Jonathan Brande
Aerosols and Sub-Neptune Diversity

Cool. Good morning, everybody.
I'm Yoni Brandi.
I'm a fifth year PhD candidate at the University of Kansas, and I've been working with Ian Crossfield on observations and models of X-Men atmospheres, and I'd like to take some time today to talk a little bit about some of the work we've been doing with Sub Neptune ex.
Planets in their atmospheric aerosols.
OK, so unlike the planets in our solar system, the most common exoplanets in the Galaxy are larger than Earth, but smaller than Uranus and Neptune.
And while we can directly study planetary environments here at home, we have no such luck with exoplanets, and so the quality of our exoplanet data is significantly lower than in situ measurements in the solar system. But we know of nearly 6000 exoplanets out there, and only 8.
Planets in the solar system.
So we sort of win in a statistical sense.
So we know that exoplanets have all sorts of bulk properties, mass radius, equilibrium temperature, and we found strong evidence for a wide range of atmospheric, atmospheric and interior compositions.
And so we've had wild success in sort of my estimation observing planetary atmospheres with facilities like Hubble and JWST.
But often we are blocked from identifying some of the specific compositions of those atmospheres.
By things like high altitude clouds and hazes, which I'm going to collectively refer to as aerosols in this talk.
So early on, a number of groups knew that this was a problem and tried to examine them at a population level. We had very few.
Hubble Spectra at first, and so early attempts had to try and merge together physically dissimilar planets to try and squeeze out some statistical power here.
But usually what you do here is you measure the strength of the 1.4 Micron.
Water vapour absorption feature in Hubble's with C3 bands simply because it's the strongest molecular absorber that we can see with Hubble.
Later, hot Jupiter data is sort of sufficient to actually apply physical cloud models, but to 1st order. If you just sort of get the strength of this feature in terms of atmospheric scale heights, that gives you a nice intercomparable metric on how clear the atmosphere is.
So later work by Ian Crossfield and Laura Cdburger used a handful of set Neptune Spectra in in a in a consistent sample to show that sub Neptunes as a group appear to have a a temperature dependent clarity trend with hotter planets.
Stronger water absorption and thus clearer atmospheres and cooler planets having weak features, and thus the inferences that they have more aerosols. And so my work throughout my PhD has been to expand on these analysis and incorporate new models to try and actually measure the properties of these these.
Aerosols and so to do this, we conducted a survey of new sub Neptune observations extending over 125 Hubble orbits.
And combined that with archival observations of other XN Neptune atmospheres to assemble a sample of 50 HST Spectra spanning about 800 Kelvin.
Using these archival Spectra, I ran a series of restricted atmospheric retrievals fitting for water vapour and cloud presence and things like that.
And then I use the best fit model Spectra to sort of back out the clarity metrics.
And so if you zoom in on this population plot, we might notice a couple of interesting things.
First, the hottest planets in our sample and the coolest planets in our sample both have the strongest atmospheric features. But the planets with middling equilibrium temperatures are all pretty flat.
And so the classical theoretical picture goes something like this in gas dominated planets, intermediate temperatures from 5 to 800 Kelvin.
Are especially efficient for photochemical haze formation. If you go hotter than this, the haze is dissociate and if you go cooler than this haze formation is suppressed and or clouds rain out and then both cases there lead to clear transmission Spectra where you can see molecular absorption we.
Weren't really in a position to physically model this process, but we did borrow a grid of atmospheric models of JIG 14B from Caroline Morley across a pretty wide range of physical parameters, modeling both clouds and hazes. As it turns out, the cloud models fit best.
Even though theoretically, maybe the hazes were were were a better choice.
But here on this plot you can sort of see how the contours show the behaviour of our best fit aerosol models and their sedimentation efficiencies and metallicities and things like that and higher sedimentation yields, more compressed clouds and clearer atmospheres and lower sedimentation as more vertically extended cloud.
And more attenuation.
So that's all nice, but there's a couple of issues with this given that we have some new JWST data.
So K218B and two I270D or two temperate exoplanets you might be familiar with.
They have clear atmospheres, but recent JWST observations indicate that maybe there are other physical processes at play here.
So K218B appears to be a typical sub Neptune with a hydrogen and helium dominated envelope significant methane absorption rather than water as as initially thought from the Hubble data and then some relatively unconstrained cloud presence.
TI-270D, on the other hand, appears to have methane and CO2 and water, but probably has a much higher.
Metalistic atmosphere overall and so has a much.
Stronger. Much larger molecular weight, deeper in its interior.
And so this implies that potentially it's it's made-up of like mixed supercritical hydrogen and water vapor and so for any given planet, if you have such a drastic increase in mean molecular weight, this could significantly reduce some of the atmospheric features you're trying to look for. So.
To move past some of the limitations of older model grids in in sort of our high precision data era.
I've been working with collaborators like Peter Gauda.
Try and update our hazards models for the Jwts Tierra and so tentatively. We're titling this code.
Which is going to be a modernized, streamlined, user friendly implementation of the Karma code, just focusing on Hay's coagulation and particle transport.
And hopefully we'll be able to speed this up to the point where we can plug it into retrievals and actually directly measure physical haze parameters in a way that that, you know, gives us the ability to move past sort of the the large model grid era. So this.
Is.
In the works, we're still working on it. Stay tuned. Sorry.
And to closeout, I'd like to take just a couple of minutes to talk about some recent observations. I've been working on and how they extend on some of the other parts of my PhD work.
Most of the sub Neptunes we studied are less than 1000 Kelvin or so, but we do know of a couple of really hot ones.
So you might be familiar with a plot like this, showing the Neptune Desert, which is an observational lack of really hot Neptune sized planets.
Usually they're much bigger or much smaller than that.
And so where do they come from?
We know that this is not a.
This is this is a real physical lack of planets.
This is not a statistical artifact.
What kinds of processes are going on to make these planets lose their atmospheres?
So as a little bit of a case study, we're going to talk about the the hot Neptune LTT 9779-B.
So it's already had transmission Spectra taken of it with nearest they look pretty flat.
So Michael Radiant and his collaborators weren't able to determine whether this is because of aerosols or because of high metalicity.
They didn't find any specific molecular absorber.
Evidence. But we took a look at this.
We took a look at a full phase curve of this planet.
And so my early analysis of the emission Spectra show evidence for strong evidence for for CO2 and tentative evidence for water, implying that this has a a fairly high metallicity and some, at least in my in my early retrieval, some unconstraint.
See the O ratio.
The rest of this data is also being worked on, so keep an eye out for that.
And there's also some.
Some other data from Lou Foulep Coulomb on the nearest emission Spectra of this target, but as of now we don't have any other hot Neptune emission Spectra.
So this is really exciting. If I put this planet in context, it might be a bit of an outlier in metallicity space, but it seems to follow previously identified mass medium trends, assuming it maintains much of its initial atmosphere, which is not at all guaranteed given its strong.
Irradiation.
Potentially.
It could have, you know, some solar like C2O ratio.
It could be much lower, but we have no good evidence on absorbers other than carbon dioxide in its atmosphere and sort of definitional A/C. O2 has a cetera ratio of 1/2, so that's not all that informative, but we do need a better understanding of of this.
Planet's atmosphere with with more, more data that we're still working on to properly infer its formation history and and understand where it came from.
I think I'm a little short for time, so I'm going to leave my conclusions up.
But data is Oh no.
Yeah, data is great.
We can statistically identify trends using both Hubble and Jdst in these sub neptunes, and if you'd like to see more of this, I'm on the job market and I would love to be supported to do more of this work.
So thank you.
Thank you so much Yoni.
We have time for one quick question.
In the.
In the upper right hand corner of your final graph, the two carbon rich objects.
What? What are their masses or radii and what kind of stars are they orbiting?
That's a good question.
I pulled this plot out of a review by Eliza Kempton, and I didn't.
I didn't.
You know closely.
Look at all the individual little points on that.
So yeah, I'm sorry about that.
Let's thank the speaker one more time. Thank you.