Next Friday 8/15 is the deadline to endorse #HabitableWorldsObservatory science cases. If you think it is important to consider whether a planet has the right geology in place to host life as we know it _before_ looking for life there, please endorse our case: bit.ly/GeochemHab_endorse #HWO25
(3/n) #HWO25 speakers, esp on 1st day, not only engaged the mind, but spoke to the soul, reminding us of the wonder & purpose that lie at the heart of our work to understand the universe, the origin of galaxies and elements, and the place of humanity in the cosmos✨🔭🧪 www.youtube.com/live/V_rPlVR...
(2/n) #HWO25 talks on STScI Research YouTube Channel🔭🧪☄️ #exoplanets #extragalactic www.youtube.com/playlist?lis...
My favourite exchange from #HWO25:
@nataliehinkel.bsky.social: That dress looks great on you!
Me, sighs: I know.
@nataliehinkel.bsky.social, laughing: Oh, okay!
Me: Oh, I'm just regretting not wearing it YESTERDAY when I gave my talk.
what a week for our future✨ #HWO25
🧵coming soon🔭🧪☄️
@mmacgreg.bsky.social @hbhammel.bsky.social @bmacastro.bsky.social @dawngelino.bsky.social
@aussiastronomer.bsky.social @stsci.edu @aura-astronomy.bsky.social @justtheletteru.bsky.social @vividreams.bsky.social @leefeinberg.bsky.social +500 others
That's a wrap folks, #HWO25 is done! In 20 years I'll be posting on whatever social media platform then exists about Earthlike planet detections and maybe even signs of life 👀
Gupta: warmer planet T-p profiles lie completely in the miscible region. As a planet cools, eventually it will intersect the critical curve, and condensate clouds will emerge. Later there is deep 'rainfall' inside the planet, leading to water deep in the interior. TOI-270d too hot for this! #HWO25
Gupta: these simulations can help determine the critical curve defining the regions of pressure-temperature space where water is miscible in all proportions, and regions where hydrogen and water are only partially miscible. Uranus and Neptune have T-p profiles strikingly close to this curve. #HWO25
Gupta: insights into atmosphere-interior interactions are critical for interpreting HWO data. Lab experiments at relevant conditions are very hard though! Quantum mechanical methods (ab initio molecular dynamics) can help us understand interactions between hydrogen and water. #HWO25
Now our final talk, by Akash Gupta on the story of hydrogen and water - new insights into the interaction of planet atmospheres and interiors. Planet formation entails interaction of hydrogen envelope with interior - are these important? Yes - likely impact structure and thermal evolution #HWO25
Gialluca: however, there are big errors on estimated crater size with impactor energy. We need to do much more impact testing to understand this better. We therefore don't want a ~25 planet sample, this might end up being reduced by 50%, so we need contingency/conservative sample sizes #HWO25
Gialluca: in general impactors only start affecting yield if the energy is greater than 0.2 J. For a ~26J impactor similar to the JWST C3 impactor, this could result in a ~30% reduction in yield. #HWO25
Having a telescope barrel reduces stray light in two ways, it minimises the risk of impacts and minimises incident stray light from background sources. For high energy impactors, the background source improvement isn't that great, but it does protect against impacts happening in the 1st place #HWO25
Gialluca: this work provides order of magnitude estimates of stray light from these rare, high energy impact events. Two models exist for predicting crater size for a given impact - give different answers, so we have an optimistic to pessimistic range of possible sizes. #HWO25
Now we have Megan Gialluca on assessing the impact of stray light due to micrometeoroid damage. Micrometeoroid damage is unavoidable for space missions. JWST has seen a rate of a couple per month, consistent with pre-launch expectations - excepting the high energy event on the C3 mirror #HWO25
Wolff: shorter correlated noise lengthscales produce the widest posteriors, and shortest lengthscales match the width of absorption lines. E.g. oxygen posteriors can be biased here. PSF chromaticity produces correlated noise at these length scales. This will be a limiting noise source for HWO #HWO25
Wolff: speckle noise can be modelled using Gaussian processes, simply specified by an amplitude and length scale. Failing to model correlated noise in retrievals biases and artificially narrows posteriors. Most retrieval studies for HWO trade space do not yet account for speckle noise. #HWO25
Now we have Nicole Wolff talking about impacts of correlated noise on retrievals of exo-Earth atmospheres. Direct images contain chromatic speckles that move radially outward with wavelength. They are a source of spectrally correlated noise coupling adjacent wavelength bins. #HWO25
Stuber: hot exozodi could reduce HWO's performance drastically, but we don't know much detail about it yet. So every estimate of yield is highly uncertain and subject to this! #HWO25
Next we have Thomas Stuber, talking about hot exozodiacal dust and its effect on HWO's performance. Debris disks are circumstellar discs, gas poor, optically thin, composed of dust fragments left over from planetesimal fragmentation. Hot dust resides within ~1 au of the star, seen in near-IR #HWO25
Brugman: if magma on an exoplanet can't erupt then plate tectonics are suppressed, there is no crust recycling or volatile release, bioessential element recycling is restricted - planet is less likely to be habitable. #HWO25
Brugman: experimental petrology involves making exoplanet magma in the lab! Tests include looking at hydrogen solubility in magma ocean and phosphorus solubility in lava. Considering geochemical habitability is also really important - are surface conditions right for hosting life? #HWO25
Now we have Kara Brugman talking about goechemical habitability. Volcanoes are a crust factory for planets and also a mechanism for transporting volatiles from the interior to the surface and therefore atmosphere. Geochemical context is therefore critical for interpreting biosignatures. #HWO25
Barstow: to do this, we need high spectral resolution to observe individual lines (~100,000). We also need a large sample. Polluted white dwarfs can be a statistical probe of dry vs wet planets. Need around 150 stars observed to pin this down. Sulphur vs silicon-rich cores needs ~50 stars. #HWO25
Barstow: white dwarfs have strong gravity, so their spectra should be hydrogen and helium. Planetary matter in the atmosphere is a transient phenomenon. UV spectroscopy is key for many species, ELT-class telescopes on the ground will only probe O, Si, Fe and Mg. HWO needed for large samples. #HWO25
Barstow: white dwarfs are also probes of matter under extreme conditions - a large enough sample could lead to better constraints on fundamental physics parameters such as the fine structure constant. #HWO25
Now we have Martin Barstow, taking the opportunity to embarrass me slightly (parental prerogative I suppose?) before going on to talk about white dwarfs as probes of exoplanet compositions. White dwarfs eat exoplanets for breakfast - they are good probes of rocky exoplanet composition. #HWO25
Min: polarimetry is a key diagnostic for distinguishing between different aerosol compositions. Outer working angle constraints are a key limitation for accessing cold gas giants - several 10s of wavelength/diameter needed. #HWO25
Min: cloud formation has a dramatic effect on gas giant spectra, the cloud height affects overall albedo but also as different species condense their spectral features are removed from the gas phase. However, we don't fully understand cloud formation, haze formation even less... #HWO25
We are back for the last session of #HWO25 with Michiel Min, describing the science case for observing cold gas giants via coronagraphy with HWO. The gas giants of our solar system have varied atmospheirc properties, clouds and chemistry. We need more targets to understand processes at work.
