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Cosmic Matters

When you set out to build a state-of-the art spectrometer for the Keck Observatory, you specify a handful of astronomically compelling science cases: high redshift observations of distant galaxies, surveys of young stellar clusters, confirming brown dwarf candidates. You gotta love the classics. In addition, there is a line that says something to the effect that the new instrument will open up new areas of astronomical research not yet dreamed about. Inspiring, and hopefully it sways a few proposal reviewers.

Being on the front-lines of astronomy means that in the evenings you will see me equipped with a Mac laptop monitoring weather conditions, an adaptive optics class commemorative mug filled with Seattle’s Market Spice black tea, and my trusted TI-81 calculator, practically an antique. It also means that while I am training people from all over the world how to effectively and efficiently operate the Keck Observatory’s newest instrument called MOSFIRE, I am privy to some of the most exciting and groundbreaking science. And — whoa! — acquiring spectra of planets was not one of MOSFIRE’s aforementioned stated science cases.

MOSFIRE is a very sensitive infrared spectrograph equipped with two technological advances: a very sensitive infrared detector with revolutionary readout electronics, and a cryogenic slitmask unit (CSU) which is a combination Swiss built extra large army knife operating with watch-like precision. The CSU has 46 pairs of bars that are positioned to an accuracy of less than half the width of a human hair. The bars’ purpose is to isolate the light from objects of interest by forming a slit and block the light from other objects in the sky that would otherwise contaminate the data. Most infrared spectrographs have only one set of stationary bars to form a slit and could therefore get one to two objects at a time. So MOSFIRE’a primary use is to gather data on a large sample of objects that, until recently, would have required weeks or months to observe.

But a few teams are employing unique observing strategies with MOSFIRE with the ambitions goal of detecting compounds like methane, carbon dioxide, and water in the atmosphere of a planet orbiting another star; signs of possible life. The teams measure differences in the light detected before and after a planet moves behind its parent star as the light from the planet blinks off. The primary problem with these observations is that Earth’s atmosphere is highly variable and contributes significantly to the noise of infrared light detected by MOSFIRE. The other big stumbling block is that a planet is a very faint relative to the star it orbits.

So this is where the combination of Keck Observatory, MOSFIRE, and pure genius come in. The largest telescopes can see the faintest objects, so Keck is a natural fit. The observers then deploy one extra wide slit (15 times the typical size) to ensure they get all the light from the star and orbiting planet. Then those geniuses deploy the rest of the bars to nearby stars to simultaneously monitor and correct for Earth’s atmospheric variations.

Yet the teams are still experimenting and converging on their observing strategies. Different telescope offsetting patterns, integration times, and detector readout schemes are being tried. Having never imagined anyone taking data so quickly, my palm is sweaty with an overheating Ti-81, calculating at 3 a.m. how quickly the observers will fill the data disk, and yes, I have submitted a request for more disk space. Those pesky geniuses.

For the past couple of decades, there has been an avalanche of exoplanet observations, and the Keck Observatory has been at the frontier characterizing hundreds of planets. Astronomers have even acquired images of planets (an initially un-imagined use of the Keck adaptive optics system). With the newly commissioned MOSFIRE, Keck again remains at the forefront of exoplanet research, getting us one step closer to answering whether life could exists around a nearby star. I have confidence in these observing teams and I hope I am supporting them and their previous unimagined usage of MOSFIRE when an exoplanet’s atmosphere is revealed.