Aaaand…we’re back! After our scintillating lunch discussion, we’re back in the ballroom for our next wave of science talks. This is our second of two sessions on Planetary Atmospheres, chaired by Cornell University Research Associate Ramses Ramirez.
The Pale Orange Dot: The Climactic and Spectral Effects of Haze in Archaen Earth’s Atmosphere (Giada Arney, University of Washington)
Giada is from the University of Washington Astronomy and Astrobiology Program. While we want to know about the habitability of distant exoplanet, Earth will always be the best-studied habitable planet. So, we want to study the habitability of Earth throughout its history. She studies the Earth through the Archean period. During this period (~3.8-3.5 billion years ago), life first developed. We had a lot of methanotrophes (methane-eating bacteria), which were prolific because methane was much more abundant than oxygen in the atmosphere. We can look at Saturn’s moon, Titan, to get a modern-day example of a methane-rich atmosphere. We think that the Archean Earth had an orange atmosphere with a methane haze, like Titan does. Since we think that the Earth at one point was hazy, this is a good phenomenon to study to understand potentially habitable worlds.
What would the climate be like on a hazy Earth-like world? As you increase the amount of methane in the atmosphere, you are increasing the methane haze. At around 30% methane the haze starts to cool the planet by shielding the sunlight, but at some point the cooling bottoms out. Conclusion: hazy worlds can be habitable. In the right conditions, it can work like a reverse greenhouse effect, cooling the planet to make it habitable.
How can we detect hazy atmospheres? Methane haze absorbs a lot of light in blue wavelengths, so objects that are missing portions of blue light in their reflection spectra are likely to be hazy. For transit transmission spectra, when you add haze into the atmosphere you can’t see as deeply into the atmosphere, so your characteristic absorption features are more muted than normal. The spectrum at the ground of a hazy planet shows that the majority of the harmful UV light is blocked, so a hazy planet might have a greater chance at habitability, since the harmful types of light are reduced. As the haze on the early Earth was biologically produced and regulated, they might even be a signature of life.
The robustness of using near-UV observations to detect and study exoplanet magnetic fields (Jake Turner, UVA)
The magnetic fields of planets give us insight into the internal structures and rotation period of exoplanets, atmospheric dynamics, formation and evolution of exoplanets, potential exomoons, habitability, and allow us to compare to solar system objects. Their method involved detecting asymmetries in the near-UV and infrared light curves. In the near-UV, you can detect the bow shock in front of the planet, like a boat going through water. This light curve should have an extended ingress and a shortened egress.
They used the Kuiper Telescope in the near-UV on 15 targets looking for exoplanet magnetic fields. On WASP-77b, they note that the transit does not look like their predicted bow-shocked magnetic field. In their 15 planets, they did not see any asymmetric transit shapes, which puts an upper limit on the potential magnetic fields of those planets. So, either those magnetic fields are really small, or perhaps this effect is not observable using that particular telescope or in that particular wavelength.
They use CLOUDY to simulate the ionization, chemical, and thermal states of the bow shock to see what the simulations say about their ability to detect the asymmetry. They find that with this, there are no species in the near-UV to cause an asymmetric transit, so their non-detections are due to their observing parameters, not a physical property of the planets. They find that near-UV transits are not robust for detecting magnetic fields, and near-UV planetary radii show variations that can be used to constrain their atmospheres.
Characterizing Transiting Exoplanet Atmospheres with Gemini/GMOS: First Results (Catherine Huitson, University of Colorado)
Main aims of Gemini/GMOS is to measure the dominant atmospheric absorbers in exoplanet atmospheres. They have broad-band, low resolution optical coverage. Their 9 planet sample has low densities and good comparison star, is comparative study , and want to understand the systematic noise sources. The survey length is 3 years, which lets them improve signal/noise and increase repeatability. With GMOS, they can get similar precision to HST, but with fewer gaps in the data which allows for better fitting of the transit curve and more accurate planetary and stellar parameters.
MOS = Multi-object spectroscopy. The two spectra are the target and the reference star of the same spectral type, so that they can compare the two stars one wavelength at a time. They get a frame every 50 seconds to build a transit light curve, and as they go wavelength-by-wavelength they can see changes in the transit light curves with wavelength, and so build a transmission spectrum. Using this method they find that WASP-4b is a cloud dominated hot Jupiter.
There are a number of observational challenges that they face during their analysis, and they are finding clever ways of solving each and every problem that arises. They can find through this method that XO-2b is a cloud-free hot Jupiter. Their first important results is that while WASP-4b and XO-2b are very similar planets in some respects, they have very different atmospheric structures, and they can detect that.
Hot and Heavy: Transiting Brown Dwarfs (Thomas Beatty, PSU)
Interesting presentation technique: start with your conclusions!
Conclusion 1: The brown dwarf desert may have an oasis.
Conclusion 2: transiting brown dwarfs provide links between hot Jupiters and field brown dwarfs, allowing us to use observations of one to understand the other (KELT-1b in particular)
Our understanding of the brown dwarf desert has evolved over the past 10 years or. As of last year, we have found 7 BD companions in this region, all around F stars (~6250 K) which are more rapidly rotating than the Sun. KELT, unlike other transiting surveys, don’t ignore F stars, which have sort of been ignored before because RV detections are difficult. But now we see that F stars may have an oasis in the BD desert.
The atmospheres of planets and dwarfs behave differently. There’s a very distinct “kink” in the color-magnitude diagram of BDs at the L/T transition (where methane becomes dominant) that doesn’t exist for planets of the same temperature. BDs have a very tight color-temperature sequence, and HJs are much more scattered. The different behavior tells us how the atmospheres are behaving, particularly with regards to carbon monoxide and methane. People postulate that the methane of HJs shouldn’t be there, because the species is highly irradiated by the star, which it wouldn’t be for BDs.
Well…KELT-1b is a highly irradiated BD in a tight orbit around its primary star. The day side of KELT-1b looks just like a field BD, a late-M or early L dwarf. They want to look at the night side of the BD to see if there’s some chemical gradient between the day and night sides. If so…well, that would be very interesting indeed and tell us about the L/T transition for irradiated BDs, and how that impacts HJs and directly imaged planets.
We now move on to the first of our poster-pop sessions. I will do my best to capture some of the dos and don’t of how to give a poster pop once I have some examples of them to work with!