Dr. Andrea Banzatti of the Space Telescope Science Institute visited today and talked about observing infrared (IR) light emitted by water vapor in protoplanetary disks.
Artist illustration of a protoplanetary disk. From http://www.keckobservatory.org/index.php/gallery/detail/milky_way/32.
Planets like the Earth are born in these protoplanetary disks, the gas and dust leftover after a star forms, and by analyzing IR light, Banzatti can estimate how much water there is in a disk and how hot it is.
Water is a key ingredient in planet formation, especially for gas giants like Jupiter, and of course, a key requirement for life. So by learning about how much water is in disks, Banzatti is helping us understanding the earliest stages in planet formation and the origins of life.
Banzatti developed a new technique to study the temperature and abundance of water in disks, and his results suggest that ice grains actually migrate around the disk, in ways that have been expected but not observed.
A light-optical microscope image of a zircon, 250 micrometers long.
Very interesting seminar today from Prof. Blair Schoene of Princeton University’s Dept. of Geosciences. Prof. Schoene discussed his work on geochronology, estimating the ages of rocks.
The Earth is very old, and figuring out the ages of rocks can be tricky. Luckily, the Earth provides some help, notably in the form of small crystals called zircons (one shown at left). Zircons are hardy little crystals that contain trace amounts of uranium (U) and lead (Pb). When zircons crystallize, they can incorporate some U into the crystal, but Pb is chemically excluded.
However, U radioactively decays into Pb at a well-known rate, and so if you find Pb in an old zircon, you know that it used to be U and formed by decay. By counting up the amount of Pb, you can estimate the zircon’s age.
Prof. Schoene and his research group use this fact to estimate the ages of rocks on the Earth’s surface. This work can tell us, for example, whether the chemistry of lavas erupted onto the surface have changed over time.
In fact, work by Schoene’s group has found preliminary indications that there may have been a big shift in the chemistry of lava flows right about the time that oxygen appeared in abundance in the Earth’s atmosphere, 2.5 billion years ago during the Great Oxygenation Event (GOE). The GOE is suspected to have devastated Earth’s biosphere — oxygen was toxic to most life at that time — and now it seems that eruptions from the Earth’s interior were affected, too.
3D view of the inner part of a collapsing gas cloud, forming a star, where a bundle of twisted magnetic field lines is surrounded at the “waist” by a dense ring. The star is shown as a red dot located near the inner edge of the ring.
Good talk today from Bo Zhao of UVA Astronomy about the effects of magnetic fields on the formation of binary stars.
Binary stars are very common, and about half of all stars have such a celestial companion. Moreover, several exoplanets have now been found in binary star systems. So the formation of these stars touches on many astronomical topics.
Bo described how magnetic fields can control the orbital evolution of binary stars and influence the accretion of mass by the stars. For example, magnetic fields can sculpt the shape of accretion disks around the stars into complex shapes, filaments and strands (as shown at left).
Since these accretion disks mass onto the young stars, understanding their shapes, dynamical evolution, and the effects of magnetic fields on both these are important for understanding the population of binary stars we can see.
Dr. Richard Gaschnig of UMD Geology gave an interesting talk today about inferring the composition of the Earth’s ancient crust from glacial sediment deposits.
Banded iron formation with tiger-eye, Mount Brockman, Australia. From http://www.pbase.com/image/94666060.
Gaschnig described detailed analyses of transition metals (TMs) to understand how the composition of minerals at the Earth’s surface might have changed over billions of years. These elements can be especially sensitive to their chemical environment, and so the TM content of ancient rocks tells us what things were like chemically as the rocks were formed.
A particularly interesting result emerged from Gaschnig’s work: the TM signatures he’s measured for some ancient rocks show evidence for initially low levels of oxygen immediately following the beginning of the Great Oxygenation Event (GOE), the phase in Earth’s history when ancient cyanobacteria became so prominent that they produced vast quantities of oxygen.
All this oxygen dramatically affected the chemical environment on the Earth, and its relatively sudden appearance in the atmosphere is reflected the mineralogy of some rocks, such as the banded iron formations shown at the right. Of course, without oxygen, most life as we know it would be impossible, but when it first appeared, the oxygen probably devastated the biosphere.
Some of Gaschnig’s rock samples dated to before and after the GOE show chemical changes in the TM content that may be consistent with the presence of oxygen but only at low levels (at least immediately after the GOE began) and so can be used to fill in some of the missing details about this dramatic chapter in Earth’s history.
Figures from Kreidberg et al. (2014). The top panel is an image of the Hubble Telescope CCD as it collected photons of many colors passing through GJ 1214 b’s atmosphere. The bottom panel shows the infrared spectra that results from analysis of that image, showing no molecular features.
The year starts with a spectacular result from Laura Kreidberg and colleagues: the super-Earth exoplanet GJ 1214 b has high altitude clouds in its atmosphere.
The image at left shows observations from the Hubble Space Telescope. These data were collected as the planet GJ 1214 b passed in front of (transited) its host star. When that happens, light emitted by the host star passes through the planet’s atmosphere, and the atmosphere can imprint a spectral signature on that light, telling us what it’s made of.
But for GJ 1214 b, as shown by the bottom at left, there were NO spectral signatures — the spectrum is completely flat. The most likely explanation is that the planet has clouds high in its atmosphere that block the star light from passing through the part of the atmosphere where spectral signatures would be imprinted.
To make such a flat spectrum, GJ 1214 b’s clouds have to be very high in its atmosphere. Kreidberg and colleagues estimate the cloud deck can’t be lower than about 1 millibar in pressure. On the Earth, cirrus clouds, some of the highest clouds, live at pressures of about 300 millibars or 10 km in altitude. Earth’s atmospheric pressure doesn’t drop to 1 millibar until an altitude of about 70 km, above a height where meteors typically burn up. So GJ 1214 b’s clouds are very unusual.