Nikku Madhusudhan

The journey begins. Welcome to Hycean Worlds. Follow us for updates: hycean.group.cam.ac.uk

Are we alone in the universe? Astronomers from @Cambridge_Astro may be a step closer to finding out. Using data from @ESA_Webb, they’ve detected possible signs of life on exoplanet K2-18b – but they remain cautious. Read more 👇 cam.ac.uk/stories/strong…

Astronomers say a new type of #exoplanet, dubbed 'Hycean' planets, could be our best chance of finding the signatures of life outside our Solar System, potentially in the next few years: bit.ly/3jefNek @cambridge_astro @CambridgeIPLU @exomadhu #space

@astromarkmarley @AgolEric @V_Parmentier The trend being discussed is of H2O abundances in transiting giant exoplanets, not the solar system trend which is based on CH4. H2O abundances in massive hot Jupiters can be significantly sub-solar even for modestly sub-solar O/H ratios; several formation mechanisms allow that.

@exomadhu @AgolEric @V_Parmentier I'm surprised that you think that I think that. The figure that is always shown includes Jupiter and Saturn and Uranus and Neptune on it. Maybe they should be removed, but then there would be less of a trend. If you include Jupiter why not 51 Eri b?

Deleted previous tweet since it came off as crankier than I intended. But would be good if the metallicity vs. mass plot did not go below stellar at high masses in the extrapolation.

@astromarkmarley @AgolEric @V_Parmentier Not all formation models that predict sub-solar oxygen extrapolate, it's not that hard to get sub-solar oxygen.

@astromarkmarley @AgolEric @V_Parmentier I am surprised you think directly-imaged planets, brown dwarfs, and close-in hot jupiters all form the same way!

@astromarkmarley @AgolEric @V_Parmentier Wrong comparison, different formation channels.. Numerous papers on this topic predicting sub-solar oxygen abundances in giant planets.

@exomadhu @AgolEric @V_Parmentier All the brown dwarf companions would like to have a word with you. Gl 229B can go first.

@astromarkmarley @AgolEric @V_Parmentier This is a common misconception. If oxygen or H2O is used as a metallicity indicator then it can actually be sub-stellar. Some formation scenarios predict this due to H2O depletion in the outer disk where the planet could have formed.

@AgolEric @V_Parmentier It's just that if the envelope accreted from the same nebula as the star you would not expect the metallicity to be below that of the star. Extrapolating the trend to below 1x isn't meaningful. Astronomer "fit a power law to everything" taken to extremes.