iiinova — where your digital self keeps evolving

Luis Welbanks @luiswel.bsky.social · 30/09/2025

The deadline for the 51 Pegasi b Fellowship is right around the corner. www.hsfoundation.org/programs/sci... Interested in theory, modeling, and discovery? Join @nixonmatthew.bsky.social, Sagnick, and me at the Exoteric Lab at ASU @seseasu.bsky.social

050

Luis Welbanks @luiswel.bsky.social · 12/08/2025

What does it mean to detect a gas in an exoplanet atmosphere? Listen to what @nixonmatthew.bsky.social and I had to say. It was a pleasure chatting with @startswithabang.bsky.social !!

2265

Luis Welbanks @luiswel.bsky.social · 09/07/2025

We need to understand the limits of our models and our data for reliable interpretations of exoplanetary spectra. First paper by my first PhD student! Happy advisor moment. Congrats @yoavrotman.bsky.social Check out his paper on the Arxiv and his thread below #exoplanets 🔭

071

Luis Welbanks @luiswel.bsky.social · 13/06/2025

I think the full title was an unfortunate Ceres of events btw, but I am no Lemoony Snicket expert

021

Luis Welbanks @luiswel.bsky.social · 12/06/2025

And sanctioned by the journal :P

030

Reposted by Luis Welbanks

Matt Nixon @nixonmatthew.bsky.social · 25/05/2025

I agree with you that saying K2-18 b “can’t” have an ocean or “isn’t” an ocean world is a stretch - we can’t totally rule it out with the present data, but it does appear that Neptune-like or gas dwarf models are consistent with what we know about the planet and require much less fine-tuning

151

Luis Welbanks @luiswel.bsky.social · 25/05/2025

"Relies on the obfuscation of how, exactly, they are defining [...] in order to garner press coverage. " & "An exceedingly generous observer might chalk up this divergence to the perennial conflict between scientists and their PR machines" Great title: [Fill in the blank] Can’t Have It Both Ways

020

Reposted by Luis Welbanks

Carl Zimmer @carlzimmer.com · 23/05/2025

Here's my follow-up story on K2-18b, the distant planet where scientists claimed to see a possible sign of life last month. In three preprints, other researcher argue that the signal is noise. nyti.ms/4jaqQRv

nyti.ms

There’s Probably No Life on K2-18b After All, Three Studies Conclude

In April, astronomers said they had detected a possible signature of life on the exoplanet K2-18b. Now, three independent analyses discount the evidence.

814834

Luis Welbanks @luiswel.bsky.social · 23/05/2025

What do you mean by original hypothesis? Just to make sure I understand correctly, are you suggesting that the discourse (online/in papers?) should say that the original hypothesis (which?) is not ruled out but neither is Wogan's or X? Not being facetious, legitimately asking.

100

Luis Welbanks @luiswel.bsky.social · 23/05/2025

In the low SNR, it is possible for the inferred properties to be shaped as much by preconceived notions for what a planet ought to be like, as by data (if we are not careful).

010

Luis Welbanks @luiswel.bsky.social · 23/05/2025

Our take-home on this specific point could be: "Reliance on Bayesian evidence alone, coupled with exploration of only a narrow part of the model space, has led to contradictory interpretations."

110

Luis Welbanks @luiswel.bsky.social · 23/05/2025

On that we say "Conversely, when all candidate models adequately fit a spectrum, a preference for one model over another does not rule out the worse-performing model."

110

Luis Welbanks @luiswel.bsky.social · 23/05/2025

2) At the same time - you could ask: can the data rule out X hypothesis? The answer may be no, and that's ok too! e.g., K2-18b MIRI - current data cannot rule out the scenario of a planet under radiative-convective-photochemical equilibrium (section Self-Consistent Models)

210

Luis Welbanks @luiswel.bsky.social · 23/05/2025

We say in our paper "When all considered candidate models are poor representations of reality, the best-performing model is simply the least inadequate and may not necessarily lead to reliable interpretations of the data."

110

Luis Welbanks @luiswel.bsky.social · 23/05/2025

Not 100% sure I understand your question(s) but let me try. 1) Constraining a parameter does not equal 'detecting' that parameter. I can add a none-sense parameter and get a tight constrain. This is the whole point of the cheese v. sponge example.

110

Luis Welbanks @luiswel.bsky.social · 23/05/2025

There is no "Bayesian police" to say what to compare or not. Any paper can compare any two models (but please contextualize!). However, if we are going to argue about 'standard practices', the "consensus" (somewhat arbitrary) is to compare relative to the full hypothesis 2/2 Thanks for engaging!

020

Luis Welbanks @luiswel.bsky.social · 23/05/2025

Sounds good! Two distinct yet complementary points. In general Welbanks & Nixon+ is not arguing against model comparisons but it is making an appeal to contextualize them. What two models did you compare? From that perspective Chubb+20 is doing that in the abstract: X sigma relative to blah. 1/2

120

Luis Welbanks @luiswel.bsky.social · 22/05/2025

Say hi to Ian and Jasmina! If you haven't done so, visit the Sheikh Zayed grand mosque. I was blown away by the beautiful interiors.

110

Luis Welbanks @luiswel.bsky.social · 22/05/2025

But how certain are we that we can ignore the uncertainties? The scientist's paradox

020

Luis Welbanks @luiswel.bsky.social · 22/05/2025

@viciykevin.bsky.social one could argue whether the "full hypothesis space" is valid or not - we discuss that in our paper. However, the comparison is performed against this full hypothesis space. This is how the comparison got its connection to 'detection'.

120

Luis Welbanks @luiswel.bsky.social · 22/05/2025

What @distantworlds.space said. Section 4 of Gasman says "In Tables 6–10 we specify the Bayes factor, B01, for each retrieval set-up, comparing the retrieval with the specified molecule (C2H2, C2H4, CH4) included versus not included" - you want to compare against your full hypothesis space.

210

Luis Welbanks @luiswel.bsky.social · 21/05/2025

Following the conventional practices of the field (nested models) and his exact results there is no detection of DMS and no detection of DMDS. #exoplanets 🔭 #K218b

020

Luis Welbanks @luiswel.bsky.social · 21/05/2025

Check out "Interpretation According to Conventional Practices" in our paper and let us know what you think arxiv.org/abs/2504.21788

200

Luis Welbanks @luiswel.bsky.social · 21/05/2025

What are your impressions of the reaction within Europe? Is the community planning to react in that way?

110

Luis Welbanks @luiswel.bsky.social · 21/05/2025

Ah! Great! How do I get a copy of the newsletter?

110

Luis Welbanks @luiswel.bsky.social · 20/05/2025

@philplait.bsky.social - is there a way to help you / crash course / @hankgreen.bsky.social? His video on the topic was great but failed to catch some of the nuance. This is declaring a detection of cheese on the Moon from only considering a cheese model and a sponge model.

120

Luis Welbanks @luiswel.bsky.social · 20/05/2025

This is a major change in interpretation within just one month, with no new data, no new retrieval framework, and no newly available cross-section data. That such a dramatic revision was needed reinforces that the original inference (detection) was overstated.

070

Luis Welbanks @luiswel.bsky.social · 20/05/2025

Offsets between instruments - vertical shifts in transit depth. Observations at different epochs may require offsets and indeed, they seem inevitable, even for big planets like WASP-39b

050

Luis Welbanks @luiswel.bsky.social · 18/05/2025

But if you are being for real, go for it! 'this is not copyright infringement'

120

Luis Welbanks @luiswel.bsky.social · 18/05/2025

I think the ghost of Magritte won't mind ;)

120

Luis Welbanks @luiswel.bsky.social · 16/05/2025

Good to see Pica-Ciamarra, Madhu+ engage with our work and correct claims from last month. Following our recommendation to expand the model space, they now find: ‘No molecule reaches 2σ significance when allowing for an offset…’ 𝐍𝐨 𝐛𝐢𝐨𝐠𝐚𝐬𝐞𝐬 𝐚𝐟𝐭𝐞𝐫 𝐚𝐥𝐥! Sec. 4.4 arxiv.org/abs/2505.10539 🔭 #exoplanets

arxiv.org

A Systematic Search for Trace Molecules in Exoplanet K2-18 b

The first transmission spectrum of the habitable-zone sub-Neptune K2-18 b with JWST has opened a new avenue for atmospheric characterisation of temperate low-mass exoplanets. The observations led to i...

1194

Luis Welbanks @luiswel.bsky.social · 14/05/2025

Still trying to process that HST and JWST are looking at the same target **simultaneously**. Moments like this fuel the part of me that grew up in awe of space and somehow ended up in a job where this is real. 🔭

040

Luis Welbanks @luiswel.bsky.social · 10/05/2025

Oh please, let's not do that! The last thing we need is to add noise and get everyone asking "is this sigma on the Trotta/Sellke scale or the Author et al scale?" Let's remember the main assumption for these model comparisons: "that the two models exhaust the model space, p(M0|d) + p(M1|d) = 1"

010

Luis Welbanks @luiswel.bsky.social · 03/05/2025

Working on this project was both fun and rewarding. I’ve kept Magritte’s The Treachery of Images in my office since my master’s—a reminder that definitions, like models, are not the thing itself. Context matters. So do the assumptions we often forget we’re making. Check out Matt's thread about it!

060

Reposted by Luis Welbanks

Gates Cambridge @gatescambridge.bsky.social · 02/05/2025

Luis Welbanks on the importance of international collaboration when it comes to space research in the latest episode of our So, now what podcast - www.gatescambridge.org/about/news/w... @luiswel.bsky.social @uniofcam.bsky.social @churchillcol.bsky.social #GatesCambridge25 #astronomy

021

Luis Welbanks @luiswel.bsky.social · 28/03/2025

Thrilled to welcome Matt Nixon and @sagnickastro.bsky.social to ASU! A core part of the 51 Peg Fellowship is community—and I’m excited to build one alongside them. We’re ready to push boundaries, think creatively, and make the most of this moment. 🪐🚀 🔗 bit.ly/41WLH48

Matt Nixon and Sagnick Mukherjee, incoming 51 Pegasi b Fellows at ASU, standing side by side and smiling in front of a bright yellow background. Text reads: ‘Welcome to the team Matt & Sagnick. See you this Fall at ASU.

2161

Luis Welbanks @luiswel.bsky.social · 20/09/2023

Things you can say in a seminar and a pre-K visit talk: "Your cloud models are not realistic"

060

Luis Welbanks @luiswel.bsky.social · 06/09/2023

I'm excited to be in DC this week to present at the #GiantMagellan2023 Community Science Meeting on #Exoplanets. I'll give a review talk on the rapid development of the field. What are your favourite model/observation results from the last 5 years? I'll make sure to give you a shout out!

170

Luis Welbanks @luiswel.bsky.social · 03/09/2023

Well, I've made the jump thanks to @afeinstein20.bsky.social. Hopefully I will be more active here than in the other place. The less happy place.

040