Physical Sciences ︱ Dr Yu Jiang Calculating the complex behaviours of multi-body asteroids

Far outnumbering the n the earliest days of the solar system, systems have been discovered in the solar planets of the solar system, the sun was orbited by a uniform disk system. In 2004, the first triple asteroid asteroids are widely believed Iof gas and dust. Over time, some of this system was found; named 87 Sylvia, it by astronomers to be material collapsed under its own gravity to has two moonlets: Romulus and Remus. responsible for shaping our eventually form smooth, spherical bodies As of June 2019, 341 binary asteroid – which we now call planets. However, this systems and 15 triple systems have been Credit: NASA/JPL/ planetary neighbourhood Processed by Kevin into its current state. Dr Yu doesn’t tell the whole story. Vast amounts found.” In his research, Dr Jiang studies M. Gill CC BY SA 2.0. Jiang at Tsinghua University of interplanetary gas and dust never the diverse behaviours which unfold in China has dedicated his coalesced into planets; much of what within these complex systems, with the research to studying the most was left came to form smaller, irregularly aim of discovering more about how the NASA engineers pose with the Galileo orbiter Asteroid 243 Ida as seen by the Galileo probe on August 28, 1993. Inset: Highest-resolution image with its main antenna open. of Ida’s moon Dactyl, recorded while Galileo was about 3,900 km away from the moon. intriguing of these bodies: large shaped bodies, named asteroids. Each solar system has transformed since its asteroids which are themselves under 1,000 kilometres in diameter, earliest days. orbited by one or more smaller asteroids encompass a diverse range of significant role in forming the planets of named 41 Daphne, which was discovered of Daphne, Peneius, has a diameter rocks. Using both computer shapes, sizes, and compositions, and can STUDYING DYNAMICAL the solar system as we know them today, in 1856. At first, astronomers thought smaller than 2 kilometres. The separation simulations and complex also display intriguing orbital behaviours. ENVIRONMENTS Dr Jiang argues that it is important for that Daphne sat by itself, but further between mass centres of Daphne and mathematical calculations, Since asteroids are so much smaller than astronomers to study these complex observations carried out in 2008 revealed Peneius is about 443 kilometres.” his work has now provided Until recently, astronomers have only been planets, their gravitational fields are far gravitational behaviours. “Generally, new insights into how our able to observe systems of individual weaker, which means that unlike planets, asteroids have irregular shapes which may solar system originally formed asteroids, but now they are aware that most of them cannot collapse to form vary over millions of years, meaning the The study of asteroids may help us to and came to evolve over time. smaller rocks, named ‘moonlets’, can orbit uniform spheres. If a person were to dynamical behaviours in their gravitational around larger asteroids, named ‘primaries’. walk across the surface of an asteroid, fields are quite complicated,” he says. understand the formation and evolution “Discovered by Galileo spacecraft in therefore, the gravitational force they “The study of asteroids may help us to of the solar system. 1993, Ida and its orbiting moonlet, Dactyl, would experience would vary extremely understand the formation and evolution is the first binary asteroid system ever widely – wholly unlike the uniform force of the solar system. My interest focuses on that a far smaller rock was actually in In planet-moon systems, the interaction of found in the Solar system,” explains Dr which we are used to on Earth. Because the dynamical environment of binary and orbit around it, named Peneius. Since the gravitational fields of the two bodies Jiang. “Since then, several binary asteroid asteroids have likely played a hugely triple systems.” this discovery, Dr Jiang has analysed this creates certain ‘equilibrium’ points. These intriguing system in detail. “Recently, I are so-called because, were a small As well as studying the movements have studied the dynamical environment body placed on this point, it would not of asteroids and moonlets, Dr Jiang in the vicinity of the binary asteroid system fall towards either body. Astronomers also analyses the behaviours which 41 Daphne,” he describes. “Daphne is a currently believe that Daphne is irregular arise as they collide with other bodies, big asteroid in the main belt; its major axis in shape, giving it a complex gravitational causing them to partially disintegrate. is larger than 200 kilometres. The moonlet field, which could host equilibrium points “In addition, grains may be generated from the impact of the cosmic debris to the primary or moonlet of a binary or triple asteroid system,” he continues. “These grains may move to planets or other asteroids. If the grains enter Earth’s atmosphere, people will see a beautiful meteor shower.” Currently, Dr Jiang is paying particular attention to these behaviours for two complex multi-body asteroid systems.

SHAPE VARIATION IN A BINARY SYSTEM In the wide gap between Mars and Jupiter sits the asteroid belt: a vast ring of interplanetary rocks which were never able to collapse to form their own planet. Elenarts/Shutterstock.com Among these asteroids is a system Projection of zero-velocity curves of 41 Daphne in xz and yz planes.

www.researchfeatures.com www.researchfeatures.com of its own. If this is the case, Daphne’s Dust grains around the triple asteroid field alone could be responsible for 216 Kleopatra. keeping Peneius in a stable orbit. “In my Behind the Research research, I considered the shape variety of Daphne, and investigated its dynamical environment as its form varied from its Dr Yu Jiang current shape to a sphere,” Dr Jiang continues. “I found that the stability of E: [email protected] T: +186 010 62795926 Daphne’s relative equilibrium points may W: https://www.researchgate.net/profile/Yu_Jiang22 change when its shape varies.” Using a combination of computer simulations and mathematical calculations, Dr Jiang was Research Objectives References able to identify how these equilibrium points would vary in position as Daphne’s Dr Jiang’s work explores the dynamical environment Jiang, Y. (2018). Dynamical environment in the vicinity of binary and triple asteroid systems. of asteroids with an application to 41 Daphne. Results I found that the stability of Daphne’s in Physics, 9, p.1511-1520. Detail Jiang, Y. (2019). Dynamical environment in the triple relative equilibrium points may change asteroid system 87 Sylvia. Astrophysics and Space Science, when its shape varies. N904, 364(4), p.60. Mengminwei Building, shape was varied. Ultimately, this allowed Sylvia is about 280 km, the two Depending on where this debris hits, Tsinghua University, him to map Peneius’ orbit around its host. moonlets, Remus and Romulus, have these grains could follow a variety Beijing, mean diameters of around 7 km and of different paths; impacting the 100084 DUST GRAIN GENERATION 18 km, respectively. The separation subsequent behaviour of the system P R China Personal Response IN A TRIPLE SYSTEM between the mass centre of Sylvia as a whole. “I investigated the motion Next, Dr Jiang looked at an even more and its two moonlets is about 707 of the grains generated in different parts Bio What fascinates you most about these binary and triple complex system, 87 Sylvia. Discovered km and 1357 km.” To investigate the of Sylvia,” Dr Jiang explains. “I have Dr Yu Jiang is an associate Professor of State Key Laboratory asteroid systems? in 1866, Sylvia was again first thought dynamics of this system, Dr Jiang now found that some of the grains may of Astronautic Dynamics, China. He is the author of more The generation and evolution of dust and debris to be on its own, but subsequent again used computer models to map impact on the surface of the primary, than 40 publications and funded by four national projects. in the binary and triple asteroid systems. observations in 2001 and 2004 revealed its gravitational environment, taking which may produce more grains; and His current research interests lie in dynamics around that two moonlets were actually in account of Sylvia’s irregular shape. some of the grains may escape the asteroids, dust dynamics, as well as motion of space debris. orbit around it. “I have also studied the In particular, he used his models to triple system and enter interplanetary dynamical environment of the triple simulate the behaviours of small grains space.” Such grains were likely to be in Funding asteroid system, 87 Sylvia,” describes of rock, which are thrown up as external orbit around the sun long before any National Natural Science Foundation of China Dr Jiang. “The mean diameter of debris collides with the system. planets, or even asteroids, had had (No. 11772356). the time to form. Therefore, studying them in more detail can tell us more about how the solar system as we know it today came into being.

NEW INSIGHTS INTO FORMATION AND EVOLUTION In the future, some astronomers are strongly hoping that a spacecraft will be sent to the asteroid belt to investigate the dynamics of a double or triple system, like Daphne or Sylvia, in unprecedented levels of detail. For such a mission to succeed, Dr Jiang’s calculations will prove critical to designing the trajectories of the spacecraft, to ensure it can safely arrive at such incredibly small, yet complex targets. The insights provided by these potential missions could one day prove invaluable to researchers in a wide variety of fields, potentially answering long-standing questions

Examples of irregular asteroid shape. Clockwise from top left: 87 Sylvia; 41 Daphne; 433 Eros; about how our solar system first formed, 216 Kleopatra. and how it evolved over time.

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