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We’ve evolved from the belief that Earth was the universe's focal point to uncovering countless galaxies, thousands of solar systems, and potentially millions of planets, with new discoveries happening regularly. Keeping track of them all is nearly impossible, especially given their vast and intricate names. However, the following planets distinguish themselves in remarkable ways.
10. Largest Rocky Planet: Kepler-10c
This planet is roughly 2.3 times larger than Earth, which might not sound overwhelmingly large—but its size qualifies it as what scientists refer to as 'mini-Neptunes.' What sets it apart, however, is its mass, which is approximately 17 times greater than Earth's, a figure far beyond what was anticipated.
The planet’s density reveals that it is composed of solid materials like rocks, which is a significant finding. Typically, planets of this size are gas giants—like Jupiter and Saturn—due to their strong gravity, which attracts vast amounts of hydrogen and helium.
9. Wettest Planet: GJ 1214b
This planet is also much larger than Earth. However, instead of rocks, its mass consists mainly of water. Scientists believe that a large portion of GJ 1214b, which was discovered in 2009, is made up of water, even though its surface temperature is much hotter than that of our world.
Scientists studied the planet’s atmosphere as it passed in front of its host star. Their findings indicated that the atmosphere is predominantly composed of water, suggesting the surface is likely water-rich as well. However, this is not regular water. Due to the intense heat and pressure, it would be a more exotic form of H2O—‘hot ice’ and ‘super fluid’ water.
The planet probably formed far from its sun, where water and ice were more abundant. Over time, it gradually drifted inward. Scientists anticipate they will begin an extensive study of the planet as soon as 2018.
8. The Youngest Planet: BD+20 1790b
It’s important to note that calling any planet 'young' is a bit of a stretch. This planet is approximately 35 million years old, which, in comparison to Earth, makes it practically a newborn—Earth is about 100 times older. This planet holds the title of the youngest known planet by a significant margin, as the previous record holder was 100 million years old.
Scientists are hopeful that this discovery will offer deeper insights into planetary evolution, especially since finding younger planets like this one is exceptionally rare. Younger planets tend to be much more active than older ones, often generating powerful magnetic fields that lead to sunspots and solar flares. These phenomena can disrupt readings, making it difficult to discern whether we are observing one planet or two. After years of studying this planet, scientists are still uncertain whether this young world has a twin.
7. Oldest Planet: Kapteyn B
The oldest known planet that could potentially support life formed only two billion years after the Big Bang. It orbits close enough to its star, Kapteyn, to maintain liquid water on its surface, unlike its twin, which is situated farther away and remains a frozen desolate world.
The Kapteyn system itself is fascinating. It lies incredibly close to our own solar system, making it one of the nearest systems known to scientists. This system and its planets once belonged to a separate, smaller galaxy. Researchers speculate that the Milky Way absorbed this galaxy, disrupting its structure and scattering its star systems to the galaxy's edges. A remnant of this consumed galaxy can be found in Omega Centauri, a galaxy 16,000 light-years away, housing planets that are not much younger than Kapteyn B.
6. Fastest Planet: COROT-Exo-7b
This planet has a mass about eight times that of Earth, yet it’s less than twice Earth’s diameter and boasts one of the fastest orbits ever discovered by scientists.
While Earth takes roughly 8,766 hours to complete its orbit around the Sun, this planet manages to finish its orbit in just 20 hours. While it’s not the hottest planet on the list (we’ll get to that one later), it’s certainly a strong contender. Scientists believe its extreme heat, ranging from 1,000 to 1,500 degrees Celsius (1,800 to 2,700 °F), is due to the molten lava that covers its surface.
This planet is also remarkable for how it was discovered. It was the first planet to be detected using the transit method, which allows scientists to determine a planet’s mass and radius. Earlier techniques only allowed scientists to measure its mass.
5. Coldest Planet: OGLE-2005-BLG-390L B
This planet is like the Milky Way’s version of the icy world of Hoth from *The Empire Strikes Back*. It holds the record as the coldest exoplanet ever discovered.
This planet orbits its star from such a great distance that it takes 10 Earth-years to complete one full orbit. The star itself is incredibly small compared to our Sun. The average temperature on this frozen world hovers around –200 degrees Celsius (–350 °F).
It also sets a record for being the farthest exoplanet from Earth, lying more than 28,000 light-years away from us.
1. Lightest Planet: KOI-314c
This planet holds the record for being the lightest known exoplanet to have its mass and size measured. Despite having a similar mass to Earth, its expansive, fluffy atmosphere of hydrogen and helium makes it roughly 60 percent larger than our planet. Its atmosphere may have been even more massive in the past, but much of it was stripped away by the heat from its red dwarf star.
To study the planet, scientists compared KOI-314c to its neighboring planet. The two worlds exert gravitational forces on each other, causing minor shifts in their transit times as they orbit their star. The second planet, KOI-314b, is much denser, with a mass over four times that of Earth, making KOI-314c only a fraction of its mass.
4. Hottest Planet: Kepler 70-B
Kepler 70-B shatters multiple records. Not only is it the hottest exoplanet ever discovered, with temperatures exceeding 7,000 degrees Celsius (12,500 °F), but it also boasts the closest orbit to its star. For comparison, the distance between Mercury and the Sun is 65 times greater than the distance between Kepler 70-B and its star. Additionally, this planet has the highest velocity and is one of the smallest exoplanets we know of.
The planet isn’t the only record-breaker—its star is quite extraordinary as well. Typically, when a star becomes a red giant, it explodes. However, this star defied expectations by stabilizing and shrinking back to a normal size. During this process, its gas giant planets were ejected from its atmosphere.
8. Youngest Planet: BD+20 1790b
It's important to remember that calling any planet “young” is a bit of a stretch. This planet is approximately 35 million years old, which, while young in the cosmic scale, is still much younger than Earth, which is about 100 times its age. This planet claims the title of the youngest known exoplanet, breaking the previous record held by a planet that was 100 million years old.
Scientists are hopeful that this discovery will give us greater insights into how planets evolve, especially since younger planets like this one are notoriously hard to find. Younger planets are far more active than older ones, often emitting powerful magnetic fields that produce sunspots and solar flares. These phenomena can distort our readings, making it challenging to determine whether we are observing one planet or two. In fact, after years of study, scientists still can't confirm whether this planet has a twin or not.
7. Oldest Planet: Kapteyn B
The oldest known planet that could potentially support life formed just two billion years after the Big Bang. Located close enough to its star, Kapteyn, this planet is capable of maintaining liquid water on its surface, unlike its twin, which is situated too far out and remains a frozen, lifeless world.
The Kapteyn system is particularly intriguing. For one, it’s one of the closest systems to our own that scientists have discovered. The planets within this system once belonged to an entirely separate, miniature galaxy. Researchers believe that the Milky Way absorbed this small galaxy, disrupting its star systems and scattering them to the outskirts. A remnant of this absorbed galaxy can still be found in Omega Centauri, a galaxy located 16,000 light-years away, with planets that are not much younger than Kapteyn B.
6. Fastest Planet: COROT-Exo-7b
This planet has a mass around eight times that of Earth, but its size is less than double Earth's diameter. It also features one of the fastest orbits discovered by scientists.
While Earth takes roughly 8,766 hours to complete its orbit around the Sun, this speedy world does it in only 20 hours. It may not be the hottest planet (we'll get to that later), but it certainly ranks high. Scientists think its blistering temperatures, ranging from 1,000–1,500 degrees Celsius (1,800–2,700 °F), are due to lava engulfing its surface.
This planet is remarkable not only for its characteristics but also for its discovery. It was the first exoplanet detected using the transit method, which scientists use to calculate a planet’s mass and radius. Prior techniques were limited to determining only the planet’s mass.
5. Coldest Planet: OGLE-2005-BLG-390L B
This planet could be described as the Milky Way's icy counterpart to Hoth from The Empire Strikes Back. It holds the record for being the coldest exoplanet ever found.
This world is so far from its star that it takes a full 10 Earth-years to complete one orbit. Its star is also incredibly small compared to ours. The average temperature on this desolate planet is around –200 degrees Celsius (–350 °F).
In addition to being the coldest, this planet is also the most distant exoplanet from Earth. It’s located more than 28,000 light-years away from our planet.
4. Hottest Planet: Kepler 70-B
Kepler 70-B doesn't just set one record, but multiple. Not only is it the hottest exoplanet discovered, with temperatures exceeding 7,000 degrees Celsius (12,500 °F), but it also boasts the closest orbit to its star. To put this in perspective, the distance between Mercury and the Sun is 65 times greater than the gap between Kepler 70-B and its star. Additionally, this planet travels at the fastest speed and is one of the tiniest exoplanets known to us.
It's not just the planet that's breaking records—its star is equally extraordinary. Typically, when a star evolves into a red giant like this one, it explodes. But this particular star managed to stabilize and contract back to a more typical size. In the process, its gas giant planets were expelled from its atmosphere.
1. Lightest Planet: KOI-314c
This exoplanet holds the title of being the lightest alien world ever measured in terms of both mass and size. Though it has a similar mass to Earth, its expansive, puffed-up atmosphere of hydrogen and helium makes it 60 percent larger than our own planet. It's possible that its atmosphere was even more massive in the past, but its red dwarf star evaporated much of it over time.
In order to study the planet, scientists compared KOI-314c with its neighboring planet. The gravitational pull between the two causes subtle changes in their orbits. The other planet, KOI-314b, is much denser and weighs more than four times the mass of Earth, making KOI-314c's weight a mere fraction of its neighbor's.
2. Darkest TrES-2b
Despite being relatively close to its star, TrES-2b is the darkest exoplanet ever observed. In our solar system, Mercury is regarded as one of the darkest planets, reflecting only about 10 percent of the Sun's light. Scientists once thought that was the limit for how dark planets could be—until TrES-2b was discovered. This planet reflects less than 1 percent of its star's light, making it darker than both coal and black acrylic paint.
Scientists are still uncertain about the cause of its extreme darkness. One hypothesis is that the planet's atmosphere contains a significant amount of sodium or titanium oxide in gaseous form, which could be responsible for this unique characteristic.
3. Weirdest Orbit Fomalhaut B, The Zombie Planet
This planet earned its eerie moniker after seemingly coming back to life. In 2008, it was initially mistaken for a mere dust cloud, but it resurfaced and gained attention once again. To make things even stranger, the planet behaves like a zombie.
Its orbit is one of the most peculiar of any known planet, as it appears to zigzag unpredictably. Scientists are still puzzled by its movement. The planet swings as close as 7.5 billion kilometers (4.5 billion miles) to its star, yet its farthest point reaches around 45 billion kilometers (27 billion miles) away.
One possibility is that a much larger planet may have displaced it from its original orbit. This theory arises from a noticeable gap in the surrounding dust and ice cloud, which hints at the presence of another planet in the system.
