Prof. Doug Hamilton — “The Origin of Titan & Hyperion”

Posted by admin on December 15, 2013
Posted in: Other Seminars.
This natural color composite was taken during the Cassini spacecraft's April 16, 2005, flyby of Titan. From http://en.wikipedia.org/wiki/Titan_%28moon%29.

This natural color composite was taken during the Cassini spacecraft’s April 16, 2005, flyby of Titan. From http://en.wikipedia.org/wiki/Titan_%28moon%29.

Interesting public talk to the National Capital Astronomers‘ monthly meeting from Prof. Doug Hamilton of UMD Astronomy.

Prof. Hamilton talked about the origin of Saturn’s moon Titan, an unusual satellite in several ways. Titan has a massive nitrogen and methane atmosphere, full of orange photochemical haze (picture at left).

Prof. Hamilton pointed out that that Saturn’s satellite system is also unique among satellite systems of giant planets: unlike the Jovian and Uranian systems, Titan is the only large moon, and it is very far from the next largest moons in the system.

Instead of forming along with its host planet, as the Jovian and Uranian satellites probably did, Prof. Hamilton suggested that several smaller satellites originally formed around Saturn. Then the moons’ orbits destabilized, and the moons collided, merging to form Titan.

This novel hypothesis solves several outstanding questions about Titan and highlights how much we still don’t understand about our own solar system.

Dr. Karl Gordon — “Dust Mapping in Galaxies: UV/Opt/NIR and far-IR/submm Probes”

Posted by admin on December 13, 2013
Posted in: DTM Astronomy Seminar.

Great talk today from Dr. Karl Gordon of the Space Telescope Science Institute (STScI) on mapping interstellar dust in the Milky Way and other galaxies.

Full sky images of dust in the Milky Way from the Pioneer 10/11 IPP data. From http://www.stsci.edu/~kgordon/pioneer_ipp/Pioneer_10_11_IPP.html.

Full sky images of dust in the Milky Way from the Pioneer 10/11 IPP data. From http://www.stsci.edu/~kgordon/pioneer_ipp/Pioneer_10_11_IPP.html.

Dr. Gordon spoke about using observations taken at infrared wavelengths to look for heat radiated by dust grains and then using those measurements to determine how hot the dust is and how much there is. The picture at right shows a map of dust in the Milky Way from one of Dr. Gordon’s papers.

Understanding the dust distributed throughout the Milky Way and other galaxies can tell us a lot about stellar evolution, the galaxies themselves, and about the conditions in those galaxies where the dust lives. And at the most fundamental level, it tells us about the planets and even life itself because the Earth and everything on it formed from this star dust.

Dr. Anne Verbiscer — “Mutual Events of Sila-Nunam, an Eclipsing Binary in the Kuiper Belt”

Posted by admin on December 6, 2013
Posted in: DTM Astronomy Seminar.
Geometry of the mutual occultations of Sila and Nunam (called ``mutual events'') over the last few years. From http://www2.lowell.edu/users/grundy/abstracts/figs/2012.Sila-Nunam.gif.

Geometry of the mutual occultations of Sila and Nunam (called “mutual events”) over the last few years. From http://www2.lowell.edu/users/grundy/abstracts/figs/2012.Sila-Nunam.gif.

Interesting talk today in the DTM Astronomy Seminar from Dr. Anne Verbiscer of UVA Astronomy.

She spoke about the Kuiper Belt binary object Sila-Nunam, two enigmatic bodies orbiting 40 times farther from the Sun than the Earth. They have radii of about 100 km, comparable to some of Saturn’s small moons, and they orbit one another every 12 days, as they both go around the Sun together every 300 years.

In recent and coming years, Sila and Nunam will occult one another several times, allowing astronomers to measure their radii, which aren’t very well known, and learn about their densities, internal structures, and orbit.

Dr. Verbiscer presented several very interesting infrared spectra and observations in visible wavelengths, showing the small dips in light from the system, as one object blocked out the other object. These observations are very challenging because objects are so small and far away, but analysis of these data are ongoing and will tell us about these strange, distant, and cold objects.

Dr. Liyan Tian — “Mantle Heterogeneity Beneath the East Pacific Rise”

Posted by admin on December 5, 2013
Posted in: DTM Seminar.

Interesting seminar by one of DTM‘s own postdocs, Dr. Liyan Tian.

At a subduction zone, one plate of oceanic lithosphere dives under another plate, which 'dewaters' to plate (blue arrows) into the overlying mantle wedge and produces arc volcanism at the surface. Part of the hydrated mantle wedge frees itself and mixes into surrounding depleted mantle. From Widom, Nature 443, 516-517 (2006).

At a subduction zone, one plate of oceanic lithosphere dives under another plate, which ‘dewaters’ to plate (blue arrows) into the overlying mantle wedge and produces arc volcanism at the surface. Part of the hydrated mantle wedge frees itself and mixes into surrounding depleted mantle. From Widom, Nature 443, 516-517 (2006).

Dr. Tian described how she uses the geochemical compostions of basalt erupted from and near mid-ocean ridges to study the composition and transport of material within the Earth’s mantle.

One element that is particularly important for her studies is lithium (Li). Dr. Tian described how Li is thought to behave chemically within the mantle in a way that allows her to trace the subduction of material into the mantle and show that it is later erupted at a mid-ocean ridge (illustrated at right).

Mandell et al. (2013) — Exoplanet Transit Spectroscopy of WASP-12 b, WASP-17 b, and WASP-19 b

Posted by admin on December 4, 2013
Posted in: Publications.
Fig. 3 from Mandel+ (2013) showing the combined-light time series for WASP-12 during transit.

Fig. 3 from Mandel+ (2013) showing the combined-light time series for WASP-12 during transit.

Very cool result that, for some reason, only just appeared in the press. Using the Hubble Space Telescope, Avi Mandell and co-authors detected spectral signatures of water in the atmospheres of several very hot, transiting exoplanets.

The figure at left shows the transit signal for WASP-12 b, a very hot gas giant planet that is so close to its host star that the star may be ripping the planet apart.

To get a sense for how impressive these detections are, consider the following: given the temperature and radius for the host star WASP-17, which is about 1,000 lightyears away, we receive about 1 pico-Watt per square meter from the star here on Earth [ (1.38 R_sun/1000 lightyears)^2 (sigma) (6509 K)^4 ~ 1 pW/m^2].

That’s about the same amount of energy we’d receive from a 1000-Watt lightbulb suspended in space 10,000 km from the Earth [1000 W / 4 pi (10000 km)^2 ~ 1 pW/m^2].

The planet WASP-17 b has a radius roughly a tenth that of its host star, giving a transit depth [(radius of the planet)^2/(radius of the star)^2] of about 1% (as seen in the figure). For comparison, the radius of a standard lightbulb is about 3 cm and that of a fruitfly is about 2 mm.

So being able to measure a spectrum for WASP-17 b in-transit is a bit like watching a fruitfly pass in front of a lit lightbulb at a distance of 10,000 km from Earth and being able to tell what color the fly’s wings are. Very cool stuff.

Mandell’s paper is here: http://adsabs.harvard.edu/abs/2013arXiv1310.2949M.

Hilke Schlichting — “Planet Formation in the Kepler Era”

Posted by admin on November 19, 2013
Posted in: DTM Seminar.

Interesting talk today from Prof. Hilke Schlichting of MIT’s Earth, Atmospheric and Planetary Sciences Dept. She discussed what we can learn about the histories and origins of planets with all the new planets and planetary candidates found by the Kepler mission.

Artist's conception of a large planetary impact. From http://www.hdwallpapersinn.com/planet-impact-wallpapers.html.

Artist’s conception of a large planetary impact of the kind that occurred during planet formation. From http://www.hdwallpapersinn.com/planet-impact-wallpapers.html.

Among the key results from Kepler are discoveries of a wide variety of orbital architectures (the arrangements of planetary orbits). The processes that gave rise to the planets determined, for example, the orbital periods of the planets.

Many Kepler planets reside in systems with multiple planets, and many members of these multiplanet systems have orbital periods that are very nearly integer multiples of one another. That is, the planets are near a mean-motion resonance, which means the planets interact strongly gravitationally.

Prof. Schlichting described one explanation for these near resonances: while the planetary systems were still very young, interactions between the nascent planets and the protoplanetary gas disks from which the planets form gently tuned the gravitational interactions between the planets, keeping them slightly out of resonance.

There has been some debate about whether the near resonances for many Kepler planetary systems mean that the planets did or did not undergone strong gas disk migration. In the simplest picture, this migration should drive planets into resonances, inconsistent with the observations of near-resonances.

But Prof. Schlichting’s modification to that picture means that the planets could have undergone migration after all. Turns out planetary systems were pretty complicated, dynamic places early on.

The Extraordinary Multi-tailed Main-belt Comet P/2013 P5; Early Cretaceous sea water in the Chesapeake Bay crater

Posted by admin on November 18, 2013
Posted in: Journal Club.
P/2013 P5 as seen by Hubble on September 10, 2013. P/2013 P5 is about 790 feet (240 m) in diameter. It has six comet-like tails of dust radiating from it like spokes on a wheel. From http://www.sci-news.com/space/science-p2013p5-hubble-asteroid-six-tails-01530.html.

The comet P/2013 P5 as seen by Hubble on September 10, 2013. P/2013 P5 is about 790 feet (240 m) in diameter. It has six comet-like tails of dust radiating from it like spokes on a wheel. From http://www.sci-news.com/space/science-p2013p5-hubble-asteroid-six-tails-01530.html.

At journal club today, we talked about two interesting papers.

The first, “The Extraordinary Multi-tailed Main-belt Comet P/2013 P5” by Jewitt and colleagues, discussed observations using the Hubble Space Telescope of a comet in the asteroid belt that displayed five cometary tails (see image at left). The tails are made of particles shed by the comet, and using the particle trajectories inferred from the tails, the authors were able to figure out when, over the last few months, the particles were launched from the comet.

The second article, “Evidence for high salinity of Early Cretaceous sea water from the Chesapeake Bay crater” by Sanford and colleagues, presented chemical analyses of water collected from under the Chesapeake Bay, in the large impact crater at the southern end of the bay. (The crater is underwater and buried by sediment, so you can’t see it even if you’re just standing on it.) The water contain subtle chemical signatures that indicate it was originally part of the Early Cretaceous North Atlantic Ocean, an extinct ocean from more than 100 million years ago. Chemical analyses of this buried water will tell scientists what the ancient ocean was like.

Rodrigo Herrera — “How reliable is the [CII] 158 micron emission as a star formation tracer?”

Posted by admin on November 15, 2013
Posted in: DTM Astronomy Seminar.
The images were created using observations from the Spitzer SINGS survey and the Herschel KINGFISH survey. Rather than stars, the images show dust between the stars, which is created by dying stars and forms some of the material from which stars are formed. The colour images are made by combining three different wavelengths. From http://www.astro.umd.edu/~rhc/bigbang/boxed/research_blog.html.

The images of many different kinds of galaxies were created using observations from the Spitzer SINGS survey and the Herschel KINGFISH survey. From http://www.astro.umd.edu/~rhc/bigbang/boxed/research_blog.html.

For today’s astronomy seminar, we had Rodrigo Herrera from University of Maryland Astronomy. Rodrigo spoke about using far infrared observations from the Herschel instrument to study star formation in nearby galaxies.

Rodrigo talked about using emission at 158 microns, created by ionized carbon atoms (CII), to probe the rates of star formation. The hottest and youngest stars in a stellar nursery, O and B stars, are thought to heat dust grains, charging them slightly. The resulting excess electrons then escape into the gas surrounding the stellar nursery, heating it. Some of that gas is ionized carbon, which cools by emitting photons at a very specific wavelength, 158 microns.

By observing how much 158-micron emission is coming from a galaxy (and applying some important corrections to account for the variation in the physical environments in each star-forming region), Rodrigo showed that astronomers could pretty accurately estimate the rate at which stars are forming throughout that galaxy.

Understanding the star formation rate is important for may aspects of astronomy, but in particular, the star formation rate is a key parameter for the Drake equation, which estimates the number of intelligent and communicating civilizations in the universe. Such civilizations probably grow up orbiting a star similar to the Sun, so knowing how often such stars form goes a long way to telling us how many extraterrestrial civilizations might be out there.

 

Prof. Richard O’Connell — “What Do We Mean by a Layered Mantle?”

Posted by admin on November 14, 2013
Posted in: DTM Seminar.

Interesting seminar today from Prof. Richard O’Connell of Harvard Geophysics. Prof. O’Connell discussed the interplay between the thermal evolution of the Earth’s interior and plate tectonics.

Flow structure of the convection cell in a model of the Earth's interior. Figure 3 from Crowley & O'Connell (2012) -- http://adsabs.harvard.edu/abs/2012GeoJI.188...61C.

Flow structure of the convection cell in a model of the Earth’s interior. Figure 3 from Crowley & O’Connell (2012) — http://adsabs.harvard.edu/abs/2012GeoJI.188…61C.

New models from Prof. O’Connell and his student John Crowley suggest that the Earth may have undergone different stages of tectonic evolution, with the tectonic plates moving quickly at some times in the Earth’s history but much more slowly at others.

The evolution between different geophysical modes may help explain a longstanding puzzle in Earth science: the amount of heat coming out of the Earth is much greater than expected and has been thought to require much more heating from radioactive isotopes than geochemical analyses allow.

If, instead, O’Connell and Crowley are right, then this large heat flow is really just a symptom of Earth’s geophysical fickleness: sometimes lots of heat comes out, other times less.

Dr. Mark Wieczorek — “Lunar Magnetism: Impacts, Dynamos and, Core Evolution”

Posted by admin on November 11, 2013
Posted in: DTM Seminar.

We had a great talk at DTM today from Dr. Mark Wieczorek, a geophysicist from the Institut de Physique du Globe de Paris.

Total magnetic field strength at the surface of the Moon as derived from the Lunar Prospector electron reflectometer experiment. From http://en.wikipedia.org/wiki/File:Moon_ER_magnetic_field.jpg.

Total magnetic field strength at the surface of the Moon as derived from the Lunar Prospector electron reflectometer experiment. From http://en.wikipedia.org/wiki/File:Moon_ER_magnetic_field.jpg.

He talked about the geophysical history of the Moon as inferred from remnant magnetic fields in lunar rocks.

Currently, the Moon does not have a large-scale magnetic field, as the Earth does, but there are smaller-scale magnetic anomalies (see figure at right). These remnant magnetic signatures probably indicate that long ago (about 3-4 billion years ag0) that Moon DID have a magnetic field.

So why did the Moon have a magnetic field long ago and why doesn’t it anymore? One exotic idea Dr. Wieczorek talked about was the idea that large asteroidal or cometary impacts could disrupt the rotation of the Moon’s mantle.

As a result, the mantle and core would rotate at different rates in different directions, which could stir up and heat fluid in the Moon’s interior. This heating could drive internal convection and produce a magnetic field, similar to the way the magnetic field in the Earth is generated.