Astronomers are particularly interested in understanding how the orbits of planets around other stars evolve. In an idealized model, orbits consist of two uniform spheres revolving around a common center of mass. However, the reality is often more intricate. These deviations from ideal models provide insights into these systems, shedding light on their geometric arrangements in the universe and the potential presence of unseen companion planets.

Recently, a team of astronomers carried out a large-scale survey of Exoplanet TrES-1 b. The researchers selected TrES-1 b to analyze its orbital changes over the last two decades, since its discovery in 2004, because it belongs to the category of exoplanets that are relatively straightforward to observe: hot Jupiters. Hot Jupiters are gas giants similar in size to our solar system’s Jupiter, but they orbit their host stars at much closer distances, sometimes completing a revolution in just a few days. TrES-1 b orbits a star with just under 90% of the mass of our Sun every three days. This brief orbital period enables astronomers to make numerous observations, facilitating the measurement of orbital changes.

The research team initially gathered data on how much light TrES-1 b blocks from Earth’s viewpoint as it transits in front of its host star, referred to as the transit light curve. Most of the optical data originated from ground-based telescopes, inclusive of contributions from citizen scientists. Additionally, they sourced relevant data from the Transiting Exoplanet Survey Satellite, the Hubble Space Telescope, and the Spitzer Space Telescope. This data allowed them to accurately measure the time it took for TrES-1 b to complete its orbit.

They also discovered that another group of astronomers had employed Spitzer’s infrared array camera. Furthermore, they identified four additional studies from 2004 to 2016 that thoroughly measured how the light from TrES-1 b’s host star was affected by its orbital dynamics, specifically through radial velocity. By combining transit light curves, eclipses, and radial velocity data, astronomers gained a holistic understanding of TrES-1 b, which they then compared with statistical models to interpret its long-term behavior.

The research team sought to fit five distinct models to their observations of TrES-1 b to determine which best represented the data. The first model represented a planet with a constant circular orbit, followed by one with a fixed and slightly elliptical orbit, representing an eccentric orbit. The third model employed a circular orbit that gradually decreases in size, termed decaying orbit. The fourth variant implemented a damped and slightly eccentric orbit, while the final model featured a subtly eccentric orbit that also progresses directionally in relation to the star over time, known as precession.

The researchers concluded that, irrespective of the data subsets used, the most plausible explanation for their findings is that TrES-1 b follows an eccentric precessional orbit. They also noted that the damped trajectory model offered a superior fit compared to the steady trajectory models. This implies that while the changes in the exoplanet’s orbit are evident, the data does not support any hypotheses suggesting no actual alterations in its trajectory.

The researchers further elaborated that the rate at which the exoplanet’s orbit is changing indicates the gravitational influence of another planet within the system. They estimated that this hypothetical planet could be no larger than 25% the size of Jupiter and would have an orbital period of no more than 7 days. However, they noted that there was no direct evidence for such a planet in their data, apart from its inferred impact on TrES-1 b. They did discover another exoplanet in the system, termed TrES-1 c, but its wide eccentric orbit is unlikely to account for the changes observed in TrES-1 b’s orbit.

In conclusion, the researchers asserted that a multifaceted methodology to investigate the orbital timings of exoplanets unveils dynamics that may be overlooked by singular observations and models. They advocated for further studies of the long-term behaviors of exoplanets, necessitating extensive monitoring, more precise radial velocity measurements, and complex simulations of multiple celestial bodies within the gravitational system.

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