UY Scuti is a colossal red supergiant star, vastly exceeding the scale of our Sun. It is one of the largest known stars, possessing a radius that dwarfs every component of our inner solar system. If UY Scuti instantly replaced our Sun, this dramatic substitution would immediately alter the fundamental physics and environment of the solar system. The consequences would range from the physical engulfment of multiple planets to a radical restructuring of all remaining orbits, transforming the system into a violent and short-lived stellar neighborhood.
The Star’s Physical Reach
The sheer volume of UY Scuti is the most immediate and destructive consequence of its presence. While the Sun’s radius is approximately 695,000 kilometers, UY Scuti’s radius is estimated to be 1,708 times larger. This translates to a radius of about 7.94 astronomical units (AU), where one AU is the Earth’s average distance from the Sun.
This enormous stellar photosphere instantly engulfs all the inner, rocky planets. Mercury, Venus, Earth, and Mars would be completely immersed within the star’s tenuous outer atmosphere. The star’s boundary would extend far past the asteroid belt, swallowing Jupiter, which orbits at 5.2 AU.
The star’s surface would reach approximately 1.18 billion kilometers from the system’s center. This boundary falls short of Saturn’s orbit (9.54 AU), but the planet would be situated precariously close to the star’s fluctuating outer edge. Saturn and its rings would orbit just outside the colossal star, constantly bathed in powerful stellar winds and intense radiation.
Gravitational and Orbital Shifts
The massive increase in the central star’s size is accompanied by a change in its mass, fundamentally altering the system’s mechanics. Our Sun has a mass of one solar mass, but UY Scuti is estimated to possess a mass in the range of seven to ten solar masses. This substantial increase in gravitational pull would immediately affect the remaining outer planets.
Kepler’s Third Law dictates that an object’s orbital period depends on the mass of the central body. With the central mass increasing up to ten times, the orbital periods of Uranus and Neptune would shorten significantly. Uranus, orbiting at 19.2 AU, would complete its path around the new star in a fraction of its current 84-year period. Neptune’s 165-year orbit would likewise accelerate dramatically, causing both ice giants to move much faster.
The system’s center of mass, known as the barycenter, would also shift due to the new distribution of mass. This shift, combined with the star’s greater gravitational influence, results in the forced acceleration of the outer planets.
Extreme Luminosity and Temperature
UY Scuti is classified as a red supergiant and has a comparatively cool surface temperature of about 3,365 Kelvin, but its total energy output is immense. The star is up to 340,000 times more luminous than the Sun, a direct result of its enormous radiating surface area. This luminosity is the next major destructive force acting on the surviving parts of the system.
The sheer flux of energy at Earth’s original distance of one AU would be 340,000 times its current level, instantly vaporizing any unengulfed material. Even the moons of the consumed planets, such as Jupiter’s Galilean satellites, would be instantly stripped of all volatile compounds and superheated. The heat flux at the orbit of Uranus (19.2 AU) would still be approximately 925 times the solar energy Earth currently receives.
This radiation would flash-heat the surfaces of Uranus and Neptune, rapidly stripping them of their icy atmospheres and volatiles. Any ice or frozen material on the remaining outer moons would sublimate almost instantly. The entire outer solar system would be subjected to a scorching, sterilizing environment where surfaces glow from the intense heat.
The Nature of the New Stellar System
The presence of UY Scuti establishes a stellar system that is both vast and fleeting. As a red supergiant, the star is in the final phases of its short, high-energy life, having already exhausted the hydrogen fuel in its core. Stars of this magnitude typically burn through their resources in only a few million years, an astronomically brief period compared to the Sun’s ten-billion-year lifespan.
The star’s immense luminosity drastically expands the area where liquid water could theoretically exist. The habitable zone would be pushed out to a distance of approximately 583 AU. This new, expanded zone is far beyond the orbits of the furthest planets, extending deep into the Kuiper Belt.
Ultimately, the new stellar system is destined for a violent end. After consuming all remaining fuel, UY Scuti will undergo a core-collapse and explode as a powerful supernova. This explosive event would be the final destructive act, scattering the remnants of the solar system into interstellar space.