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ultraviolet image of CW Leonis

The sooty cloud surrounding the carbon star CW Leonis is known to contain more than 50 types of molecules, and the remaining unassigned spectral lines hint that many more molecules are present. Can a laboratory study of a metallic molecule help us identify some of these mystery spectral lines?

Searching Space for Chemical Compounds

Hubble Space Telescope image of CW Leonis

Another view of CW Leonis, this time from the Hubble Space Telescope. This image highlights the dusty layers shed by this evolved star. [ESA/Hubble & NASA, T. Ueta, H. Kim; CC BY 4.0]

Astronomers have discovered more than 200 molecules in space since the first molecule was found in 1937. These discoveries confirmed something incredible — that in the cold, sparse space environment, individual atoms can link up to form complex molecules. Finding molecules in space represents both a challenge and an opportunity: how can we explain the presence of molecules in such an unforgiving environment, and how can we use the fact that they do exist to learn about the chemistry of interstellar and circumstellar space?

One of the best sites to study extraterrestrial molecules is in the dusty shroud and outflows of the star CW Leonis, also known as IRC+10216. CW Leonis is a carbon star: a supergiant star with a high abundance of carbon in its atmosphere. Among CW Leonis’s many molecules are metal-containing species like silicon dicarbide (SiC2), leading researchers to wonder if similar molecules might be responsible for any of the remaining unidentified lines in CW Leonis’s spectrum.

plot of the magnesium dicarbide energy levels and the transitions observed in the lab and in the astrophysical site

Summary of the known transitions and energy levels for magnesium dicarbide, as determined from laboratory and astrophysical observations. [Changala et al. 2022]

Making Magnesium Molecules

A team led by Bryan Changala‬ (Center for Astrophysics ∣ Harvard & Smithsonian) focused their search on magnesium dicarbide (MgC2). Changala and collaborators considered it likely that CW Leonis’s dusty shroud contains magnesium dicarbide because it’s chemically similar to the already-discovered silicon dicarbide, and many other magnesium-containing molecules have been found there.

How do you determine if a star’s spectral lines are due to a particular molecule, though? In order to be confident that we’ve discovered a molecule in space, we need to know its spectrum, which is best determined by studying the molecule in a lab. In the case of magnesium dicarbide, researchers have used quantum mechanical models to predict the molecule’s spectrum but had never confirmed it in a lab.

Changala‬ and coauthors combined magnesium atoms with acetylene molecules, which are made of carbon and hydrogen, hoping to synthesize magnesium dicarbide. The team successfully matched a spectral line from their sample to a line predicted by quantum mechanical models and performed additional tests to ensure that the molecule they created was actually magnesium dicarbide.

Seeking a Spectral Match

plot of one of the spectral lines attributed to magnesium dicarbide

Example of a spectral line attributed to magnesium dicarbide. The fitted line profile is shown in red, and the blue “U” indicates unidentified lines. [Adapted from Changala et al. 2022]

Ultimately, Changala and collaborators used the spectrum of the newly synthesized molecule to assign 14 of CW Leonis’s unknown spectral lines to magnesium dicarbide and its isotopologues — molecules with the same chemical formula and structure in which one or more atoms has a different number of neutrons.

What does the discovery of magnesium dicarbide in CW Leonis’s spectrum tell us? By comparing the abundance of magnesium dicarbide in the star’s surroundings with the abundances of other magnesium-containing molecules, researchers might be able to glean how these molecules are made. Additionally, these observations may help us understand how metals affect the chemistry of carbon-rich environments like the surroundings of carbon stars, helping to lift the veil on these dusty objects.

Citation

“Laboratory and Astronomical Discovery of Magnesium Dicarbide, MgC2,” P. B. Changala et al 2022 ApJL 940 L42. doi:10.3847/2041-8213/aca144

JWST image of the Tarantula Nebula

It’s been a big year for astronomy. We’ve seen the first image of the Milky Way’s central supermassive black hole, witnessed the launch of new space missions, and finally set eyes upon the first observations from JWST. As 2022 draws to a close, let’s take a look back at some of the amazing science we covered on AAS Nova this year. Here are the top 10 most-read posts of 2022:

10. Featured Image: A Twisted Magnetic Rope

Visualization of a magnetic flux rope

Visualization of a magnetic flux rope. [Adapted from Hu et al. 2022]

A team led by Qiang Hu used a new quasi-three-dimensional fitting method to analyze spacecraft data of a passing solar storm. This new technique helped the team understand the structure of the storm’s magnetic field. The resulting simulations show three-dimensional winding behavior that was not present in one- or two-dimensional models of the same event, allowing the team to get a better grasp on the intricate plasma physics at play.

image of the Sun releasing two coronal mass ejections

Two coronal mass ejections launched from the Sun in November 2000, as seen by the Solar and Heliospheric Observatory. [ESA/NASA/SOHO]

9. Caught in a Solar Storm on the Way to Mars

Two spacecraft at different distances from the Sun happened to lie along the same solar magnetic field line when a powerful solar storm swept through the solar system. A team led by Shuai Fu, Zheyi Ding, and Yongjie Zhang studied the data from the two spacecraft in order to understand how high-energy particles from the Sun travel through the solar system — knowledge that will be critical when planning for crewed space missions traveling beyond Earth’s protective magnetic field.

8. Hydrate or Die-drate: Was Venus Ever Habitable?

side-by-side images of Venus's surface today and an imagining of what its surface might have looked like in the past

Radar image of Venus’s surface today (left) and an imagined version of its past surface (right). [NASA/Jet Propulsion Laboratory-Caltech (left) and NASA (right)]

Astrobites’s Katya Gozman reported on research by Joshua Krissansen-Totton and collaborators, who used models of Venus’s atmosphere and interior to explore the possibility of our hellish planetary neighbor hosting liquid water on its surface in the distant past. Their results may have deepened the mystery of Venus’s past habitability, showing that conditions on present-day Venus are compatible with two pasts: one in which Venus never had surface water, and one in which it had deep oceans for up to 3.5 billion years.

Artist's impression of a quasar

Artist’s impression of a quasar. [S. Munro; CC BY 4.0]

7. Clues from Quasars in the Early Universe

Quasars — ultra-bright, accreting supermassive black holes in the early universe — are visible up to 13 billion light-years away, providing a way to study young supermassive black holes. But how exactly these black holes become supermassive in less than a billion years is still unknown. A team led by Jinyi Yang approached this question by using infrared spectroscopy to determine the masses and accretion rates of more than three dozen quasars in the first billion years after the Big Bang. The team’s efforts yielded an estimate of the masses of the “seeds” from which the quasars grew, but how the seeds themselves came to be is still a mystery!

6. How Do Milky Way–Like Galaxies Grow?

NGC 6744, a Milky Way–like galaxy

NGC 6744 is thought to be similar to the Milky Way in size and structure. [ESO; CC BY 4.0]

A team led by Maryam Hasheminia explored the evolution of Milky Way–like spiral galaxies, seeking to understand if similar galaxies’ stars form first in the galactic center, the galactic outskirts, or equally throughout the galaxy. Using observations of suitable galaxies from survey data, the team found that all parts of these galaxies form stars at about the same pace, which is at odds with one of the leading hypotheses for how galaxies grow.

Hubble Space Telescope image of galaxy cluster Abell 2744

Galaxy cluster Abell 2744 — the focus of the GLASS Early-Release Science program. [NASA, ESA, and J. Lotz, M. Mountain, A. Koekemoer, and the HFF Team (STScI)]

5. Through the Looking GLASS with JWST

At long last, JWST is operational! In the first of several focus issues, researchers introduced the Grism Lens-Amplified Survey from Space (GLASS) Early-Release Science program. This program, led by Tommaso Treu, focuses on the epoch of reionization, during which the first stars in the universe were born. Studying galaxies in the first billion years after the Big Bang is critical to understanding this era, and JWST gives us a window into reionization like we’ve never had before.

4. Winding Up to a Quadrillion Electronvolts of Energy

Artist's impression of a pulsar in a binary system

Artist’s impression of a pulsar in a binary system with another star. [NASA’s Goddard Space Flight Center]

Where do high-energy particles and photons come from? Andrei Bykov and collaborators tested a model in which the winds from a star and its compact object companion collide, accelerating protons to petaelectronvolt energies — that’s one quadrillion electronvolts — and creating gamma rays and neutrinos. This model might help to explain the rare but remarkable detections of extremely high-energy photons over the past decade.

Event Horizon Telescope image of the Milky Way's supermassive black hole

The first Event Horizon Telescope image of the Milky Way’s supermassive black hole. [EHT Collaboration; CC BY 4.0]

3. First Image of the Milky Way’s Supermassive Black Hole

In 2019, the planet-wide Event Horizon Telescope delivered the first-ever image of a galaxy’s central supermassive black hole, and this year, we got a similar view of our nearest and dearest supermassive black hole: Sagittarius A*. The images showed a bright ring of emission corresponding to extremely hot gas orbiting close to the black hole, as well as a dark shadow inside the ring that contains the black hole’s event horizon. These images provided another test of Einstein’s general theory of relativity, which passed with flying colors yet again.

2. Solving a Fifty-Year Star-Formation Mystery

photograph of the lupus 3 star-forming region

Lupus 3, a star forming region about 600 light-years away. [ESO/R. Colombari; CC BY 4.0]

Models and observations have disagreed on the Milky Way’s star formation rate for decades, with models suggesting that our galaxy should be forming stars faster than it is. Neal Evans and collaborators suggested that the mismatch can be resolved by reassessing two of the most important factors that determine the star formation rate: the masses of the Milky Way’s molecular gas clouds and how efficiently they form stars. In particular, accounting for the impact of metallicity — the abundance of elements heavier than helium — in molecular clouds might bring this long-standing mystery to a close.

simulation of matter spiraling around a pair of black holes

Simulation of matter spiraling around a pair of supermassive black holes. [Adapted from Gutiérrez et al. 2022]

1. Bringing Supermassive Black Hole Mergers to Light

Unsurprisingly, the most-read article of 2022 is about a frequent favorite of astronomers and astronomy enthusiasts alike: black holes! A team led by Eduardo Gutiérrez used simulations to probe the electromagnetic radiation generated when supermassive black holes collide and merge. The team’s results may provide a way to distinguish binary supermassive black holes approaching a merger from single supermassive black holes, hopefully letting us catch them colliding for the first time.

Thank you for joining us for another year of great science — we can’t wait to see the discoveries that 2023 will bring!

photograph of a telescope's field of view with numerous bright satellite trails cutting across the image

Editor’s Note: In these last two weeks of 2022, we’ll be looking at a few selections that we haven’t yet discussed on AAS Nova from among the most-downloaded articles published in AAS journals this year. The usual posting schedule will resume in January.

Impact of the SpaceX Starlink Satellites on the Zwicky Transient Facility Survey Observations

number of images containing satellite tracks and the cumulative number of satellites over time

Number of Zwicky Transient Facility images containing Starlink satellite tracks (blue bars) and the cumulative number of satellites (red line) as a function of time. [Mróz et al. 2022]

Published January 2022

Main takeaway:

Przemek Mróz (University of Warsaw, Poland) and collaborators counted how many images from the Zwicky Transient Facility, which operates a telescope that scans the entire northern sky every two days, contain streaks from Starlink satellites passing through the field of view. The percentage of satellite-streaked images increased by a factor of nearly 36 in less than two years, highlighting the growing presence of satellite constellations and their potential impact on ground-based astronomy.

Why it’s interesting:

The number of Earth-orbiting satellites has increased dramatically in the past few decades and is expected to continue increasing. Though each satellite track obscures a small fraction of a telescope’s field of view — Mróz’s team calculated that a single track covers just 0.04% of the Zwicky Transient Facility’s detector — the chances of a passing satellite marring an astronomical image will increase as the number of satellites skyrockets.

Prospects for future satellites, and what this means for observations going forward:

Much of the recent growth in the satellite population has been driven by the addition of thousands of SpaceX Starlink satellites, which aim to provide internet access for remote or rural areas; as of this writing, there are more than 3,300 Starlink satellites in orbit. This is a small fraction of the nearly 20,000 Starlink satellites that have already been approved, with further additions to the Starlink family already planned. Mróz and collaborators found that Starlink satellites have yet to dramatically affect observations by the Zwicky Transient Facility, partially due to image processing techniques that remove the satellite trails, but other observatories may suffer more negative impacts due to the specifics of their detectors. Though efforts to dull the shine of Starlink satellites have dimmed the satellites by a factor of 4.6, they are still brighter than was recommended in the first Satellite Constellations workshop report.

Citation

Przemek Mróz et al 2022 ApJL 924 L30. doi:10.3847/2041-8213/ac470a

illustration of the solar system

Editor’s Note: In these last two weeks of 2022, we’ll be looking at a few selections that we haven’t yet discussed on AAS Nova from among the most-downloaded articles published in AAS journals this year. The usual posting schedule will resume in January.

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

Published September 2022

Main takeaway:

Pam Vervoort (University of California, Riverside) and collaborators used N-body simulations and climate models to study how the presence of a Jupiter-like planet affects the long-term habitability of an Earth-like planet in the same planetary system. The team’s simulations showed that if Jupiter’s orbit were more elliptical, more of Earth’s surface might be habitable than it is today.

Why it’s interesting:

With the number of confirmed exoplanets now above 5,000, many astronomers have switched from finding planets to characterizing them. Among the possible characterizations of an exoplanet is determining if it’s within its host star’s habitable zone. While the concept of the habitable zone is simple — and it’s straightforward to estimate if a planet is currently in a star’s habitable zone based on the luminosity of the star and the orbital distance of the planet — the actual location of a star’s habitable zone is expected to change over time. As stars age, their luminosity changes, and the dynamics of multi-planet systems can shift a planet’s orbital distance. Vervoort and collaborators’ simulations provide a way to estimate the impacts of some of these changes.

How a neighboring Jupiter-like planet affects habitability:

plots of simulated sea ice cover, eccentricity, obliquity, and fractional habitability for four versions of the model

Sea ice cover, eccentricity (how elliptical the orbit is), and obliquity (how tilted the planet is), and fractional habitability of an Earth-like planet in a system with a Jupiter-like planet with varying orbital parameters. Click to enlarge. [Vervoort et al. 2022]

Jupiter is often credited with helping to keep Earth habitable — by redirecting certain comets safely out of the inner solar system, for example — but is the largest planet in our solar system as helpful as it could be? Not so, say Vervoort and collaborators. The team’s simulations show that Earth’s habitability (as measured by the fraction of the planet with a hospitable air temperature and no sea ice) would be higher if Jupiter’s orbit were significantly more elliptical than it is today. While we won’t be coaxing Jupiter into a more elliptical orbit to boost Earth’s habitable area anytime soon, the results of this study can inform our investigations of potentially Earth-like planets around other stars, helping us to discern which of the growing population of exoplanets might be habitable.

Citation

Pam Vervoort et al 2022 AJ 164 130. doi:10.3847/1538-3881/ac87fd

artist's impression of an active galactic nucleus emitting a jet

Editor’s Note: In these last two weeks of 2022, we’ll be looking at a few selections that we haven’t yet discussed on AAS Nova from among the most-downloaded articles published in AAS journals this year. The usual posting schedule will resume in January.

Probing the Innermost Regions of AGN Jets and Their Magnetic Fields with RadioAstron. V. Space and Ground Millimeter-VLBI Imaging of OJ 287

Published January 2022

Main takeaway:

A team led by José Gómez (Institute of Astrophysics of Andalusia – Spanish National Research Council) presented new observations of OJ 287, an active galactic nucleus that hosts one of the most massive supermassive black holes currently known. These new data allowed researchers to study the magnetic fields very close to this superlative active galactic nucleus.

Why it’s interesting:

Radio flare seen from OJ 287

An example of a flare from OJ 287, seen at multiple radio frequencies. Click to enlarge. [Gómez et al. 2022]

OJ 287 is a well-studied target that has shown intriguing behavior in the past. Even among active galactic nuclei, OJ 287 is active, flaring so brightly due to material accreting onto its supermassive black hole that its outbursts were captured on photographic plates in the late 19th century. Notably, its outbursts follow a roughly 12-year pattern, which astronomers believe is due to the presence of a second supermassive black hole in orbit about the first. OJ 287 also emits a jet, the orientation of which is thought to vary considerably every 24–30 years, though the reason for this variation is unclear.

More details on these new observations:

Gómez and collaborators used arrays of radio telescopes (including one telescope in space!) to perform long-baseline interferometry. This technique combines data from multiple telescopes to yield the same resolving power as a single telescope as large as the greatest distance between two telescopes in the array. These data included information about the polarization (i.e., orientation) of the radio waves, which in turn helped the team understand OJ 287’s magnetic field structure. The new observations showed that the jet emitted by OJ 287 is bent — likely due to the accretion disk very close to the central black hole changing over time — and has a helical magnetic field. The observed magnetic field structure aligns with our theories of how active galactic nucleus jets are produced.

Citation

José L. Gómez et al 2022 ApJ 924 122. doi:10.3847/1538-4357/ac3bcc

JWST image of a galaxy cluster

Editor’s Note: In these last two weeks of 2022, we’ll be looking at a few selections that we haven’t yet discussed on AAS Nova from among the most-downloaded articles published in AAS journals this year. The usual posting schedule will resume in January.

The Sparkler: Evolved High-Redshift Globular Cluster Candidates Captured by JWST

Published September 2022

Main takeaway:

Lamiya Mowla and Kartheik Iyer from the University of Toronto, Canada, led an analysis of JWST observations of the SMACS J0723.3-7327 field — the first JWST image ever released. The team focused on multiple compact sources surrounding a strongly lensed galaxy in this image. These compact sources, dubbed “sparkles” by the research team, are likely globular clusters.

Why it’s interesting:

close-ups of the three images of the Sparkler galaxy

Left panel: Portion of the SMACS J0723.3-7327 field with the three images of the Sparkler labeled. Panels 1, 2, and 3: Close-ups of each of the three images of the Sparkler. Click to enlarge. [Mowla et al. 2022]

SMACS J0723.3-7327 is a galaxy cluster located about 4 billion light-years from Earth. While the galaxies within the cluster are spectacular in their own right, it’s a galaxy behind the cluster that’s the subject of this study; the immense gravity of the galaxy cluster bends the light from an even more distant galaxy dubbed “the Sparkler,” creating three distinct images of the galaxy. The three images of the Sparkler each contain up to a dozen sparkles, and further analysis of these sparkles reveals them to be spatially unresolved, red in color, and with no evidence of active star formation. Based on these properties, the team suggested that we’re seeing individual globular clusters in a galaxy billions of light-years away!

What the Sparkler can tell us about globular cluster formation:

The timeline for the formation of globular clusters is uncertain, with competing theories suggesting that they either require the particular conditions present very early in the universe to form, or they form continuously as galaxies evolve. Given the red color of these clusters and their lack of star formation, Mowla and Iyer’s team suggest that these clusters are highly evolved, with an age of 3.9–4.1 billion years. This means that the clusters formed at a redshift of 7–11, corresponding to when the universe was roughly 400–800 million years old, shortly after the first stars began to shine. While more analysis of these observations is required to fully understand the nature of the sparkles, early results suggest that globular cluster formation coincides with the earliest stages of galaxy assembly.

Citation

Lamiya Mowla et al 2022 ApJL 937 L35. doi:10.3847/2041-8213/ac90ca

photograph of the asteroid Ryugu

Editor’s Note: In these last two weeks of 2022, we’ll be looking at a few selections that we haven’t yet discussed on AAS Nova from among the most-downloaded articles published in AAS journals this year. The usual posting schedule will resume in January.

CI Asteroid Regolith as an In Situ Plant Growth Medium for Space Crop Production

Published July 2022

Main takeaway:

Steven Russell (University of Wisconsin−Madison; University of North Dakota) and collaborators studied the possibility of growing plants in soil derived from the loose surface material, or regolith, of asteroids. While lettuce, radishes, and peppers all grew in mixtures of simulated regolith and peat moss, increasing the amount of regolith decreased the yield of each plant, and no seeds sprouted in pure regolith.

Why it’s interesting:

If humans want to explore the solar system, we’re going to need a way to produce substantial amounts of food in space. One possible plant-growing medium is asteroid regolith, which is abundant in our solar system. Recent studies of meteorites as well as spacecraft missions to asteroids, such as the Hayabusa2 mission to Ryugu and the OSIRIS-REx mission to Bennu, have suggested that certain types of asteroids called carbonaceous asteroids contain nearly unaltered material left over from the formation of our solar system. These primitive asteroids are particularly promising sources of “soil” since they contain small amounts of carbon, minerals, and nutrients.

What we learned from sowing seeds in asteroid dirt:

experimental results

Experimental results 55 days after planting. The pots with no visible growth contain pure simulated regolith. [Adapted from Russell et al. 2022]

Russell and collaborators found that all three vegetable types grew in a mixture of simulated asteroid regolith and peat moss, but no vegetable seeds sprouted in pure simulated regolith. On average, seeds planted in more regolith and less peat moss showed less growth, as measured by the leaf area, plant height, and overall mass of plant matter. The authors attributed this trend to how compact the simulated regolith is — preventing air and water from reaching the plants’ roots — as well as the dearth of necessary nutrients. This suggests that asteroid regolith will need to be adapted in some way before it can be used to grow plants, such as by mixing in plant matter to make it less compact.

Citation

Steven. J. Russell et al 2022 Planet. Sci. J. 3 155. doi:10.3847/PSJ/ac74c9

photograph of the Large Magellanic Cloud

Editor’s Note: In these last two weeks of 2022, we’ll be looking at a few selections that we haven’t yet discussed on AAS Nova from among the most-downloaded articles published in AAS journals this year. The usual posting schedule will resume in January.

Discovery of PSR J0523-7125 as a Circularly Polarized Variable Radio Source in the Large Magellanic Cloud

Published May 2022

ASKAP polarized light images of the Large Magellanic Cloud and the new pulsar

Total intensity (left) and circularly polarized intensity (right) images of part of the Large Magellanic Cloud at 888 megahertz, as seen by ASKAP. The zoomed-in images show the location of the newly discovered pulsar. Click to enlarge. [Wang et al. 2022]

Main takeaway:

A team led by Yuanming Wang (The University of Sydney, Australia) reported the discovery of a pulsar — the dense, rapidly spinning remnant of a massive star’s core — using radio continuum data from the Australian Square Kilometre Array Pathfinder (ASKAP). The newfound pulsar is located in the Large Magellanic Cloud, a satellite galaxy of the Milky Way, and its discovery may pave the way for astronomers to find other extragalactic pulsars with unusual properties.

Why it’s interesting:

The newly discovered pulsar, PSR J0523−7125, is one of the most luminous known radio pulsars, but several aspects of its radio signal made it difficult to find: while most pulsars are identified via their brief flashes of radio emission, PSR J0523−7125’s pulses are uncharacteristically broad, and its radio emission falls off sharply at higher frequencies. Wang and collaborators observed the new pulsar as part of the Variables and Slow Transients (VAST) survey and identified it based on its high degree of circular polarization and lack of a multiwavelength counterpart.

Prospects for finding further pulsars:

This work by Wang and collaborators shows that radio surveys are a viable means of discovering pulsars with unusual pulse properties. The combination of circular polarization data with multiwavelength images is especially useful, allowing researchers to identify sources that emit circularly polarized light but are absent in optical images. The authors also posit that future searches with the Next Generation Very Large Array — a network of 263 radio dishes scheduled to begin construction in 2026 — could lead to the first discovery of a pulsar in another neighboring galaxy, Andromeda.

Citation

Yuanming Wang et al 2022 ApJ 930 38. doi:10.3847/1538-4357/ac61dc

photograph of a butte near Jezero crater on Mars

Humans have used robotic surrogates to explore Mars’s geology since 1997, when the Sojourner rover crawled the length of a football field on the red planet’s surface. But while the robots we’ve sent to Mars have grown more sophisticated over time, one question in particular lingers: would rover-collected and human-collected data from the same rocks lead us to the same conclusions?

Remote Investigations of the Red Planet

The Mars rovers have advanced our understanding of Mars’s current geology and past history, including providing evidence that our neighboring planet once had persistent liquid water on its surface. But while the Mars rovers have extended geologists’ reach by millions of miles, robotic rovers and human geologists are not the same: a rover’s resources are exceedingly scarce, requiring teams of scientists on Earth to plan its observations carefully, while a human team can operate more flexibly and make decisions on the fly.

It’s possible that the inherent limitations of rover data affect the conclusions that scientists on Earth draw from those data. Since we can’t (yet) send human geologists to Mars to compare their observations to those made by the Mars rovers, scientists got creative and instead used human rovers on Earth to learn more about this issue.

Thinking Like a Rover

aerial view of the field site

Aerial view of the field site in Iceland, acquired with a drone to mimic orbital data. [Yingst et al. 2022]

Aileen Yingst (Planetary Science Institute) and collaborators traveled to Tjörnes peninsula in Iceland to study a 60-meter-high rock outcropping that could serve as an analogue for the layered rocks seen in Jezero crater on Mars, which the Perseverance rover is currently exploring. The rocks in Jezero crater, similar to those on the Tjörnes peninsula, likely contain layers of volcanic and sedimentary materials.

Yingst and coauthors asked a human team and a “rover” team to investigate the rock outcropping using commercial instruments with similar resolution to those on the Mars rover. The human team used standard field techniques to study the outcropping while the rover team studied the rocks remotely, directing just two team members to act as the “rover” and take measurements based on the instructions of team members who were not at the field site. Both teams planned their investigations using aerial photographs of the region, similar to how rover missions use images from orbiting spacecraft for reconnaissance.

images collected by the rover team

Images collected by the rover team. Click to enlarge. [Yingst et al. 2022]

Notes for the Future

Yingst and collaborators found that the rover team was typically able to determine if materials were volcanic or sedimentary, but the human team made more accurate and more detailed assessments, and they were able to place the materials in context. This may have been because the human team was able to trace rock layers horizontally and make observations from various distances, which allowed them to determine if certain features were continuous between regions as well as determine the scale of the features.

The authors noted that the ability to make observations from different distances or angles was crucial to the traditional field team’s success. This finding might prompt future Mars rover investigations to allocate more time to collecting images at certain resolutions, if those images might hold the key to correct identifications.

Citation

“Using Rover-analogous Methodology to Discriminate Between Volcanic and Sedimentary Origins in Successions Dominated by Igneous Composition,” R. Aileen Yingst et al 2022 Planet. Sci. J. 3 240. doi:10.3847/PSJ/ac8429

artist's impression of a collapsar and an associated gamma-ray burst

Researchers are still working out where heavy metals are made in the universe. A recent publication explores ways to tell if elements heavier than iron can be created when extremely massive stars collapse to form black holes.

Making Heavy Metals

In the cores of stars, nuclear fusion combines light elements into heavier ones, with the largest stars generating elements up to iron. But elements bulkier than iron must arise elsewhere, since a star that attempts to create anything heavier is doomed to collapse in a supernova explosion.

illustration of two neutron stars approaching a merger.

An illustration of two neutron stars approaching a merger. [ESO/L. Calçada; CC BY 4.0]

About half of the elements beyond iron on the periodic table are thought to form through something called the r-process, in which atoms rapidly capture multiple neutrons in a dense, hot environment. Core-collapse supernovae were early contenders for r-process production, but simultaneous observations of light and gravitational waves from colliding neutron stars cemented mergers as an important source of heavy elements. Now, researchers are searching for ways to determine if certain supernovae could be sites of r-process element creation after all.

Collapsars as Candidates

Collapsars are rapidly rotating massive stars that explode as supernovae when they can no longer sustain nuclear fusion, ultimately creating a black hole. As the star’s core collapses, material in the outer layers forms an accretion disk, in which conditions for r-process element formation may exist. To probe the possible role that collapsars play in generating r-process elements, Jennifer Barnes (University of California, Santa Barbara) and Brian Metzger (Columbia University and Flatiron Institute) modeled the effects of r-process nucleosythesis on the light curves of collapsars exploding as supernovae.

illustration of the authors' model

An illustration of the authors’ model, in which r-process-enriched material is surrounded by an r-process-poor shell. [Barnes & Metzger 2022]

Barnes and Metzger first used an analytical model to predict when the presence of r-process products might be observable as the supernova’s emission rises and falls, as well as how best to observe these effects. The team found that it may be possible to discern whether a collapsar explosion contains r-process material by making long-wavelength observations several months after the explosion, depending on how the material is distributed, but early in the explosion might offer a better chance of identifying these events.

Light Curve Modeling

As a follow-on to their initial investigation, the team modeled the evolution of light curves from collapsar explosions that produce varying amounts of r-process material. These models explore how supernova light curves change as a function of the mass ejected in the explosion, the velocity of the ejected mass, the amount of nickel-56 (a radioactive form of nickel that decays into cobalt-56, creating the characteristic shape of many supernova light curves), and the amount and distribution of r-process material.

modeled light curves showing the effect of changing the degree of mixing.

Demonstration of how the degree of mixing (ψmix) affects the resultant light curve. As the degree of mixing increases (higher ψmix), the emission shifts toward the near-infrared. Click to enlarge. [Barnes & Metzger 2022]

In general, the presence of r-process material causes supernova light curves to shift toward redder frequencies, though the distribution of the material plays a large role in how visible this effect is; material concentrated at the center of the explosion will have little effect, while material mixed throughout will have a larger effect. Ultimately, the authors concluded that monitoring supernovae for ~75 days after they explode could be a viable way to identify collapsars that produce r-process elements, paving the way for near-infrared follow-up observations with JWST.

Citation

“Signatures of r-process Enrichment in Supernovae from Collapsars,” Jennifer Barnes and Brian D. Metzger 2022 ApJL 939 L29. doi:10.3847/2041-8213/ac9b41

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