Jackson & Lorenz (2015) — A Multi-Year Dust Devil Vortex Survey Using a In-Situ Sensor Network

Posted by admin on February 7, 2015
Posted in: Brian's publications. Tagged: , , , .
Pressure variations (in hectoPascal, hPa) vs. local time for one dust devil pressure dip. The blue curve shows our model fit.

Pressure variations (in hectoPascal, hPa) vs. local time for one dust devil pressure dip. The blue curve shows our model fit.

Dust devils occur in arid climates on the Earth and ubiquitously on Mars. Martian dust devils have been studied with orbiting and landed spacecraft, while most studies of terrestrial dust devils have involved manned monitoring of field sites, which can be costly both in time and personnel. As an alternative approach, my colleague Ralph Lorenz and I performed a multi-year in-situ survey of terrestrial dust devils using pressure loggers deployed at El Dorado Playa in Nevada, USA, a site known for dust devil activity.

When a dust devil passed over our pressure sensors, it appeared as a pressure dip in the time series, as illustrated in the figure. By modeling these signals, we learned a lot of about dust devils. For instance, in spite of expectations, we found signals that looked a lot like dust devils that occurred at night and even in the winter. So do dust devils happen year-round, day and night? More work will help us figure it out.

Our paper on this study will appear soon in the Journal of Geophysical Research Planets.

Research Updates — 2015 Jan 30

Posted by admin on February 1, 2015
Posted in: BSU Journal Club. Tagged: , , , , , , , .
From https://emps.exeter.ac.uk/physics-astronomy/research/astrophysics/phd-opportunities/modelling-shock-waves/.

From https://emps.exeter.ac.uk/physics-astronomy/research/astrophysics/phd-opportunities/modelling-shock-waves/.

On Friday, everyone in our research group gave a little update on what they’ve been up to.

Liz and Jennifer talked about Parmentier et al.’s (2013) paper on the meteorology of hot Jupiters and how condensates are transported throughout these dynamic atmospheres.

Emily talked about working through the first few chapters of Murray & Dermott’s classic Solar System Dynamics. She will eventually study the orbital dynamics of systems of exoplanets very close to their host stars.

Brenton discussed his reading of Balme & Greeley (2006) on dust devils in preparation for working with me on terrestrial and Martian dust devils. A very exciting possibility, Brenton and the rest of the group said dust devils are common just south of Boise. Good chance we can do some in-situ monitoring locally.

Nathan spoke briefly about looking for more very short-period planets using data from the Kepler and K2 missions.

In attendance were Liz Kandziolka, Jennifer Briggs, Emily Jensen, Brenton Peck, Nathan Grigsby, Trent Garrett, and Tiffany Watkins.

Crossfield+ (2015) — Three New Planets Around a Nearby M-Dwarf Star

Posted by admin on January 23, 2015
Posted in: BSU Journal Club. Tagged: , , , .
Mechanical failures interrupted Kepler's original mission, but the telescope is still hunting exoplanets. From http://www.nature.com/news/three-super-earth-exoplanets-seen-orbiting-nearby-star-1.16740.

Mechanical failures interrupted Kepler’s original mission, but the telescope is still hunting exoplanets. From http://www.nature.com/news/three-super-earth-exoplanets-seen-orbiting-nearby-star-1.16740.

Discussed a brilliant paper today in journal club from Ian Crossfield and collaborators, in which they announce the discovery of a three-planet system around a nearby M-dwarf star.

The team found the new system in data from the re-incarnated Kepler mission called K2. This system is only the second discovered by the mission (the first was announced a few months ago).

This new system is especially exciting because, as the authors point out, it is observable by other available facilities, allowing astronomers to characterize the planets and star in detail.

The outermost planet in the system, with an orbital period of 45 days, is very near the inner edge of the system’s habitable zone and has a temperature of about 310 K (100 F), making it plausibly habitable. Combined with the fact that we can probably characterize the planet in detail, there’ll probably be a flurry of exciting studies of the system very soon.

Journal club was attended by Jennifer Briggs, Trent Garrett, Nathan Grigsby, Emily Jensen, Liz Kandziolka, and Brenton Peck.

AAS 225 — Day 3

Posted by admin on January 9, 2015
Posted in: Meetings. Tagged: .
Three planets in the Kepler-11 system as they simultaneously transit their star as imagined by by a NASA artist (Image credit: NASA). From http://ciera.northwestern.edu/Research/highlights/research_highlights.php#ForeignWorlds.

Three planets in the Kepler-11 system as they simultaneously transit their star as imagined by by a NASA artist (Image credit: NASA). From http://ciera.northwestern.edu/Research/highlights/research_highlights.php#ForeignWorlds.

Great finish to the meeting, and thankfully no big disasters at my special session.

Lots of excellent talks, but the talk that stood out for me was Sarah Ballard’s, in which she addressed an impressively simple but compelling question: Is there a difference between planetary systems where we’ve only found one planet and systems where we’ve found more than one?

This question is important because such a difference could point to different formation and/or evolutionary processes in these systems, and so comparison of these systems could elucidate subtle but significant aspects of planet formation.

In fact, Ballard did find the two types of planetary system are different, and that, for some reason, about half of M-dwarf stars that host planets have only one.

She also found modest but intriguing differences in the stars that host single planet: their features suggest they may be older than stars with multi-planet systems. Does that mean that single-planet stars used to have multiple planets but enough time has passed that the system became dynamically unstable, leaving behind a single planet?

AAS 225 — Day 2

Posted by admin on January 8, 2015
Posted in: Meetings. Tagged: .
Blue glacial ice. From http://upload.wikimedia.org/wikipedia/commons/1/10/JoekullsarlonBlueBlockOfIce.jpg.

Blue glacial ice. From http://upload.wikimedia.org/wikipedia/commons/1/10/JoekullsarlonBlueBlockOfIce.jpg.

I really enjoyed Aomawa Shields‘s dissertation talk in the “Extrasolar Planets: Host Stars and Interactions” session, in which she discussed how different stellar types could influence the climates of putative Earth-like planets.

She highlighted how the ice-albedo feedback would operate differently on planets orbiting M-dwarfs as compared to those orbiting F-stars. Since they are so cool, M-dwarfs shine primarily in infrared (IR) wavelengths, while F-stars are much hotter and emit in the visible and ultraviolet (UV). At the same time, water ice primarily absorbs IR but reflects visible light.

Therefore, around an M-dwarf, the ice on an Earth-like planet’s surface would absorb a lot of the stellar insolation, heating the planet, while around an F-star, the ice would reflect it, keeping the planet cool. As a consequence, Shields argued that M-dwarf planets have climates more stable against global ice ages than F-star planets. So although there may be other challenges to life on an M-dwarf planet, climate stability is probably not one of them.

AAS 225 — Day 1

Posted by admin on January 7, 2015
Posted in: Meetings, Uncategorized. Tagged: .
The radial velocity method to detect exoplanet is based on the detection of variations in the velocity of the central star, due to the changing direction of the gravitational pull from an (unseen) exoplanet as it orbits the star. When the star moves towards us, its spectrum is blueshifted, while it is redshifted when it moves away from us. By regularly looking at the spectrum of a star - and so, measure its velocity - one can see if it moves periodically due to the influence of a companion. From http://en.wikipedia.org/wiki/Doppler_spectroscopy#mediaviewer/File:ESO_-_The_Radial_Velocity_Method_%28by%29.jpg.

The radial velocity method to detect exoplanet is based on the detection of variations in the velocity of the central star, due to the changing direction of the gravitational pull from an (unseen) exoplanet as it orbits the star. From http://en.wikipedia.org/wiki/Doppler_spectroscopy#mediaviewer/File:ESO_-_The_Radial_Velocity_Method_%28by%29.jpg.

Another great day at the AAS meeting. One talk that stuck out for me was the dissertation talk from Ben Nelson (PSU). I was amazed at how much he was able to squeeze into his 15 minutes and still not lose the audience.

Among the things he covered was his new MCMC code, RUNDMC, specially suited to analyze radial velocity (RV) observations of planetary systems and thoroughly but quickly sample the sprawling parameter space associated with these systems. He applied his code to several systems to understand how robustly different planetary configurations could be detected in those systems, including whether the RV data favored additional planets in a system or other kinds of variability.

AAS 225 — Day 0

Posted by admin on January 6, 2015
Posted in: Meetings, Uncategorized. Tagged: .

Lots of amazing presentations today, running the gamut from transmission spectroscopy of hot Neptune-like planets to the detailed and puzzling architectures of multi-planet systems. But two talks really stuck out for me.

belts-plasmapause_1 The first one, by Prof. Dan Baker at U Colorado, covered recent developments in the study of the Van Allen radiation belts (which Van Allen preferred to call “zones” — when asked by a reporter what was the function of Van Allen belts, he said they hold up Van Allen’s pants). As a member of the Radiation Belt Storm Probe mission,  Baker explained what we understand and what remains mysterious about these powerful celestial phenomena suspended above our heads, including a bizarre “glass wall” that keeps charged particles at bay.

philae-landing-rosetta-photos

The European Space Agency’s Rosetta spacecraft captured these photos of the Philae lander descending toward, and then bouncing off, the surface of Comet 67P/Churyumov–Gerasimenko during its historic touchdown on Nov. 12, 2014. Credit: ESA/Rosetta/MPS for OSIRIS Team MPS/UPD/LAM/IAA/SSO/INTA/UPM/DASP/ID — http://www.space.com/27788-philae-comet-landing-bounce-photos.html

In the afternoon, Dr. Paul Weissman gave the most recent updates on the Rosetta mission, still in orbit around Comet Churyumov-Gerasimenko (which Weissman called “comet CG”). Following up on the more-exciting-than-expected landing of the Philae spacecraft, Weissman explained that the lander struck a surprisingly hard sub-surface layer (comparable in strength to solid ice), which probably contributed to the lander’s unplanned ballistic trajectory around the comet. Lots of other interesting science, including more evidence about the origin of Earth’s water.

AAS 225 — Day -2

Posted by admin on January 3, 2015
Posted in: Meetings. Tagged: , .

python.sh-600x600The new year finds me in Seattle two days before the AAS 225 meeting officially begins to attend the Software Carpentry workshop. This workshop is put on by a volunteer organization that teaches scientists how to write and maintain robust code.

On the first day, we covered some shell scripting, basic python, and the ipython notebook. Just the first few lessons are already hugely useful for me, and the teachers are doing a great job explaining things clearly. They are also using a variety of tools to record and document the workshop. I’ve pasted links to those records below.

Very much looking forward to Day 2.

Useful links and particularly useful notes:

Luger & Barnes (2014) — Water Loss and Build-Up of Abiotic Oxygen on Planets Orbiting M-Dwarf Stars

Posted by admin on December 7, 2014
Posted in: BSU Journal Club.
Total amount of water lost for a 1 Earth-mass planet.

Total amount of water lost for a 1 Earth-mass planet.

In journal club on Friday, we discussed a fascinating paper that presented some problematic results for detecting life on other planets. Luger and Barnes (2014) looked at what could happen to the water on Earth-like planets orbiting many different kinds of stars.

Like the Sun, all stars produce x-rays and ultraviolet light (UV), but not all stars produce the same amount. In fact, stars much less massive than the Sun produce a lot more.

That’s a problem for life on planets orbiting these stars because x-rays and UV (collectively called XUV) can photodissociate (or break-up) water molecules in the atmosphere. Once the water is broken into hydrogen and oxygen atoms, the hydrogen can escape to space so the water is permanently lost, leaving behind the oxygen.

And this isn’t just a hypothetical scenario — Venus probably had oceans, like the Earth, and lost them this way. Of course, water is necessary for life as we know it, so a planet that loses its water can’t host life.

Luger and Barnes modeled this process and found that a lot of planets that might otherwise be suitable for life could actually lose a lot of water. The figure at left shows how much water could be lost for planets in the habitable zones of stars from about 0.1 to 0.9 solar masses (M⊙). The dark red region shows that most of the planets would actually lose at least 1 oceans-worth of water.

So not only would these planets be bone-dry, they could have a lot of oxygen in their atmospheres. On the Earth, oxygen is produced by photosynthetic planets and algae, and so its presence in a planet’s atmosphere is usually thought of as a smoking gun for life. If Luger and Barnes are right, their results may spell trouble for the search for life elsewhere in the universe.