Dear ExoClock participants,
We hope you are all doing well!
As we are approaching the Summer Solstice, we would like to wish you Happy Solstice, enjoy the longest day of the year!
We would also like to welcome the new members.
We send out a newsletter like this every month, while you can read the past newsletters, watch the past meetings, and have access to other educational material at:
http://www.exoclock.space/users/material
We organise meetings dedicated to new ExoClock members. These meetings are held just after our regular monthly meeting. The beginner’s meeting is usually held on a Friday, one or two weeks after the monthly meetings. In these meetings, newcomers can ask questions of any level related to the operation of the website, observations of transits, data analysis etc. Note that these meetings are not recorded.
Finally, we have a Slack channel for more direct communication and if you would like to join, follow this link: https://join.slack.com/t/exoclock/shared_invite/zt-1t5l875v6-x0s8s553kT8nbCvbyo7boA
In this newsletter, we discuss:
1. Announcements
1.1. ExoClock publication
1.2. Fifth Annual ExoClock meeting – registration page
1.3. Euro planet Iberian Node Award for amateur astronomers
1.4. Synchronous observations campaigns
2. Highlighted Observations
3. Exoplanet CV of TrES-2b
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1. Announcements
1.1 ExoClock publication
We are excited to share that we have submitted our latest paper entitled:
“ExoClock Project IV: A homogeneous catalogue of 620 updated exoplanet Ephemerides”
The extensive analysis indicated that about 45% of the Ariel targets needed updates, showcasing the importance of ExoClock for the mission’s success.
Currently, we are waiting for the response of the reviewers, and we will come back to you when we have updates.
If you are a co-author and have requested additional authors to be added, we will contact you next week to take action before we submit the revised version.
Stay tuned!
1.2 Fifth Annual ExoClock Meeting
We are very excited about this year’s annual ExoClock meeting, which will take place in Madrid in a hybrid format, on the 3rd and the 4th of October 2025.
This event is a fantastic opportunity for the ExoClock community to come together, connect with other members, Ariel scientists, deepen our understanding of the project and the mission, and of course, have fun.
We are eagerly awaiting to see you in person, and for those that are unable to make it, you can still participate online!
You can register on the following link:
https://www.eventbrite.com/e/5th-exoclock-annual-meeting-tickets-1422306349579, please consider using the same form if you wish to submit an abstract for an oral or poster presentation.
If you wish to be considered for the visit at the Royal Observatory of Madrid, please indicate it on the registration page.
Registration is mandatory for participation, and a fee of €50 is required for in-person attendance. We will send a follow-up email for the payment, closer to the meeting.
The abstract submission deadline is the 30th of August!
Please share the meeting with any interested communities!
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1.3 Euro planet Iberian Node Award for amateur astronomers
Congratulations to the team of Sabadell for receiving the Iberian Award for amateur astronomers for their collaboration with ExoClock! We are very proud of you!
More information here (in Spanish):
https://v2.federacionastronomica.es/
1.4 Synchronous observations campaign
Synchronous Observations are used to notice simultaneously transit observations of challenging exoplanet targets to increase the S/N. These are often cases where single-site observations may be insufficient due to low signal-to-noise ratios, long transit durations, or other observational difficulties.
By observing the same transit from multiple locations at the same time, we ensure better coverage and data reliability, helping to confirm transits and refine ephemeris for otherwise hard-to-characterize systems.
In our previous campaigns, we covered TOI- 5704b and TOI-2136b.
We are currently analysing the data, and we will share some brief updates on the next meeting. We will have another campaign on the 10th of July for Kepler-411c, a high-priority target. Please note down the date and if you have clear skies, go ahead and observe it!
• The transit happens between Thursday the 10th of July, 23:19 UTC and Friday the 11th of July 02:54 UTC.
• Use a red photometric filter, a luminance filter, or no filter at all. • Join the campaign if you have a telescope of 12 in. or larger.
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• Remember that the transit will not appear in your scheduler! To check whether the transit is observable from your location at the exact time, please consider using the exo-worlds-spies scheduler: https://www.exoworldsspies.com/en/scheduler/ You have to indicate a telescope of 40 inches (ca. 1 metres); otherwise it will not appear.
• If you manage to observe the transit, please submit the light curve as usual to ExoClock and include the comment: “This is part of the synchronous campaign”.
2. Highlighted observations
We would like to thank you all for the observations you contributed during the previous months! We have selected WASP-148b, a target that was initially flagged as an alert, due to a shift of 10 minutes that was identified through your observations. The planet’s observations were highlighted in our June newsletter three years ago (2022!). This time we highlight the target for the additional observations and the long coverage that allowed to flag it a target with TTVs. You can clearly see on the O-C diagram the planet’s TTVs, which is because the planet is part of a multiplanetary system, and this is also described in our latest paper.
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3. ‘Exoplanet CV of TrES-2b’
These CV articles aim to enrich your background knowledge on the Ariel candidates. The articles feature one exoplanet each month and are written by our literature team. This month we are featuring TrES-2b. The article is attached in the next page. Enjoy.
Clear Skies,
the ExoClock team
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“CV” of TrES-2b
by Alex Capildeo, ExoClock Literature Team Member
Meet TrES-2b — The Darkest Known Exoplanet.
Imagine a planet so dark it barely reflects any light at all. That’s TrES-2b — a strange and fascinating exoplanet discovered in 2006 by the Trans-Atlantic Exoplanet Survey. Classified as a hot Jupiter, TrES-2b is a gas giant about the size of Jupiter, but it orbits extremely close to its star — much closer than Mercury orbits our Sun. In fact, it orbits around its star in just 2.47 days. (O’Donovan et al. 2006). It was also the first exoplanet observed by the Kepler Space Telescope, which is why it’s sometimes called Kepler-1b.
TrES-2b is likely tidally locked, meaning one side always faces the star while the other side remains in eternal night. This creates extreme temperature differences between its hot day side and freezing cold night side.
But what really makes this planet stand out is how incredibly dark it is. TrES-2b is the darkest exoplanet ever found. It reflects almost no visible light — nearly everything that hits it gets absorbed. Some studies estimate its albedo (which is a measure of the reflectivity) to be as low as 2%, or even under 1% (Kipping & Spiegel 2011; Estévez et al. 2013). For comparison, Earth reflects about 30% of the sunlight. That means that TrES-2b is at least 15 times darker than our planet. It’s like a giant ball of charcoal drifting through space.
So how do astronomers measure this? They use a technique called secondary eclipse observations. When the planet passes behind its star from our viewpoint, astronomers compare the total light before and during the eclipse. This allows them to isolate the planet’s contribution and determine how much light it reflects.
Recent studies suggest that TrES-2b may be experiencing transit timing variations (TTVs), where its orbital timing subtly shifts over time (Biswas et al. 2024). This could indicate the gravitational influence of another, as yet unseen, planet in the system — a hidden companion waiting to be discovered. However, there is no strong evidence, and therefore more observations are needed to confirm whether TrES-2b has TTVS.
TrES-2b is a well-studied target in the ExoClock project, with 119 observations, including 23 recent ones (as of June 2025). You can see all data points on the O-C diagram below (figure 1). Its bright host star and short orbital period make it possible to observe, even with telescopes as small as 5 inches (ca. 13 centimetres).
While it might currently be considered a low-priority target, its unique darkness, potential orbital changes, and mysterious atmosphere make it a fascinating object to keep watching.
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Figure 1: The O-C diagram of TrES-2b from the ExoClock database. TrES-2b is one of the most thoroughly observed exoplanets, with extensive data collected from space missions, scientific literature, and numerous contributions from the ExoClock community.
References:
[1] O’Donovan et al. 2006 (https://ui.adsabs.harvard.edu/abs/2006ApJ…651L…61O/abstract) [2] Kipping & Spiegel 2011 (https://ui.adsabs.harvard.edu/abs/2011MNRAS.417L…88K/abstract) [3] Estévez et al. 2013 (https://ui.adsabs.harvard.edu/abs/2013ApJ…772…51E/abstract) [4] Biswas et al. 2024 (https://ui.adsabs.harvard.edu/abs/2024AJ….168.176B/abstract)
