The Sun is a stable G-type main-sequence star that has provided consistent energy for our solar system for billions of years. UY Scuti is a pulsating red supergiant star located nearly 6,000 light-years away in the constellation Scutum. Swapping our star for UY Scuti instantly transforms the celestial mechanics and environmental conditions of our cosmic neighborhood. This hypothetical scenario shows the limits of stellar size and the power of a star nearing the end of its short life.
The Immense Scale of UY Scuti
The most immediate consequence of this stellar swap would be the obliteration of the inner solar system by UY Scuti’s physical size. Estimates for the star’s radius vary due to its pulsating nature, but its visible surface is hundreds of times the radius of the Sun. If centered where the Sun is now, this colossal star would extend far beyond the orbit of Mars.
The star’s fiery outer layers would engulf Mercury, Venus, and Earth, vaporizing them instantly within the star’s atmosphere. Even the Asteroid Belt, which orbits at an average distance of 2 to 3.2 Astronomical Units (AU), would be consumed by the star’s volume. Extreme estimates suggest UY Scuti’s radius could reach nearly 8 AU, easily swallowing the gas giant Jupiter (5.2 AU).
The inner planets would be completely absorbed into the supergiant’s tenuous, hot atmosphere. For Earth, its iron core and silicate crust would vaporize and mix with the hydrogen, helium, and heavier elements flowing from the star’s core. The physical presence of UY Scuti alone renders the inner half of the solar system extinct.
The New Energy and Radiation Environment
Despite UY Scuti’s relatively cool surface temperature of approximately 3,365 Kelvin—much cooler than the Sun’s 5,778 Kelvin—its immense surface area translates to a staggering energy output. The star is hundreds of thousands of times more luminous than the Sun, with estimates ranging from 124,000 to over 340,000 times the Sun’s brightness. This massive increase in energy drastically shifts the location of the habitable zone, the region where liquid water could exist on a planetary surface.
The new habitable zone would be pushed out to a distance between 350 and 580 AU, far past the orbits of all known planets. This places the region of potential habitability deep within the Kuiper Belt. Icy bodies in this distant zone might develop warm, subsurface oceans as the heat penetrates their crusts.
The outer planets that survive, such as Saturn, Uranus, and Neptune, would be bathed in a flood of radiation. This intense light and heat would dramatically alter their atmospheres, causing them to swell and possibly initiating rapid mass loss. The star’s powerful stellar wind, a massive outflow of gas and dust characteristic of red supergiants, would bombard the remaining planetary surfaces and moons.
Gravitational and Orbital Dynamics
UY Scuti introduces a significant change in the system’s gravitational center, affecting the orbits of the surviving outer planets. UY Scuti is substantially more massive than the Sun, estimated to weigh between 7 and 10 solar masses. This increase in mass directly dictates the orbital mechanics of the entire system, according to Kepler’s Third Law.
The surviving gas and ice giants would find their orbital periods dramatically shortened due to the stronger gravitational pull. If the star’s mass were increased sevenfold, the time it takes for a planet to complete an orbit would decrease by a factor of nearly three. The planets would speed up and follow tighter, faster paths.
This dynamic change would also destabilize the delicate long-term balance of the outer solar system. The increased gravitational influence would begin to perturb the orbits of the remaining planets, moons, and distant Kuiper Belt objects. This gravitational stirring would likely lead to a period of instability, potentially resulting in planetary collisions, ejections from the system, or capture into new, highly elliptical orbits.
The Inevitable Stellar Collapse
The final consequence of having UY Scuti as our star is its short lifespan. The Sun will shine for approximately ten billion years, but UY Scuti, having entered its red supergiant phase, is nearing the end of its nuclear fuel supply. Stars this massive burn through resources quickly, meaning UY Scuti has a remaining life expectancy measured in only a few million years.
The star is currently fusing helium in its core, a temporary process that will soon lead to the fusion of increasingly heavier elements. This culminates in the formation of an iron core, which cannot sustain nuclear fusion. This causes the star to suffer a gravitational collapse, resulting in a core-collapse supernova explosion.
This supernova would briefly outshine an entire galaxy, releasing a flood of high-energy radiation, including gamma rays and X-rays, across the solar system. Depending on the final mass of the collapsed core, the stellar remnant would be either a dense neutron star or a stellar-mass black hole. The explosion would leave behind a dark stellar corpse at the center of a devastated system.