TOI-561 is a star that has captured the interest of astronomers due to its unique characteristics and the planetary system it hosts. Located in the constellation of Sextans, this star is not just another point of light in the night sky; it has a story that spans 10 billion years and includes a rarity among planetary systems. Despite its old age and low metallicity, TOI-561 is a key to understanding the formation and evolution of planets in the early universe.
Basic Characteristics of TOI-561
TOI-561 is a star with properties that somewhat resemble our Sun, but with notable differences. It has about 80% of the Sun’s mass and size, making it slightly smaller and less massive. However, what sets TOI-561 apart is its advanced age. At an estimated 10 billion years old, TOI-561 has been shining for more than twice the time our Sun has. This makes TOI-561 one of the ancient stars that have witnessed a significant portion of the Milky Way’s history.
Galactic Thick Disc Membership
This star is part of an intriguing group known as the Galactic thick disc stars. These stars are characterized by their orbits, which take them above and below the plane of the Milky Way, and their composition, which contains fewer heavy metals like iron or magnesium compared to stars in the thin disc, such as our Sun. The scarcity of heavy metals in TOI-561 suggests that it formed at a time when the universe had not yet been enriched by the numerous cycles of star birth and death that create these elements.
The Planetary System of TOI-561
Surrounding TOI-561 are at least three small transiting planets, designated as TOI-561b, c, and d. These planets pass in front of the star from our point of view, causing slight dimming in the star’s brightness, which allows astronomers to detect their presence and infer their properties. The discovery of these planets is remarkable because they exist around a star that is both ancient and metal-poor, challenging some of the existing theories about planet formation.
TOI-561b: A Rocky World Close to the Star
The innermost planet, TOI-561b, is a particularly interesting world. It is a rocky planet, similar in nature to Earth, but it orbits very close to its host star, completing a revolution every 0.45 days. This proximity means that TOI-561b is likely extremely hot and inhospitable to life as we know it. Its existence raises questions about how a rocky planet could have formed and survived in such a hostile environment, especially around such an old star.
TOI-561c and TOI-561d: Outer Companions
The other two confirmed planets, TOI-561c and TOI-561d, orbit farther out from the star. Less is known about these planets compared to TOI-561b, but their detection adds to the evidence that planet formation was possible even in the early universe under conditions that differ significantly from those around younger, metal-rich stars like the Sun.
Significance of the Discovery
The discovery of the planetary system around TOI-561 is a milestone for astronomers. It provides a unique opportunity to study the conditions of planet formation and survival in a metal-poor environment, which could be similar to the conditions present in the early universe. The existence of these planets around one of the oldest known stars challenges current models and suggests that planets could form much earlier and with fewer heavy elements than previously thought.
The study of TOI-561 and its planets continues to yield valuable insights into the history of our galaxy and the processes that lead to the formation of planetary systems. As observations and technologies improve, we may uncover more secrets held by this ancient star and its companions, further expanding our understanding of the cosmos.
