Hot Jupiters under scrutiny – ATUS delivers new data

Some exoplanets live dangerously: they orbit their host stars at extremely close distances, exposed to intense radiation and strong tidal forces. These so-called hot Jupiters – gas giants similar to Jupiter or Saturn with orbital periods of just a few days – are unknown in our Solar System, but common in other planetary systems. Some observations in recent years suggest that many of these planets may gradually spiral into their host stars on astronomically short timescales, ultimately being destroyed. A prominent example is the extrasolar planet WASP-12 b, whose orbital period is measurably decreasing – implying a remaining lifespan of only about three million years!

In recent years, similar indications have been suggested for the hot Jupiter TrES-5 b. Changes in orbital period can be inferred from so-called transit times, i.e., by accurately measuring the times at which a planet passes in front of its host star. However, such miniscule effects are difficult to detect: changes only become measurable over many orbits and require long-term, regular observations, ideally spanning more than a decade.

Marvin Rothmeier, a former student at the University of Stuttgart, shed new light on this question as part of his master's thesis at the Institute of Space Systems (IRS). In close collaboration with an international research team, the existing data set was carefully evaluated and significantly expanded: His study incorporates 13 new transit observations obtained between 2016 and 2024 with ATUS, the Astronomical Telescope of the University of Stuttgart, as well as 114 transit observations from NASA's Transiting Exoplanet Survey Satellite (TESS). The light curves were then analyzed in a uniform manner, yielding highly precise and directly comparable transit times.

The new results lead to a markedly different interpretation: While earlier studies suggested a steadily decreasing orbital period, the expanded data set shows no convincing evidence that TrES-5 b is measurably approaching its host star. Unlike WASP-12 b, the planet may not be doomed after all.
The study also highlights the value of smaller telescopes such as ATUS for exoplanet research: while large ground-based facilities and space missions cannot regularly monitor all known planets, long-term and consistent observations from smaller telescopes can help fill crucial gaps. The results also underscore how strongly scientific conclusions depend on the scope and homogeneity of available data – and how important long-term, accessible data archives are for such studies, even though these are still largely unavailable. This was also recognized by the referees of the renowned journal The Planetary Science Journal in which the study was recently published.

The University of Stuttgart Astronomical Telescope (ATUS) is a 0.6-meter Ritchey-Chrétien telescope for precise time-resolved observations. Originally designed as a test platform to support the SOFIA flying observatory, the instrument was continuously developed and optimized during its deployment at the Sierra Remote Observatories (SRO) in California.
Today, ATUS is a versatile scientific instrument used in fields such as exoplanet research, stellar occultation observations, and space situational awareness. At the same time, the telescope serves as a training platform for students and a test environment for new instruments. Karsten Schindler, who co-supervised Marvin Rothmeier together with André Beck during his master’s thesis at the IRS, has summarized the potential of ATUS in a paper that was recently published in the prestigious journal Publications of the Astronomical Society of the Pacific (PASP).
He is currently working with colleagues at the University of Stuttgart on preparations for the relocation of ATUS to the southern hemisphere. Until the telescope is back in operation there, the data collected in California will continue to make important contributions to astronomical research.

Original publications:

• Doomed Worlds II: Reassessing Suggestions of Orbital Decay for TrES-5 b, Rothmeier et al., Planetary Science Journal 6 292 (2025)
• The Astronomical Telescope of the University of Stuttgart (ATUS): Development, Optimization, and Lessons Learned,
  Karsten Schindler et al 2026 PASP 138 035001

Further Links:

• The Astronomical Telescope of the University of Stuttgart
• Planetary Science Institute: Finding the next doomed worlds
• The Short Period Planets Group — S(u)PerP(i)G
• Sierra Remote Observatories (SRO)

Aerospace research at the University of Stuttgart
Aerospace studies in Stuttgart form a unique interdisciplinary think tank for key technologies in space and on Earth. Researchers at the University of Stuttgart bring together expertise from the fields of climate and energy research, communications technology, propulsion technology, and AI-assisted flight. A central focus is the exploration of sustainable technological solutions aimed at minimizing the environmental impact of aerospace. Research is conducted in an interdisciplinary manner and in close collaboration with regional and international partners from academia and industry, for example within the framework of the Collaborative Research Centers ATLAS (SFB 1667) and SynTrac (SFB-TRR 364). As a partner of THE Aerospace LÄND, the University of Stuttgart contributes to the implementation of Baden-Württemberg’s state strategy to shape aerospace in a sustainable, digital, and collaborative manner by 2050. The University offers its students a solid engineering and application-oriented education. In promoting young talent, it cooperates with the “Future Initiative for Young Talent in Aerospace,” an initiative of the state of Baden-Württemberg dedicated to strengthening the promotion of young talent in STEM fields.