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Kevin Hardegree-Ullman

@kevinkhu.bsky.social

2.5K followers 260 following 270 posts

Research Scientist at Caltech/IPAC-NExScI studying all things related to exoplanets! Opinions are my own. https://kevinkhu.com

kevinkhu.com

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Kevin Hardegree-Ullman @kevinkhu.bsky.social · Aug 11

Kepler mission: smaller stars have more short-period, small #exoplanets.

Theory: the smallest stars won’t have enough disk material to make small planets so there must be a turnover.

Kepler+K2: We have found a turnover!

Check out our newest Scaling K2 paper: arxiv.org/abs/2508.05734

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🔭🧪☄️

Scaling K2 VIII: Short-Period Sub-Neptune Occurrence Rates Peak Around Early-Type M Dwarfs

We uniformly combined data from the NASA Kepler and K2 missions to compute planet occurrence rates across the entire FGK and M dwarf stellar range. The K2 mission, driven by targets selected by guest ...

arxiv.org

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Reposted by Kevin Hardegree-Ullman

Gijs D Mulders @gijsmulders.com · 8h

How do giant planets influence the type of #exoplanets that form in the habitable zone?

A thread 1/🧵

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Kevin Hardegree-Ullman @kevinkhu.bsky.social · 2d

Hey, that narrator sounds familiar!

Check out our new NASA #Exoplanet Archive homepage overview! 🔭

youtu.be/RHbvnodAX3g

A Quick Tour of the NASA Exoplanet Archive Homepage

YouTube video by NASA Exoplanet Archive

youtu.be

Kevin Hardegree-Ullman @kevinkhu.bsky.social · 6d

Now I want a statistical survey of astronomers' favorite planets. But at least K2-138 made this article's list. 🤣

Dr. Jessie Christiansen @aussiastronomer.bsky.social · 6d

This week (!) is the 30th anniversary of the announcement of 51 Pegasi b, the first exoplanet found orbiting a star like our Sun - since then, we've found over 6,000!

To celebrate, @alexwitze.bsky.social and @nature.com collected some astronomers' favourite planets:

www.nature.com/articles/d41...

These alien planets are astronomers’ favourites: here’s why

Space scientists look back on 30 years of exoplanet discoveries — from rows of massive ‘super-Earths‘ to worlds with perfectly synchronized orbits.

www.nature.com

Kevin Hardegree-Ullman @kevinkhu.bsky.social · 6d

Do you even lift?

Two turtles (larger round one on the left, very flat one on the right) sitting on a rock with some moss on it in the middle of a very green pond.

Kevin Hardegree-Ullman @kevinkhu.bsky.social · 12d

The Arecibo sky bridge, as seen from the secondary support structure in 2013. Sadly, this bridge no longer exists. 😞

A fisheye lens image looking through a support structure for the Arecibo Radio Observatory secondary mirror toward the sky bridge used to walk onto the secondary structure. A support tower is seen near the end of the bridge.

Reposted by Kevin Hardegree-Ullman

Kevin Hardegree-Ullman @kevinkhu.bsky.social · 13d

Join me at Colorado State University's Madison-Macdonald Observatory 60th anniversary celebration on October 17th from 3-8:30 pm! 🔭

There will be solar observing, physics demos, and stargazing, and I will be presenting a public lecture about #exoplanets!

www.physics.colostate.edu/about/astron...

Madison-Macdonald Observatory’s 60th Anniversary – Department of Physics | CSU

www.physics.colostate.edu

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Kevin Hardegree-Ullman @kevinkhu.bsky.social · 13d

Madison-Macdonald Observatory’s 60th Anniversary – Department of Physics | CSU

www.physics.colostate.edu

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Kevin Hardegree-Ullman @kevinkhu.bsky.social · 14d

Also, this was made the old fashioned (non-AI) way with a bit of elbow grease and (too much) time spent making modifications in GIMP.

Reposted by Kevin Hardegree-Ullman

Karen Masters @karenlmasters.bsky.social · 14d

I'm hiring at Haverford - a 2 year NASA funded postdoc to work on Galaxy Zoo with Roman Space Telescope Data: www.haverford.edu/human-resour... 👩‍🔬🔭

Postdoctoral Researcher in Extragalactic Astrophysics

Haverford College invites applications for our full-time (37.5 hours per week), fixed-term (2 year appointment), exempt, benefits-eligible Postdoctoral Research in Extragalactic Astrophysics opportuni...

www.haverford.edu

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Kevin Hardegree-Ullman @kevinkhu.bsky.social · 14d

The original source material from Murderbot on Apple TV+.

A screenshot of the show-within-a-show "The Rise & Fall of Sanctuary Moon" in the Apple TV+ series Murderbot.

Kevin Hardegree-Ullman @kevinkhu.bsky.social · 14d

I gave a talk about my paper last month with this as the title slide. Can you tell I recently watched #Murderbot? 🔭 #Exoplanets

A heavily modified version of a screenshot of the show-within-a-show "The Rise & Fall of Sanctuary Moon" in the Apple TV+ series Murderbot. The title now reads "The Rise & Fall of Sub-Neptune" to reflect a recent paper by Kevin Hardegree-Ullman in which the population of sub-Neptune exoplanets experiences a rise toward cool stars, then a fall when you reach stars cooler than about 3750 Kelvin.

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Kevin Hardegree-Ullman @kevinkhu.bsky.social · 21d

You can access parameters for all 6,007 planets on the NASA Exoplanet Archive at exoplanetarchive.ipac.caltech.edu!

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Reposted by Kevin Hardegree-Ullman

Dr. Jessie Christiansen @aussiastronomer.bsky.social · 21d

Sometimes 2025 just feels like a lot, and you need an excuse to celebrate your fabulous team (and the whole exoplanet community!) reaching a new milestone…

Happy 6,000 Confirmed Exoplanets Day, everybody!!!!

(You may recognize the narrator of the video at the link! 🫣)

www.nasa.gov/universe/exo...

A close-up photo of a box of cupcakes with gold candles spelling out ‘6000’.

A group of smiling people - scientists, engineers, data analysts and writers - standing behind a table of goodies.

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Kevin Hardegree-Ullman @kevinkhu.bsky.social · 21d

On the way to daycare, my 3 year old saw me bringing my Hot Wheels Mars Rovers to work today.

3 yo: I want to go to Mars... with you. We go on rocket ship to Mars.

Me: 🥹

A gold-plated 1997 Hot Wheels Sojurner Mars Rover and a 2012 Hot Wheels Curiosity Mars Rover sitting on the box for Sojourner.

Kevin Hardegree-Ullman @kevinkhu.bsky.social · 28d

Extra observing time tonight because I got bad weather last month? I'll take it! 🔭

Reposted by Kevin Hardegree-Ullman

Johanna Teske @johannateske.bsky.social · Sep 4

The advertisement for Carnegie EPL's 2026 postdoctoral fellowship is out! aas.org/jobregister/... We are also happy to host external fellowships like NHFP, NSF, and 51 Peg b (the latter is due Oct 3rd, one month away!). Please feel free to reach out if you have questions. (1/2)

aas.org

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Reposted by Kevin Hardegree-Ullman

Dr. Jessie Christiansen @aussiastronomer.bsky.social · Sep 2

Hey #exoplaneteers (and other early career folks) - applications for the 2026 NASA Hubble Fellowship Program are open!

www.stsci.edu/stsci-resear...

Announcement of Opportunity

Find in-depth information about the NASA Hubble Fellowship Program (NHFP) and its requirements.

www.stsci.edu

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Kevin Hardegree-Ullman @kevinkhu.bsky.social · Aug 28

Thanks, and congrats to the team for the cool discoveries!

Kevin Hardegree-Ullman @kevinkhu.bsky.social · Aug 28

This has been stuck in my head ever since the WISPIT #exoplanet announcements yesterday. 🫠

youtu.be/j_QLzthSkfM

Devo - Whip It (Official Music Video) | Warner Vault

YouTube video by Warner Records Vault

youtu.be

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Reposted by Kevin Hardegree-Ullman

Gabe Weible @gabeweible.bsky.social · Aug 26

The press release from @stewardobservatory.bsky.social is online now: news.arizona.edu/news/growing... #exoplanets ☄️🧪🔭

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Kevin Hardegree-Ullman @kevinkhu.bsky.social · Aug 26

Our now published paper can be found here! iopscience.iop.org/article/10.3...

#exoplanets

A plot of planet occurrence rates in planets per 100 stars on the y-axis versus host star effective temperature in K on the x-axis between 3200 and 6900 K. Occurrence rates are computed separately for super-Earths (green) and sub-Neptunes (blue) with orbital periods between 1 and 40 days. A power law was fitted to the super-Earths and a double broken power law was fitted to the sub-Neptunes, showing breaks at 3750 K and 5758 K.

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Reposted by Kevin Hardegree-Ullman

Sabina Sagynbayeva @sabinastro.bsky.social · Aug 25

My first press coverage 🥹

protect.checkpoint.com/v2/r01/___ht...

Astronomers Map Stellar ‘Polka Dots’ Using NASA’s TESS, Kepler - NASA Science

Scientists have devised a new method for mapping the spottiness of distant stars by using observations from NASA missions of orbiting planets crossing their

protect.checkpoint.com

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Reposted by Kevin Hardegree-Ullman

Kevin Hardegree-Ullman @kevinkhu.bsky.social · Aug 23

Quite astonishing that we can be observing right now ~50 km from where this volcano is spewing its guts. This is our last night of August IRTF observations with @sakhee-space.bsky.social! 🌋 🔭

A picture of a computer screen showing telescope controls on the left and a volcano erupting on the right.

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Kevin Hardegree-Ullman @kevinkhu.bsky.social · Aug 23

Quite astonishing that we can be observing right now ~50 km from where this volcano is spewing its guts. This is our last night of August IRTF observations with @sakhee-space.bsky.social! 🌋 🔭

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Kevin Hardegree-Ullman @kevinkhu.bsky.social · Aug 22

research.iac.es/proyecto/exo...

Exoplanet atmospheres

research.iac.es

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