Study Finding: Gravitational Instability in a Planet-forming Disk

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Credit: Peter Schmidt from Pixabay

Nature abstract of the study findings:

The canonical theory for planet formation in circumstellar disks proposes that planets are grown from initially much smaller seeds. The long-considered alternative theory proposes that giant protoplanets can be formed directly from collapsing fragments of vast spiral arms induced by gravitational instability—if the disk is gravitationally unstable. For this to be possible, the disk must be massive compared with the central star: a disk-to-star mass ratio of 1:10 is widely held as the rough threshold for triggering gravitational instability, inciting substantial non-Keplerian dynamics and generating prominent spiral arms. Although estimating disk masses has historically been challenging, the motion of the gas can reveal the presence of gravitational instability through its effect on the disk-velocity structure. Here we present kinematic evidence of gravitational instability in the disk around AB Aurigae, using deep observations of 13CO and C18O line emission with the Atacama Large Millimeter/submillimeter Array (ALMA). The observed kinematic signals strongly resemble predictions from simulations and analytic modelling. From quantitative comparisons, we infer a disk mass of up to a third of the stellar mass enclosed within 1″ to 5″ on the sky.

Citation: Speedie, J., Dong, R., Hall, C. et al. Gravitational instability in a planet-forming disk. Nature 633, 58–62 (2024).
https://doi.org/10.1038/s41586-024-07877-0

Study-related stories:

MIT News

Space Daily

Universe Today

Space Stories: Oceans on Ariel, Dinosaur-Killer Asteroid from Beyond Jupiter, and the Launch of the Polaris Dawn Mission

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Image (Credit): Uranus and distant galaxies as seen by the James Webb Space Telescope. (NASA, ESA, CSA, STScI)

Here are some recent stories of interest.

—Forbes: “NASA’s Webb Telescope Finds Evidence For An Ocean World Around Uranus“

New observations by the James Webb Space Telescope suggest that an icy moon around Uranus may have an underground liquid ocean. Ariel is one of 27 moons around Uranus, the seventh planet from the sun and the third largest planet in the solar system. It’s one of four moons that scientists have long been interested in as part of a search for water across the solar system, the others being Umbriel, Titania and Oberon.

—Nature: “Dinosaur-killing Chicxulub Asteroid Formed in Solar System’s Outer Reaches“

The object that smashed into Earth and kick-started the extinction that wiped out almost all dinosaurs 66 million years ago was an asteroid that originally formed beyond the orbit of Jupiter, according to geochemical evidence from the impact site in Chicxulub, Mexico. The findings, published on 15 August in Science, suggest that the mass extinction was the result of a train of events that began during the birth of the Solar System. Scientists had long suspected that the Chicxulub impactor, as it is known, was an asteroid from the outer Solar System, and these observations bolster the case.

—Space Daily: “Polaris Dawn Mission Set for August 26 to Advance Commercial Space Exploration“

The Polaris Program, focused on testing and developing new spaceflight technology, is preparing to launch its first mission, Polaris Dawn, aboard SpaceX’s Falcon 9 rocket on Monday, August 26, 2024. This mission marks a significant step forward in commercial space exploration. Key objectives include testing a next-generation spacesuit during the first commercial spacewalk, attempting to achieve the highest altitude for a human spaceflight since the Apollo missions, and evaluating a new communication system through Starlink.

Study Findings: Feasibility of Keeping Mars Warm with Nanoparticles

Posted on by onespaceman2000
Image (Credit): Frost on Olympus Mons (,shaded in blue). (ESA/DLR/FU Berlin)

Science Advances abstract of the study findings:

One-third of Mars’ surface has shallow-buried H2O, but it is currently too cold for use by life. Proposals to warm Mars using greenhouse gases require a large mass of ingredients that are rare on Mars’ surface. However, we show here that artificial aerosols made from materials that are readily available at Mars—for example, conductive nanorods that are ~9 micrometers long—could warm Mars >5 × 103 time smore effectively than the best gases. Such nanoparticles forward-scatter sunlight and efficiently block upwelling thermal infrared. Like the natural dust of Mars, they are swept high into Mars’ atmosphere, allowing delivery from the near-surface. For a 10-year particle lifetime, two climate models indicate that sustained release at 30 liters per second would globally warm Mars by ≳30 kelvin and start to melt the ice. Therefore, if nanoparticles can be made at scale on (or delivered to) Mars, then the barrier to warming of Mars appears to be less high than previously thought.

Citation: Ansari S, Kite ES, Ramirez R, Steele LJ, Mohseni H, Feasibility of keeping Mars warm with nanoparticles, Science Advances, (2024).
10.1126/sciadv.adn4650

Study-related stories:

Space.com

Universe Today

Northwestern University

Space Quote: Vast Water Reserves May Exist Within Martian Crust

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Image (Credit): Martian surface as captured by NASA’s Perseverance Mars rover (NASA/JPL-Caltech/ASU/MSSS)

“These new results demonstrate that liquid water does exist in the Martian subsurface today, not in the form of discrete and isolated lakes, but as liquid water-saturated sediments, or aquifers…On Earth, the subsurface biosphere is truly vast, containing most of the prokaryotic diversity and biomass on our planet. Some investigations even point to an origin of life on Earth precisely deep in the subsurface. Therefore, the astrobiological implications of finally confirming the existence of liquid water habitats kilometers beneath the surface of Mars are truly exciting.”

–Statement by Alberto Fairén, a visiting interdisciplinary planetary scientist and astrobiologist within the department of astronomy at Cornell University, regarding a recent study reporting vast quantities of water may reside between 7 and 12 miles beneath the Martian surface. The study utilized data from NASA’s InSight lander.

Study Findings: Archaeology in Space: The Sampling Quadrangle Assemblages Research Experiment (SQuARE) on the International Space Station. Report 1: Squares 03 and 05

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Image (Credit): A cutaway image of the International Space Station’s US Orbital Segment, showing the locations of Square 03 (at upper center, in yellow) and 05 (at lower right, in orange). (Tor Finseth, by permission, modified by Justin Walsh)

PLoS ONE abstract of the study findings:

Between January and March 2022, crew aboard the International Space Station (ISS) performed the first archaeological fieldwork in space, the Sampling Quadrangle Assemblages Research Experiment (SQuARE). The experiment aimed to: (1) develop a new understanding of how humans adapt to life in an environmental context for which we are not evolutionarily adapted, using evidence from the observation of material culture; (2) identify disjunctions between planned and actual usage of facilities on a space station; (3) develop and test techniques that enable archaeological research at a distance; and (4) demonstrate the relevance of social science methods and perspectives for improving life in space. In this article, we describe our methodology, which involves a creative re-imagining of a long-standing sampling practice for the characterization of a site, the shovel test pit. The ISS crew marked out six sample locations (“squares”) around the ISS and documented them through daily photography over a 60-day period. Here we present the results from two of the six squares: an equipment maintenance area, and an area near exercise equipment and the latrine. Using the photographs and an innovative webtool, we identified 5,438 instances of items, labeling them by type and function. We then performed chronological analyses to determine how the documented areas were actually used. Our results show differences between intended and actual use, with storage the most common function of the maintenance area, and personal hygiene activities most common in an undesignated area near locations for exercise and waste.

Citation: Walsh JSP, Graham S, Gorman AC, Brousseau C, Abdullah S, Archaeology in space: The Sampling Quadrangle Assemblages Research Experiment (SQuARE) on the International Space Station. Report 1: Squares 03 and 05. PLoS ONE 19(8): e0304229 (2024).
https://doi.org/10.1371/journal.pone.0304229

Study-related stories:

ScienceAlert

Archaeology Magazine

Popular Science