Astronauts
Astronomy
Constellation
Deep Sky Objects
Moon
Stargazing
Telescope
About Us Contact Us Privacy Policy Accuracy & Corrections Terms & Condition
COPYRIGHT. All contents of on the site comporting the StarLust branding are Copyright 2019. All rights reserved.
STARLUST.ORG / ASTRONOMY

The Largest Planet in The Universe

Jupiter may be the King of the Planets, but that’s just in our solar system. What’s the biggest planet in the solar system? What do we know about it?
UPDATED AUG 9, 2024
ROXs 42 Bb
ROXs 42 Bb

Jupiter may be massive at over 11x times wider than Earth, but size is relative. We always have to ask how big an object is in comparison to something else because as the saying goes, “there’s always a bigger fish” or shark or whale. While Jupiter may be big, it’s about a tenth the size of our Sun, and it’s easy to spiral out from there to other stars and galaxies, making Jupiter as tiny as a grain of sand.

But, let’s keep it simple. What’s the biggest planet out there?

First of all, we have to define what we mean by the largest. Big can imply the surface area of an object as well as its volume or its mass. While these things tend to correlate fairly well here on Earth, especially in our daily lives,  in the universe, things get a little weird and counterintuitive as we get bigger. 

Above a certain mass, the atoms begin to compress so drastically that it actually shrinks the planet in terms of surface area. For instance, Jupiter is three times Saturn’s mass, but only slightly larger in terms of width (11x that of Earth compared to 10x respectively).

However, there are some exceptions. There are puffy planets outside of our solar system made of much lighter elements that have been observed as up to twice as wide as Jupiter but containing much less mass such as WASP-17b which was discovered in 2009 with twice the radius of Jupiter, but only 48.6% of Jupiter’s mass or TOI-3757b which we discussed in our previous article on the coolest and weirdest exoplanets

There are many other discovered large puffy planets that have low mass, but up to 2x the width of Jupiter seems to be the limit according to what we have discovered so far.

Astronomers tend to consider mass as the most important factor when defining the largest in terms of astronomical bodies, so we will follow their lead for this article.

The largest planet discovered so far

While we are always discovering new objects and the number of confirmed planets orbiting stars other than our own, known as exoplanets, continues to rise (almost 5,500 confirmed and almost 9,800 candidates as of early August 2023), the current largest planet discovered is ROXs 42 Bb.

Meet exoplanet ROXs 42 Bb

This gas giant (like Jupiter) discovered in 2013 lies nearly 500 lightyears away orbiting an M-type (red dwarf) star (ROXs 42 B) 1.34 times as wide as our Sun but cooler and dimmer.

ROXs 42 Bb’s radius is 1.12 times that of Jupiter’s with a mass of 9 Jupiters. This means that while it is only about 12% wider than Jupiter it “weighs” or is as massive 9 Jupiters.

ROXs 42 Bb takes 1,968.3 Earth years to complete one orbit around its star which lies 157 times further away than Earth lies from the Sun. This is a very big planet lying very far away from its star.

It was found using Direct Imaging, meaning that observatories were able to actually image it by covering up the overpowering light of its star. This form of exoplanet detection is relatively new in the age of exoplanet hunting, but expanding rapidly.

It is still unclear how this planet formed with current proposals including the gradual accumulation of gas, dust, and other materials (accretion) from the core of the star, gravitational instability in the system, or formation more similar to a binary star, but failed.

Preliminary models suggest an effective temperature (calculated by determining how much of the star’s light it receives and disregarding atmospheric effects) of over 3,000 degrees Fahrenheit or 1730 degrees Celsius compared to Earth’s effective temperature of 2.2 degrees Fahrenheit (-19 degrees Celsius).

Its atmosphere is likely cloudy and dusty though continued study is needed.

Important note: it is extremely difficult to define the line between a giant planet and a brown dwarf, which are essentially failed stars since they didn’t gain quite enough mass to start nuclear fusion in the core.

Brown dwarfs are currently classified as approximately 13 times the mass of Jupiter, meaning ROXs 42 Bb still lie within the current definition of a gas giant according to current data. At least 5 potential exoplanets around ROXs 42Bb could be brown dwarfs due to ranging data that is still being confirmed.

Conclusion

While Jupiter is the largest planet in our solar system, it certainly isn’t the largest planet out there. While “big” is both relative to what it is being compared to and dependent on the definition (surface area, mass, etc.), there are many detected and likely undetected planets in space bigger than Jupiter. 

While there are puffy planets that have been discovered as up to twice the width of Jupiter, but a fraction of the mass, the current acknowledged largest planet discovered is ROXs 42 Bb at only 12% wider than Jupiter but 9 times as massive.

The beauty of space exploration is that this record holder may be beaten at any point, but it is currently the heavyweight champion of the discovered planets in the universe.

MORE ON STAR LUST
The mission, named Starlink 17-1, sent 24 broadband internet satellites from the Vandenberg Space Force Base.
11 hours ago
A Falcon 9 rocket launched the SpaceX Starlink missions from Cape Canaveral Space Force Station.
1 day ago
The launch took place amid the talks of replacing the Minuteman III ICBM with the LGM-35 Sentinel.
2 days ago
In an announcement in the Oval Office alongside the Secretary of Defense, Trump revealed his plans for the $175 billion program.
5 days ago
A local environmental advocacy group highlights through several letters how increased launches will impact the flora and fauna.
5 days ago
The Discriminating Space Sensor (DSS) is being developed to greatly enhance the capability to differentiate real missile threats from irrelevant clutter.
6 days ago
SpaceX's increased launch approval from the FAA mandates environmental monitoring in collaboration with wildlife experts.
7 days ago
Acting NASA chief Janet Petro addresses the successful Blue Ghost Moon Mission and the touchdown of the private lunar lander.
May 20, 2025
On May 14 at Spaceport America in New Mexico, a subscale rocket powered by Venus Aerospace's Rotating Detonation Rocket Engine (RDRE) successfully launched at 9:37 a.m.
May 19, 2025
These technologies have recorded incredible progress for space applications.
May 17, 2025
Josef Aschbacher lauded the ESA for achieving leadership roles in some space fields despite less being spent on it compared to the U.S. and China.
May 17, 2025
Musk has announced that he will detail SpaceX's Mars plan before the launch of the Starship flight in Starbase.
May 16, 2025
The companies will work collectively to build a secure military and commercial communication network.
May 15, 2025
A 'static fire' test for an extended period was conducted with a Starship upper stage at the Starbase site in South Texas.
May 15, 2025
The startup that builds solid rocket motors will use the funding to complete construction of a new 'energetics campus' outside Austin in Texas.
May 14, 2025
This move reverses the earlier indications that the NSC might be dissolved. 
May 14, 2025
NASA’s second super-pressure balloon floated over the country’s North Island by following its wind pattern before moving away.
May 14, 2025
NASA has canceled its commercial partnership plan for the VIPER moon rover launch and will pursue 'alternative approaches' instead.
May 12, 2025
If someone were orbiting the Moon, an observer on Earth would think they're 168 football fields away from the correct location.
May 10, 2025
SpaceX is now allowed to conduct up to 25 Starship launches and landings in a year, compared to the previous 5.
May 9, 2025