Disks and the Origins of Planetary Systems
Sanford Davis, Lead Co-Investigator
Co-Investigators: Jack Lissauer, Greg Laughlin, David Hollenbach, Uma Gorti,
Denis Richard, Kevin Zahnle
TEAM MEMBERS PRESENT RESEARCH AT NAI EXECUTIVE COUNCIL MEETING
Team members were invited to present their research at the NASA Astrobiology Institute (NAI) Executive Council meeting held on January 17-18, 2013, at Ames Research Center.
Principal Investigator, Dave Des Marais, talked about the overall theme of the Ames Team research, "Early Habitable Environments and the Evolution of Complexity," and explained the four approaches to understanding the origins of life.
Sandy Davis talked about "Solar System Evolution," and the research within his group. Jack Lissauer continued by giving an overview of NASA's Kepler Mission. He also discussed the simulations of delivery of water to terrestrial planets.
SCIENCE CHANNEL'S "THROUGH THE WORMHOLE" TAKES A RIDE ON SANTA CRUZ BOARDWALK'S BUMPER CARS FOR FUTURE EPISODE
A Science Channel TV crew along with Ames Team member and UCSC Astronomy Professor Greg Laughlin used the Speed Bump ride as a visual analogy to illustrate the concept of gravity assist in outer space.
The crew approached Laughlin and the Santa Cruz Boardwalk to shoot an episode of "Through the Wormhole." Hosted by Morgan Freeman, the series explores scientific questions. The episode, titled "Can we outlive the sun?" is expected to air in the show's fourth season in 2013.
"In billions of years, the sun will get so bright and luminous that life on Earth will be in big trouble," Laughlin said. To preserve life forms, humans would have to find a way for Earth to move away from the sun by expanding the orbit, Laughlin said. That's where asteroids, gravity and the Boardwalk's bumper cars come in. "You could cause our planet to slowly expand its orbit by having asteroids flying by the Earth hundreds of thousands of times," Laughlin said. "This is what I'm showing when I'm driving around our little Earth with my magnet."
Using a metal reproduction of the Earth, a yellow beach ball for the sun and a red magnet, Laughlin and camera operators rode bumper cars, circling their miniature solar system to mimic asteroids.
"That is the heart of all this: working with scientists like Greg on a visual that's both accurate and attractive to a mass audience," director Savas Georgalis said.
In real space, this merry-go-round action produces a double effect, Laughlin explained. Because of gravity, the mass of the asteroid entering in our orbit produces a force that slightly pulls the Earth forward, causing our planet to expand the trajectory of its orbit. Simultaneously, gravity forces the asteroid to deviate from its trajectory while gaining speed. This latter phenomenon, used by scientists as a "gravity assist" to speed spacecrafts, is ultimately the most interesting part, Laughlin said.
"Whether we can outlive the sun is the last thing we need to worry about. We don't have the technology to control asteroids and this won't be an issue before a billion years," Laughlin said. "It's a just a dramatic way of showing how gravity assist works.
NASA sent its spacecraft New Horizons in Jupiter's orbit and it gave it a huge boost on its trip to Pluto, Laughlin said. "That will enable us to discover how Pluto looks like years ahead of schedule."
The Boardwalk provided the shooting location to tackle the complex matter, Georgalis said. The director said he is comfortable working with Laughlin, who often pushes TV crews to shoot in Santa Cruz. In 2009, the scientist brought the crew to the Boardwalk for a History Channel piece on Jupiter's inside chemical activity.
"Santa Cruz is a great town for filming opportunities: we have the ocean, the Boardwalk, the redwood forests," Laughlin said. "If people see the show and want to come visit Santa Cruz as result, that means I've done my job."
CONSTRAINTS ON PROTOPLANETARY DISK LIFETIMES AND IMPLICATIONS FOR PLANET FORMATION
Giant planets form in circumstellar disks within the first tens of Myr after the protostar is formed. A key constraint governing the formation of gas and ice-giants versus terrestrial rocky planets is the timescale for gas clearing in a disk. An earlier sensitive search for gas emission lines in the infrared with Spitzer of 10--100 Myr old sun-like stars with small dust excess concluded that most of the gas has already dispersed, with too little left to form Jupiter--mass planets. Here we investigate whether young 10--100 Myr stars with debris disk systems still have enough remnant gas to form planets like Uranus and Neptune.
We are conducting a survey of evolved, gas disks for [OI]63um line emission using the PACS instrument on the Herschel Space Observatory. [OI] is a sensitive probe for measuring small amounts of remnant gas, as little as 1 Earth mass of gas from a disk at 100pc, and can thus trace the gas disk as it dissipates due to photoevaporation by the central star. In addition to setting constraints on the time available for giant planet formation, we seek to understand the nature of gas disk dispersal and the spatial regions where the gas disk survives the longest. Here we present Herschel [OI] spectroscopy to derive gas masses for three older (10--100 Myr) disk systems that harbor suspected planets and/or show signs of an evolved dust disk structure: HR 8799, HD 377, and RXJ1852.3-3700 (See Figure).
From our thermochemical gas disk models and the non-detections in HR8799 and HD377, we conclude that both these disks have too little mass to form Jupiter or Neptune analogs. One of our sources, RXJ1852.3-3700, was detected in [OI]. Based on an earlier Spitzer dectection of [NeII]12.8um, no H_2 emission and from a previous non-detection of CO sub-millimeter emission, we constructed models of the gas disk around this source. We find two possibilities consistent with the gas emission. In the first case, the disk is very tenuous and extended, resulting in photodissociation of molecules. There is not enough gas (16M_E from 16-500AU) to further form planets, but there is enough gas to affect planet orbits. In the second case, the disk is massive (150M_E from 16-70AU) and truncated due to photoevaporation by FUV (6-13.6eV) photons from the star. This disk retains sufficient gas to form planets. Our models predict [CII]157um emission detectable by PACS for the tenuous disk, but not the truncated massive disk, and can thus break the degeneracy. [CII] emission is the target of a future Herschel study. (Geers, V., Gorti, U., Meyer, M., Mamajek, E., Benz, A. & Hollenbach, D. 2012, submitted to ApJ) .
NASA / OHLONE COLLEGE SCIENCE NIGHT SEMINAR PROGRAM
---Astrobiology: Looking for Life Elsewhere in the Universe---
The smallest planet detected so far is about twice the size of Earth, but the new Kepler space telescope, run by NASA Ames Research Center, should be able to detect Earth-like planets.
Colin Goldblatt, NASA researcher of geochemistry and co-evolution of life and Earth's climate, discussed the following questions:
Is there life on these planets?
What would it be like and how would we go about finding it?
How does studying the Earth help us answer these questions?
Goldblatt researches the co-evolution of life and Earth's climate and geochemistry and what this tells us about whether life exists elsewhere on the universe.
Does life control its environment for its own benefit, or has life on Earth hung on for 4 billion years by luck?
How has Earth's atmosphere changed over Earth history?
What does this mean for the future of life on Earth?
His research focuses on the evolution of oxygen and nitrogen in Earth's atmosphere and long-term climate change. Along the way, Goldblatt has been involved in Antarctic oceanography, evaluating a proposed 'geoengineering' solution to climate change, and evaluating the accuracy of a model for the strength of the greenhouse effect used in a climate model. Goldblatt completed his PhD in the Earth System Modeling group in the School of Environmental Sciences at the University of East Anglia and is now a Postdoctoral Fellow at NASA Ames Research Center, where he is a member of the NASA Astrobiology Institute Ames Team.
AMES TEAM RESEARCH
NEWS AND HIGHLIGHTS:
Cosmic Distribution of Chemical Complexity
Disks and the Origins of Planetary Systems
Mineralogical Traces of Early Habitable Environments
Origins of Functional Proteins and the Early Evolution of Metabolism