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image of planetary pebbles around the planets

Image Courtesy of NASA/JPL-Caltech

SwRI scientists think "planetary pebbles" were building blocks for the largest planets

Researchers at Southwest Research Institute (SwRI) and Queen's University in Canada have unraveled the mystery of how Jupiter and Saturn likely formed. This discovery, which changes our view of how all planets might have formed, was published in the Aug. 20 issue of Nature.

The largest planets in the solar system likely formed first. Jupiter and Saturn, which are mostly hydrogen and helium, presumably accumulated their gasses before the solar nebula dispersed. Observations of young star systems show that the gas disks that form planets usually have lifetimes of only 1 million to 10 million years, which means the gas giant planets in our solar system probably formed within this time frame. In contrast, the Earth probably took at least 30 million years to form, and may have taken as long as 100 million years. So how could Jupiter and Saturn have formed so quickly?

The most widely accepted theory for gas giant formation is the so-called core accretion model. In this model, a planet-sized core of ice and rock forms first. Then, an inflow of interstellar gas and dust attaches itself to the growing planet. However, this model has an Achilles heel; specifically, the very first step in the process. To accumulate a massive atmosphere requires a solid core roughly 10 times the mass of Earth. Yet these large objects, which are akin to Uranus and Neptune, had to have formed in only a few million years.

In the standard model of planet formation, rocky cores grow as similarly sized objects accumulate and assimilate through a process called accretion. Rocks incorporate other rocks, creating mountains; then mountains merge with other mountains, leading to city-sized objects, and so on. However, this model is unable to produce planetary cores large enough, in a short enough period of time, to explain Saturn and Jupiter.

"The timescale problem has been sticking in our throats for some time," said Dr. Hal Levison, an Institute scientist in the SwRI Planetary Science Directorate and lead author of the paper. Titled "Growing the Gas Giant Planets by the Gradual Accumulation of Pebbles," the paper is co-authored by SwRI Research Scientist Dr. Katherine Kretke and Dr. Martin Duncan, a professor at Queen's University in Kingston, Ontario.

"It wasn't clear how objects like Jupiter and Saturn could exist at all," continued Levison. New calculations by the team show that the cores of Jupiter and Saturn could form well within the 10-million-year time frame if they grew by gradually accumulating a population of planetary pebbles – icy objects about a foot in diameter. Recent research has shown that gas can play a vital role in increasing the efficiency of accretion. So, pebbles entering orbit can spiral onto the protoplanet and assimilate, assisted by a gaseous headwind.

In their article, Levison, Kretke, and Duncan show that pebble accretion can produce the observed structure of the solar system as long as the pebbles formed slowly enough that the growing planets have time to gravitationally interact with one another.

"If the pebbles form too quickly, pebble accretion would lead to the formation of hundreds of icy Earths," said Kretke. "The growing cores need some time to fling their competitors away from the pebbles, effectively starving them. This is why only a couple of gas giants formed."

"As far as I know, this is the first model to reproduce the structure of the outer solar system, with two gas giants, two ice giants (Uranus and Neptune), and a pristine Kuiper Belt," said Levison.

"After many years of performing computer simulations of the standard model without success, it is a relief to find a new model that is so successful," added Duncan.

Levison is the principal investigator of the research, funded through a National Science Foundation Astronomy and Astrophysics Research Grant.

Contact Levison at (303)546-9670 or

image of Daniel Durda, Ph.D.

SwRI's Durda awarded Sagan Medal

The Division for Planetary Sciences (DPS) of the American Astronomical Society has awarded its 2015 Carl Sagan Medal to Dr. Daniel D. Durda, a principal scientist at Southwest Research Institute (SwRI).

The Sagan Medal recognizes outstanding scientific communication to the general public by an active planetary scientist. Durda was selected in honor of his numerous promotional activities, such as providing television commentaries, writing for popular science journals, and other projects involving education and public outreach. He is a well-known space artist and has internationally exhibited his art, often providing his work to illustrate books and news items in science magazines and web articles.

The DPS award commemorates the late astronomer Carl Sagan, who was known for exploring the grandeur of the universe in lectures, books, and on television as host of the science series "Cosmos."

"Considering that I am in this field because of Carl Sagan and "Cosmos," this means more to me than I can find the words for," said Durda. "The planetary science community operates on the frontier of science and exploration. Being able to share my knowledge and help to popularize the amazing research results of my colleagues in the field is a great privilege."

At SwRI, Durda studies the collisional and dynamical evolution of asteroids, the effects of cratering impacts on planets and asteroids, and the geologic properties and processes on their surfaces. Asteroid 6141 Durda is named in his honor. He is an active pilot and has served as flight astronomer for airborne astronomical imaging systems flown aboard NASA and military high-altitude aircraft.

Durda enjoys sharing his personal interests and expertise with the public. He holds multiple scuba and cave diving certifications, including full cave and cave recovery specialist, and has served as the Colorado and Arizona regional coordinator for the International Underwater Cave Rescue and Recovery team. He is an avid hiker, birder, and amateur naturalist.

DPS presented the Sagan Medal and a cash award at its 47th Annual Meeting in National Harbor, Md., in November.

Contact Durda at (303) 546-9670 or

image of technician with new pollution abatement system

New pollution abatement system significantly reduces emissions at SwRI

Southwest Research Institute (SwRI) has added a custom-designed, state-of-the-art pollution abatement system to its Steiner tunnel fire test facility, a 25-foot vented tunnel for testing construction materials, reducing the amount of hazardous waste emitted by nearly 90 percent. The $900,000 system removes acid gases, volatile organics, metal vapor, and particulate matter that may occur as an aftereffect from fire research.

This system is the first of several SwRI Fire Technology Department renovations and upgrades, which includes the development and installation of a $2.5 million custom pollution abatement system to handle emissions for furnace fire, jet fire, and car burn facilities. SwRI recently received a $500,000 grant from the Texas Commission on Environmental Quality to help defray the cost of installing this technology. The new system was fully operational in October 2015.

"ASTM E84 can be an extremely challenging test, and most Steiner tunnels do not have pollution abatement systems," said Dr. Matt Blais, director of the SwRI Fire Technology Department. "Our new system for the Steiner tunnel/ASTM E84 test increases reliability by 50 percent and reduces hazardous waste by 90 percent while removing odors, acid gas, and particulate with greater efficiency. The end result is a more reliable test that produces less waste and is more environmentally friendly."

Using ASTM E84, Standard Test Method for Surface Burning Characteristics of Building Materials, SwRI subjects construction materials, such as wall coverings, foam insulation, and more, to a controlled burn to measure smoke and flame development indexes. Annually, SwRI conducts more than 500 of these evaluations in its Steiner tunnel facility along with custom fire research.

The new system provides controlled air flow to allow faster heating and cooling of the tunnel, improving overall operational efficiency to help meet client demands.

Last year, SwRI installed a $2 million baghouse air pollution control device to reduce particulate emissions from its diesel engine labs, reducing the Institute’s overall particulate emissions by more than 50 percent.

Combined, SwRI has invested approximately $5 million in pollution abatement equipment in the last few years.

Contact Blais at (210) 522-3524 or

SwRI receives $3.2 million contract from U.S. Energy Department for solar power research

Southwest Research Institute (SwRI) has been awarded a $3.2 million contract by the U.S. Department of Energy SunShot Initiative. The contract is part of an $8.8 million effort to design, manufacture, and test an ultra-high-efficiency supercritical carbon dioxide (sCO2) compressor-expander for power generation at concentrating solar power (CSP) plants. CSP plants use mirrors to concentrate the energy from the sun to drive traditional steam turbines or engines that create electricity.

SwRI turbomachinery engineers will collaborate with Samsung Techwin America (STA) to develop an integrally geared compressor-expander, or "compander," for use in an sCO2 plant. The compander is a turbine through which a high-pressure gas is expanded to drive a multi-stage gear compressor. This integrally geared compander (IGC) has the potential to improve efficiency, modularity, and process control. The technology provides a critical step toward making sCO2 CSP power plants commercially viable.

"This project is one of 11 sCO2 power cycle projects SwRI is conducting for the Energy Department. The goal of these projects is to develop the critical technology building blocks needed to make sCO2 power cycles technically feasible and commercially viable," said Dr. Klaus Brun, a program director in SwRI's Mechanical Engineering Division.

IGCs increase overall machinery efficiency, and are widely used in both air separation and process gas industries. Because all of the turbomachinery elements are integrated into a single machine, the design optimally lends itself to a modular power block, making it suitable for waste heat recovery, fossil fuel power plants, and especially CSP applications.

"STA is pleased to collaborate with SwRI on the design of an IG compressor-expander and believes that this technology will provide viable solutions to many of the practical challenges associated with sCO2 power cycles," said Dr. Karl Wygant, vice president for the STA Turbomachinery Design and Development Center in Houston.

The compander design project also includes development of an sCO2 compressor impeller that incorporates novel flow path designs for maximizing compressor efficiency and mechanical reliability under a wide range of inlet conditions. These novel flow path designs are enabled through direct metal laser sintering, an additive manufacturing process that increases design flexibility and produces high-strength parts.

The project, which will be conducted in three phases, began in October 2015 and will continue through September 2018 pending awards for subsequent phases. SwRI project managers for the newly funded contract are Group Leader Dr. Tim Allison and Research Engineer Dr. Jason Wilkes, both of SwRI's Mechanical Engineering Division. For more information about SwRI's Machinery Program, visit

Contact Brun at (210) 522-5449 or

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Southwest Research Institute® (SwRI®), headquartered in San Antonio, Texas, is a multidisciplinary, independent, nonprofit, applied engineering and physical sciences research and development organization with 9 technical divisions.