Josh Lothringer

Distribution of the topics of approved proposals for ESPRESSO in Period 117. 74.6 Transit follow up, 3.5% studies of systems around binaries (unclear if its transiting systems), 0.3% for RM studies, 11% for stellar physics, 0.4% for milky way studies, and 10.2% for cosmology.

Been checking the science topics of the proposals approved by the ESO OPC for ESPRESSO. 75% of the time went to one type of proposal. Statistics-focused follow up of transiting systems. There isn't a single proposal focused on discoveries, atmospheres, or anything low-mass planets 🔭#exoplanets

One of my new fav. astronomy plots - so much cool physics in one plot!

New job opportunity at @stsci.edu: Senior Astronomical Data Scientist for data analysis tools, working closely with my team and me.

This role is very similar to mine. If you have questions, I'm happy to answer them. 🧪🔭

Group of people standing in a room with posters and models related to space exploration, including a banner for the Nancy Grace Roman Space Telescope.

Applications are open for STScI's Space Astronomy Summer Program: an opportunity for college students to work with researchers and staff on projects that include astrophysics research; science software engineering; science instrument calibration; and science public outreach: https://bit.ly/4ptMkfs 🔭

Huge kudos to Utah Valley University undergrad Austin Baldwin, who led the data analysis. When I first analyzed the data, I didn't see the large absorption because of a software bug sorting the wavelengths from the echelle data 😬. Austin built a pipeline from scratch, revealing the awesome result!

A plot of escape velocity versus XUV flux with some points from different planets as data points. Planets with Mg II escape appear above a trend line, while planets without Mg II escape appear below the trend line.

When we compare to other Mg II observations, we can start to see a trend in the traditional cosmic shoreline framework: planets with low surface gravity and high XUV irradiation exhibit Mg II escape.

BUT planets around very hot stars may not see enough chromospheric XUV flux to drive Mg II escape!

Compared to previous NUV observations, this is the most-precise and best-resolved Mg II escape feature, allowing us to measure the Doppler shift and line widths. The gas appears to be moving towards the star at ~30-40 km/s and the lines are broader than expected, also indicating high velocity.

A spectrum (transit depth versus wavelength) showing two large bumps, which models and data agree is the Mg II absorption feature.

The Mg II ion has a huge feature at 0.28 microns, which we can resolve with Hubble. The absorption is well past the planet's gravity, indicating extreme escape of gas: we calculate about 10^12.5 grams per sec. @brettmorr.is told us this is about 2x the mass of all elephants on Earth... per second! 😂

A High-Resolution NUV Transmission Spectrum of KELT-9b: Mg II and Fe II Escaping from the Hottest Known Giant Planet We present high-resolution NUV observations from Hubble Space Telescope's (HST) Space Telescope Imaging Spectrograph (STIS) data for the hottest known gas planet, KELT-9b. Observations were collected ...

ICYMI: Over the winter holidays, my student's paper on KELT-9b was accepted: arxiv.org/abs/2512.19662!

With the Hubble Space Telescope's STIS instrument, we find enormous escape of metal ions from the hottest hot Jupiter, KELT-9b! 🪐🔭💫

Very good news for NASA Science in the compromise 2026 funding bill released by Congress today:

Trump moves to dismantle major US climate research center in Colorado The Trump administration is breaking up the National Center for Atmospheric Research, taking aim at one of the world's leading climate research labs.

Exclusive: The Trump administration is moving to dismantle the National Center for Atmospheric Research in Colorado, according to a senior White House official, taking aim at one of the world's leading climate research labs.

The CHesapeake bay area EXOplanet Meeting #CHEXO12 has started @jhuapl.bsky.social with a nice and big crowd despite the snow!

www.chexo.org #exoplanets

A logo "HSLA" which stands for Hubble Spectroscopic Legacy Archive, has three stylized spectra with rainbow colors radiating from left to right. In the background are stars, galaxies, and a giant planet.

Hey #astrosci community! After working on this project for 3 years, there's a new Hubble Spectroscopic Legacy Archive that's just been newly made available at @stsci.edu: archive.stsci.edu/missions-and... follow me to learn more! (1/n)

Thanks!!!

Thanks, Jake!!

The Library of Exoplanet Atmospheric Composition Measurements: Population Level Trends in Exoplanet Composition with ExoComp The present-day bulk elemental composition of an exoplanet can provide insight into a planet's formation and evolutionary history. Such information is now being measured for dozens of planets with sta...

Take a look at the paper, now accepted to AJ, for more info: arxiv.org/abs/2510.26785.

The code and calculations used in the paper are available at the GitHub linked above. The data used in the paper is available here: jlothringer.github.io/LExACoM_MRT_....

We hope this is just the start at looking at these population-level trends, now with more robust and reliable measurements. We'll continue to collect measurements as they become available and update the table. We plan to extend this to include free retrieval results (e.g., H2O, CO2 measurements).

Even though the trends are a bit offset, the transit and eclipse spectroscopy samples show very consistent mass-metallicity slopes! Both are steeper than the Solar System trend - perhaps interesting... All this is also consistent with interior bulk metallicity inferences.

C/H versus planet mass, showing increasing metallicity towards smaller planet masses.

Same as left, but for O/H versus mass.

One of the highlights is the planet mass-(atmospheric) metallicity trend. While such a trend was somewhat controversial with HST measurements, this newer sample shows a much cleaner relationship. With ExoComp, we can break it down between O/H and C/H and compare directly to the Solar System.

Planet metallicity versus equilibrium temperature.

C/O versus equilibrium temperature. No trend is seen.

4 panel plots showing planet metallicity and C/O versus stellar metallicity and mass. No obvious trends are seen.

There don't seem to be obvious trends or correlations between planet metallicity, C/O, temperature, stellar metallicity, or stellar mass. But carbon-dominated C/O > 1 planets appear to be rare, if any exist at all!

Left: A plot of O/H versus sub-sample (direct spectroscopy, eclipse spectroscopy, etc.). Right: The same but C/O versus sub-sample. Transit spectroscopy shows low C/O.

A plot showing C/O versus metallicity.

After we standardize the 65 atmosphere measurements from JWST and 8m-class telescopes, we can look for trends! And we see some surprises...

The first was that exoplanets measured by transit spectroscopy have low C/O compared to those measured in eclipse. It's not obvious why.

GitHub - jlothringer/exocomp: Exocomp is a toolkit with functions and utilities for normalizing measurements from different retrievals of exoplanets and brown dwarfs. Exocomp is a toolkit with functions and utilities for normalizing measurements from different retrievals of exoplanets and brown dwarfs. - jlothringer/exocomp

ExoComp allows one to convert between different solar abundance references and different definitions of metallicity and C/O. Other tools include fitting metallicity, C/O, and refrac./vol. ratios to sets of atomic and molecular abundances (like from a free retrievals).

github.com/jlothringer/...

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 😀).

Even back in 1850, the biomass of humans matched that of all wild land animals? Not what I would have thought!

Now extended to Monday 10/20, FYI!

chexo.org - CHEXO #12 The Chesapeake Bay Area Exoplanet Meeting brings together all lovers of exoplanets and related science from the DC area and beyond. This series of one-day meetings enable the sharing of ideas in an in...

Abstracts are due by tomorrow for the 12th installment of the Chesapeake Bay Area Exoplanet Meeting!

The meeting will be December 5th, 2025 at JHU Applied Physics Lab. Hope to see you there.

www.chexo.org/chexo12

The last day to register for STScI's fall workshop is today!

www.stsci.edu/contents/eve...

A leading Democrat in the Senate just released an important report documenting how NASA has been working to implement the president's proposed budget, not Congressionally approved funds, in slashing missions. Read more ⬇️

An example fit to a JWST/MIRI F1500W eclipse observation of GJ 3929b collected by the Rocky Worlds DDT Program.

New HLSP: First results from the Rocky Worlds DDT program are now available at MAST! This release includes calibrated light curves, model fits, preliminary eclipse depth estimation, and auxiliary data for GJ 3929 b. archive.stsci.edu/hlsp/rocky-w... #HLSP #RockyWorlds #JWST #HST #Exoplanets #MAST 🔭

Registration is open now for our fall workshop on Atmospheric Escape and Replenishment in Planetary Systems!

🔭 #exoplanets