Dr Ryan MacDonald
@distantworlds.space
Lecturer in Extrasolar Planets πͺ π at the University of St Andrews π΄σ §σ ’σ ³σ £σ ΄σ Ώ
Pinned
Dr Ryan MacDonald
@distantworlds.space
Β· Nov 2
I'm excited to announce that I will be joining the University of St Andrews as a Lecturer in Extrasolar Planets in June 2025! π πͺ π π π΄σ §σ ’σ ³σ £σ ΄σ Ώ
If you're interested in pursuing a PhD, postdoc, or fellowship in exoplanet atmospheres in beautiful Scotland (from Autumn 2025), please feel free to get in touch.
If you're interested in pursuing a PhD, postdoc, or fellowship in exoplanet atmospheres in beautiful Scotland (from Autumn 2025), please feel free to get in touch.
Reposted by Dr Ryan MacDonald
BPSC2026 Registration and Abstract Submission is open!
Information on rates, discounted accommodation and abstract format can be found here bpsc2026.wp.st-andrews.ac.uk/registration/
Early bird rates are available til 9th May 2026, which is the same day as the abstract deadline!
Information on rates, discounted accommodation and abstract format can be found here bpsc2026.wp.st-andrews.ac.uk/registration/
Early bird rates are available til 9th May 2026, which is the same day as the abstract deadline!
Registration β BPSC2026
bpsc2026.wp.st-andrews.ac.uk
February 3, 2026 at 11:58 AM
BPSC2026 Registration and Abstract Submission is open!
Information on rates, discounted accommodation and abstract format can be found here bpsc2026.wp.st-andrews.ac.uk/registration/
Early bird rates are available til 9th May 2026, which is the same day as the abstract deadline!
Information on rates, discounted accommodation and abstract format can be found here bpsc2026.wp.st-andrews.ac.uk/registration/
Early bird rates are available til 9th May 2026, which is the same day as the abstract deadline!
We're excited to be hosting the British Planetary Society Conference in St Andrews this summer!
One of our aims for BPSC 2026 is to connect the Solar System #planetaryscience and #Exoplanets communities.
Be sure to follow the conference page for more details:
β¬οΈπͺππ§ͺβ¬οΈ
One of our aims for BPSC 2026 is to connect the Solar System #planetaryscience and #Exoplanets communities.
Be sure to follow the conference page for more details:
β¬οΈπͺππ§ͺβ¬οΈ
Our website for the British Planetary Society Conference 2026 is now live!
π 9-11 June, 2026
π― St Andrews, Scotland π΄σ §σ ’σ ³σ £σ ΄σ Ώ
Our website contains details on how to get to St Andrews and the conference accommodation. Registration details will be added soon.
bpsc2026.wp.st-andrews.ac.uk
π 9-11 June, 2026
π― St Andrews, Scotland π΄σ §σ ’σ ³σ £σ ΄σ Ώ
Our website contains details on how to get to St Andrews and the conference accommodation. Registration details will be added soon.
bpsc2026.wp.st-andrews.ac.uk
January 14, 2026 at 5:57 PM
We're excited to be hosting the British Planetary Society Conference in St Andrews this summer!
One of our aims for BPSC 2026 is to connect the Solar System #planetaryscience and #Exoplanets communities.
Be sure to follow the conference page for more details:
β¬οΈπͺππ§ͺβ¬οΈ
One of our aims for BPSC 2026 is to connect the Solar System #planetaryscience and #Exoplanets communities.
Be sure to follow the conference page for more details:
β¬οΈπͺππ§ͺβ¬οΈ
After the event, one of the other academics thanked me for speaking out, saying they feel like they're losing their mind being inundated by the push to use AI for everything.
It really matters that we clearly say out loud the dangers of AI in education (and wider society).
It really matters that we clearly say out loud the dangers of AI in education (and wider society).
December 11, 2025 at 6:25 PM
After the event, one of the other academics thanked me for speaking out, saying they feel like they're losing their mind being inundated by the push to use AI for everything.
It really matters that we clearly say out loud the dangers of AI in education (and wider society).
It really matters that we clearly say out loud the dangers of AI in education (and wider society).
I attended a welcome event for new academic staff recently. Two of the new faculty there were extremely pro-AI and said things like: "I require my students to use AI, telling them they will learn too slowly if they don't".
I pushed back, citing the damage to learning from cognitive offloading.
I pushed back, citing the damage to learning from cognitive offloading.
December 11, 2025 at 6:25 PM
I attended a welcome event for new academic staff recently. Two of the new faculty there were extremely pro-AI and said things like: "I require my students to use AI, telling them they will learn too slowly if they don't".
I pushed back, citing the damage to learning from cognitive offloading.
I pushed back, citing the damage to learning from cognitive offloading.
Reposted by Dr Ryan MacDonald
Job vacancy π»π
Passionate about building vibrant professional communities?
The RAS is seeking a dynamic Head of Membership to develop and deliver our membership strategy and play a pivotal role in growing our membership through retention and recruitment.
Apply hereπ
ras.ac.uk/news-and-pre...
Passionate about building vibrant professional communities?
The RAS is seeking a dynamic Head of Membership to develop and deliver our membership strategy and play a pivotal role in growing our membership through retention and recruitment.
Apply hereπ
ras.ac.uk/news-and-pre...
October 24, 2025 at 11:57 AM
Job vacancy π»π
Passionate about building vibrant professional communities?
The RAS is seeking a dynamic Head of Membership to develop and deliver our membership strategy and play a pivotal role in growing our membership through retention and recruitment.
Apply hereπ
ras.ac.uk/news-and-pre...
Passionate about building vibrant professional communities?
The RAS is seeking a dynamic Head of Membership to develop and deliver our membership strategy and play a pivotal role in growing our membership through retention and recruitment.
Apply hereπ
ras.ac.uk/news-and-pre...
The Norman Lockyer Fellowship is a great opportunity for postdoc research in #Exoplanets, and we'd love to host you at St Andrews!
Feel free to reach out if you're interested in joining our exoplanet group in beautiful Scotland π΄σ §σ ’σ ³σ £σ ΄σ Ώπͺ
Feel free to reach out if you're interested in joining our exoplanet group in beautiful Scotland π΄σ §σ ’σ ³σ £σ ΄σ Ώπͺ
π§βπ¬ Need funding to support your research?π§βπ¬
We're now accepting applications for the Norman Lockyer Fellowship, offered to outstanding candidates to enable them to pursue research in the UK in the disciplines advanced by the Royal Astronomical Society. ππͺ
‡οΈ
We're now accepting applications for the Norman Lockyer Fellowship, offered to outstanding candidates to enable them to pursue research in the UK in the disciplines advanced by the Royal Astronomical Society. ππͺ
‡οΈ
October 3, 2025 at 11:47 AM
The Norman Lockyer Fellowship is a great opportunity for postdoc research in #Exoplanets, and we'd love to host you at St Andrews!
Feel free to reach out if you're interested in joining our exoplanet group in beautiful Scotland π΄σ §σ ’σ ³σ £σ ΄σ Ώπͺ
Feel free to reach out if you're interested in joining our exoplanet group in beautiful Scotland π΄σ §σ ’σ ³σ £σ ΄σ Ώπͺ
Trotta (2008)
arxiv.org/abs/0803.4089
arxiv.org/abs/0803.4089
October 1, 2025 at 6:53 PM
Trotta (2008)
arxiv.org/abs/0803.4089
arxiv.org/abs/0803.4089
Many congratulations, Dr Boldt-Christmas! π
Love the front cover transiting planet atmosphere graphic on your thesis!
Love the front cover transiting planet atmosphere graphic on your thesis!
September 26, 2025 at 11:15 PM
Many congratulations, Dr Boldt-Christmas! π
Love the front cover transiting planet atmosphere graphic on your thesis!
Love the front cover transiting planet atmosphere graphic on your thesis!
Afraid not. Microlensing relies on a chance alignment between two distant stars, so you see the planet once and then it's gone forever.
September 17, 2025 at 8:13 PM
Afraid not. Microlensing relies on a chance alignment between two distant stars, so you see the planet once and then it's gone forever.
The telescope that discovered this planetary system was named after the beer π
September 13, 2025 at 5:41 AM
The telescope that discovered this planetary system was named after the beer π
Finally, it's important to highlight that none of this would have been possible without the leadership of Nikole Lewis, who is the PI of this initial TRAPPIST-1e reconnaissance program.
I was fortunate enough to be a postdoc at Cornell with Nikole, and she is a truly *fantastic* advisor and mentor!
I was fortunate enough to be a postdoc at Cornell with Nikole, and she is a truly *fantastic* advisor and mentor!
September 9, 2025 at 11:14 PM
Finally, it's important to highlight that none of this would have been possible without the leadership of Nikole Lewis, who is the PI of this initial TRAPPIST-1e reconnaissance program.
I was fortunate enough to be a postdoc at Cornell with Nikole, and she is a truly *fantastic* advisor and mentor!
I was fortunate enough to be a postdoc at Cornell with Nikole, and she is a truly *fantastic* advisor and mentor!
We have follow-up observations of TRAPPIST-1e ongoing (led by NΓ©stor Espinoza and Natalie Allen), which will provide 15 (!) more transits of TRAPPIST-1e.
So if TRAPPIST-1e does indeed have an atmosphere, we will soon have the data to settle the enigma of this world.
So if TRAPPIST-1e does indeed have an atmosphere, we will soon have the data to settle the enigma of this world.
September 9, 2025 at 11:14 PM
We have follow-up observations of TRAPPIST-1e ongoing (led by NΓ©stor Espinoza and Natalie Allen), which will provide 15 (!) more transits of TRAPPIST-1e.
So if TRAPPIST-1e does indeed have an atmosphere, we will soon have the data to settle the enigma of this world.
So if TRAPPIST-1e does indeed have an atmosphere, we will soon have the data to settle the enigma of this world.
Our constraints on potential atmospheres with molecules heavier than H2 and He (secondary atmospheres) are presented in our second TRAPPIST-1e paper, led by @ana-glidden.bsky.social at MIT. Be sure to check out the paper!
iopscience.iop.org/article/10.3...
So what comes next?
iopscience.iop.org/article/10.3...
So what comes next?
September 9, 2025 at 11:14 PM
Our constraints on potential atmospheres with molecules heavier than H2 and He (secondary atmospheres) are presented in our second TRAPPIST-1e paper, led by @ana-glidden.bsky.social at MIT. Be sure to check out the paper!
iopscience.iop.org/article/10.3...
So what comes next?
iopscience.iop.org/article/10.3...
So what comes next?
Technical point: retrievals of flat transmission spectra for rocky planets usually result in corner plots resembling the prior.
For TRAPPIST-1e, we don't see this behaviour, with the CH4 posterior pushing to include this molecule.
We haven't detected CH4, but future observations can assess this.
For TRAPPIST-1e, we don't see this behaviour, with the CH4 posterior pushing to include this molecule.
We haven't detected CH4, but future observations can assess this.
September 9, 2025 at 11:14 PM
Technical point: retrievals of flat transmission spectra for rocky planets usually result in corner plots resembling the prior.
For TRAPPIST-1e, we don't see this behaviour, with the CH4 posterior pushing to include this molecule.
We haven't detected CH4, but future observations can assess this.
For TRAPPIST-1e, we don't see this behaviour, with the CH4 posterior pushing to include this molecule.
We haven't detected CH4, but future observations can assess this.
Statistically, our current four-transit spectrum of TRAPPIST-1e can also be fit by a flat line (i.e. a featureless spectrum). So we can't rule out a bare rock with these data.
There's also the important caveat that an incomplete stellar contamination correction could also imprint spectral features.
There's also the important caveat that an incomplete stellar contamination correction could also imprint spectral features.
September 9, 2025 at 11:14 PM
Statistically, our current four-transit spectrum of TRAPPIST-1e can also be fit by a flat line (i.e. a featureless spectrum). So we can't rule out a bare rock with these data.
There's also the important caveat that an incomplete stellar contamination correction could also imprint spectral features.
There's also the important caveat that an incomplete stellar contamination correction could also imprint spectral features.
Intriguingly, forward models with N2 + CH4 provided a great fit to TRAPPIST-1e's transmission spectrum π―
We found the same solution independently through atmospheric retrievals, which latched onto CH4 absorption as a potential explanation. π
But this is not (yet!) an atmospheric detection.
We found the same solution independently through atmospheric retrievals, which latched onto CH4 absorption as a potential explanation. π
But this is not (yet!) an atmospheric detection.
September 9, 2025 at 11:14 PM
Intriguingly, forward models with N2 + CH4 provided a great fit to TRAPPIST-1e's transmission spectrum π―
We found the same solution independently through atmospheric retrievals, which latched onto CH4 absorption as a potential explanation. π
But this is not (yet!) an atmospheric detection.
We found the same solution independently through atmospheric retrievals, which latched onto CH4 absorption as a potential explanation. π
But this is not (yet!) an atmospheric detection.
In Paper #2, we ran a grid of atmospheric models considering combinations of strong infrared absorbers (CO2 / CH4) and transparent background gases (N2 / H2).
The figure below (from Glidden+2025) shows the range of excluded partial pressures.
Big takeaway: large CO2 concentrations are unlikely.
The figure below (from Glidden+2025) shows the range of excluded partial pressures.
Big takeaway: large CO2 concentrations are unlikely.
September 9, 2025 at 11:14 PM
In Paper #2, we ran a grid of atmospheric models considering combinations of strong infrared absorbers (CO2 / CH4) and transparent background gases (N2 / H2).
The figure below (from Glidden+2025) shows the range of excluded partial pressures.
Big takeaway: large CO2 concentrations are unlikely.
The figure below (from Glidden+2025) shows the range of excluded partial pressures.
Big takeaway: large CO2 concentrations are unlikely.
The observations, stellar contamination GP magic πͺ, and H2-upper limit we've discussed so far are covered in our first TRAPPIST-1e paper, led by NΓ©stor Espinoza at STScI (not on Bluesky). Be sure to check out the paper!
iopscience.iop.org/article/10.3...
Next, we looked for secondary atmospheres.
iopscience.iop.org/article/10.3...
Next, we looked for secondary atmospheres.
September 9, 2025 at 11:14 PM
The observations, stellar contamination GP magic πͺ, and H2-upper limit we've discussed so far are covered in our first TRAPPIST-1e paper, led by NΓ©stor Espinoza at STScI (not on Bluesky). Be sure to check out the paper!
iopscience.iop.org/article/10.3...
Next, we looked for secondary atmospheres.
iopscience.iop.org/article/10.3...
Next, we looked for secondary atmospheres.
Our first result was a firm rejection of any significant amount of hydrogen in TRAPPIST-1e's atmosphere.
Irrespective of the cloud-surface pressure, we find a H2 abundance limit of < 80% (to 3Ο). This is a significant improvement over what was possible with Hubble data.
Irrespective of the cloud-surface pressure, we find a H2 abundance limit of < 80% (to 3Ο). This is a significant improvement over what was possible with Hubble data.
September 9, 2025 at 11:14 PM
Our first result was a firm rejection of any significant amount of hydrogen in TRAPPIST-1e's atmosphere.
Irrespective of the cloud-surface pressure, we find a H2 abundance limit of < 80% (to 3Ο). This is a significant improvement over what was possible with Hubble data.
Irrespective of the cloud-surface pressure, we find a H2 abundance limit of < 80% (to 3Ο). This is a significant improvement over what was possible with Hubble data.
Using GPs to account for the stellar contamination, we combined the time-independent spectral information from the four transits to produce the spectrum of TRAPPIST-1e shown in the press release.
We then turned to atmospheric models to see if there were any signatures of atmospheric absorption.
We then turned to atmospheric models to see if there were any signatures of atmospheric absorption.
September 9, 2025 at 11:14 PM
Using GPs to account for the stellar contamination, we combined the time-independent spectral information from the four transits to produce the spectrum of TRAPPIST-1e shown in the press release.
We then turned to atmospheric models to see if there were any signatures of atmospheric absorption.
We then turned to atmospheric models to see if there were any signatures of atmospheric absorption.
We turned to Gaussian Processes (GPs) to fit the stellar contamination affecting the TRAPPIST-1e spectra.
Since:
Observed_spectrum_i = contamination_i * planet_spectrum
The idea is to extract the time-independent (non-GP) common factor caused by any planetary atmosphere.
Since:
Observed_spectrum_i = contamination_i * planet_spectrum
The idea is to extract the time-independent (non-GP) common factor caused by any planetary atmosphere.
September 9, 2025 at 11:14 PM
We turned to Gaussian Processes (GPs) to fit the stellar contamination affecting the TRAPPIST-1e spectra.
Since:
Observed_spectrum_i = contamination_i * planet_spectrum
The idea is to extract the time-independent (non-GP) common factor caused by any planetary atmosphere.
Since:
Observed_spectrum_i = contamination_i * planet_spectrum
The idea is to extract the time-independent (non-GP) common factor caused by any planetary atmosphere.
When we modelled the stellar contamination (similar to previous studies on TRAPPIST-1b,c, d), the models couldn't simultaneously explain the entire wavelength range.
Simply put, our stellar models for ultra-cool M-dwarf stars like TRAPPIST-1 don't work π±
So we had to try something new...
Simply put, our stellar models for ultra-cool M-dwarf stars like TRAPPIST-1 don't work π±
So we had to try something new...
September 9, 2025 at 11:14 PM
When we modelled the stellar contamination (similar to previous studies on TRAPPIST-1b,c, d), the models couldn't simultaneously explain the entire wavelength range.
Simply put, our stellar models for ultra-cool M-dwarf stars like TRAPPIST-1 don't work π±
So we had to try something new...
Simply put, our stellar models for ultra-cool M-dwarf stars like TRAPPIST-1 don't work π±
So we had to try something new...
We observed TRAPPIST-1e four times with JWST in 2023 to measure how the apparent size of the planet changes with colour (i.e. transmission spectra) - more on why this took 2 years in a moment!
Our spectra show *huge* wavelength-dependent features that are caused by active regions on the star β΄οΈ
Our spectra show *huge* wavelength-dependent features that are caused by active regions on the star β΄οΈ
September 9, 2025 at 11:14 PM
We observed TRAPPIST-1e four times with JWST in 2023 to measure how the apparent size of the planet changes with colour (i.e. transmission spectra) - more on why this took 2 years in a moment!
Our spectra show *huge* wavelength-dependent features that are caused by active regions on the star β΄οΈ
Our spectra show *huge* wavelength-dependent features that are caused by active regions on the star β΄οΈ
TRAPPIST-1e is 92% Earth's size, 69% Earth's mass, and is illuminated by 66% of the integrated light that Earth receives.
This means TRAPPIST-1e can potentially have liquid surface water *if* it has an atmosphere with a sufficient greenhouse effect.
So TRAPPIST-1e was a priority target for JWST.
This means TRAPPIST-1e can potentially have liquid surface water *if* it has an atmosphere with a sufficient greenhouse effect.
So TRAPPIST-1e was a priority target for JWST.
September 9, 2025 at 11:14 PM
TRAPPIST-1e is 92% Earth's size, 69% Earth's mass, and is illuminated by 66% of the integrated light that Earth receives.
This means TRAPPIST-1e can potentially have liquid surface water *if* it has an atmosphere with a sufficient greenhouse effect.
So TRAPPIST-1e was a priority target for JWST.
This means TRAPPIST-1e can potentially have liquid surface water *if* it has an atmosphere with a sufficient greenhouse effect.
So TRAPPIST-1e was a priority target for JWST.
Previously, on TRAPPIST-1:
β‘οΈ No thick atmospheres on TRAPPIST-1b,c (Greene+2023, Lim+2023, Zieba+2023, Radica+2025, Gillon+2025).
β‘οΈ Earth-like atmospheres ruled out for TRAPPIST-1d (Piaulet-Ghorayeb+2025) - see thread below.
Now we turn to a planet more firmly in the habitable zone: TRAPPIST-1e.
β‘οΈ No thick atmospheres on TRAPPIST-1b,c (Greene+2023, Lim+2023, Zieba+2023, Radica+2025, Gillon+2025).
β‘οΈ Earth-like atmospheres ruled out for TRAPPIST-1d (Piaulet-Ghorayeb+2025) - see thread below.
Now we turn to a planet more firmly in the habitable zone: TRAPPIST-1e.
September 9, 2025 at 11:14 PM
Previously, on TRAPPIST-1:
β‘οΈ No thick atmospheres on TRAPPIST-1b,c (Greene+2023, Lim+2023, Zieba+2023, Radica+2025, Gillon+2025).
β‘οΈ Earth-like atmospheres ruled out for TRAPPIST-1d (Piaulet-Ghorayeb+2025) - see thread below.
Now we turn to a planet more firmly in the habitable zone: TRAPPIST-1e.
β‘οΈ No thick atmospheres on TRAPPIST-1b,c (Greene+2023, Lim+2023, Zieba+2023, Radica+2025, Gillon+2025).
β‘οΈ Earth-like atmospheres ruled out for TRAPPIST-1d (Piaulet-Ghorayeb+2025) - see thread below.
Now we turn to a planet more firmly in the habitable zone: TRAPPIST-1e.