Evaporating Planets and Exoplanet Interiors with JWST

I’m pleased to announce three out-of-cycle opportunities to work with Penn State astronomers — including me! — through the NASA Nexus for Exoplanet System Science.  This cross-disciplinary research network is soliciting applications due July 1 for Nasa Postdoctoral Program fellows to come to Penn State to work on projects that cross disciplines and NExSS teams.  I’ll describe the two with me in these blog posts; the third is to work with Eric Ford on the statistical properties of exoplanets (read the ad!)

Before you apply, please contact us so that we can help you craft a winning proposal.


Below is the first opportunity.  I blogged about the second one here.

Evaporating Planets and Exoplanet Interiors with JWST.

We don’t really know what the interior of rocky planets are like. Even the Earth’s interior is mysterious: we can’t really go down and sample it, and there are big arguments about whether the samples we get from volcanoes are representative.  As a result, we don’t really know whether the mantle well-mixed, and we don’t know the water content of the Earth’s interior to an order of magnitude!

But these questions matter: the origin of Earth’s volatile budget and its plate tectonics are both highly uncertain and key components of the story of its habitability.  We need to know answers to these questions about exoplanets, but that seems pretty unlikely considering we can’t even agree on the answer for Earth, for which we will always have much more information than distant exoplanets.

Artist’s impression of a planet helpfully preparing a representative, backlit sample of its interior for study by astronomers.

Enter Kepler.

Among the new classes of exoplanets discovered by Kepler, KIC 12557548 represents the prototype of one that has particularly caught my eye: “evaporating” planets, a subset of “ultra-short period” planets (with periods less that 1 day).

These planets show highly asymmetric light curves, typically orbit M or K dwarfs, and are apparently rocky planets (or their leftover metallic cores) being ablated or evaporated by the intense instellation of their host star.  This process is, in some cases, stochastic, giving rise not just to asymmetric transits but extremely variable depths:

Transits of KIC 12557548, from Fig. 2 of Rappaport et al. 2012

Transits of KIC 12557548 b, from Fig. 2 of Rappaport et al. 2012

KIC 12557548 is not alone.  At least three other similar planets have been detected, including K2-22 which is in many ways much easier to study.  Here, we have what appears to be representative samples of the interiors of exoplanet being spewed into space right where we can study them with spectrographs.

Can we do mineralogy of these materials? Can we study the hydration levels of the rock? Can we compute the volatile inventory of these planets’ mantles? Were these planets once habitable? Are these in fact the metallic cores of once-rocky planets, meaning that they likely once had magnetic fields?

Steve Desch introduces us to lots of exoplanets

Steve Desch introduces us to lots of exoplanets

I don’t know, but I’m dying to find out. Before he left for industry, PSU research associate Ming Zhao laid the groundwork for this study in coordination with Steve Desch’s NExSS group at ASU.  Steve’s group has been thinking hard about the infrared spectroscopic signatures of the minerals of these planets, and what they can tell us about the planet formation process, these planets’ past potential for habitability, and planet formation generally.

Neal Turner, another NExSS PI, has also been thinking about these effluents’ properties, their interaciton with their host star’s magnetic fields and winds, and, very importantly, how they might be affected by the intense instellation they receive.

Are you an emerging researcher in astrophysics or planetary science interested by this problem? Please consider applying to our NPP opportunity by July 1.  The arrangement we have in mind is that you will work at Penn State with me primarily, co-advised by Steve (including trips to ASU to work on the planetary science side) and Neal (ditto for JPL and the stellar effects side).

If you are going to do this, please get in touch with us directly so that we can help you craft a competitive proposal to NASA.

I hope to see you soon at Penn State!



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