When we look up at the sky, we see stars shining like tiny dots. But many of those stars have planets orbiting around them, just like Earth orbits the Sun. These planets outside our Solar System are called exoplanets. Some are huge like Jupiter, and some are much smaller — even smaller than Mercury, the smallest planet in our Solar System. Today, we are going to explore the smallest known planet in the entire universe — a tiny world called Kepler-37b.
The Smallest Planet in the Universe: Meet Kepler-37b
Kepler-37b is the smallest confirmed exoplanet discovered so far. It is even smaller than Mercury, and nearly the same size as Earth’s Moon! This tiny planet was discovered by NASA using the Kepler Space Telescope, which looked for changes in light from stars to find planets.
Kepler-37b orbits a star named Kepler-37, located about 215 light-years away from Earth in the constellation Lyra. The planet was first confirmed in 2013, and it amazed scientists because of its incredibly small size.
How Small Is Kepler-37b?
Let’s compare:
- Kepler-37b Diameter: About 3,900 km
- Earth’s Moon Diameter: About 3,475 km
- Mercury Diameter: About 4,880 km
So, Kepler-37b is smaller than Mercury, and just slightly larger than our Moon. This makes it the smallest known planet outside our Solar System that we have discovered so far.
How Was It Discovered?
NASA used a method called the transit method. Here’s how it works:
- The Kepler telescope watched thousands of stars.
- If a planet passed in front of a star, it blocked a little bit of the star’s light.
- That small dip in brightness was recorded as a possible planet.
But with something as small as Kepler-37b, the drop in light is tiny — less than 20 parts per million. It was extremely hard to detect. This discovery proved that Kepler’s instruments were very precise, and it gave hope that many small planets might be out there waiting to be found.
What Is Kepler-37b Made Of?
Kepler-37b is probably a rocky planet, like Earth and Mercury. But because it’s very close to its star, it’s extremely hot. Scientists believe:
- It has no atmosphere.
- It has no water or life as we know it.
- The surface is likely dry and covered in rock or metal.
In other words, Kepler-37b is a scorched, rocky world that might look like a burnt-out version of Mercury.
How Hot Is Kepler-37b?
Kepler-37b orbits very close to its star — even closer than Mercury is to the Sun. As per NASA Science reports Its orbit takes only 13.4 days, so a year on this planet is just under two weeks!
Because of this, temperatures on the planet may reach 700 to 800 degrees Celsius (1,300–1,500°F). That’s hot enough to melt lead, and definitely too hot for life to exist.
The Kepler-37 System
Kepler-37b is not alone. It has at least two other sibling planets:
- Kepler-37c – Larger than Kepler-37b but smaller than Earth.
- Kepler-37d – A bit larger than Earth.
All three planets orbit the same star, and all are likely rocky worlds. But only Kepler-37b stands out for being the smallest.
Why Is Kepler-37b’s Discovery Important?
The discovery of Kepler-37b is very important for several reasons:
- Proves tiny planets exist: Before this, we didn’t know if very small planets were even possible outside our Solar System.
- Improves planet hunting: It showed that telescopes like Kepler could find even the tiniest worlds.
- Expands our knowledge: It helped scientists understand how planets form and survive around stars.
This planet gave us hope that there may be other Earth-sized or smaller planets in the galaxy — maybe even with conditions for life.
How Many Small Planets Are Out There?
Kepler-37b is the smallest we’ve found so far, but it might not be the only one. NASA’s Kepler and TESS missions have already found thousands of exoplanets, many of them small.
Astronomers believe that small rocky planets may be very common, especially around stars smaller than our Sun. Some of these planets might even be in the “habitable zone” — where temperatures are just right for liquid water.
Could There Be Planets Smaller Than Kepler-37b?
Yes — it’s possible! Kepler-37b is the smallest confirmed planet, but there could be even smaller planets that we haven’t found yet. Our current telescopes have limits. But future missions like the James Webb Space Telescope (JWST) and other advanced observatories may soon find even tinier worlds.
Other Tiny Worlds in Our Solar System
Although Kepler-37b is the smallest known planet in the universe, let’s compare it with some small worlds in our own solar system:
- Pluto (no longer considered a planet): 2,377 km wide
- Ceres (largest asteroid): 940 km wide
- Earth’s Moon: 3,475 km wide
This shows how small Kepler-37b really is. It’s closer to the Moon’s size than any of the main planets.
What Makes a Planet a Planet?
To be called a planet, an object usually must:
- Orbit a star.
- Be mostly spherical in shape.
- Have cleared its orbit of other objects.
Kepler-37b fits these rules, which is why it’s considered a real planet — not just an asteroid or moon.
The Future of Planet Hunting
The discovery of Kepler-37b was a big step in space exploration. But it’s just the beginning. In the future, scientists hope to:
- Find planets even smaller than Kepler-37b.
- Study their atmospheres using advanced telescopes.
- Discover Earth-like worlds in other solar systems.
As our tools get better, we might find a whole new class of tiny planets — or even ones that surprise us in size, shape, or habitability.
Fun Facts
- Kepler-37b is 30% smaller than Earth’s Moon.
- It takes only 13 days to go around its star.
- Its discovery proved how powerful the Kepler telescope really was.
- It might be one of billions of tiny planets in the Milky Way galaxy.
Final Thoughts
The universe is full of mysteries. While giant planets and stars often get the spotlight, small objects like Kepler-37b remind us that even the tiniest things can be incredibly important. This tiny planet — smaller than our Moon — changed how we think about space and what’s possible beyond our Solar System.
The more we search, the more we realize: In space, even the smallest worlds can open the biggest questions.
FAQs
Q1: What is the smallest planet ever discovered?
A: Kepler-37b is currently the smallest known exoplanet. It is even smaller than Earth’s Moon and was discovered by NASA’s Kepler Space Telescope in 2013.
Q2: How small is Kepler-37b?
A: Kepler-37b has a diameter of about 3,865 kilometers (2,400 miles), which is roughly 30% smaller than Mercury and just slightly larger than our Moon.
Q3: Can Kepler-37b support life?
A: No, Kepler-37b is too close to its star and has extremely high surface temperatures. It likely does not have an atmosphere or water, making life as we know it impossible there.
Q4: Where is Kepler-37b located?
A: Kepler-37b is located about 210 light-years away from Earth in the Lyra constellation.
Q5: How was Kepler-37b discovered?
A: It was discovered by the Kepler Space Telescope using the transit method, where a planet passes in front of its star and slightly dims the light we observe from Earth.
Q6: Does Kepler-37b have moons or rings?
A: Scientists have not detected any moons or rings around Kepler-37b, and due to its small size and closeness to its star, it’s unlikely that it has any.
Q7: Is Kepler-37b smaller than Pluto?
A: No, Pluto is smaller. While Kepler-37b is the smallest exoplanet ever found, Pluto (a dwarf planet) is even smaller in diameter.
Q8: What kind of star does Kepler-37b orbit?
A: It orbits a star very similar to our Sun, called Kepler-37, which is slightly cooler and smaller than the Sun.
Q9: How long does a year last on Kepler-37b?
A: A year on Kepler-37b is only about 13 Earth days long because it orbits very close to its star.
Q10: Could future telescopes study Kepler-37b in more detail?
A: Yes, with the help of more powerful space telescopes like the James Webb Space Telescope, scientists may learn more about this tiny planet’s composition and atmosphere (if any).
