NanoRacks-NanoRocks: Collisional Evolution of Particles and Aggregates in Microgravity (NanoRacks-NanoRocks) - 11.22.16
The Earth, asteroids and other rocky bodies in the solar system all formed from a cloud of dust and gas surrounding the Sun, but scientists are unsure how small chunks coalesced into larger bodies like the planets. NanoRacks-NanoRocks: Collisional Evolution of Particles and Aggregates in Microgravity (NanoRacks-NanoRocks) explores low-energy collisions in microgravity to shed light on the formation of planetisimals, the building blocks of planets. The experiment studies a large sample of collisions at very low velocities during a long duration on the International Space Station, providing important insight into the nature of the early evolution of the solar system. Science Results for Everyone
Putting a ring on it. Investigators recorded slow, low-energy collisions in space of various tiny particles similar to those found in protoplanetary disks and planetary ring systems such as Saturn’s. The way particle rings evolve depends on the behaviors of these small collisions, which can only truly be observed in microgravity. Data show ricocheting particle collisions, resulting in random loss of internal energy, and very low-energy collisions leading to systematic formation of structures and clusters. Fundamental data on collisions between particles in these environments could help solve the mystery of the age and origin of Saturn’s rings and how early planets formed. Experiment Details
OpNom: NanoRacks Module-24
Joshua Colwell, Ph.D., UCF Dept. of Physics, Orlando, FL, United States
Adrienne Dove, Ph.D. , UCF Dept. of Physics, Orlando, FL, United States
NanoRacks LLC, Webster, TX, United States
Sponsoring Space Agency
National Aeronautics and Space Administration (NASA)
National Laboratory (NL)
ISS Expedition Duration
September 2014 - March 2016
- NanoRacks-NanoRocks: Collisional Evolution of Particles and Aggregates in Microgravity (NanoRacks-NanoRocks) is an experimental study of the physics of collisions between aggregate types and between monomers and aggregates at the sizes and velocities relevant for planetary formation and planetary ring collisional evolution. This research provides further qualitative and quantitative data in understanding planetary formation evolution on a macro scale.
- In order to treat collisional evolution in a probabilistic approach, the experimental database for such collisions must be significantly expanded so that there are reliable estimates of the probabilities of certain rare outcomes (such as sticking at large impact speeds). The environment of the ISS with this proposed experiment architecture provides a significant expansion of the number of collisional outcomes observed at low impact speeds.
- The quantitative increase in data of this type is a geometric expansion and provides further illumination on the nature of planetary formation.
NanoRacks-NanoRocks: Collisional Evolution of Particles and Aggregates in Microgravity (NanoRacks-NanoRocks) is an experimental exploration of low-energy collisions in protoplanetary disks to better understand the conditions and processes that lead to the formation of planetesimals, the building blocks of planets. The same sorts of collisions also take place in planetary ring systems, such as Saturn’s rings. The experiment takes advantage of the long-duration and high quality of microgravity on the International Space Station (ISS) to obtain a large sample of collisional outcomes at very low velocities (< 10 cm/s). The experiment consists of chambers containing different populations of particles and aggregates. The chambers are agitated by varying amounts inducing collisions between the particles. Video of the collisions indicate the collision parameters (mass, density and composition of particles, and collision velocities) that lead to sticking, rebound, and fragmentation of aggregates. In the case of rebound the coefficient of restitution (a measure of the dissipation of energy) is measured. These results have a direct scientific application to the question of the collisional evolution of Saturn’s rings, where particles undergo frequent collisions at speeds as low as 1 mm/s, as well as the conditions necessary for the earliest stages of planet formation.
The age of Saturn’s rings, and hence their origin, remains an open issue. The dissipation of kinetic energy in interparticle collisions is a key parameter in understanding the long-term evolution of the system. The data from the proposed experiments will illuminate the velocity-dependent coefficient of restitution for collisions in planetary rings. This parameter has a significant effect on the pace of angular momentum transfer across the rings in numerical simulations of rings, but is currently poorly known.
The formation of km-sized or larger planetesimals remains an open problem in the standard theory of planet formation. Once objects are larger than approximately 10 km, gravity enables accretional growth of these planetesimals into larger objects and ultimately planets. Condensation and electrostatic surface forces can explain the growth of mm-sized objects in the nebula. Objects that are on the order of 1 meter in size, however, are subject to rapid orbital evolution; any theory of planet formation must grow objects from mm-scale to km-scale quickly enough to avoid this orbital decay of the intermediate-sized objects. Gravitational instability, which forms planetesimals directly through local collapse of patches in the disk, and pairwise accretional growth of particles each has difficulties producing planetesimals in the protoplanetary disk environment as it is currently understood. It is possible that some combination of these processes took place, depending on the local conditions in the protoplanetary nebula. A major source of uncertainty in the accretional growth model is the behavior of small objects and aggregates of dust colliding at the low speeds expected (~0.1 – 10 m/s). The proposed experiments add much-needed data to these models to help determine the conditions under which accretional growth produces planetesimals.
Additionally, the data collected on inter-particle collisions and the behavior of dense particle systems in a low gravity environment informs the development of hardware and procedures for operation on the surfaces of small airless bodies, such as asteroids, where there is very low gravity and surface regolith disturbances may occur.
Asteroids, moons, planets and the rings of Saturn all form from countless collisions of small particles. As these bodies grow in size, their gravity attracts more rocks and dust, further increasing their mass. In addition to explaining the physical origins of the solar system, understanding the behavior of dense particle systems in microgravity is important for future missions on small, rocky bodies without significant atmospheres, like asteroids. Results from the NanoRacks-NanoRocks investigation provide new data on particle dispersal and disturbance.
How the Earth formed from a cloud of dust and gas is a fundamental question in science. NanoRacks-NanoRocks studies similar phenomenon on a much smaller scale, by examining several small-particle collisions over a long period of time. Results from the investigation shed new light on how the Earth and other rocky planets coalesced billions of years ago.
Operational Requirements and Protocols
Decadal Survey Recommendations
Information Pending^ back to top
Planetary scientists believe that suns and planets formed from the gravitational collapse of an immense cloud of gas and dust through collisions and clumping of the tiny solids into planetesimals (small celestial bodies made of dust, rock, and other materials) and eventual runaway growth to form the sun, and rocky and gaseous planets. An early critical stage of this process is the growth of solid bodies from mm-sized round molten or partially melted droplets, or “chondrules,” and aggregates to kilometer sized planetesimals where gravity becomes an important force for further growth. The objective of the NanoRocks experiment is to study the slow-speed/low-energy collisions of mm-sized particles of different shapes and materials that occurred in protoplanetary disks and planetary ring systems. Particles in Saturn’s main rings collide at speeds on the order of 1 cm/s, and clumping of particles in Saturn’s rings has been observed by the Cassini spacecraft. During its year-and-a-half in orbit, NanoRocks performed over 150 collision experiments with eight different particle samples per experiment, giving a large sample of individual collisions to study. Video of the collisional dissipation of energy shows that the presence of “regolith” or small grains on the surfaces of the particles makes collisions much less elastic. Particles showed clumping behavior at a few mm/s, near the highest speeds studied in the experiment. In addition, very low energy collisions in the NanoRocks many particle systems lead to the systematic formation of structures and clusters after a settling period. The evolution of the ring depends on the amount of energy dissipated in these low energy collisions, and experimental observations of this type of collisions can only be made under the long-term microgravity conditions of the International Space Station (ISS). With the age and origin of Saturn’s rings remaining a major unknown in our understanding of the solar system, there is a critical need for fundamental data on the collisional interactions between particles in an environment like that of the rings of Saturn.^ back to top
Ground Based Results Publications
Center for Microgravity Research and Education
NanoRacks-NanoRocks Raw Video Sample
NanoRacks-NanoRocks Sample Video
The inner workings of the NanoRacks-NanoRocks investigation. From top to bottom: control circuit board (from Celestial Circuits), LEDs, mirror, camera, experiment tray, electromagnet, springs, and stability pins. Image courtesy of University of Central Florida.
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All hands in! The NanoRacks-NanoRocks developers assembling the module. Image courtesy of University of Central Florida.
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Teamwork! Holding elements of the NanoRacks-NanoRocks investigation in place to test the field of view of the camera (the output in real time on an old tv). Image courtesy of University of Central Florida.
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Camera image of the experiment tray from NanoRacks-NanoRocks showing the picture size and resolution of the experiment. Image courtesy of University of Central Florida.
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