Brian Jackson

Good talk today from one of our own, Dr. Jackie Faherty, a Hubble fellow here at Carnegie.

Artist’s impression of the disc of dust and gas around a brown dwarf. From http://en.wikipedia.org/wiki/File:Artist%E2%80%99s_impression_of_the_disc_of_dust_and_gas_around_a_brown_dwarf.jpg.

Faherty talked about brown dwarfs (BD), a relatively new class of astronomical object that straddles the border between planets and stars. Brown dwarfs typically have masses between 13 and 75 times that mass of Jupiter and are made mostly of hydrogen gas, with lots of complex and interesting molecules mixed into their atmospheres.

Faherty studies the motion and distances of BDs using an age-old technique called parallax determination. It is very important to accurately estimate the distance for a BD because combining that estimate with measurements of a BD’s brightness and temperature gives a sense of the BD’s age — critical for understanding how BDs evolve over time.

BDs exhibit a bewildering variety of compositions and evolutionary behavior — some have variable clouds and weather — and the field is moving very rapidly. For example, astronomer Ian Crossfield just this year produced the first image of a BD’s atmosphere. And, in her talk, Faherty highlighted important similarities and differences between BDs and gas giant planets and showed how they may help unravel the mysteries of planet formation.

Great talk from Ronni Grapenthin of UC Berkeley’s Seismology Lab. Dr. Grapenthin discussed how he uses high-precision and high data-rate GPS measurements to link the motions of the Earth’s crust to geophysical processes, including earthquakes and volcanic eruptions.

One of the neatest things he showed was a video of GPS displacements during the huge Tōhoku earthquake in Japan three years ago (above). The left panel shows lateral displacement (the largest arrows reflect only a few meters of displacement, not hundreds of kilometers, as it may seem), while the right panel shows vertical displacement. The waves associated with the earthquake and an aftershock are shown pretty dramatically, as they propagate through the Earth’s surface away from the earthquake source.

In the near-term, Grapenthin is helping to develop an early warning system for earthquakes in California using these kind of GPS data, which could help save many lives.

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.