The search for exoplanets is one of the most exciting frontiers in modern astronomy. Using cutting-edge space telescopes and ground-based observatories, astronomers have made significant strides in identifying distant worlds beyond our solar system. One of the latest groundbreaking discoveries in this quest is TOI-2005 b, a warm Jupiter-sized exoplanet located more than 1,000 light years away. Detected by NASA’s Transiting Exoplanet Survey Satellite (TESS), this unusual planet orbits a rapidly rotating star on a highly eccentric orbit. The findings were reported on March 25, 2025, in a paper posted on the arXiv pre-print server.
The discovery of TOI-2005 b adds another exciting chapter to TESS’s ongoing mission to explore and catalog exoplanets. Since its launch in 2018, TESS has been surveying around 200,000 of the brightest stars near our Sun, using the transit method to detect exoplanets. The satellite’s method involves watching for small dips in a star’s light curve, which occur when a planet passes in front of it from our viewpoint—this is known as a transit. So far, TESS has detected over 7,500 potential exoplanet candidates, known as TESS Objects of Interest (TOIs), and confirmed 620 of them.
A Far-Away World with an Eccentric Orbit
TOI-2005 b is located about 1,070 light years away from Earth, orbiting an F-type star known as TOI-2005, which is more massive and hotter than our Sun. This star is rapidly rotating, a trait common in younger stars, and has recently been monitored by TESS, which detected a transit signal in its light curve. This prompted a team of astronomers led by Allyson Bieryla of the Harvard-Smithsonian Center for Astrophysics (CfA) to investigate further.
In their study, the astronomers confirm that the transit signal detected by TESS is indeed planetary in nature. This confirmation was made possible through a series of follow-up observations, including ground-based photometric, spectroscopic, and diffraction-limited imaging observations. These additional observations helped to solidify the presence of TOI-2005 b as a bona fide exoplanet and provided more detailed information about its characteristics.
TOI-2005 b: A Jupiter-Sized Planet on a Wild Ride
TOI-2005 b is classified as a “warm Jupiter,” a type of gas giant that is similar in size to Jupiter but orbits much closer to its host star. Specifically, TOI-2005 b has a radius of about 1.07 times that of Jupiter, making it roughly the same size as our gas giant. However, unlike Jupiter, which orbits our Sun at a distance of about 5.2 AU (astronomical units), TOI-2005 b resides much closer to its star—just 0.16 AU, or roughly one-sixth the distance between Earth and the Sun. This proximity results in a periastron (closest approach) equilibrium temperature of approximately 2,100 K, which is significantly higher than the temperatures found on Earth and is more typical of “hot Jupiters”—planets that are heated intensely by their nearby stars.
What makes TOI-2005 b particularly interesting is its highly eccentric orbit. The planet’s orbit has an eccentricity of approximately 0.6, meaning that its distance from its star varies significantly during its orbital period. This eccentricity is much higher than the nearly circular orbits of most known hot Jupiters. As a result, TOI-2005 b experiences dramatic fluctuations in stellar irradiation as it moves along its elliptical orbit. At its closest approach (periastron), the planet receives an intense burst of stellar radiation, while at its farthest point (apastron), the amount of energy it receives is significantly lower. These fluctuations in energy could lead to significant temperature variations across the planet’s surface.
TOI-2005 b completes an orbit around its star every 17.3 days, meaning that it experiences rapid changes in the amount of energy it receives from its host star. Unlike most hot Jupiters, which have circular orbits that result in a constant balance between day and night sides, TOI-2005 b’s eccentric orbit means that its day and night sides are likely to experience very different conditions, further adding to the planet’s uniqueness.
A Planet on the Move: Tidal Migration and Orbital Evolution
One intriguing possibility raised by the astronomers is that TOI-2005 b may be undergoing high-eccentricity tidal migration. In simpler terms, this means that the planet’s orbit could be slowly shrinking over time as a result of tidal interactions between the planet and its star. These interactions cause energy dissipation within the planet, which can gradually circularize its orbit.
If this process continues, the planet’s orbit may eventually become more circular, and TOI-2005 b could end up orbiting at a distance of just 0.101 AU from its star. This prediction suggests that TOI-2005 b might be in a transitional phase, moving from an eccentric orbit toward a more circular one over the course of the planetary system’s evolution. If this process occurs, the planet’s orbital period would also decrease, potentially leading to a very different environment than the one it currently experiences.
The Parent Star: A Hot, Massive F-Type Star
The parent star of TOI-2005 b is a relatively young F-type star, approximately twice the size of the Sun. With a mass of around 1.59 times that of our Sun, the star has a much higher effective temperature of about 7,130 K compared to the Sun’s 5,778 K. This higher temperature means that TOI-2005 radiates much more energy, contributing to the hot environment of its close-in planet, TOI-2005 b.
The star is estimated to be around 1.6 billion years old, making it significantly younger than the Sun, which is about 4.6 billion years old. The star’s youth, along with its rapid rotation, suggests that it may still be in an active phase of stellar evolution, which could have implications for the habitability of any potential exoplanets in its system. However, TOI-2005 b is not in any position to support life due to its extreme temperatures, making it an unlikely candidate for habitability.
A Glimpse Into the Future of Exoplanet Studies
The discovery of TOI-2005 b is a fascinating addition to our growing catalog of exoplanets. It highlights the ability of TESS to detect not only the more common exoplanets but also the more unusual and complex systems that challenge our understanding of planetary formation and evolution. The planet’s eccentric orbit, combined with the dramatic changes in stellar irradiation it experiences, make it a unique target for future study.
As more data from TESS and other telescopes become available, astronomers hope to learn more about planets like TOI-2005 b and the processes that shape their orbits. Whether it’s studying the migration of warm Jupiters or investigating the diversity of planetary systems, discoveries like this provide critical insights into the complexity of the universe and the dynamic processes that govern it.
In the coming years, missions like the James Webb Space Telescope (JWST) will provide even more detailed observations of exoplanets like TOI-2005 b, allowing scientists to examine their atmospheres, composition, and physical properties with greater precision. While TOI-2005 b may not be a candidate for life, it offers a unique window into the diversity of planets that exist beyond our solar system, deepening our understanding of the vast and varied cosmos.
The discovery of TOI-2005 b is a testament to the power of modern astronomical tools, and as we continue to explore the stars, there is no telling what other strange and wonderful worlds await our discovery.
Reference: Allyson Bieryla et al, TOI-2005b: An Eccentric Warm Jupiter in Spin-Orbit Alignment, arXiv (2025). DOI: 10.48550/arxiv.2503.20069