NASA Lucy Images Reveal Asteroid Dinkinesh to be Surprisingly Complex - UNIVERSE

Images from the November 2023 flyby of asteroid Dinkinesh by NASA’s Lucy spacecraft show a trough on Dinkinesh where a large piece — about a quarter of the asteroid — suddenly shifted, a ridge, and a separate contact binary satellite (now known as Selam). Scientists say this complicated structure shows that Dinkinesh and Selam have significant internal strength and a complex, dynamic history.

Panels a, b, and c each show stereographic image pairs of the asteroid Dinkinesh taken by the NASA Lucy Spacecraft’s L’LORRI Instrument in the minutes around closest approach on Nov. 1, 2023. The yellow and rose dots indicate the trough and ridge features, respectively. These images have been sharpened and processed to enhance contrast. Panel d shows a side view of Dinkinesh and its satellite Selam taken a few minutes after closest approach. NASA/GSFC/SwRI/Johns Hopkins APL/NOIRLab

“We want to understand the strengths of small bodies in our solar system because that’s critical for understanding how planets like Earth got here,” said Hal Levison, Lucy principal investigator at the Boulder, Colorado, branch of the Southwest Research Institute in San Antonio, Texas. “Basically, the planets formed when zillions of smaller objects orbiting the Sun, like asteroids, ran into each other. How objects behave when they hit each other, whether they break apart or stick together, has a lot to do with their strength and internal structure.” Levison is lead author of a paper on these observations published May 29 in Nature.

On November 1, 2023, NASA’s Lucy spacecraft flew by the main-belt asteroid Dinkinesh. Now, the mission has released pictures from Lucy’s Long Range Reconnaissance Imager taken over a roughly three-hour period, providing the best views of the asteroid to date. During the flyby, Lucy discovered that Dinkinesh has a small moon, which the mission named “Selam,” a greeting in the Amharic language meaning “peace.” Lucy is the first mission designed to visit the Jupiter Trojans, two swarms of asteroids trapped in Jupiter’s orbit that may be “fossils” from the era of planet formation. Credit: NASA’s Goddard Space Flight Center. Download this video and more at: https://svs.gsfc.nasa.gov/14596/

Researchers think that Dinkinesh is revealing its internal structure by how it has responded to stress. Over millions of years rotating in the sunlight, the tiny forces coming from the thermal radiation emitted from the asteroid’s warm surface generated a small torque that caused Dinkinesh to gradually rotate faster, building up centrifugal stresses until part of the asteroid shifted into a more elongated shape. This event likely caused debris to enter into a close orbit, which became the raw material that produced the ridge and satellite.

Stereo movie of asteroid Dinkinesh from NASA’s Lucy spacecraft flyby on Nov. 1, 2023. NASA/GSFC/SwRI/Johns Hopkins APL/NOIRLab/Brian May/Claudia Manzoni

If Dinkinesh were much weaker, more like a fluid pile of sand, its particles would have gradually moved toward the equator and flown off into orbit as it spun faster. However, the images suggest that it was able to hold together longer, more like a rock, with more strength than a fluid, eventually giving way under stress and fragmenting into large pieces. (Although the amount of strength needed to fragment a small asteroid like Dinkinesh is miniscule compared to most rocks on Earth.)

“The trough suggests an abrupt failure, more an earthquake with a gradual buildup of stress and then a sudden release, instead of a slow process like a sand dune forming,” said Keith Noll of NASA’s Goddard Space Flight Center in Greenbelt, Maryland, project scientist for Lucy and a co-author of the paper.

“These features tell us that Dinkinesh has some strength, and they let us do a little historical reconstruction to see how this asteroid evolved,” said Levison. “It broke, things moved apart and formed a disk of material during that failure, some of which rained back onto the surface to make the ridge.”

The researchers think some of the material in the disk formed the moon Selam, which is actually two objects touching each other, a configuration called a contact binary. Details of how this unusual moon formed remain mysterious.

Stereo movie of Selam from NASA’s Lucy spacecraft flyby on Nov. 1, 2023. NASA/GSFC/SwRI/Johns Hopkins APL/NOIRLab/Brian May/Claudia Manzoni

Dinkinesh and its satellite are the first two of 11 asteroids that Lucy’s team plans to explore over its 12-year journey. After skimming the inner edge of the main asteroid belt, Lucy is now heading back toward Earth for a gravity assist in December 2024. That close flyby will propel the spacecraft back through the main asteroid belt, where it will observe asteroid Donaldjohanson in 2025, and then on to the first of the encounters with the Trojan asteroids that lead and trail Jupiter in its orbit of the Sun beginning in 2027.

Lucy’s principal investigator is based out of the Boulder, Colorado, branch of Southwest Research Institute, headquartered in San Antonio. NASA’s Goddard Space Flight Center in Greenbelt, Maryland, provides overall mission management, systems engineering, and safety and mission assurance. Lockheed Martin Space in Littleton, Colorado, built and operates the spacecraft. Lucy is the 13th mission in NASA’s Discovery Program. NASA’s Marshall Space Flight Center in Huntsville, Alabama, manages the Discovery Program for the Science Mission Directorate at NASA Headquarters in Washington.

For more information about NASA’s Lucy mission, visit: https://science.nasa.gov/mission/lucy 

Source: NASA Lucy Images Reveal Asteroid Dinkinesh to be Surprisingly Complex - NASA

Ornithologists discover world's largest hummingbird is actually two species

Measured against a typical nectar feeder, the size of a Giant Hummingbird is even more astonishing. Credit: Xiaoni Xu | Macaulay Library | Cornell Lab of Ornithology

The Giant Hummingbird of western South America is not one species but two, according to an international group of researchers. The northern population stays in the high Andes year-round while the southern population migrates from sea level up to 14,000 feet for the nonbreeding months. The two species appear identical. But looks deceive—their genomes and behaviors tell a different story.

A paper announcing the find was published in the journal Proceedings of the National Academy of Sciences.

"These are amazing birds," said lead author Jessie Williamson, a National Science Foundation Postdoctoral Fellow and Rose Postdoctoral Fellow at the Cornell Lab of Ornithology. "They're about eight times the size of a Ruby-throated Hummingbird. We knew that some Giant Hummingbirds migrated, but until we sequenced genomes from the two populations, we had never realized just how different they are."

"They are as different from each other as chimpanzees are from bonobos," said senior author Chris Witt at the University of New Mexico. "The two species do overlap on their high elevation wintering grounds. It's mind-boggling that until now nobody figured out the Giant Hummingbird mystery, yet these two species have been separate for millions of years."

At first, the research goal was simply to learn where the migratory population went—a journey tracked with geolocators and satellite transmitters. The researchers actually tracked eight individual hummingbirds migrating up to 5,200 miles from the Chilean coast up to the Andes of Peru and back. Williamson says that's one of the longest, if not the longest hummingbird migration in the world. The out-and-back journey is longer than the distance from New York City to Istanbul, Turkey. 

A Southern Giant Hummingbird takes flight with a geolocator backpack to track its migration. Credit: Jessie Williamson.

The authors say the shift in migratory behavior is what drove speciation, though there's no way to tell whether migratory behavior was gained by one species or lost by the other. Until now, there had been only one known species on this branch of the hummingbird family tree, while the Giant Hummingbird's closest relatives––the world's smallest hummingbirds––diversified into 165 distinct hummingbird species.

The researchers are proposing straightforward common names: Northern Giant Hummingbird and Southern Giant Hummingbird. The southern migrant species will retain the Latin name, Patagona gigas. The proposed scientific name for the resident northern population is Patagona chaski. "Chaski" is Quechua for "messenger." Quechua is the name for a family of Indigenous languages that spread from Peru to other neighboring countries.

The researchers relied on support and local knowledge from landowners and villages in Peru and Chile. Co-author Emil Bautista's village in Peru was a homebase for this project and the community supported the scientists' work. But even with more than 15 years of field experience, Bautista admits this fieldwork was the hardest he's ever done.

"Capturing Giant Hummingbirds is very challenging," he said. "They watch everything and they know their territories well. We had to be strategic in choosing sites for our nets. If Giant Hummingbirds see something unusual, they won't visit that spot. They are more observant than other birds."

Elevational ascent of a Giant Hummingbird, illustrated by high-resolution Argos satellite tracking data. During a period of 21 days, the bird showed bursts of ascent interspersed with pauses and even slight downward movements. The bird stopped at mid-elevations to acclimatize before ascending the high peaks of the Andes. Credit: Jessie Williamson.

Right now, Giant Hummingbird populations, north and south, are stable and the species are common within their ranges—some even visit backyard nectar feeders. The team plans to continue research on these enigmatic birds.

"We have to figure out where these two forms come together and how they interact," said Witt. "Do they compete, is one dominant over the other, how might they partition resources, and do they mix or spatially segregate within the winter range? Lots of interesting questions to pursue!"

"I'm really interested in how Southern Giant Hummingbirds make such dramatic shifts in elevation during migration. They travel from sea level to the high Andes in just a few weeks," said Williamson. "They're like miniature mountain climbers. How do they change their physiology to facilitate these movements?" 

by Cornell University

Source: Ornithologists discover world's largest hummingbird is actually two species (phys.org)