DART impact provided real-time data on evolution of asteroid's debris
IMAGE: THESE THREE PANELS CAPTURE THE BREAKUP OF THE ASTEROID DIMORPHOS WHEN IT WAS DELIBERATELY HIT BY NASA'S 1,200-POUND DOUBLE ASTEROID REDIRECTION TEST MISSION SPACECRAFT ON SEPTEMBER 26, 2022. HUBBLE SPACE TELESCOPE HAD A RINGSIDE VIEW OF THE SPACE DEMOLITION DERBY. THE TOP PANEL, TAKEN 2 HOURS AFTER IMPACT, SHOWS AN EJECTA CONE OF AN ESTIMATED 1,000 TONS OF DUST. view more
CREDIT: NASA, ESA, STSCI, JIAN-YANG LI (PSI)
When asteroids suffer natural impacts in space, debris flies off from the point of impact. The tail of particles that form can help determine the physical characteristics of the asteroid. NASA’s Double Asteroid Redirection Test mission in September 2022 gave a team of scientists including Rahil Makadia, a Ph.D. student in the Department of Aerospace Engineering at the University of Illinois Urbana-Champaign, a unique opportunity—to observe the evolution of an asteroid’s ejecta as it happened for the first time.
“My work on this mission so far has been to study the heliocentric changes to the orbit of Didymos and its smaller moon Dimorphos—the target of the DART spacecraft,” said Makadia. “Even though it hit the secondary, there are still some changes in the entire system’s orbit around the sun because the entire system feels the consequences of the impact. The ejecta that escapes the system provides an extra boost in addition to the impact. So, to accurately determine where the system will be in 100 years, you need to know the contribution of the ejecta that escaped the system.”
The team observed a 33-minute change in the orbit after DART’s impact. Makadia said, if there were no ejecta, the period change would have been less than 33 minutes. But because some ejecta escaped the gravitational pull of Dimorphos, the orbit period change is higher than if there were no ejecta at all.
These three panels capture the breakup of the asteroid Dimorphos when it was deliberately hit by NASA's 1,200-pound Double Asteroid Redirection Test mission spacecraft on September 26, 2022. Hubble Space Telescope had a ringside view of the space demolition derby. The top panel, taken 2 hours after impact, shows an ejecta cone of an estimated 1,000 tons of dust. The center frame shows the dynamic interaction within the asteroid's binary system that starts to distort the cone shape of the ejecta pattern about 17 hours after the impact. The most prominent structures are rotating, pinwheel-shaped features. The pinwheel is tied to the gravitational pull of the companion asteroid, Didymos. In the bottom frame Hubble next captures the debris being swept back into a comet-like tail by the pressure of sunlight on the tiny dust particles. This stretches out into a debris train where the lightest particles travel the fastest and farthest from the asteroid. The mystery is compounded when Hubble records the tail splitting in two for a few days.
The study, published in the journal Nature, focused on the Hubble Space Telescope's measurements of the ejecta, beginning 15 minutes after the impact to 18 ½ days after the impact. The images showed the exact evolution of the tail and how it evolved over time.
You can watch a video that condenses images from 18 ½ days down to 19 seconds.
“After a few days, the primary force acting on these ejecta particles becomes solar radiation pressure,” Makadia said. “The photons emitted from the sun exert an acceleration on these small particles, and they evolve into a straight tail in an anti-solar direction.
“There have been cases in which it was determined that a natural impact caused the observed active asteroid. But because this one was very much intended, we could have telescopes pointed at it before and after the impact and study its evolution.”
He said they’ll use the data about how this ejecta evolves to understand how the entire system's orbit changes as well.
“Now that we have this treasure trove of data, we can make educated guesses about other tails we might observe,” Makadia said. “Depending on what kind of particles are in the tail and their sizes, we can figure out how long ago that impact happened. And we’ll be able to understand the ejecta that escape the system and change the entire system’s heliocentric orbit.”
Makadia, who earned his B.S. in 2020 from UIUC, said almost all of his work is computational.
“To calculate where an asteroid will be on a given date, we need to propagate all the possible locations that the asteroid could be at an initial time, not just one nominal solution. That requires a lot of computational power and understanding of how orbits are affected by small forces, like solar radiation pressure as well as gravity from all kinds of sources within the solar system.
“I developed simulations to study the heliocentric changes when I first started working on my Ph.D. to make sure we have a propagator that can impart all these impulses that are coming from the escaping ejecta. Now I'm developing an orbit determination tool so once we do have enough observations, we can extract this information about the heliocentric change to the system.”
About the project, Makadia said, “This is 100 percent the most exciting thing in my life. It’s absolutely real but so astonishing. Even now, whenever people ask about it, it sounds like I'm talking about a movie plot rather than an actual thing that happened.”
The NASA/Johns Hopkins University Applied Physics Laboratory Double Asteroid Redirection Test team which includes Rahil Makadia, his adviser Siegfried Eggl, and Bhaskar Mondal who is another one of Eggl’s Ph.D. students, is receiving the 2023 AIAA Award for Aerospace Excellence. The award states it is “In recognition of humanity’s first time purposely changing the motion of a celestial object by a team of protectors of our home planet.”
The study, “Ejecta from the DART-produced active asteroid Dimorphos,” by Jian-Yang Li, et al., is published in the journal Nature. DOI: 10.1038/s41586-023-05811-4
Johns Hopkins Applied Physics Lab built and operated the DART spacecraft and manages the DART mission for NASA’s Planetary Defense Coordination Office as a project of the agency’s Planetary Missions Program Office. LICIACube is a project of the Italian Space Agency, carried out by Argotec. Neither Dimorphos nor Didymos pose any hazard to Earth before or after DART’s controlled collision with Dimorphos. For more information about the DART mission, visit https://www.nasa.gov/dart or https://dart.jhuapl.edu.
JOURNAL
Nature
ARTICLE TITLE
Ejecta from the DART-produced active asteroid Dimorphos
ARTICLE PUBLICATION DATE
1-Mar-2023
Protostar in spiral arms
IMAGE: THE NICOLAUS COPERNICUS UNIVERSITY (TORUN, POLAND) SCIENTISTS: DR HABIL. ANNA BARTKIEWICZ, NCU PROF. AND MGR MICHAL DURJASZ view more
CREDIT: ANDRZEJ ROMANSKI/NCU
An international team of astronomers, which includes three researchers affiliated with the Nicolaus Copernicus University (Torun, Poland), has succeeded in mapping the protostellar disk with the highest precision known today. The discovery provides evidence predicted by the theory of episodic accretion.
The work was recognized by the journal Nature Astronomy, where an article has just been published "A Keplerian disk with a four-arm spiral birthing an episodically accreting high-mass protostar". Among the authors - an international group of astronomers specializing in observations of maser emissions - were three researchers affiliated with the Institute of Astronomy at the NCU Faculty of Physics, Astronomy and Informatics: dr. habil. Anna Bartkiewicz, NCU Prof., mgr Michal Durjasz, and dr. Mateusz Olech, who defended his doctorate at the Faculty and is now part of the team of the Space Radio Diagnostics Centre at the University of Warmia and Mazury in Olsztyn).
Joint effort
In his scientific work, dr habil. Anna Bartkiewicz, NCU Prof. is concerned with the study of star-forming objects showing the ring structure of the methanol maser. With the help of the European VLBI Network, she precisely determines the natural motions of the maser clouds at the level of a few kilometres per second. She is currently leading the Opus grant of the National Science Centre "Space masers as a tool for identifying accretion explosions of massive protostars". Michal Durjasz, a PhD student at the Nicolaus Copernicus University Doctoral School of Exact and Natural Sciences, has also made a major contribution to the research, working on areas of massive stars with abrupt changes in methanol maser emission. Both researchers belong to the IDUB Centre of Excellence "Astronomy and Astrophysics" Mateusz Olech, on the other hand, is interested in star-forming regions and periodic changes of methanol masers around massive protostars.
The article, and especially the research that preceded it, is the result of a successful collaboration between experts from around the world.
Observational data acquired from 24 radio telescopes from around the world contributed to our discovery, which was then carefully correlated by teams at three centres on three different continents, explains dr Ross Burns of the National Astronomical Observatory of Japan, first author of the paper. - Around 150 people were involved, and we would like to express our gratitude to them for their efforts, hoping for further collaboration in the future.
Right: Map of the 6.7 GHz methanol maser emission in G358-MM1, imaged using heatwave mapping. The cross in the center represents the location of the high-mass protostar determined in millimetre wavelength interferometric imaging. Spiral structures can be seen, wrapping around the protostar in a clockwise direction. Colours show the velocity of gas. Regions in blue are moving toward us while red regions show gas that is moving away. Overall, the colours indicate that the system is rotating, in the form of a Keplerian disk, around G358-MM1 Credit: Charles Willmott and Ross Burns
CREDIT
Credit: Charles Willmott and Ross Burns
Mysteries of the stars
The researchers focused on observations of massive stars, i.e. those with masses greater than eight masses of the Sun. They play a key role in the production of the elements necessary to build life in the Universe and also influence the formation and evolution of galaxies. The most massive stars die and become enigmatic black holes.
Despite their importance in the Universe, the process of massive star formation has been shrouded in mystery for many decades.
So far, there has been no single theory accepted by the entire scientific community to explain their formation, explains Professor Anna Bartkiewicz. - It has only recently been confirmed that massive stars are born in the centres of rotating disks composed of gas and dust. Protostellar disks, as they are called, have a radius of about one thousand astronomical units, i.e., the average distance between the Earth and the Sun multiplied by one thousand [the astronomical unit, or conventional measure of distance used in astronomy, is the average distance between the Earth and the Sun; i.e., 149597870.7 km, or - editor's note].
One theory of massive star formation that is becoming increasingly popular among researchers is episodic accretion.
Accretion, or the deposition of matter on a star. It involves clouds of dusty gas occasionally 'breaking off' and dropping from the disk onto a growing protostar, i.e., a young star located in the centre, explains mgr Michał Durjasz, - During such surges in the rate of matter accretion, the star accumulates more than half of the mass it gains during the formation stage. These accretion rate surges, or episodic accretion, are very rare events: they occur every hundreds or thousands of years and last from a few months to a few years.
Until now, astronomers have only witnessed a few such phenomena. The most recent and most thoroughly studied was the rapid accretion of the massive protostar G358-MM1 (the name is related to the object's coordinates in the sky) in 2019.
- The episodic accretion theory suggests that protostellar disks are massive and inhomogeneous. Due to the influence of their own gravity, spiral arms may appear in them, adds dr Mateusz Olech. - The very observation of protostellar disks in the areas of birth of massive stars is a challenge for astronomers - they are formed in dense molecular clouds that are impenetrable to conventional optical astronomy. Observing potential spiral arms is even more challenging.
Disk map
In the latest publication in Nature Astronomy, an international team of astronomers specialising in observations of maser emission - which is the naturally-occurring cosmic counterpart of a laser at microwave radio wavelengths - has been able to obtain maps of the protostellar disk with the highest precision known today. Using a network of radio telescopes, so-called very long baseline interferometry (VLBI), the scientists discovered spiral arms in the rotating disk of a high-mass protostar - G358-MM1. This is the same protostar that underwent rapid accretion in 2019.
The team used a new technique called 'heat-wave mapping', which produces a set of maps of the brightened masers of methanol molecules at different stages of an event. A total of 24 radio telescopes from Oceania, Asia, Europe and America were used. This allowed us to image the G358-MM1 spiral disk with a resolution of one angular millisecond, i.e., 1/3600000th of a degree, explains Prof Bartkiewicz. - G358-MM1 has four spiral arms that wrap around the protostar. These help to carry material from the disk to the centre of the system, where it can reach the protostar. If more spiral systems and this type of brightness are discovered, astronomers will be able to understand better the processes that accompany the birth of high-mass stars, which are the true cradle of life in the Universe.
The discovery provides observational evidence for several aspects predicted by episodic accretion theory: a rotating disk, rapid brightening and a spiral structure that helps 'feed' a growing high-mass protostar. The team will continue to search for such bursts of maser emission, using a global collaboration of traditional radio telescopes called the Maser Monitoring Organisation (M2O https://www.masermonitoring.com/). So far, only three rapid brightening high-mass protostars have been observed, but the researchers hope to find many more.
METHOD OF RESEARCH
Observational study
SUBJECT OF RESEARCH
Not applicable
ARTICLE TITLE
A Keplerian disk with a four-arm spiral birthing an episodically accreting high-mass protostar
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