Milky Way. Comparing this scenario to data from current and future space telescopes will help clarify the evolution of our home Galaxy.

Astronomy is revealing the structure of the Milky Way Galaxy in which we live in increasing detail. We know that it is a disk galaxy, with two- or four- armed spirals, with a straight bar in the middle connecting the spirals. Now, we also know that the inner part of the bar has a “peanut-shaped bulge,” places where the bar is thicker, sticking out above and below the mid plane of the Milky Way Galaxy and a “nuclear bulge,” which is disky and located in the central part of the Milky Way. Some other galaxies, but not all, exhibit similar two-type bulges.

Like dieters who suddenly find bulges sticking out, astronomers asked the question, “How did the two-type bulges form?” To answer this question a team led by Junichi Baba at the National Astronomical Observatory of Japan (NAOJ) simulated one possible scenario for a Milky-Way-like galaxy on “ATERUI II” at NAOJ, the world’s most powerful supercomputer dedicated to astronomy. The team’s simulation is the most complete and accurate to date, including not only the stars in the galaxy, but also the gas. It also incorporates the birth of new stars from the gas and the deaths of stars as supernovae.

The formation of a bar helps to channel gas into the central part of the galaxy, where it triggers the formation of new stars. So it might be reasonable to assume that the nuclear bugle in the galaxy is created from new stars born there. But the simulations show that there are almost no new stars in the bar outside the nuclear bulge, because the bar is so effective at channeling gas towards the center. This means that pigging-out on gas is not the reason that a peanut-shaped bulge develops in the bar. Instead, the team finds that gravitational interactions can drive some of the stars into orbits which take them above and below the mid plane.

The most exciting part is that the simulation provides a testable scenario. Because the peanut-shaped bulge acquires no new stars, all of its stars must predate the formation of the bar. At the same time, the bar channels gas to the central region where it creates many new stars. So almost all of the stars in the nuclear bulge will have been born after the bar formed. This means that the stars in the peanut-shaped bulge will be older than the stars in the nuclear bulge, with a clear break between the ages. This break corresponds to the time when the bar formed.

Data from the European Space Agency’s Gaia probe and Japan’s future JASMINE satellite will allow us to determine the motions and ages of the stars and test this scenario. If astronomers can detect a difference between the ages of the stars in peanut-shaped and nuclear bulges, it will not only prove that overeating is not to blame for the peanut-shaped bulge, it will tell us the age of the bar in the Milky Way Galaxy.

The Internal Line-of-Sight Kinematics of NGC 346: The Rotation of the Core Region

by Peter Zeidler, Elena Sabbi, Antonella Nota in The Astrophysical Journal

Stars are the machines that sculpt the universe, yet scientists don’t fully know how they form. To understand the frenzied ‘baby boom’ of star birth that occurred early in the universe’s history, researchers turned to the Small Magellanic Cloud, a satellite galaxy of the Milky Way. This nearby galaxy has a simpler chemical composition than the Milky Way, making it similar to the galaxies found in the younger universe, when heavier elements were more scarce. This allows it to serve as a proxy for the early universe.

Two separate studies — the first with the Hubble Space Telescope, and the second with the European Southern Observatory’s Very Large Telescope — recently came to the same conclusion. Using different methods, the independent teams found young stars spiraling into the center of a massive star cluster called NGC 346 in the Small Magellanic Cloud. This river-like motion of gas and stars is an efficient way to fuel star birth, researchers say. The teams’ results show that the process of star formation in the Small Magellanic Cloud is similar to that in our own Milky Way.

Nature likes spirals — from the whirlpool of a hurricane, to pinwheel-shaped protoplanetary disks around newborn stars, to the vast realms of spiral galaxies across our universe. Now astronomers are bemused to find young stars that are spiraling into the center of a massive cluster of stars in the Small Magellanic Cloud, a satellite galaxy of the Milky Way. The outer arm of the spiral in this huge, oddly shaped stellar nursery called NGC 346 may be feeding star formation in a river-like motion of gas and stars. This is an efficient way to fuel star birth, researchers say.

A color-composite image of NGC 346, composed of the F658N (Hα, red), F814W (green), and F555W (blue) HST data.

The Small Magellanic Cloud has a simpler chemical composition than the Milky Way, making it similar to the galaxies found in the younger universe, when heavier elements were more scarce. Because of this, the stars in the Small Magellanic Cloud burn hotter and so run out of their fuel faster than in our Milky Way. Though a proxy for the early universe, at 200,000 light-years away the Small Magellanic Cloud is also one of our closest galactic neighbors. Learning how stars form in the Small Magellanic Cloud offers a new twist on how a firestorm of star birth may have occurred early in the universe’s history, when it was undergoing a “baby boom” about 2 to 3 billion years after the big bang (the universe is now 13.8 billion years old).

The new results find that the process of star formation there is similar to that in our own Milky Way. Only 150 light-years in diameter, NGC 346 boasts the mass of 50,000 Suns. Its intriguing shape and rapid star formation rate has puzzled astronomers. It took the combined power of NASA’s Hubble Space Telescope and the European Southern Observatory’s Very Large Telescope (VLT) to unravel the behavior of this mysterious-looking stellar nesting ground.

“Stars are the machines that sculpt the universe. We would not have life without stars, and yet we don’t fully understand how they form,” explained study leader Elena Sabbi of the Space Telescope Science Institute in Baltimore. “We have several models that make predictions, and some of these predictions are contradictory. We want to determine what is regulating the process of star formation, because these are the laws that we need to also understand what we see in the early universe.”

The gas velocity map. To guide the reader, we indicated the Sabbi et al. (2007) subclusters.

Researchers determined the motion of the stars in NGC 346 in two different ways. Using Hubble, Sabbi and her team measured the changes of the stars’ positions over 11 years. The stars in this region are moving at an average velocity of 2,000 miles per hour, which means that in 11 years they move 200 million miles. This is about 2 times the distance between the Sun and the Earth. But this cluster is relatively far away, inside a neighboring galaxy. This means the amount of observed motion is very small and therefore difficult to measure. These extraordinarily precise observations were possible only because of Hubble’s exquisite resolution and high sensitivity. Also, Hubble’s three-decade-long history of observations provides a baseline for astronomers to follow minute celestial motions over time.

The second team, led by Peter Zeidler of AURA/STScI for the European Space Agency, used the ground-based VLT’s Multi Unit Spectroscopic Explorer (MUSE) instrument to measure radial velocity, which determines whether an object is approaching or receding from an observer.

“What was really amazing is that we used two completely different methods with different facilities and basically came to the same conclusion, independent of each other,” said Zeidler. “With Hubble, you can see the stars, but with MUSE we can also see the gas motion in the third dimension, and it confirms the theory that everything is spiraling inwards.”

“A spiral is really the good, natural way to feed star formation from the outside toward the center of the cluster,” explained Zeidler. “It’s the most efficient way that stars and gas fueling more star formation can move towards the center.”

Half of the Hubble data for this study of NGC 346 is archival. The first observations were taken 11 years ago. They were recently repeated to trace the motion of the stars over time. Given the telescope’s longevity, the Hubble data archive now contains more than 32 years of astronomical data powering unprecedented, long-term studies.

“The Hubble archive is really a gold mine,” said Sabbi. “There are so many interesting star-forming regions that Hubble has observed over the years. Given that Hubble is performing so well, we can actually repeat these observations. This can really advance our understanding of star formation.”

Density, not radius, separates rocky and water-rich small planets orbiting M dwarf stars

by Rafael Luque and Enric Pall in Science

Water is the one thing all life on Earth needs, and the cycle of rain to river to ocean to rain is an essential part of what keeps our planet’s climate stable and hospitable. When scientists talk about where to search for signs of life throughout the galaxy, planets with water are always at the top of the list.

A new study suggests that many more planets may have large amounts of water than previously thought — as much as half water and half rock. The catch? All that water is probably embedded in the rock, rather than flowing as oceans or rivers on the surface.

“It was a surprise to see evidence for so many water worlds orbiting the most common type of star in the galaxy,” said Rafael Luque, first author on the new paper and a postdoctoral researcher at the University of Chicago. “It has enormous consequences for the search for habitable planets.”

Sample of small transiting planets around M dwarfs (STPMs) as of 21 July 2021.

Thanks to better telescope instruments, scientists are finding signs of more and more planets in distant solar systems. A larger sample size helps scientists identify demographic patterns — similar to how looking at the population of an entire town can reveal trends that are hard to see at an individual level. Luque, along with co-author Enric Pallé of the Institute of Astrophysics of the Canary Islands and the University of La Laguna, decided to take a population-level look at a group of planets that are seen around a type of star called an M-dwarf. These stars are the most common stars we see around us in the galaxy, and scientists have catalogued dozens of planets around them so far. But because stars are so much brighter than their planets, we cannot see the actual planets themselves. Instead, scientists detect faint signs of the planets’ effects on their stars — the shadow created when a planet crosses in front of its star, or the tiny tug on a star’s motion as a planet orbits. That means many questions remain about what these planets actually look like.

“The two different ways to discover planets each give you different information,” said Pallé. By catching the shadow created when a planet crosses in front of its star, scientists can find the diameter of the planet. By measuring the tiny gravitational pull that a planet exerts on a star, scientists can find its mass.

By combining the two measurements, scientists can get a sense of the makeup of the planet. Perhaps it’s a big-but-airy planet made mostly out of gas like Jupiter, or a small, dense, rocky planet like Earth. These analyses had been done for individual planets, but much more rarely for the entire known population of such planets in the Milky Way galaxy. As the scientists looked at the numbers — 43 planets in all — they saw a surprising picture emerging. The densities of a large percentage of the planets suggested that they were too light for their size to be made up of pure rock. Instead, these planets are probably something like half rock and half water, or another lighter molecule. Imagine the difference between picking up a bowling ball and a soccer ball: they’re roughly the same size, but one is made up of much lighter material.

Dependence of the STPM sample on orbital period.

It may be tempting to imagine these planets like something out of Kevin Costner’s Waterworld: entirely covered in deep oceans. However, these planets are so close to their suns that any water on the surface would exist in a supercritical gaseous phase, which would enlarge their radius. “But we don’t see that in the samples,” explained Luque. “That suggests the water is not in the form of surface ocean.” Instead, the water could exist mixed into the rock or in pockets below the surface. Those conditions would be similar to Jupiter’s moon Europa, which is thought to have liquid water underground.

“I was shocked when I saw this analysis — I and a lot of people in the field assumed these were all dry, rocky planets,” said UChicago exoplanet scientist Jacob Bean, whose group Luque has joined to conduct further analyses.

The finding matches a theory of exoplanet formation that had fallen out of favor in the past few years, which suggested that many planets form farther out in their solar systems and migrate inward over time. Imagine clumps of rock and ice forming together in the cold conditions far from a star, and then being pulled slowly inward by the star’s gravity.

Though the evidence is compelling, Bean said he and the other scientists would still like to see “smoking gun proof” that one of these planets is a water world. That’s something the scientists are hoping to do with JWST, NASA’s newly launched space telescope that is the successor to Hubble.

Making BEASTies: dynamical formation of planetary systems around massive stars

by Richard J Parker, Emma C Daffern-Powell in Monthly Notices of the Royal Astronomical Society: Letters

Jupiter-sized planets can be stolen or captured by massive stars in the densely populated stellar nurseries where most stars are born, a new study has found.

Researchers from the University of Sheffield have proposed a novel explanation for the recently discovered B-star Exoplanet Abundance STudy (BEAST) planets. These are Jupiter-like planets at large distances (hundreds of times the distance between the Earth and the Sun) from massive stars. Until now their formation has been something of a mystery, as massive stars emit large amounts of ultraviolet radiation that stops planets from growing to the size of Jupiter — the largest planet in our solar system.

Dr Emma Daffern-Powell, Co-author of the study, from the University of Sheffield’s Department of Physicsand Astronomy added: Our previous research has shown that in stellar nurseries stars can steal planets from other stars, or capture what we call ‘free-floating’ planets. We know that massive stars have more influence in these nurseries than Sun-like stars, and we found that these massive stars can capture or steal planets — which we call ‘BEASTies’.

“Essentially, this is a planetary heist. We used computer simulations to show that the theft or capture of these BEASTies occurs on average once in the first 10 million years of the evolution of a star-forming region.”

Dr Richard Parker, Lecturer in Astrophysics in the University of Sheffield’s Department of Physics and Astronomy explains: “The BEAST planets are a new addition to the myriad of exoplanetary systems, which display incredible diversity, from planetary systems around Sun-like stars that are very different to our Solar System, to planets orbiting evolved or dead stars.

“The BEAST collaboration has discovered at least two super-Jovian planets orbiting massive stars. Whilst planets can form around massive stars, it is hard to envisage gas giant planets like Jupiter and Saturn being able to form in such hostile environments, where radiation from the stars can evaporate the planets before they fully form.
“However, our simulations show that these planets can be captured or stolen, on orbits very similar to those observed for the BEASTies. Our results lend further credence to the idea that planets on more distant orbits (more than 100 times the distance from Earth to Sun) may not be orbiting their parent star.”

Gamma-ray emission from the Sagittarius dwarf spheroidal galaxy due to millisecond pulsars

by Roland M. Crocker, Oscar Macias, Dougal Mackey, et al in Nature Astronomy

A team of researchers, including UvA physicists and astronomers, has studied gamma rays caused by the Sagittarius Dwarf, a small neighbouring galaxy of our Milky Way. They showed that all the observed gamma radiation can be explained by millisecond pulsars, and can therefore not be interpreted as a smoking gun signature for the presence of dark matter.

The center of our galaxy is blowing a pair of colossal bubbles of gamma radiation (the magenta structures in the image above) that span a whopping 50,000 light-years across. Discovered with the Fermi Gamma-ray Space Telescope about a decade ago, the source of this hourglass-shaped phenomenon remains unclear.

These Fermi bubbles are patched with a few enigmatic substructures of very bright gamma-ray emission. One of the brightest spots, the so-called Fermi cocoon, is found in the southern lobe and was originally thought to be due to past outbursts from the Galaxy’s supermassive black hole.

The Fermi bubbles, including the cocoon substructure, and the Sgr dSph galaxy.

A team including Oscar Macias at the University of Amsterdam & Kavli IPMU and Roland Crocker at the Australian National University analyzed data from the GAIA and Fermi space telescopes to reveal that the Fermi cocoon is actually due to emission from the Sagittarius dwarf galaxy. This satellite galaxy of the Milky Way is seen through the Fermi bubbles from our position on Earth . Due to its tight orbit around our galaxy and previous passages through the galactic disk, it has lost most of its interstellar gas and many of its stars have been ripped from its core into elongated streams.

Given that the Sagittarius dwarf is completely quiescent — it has no gas, and no stellar nurseries — there are only a few possibilities for its gamma-ray emission, including (1) a population of unknown millisecond pulsars or (2) dark matter annihilations.

Millisecond pulsars are the remnants of certain types of stars, significantly more massive than the Sun, that are in close binary systems, and now blast out cosmic particles as a result of their extreme rotational energies. The electrons fired by millisecond pulsars collide with low-energy photons of the Cosmic Microwave Background, propelling them to become high-energy gamma radiation.

Measured photon counts (left), best-fit baseline + Sgr dSph model (middle), and the fractional residuals (Data — Model)/Model (right).

Crocker, Macias and collaborators have convincingly demonstrated that the gamma-ray cocoon is explained by millisecond pulsars in the Sagittarius dwarf, and that the dark matter hypothesis is strongly disfavoured. This discovery sheds light on millisecond pulsars as efficient accelerators of highly energetic electrons and positrons. It also suggests that similar physical processes could be ongoing in other dwarf satellite galaxies of the Milky Way. This is highly significant because dark matter researchers have long believed that an observation of gamma rays from a dwarf satellite would be a smoking gun signature for dark matter annihilation.

3D Orbital Architecture of a Dwarf Binary System and Its Planetary Companion

by Salvador Curiel, Gisela N. Ortiz-León, Amy J. Mioduszewski, Joel Sanchez-Bermudez in The Astronomical Journal

By precisely tracing a small, almost imperceptible, wobble in a nearby star’s motion through space, astronomers have discovered a Jupiter-like planet orbiting that star, which is one of a binary pair. Their work, using the National Science Foundation’s Very Long Baseline Array (VLBA), produced the first-ever determination of the complete, 3-dimensional structure of the orbits of a binary pair of stars and a planet orbiting one of them. This achievement, the astronomers said, can provide valuable new insights on the process of planet formation.

Though more than 5,000 extrasolar planets have been discovered so far, only three have been discovered using the technique — called astrometry — that produced this discovery. However, the feat of determining the 3-D architecture of a binary-star system that includes a planet “cannot be achieved with other exoplanet discovery methods,” said Salvador Curiel, of the National Autonomous University of Mexico (UNAM).

“Since most stars are in binary or multiple systems, being able to understand systems such as this one will help us understand planet formation in general,” Curiel said.

The two stars, which together are called GJ 896AB, are about 20 light-years from Earth — close neighbors by astronomical standards. They are red dwarf stars, the most common type in our Milky Way galaxy. The larger one, around which the planet orbits, has about 44 percent of the mass of our Sun, while the smaller is about 17 percent as massive as the Sun. They are separated by about the distance of Neptune from the Sun, and orbit each other once every 229 years.

The intensity maps of GJ 896A (left panel) and GJ 896B (right panel) taken on 2020 September 13 are shown here as an example.

For their study of GJ 896AB, the astronomers combined data from optical observations of the system made between 1941 and 2017 with data from VLBA observations between 2006 and 2011. They then made new VLBA observations in 2020. The continent-wide VLBA’s supersharp resolution — ability to see fine detail — produced extremely precise measurements of the stars’ positions over time. The astronomers performed extensive analysis of the data that revealed the stars’ orbital motions as well as their common motion through space.

Detailed tracing of the larger star’s motion showed a slight wobble that revealed the existence of the planet. The wobble is caused by the planet’s gravitational effect on the star. The star and planet orbit a location between them that represents their common center of mass. When that location, called the barycenter, is sufficiently far from the star, the star’s motion around it can be detectable.

The astronomers calculated that the planet has about twice the mass of Jupiter and orbits the star every 284 days. Its distance from the star is slightly less than Venus’ distance from the Sun. The planet’s orbit is inclined roughly 148 degrees from the orbits of the two stars.

Absolute astrometry of the M Dwarf GJ 896A using the VLBA observations and including only the parallax and proper motions in the fit. The upper-left panel shows the observed data and the astrometric fit obtained when fitting only the proper motions and parallax of the star. The upper-right and lower panels show large residuals, having a well-defined long-term temporal trend.

“This means that the planet moves around the main star in the opposite direction to that of the secondary star around the main star,” said Gisela Ortiz-León, of UNAM and the Max Planck Institute for Radioastronomy. “This is the first time that such dynamical structure has been observed in a planet associated with a compact binary system that presumably was formed in the same protoplanetary disk,” she added.
“Additional detailed studies of this and similar systems can help us gain important insights into how planets are formed in binary systems. There are alternate theories for the formation mechanism, and more data can possibly indicate which is most likely,” said Joel Sanchez-Bermudez, of UNAM. “In particular, current models indicate that such a large planet is very unlikely as a companion to such a small star, so maybe those models need to be adjusted,” he added.

The astrometric technique will be a valuable tool for characterizing more planetary systems, the astronomers said. “We can do much more work like this with the planned Next Generation VLA (ngVLA),” said Amy Mioduszewski, of the National Radio Astronomy Observatory. “With it, we may be able to find planets as small as the Earth.”

Patchy Proton Aurora at Mars: A Global View of Solar Wind Precipitation Across the Martian Dayside From EMM/EMUS

by Michael S. Chaffin, Christopher M. Fowler, Justin Deighan, et al in Geophysical Research Letters

NASA’s MAVEN (Mars Atmosphere and Volatile Evolution) mission and the United Arab Emirates’ Emirates Mars Mission (EMM) have released joint observations of dynamic proton aurora events at Mars. Remote auroral observations by EMM paired with in-situ plasma observations made by MAVEN open new avenues for understanding the Martian atmosphere. This collaboration was made possible by recent data-sharing between the two missions and highlights the value of multi-point observations in space.

In the new study, EMM discovered fine-scale structures in proton aurora that spanned the full day side of Mars. Proton aurora, discovered by MAVEN in 2018, are a type of Martian aurora that form as the solar wind, made up of charged particles from the Sun, interacts with the upper atmosphere. Typical proton aurora observations made by MAVEN and ESA’s (the European Space Agency) Mars Express mission show these aurora appearing smooth and evenly distributed across the hemisphere. By contrast, EMM observed proton aurora that appeared highly dynamic and variable. These “patchy proton aurora” form when turbulent conditions around Mars allow the charged particles to flood directly into the atmosphere and glow as they slow down.

Emirates Mars Ultraviolet Spectrometer (EMUS) and Mars Atmosphere and Volatile EvolutioN (MAVEN) observations during a patchy proton aurora event on 11 August 2021.

“EMM’s observations suggested that the aurora was so widespread and disorganized that the plasma environment around Mars must have been truly disturbed, to the point that the solar wind was directly impacting the upper atmosphere wherever we observed auroral emission,” said Mike Chaffin, a MAVEN and EMM scientist based at the Laboratory for Atmospheric and Space Physics at the University of Colorado Boulder and lead author of the study. “By combining EMM auroral observations with MAVEN measurements of the auroral plasma environment, we can confirm this hypothesis and determine that what we were seeing was essentially a map of where the solar wind was raining down onto the planet.”

Normally it is difficult for the solar wind to reach Mars’ upper atmosphere because it is redirected by the bow shock and magnetic fields surrounding the planet. The patchy proton aurora observations are therefore a window into rare circumstances — ones during which the Mars-solar wind interaction is chaotic. “The full impact of these conditions on the Martian atmosphere is unknown, but EMM and MAVEN observations will play a key role in understanding these enigmatic events,” said Chaffin.

The data-sharing between MAVEN and EMM has enabled scientists to determine the drivers behind the patchy proton aurora. EMM carries the Emirates Mars Ultraviolet Spectrograph (EMUS) instrument, which observes the Red Planet’s upper atmosphere and exosphere, scanning for variability in atmospheric composition and atmospheric escape to space. MAVEN carries a full suite of plasma instruments, including the Magnetometer (MAG), the Solar Wind Ion Analyzer (SWIA), and the SupraThermal And Thermal Ion Composition (STATIC) instrument used in this study.

“EMM’s global observations of the upper atmosphere provide a unique perspective on a region critical to MAVEN science,” said MAVEN Principal Investigator Shannon Curry, of UC Berkeley’s Space Sciences Laboratory. “These types of simultaneous observations probe the fundamental physics of atmospheric dynamics and evolution and highlight the benefits of international scientific collaboration.”

EMM Science Lead Hessa Al Matroushi agreed. “Access to MAVEN data has been essential for placing these new EMM observations into a wider context,” she said. “Together, we’re pushing the boundaries of our existing knowledge not only of Mars, but of planetary interactions with the solar wind.”

Multi-vantage-point measurements have already proven to be an asset in Earth and heliophysics research. At Mars, over half a dozen orbiters are now taking science observations and with Mars’ southern hemisphere currently experiencing summer, when proton aurora is known to be most active, multi-vantage-point observations will be critical to understanding how these events form. The collaboration between EMM and MAVEN demonstrates the value of discovery-level science about the Martian atmosphere with two spacecraft simultaneously observing the same region.

Topographically Influenced Evolution of Large-scale Changes in Comet 67P/Churyumov–Gerasimenko’s Imhotep Region.

by Abhinav S. Jindal, Samuel P. D. Birch, Alexander G. Hayes, Orkan M. Umurhan, Raphael Marschall, Jason M. Soderblom, Jean-Baptiste Vincent, Dennis Bodewits in The Planetary Science Journal

With an eye toward a possible return mission years in the future, Cornell University astronomers have shown how smooth terrains — a good place to land a spacecraft and to scoop up samples — evolve on the icy world of comets.

By applying thermal models to data gathered by the Rosetta mission — which caught up to the barbell-shaped Comet 67P/Churyumov-Gerasimenko almost a decade ago — they show that the topography influences the comet’s surface activity across hundreds of meters.

“You can have a uniform surface composition on comets and still have hotspots of activity,” said lead author Abhinav S. Jindal, a graduate student in astronomy and member of the research group of Alexander Hayes, associate professor of astronomy. “The topography is driving the activity.”

Overview of the Imhotep region. (a) The Imhotep region (highlighted in yellow) lies on the large lobe of 67P and has the equator (dashed green line) passing through its northern portion. (b) Imhotep consists of a central deposit of smooth terrains bounded by high-standing topography on all sides. (c) Shown is the topography surrounding Imhotep as viewed from the north of Imhotep.

Comets are icy bodies made of dust, rocks and gas left over from the solar system’s formation about 4.6 billion years ago, Jindal said. They form in the solar system’s outer fringes and have spent eternity cruising through the dark, cosmic freezer of space, far from the sun’s heat.

“Their chemistry has not changed much from when comets formed, making them ‘time capsules’ preserving primordial material from the birth of the solar system,” Jindal said, explaining that these bodies likely seeded early Earth with water and key building blocks of life.
“As some of these comets have been pulled into the inner solar system,” he said, “their surfaces undergo changes. Science is trying to understand the driving processes.”

Georeferenced images of the Imhotep region.

As Comet 67P loops its way back toward the sun, the body speeds by it to a point called perihelion — its closest approach — and the comet warms up. The Rosetta mission followed the comet as it rounded the sun and studied its activity. The smooth terrains serve as locations where the most changes were observed, making them key to grasping the surface’s evolution.

Jindal and the researchers examined the evolution of 16 topographic depressions in the Imhotep region — the largest smooth terrain deposit on 67P — between June 5, 2015, when activity was first observed, and Dec. 6, 2015, when the final large-scale changes were observed.

The comet went through a process called sublimation — in which the icy parts turned gaseous in the sun’s heat. The comet’s smooth Imhotep region showed a complex pattern of simultaneous eroding scarps (the steep edges of arc-shaped depressions) and material deposition. Jindal believes science will one day return to Comet 67P. “These comets are helping us to answer the question of where we come from,” he said.