Deep Time · Deep Time
The Red Giant Sun
▶ Explore this system live in the app
This is how it ends.
Fast-forward about 7.6 billion years, to the very tip of the Sun's red giant branch: the last, most dramatic moment of a transformation that actually plays out over hundreds of millions of years. Freezing it into one scene compresses a long, slow process into a single snapshot, the same way the Proto-Solar System preset compresses the solar system's messy infancy.
- A swollen, dying Sun has ballooned to roughly 256 times its current width and thousands of times brighter, even as its surface cools to a dim orange-red. It's already shedding a meaningful fraction of its own mass as a dense stellar wind, a preview of the white dwarf ember it will eventually leave behind.
- Mercury and Venus are gone. Both were engulfed outright once the Sun's photosphere swelled past their old orbits, their rock and metal now stirred into the Sun's own bloated outer layers.
- Earth sits on a genuine knife's edge. Its oceans boiled away a billion years earlier, and whether the scorched cinder that's left gets dragged in and vaporized, or merely grazes the Sun's surface and survives as a dead husk, is a real, unresolved argument among astronomers, per the Future of Earth models.
- Saturn's rings vanished long ago, stripped away by "ring rain" on a timescale of mere hundreds of millions of years, ages before the Sun ever reached this stage.
- Europa and Titan each get a brief second spring, warmed enough by the swollen Sun for their ice to thaw and, very briefly on a geological clock, pool as liquid water at the surface: one of the strangest genuine predictions in solar system science.
The Sun's exact brightness shifts throughout its giant-branch evolution rather than holding still at one number, so exactly which outer moons get their moment of warmth moves around too. Treat the "second spring" window here as illustrative rather than a fixed date.
Celestial Bodies (13)
The Red Giant Sun
star · system center · 356,352,000 km diameter
Class M (Red Giant) ~256x Current Radius Engulfing
Roughly 256 times its current width and thousands of times brighter, but cooler at the surface: barely 3,000°C, dim enough to glow deep orange-red rather than white-hot. It has already shed a meaningful share of its own mass into space as a dense stellar wind.
The Great Mass-Loss Wind
region · orbits The Red Giant Sun · 178,176,000 km–260,000,000 km
A dense, roiling stream of gas the dying Sun is hurling into space, fast enough that it will eventually carry off close to a third of the Sun's entire mass. Where that mass goes matters: losing it loosens the Sun's grip on everything still orbiting, letting every surviving planet's orbit slowly stretch outward.
The Ashes of Mercury & Venus
region · orbits The Red Giant Sun · 57,908,617 km–108,159,261 km
Consumed Worlds No Longer Exist
There's nothing left to see here, which is the point. Mercury and Venus no longer exist as separate worlds: both were swallowed whole as the Sun's photosphere swelled past their old orbits, their rock and metal now stirred into the Sun's own bloated outer layers.
Earth, On the Brink
planet · orbits The Red Giant Sun · 179,517,445 km · 12,742 km diameter
Scorched Husk Earth-Sized Engulfment Disputed
Earth's oceans boiled away roughly a billion years before the Sun ever reached this stage, leaving a scorched, airless rock long before this moment arrived. Whether it's even still here at all is genuinely disputed: the Sun's mass loss stretches every planet's orbit outward, but the bloated Sun's own tides drag right back on anything still this close. Most models give Earth a real chance of being dragged in and vaporized outright; the rest leave it a dead, tidally-battered cinder grazing the Sun's own surface.
Mars, Baked Dry
planet · orbits The Red Giant Sun · 227,987,155 km · 6,779 km diameter
🪨 Desert Sub-Earth Overheated
Mars was never close enough to be swallowed, but it's no refuge either. At the Sun's peak brightness, Mars catches more light than Venus does today, more than enough to boil off its polar ice caps and any lingering trace of atmosphere for good.
The Roasted Asteroid Belt
region · orbits The Red Giant Sun · 329,115,316 km–478,713,186 km
Planetesimals Devolatilized
Whatever ice was ever hiding inside these rocks sublimated away long ago. What's left is a dry, sun-blasted gravel field, thinner and duller than the asteroid belt of any earlier era.
Jupiter
planet, gas-giant · orbits The Red Giant Sun · 778,507,319 km · 139,820 km diameter
🪐 Gas Giant Drifting Outward
Jupiter's orbit has already begun creeping outward as the Sun sheds its own mass, the first stretch of a drift that will continue long after this snapshot, once the Sun finishes collapsing into a white dwarf.
Europa, A Second Spring
moon, ice · orbits Jupiter · 670,900 km · 3,122 km diameter
🌊 Thawed Ice Moon Transient Habitability
For a stretch of the Sun's giant phase, a moon like Europa can catch enough warmth to thaw at the surface, its ancient subsurface ocean briefly reaching daylight before the deep freeze returns for good. Whether that window lands exactly here, earlier, or later in the Sun's long swelling depends on the model, but a real stretch of habitability, this far out, is one of the strangest predictions in all of solar system science.
Saturn (Ringless)
planet, gas-giant · orbits The Red Giant Sun · 1,433,536,556 km · 116,464 km diameter
🪐 Gas Giant Ringless
Saturn's rings are long gone by now. Icy ring material has been raining down onto the planet on a timescale of a few hundred million years, nowhere near long enough to have survived the billions of years it took the Sun to reach this stage.
Titan, A Second Spring
moon, ice · orbits Saturn (Ringless) · 1,221,870 km · 5,149 km diameter
🌊 Thawed Ice Moon Transient Habitability
Titan's thick nitrogen atmosphere and deep reserves of water ice give it its own shot at a temporary thaw during the Sun's giant phase, briefly pooling liquid water across a landscape otherwise built out of frozen hydrocarbons.
Uranus
planet, gas-giant, ice-giant · orbits The Red Giant Sun · 2,875,031,718 km · 50,724 km diameter
🧊 Ice Giant Largely Unchanged
Far enough out that the Sun's dramatic new size barely registers as more than an unusually bright point of light, Uranus rides out the Sun's giant phase largely unchanged.
Neptune
planet, gas-giant, ice-giant · orbits The Red Giant Sun · 4,504,391,887 km · 49,244 km diameter
🧊 Ice Giant Largely Unchanged
The outermost planet, still cold and dark, still too far out to feel much from a Sun that, even swollen to giant size, has only gotten a little less faint from way out here.
The Awakening Kuiper Belt
region · orbits The Red Giant Sun · 4,487,936,121 km–7,479,893,535 km
Icy Planetesimals Reactivated
Out here, the Sun's dramatically increased output finally makes a real difference: icy bodies that have sat inert for billions of years start sublimating in earnest, throwing off comet tails on a scale the Kuiper Belt has never produced before.