The Smallest and Largest Planet in the Solar System

The Smallest and Largest Planet in the Solar System

Our solar system is comprised of a family of fascinating stellar bodies, all with their own unique characteristics, atmospheres, terrains, and environments. They’ve fascinated astronomers for centuries and long been the subject of speculation and discussion. Some of said discussion involves their size: which is the largest planet, and which is the smallest planet?

This question seems easy, but as astronomers continue to discover new things about our system, different answers come to light. We’ll tell you more about them, along with some interesting factoids about each planet.

What is the Largest Planet in the Solar System?

Fifth from the Sun and largest planet, here resides mighty Jupiter. Known primarily for its Great Red Spot, it was originally discovered by Galileo in 1610, remaining one of the most significant discoveries since. Jupiter plays an integral role in our system, from what we’ve learned to its gravitational pull. (Trying to find out how many planets there are in the solar system? Click here.)

The Great Red Spot is a massive storm which has existed for centuries, perhaps longer. It’s large enough it would consume Earth, while the rest of the planet is made of windy, cold elements. This is why it’s referred to as a “gas giant,” as there’s no known surface and its cloudy swirls are primarily composed of ammonia and water.

We know the body of Jupiter is made of hydrogen and helium, but if it has a solid surface, we’ll never know until we explore beyond its atmosphere. Because of this, Jupiter is incapable of supporting life as we know it. However, because of its immense gravity, Jupiter has many moons – over 72. These moons are unique in their own right and may have conditions suitable for living organisms.

Jupiter’s Moons

Because it’s the largest planet in the solar system, Jupiter boasts a massive gravitational field which snares asteroids and other rocky objects. Some of them fall into its stormy atmosphere, while others remain in orbit. Those that have are now part of the planet’s moon family.

As of now, it’s estimated there are at least 79, but potentially more. While there are too many to list in one go, some of Jupiter’s moons are worth inspecting. (Click here to find out how many stars there are in the solar system.)


One of the key ingredients to creating/sustaining life is water. Our ocean is an indicator of how diverse it can be. Europa is much like this; scientists believe beneath its icy surface are deep oceanic reservoirs of salt-water. This means Europa is potentially the best area for discovering/supporting life, even more than Mars!


Jupiter isn’t just the largest world, it has also the largest moon. Ganymede takes that title, and is large enough it has its own magnetic field. Even more interesting is it has a very thin oxygen laced atmosphere and underground ocean – although these aren’t suitable for life support (as of now).


Io grabs attention for being the most volcanically active moon in the solar system. Volcanic activity is a rare trait, especially for moons, so it suggests deeper geologic activity.


The last moon of notable mention is the third largest lunar object in our solar system. Its cratered surface suggests it’s geologically dead, however, further observations may suggest there is an ocean of brine (salty) water beneath. (Looking to get a closer look at some of these astronomical bodies? Check out our favorite solar telescopes, here.)

What is the Smallest Planet in the Solar System

What is the Smallest Planet in the Solar System?

Like a David to its Goliath, there is also the smallest planet in our system. This title goes to Mercury, the first planet in the system and one of the hottest (naturally). To get an idea of how tiny Mercury is, it’s only slightly larger than our moon. (Click here for a solar system chart that explains all of these bodies.)

Because of its proximity to the sun, Mercury cannot support life. Its atmosphere and magnetosphere are also too thin to provide adequate solar protection. Organism would have to be capable of withstanding days of over 400 degrees Celsius (and nights hundreds of degrees below zero). The atmosphere is comprised of Nitrogen, Helium, Potassium, and some Oxygen, but not enough for breathable conditions.

It’s also the “fastest” planet in the system. Its relation in distance to the sun means Mercury has a yearly orbit of 88 Earth days. In other words, Mercury would complete almost 4 solar orbits in the time it takes Earth to complete one. However, while it creates a quick solar orbit, a single day on Mercury is much, much longer. In fact, it would take 58 Earth days for Mercury to accomplish one full rotation.

Mercury was first discovered centuries ago in the 14th century BC by Assyrian astronomers, although who specifically discovered it is unknown. Also, exploring the planet has proven difficult. Two probes have visited since the 70’s, though imaging is challenging. Naturally, probes can’t land on the surface due to the extreme heat and radiation, so orbit imaging must suffice for now. (While you’re here, you may want to consider checking out our guide to building a solar system mobile for your favorite youngster.)

Where did these planets come from

Where did these planets come from?

So how do small and large planets like Jupiter and Mercury come to be? The answer is complicated so we’ll break it down into an easy explanation.

The Solar System was created roughly 4.6 billion years ago, and a variety of occurrences formed the planets making up the stellar bodies. We can’t explain it all in one sitting, but the general pattern is similar. For example, the sun caught objects in its gravitational pull during the system’s formation. Mercury was one of those objects, a rocky body caught in orbit. (Trying to bring some of these heavenly bodies to life? Check out our guide on solar system projectors!)

Jupiter too was formed in a similar manner. But how does a gas giant come to be? Essentially, gasses and cosmic dust swirled together to start forming what we know as Jupiter. During this process – where material in a “solar nebula” combine together – Jupiter wasn’t large enough to become a star, so instead formed as a gas giant. Eventually, this material orbited the sun, making up our modern solar system today. This is a simplified explanation but gives you a general idea of how it occurred.


While it’s easy to get the question confused about the smallest and largest planets in our system, the fact remains today: Mercury is the smallest and Jupiter the largest. Some think Pluto is the smallest (remember, it’s now a Dwarf Planet) and Saturn is the largest, but now you know otherwise. (Looking for some great solar-themed products? Check out our list of our favorite solar filters for camera lenses!)

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