Awards and Masursky Lecture: Dr. Robert Pepin

It’s 1:30pm Monday and we’re settling into our first LPSC plenary session: The Masursky Lecture. Prior to the lecture they are handing out a series of awards, including an early career achievement award that goes to 6 students who have shown outstanding progress in their career in planetary science. This meeting is actually 30% student attendees, and these awards help pay for 6 of the best to come here and present. In introducing this award they noted their were many strong applications from many students with extensive publications and research. This years 6 awardees were all women. Unfortunately, their names are not listed on an overhead or in the conference book. If I can find them written down somewhere, I’ll add them into this entry.

The atmosphere of this awards ceremony is very damp. I mean that quite literally. The announcements are not only being punctuated by our applause, but also by spectacular thunder. There is an amazing downpour going on outside, and my suit jacket is hanging on a chair drying out. In about 50 feet it got soaked through. It was amusing to see several of us adults with students and rental cars dropping our students off at the door and then making made dashes across the parking lot to get to the building. All I could tell Rebecca as we watched the downpour was “Welcome to Texas.” (The rain drops were actually bouncing.)

They are now listing all the amazing achievements of Dr. Robert Pepin, the Masursky prize winner. He is the author of several books and over 150 papers. He sits on many committees and leads many large projects. His work focuses on, well, astronomical dust. It doesn’t sound interesting to most, but dust is at the heart of star and planetary formation.

Through careful astronomical observations of dust in clouds, astronomers have been able to figure out the structure of interstellar dust. These grains have an silicate core surrounded by organic materials. These grainy structures come in many shapes. (One looks, in his words, like a Mandorbort turtle). These grainy structures are amorphous and are seeded by materials from stars. This is material like the stuff being actively pulled off of the star Mira.

From spectra and polarimetry astronomers have studied this dust at a distance - observing it in clouds like the Bok Globules. Planetary scientists like Pepin are able to study these grains more directly. He studies the grains that have been trapped within meteors and captured in aerogel as from comets.

The StarDust Aerogel dust-capture program provided astronomers their first chance to examine in a laboratory material from the solar system that is basically in its raw form. The aerogel

The dust they are finding appears to have formed in high temperature environoments - enevironments the comet could not have endured! - implying these chrystalline grains come somewhere else. The composition of the grains appears completely average for our solar system, implying they are native and not something that came from beyond our solar system. This is direct evidence that comets are filled with stellar silicate dusts that have mixed back into the galaxy.

Comets aren’t the only place we’re finding this type of dust. In asteroids (which we observe in laboratories after they’ve opted to become meteors), dust grains are also seen. These are considered some of the first forming (condensing) materials in the solar system. We judge their age by looking at isotope ratios (the ratio of atoms with 1 number of neutrons to atoms with a different number of neutrons - in this case the oxygen isotopes). What is amazing is the same types of grains are being found in comets and in inclusions in asteroids.

What’s funny is some jeweler somewhere made slices of a meteor into pendents and the pendents have inclusions (called condules) with dust grains in them. For just $45.95 you can order one of these pendents (from an unlisted site) and where something older than the Earth around your neck. The speaker is saying that Salvador Dali asked a scientist he knew to brings a selection of these condules  to his private railroad car so he could commune with the ancient energy in the condule. Oh my!

In addition to silicates and organics, they are also finding noble gases - gases that prefer not to bond with things - trapped in the grains.

By studying all these grains that are embedded in such different objects as comets and asteroids, it is possible to start to piece together a more detailed model of how our solar systems early solar nebula mixed particles. In the early nebula magnetic field lines tangling and untangling themselves in a process call magnetic reconnection may have sent huge amounts of energy fluxing through the solar system. This large energy surge could have lofted chunks of gas and dust out of the solar nebula. This flung material would then have gravitationally rained back into the solar system with material falling back into the disk at distances like that of Neptune or larger. This would effectively mix material through out the solar system, allowing forming asteroids and comets to both contain identical grains.

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