the_guruji's recent activity
-
Comment on Planet K2-18 b has an ocean and atmosphere that could support life in ~space
-
Comment on The Ring Nebula comes into focus, and it's astounding in ~space
the_guruji Link ParentToday's APOD: https://apod.nasa.gov/apod/ap230814.html, shows a reprocess of the data. The data might already be available on MAST. Good luck with the processing though; almost all professional...Today's APOD: https://apod.nasa.gov/apod/ap230814.html, shows a reprocess of the data. The data might already be available on MAST.
Good luck with the processing though; almost all professional astronomical data looks terrible (from an astrophotography point of view): plenty of artefacts, banding (especially with NIRCam) and other minor defects to work around. I'd given it a bit of a try but damn there's a lot of work needed to fix those and I'm not particularly handy with GIMP.
-
Comment on The Ring Nebula comes into focus, and it's astounding in ~space
the_guruji Link ParentI think it's likely because this hasn't been processed by STScI but rather by a third party. The colour palette, for example, is very different from what STScI processed JWST images tend to look...I think it's likely because this hasn't been processed by STScI but rather by a third party. The colour palette, for example, is very different from what STScI processed JWST images tend to look like (ofc that's just artistic choice here).
In any case the original science data will be available publicly soon enough so there'll be a bunch more people processing it (maybe even STScI).
-
Comment on APOD - Astronomy Picture of the Day in ~space
the_guruji LinkOne of my favourite APODs is one of the Ring Nebula: https://vanderbei.princeton.edu/images/NJP/m57.html (linking to the original imager's website, which has improved versions). The light has been...One of my favourite APODs is one of the Ring Nebula: https://vanderbei.princeton.edu/images/NJP/m57.html (linking to the original imager's website, which has improved versions).
The light has been passed through a diffraction grating. Every source in the sky appears undiffracted (like a normal image) and off to the left and right, you get the first order diffraction streaks. So each streak there can be matched to a normal-looking star. The stellar spectra are mostly continuous emission (there are absorption lines, but not obviously visible in this image). However the ring nebula has emission mostly from just two wavelengths here: [OIII] (around 500 nm: the cyan one) and H-alpha (about 660 nm: the red one). It's just a very obvious demonstration of how different the emission from planetary nebulae are from that of stars.
(disclaimer: I have experience in research astronomy, but not any in exoplanets, and especially not in the chemistry and modelling of exoplanet atmospheres, so opinions are closer to uneducated feelings rather than informed decisions)
Story time: I've been following this particular exoplanet on and off because the paper announcing that water had been found in it's atmosphere using Hubble[1] was the first I'd read through completely. A bunch of other papers confirmed this detection, including one from the group responsible for this recent JWST work, who proposed that this planet could be an ocean planet. This was not just based on the water detection, it used the radius and mass of the planet (less dense than Earth but more than, say, Neptune), and also a lot of modelling to come up with a few models: one was the aforementioned ocean planet with a thin hydrogen-rich atmosphere (which the authors in subsequent papers seem to have dubbed Hycean planets), the others involved much deeper hydrogen rich atmospheres.
Then, a group in 2021/22 basically put forward a few papers claiming that the water features observed in the transmission spectrum was more likely due to methane than water, and observing in longer wavelengths should help resolve the degeneracy, which JWST could do.
The analysis of the spectra is difficult; the resolution is fairly low (the original Hubble spectrum had like 17 data points from 1.1 µm to 1.7 µm with a slight bump at 1.4 µm. All inferences were done by forward modelling, i.e. considering a bunch of exoplanet atmosphere models and figuring out the relative abundances of the gases considered, and weighing each model against the other to see which better explained the data (search term is “atmospheric retrieval”). And this was data from 5 transits of the planet spread out over 3 or so years.
So I've been waiting a while for the results from JWST to resolve this, and looks like it only took one transit (with each of the two instruments used, so two in total, although the spectra is still pretty noisy but there's follow-up observations planned) and well turns out there's no water and it was indeed methane; they have a fairly strong detection of carbon dioxide as well. In addition they have a marginal detection of DMS (Dimethyl Sulphide) which the authors mention is only produced biologically on earth.[2]. They are careful to say that this detection needs confirmation which is coming with a MIRI observation of the transit which will again observe at longer wavelengths to confirm it.
I will say that I am not 100% on board with the ocean planet idea, mostly because it's been just this one group doing that kind of modelling that I've seen. The lead author in their talk a few days ago[3] suggests that only one out of the three originally considered models is compatible with the observed abundances. I guess this just means more waiting for other groups to confirm this, or to come up with other models, or perhaps even refine the inferences.
One thing that was true during the publication of the original paper, as well as now, is the way the outreach is handled; which is with misplaced optimism (I'll be generous here). Scientific American ran an article titled “No, the Exoplanet K2-18 b Is Not Habitable”[4] in the aftermath of a rushed initial publication of the original 2019 paper followed by copious amounts of “hype” from the authors, and a very generous interpretation of the results and statements by the media. I suppose if that DMS confirmation arrives, we'll be looking at yet another cycle of this.
[1]: 2019 paper published in Nature by Tsiaras et al. using Hubble data, claiming detection of water. Preprint here: https://arxiv.org/abs/1909.05218.
[2]: 2023 paper by Madhusudhan et al. using JWST data (the one in the news right now): https://arxiv.org/abs/2309.05566.
[3]: Talk from the lead author as part of the First Year of JWST Science conference: YouTube video, playback should start at 51:20 or so: https://www.youtube.com/watch?v=UStzmuATLuM&t=3080s
[4]: Rushed due to the expiry of the proprietary period of some of the early transit data, and a possibly scoop attempt by another group; there's more to say here about how proprietary periods help reduce sloppy science but this comment is long enough as it is.
P.S.: Lots of talks there, and lots of nice results including this one: https://astrodon.social/@kellylepo/111059590529996351 (a mastodon thread; scroll up for earlier results; likely more to come) first clear signals of a compact object at the center of the remnant of SN 1987A.