Thanks for the shoutout! The paper that formulated this framework is Batygin 2018 which considered only hot start as the initial condition. It would be very interesting if there are any future theoretical papers on these predictions, and as as observer we hope to expand and go to lower mass planets!
I am excited about the new discoveries from Gaia DR4, which can be followed by several instruments similar to KPIC, such as VLT/HiRISE and Subaru/REACH, and upcoming instruments such as Keck/HISPEC.
We also looked into 200+ spin measurements in the literature. In addition to rotational rates or velocities, we find that specific angular momentum is a nice parameter, and we found that 5–40 Mjup objects retain higher angular momentum compared to 40–100 Mjup objects after 10 Myr.
Our result is consistent with what Bryan et al. 2020 found in their spin survey, where companions of 10–30 Mjup (and mass ratio >0.8%) show (slow) spins at 10% of breakup speed. Thanks to Keck/KPIC, we can measure spins for imaged planets at close separation, including HR 8799 planets and AF Lep b.
When we assume the companion inclinations align with their orbits, we find 4-4.5 sigma significance of the spins of the brown dwarf companions and giant planets in our sample, and when we assume random inclinations for our companions, the significance drops to 1.6-2.1 sigma due to larger errors.
We find that when the mass is below 10 Mjup and the mass ratio is below 0.8% (as our gold standard planet sample, a conservative definition of planets), the mass/mass ratio dependent trends show up, while companions between 10 and 40 Mjup show slower rotation.
The “spin” in this survey is parameterized by fractions of breakup speed, evolved to 10 Myr (a characteristic age for typical disk lifetime), so you can think of the spin here as normalized by mass and age.
Our sample is constructed from the largest vsini substellar companion sample of 30+ brown dwarf companions and giant planets from Keck/KPIC. We are able to measure the spin (or vsini, the projected rotational velocity) of these imaged giant planets and brown dwarf companions beyond 5 au.
It is super nice to put this paper out with @thejason.wang and the KPIC team! (The short takeaway is above, and more details of our paper are summarized as follows)
The results can be nicely explained by the theoretical prediction of disk braking during their early lifetime, as a function of mass and mass ratio. We also found that brown dwarf companions show slower spins than isolated brown dwarfs, as their disks are different.
I am super excited to share our new paper on the spin of brown dwarfs and giant planets, accepted to AJ earlier this month. With the large spin survey, we found the first clear evidence that the spins of giant planets and brown dwarf companions (>5 au) are distinct.
arxiv.org/abs/2601.05976
The Fomalhaut system continues to deliver unexpected surprises!
Congrats on the big survey results and beautiful orbit fits!
I’m attending the #AAS247 this week. Look forward to catching up with friends and colleagues!
New orbit movie just dropped. This one is for the newly discovered circumbinary planet HD 143811 AB b. This 9-year timelapse was made through an international collaboration with me, Nathalie Jones (Northwestern graduate student), and Vito Squicciarini (Exeter postdoc)
A remarkable old, low metallicity, transiting brown dwarf. arxiv.org/abs/2512.06069
We are hiring a new Assistant Professor in Astrophysics at Trinity College Dublin!! ☘
Job ad here: aas.org/jobregister/...
Deadline: Jan 02 2026
Please share widely! 🪐🔭
Great work on putting these different types of planets measurements together Josh!!
A logo with text "ExoComp" with a robot scanning the "O".
We've collected 65 individual exoplanet atmosphere composition measurements to look for population-level trends 🔭 #exoplanets
To do this, we had to create a toolkit to standardize between definitions of . We call it ExoComp. (Yes, that's a Star Trek reference 😀).
SAVE THE DATE! The 11th AAS Topical Conference Series (AASTCS): Exoplanet Atmospheres 2026 will take place in Denver. Join astronomers, planetary scientists & researchers from around the world for an in-depth exploration of one of the most dynamic fields in science today. More details soon 🔭
Evan has extended our cloudy Diamondback evolution models to higher Teff with PHOENIX models at the high end. This permits all model tracks to start at the same young age. We call this model variation Red Diamondback.
Very glad that Aisha’s SPHINX models have an extension with the Sonora family now
Congrats! Finding Y dwarfs at 1-2 kpc is amazing
Figure from Squicciarini et al. showing three panels with a white dot on a black and blue stippled background, indicating the location of the planet in GPI and SPHERE IRDIS data.&10;
Three panel image from Jones et al. showing a white dot on a stippled background. The planet is in the 11 o'clock position in all three images.
Two papers announcing the discovery of a directly imaged 6 Jupiter mass planet around binary system HD 143811 AB Squicciarini+ and Jones+ in Sco-Cen - Keck, Gemini and VLT all imaging this companion and confirmed with several years of common proper motion. #astrodon #exoplanet #exosci
A quick advert for the ✨✨✨Official✨✨✨ release of the Virga cloud code (the python version of everyone's favorite EddySed model by @markmarley.bsky.social and Andy Ackerman).
arxiv.org/abs/2508.15102
Image of a poster describing the different Sonora models, including Bobcat, Diamondback, Elf Owl, Flame Skimmer, and Gila monster.
I liked Caroline Morley's Exoclimes poster describing our Sonora model set so much that I'm going to hang up a replica in my office.
The 51 Peg b postdoctoral fellowship is out and Northwestern is one of the possible host institutions. Come join us! More information about the range of planetary astronomy research and other opportunities (like PI of Keck proposals) here: ciera.northwestern.edu/opportunitie....
Nice talk today! Congrats!
We are delighted to announce fourteen postdocs will be joining the CIERA community in fall 2025. Please join us in extending a warm welcome to these fantastic researchers!
Maybe these slow rotating weirdos are binary star systems! Find out more in this @aunz.theconversation.com article by Iris de Ruiter theconversation.com/mysterious-r... 🔭🧪
