The unexpected visitor belongs to a class of icy bodies found in space between Jupiter and Neptune. Called “Centaurs,” they become active for the first time when heated as they approach the Sun, and dynamically transition into becoming more comet-like.

Visible-light snapshots by NASA’s Hubble Space Telescope reveal that the vagabond object shows signs of comet activity, such as a tail, outgassing in the form of jets, and an enshrouding coma of dust and gas. Earlier observations by NASA’s Spitzer Space Telescope gave clues to the composition of the comet-like object and the gasses driving its activity.

“Only Hubble could detect active comet-like features this far away at such high detail, and the images clearly show these features, such as a roughly 400,000-mile-long broad tail and high-resolution features near the nucleus due to a coma and jets,” said lead Hubble researcher Bryce Bolin of Caltech in Pasadena, California.

Describing the Centaur’s capture as a rare event, Bolin added, “The visitor had to have come into the orbit of Jupiter at just the right trajectory to have this kind of configuration that gives it the appearance of sharing its orbit with the planet. We’re investigating how it was captured by Jupiter and landed among the Trojans. But we think it could be related to the fact that it had a somewhat close encounter with Jupiter.”

The team’s paper appears in the February 11, 2021 issue of The Astronomical Journal.

The research team’s computer simulations show that the icy object, called P/2019 LD2 (LD2), probably swung close to Jupiter about two years ago. The planet then gravitationally punted the wayward visitor to the Trojan asteroid group’s co-orbital location, leading Jupiter by about 437 million miles.

Bucket Brigade

The nomadic object was discovered in early June 2019 by the University of Hawaii’s Asteroid Terrestrial-impact Last Alert System (ATLAS) telescopes located on the extinct volcanoes, one on Mauna Kea and one on Haleakala. Japanese amateur astronomer Seiichi Yoshida tipped off the Hubble team to possible comet activity. The astronomers then scanned archival data from the Zwicky Transient Facility, a wide-field survey conducted at Palomar Observatory in California, and realized that the object was clearly active in images from April 2019.

They followed up with observations from the Apache Point Observatory in New Mexico, which also hinted at the activity. The team observed the comet using Spitzer just days before the observatory’s retirement in January 2020, and identified gas and dust around the comet nucleus. These observations convinced the team to use Hubble to take a closer look. Aided by Hubble’s sharp vision, the researchers identified the tail, coma structure and the size of the dust particles and their ejection velocity. These images helped them confirm that the features are due to relatively new comet-like activity.

Although LD2’s location is surprising, Bolin wonders whether this pit stop could be a common pull-off for some sunward-bound comets. “This could be part of the pathway from our solar system through the Jupiter Trojans to the inner solar system,” he said.

The unexpected guest probably will not stay among the asteroids for very long. Computer simulations show that it will have another close encounter with Jupiter in about another two years. The hefty planet will boot the comet from the system, and it will continue its journey to the inner solar system.

“The cool thing is that you’re actually catching Jupiter flinging this object around and changing its orbital behavior and bringing it into the inner system,” said team member Carey Lisse of the Johns Hopkins University Applied Physics Laboratory (APL) in Laurel, Maryland. “Jupiter controls what’s going on with comets once they get into the inner system by altering their orbits.”

The icy interloper is most likely one of the latest members of the so-called “bucket brigade” of comets to get kicked out of its frigid home in the Kuiper belt and into the giant planet region through interactions with another Kuiper belt object. Located beyond Neptune’s orbit, the Kuiper belt is a haven of icy, leftover debris from our planets’ construction 4.6 billion years ago, containing millions of objects, and occasionally these objects have near misses or collisions that drastically alter their orbits from the Kuiper belt inward into the giant planet region.

The bucket brigade of icy relics endure a bumpy ride during their journey sunward. They bounce gravitationally from one outer planet to the next in a game of celestial pinball before reaching the inner solar system, warming up as they come closer to the Sun. The researchers say the objects spend as much or even more time around the giant planets, gravitationally pulling on them — about 5 million years — than they do crossing into the inner system where we live.

“Inner system, ‘short-period’ comets break up about once a century,” Lisse explained. “So, in order to maintain the number of local comets we see today, we think the bucket brigade has to deliver a new short-period comet about once every 100 years.”

An Early Bloomer

Seeing outgassing activity on a comet 465 million miles away from the Sun (where the intensity of sunlight is 1/25th as strong as on Earth) surprised the researchers. “We were intrigued to see that the comet had just started to become active for the first time so far away from the Sun at distances where water ice is barely starting to sublimate,” said Bolin.

Water remains frozen on a comet until it reaches about 200 million miles from the Sun, where heat from sunlight converts water ice to gas that escapes from the nucleus in the form of jets. So the activity signals that the tail might not be made of water. In fact, observations by Spitzer indicated the presence of carbon monoxide and carbon dioxide gas, which could be driving the creation of the tail and jets seen on the Jupiter-orbiting comet. These volatiles do not need much sunlight to heat their frozen form and convert them to gas.

Once the comet gets kicked out of Jupiter’s orbit and continues its journey, it may meet up with the giant planet again. “Short-period comets like LD2 meet their fate by being thrown into the Sun and totally disintegrating, hitting a planet, or venturing too close to Jupiter once again and getting thrown out of the solar system, which is the usual fate,” Lisse said. “Simulations show that in about 500,000 years, there’s a 90% probability that this object will be ejected from the solar system and become an interstellar comet.”

Video: https://www.youtube.com/watch?v=x-Ikmr5IPys&feature=emb_logo

“If there was a COVID-like pandemic occurring in important bacterial populations it would be difficult to tell, because before this study, we lacked the affordable and accurate tools necessary to study viral infections in uncultured bacterial populations,” said study corresponding author Sarah Preheim, a Johns Hopkins assistant professor of environmental health and engineering.

The findings were published today in Nature Microbiology.

Sick bacteria are stymied in their function as decomposers and as part of the foundation of the food web in the Chesapeake Bay and other waterways. Determining viral infections in bacteria traditionally relies on culturing both bacteria and virus, which misses 99% of bacteria found in the environment because they cannot be grown in culture, Preheim says, adding that tests of viral infections in uncultured bacteria are expensive and difficult to apply widely, not unlike the early stages of COVID-19 testing.

The key to making a test of viral infections for uncultured bacteria faster and more affordable was to isolate single bacterial cells in a small bubble (i.e. an emulsion droplet) and fuse the genes of the virus and bacteria together once inside.

“The fused genes act like name tags for the bacteria and viruses,” said lead author Eric Sakowski, a former postdoctoral researcher in Preheim’s laboratory who is now an assistant professor at Mount St. Mary’s University. “By fusing the genes together, we are able to identify which bacteria are infected, as well as the variant of the virus that is causing the infection.”

The resulting test provides a novel way to screen for viral infections in a subset of bacterial populations. The test allows researchers to identify a link between environmental conditions and infections in Actinobacteria, one of the most abundant bacterial groups in the Chesapeake Bay and one that plays a crucial role in decomposing organic matter, making nutrients available to plants and photosynthetic algae.

Though the researchers developed this tool studying the Chesapeake Bay, they say their approach could be widely applied across aquatic ecosystems, shedding light on viral ecology and helping predict — and even prevent — devastating environmental impacts.

“This testing tool allows us to track viral infections more easily, so we can monitor these infections to see when they are most likely to have important environmental consequences,” Preheim said.

Sakowski said the new test could someday also affect how we treat bacterial infections.

“Viruses show potential for treating infections caused by antibiotic-resistant bacteria,” he said. “Knowing which viruses most effectively infect bacteria will be critical to this type of treatment.”

Preheim’s team also included Johns Hopkins doctoral student Keith Arora-Williams, and Funing Tian, Ahmed A. Zayed, Olivier Zablocki, and Matthew B. Sullivan, all from the Ohio State University.

Support was provided by the National Science Foundation and the Gordon E. and Betty I. Moore Foundation.

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For the study, researchers at NCI, part of the National Institutes of Health, collaborated with two health care data analytics companies (HealthVerity and Aetion, Inc.) and five commercial laboratories. The findings were published on Feb. 24 in JAMA Internal Medicine.

“While cancer research and cancer care remain?the?primary?focus of NCI’s work, we were eager to lend our expertise in serological sciences to help address the global COVID-19 pandemic, at the request of Congress,” said NCI Director Norman E. “Ned” Sharpless, M.D., who was one of the coauthors on the study. “We hope that these results, in combination with those of other studies, will inform future public health efforts and help in setting policy.”

“The data from this study suggest that people who have a positive result from a commercial antibody test appear to have substantial immunity to SARS-CoV-2, which means they may be at lower risk for future infection,” said Lynne Penberthy, M.D., M.P.H., associate director of NCI’s Surveillance Research Program, who led the study. “Additional research is needed to understand how long this protection lasts, who may have limited protection, and how patient characteristics, such as comorbid conditions, may impact protection. We are nevertheless encouraged by this early finding.”

Antibody tests — also known as serology tests — detect serum antibodies, which are immune system proteins made in response to a specific foreign substance or infectious agent, such as SARS-CoV-2.

This study was launched in an effort to better understand whether, and to what degree, detectable antibodies against SARS-CoV-2 protect people from reinfection with the virus. Working with HealthVerity and Aetion, NCI aggregated and analyzed patient information collected from multiple sources, including five commercial labs (including Quest Diagnostics and Labcorp), electronic medical records, and private insurers. This was done in a way that protects the privacy of an individual’s health information and is compliant with relevant patient privacy laws.

The researchers ultimately obtained antibody test results for more than 3 million people who had a SARS-CoV-2 antibody test between Jan. 1 and Aug. 23, 2020. This represented more than 50% of the commercial SARS-CoV-2 antibody tests conducted in the United States during that time. Nearly 12% of these tests were antibody positive; most of the remaining tests were negative, and less than 1% were inconclusive.

About 11% of the seropositive individuals and 9.5% of the seronegative individuals later received a nucleic acid amplification test (NAAT) — sometimes referred to as a PCR test — for SARS-CoV-2. The research team looked at what fraction of individuals in each group subsequently had a positive NAAT result, which may indicate a new infection. The study team reviewed NAAT results at several intervals: 0-30 days, 31-60 days, 61-90 days, and >90 days because some people who have recovered from a SARS-CoV-2 infection can still shed viral material (RNA) for up to three months (although they likely do not remain infectious during that entire period).

The team found that, during each interval, between 3% and 4% of the seronegative individuals had a positive NAAT test. But among those who had originally been seropositive, the NAAT test positivity rate declined over time. When the researchers looked at test results 90 or more days after the initial antibody test (when any coronavirus detected by NAAT is likely to reflect a new infection rather than continued virus shedding from the original infection), only about 0.3% of those who had been seropositive had a positive NAAT result — about one-tenth the rate in those who had been seronegative.

Although these results support the idea that having antibodies against SARS-CoV-2 is associated with protection from future infection, the authors note important limitations to this study. In particular, the findings come from a scientific interpretation of real-world data, which are subject to biases that may be better controlled for in a clinical trial. For example, it is not known why people who had tested antibody positive went on to have a PCR test. In addition, the duration of protection is unknown; studies with longer follow-up time are needed to determine if protection wanes over time.

To continue to comprehensively address this important research question, NCI is supporting clinical studies that monitor infection rates in large populations of people whose antibody status is known. These are known as “seroprotection” studies. NCI is also sponsoring ongoing studies using real-world data to assess the longer-term effect of antibody positivity on subsequent infection rates.

This research is part of a $306 million effort that NCI has taken on at the request of Congress to develop, validate, improve, and implement serological testing and associated technologies applicable to COVID-19. Through this appropriation, NCI is working with the Department of Health and Human Services; the National Institute of Allergy and Infectious Diseases, another part of NIH; and other government agencies to apply its expertise and advanced research capabilities to respond to this pandemic, including efforts to rigorously characterize the performance of serology assays.

A team of researchers from the University of Exeter’s flagship Living Systems Institute has discovered how the model alga Chlamydomonas is seemingly able to scan the environment by constantly spinning around its own body axis in a corkscrewing movement. This helps it respond to light, which it needs for photosynthesis.

The tiny alga, which is found abundantly in fresh-water ponds across the world, swims by beating its two flagella, hair-like structures that adopt a whip-like movement to move the cell. These flagella beat in much the same way as the cilia in the human respiratory system.

Chlamydomonas cells are able to sense light through a red eye spot and can react to it, known as phototaxis. The cell rotates steadily as it propels itself forwards using a sort of breaststroke, at a rate of about once or twice a second, so that its single eye can scan the local environment.

However, the intricate mechanism that allows the alga to achieve this helical swimming has been previously unclear.

IN the new study, the researchers first performed experiments which revealed that the two flagella in fact beat in planes that are slightly skewed away from each other.

Then, creating a sophisticated computer model of Chlamydomonas, they were able to simulate the flagella movement and reproduce the observed swimming behaviour.

The researchers discovered that the flagella were able to move the Chlamydomonas in a clockwise fashion with each power stroke, and then anticlockwise on the reverse stroke — akin to how a swimmer rocks back and forth when switching from one arm to another. Except here the cell feels no inertia.

Furthermore, they also deduced how simply by exerting slightly different forces on the two flagella, the alga can even steer, rather than just move in a straight line.

The researchers were able to show that by adding in an additional influence, such as light, the alga can navigate left or right by knowing which flagellum to stroke harder than the other.

Dr Kirsty Wan, who led the study said: “The question of how a cell makes these types of precise decisions can be a matter of life or death. It’s quite a remarkable feat of both physics and biology, that a single cell with no nervous system to speak of is able to do this…It’s an age-old mystery that my group is currently working hard to solve.”

For the study, the researchers were able to test various scenarios to determine which variables were influencing the trajectory. Their study showed that by varying different parameters, such as if one flagella is slightly stronger than another, the tilt plane of the flagella or its beat pattern, the algae can manipulate its own movement.

Team member Dr Dario Cortese added: “The agreement of our model with the experiments is surprising really, that we could effectively capture the complex 3D beat of the flagella with a very simple movement of a bead going around in circles.”

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“The ability to flexibly learn in new situations makes it possible to adapt to an ever-changing world,” noted Joshua A. Gordon, M.D., Ph.D., a senior author on the study and director of the National Institute of Mental Health, part of NIH. “Understanding the neural basis of this flexible learning in animals gives us insight into how this type of learning may become disrupted in humans.”

Dr. Gordon co-supervised the research project with Joseph A. Gogos, M.D., Ph.D., and Alexander Z. Harris, M.D., Ph.D., both of Columbia University, New York City.

Whenever we encounter new information, that information must be consolidated into a stable, lasting memory for us to recall it later. A key mechanism in this memory consolidation process is long-term potentiation, which is a persistent strengthening of neural connections based on recent patterns of activity. Although this strengthening of neural connections may be persistent, it can’t be permanent, or we wouldn’t be able to update memory representations to accommodate new information. In other words, our ability to remember new experiences and learn from them depends on information encoding that is both enduring and flexible.

To understand the specific neural mechanisms that make this plasticity possible, the research team, led by Alan J. Park, Ph.D., of Columbia, examined spatial learning in mice.

Spatial learning depends on a key circuit between the ventral hippocampus (a structure located in the middle of the brain) and the medial prefrontal cortex (located just behind the forehead). Connectivity between these brain structures strengthens over the course of spatial learning. If the connectivity remains at maximum strength, however, it impairs later adaptation to new tasks and rules. The researchers hypothesized that exposure to a new experience may serve as an environmental trigger that dampens established hippocampal-prefrontal connectivity, enabling flexible spatial learning.

In the first task, the researchers trained mice to navigate a maze in a certain way to receive a reward. Some of the mice were then allowed to explore a space they hadn’t seen before, while others explored a familiar space. The mice then engaged in a second spatial task, which required that they switch to a new navigation strategy to get a reward.

As expected, all of the mice favored their original navigation strategy at first. But the mice that had explored a new space gradually overcame this bias and successfully learned the new navigation strategy about halfway through the 40-trial training session. When the researchers tested a subset of the mice on the first task again, they found that the novelty-exposed mice were able to switch back to the original strategy, indicating that they updated and chose their strategy according to the task demands.

Additional findings showed that the effects of novelty extended beyond new spaces: Encountering new mice before the second task also enhanced learning of the new reward strategy.

Changes in brain activity throughout training revealed the neuronal mechanisms that drive this novelty-enhanced learning. In rodents, there is a well-defined firing pattern in the hippocampus known as the theta wave, which is thought to play a central role in learning and memory. When Park and coauthors examined recordings from the ventral hippocampus, they found that the theta wave became stronger during exploration of the novel arena and the hour that followed; the theta wave decreased as the mice became familiar with the arena over the next two days. The researchers found that novelty exposure also disrupted encoding of the original navigation strategy, reorganizing the firing pattern of individual neurons in the ventral hippocampus to bring them in sync with the theta wave.

At the same time, neurons in the medial prefrontal cortex showed decreased theta wave synchrony, and correlations between hippocampal activity and prefrontal activity weakened. These and other findings suggest that novelty exposure dampened the synaptic connections between the ventral hippocampus and medial prefrontal cortex, resetting the circuit to allow for subsequent strengthening of connectivity associated with learning.

By triggering this reset, novelty appears to facilitate strategy updating in response to the task’s specific reward structure. Machine learning analyses indicated that, following novelty exposure, ventral hippocampal neurons switched encoding from a strategy that predicted reward on the first task to one that predicted reward on the second task. The task-specific information was then relayed to the medial prefrontal neurons, which updated encoding accordingly.

On a chemical level, the neurotransmitter dopamine acts as a key mediator of this plasticity. Several experiments showed that activating dopamine D1-receptors in the ventral hippocampus led to novelty-like effects, including dampened hippocampal-prefrontal connectivity and enhanced learning. Blocking D1-receptors prevented these novelty-induced effects.

Together, these findings shed light on some of the brain mechanisms that play a role in flexible information encoding.

“Our study points to novelty as one way to trigger the circuitry reset that facilitates spatial learning in mice,” said Park. “The next step is to build on these findings and explore whether novelty plays a similar role in human memory and learning.”