Making exoplanet news right here at Astronomy

Posted by Korey Haynes
on Friday, June 12, 2015

My co-authors and I found a stratosphere on WASP-33 b, a layer that gets hotter with altitude, instead of cooler. // NASA/Goddard
Most days, I get to report about other scientists’ discoveries. But today, I’ll toot my own horn a bit.

I’ve been here at Astronomy for six months now. But before that, I was a graduate student researching exoplanets, worlds beyond our solar system. And not just any worlds, but the massive planets called hot Jupiters, orbiting extremely close to their stars and heated to thousands of degrees. Specifically, I looked at their atmospheres, hoping to see water in enough detail that I could say something about the temperature, composition, and structure of these gas giants’ outer layers. And for the last paper I conducted as a researcher, I found something pretty cool: One of my planets, WASP-33 b, has a stratosphere, a layer that gets hotter as you go up in altitude, instead of cooler.

Earth has such a stratosphere thanks to the ozone layer, but ozone has no hope of existing in my super-hot Jupiter. So what causes the stratosphere on my planet? Astronomers long before me theorized it could be a substance called titanium oxide, and my team and I found signs for that, too. Double win!

You can read more details about my findings over on our News page. But for this blog, I thought I’d tell you more about what the discovery means to me, both personally and in the context of the ongoing scientific process.

As I mentioned, this was my last paper as a researcher. I defended my thesis right before I came to Astronomy, but publishing a paper — making corrections, catching every last typo, double- and triple-checking all your citations, explaining every last step to your editor and co-authors’ satisfaction — takes quite a while. So, six months after I left my university and NASA center near D.C. (where I conducted the research) and moved to Milwaukee, I finally get to see my paper’s final form. It feels good to fully wrap up such an important stage of my life.

And it’s nice to feel so solid about our results. The struggle of science is proving something new. And that’s very difficult. So, perhaps not surprisingly, my first paper on this subject found somewhat inconclusive results (my contribution was analyzing three of the five hot Jupiters in that study). We successfully observed water vapor but also found hazes that made it difficult to say with certainty exactly what those atmospheres looked like in terms of their detailed composition or structure. We could rule out a few things, but there were a lot of options left open.

And I wasn’t alone. Quite a few scientists have looked at various hot Jupiters and thought they’d found these stratospheres, only to have subsequent studies disagree. In most past cases, both sides were basing their results on what we call photometric, instead of spectroscopic, information (if photometric data tells you whether a planet is red or yellow, spectroscopic data tells you whether it’s rust red, crimson, scarlet, puce, vermillion, carmine … you get the picture). And while photometric data can tell you whether a planet has a stratosphere or not, you need the spectral data to tell you what’s causing it. It’s only in the past few years that instruments like Hubble’s Wide Field Planetary Camera 3 could provide this spectral information.

In my last paper, I could do both. I could prove the existence of my planet’s stratosphere, and I could point to part of the spectrum where the atmosphere absorbed a very particular color, revealing the substance responsible.

Of course, I didn’t do this alone. Another scientist named Drake Deming was the one who selected this planet, WASP-33 b, to observe with Hubble. This is to say I didn’t just get lucky; Drake and others knew from prior studies that WASP-33 b was a very good bet to find these results, and they made their case to the reviewers and TAC (telescope allocation committee) that decides which projects get the invaluable Hubble time.

I did the bulk of data reduction and analysis. This is the long, painstaking process of getting more or less raw data from Hubble and the folks at the Space Telescope Science Institute, who run Hubble, and turning it into usable information. You have to understand every little quirk of the instrument (and there are a few), find every time a cosmic ray lit up your detector, account for every nonresponsive pixel. It’s a long haul.

Once I had my final product, there still wasn’t a lot it told me. These days, I can tell you some rough information from staring at a spectrum, but to report anything useful, I had to hand the data over to our modeler, Nikku Madhusudhan. Madhu compared my data to tens of thousands of models, some very similar to one another, some wildly different. The model that is closest to my data wins, and he can then explain what kind of model it is — our stratospheric model, in this case.

And of course my adviser, Avi Mandell, was there every step of the way, guiding my work and asking a million questions and suggesting new avenues of inquiry. Heather Knutson, the last member of our team, contributed key suggestions and pointed our way forward. And Drake’s contributions didn’t end with his proposal; he and I traded data products at every stage to check our methods.

Science is collaborative in so many ways. Far beyond my co-authors, this work rests heavily on the work other astronomers did before me, and my results are only one brick in the infinite road of exoplanet science we’re still building. It’s work that has no end. But for me, I get to kick back and watch a movie NASA made just for my paper. Not bad for a few years’ work.

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