Exoplanets & Exomoons

A Virtual Planet Simulator for Modeling Distant Worlds Across Time

By Keith Cowing
Press Release
University of Washington
September 19, 2019
Filed under
A Virtual Planet Simulator for Modeling Distant Worlds Across Time
Reproduction of Figure 7 in Luger & Barnes (2015) using VPLanet. Shown here is the total amount of water lost (left) and the total amount of atmospheric oxygen that builds up (right) due to atmospheric escape on an Earth-mass planet orbiting different mass M dwarfs (vertical axes) and at different relative positions in the HZ (horizontal axes). The HZ is bounded by the recent Venus (RV) limit at the inner edge and the early Mars (EM) limit at the outer edge; the runaway greenhouse and maximum greenhouse limits are shown as dashed lines. The amount of water lost is somewhat lower than in Luger & Barnes (2015) due primarily to the lower escape efficiency assumed here. Approximate runtime: 10 minutes. examples/AbioticO2
University of Washington

University of Washington astrobiologist Rory Barnes has created software that simulates multiple aspects of planetary evolution across billions of years, with an eye toward finding and studying potentially habitable worlds.

Barnes, a UW assistant professor of astrobiology, astronomy and data science, released the first version of VPLanet, his virtual planet simulator, in August. He and his co-authors described it in a paper accepted for publication in the Publications of the Astronomical Society of the Pacific.

“It links different physical processes together in a coherent manner,” he said, “so that effects or phenomena that occur in some part of a planetary system are tracked throughout the entire system. And ultimately the hope is, of course, to determine if a planet is able to support life or not.”

VPLanet’s mission is three-fold, Barnes and co-authors write. The software can:

* simulate newly discovered exoplanets to assess their potential to possess surface liquid water, which is a key to life on Earth and indicates the world is a viable target in the search for life beyond Earth

* model diverse planetary and star systems regardless of potential habitability, to learn about their properties and history, and

* enable transparent and open science that contributes to the search for life in the universe

The first version includes modules for the internal and magnetic evolution of terrestrial planets, climate, atmospheric escape, tidal forces, orbital evolution, rotational effects, stellar evolution, planets orbiting binary stars and the gravitational perturbations from passing stars.

It’s designed for easy growth. Fellow researchers can write new physical modules “and almost plug and play them right in,” Barnes said. VPLanet can also be used to complement more sophisticated tools such as machine learning algorithms.

An important part of the process, he said, is validation, or checking physics models against actual previous observations or past results, to confirm that they are working properly as the system expands.

“Then we basically connect the modules in a central area in the code that can model all members of a planetary system for its entire history,” Barnes said.

And though the search for potentially habitable planets is of central importance, VPLanet can be used for more general inquiries about planetary systems.

“We observe planets today, but they are billions of years old,” he said. This is a tool that allows us to ask: ‘How do various properties of a planetary system evolve over time?'”

The project’s history dates back almost a decade to a Seattle meeting of astronomers called “Revisiting the Habitable Zone” convened by Victoria Meadows, principal investigator of the UW-based Virtual Planetary Laboratory, with Barnes. The habitable zone is the swath of space around a star that allows for orbiting rocky planets to be temperate enough to have liquid water at their surface, giving life a chance.

They recognized at the time, Barnes said, that knowing if a planet is within its star’s habitable zone simply isn’t enough information: “So from this meeting we identified a whole host of physical processes that can impact a planet’s ability to support and retain water.”

Barnes discussed VPLanet and presented a tutorial on its use at the recent AbSciCon19 worldwide astrobiology conference, held in Seattle.

The research was done through the Virtual Planetary Laboratory [https://depts.washington.edu/naivpl/content/welcome-virtual-planetary-laboratory], and the source code is available online [https://github.com/VirtualPlanetaryLaboratory/vplanet].

“VPLanet: The Virtual Planet Simulator,” Rory Barnes et al., 2019, to appear in Publications of the Astronomical Society of the Pacific [https://iopscience.iop.org/journal/1538-3873, preprint: https://arxiv.org/abs/1905.06367].

Barnes’s other faculty co-authors are astronomy professor Tom Quinn; Cecilia Bitz, professor of atmospheric sciences; and research scientist Pramod Gupta. Other UW co-authors are doctoral students David Fleming, Rodolfo Garcia, and Hayden Smotherman; and undergraduate researchers Caitlyn Wilhelm, Benjamin Guyer and Diego McDonald.

Other co-authors are Peter Driscoll of the Carnegie Institution for Science; Rodrigo Luger of the Flatiron Institute, Patrick Barth of the Max Planck Institute for Astronomy in Heidelberg, Germany, Russell Deitrick of the University of Bern, Shawn Domagal-Goldman of the NASA Goddard Space Flight Center and John Armstrong of Weber State University.

The research was funded by a grant from the NASA Astrobiology Program’s Virtual Planetary Laboratory team, as part of the Nexus for Exoplanet System Science research coordination network, or NExSS. Grant numbers: VPL under cooperative agreement #NNA13AA93A. NASA grants #NNX15AN35G, #13-13-NA17 0024, and #80NSSC18K0829. NASA Earth and Space Science Fellowship Program grant #80NSSC17K0482.


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