Planetary Science

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Venus

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Venus is one of the most intriguing planets in our solar system. The planet is about the same size as Earth with a similar density, and so planetary scientists assume Venus must have an internal structure similar to Earth's. But Venus has no system of plate tectonics. On Earth, plate tectonics is responsible for recycling carbon and maintaining a clement atmosphere suitable for life as we know it.

The surface of Venus is covered with volcanic and tectonic features, including rifts and coronae. There over 500 coronae, quasi-circular volcano-tectonic features, on Venus. They are believed to form via small-scale mantle upwellings, lithospheric instability, or a combination thereof.

Coronae and rifts commonly occur together, including many coronae that lie outside of the extensional zone. However the genetic link between the two has remained unclear.

In our recent paper, Lindy Elkins-Tanton, Suzanne Smrekar, and I propose a mechanism for the formation of off-rift coronae due to the rifting process. We model the interaction of a rising mantle plume associated with a rift with a preexisting layer of dense material at the lithosphere-mantle boundary and show that a rift and its associated off-rift coronae are genetically linked. We calculate the resulting surface topographies, melt volumes, and Bouguer gravity anomalies and find a correlation to observations.

More robust comparisons between our results and observations of the Venusian surface would require high resolution altimetry, SAR imaging, spectroscopy, and gravity data for coronae in Parga Chasma.

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Moon

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The giant impact hypothesis for the origin of the Earth’s moon begins with a wayward planetesimal colliding with the early Earth and ends with the creation of a hot, young moon, likely with a global magma ocean.

The next logical step, based on the mantle cumulate crystallization sequence, is a flotation crust of plagioclase crystals which would form an anorthosite crust. Early calculations of the expected anorthosite content of the Moon did not match initial measurements of Apollo samples, and more recently have not matched Clementine measurements or SELENE measurements, because they assumed interstitial melt would freeze.

By considering a physical model of a magma ocean with an accumulating flotation lid, significant escape of melt can take place for reasonable physical parameters and timescales of melt migration, thus allowing for more nearly pure lunar anorthosites, consistent with observations.

This model encounters some difficulty in explaining the expulsion of melt for the near-surface crust that presumably dominates the Apollo samples. We invoke impacts and tidal heating to explain this discrepancy.

For more information, see the paper I coauthored with Dave Stevenson.

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Hot Jupiters

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Of the many types of exoplanets that scientists have discovered, hot Jupiters are one of the most intriguing groups. Hot Jupiters are Jovian planets orbiting their host stars within about 0.5 AU. They only make up a tiny portion of all exoplanets, but they have no analog in our solar system.

One popular technique for determining the components in a hot Jupiter's atmosphere is secondary eclipse spectroscopy. A secondary eclipse occurs when the hot Jupiter moves behind the host star. We can quantify the reflected light coming from the hot Jupiter to get an idea of what atmospheric species are present. For more information on secondary eclipses and other techniques used to learn about hot Jupiters, see this presentation by Heather Knutson.

An emerging technique used to characterize hot Jupiters involves taking a high-resolution ground-based spectrum in the near infrared. Then, one can treat the star-planet system as a spectroscopic binary and watch the planet's spectrum shift (due to the Doppler effect) back and forth relative the the star's spectrum in the course of an orbit. Using the NIRSPEC instrument at Keck Observatory, this technique yielded a detection of water vapor on tauBoo b. This technique has also had great success with the high resolution of CRIRES, allowing scientists to characterize high speed winds on exoplanets as well very high planetary rotation rates.

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Binary Stars

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Hot Jupiters are such a mystey to scientists because they could not have possibly formed in situ. There is not enough material present in a protoplanetary disk at such small orbital distances to build a gas giant planet. Therefore, the planet must have formed further out in the protoplanetary disk and migrated inwards. But how did it migrate?

One hypothesis is that a close binary companion of a host star may drive three-body interactions and explain the exoplanet’s small semi-major axis. This is a compelling hypothesis because previous surveys have shown that half of all stars occur in binary systems.

I am involved in a three-part survey to detect companion stars to hot Jupiter hosts. The first part detects the massive companions with smaller separations using long-term radial velocity monitoring. The second part uses adaptive optics to directly image widely-separated compantion. The third part involves the careful analysis of high-resolution infrared spectra of hot Jupiter host stars.

For the third portion, we remove the signal of the host star with a library of standard spectra and we are able to detect the presence of a colder star having a high contrast to the host star in the infrared. Based on the limits of this method, the detectable binary companions would be located within 50 to 200 astronomical units from the host star. The detection of a known binary companion associated with WASP-2 and serves as a proof of method.

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My Interests

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I lived in Washington, DC, from August 2011 to June 2012. In that time, I learned how to apply my skills as a budding scientist to the science policy realm. I am particularly interested in the relationship between NASA and the federal government.

At the Space Studies Board, I spent the crux of my time working on the Flight Research report in Fall 2011 and the Report on NASA's Strategic Direction report in Spring and Summer 2012. The Flight Research report evaluated the ability of NASA's Aeronautics Research Mission Directorate to fulfill its mission. The Strategic Direction Report had a much larger scope and followed in the footsteps of the Lyles Report and the Augustine Reports (to name a few). The report aimed to determine if NASA as a whole is capable of carrying out the multiple duties assigned to it over the years. My role on the Strategic Direction report also involved acting as a research assistant to Committee Chair Albert Carnesale at UCLA during the summer of 2012.

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Useful Links

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Below is a list of sites I regularly read to keep up on space policy in Washington:
Space News
The Space Review
Space Policy Online
The Politics of Space
Space Politics (until September 2014)

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More Information

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Publications

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[3] Piskorz, D., Knutson, H.A., Ngo, H., et al. 2015 "Friends of Hot Jupiters. III. An Infrared Spectroscopic Search for Low-Mass Stellar Companions" The Astrophysical Journal, 814, 2, 1-14, doi:10.1088/0004-637X/814/2/148.

[2] Piskorz, D., Elkins-Tanton, L.T., and Smrekar, S.E. 2014. "Coronae Formation on Venus via Extension and Lithospheric Instability" Journal of Geophysical Research-Planets, 119, 12, 2568-2582, doi:10.1002/2014JE004636.

[1] Piskorz, D. and Stevenson, D.J. 2014. "The Formation of Pure Anorthosite on the Moon" Icarus, 239, 238-243, doi:10.1016/j.icarus.2014.06.015.

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CV

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Click here to download a copy of my CV.

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Contact

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M A I L
California Institute of Technology
Division of Geological and Planetary Sciences
1200 East California Boulevard, MC 150-21
Pasadena, CA 91125

O F F I C E
South Mudd #154

E M A I L
dpiskorz[at]gps.caltech.edu

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Credits

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Planetary Science: NASA/JPL. Unscaled montage of the solar system planets (and Pluto).
Venus: NASA/JPL. This image was adapted from radar data taken by the Magellan spacecraft that visited Venus in the early 1990's.
Moon: NASA. This timeless photo is called Earthrise and was taken by Astronaut William Anders on 24 December 1968. He snapped this picture while Apollo 8 was in orbit around the Moon.

Astronomy: Keck Observatory. Most of the data I use for my hot Jupiter and binary star projects come from Keck Observatory.
Binary Stars: From an article on interactions between hot Jupiters and their stars.
Hot Jupiters: From an article on the detection of water vapor in tauBoo's atmosphere.

Space Policy: Astronaut Chris Hadfield, taken from the International Space Station in January 2013.
My Interests: Full moon over DC from National Geographic.
Useful Links: The Earth at night taken by a NASA-NOAA satellite.

More Information: Michael Wong, taken in San Diego, California, in October 2014.
Publications: Danielle Piskorz, taken in Pasadena, California, in November 2014.
CV: A photo of my lovely alma mater in Cambridge, Massachusetts.
Contact: Danielle Piskorz, taken in Carmel, California, in October 2014.
Credits: Danielle Piskorz, taken in Pasadena, California, in August 2014.

HTML/CSS code: Codrops. This website design is adapted from the CSS3 Content Navigator tutorial.

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