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Avalanches, not internal pressure, cause comet nuclei outbursts

17 Oct 2016, 19:45 UTC
Avalanches, not internal pressure, cause comet nuclei outbursts

Avalanches, not internal pressure, cause comet nuclei outbursts
Press release issued by the Planetary Science Institute and the joint 48th annual meeting of the Division for Planetary Sciences (DPS) of the American Astronomical Society (AAS) and 11th annual European Planetary Science Congress (EPSC).
Outbursts of comet nuclei are likely caused by surface avalanches rather than geyser-like eruptions from within, research by the Planetary Science Institute’s Jordan Steckloff shows.
Rapid asymmetric brightening events of comets have been observed for decades and have long been thought to be the result of some sort of eruption of materials from deep within the interior of a comet, said Steckloff, a PSI Associate Research Scientist.
Steckloff’s abstract “Are Comet Outbursts the Result of Avalanches?” was presented today at a press conference at the joint 48th meeting of the American Astronomical Society (AAS) Division for Planetary Sciences (DPS) and 11th European Planetary Science Congress (EPSC) in Pasadena, California.
High-resolution images from Rosetta observations of 67P/Churyumov-Gerasimenko show outbursts that resemble plumes of material from geysers on Earth.
“However, there is a major problem with this model. There is no internal heat source on comets to power geyser-like eruptions,” Steckloff said. “Instead, these outburst plumes are the natural result of avalanches.”
The surfaces of comets have regions at the base of slopes and cliffs that are rich in icy materials, and are actively sublimating, with ice turning directly into gas. As this gas leaves the surface of the comet, it produced a weak breeze, Steckloff said. When granular materials on comets slide downslope or over a cliff, they enter this sublimation breeze and are blown into a tightly collimated plume of material that leaves the surface of the nucleus.
This model is consistent with data collected by the Rosetta spacecraft, and provides a physical mechanism that allows these outbursts to be studied to determine where on the surface they came from and how much material avalanched downslope.
“Ultimately, understanding this novel mechanism of outbursting may allow the surface processes of distant comets to be studied from Earth through ground-based observations of their outbursts,” Steckloff said.
Images:
Comparison of numerical model with observations. Left: A two-­layer model produces a transient, highly collimated avalanche plume. Credit: Steckloff/PSI. Right: observations of 67P/Churyumov-Gerasimenko. Credit: ESA/Rosetta/MPS for OSIRIS Team

Annotated comparison of numerical model with observations. Left: A two-­layer model produces a transient, highly collimated avalanche plume, showing influence of dust and ice. Credit: Steckloff/PSI. Right: observations of 67P/Churyumov-Gerasimenko. Credit: ESA/Rosetta/MPS for OSIRIS Team

Media Contacts:
Alan Fischer
PSI Public Information Officer
+1 520-382-0411, +1 520-622-6300
fischer@psi.edu
Anita Heward
European Planetary Science Congress (EPSC) Press Officer
+44 (0)77 5603 4243
anita.heward@europlanet-eu.org
Science Contact:
Jordan Steckloff
PSI Associate Research Scientist
+1 248-227-9413
jordan@psi.edu
Further information:
The Planetary Science Institute is a private, nonprofit 501(c)(3) corporation dedicated to solar system exploration. It is headquartered in Tucson, Arizona, where it was founded in 1972. PSI scientists are involved in numerous NASA and international missions, the study of Mars and other planets, the Moon, asteroids, comets, interplanetary dust, impact physics, the origin of the solar system, extra-solar planet formation, dynamics, the rise of life, and other areas of research. They conduct fieldwork on all continents around the world. They also are actively involved in science education and public outreach through school programs, children’s books, popular science books and art. PSI scientists are based in 25 states and the District of Columbia, and work from various locations around the world.
The joint 48th meeting of the Division for Planetary Sciences (DPS) and 11th European Planetary Science Congress (EPSC) in Pasadena, California, is second time DPS and EPSC have been joined into one meeting. The goal of the joint meeting is to strengthen international scientific collaboration in all areas of planetary science. This is the first time that EPSC, which provides the dissemination platform for the Europlanet 2020 Research Infrastructure, is held outside Europe. Follow: #dpsepsc, @DPSMeeting, @europlanetmedia, and @AAS_Press on Twitter.

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