NASA’s Hubble Sees Asteroids Colliding at Nearby Star for First Time - UNIVERSE

Like a game of cosmic bumper cars, scientists think the early days of our solar system were a time of violent turmoil, with planetesimals, asteroids, and comets smashing together and pelting the Earth, Moon, and the other inner planets with debris. Now, in a historical milestone, NASA’s Hubble Space Telescope has directly imaged similar catastrophic collisions in a nearby planetary system around another star, Fomalhaut.

“This is certainly the first time I’ve ever seen a point of light appear out of nowhere in an exoplanetary system,” said principal investigator Paul Kalas of the University of California, Berkeley. “It’s absent in all of our previous Hubble images, which means that we just witnessed a violent collision between two massive objects and a huge debris cloud unlike anything in our own solar system today. Amazing!"

Just 25 light-years from Earth, Fomalhaut is one of the brightest stars in the night sky. Located in the constellation Piscis Austrinus, also known as the Southern Fish, it is more massive and brighter than the Sun and is encircled by several belts of dusty debris.

This composite Hubble Space Telescope image shows the debris ring and dust clouds cs1 and cs2 around the star Fomalhaut. Fomalhaut itself is masked out to allow the fainter features to be seen. Its location is marked by the white star.

Image: NASA, ESA, Paul Kalas (UC Berkeley); Image Processing: Joseph DePasquale (STScI)

In 2008, scientists used Hubble to discover a candidate planet around Fomalhaut, making it the first stellar system with a possible planet found using visible light. That object, called Fomalhaut b, now appears to be a dust cloud masquerading as a planet—the result of colliding planetesimals. While searching for Fomalhaut b in recent Hubble observations, scientists were surprised to find a second point of light at a similar location around the star. They call this object “circumstellar source 2” or “cs2” while the first object is now known as “cs1.”

Tackling Mysteries of Colliding Planetesimals

Why astronomers are seeing both of these debris clouds so physically close to each other is a mystery. If the collisions between asteroids and planetesimals were random, cs1 and cs2 should appear by chance at unrelated locations. Yet, they are positioned intriguingly near each other along the inner portion of Fomalhaut’s outer debris disk.

Another mystery is why scientists have witnessed these two events within such a short timeframe. “Previous theory suggested that there should be one collision every 100,000 years, or longer. Here, in 20 years, we've seen two,” explained Kalas. “If you had a movie of the last 3,000 years, and it was sped up so that every year was a fraction of a second, imagine how many flashes you'd see over that time. Fomalhaut’s planetary system would be sparkling with these collisions.”

Collisions are fundamental to the evolution of planetary systems, but they are rare and difficult to study.

This artist's concept shows the sequence of events leading up to the creation of dust cloud cs2 around the star Fomalhaut. In Panel 1, the star Fomalhaut appears in the top left corner. Two white dots, located in the bottom right corner, represent the two massive objects in orbit around Fomalhaut. In Panel 2, the objects approach each other. Panel 3 shows the violent collision of these two objects. In Panel 4, the resulting dust cloud cs2 becomes visible and starlight pushes the dust grains away from the star.

Artwork: NASA, ESA, STScI, Ralf Crawford (STScI)

“The exciting aspect of this observation is that it allows researchers to estimate both the size of the colliding bodies and how many of them there are in the disk, information which is almost impossible to get by any other means,” said co-author Mark Wyatt at the University of Cambridge in England. “Our estimates put the planetesimals that were destroyed to create cs1 and cs2 at just 37 miles or 60 kilometers across, and we infer that there are 300 million such objects orbiting in the Fomalhaut system.”

“The system is a natural laboratory to probe how planetesimals behave when undergoing collisions, which in turn tells us about what they are made of and how they formed,” explained Wyatt.

Cautionary Tale

The transient nature of Fomalhaut cs1 and cs2 poses challenges for future space missions aiming to directly image exoplanets. Such telescopes may mistake dust clouds like cs1 and cs2 for actual planets.

“Fomalhaut cs2 looks exactly like an extrasolar planet reflecting starlight,” said Kalas. “What we learned from studying cs1 is that a large dust cloud can masquerade as a planet for many years. This is a cautionary note for future missions that aim to detect extrasolar planets in reflected light."

Looking to Future

Kalas and his team have been granted Hubble time to monitor cs2 over the next three years. They want to see how it evolves—does it fade, or does it get brighter? Being closer to the dust belt than cs1, the expanding cs2 cloud is more likely to start encountering other material in the belt. This could lead to a sudden avalanche of more dust in the system, which could cause the whole surrounding area to get brighter.

Credit: NASA's Goddard Space Flight Center; Lead Producer: Paul Morris

“We will be tracing cs2 for any changes in its shape, brightness, and orbit over time,” said Kalas, “It’s possible that cs2 will start becoming more oval or cometary in shape as the dust grains are pushed outward by the pressure of starlight.”

The team also will use the NIRCam (Near-Infrared Camera) instrument on NASA’s James Webb Space Telescope to observe cs2. Webb’s NIRCam has the ability to provide color information that can reveal the size of the cloud’s dust grains and their composition. It can even determine if the cloud contains water ice. 

Hubble and Webb are the only observatories capable of this kind of imaging. While Hubble primarily sees in visible wavelengths, Webb could view cs2 in the infrared. These different, complementary wavelengths are needed to provide a broad multi-spectral investigation and a more complete picture of the mysterious Fomalhaut system and its rapid evolution.

This research appears in the December 18 issue of Science.

The Hubble Space Telescope has been operating for over three decades and continues to make ground-breaking discoveries that shape our fundamental understanding of the universe. Hubble is a project of international cooperation between NASA and ESA (European Space Agency). NASA's Goddard Space Flight Center in Greenbelt, Maryland, manages the telescope and mission operations. Lockheed Martin Space, based in Denver, also supports mission operations at Goddard. The Space Telescope Science Institute in Baltimore, which is operated by the Association of Universities for Research in Astronomy, conducts Hubble science operations for NASA. 

Source: NASA’s Hubble Sees Asteroids Colliding at Nearby Star for First Time - NASA Science

Turning plastic waste into valuable chemicals with single-atom catalysts - Nanotechnology - Nanomaterials

Pathways for toluene production from crude oil and PS waste. Credit: Wang et al.

The rapid accumulation of plastic waste is currently posing significant risks for both human health and the environment on Earth. A possible solution to this problem would be to recycle plastic waste, breaking it into smaller molecules that can be used to produce valuable chemicals.

Researchers at Nanjing Forestry University and Tsinghua University recently introduced a new approach to convert polystyrene (PS), a plastic widely used to pack some foods and other products, into toluene, a hydrocarbon that is of value in industrial and manufacturing settings. Their proposed strategy, outlined in a paper published in Nature Nanotechnology, entails heating polystyrene waste in hydrogen and breaking it down into smaller vapor molecules, a process known as hydro-pyrolysis.

Life-cycle and techno-economic analyses performed by the team showed that the newly introduced process could reduce the carbon footprint of toluene production by 53%, producing toluene at an estimated cost of $0.61/kg, which is below the current industry benchmark.

"This work is based on our earlier development of a two-stage fixed-bed reactor and was inspired by the unique activity and stability of single-atom catalysts in plastic hydrogenolysis," Dr. Zedong Zhang, co-author of the paper, told Phys.org.

"We found that tuning Ru active centers at the atomic level enables control of product selectivity and keeps the high reactivity in polystyrene conversion. The main objective of this study was to demonstrate that single-atom catalysts can overcome the traditional yield–selectivity trade-off and offer new routes for plastic upcycling."

Credit: Wang et al.

Breaking down waste into smaller molecules

The team's proposed strategy for converting plastic waste into smaller molecules relies on a single reactor system that implements two separate steps. The first step, known as pyrolysis, consists in heating up solid PS to high temperatures, until it breaks apart.

The hot vapors derived from this step subsequently flow into a second part of the reactor that contains a catalyst and hydrogen gas. Here, a reaction known as hydrogenolysis takes place, via which hydrogen cuts chemical bonds in the vapor molecules and shapes them into the desired chemical (i.e., toluene).

"In our experiments, solid PS was converted into vapor intermediates in the first reactor (475℃, 0.4MPa) and then selectively transformed into toluene over a Ru single-atom catalyst in the second reactor (275℃, 0.4MPa)," explained Dr. Zhang.

"In collaboration with Dr. Jia Wang and Prof. Jianchun Jiang, we validated this approach through Lab-scale catalytic tests and scale-up experiments, including higher feed amounts and larger fixed-bed reactors."

Further improvement and possible applications

In initial tests, the approach developed by these researchers enabled the conversion of PS into toluene with a selectivity of over 99% and a toluene yield of 83.5%. Notably, the method also led to 53% less carbon emissions compared to current strategies to produce toluene.

"We believe that this tandem catalytic hydrogenolysis strategy offers a promising route for upcycling waste plastics into petrochemical feedstocks," said Dr. Zhang.

"Beyond the current study, we are working toward continuous solid feeding to enable longer operation times and larger-scale plastic conversion. More broadly, the unique properties of single-atom catalysts in plastic hydrogenolysis could help reshape how catalytic plastic conversion is designed."

In the future, the reactor designed by the researchers could be improved and adapted to enable the conversion of PS into other chemicals or fuels. If deployed in real-world settings, it could eventually contribute to the reduction of plastic pollution on Earth.

"Our future research will focus on developing single-atom catalysts with enhanced selectivity for plastic hydrogenolysis, with the goal of better controlling product distribution," added Dr. Zhang. "At the same time, we aim to further explore scalable tandem fixed-bed reactor designs to support longer operation times and higher plastic throughput."

by Ingrid Fadelli, Phys.org

edited by Gaby Clark, reviewed by Robert Egan 

Source: Turning plastic waste into valuable chemicals with single-atom catalysts