TOI-5788 b is a super-Earth — a type of planet bigger than our own Earth but smaller than the giant planets in our solar system. It sits 318 light-years away, which sounds enormous, and it is. Yet by the standards of our galaxy, that is actually a fairly close neighbor. Scientists announced the discovery in 2026, and it has already given us a lot to think about.
Where in the Sky We Find TOI-5788 b
TOI-5788 b lies 318 light-years from Earth. A light-year is the distance light travels in one year — about 9.5 trillion kilometers. At that distance, even a signal traveling at the speed of light would take 318 years to arrive. No spacecraft we have today could reach it in a human lifetime.
Even so, 318 light-years puts TOI-5788 b well within the part of the Milky Way that astronomers study in detail. Many of the exoplanets — that means planets orbiting stars other than our Sun — we know best are roughly in this range. The universe is vast, and this world is just one small dot in it.
What Kind of World Is TOI-5788 b?
TOI-5788 b belongs to a category called super-Earths. Super-Earths are planets with a radius (that is, the distance from the center to the surface) somewhere between Earth’s size and Neptune’s size. They are one of the most common types of planet we have found around other stars, yet our own solar system has none at all.
The tricky thing about super-Earths is that the name does not tell you very much about what they are actually like inside. Some super-Earths are thought to be mostly rock, like Earth but bigger. Others might be wrapped in thick layers of water — scientists sometimes call these water worlds. Still others could have dense, heavy atmospheres made mostly of hydrogen and helium. Without more measurements, it is often hard to know which kind a particular super-Earth is.
For TOI-5788 b, scientists have measured both its size and its mass. That combination is very useful, and it gives us real clues — which we will look at in the next section.
Size, Mass, and What They Tell Us
TOI-5788 b has a radius of 1.53 times Earth’s radius. So picture Earth, then imagine stretching it out about halfway more. It is noticeably bigger, but not overwhelmingly so.
Its mass — that is, how much matter it contains — is 3.72 times Earth’s mass. That is more than three and a half times the stuff that makes up our whole planet, packed into a world only about half again as wide.
These two numbers together let scientists calculate density. Density is a measure of how much mass is packed into a given volume. A ball of iron is denser than a ball of foam the same size. When a planet has a high density, it is probably made mostly of rock or metal. When density is low, the planet likely contains lots of light materials — gas, ice, or water.
For TOI-5788 b, the density that comes from these numbers suggests it is probably a rocky world, possibly with some heavier elements in its core. It does not seem to be dominated by light gases. But scientists are careful here — getting a truly confident picture of what is inside a planet 318 light-years away is very hard. The best we can say is that the numbers point toward a denser composition, likely rocky. You can explore how size and mass relate to each other for many known planets using the mass-radius diagram.
It is also worth knowing that there is a size range — roughly between 1.5 and 2 times Earth’s radius — where planet types seem to shift. Smaller planets in this range tend to be rocky. Slightly larger ones often have thick gas envelopes. TOI-5788 b sits right at the edge of that range, which makes it especially interesting to researchers.
A Scorching Orbit
One year on TOI-5788 b lasts just 6.34 Earth days. That is how long it takes to complete one full orbit around its star. To do this so quickly, the planet must be orbiting very close in — much closer to its star than Mercury is to our Sun.
Being that close comes with a cost: heat. Scientists estimate the planet’s surface temperature is around 910 K, or about 637 degrees Celsius. That is hot enough to melt lead. It is also far too hot for liquid water to exist on the surface, at least under the conditions we understand today.
This means TOI-5788 b does not sit in what astronomers call the habitable zone — the range of distances from a star where liquid water could exist on a planet’s surface. Instead, it orbits deep inside the inner edge of that zone, baking under intense starlight. Whether it ever had different conditions in the past, we simply do not know.
How Scientists Found It
TOI-5788 b was discovered in 2026 using the transit method. This technique works by watching a star very carefully over time. When a planet passes in front of its star — an event called a transit — it blocks a tiny bit of the star’s light. Scientists can measure that dip in brightness. From the depth and timing of the dip, they can figure out the planet’s size and how long its orbit is.
The transit method works especially well for planets with short orbits, because those planets transit their star more often, giving scientists more chances to observe them. TOI-5788 b, with its 6.34-day year, is a good candidate for this approach.
The Star TOI-5788
TOI-5788 b orbits a star called TOI-5788. The star’s surface temperature is 5,615 K. For comparison, our Sun’s surface is about 5,778 K. So TOI-5788 is a little cooler than the Sun, which makes it slightly dimmer and a bit more orange in color. It belongs to a category of stars known as G-type or K-type stars, which are considered fairly calm and long-lived. Scientists have not published other details about the star’s size or age in the data available so far.
A Two-Planet System
TOI-5788 b is not alone. Astronomers have found at least two planets in this system so far. The second planet’s details — its size, mass, and orbit — have not been published in the data available for this article. Multi-planet systems are common across the galaxy, and finding one here suggests the system formed from a rich disk of gas and dust, just as our own solar system did.
Studying systems like TOI-5788 helps scientists understand the full range of planets that form around Sun-like stars. If you want to see how TOI-5788 b’s size compares to other known worlds, the size comparison tool lets you set planets side by side. TOI-5788 b is one world among billions, but each one we study adds a little more to the picture of what is out there.