The new findings are part of a suite of papers published today by the team behind NASA’s Origins, Spectral Interpretation, Resource Identification, Security-Regolith Explorer (OSIRIS-REx) mission. And they come just three months after OSIRIS-REx first encountered Bennu on Dec. 3, 2018.

Since then, the spacecraft has completed a few dozen laps around the asteroid, which is about as tall as the Empire State Building, circling Bennu from a distance of about a mile. And those early circuits are giving scientists a whole new look at this mysterious rock, said CU Boulder’s Daniel Scheeres, who leads the mission’s radio science team.

In research appearing in Nature Astronomy, for example, his team reports the mass of that asteroid: a respectable 73 billion kilograms.

But Scheeres and his colleagues are also working to develop a map of the asteroid’s gravitational pull. Their findings suggest that Bennu exists in a delicate balance between two competing forces, the result of the asteroid’s wild spin. Bennu completes a full revolution about once every four hours.

And, Scheeres said, those forces could play an important role in the asteroid’s long-term evolution — and potential demise.

“When you spin this guy up, you create a competition between the gravity that’s holding you down and the centrifugal acceleration, which is trying to throw you off,” said Scheeres, distinguished professor in the Ann and H.J. Smead Department of Aerospace Engineering Sciences who leads the mission’s radio science team.

To study those forces, Scheeres and his colleagues use OSIRIS-REx’s navigational instruments to measure the minute tug that the asteroid exerts on the spacecraft.

And they dug up more than they expected. Based on the group’s calculations, the region around Bennu’s equator is trapped within a gravitational feature called a rotational Roche lobe — something that scientists had not yet clearly observed on an asteroid.

In practice, that feature gets weird. If you were standing inside the boundaries of Bennu’s Roche lobe and slipped on a banana peel, for example, not much would happen — you’d be captured by the lobe and fall back to the surface.

“But if you were outside of the Roche lobe and slipped on a banana peel, you would roll toward the equator,” Scheeres said. “And you could gain enough energy so that you’d roll off the equator and maybe up into orbit and then out into space.”

It sounds like the sort of environment that Lewis Carroll could appreciate. But it also matters for the lifespan of Bennu, he added.

That’s because radiation from the sun is causing Bennu to spin faster and faster over time. And as the asteroid’s whirling builds up speed, its Roche lobe might also be shrinking, along with the forces that are holding Bennu together.

“As that Roche lobe narrows further and further around the equator, it becomes easier and easier for this asteroid to lose material,” Scheeres said. “So far, that material has been trapped by gravity, but at some point, if the asteroid keeps spinning faster, then you fall off the cliff.”

In other words, Bennu could be in the process of spinning itself into oblivion.

Understanding those physics matters for advance OSIRIS-REx’s scientific mission, too, said Jay McMahon, an assistant professor in aerospace engineering and a co-author of the new study.

He explained that in 2020, mission scientists will nudge OSIRIS-REx to within a few feet of Bennu, using the spacecraft’s retractable arm to collect a sample of material from the surface. And to do that safely, they will need to know the rock’s physics inside and out.

“You need to know the gravitational field for spacecraft operations, really to enable all the other science,” McMahon said.

“When you’re going to a new world, you have some idea of what it might look like,” Scheeres said. “Then you actually go there, and you can start comparing what you thought it might look like versus reality.”

The University of Arizona leads science operations for OSIRIS-REx, which was built by the Colorado-based Lockheed Martin Space. NASA’s Goddard Space Flight Center in Maryland manages the overall mission.

Coauthors on the new study include CU Boulder graduate students Andrew French and Daniel Brack and Paul Sánchez, senior research associate at CU Boulder’s Colorado Center for Astrodynamics Research. Former CU Boulder graduate students Masatoshi Hirabayashi, Stefaan Van wal, Jason Leonard, Yu Takahashi, Jeroen Geeraert, Pete Antreasian, Dolan Highsmith, Mike Moreau and E. Beau Bierhaus also contributed to the paper.

Instead, new research by McMaster behavioural scientists shows that in certain cases evolution works in the opposite direction, reversing individual improvements to benefit related members of the same group.

The research appears in the Journal of Evolutionary Biology, where lead author David Fisher shows that the increased evolution of selfless traits — such as sharing food and keeping watch for one another — is mathematically equivalent to the decreased evolution of individually beneficial traits.

“They’re two sides of the same coin,” Fisher explains. “On one side, traits evolve that benefit your kin, but don’t benefit you, because you’re helping your siblings or cousins. On the other side, traits that benefit you but cost your neighbours don’t evolve, because you’re causing damage to related individuals.”

The work is part of the ongoing effort to understand the paradox of altruistic behaviour in the wild, explains Fisher, a research fellow in McMaster’s Department of Psychology, Neuroscience and Behaviour.

Fisher goes on to show that another way evolution can go backwards is through the evolution of an individual’s negative effects on neighbours and group members. For example, a fast-growing tree may take all the sunlight, water and nutrients out of the environment, causing its neighbours to grow slowly. In the next generation, more trees are fast-growing but are also nasty neighbours. As a result, negative social effects are much more prevalent, and so everyone’s growth is reduced.

“That means evolution has gone backwards. Even though growing quickly is beneficial, because of these negative social effects, the population, on average, grows more slowly,” he says.

Fisher plans to travel to Ecuador this summer to study co-operative spiders, and whether changes in individual and group benefits can explain why co-operation diminishes at higher elevations.

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These findings suggest a previously unknown mechanism for microbes to save energy in lean times. Earlier research has shown that bacteria switch from a mobile to stationary phase in the face of nutrient depletion, but it has been unclear how they deactivate their large, energy-intensive flagella.

The authors of the new study used electron microscopy to get a 3-D look at Gammaproteobacteria that have one or more flagella clustered at one end of each cell. Focusing on two species, Plesiomonas shigelloides and Vibrio fischeri, they saw that microbes living in a nutrient-abundant environment had few partial flagella, but microbes in nutrient-depleted conditions had many more partial flagellar structures.

Further experiments confirmed that these partial structures were relics of flagella that had been ejected, and that a nutrient-depleted environment was indeed the trigger. So, like mountaineer Aron Ralston cutting off his own arm to avoid certain death in the film 127 Hours, bacteria cut off their own tails to avoid starvation.

Flagella are driven by tiny motors embedded in the cell membrane, so ejecting the flagella runs the risk of leaving empty motors with wide-open portals that would allow spillage of the insides of the cell into the environment. Intriguingly, the researchers found that an unidentified protein plugs up the relics of flagellar motors, and they hypothesize that this plug prevents leakage of cellular contents through the resulting hole in the cell membrane.

In the future, additional research could clarify the molecular details of the ejection process, including the identity of the plug protein.

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Rice University bioengineers and their colleagues have developed a technique to grow live bone to repair craniofacial injuries by attaching a 3D-printed bioreactor — basically, a mold — to a rib. Stem cells and blood vessels from the rib infiltrate scaffold material in the mold and replace it with natural bone custom-fit to the patient.

Researchers at Rice, the University of Texas Health Science Center at Houston (UTHealth) and Baylor College of Medicine led the study, and the results appear in the Proceedings of the National Academy of Sciences.

Led by bioengineer Antonios Mikos, a pioneer in the field of tissue engineering, the researchers combined technologies they have developed during a decade-long program funded by the Armed Forces Institute of Regenerative Medicine. The goal is to advance craniofacial reconstruction by taking advantage of the body’s natural healing powers.

The technique is being developed to replace current reconstruction techniques that use bone graft tissues harvested from different areas in a patient, such as the lower leg, hip and shoulder.

“A major innovation of this work is leveraging a 3D-printed bioreactor to form bone grown in another part of the body while we prime the defect to accept the newly generated tissue,” said Mikos, the Louis Calder Professor of Bioengineering and Chemical and Biomolecular Engineering at Rice and a member of the National Academy of Engineering and National Academy of Medicine.

“Earlier studies established a technique for creating bone grafts with or without their own blood supply from real bone implanted into the chest cavity,” said co-author Mark Wong, a professor, chair and program director of the Department of Oral and Maxillofacial Surgery with the School of Dentistry at UTHealth. “This study demonstrated that we could create viable bone grafts from artificial bone substitute materials.

“The significant advantage of this approach is that you do not need to harvest a patient’s own bone to make a bone graft, but that other non-autogenous sources can be used,” he said.

To prove their concept, the researchers made a rectangular defect in the mandibles of sheep. They created a template for 3D printing and printed an implantable mold and a spacer, both made of PMMA, also known as bone cement. The goal of the spacer is to promote healing and prevent scar tissue from filling the defect site.

They removed enough bone from the animal model’s rib to expose the periosteum, which served as a source of stem cells and vasculature to seed scaffold material inside the mold. Test groups included crushed rib bone or synthetic calcium phosphate materials to make the biocompatible scaffold.

The mold, with the rib side open to create a tight interface, stayed in place for nine weeks before removal and transfer to the site of the defect, replacing the spacer. In the animal models, the new bone knitted to the old and soft tissue grew around and covered the site.

“We chose to use ribs because they’re easily accessed and a rich source of stem cells and vessels, which infiltrate the scaffold and grow into new bone tissue that matches the patient,” Mikos said. “There’s no need for exogenous growth factors or cells that would complicate the regulatory approval process and translation to clinical applications.”

Ribs offer another advantage. “We can potentially grow new bone on multiple ribs at the same time,” said co-author Gerry Koons, an M.D./Ph.D. student at Rice and Baylor currently working in Mikos’ lab.

Using PMMA for the mold and spacer was a simple decision, Mikos said, as it has been regulated as a medical device for biological applications for decades. In World War II, when PMMA was used as a windshield for fighter planes, doctors noticed that shards embedded in injured pilots did not cause inflammation and thus considered it benign.

While the study’s initial goal is to improve the treatment of battlefield injuries, the big picture includes civilian surgeries as well.

“We’re delighted to bring together this diversely talented team and deliver promising outcomes to the future healing of the wounded warrior and other patients in need of advanced treatments for the jaw and face,” Mikos said.