TIC 139702105 b is an exoplanet — a planet that orbits a star outside our own solar system. It sits about 299 light-years from Earth, which means light, the fastest thing in the universe, would take 299 years to travel from there to here. Scientists placed it in a category called mini-Neptunes, a fascinating group of worlds that are bigger than Earth but smaller than the ice giants in our solar system.
Where in the Sky Is TIC 139702105 b?
At 299 light-years away, TIC 139702105 b is far beyond anything we could ever visit with today’s spacecraft. Even so, on the scale of our galaxy — the Milky Way, which stretches roughly 100,000 light-years across — this planet is actually a fairly close neighbor. Its host star, TIC 139702105, is one of countless stars in our region of the galaxy. As far as we know, TIC 139702105 b is the only planet confirmed in this system so far.
How Scientists Found It
Astronomers discovered TIC 139702105 b in 2026 using a technique called the transit method. A transit happens when a planet passes in front of its star, as seen from Earth. When that occurs, the star looks just a tiny bit dimmer — like a bug walking across a lamp. Sensitive telescopes can detect that small dip in light. By measuring how often the dip repeats and how deep it is, scientists can figure out the planet’s orbital period (how long its year is) and get a good estimate of its size.
The transit method is one of the most successful tools astronomers have for finding exoplanets. It works especially well when a planet orbits close to its star, because close-in planets transit more often and are therefore easier to catch in the data.
Size and Mass — What the Numbers Tell Us
TIC 139702105 b has a radius of 2.45 times Earth’s radius. That means if you could line up Earths side by side, you would need about two and a half of them to stretch across this planet. You can get a real feel for that difference using a size comparison tool to place Earth and mini-Neptunes next to each other.
Scientists have also measured its mass at 6.59 times Earth’s mass. That is useful, because when you know both the size and the mass of a world, you can calculate its density — that is, how much matter is packed into a given amount of space. Density is one of the best clues we have about what a planet is made of on the inside.
A planet made mostly of rock, like Earth, tends to be dense and heavy for its size. A planet made mostly of gas and water tends to be less dense. TIC 139702105 b’s combination of size and mass points to a world that is less dense than a purely rocky planet — suggesting it has a significant envelope of lighter material, such as gas or water, surrounding a denser core. You can explore how size and mass relate to planetary structure on the mass-radius diagram, which shows how different types of worlds cluster together.
Inside a Mini-Neptune — Layers and Composition
Mini-Neptunes are one of the most common types of planets that telescopes have found around other stars, yet we have none in our own solar system. That makes them both fascinating and a little mysterious.
Scientists think a typical mini-Neptune has a few distinct layers. At the center, there is probably a rocky or metallic core — a ball of dense material similar to what sits at the heart of Earth. Surrounding that core may be a thick layer of water, ice, or other heavier compounds in a state that is neither purely liquid nor purely gas, because of the extreme pressure. On top of that, there is likely a deep atmosphere made mostly of hydrogen and helium, the lightest gases in the universe.
For TIC 139702105 b specifically, scientists haven’t yet measured its atmosphere directly, so we don’t know exactly how thick that outer gas layer is or what it contains. What the mass and radius together do suggest is that this planet is not purely rocky — there is almost certainly a meaningful layer of lighter material. Whether that layer is mainly gas, water, or a mix of both is something researchers are still working to understand.
A Year That Lasts Less Than a Week
One of the most striking things about TIC 139702105 b is how fast it travels around its star. One full orbit — one year on this planet — takes just 6.84 Earth days. That is less than a week. By comparison, Earth takes 365 days to complete one orbit around the Sun.
To move that quickly, TIC 139702105 b must orbit very close to its star. Close-in orbits mean the planet receives a large amount of energy and heat from its star. Scientists haven’t published a surface temperature measurement for TIC 139702105 b yet, but worlds in such tight orbits are generally expected to be quite warm — far too warm to be in the habitable zone, which is the range of distances from a star where liquid water could possibly exist on a planet’s surface. This planet sits well inside that zone, meaning conditions there are likely harsh.
The Star It Orbits
The star TIC 139702105 has a surface temperature of 5,742 Kelvin. Kelvin is a temperature scale scientists use; 0 Kelvin is the coldest anything can ever be, and 5,742 K is extremely hot by everyday standards. For comparison, our own Sun has a surface temperature of about 5,778 K, so this star is very slightly cooler than the Sun and likely quite similar to it in character — what astronomers call a solar-type star. That said, scientists haven’t published full details about TIC 139702105’s size or age yet, so we should be cautious about reading too much into just one number.
What We Still Don’t Know
TIC 139702105 b was only confirmed in 2026, so research is still in its early stages. Scientists haven’t yet measured its atmospheric composition, its exact internal structure, or whether it has any moons. We also don’t know if there are other planets in the same system that simply haven’t been detected yet — one confirmed planet doesn’t always mean only one planet exists.
What we do know is enough to place TIC 139702105 b in a scientifically interesting category. Mini-Neptunes like this one help astronomers understand how planets form, how they hold onto their atmospheres under intense heat, and why our own solar system looks different from so many others. Each new world added to the catalog is one more piece of a very large puzzle that scientists are slowly putting together.