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Every planet we've found so far, unlike Earth, has proven to be hostile. While some could become suitable for human habitation with the right technological advancements, challenges such as the lack of oxygen and water remain. Others, however, will always be inhospitable to life.
These dangerous planets are capable of wiping out any creature that comes too close or attempts to settle there. Many of the planets on this list are not just unbearably hot or cold; they have extreme conditions that make life impossible.
10. HD 189733b
In 2005, astronomers discovered HD 189733b, a Jupiter-sized exoplanet located 63 light-years away, with a unique Earth-like blue hue. However, unlike Earth, the planet's blue appearance is not due to oceans or seas, but rather its silicate-rich clouds.
HD 189733b is a deadly exoplanet. The first challenge is its incredibly fast winds, reaching speeds of 8,700 kilometers per hour (5,400 mph). This is seven times the speed of sound, a mind-blowing velocity. To put it in perspective, the winds of the infamous Hurricane Katrina reached only 280 kilometers per hour (175 mph).
Then there’s the rain. Due to the silicate-heavy clouds on HD 189733b, molten glass rain falls from the skies. But it doesn't fall straight down; instead, the extreme winds cause this unusual rain to travel sideways.
Even if we managed to avoid the rain, the intense heat of the planet would still pose a threat. HD 189733b is so close to its star that the temperatures are extreme. To illustrate, the exoplanet completes one orbit around its star in just 2.2 Earth days. Remarkably, a single day on HD 189733b also lasts 2.2 Earth days.
The gravitational interaction between a planet and its star can lead to a phenomenon called tidal locking, where a planet's day and year last the same amount of time. This happens when a planet rotates on its axis in the same period it takes to complete one orbit around its star. This is similar to how the Moon is tidally locked to Earth. (Rotation determines day and night, while revolution defines a year.)
A tidally locked planet always presents the same side to its sun, resulting in one half experiencing constant daylight, while the other half is forever in darkness.
9. CoRoT-7b
In February 2009, astronomers using the Convection, Rotation and Planetary Transits (CoRoT) satellite discovered an exoplanet in the Monoceros constellation, 480 light-years away from Earth. It was named CoRoT-7b.
CoRoT-7b is a rocky, Earth-like exoplanet, though it was once a Saturn-sized hot Jupiter — a term for massive, gas-filled planets with tight orbits around their stars. While its rocky surface might support life, CoRoT-7b is far from a hospitable place.
To begin with, CoRoT-7b's atmosphere is filled with minerals that form rock clouds. These clouds release pebbles and small rocks that fall like rain. Even if humans could survive this, they would be overwhelmed by the exoplanet’s extreme surface temperature.
Our Earth is 60 times farther from the Sun than CoRoT-7b is from its star. During the day, the star in CoRoT-7b's sky appears 360 times larger than our own Sun does from Earth. Additionally, CoRoT-7b may be tidally locked to its star, meaning that both a day and a year last only 20.4 hours.
As you might expect, this causes one side of the exoplanet to face the star constantly. The temperature on that side ranges from 1,980 degrees Celsius (3,600 °F) to 2,300 degrees Celsius (4,220 °F), hot enough to melt rock. Astronomers believe that the rocks on this side are molten because they can’t stay solid at such extreme temperatures.
8. KELT-9b
Exoplanet KELT-9b holds the record for being the hottest planet ever discovered. Its star’s temperature is around 9,700 degrees Celsius (17,500 °F), nearly double the surface temperature of our Sun at 5,480 degrees Celsius (9,900 °F). The temperature during the day on KELT-9b reaches about 4,300 degrees Celsius (7,800 °F), which is still incredibly hot. Most stars in the universe don’t even come close to this temperature.
As you read this, KELT-9b is so hot that its hydrogen-rich atmosphere is boiling off and escaping into space, eventually reaching star KELT-9, around which the exoplanet orbits. Star KELT-9 is enormous, being three times the size of our Sun. KELT-9b itself is twice the size of Jupiter and three times heavier.
The extreme heat is caused by the short distance between KELT-9 and KELT-9b. They are so close that the exoplanet completes an orbit in just 1.5 days. To put this in perspective, Mercury is 10 times farther from our Sun than KELT-9b is from KELT-9.
Astronomers predict that KELT-9b will lose its entire atmosphere to star KELT-9 in just 200 Earth years. By then, KELT-9 will have expanded so much that it could possibly touch the exoplanet. However, astronomers do not foresee the exoplanet crashing into the star.
7. WASP-121b
WASP-121b is an incredibly strange exoplanet. First off, it doesn’t have a spherical shape but instead resembles a football. And just to clarify, we mean American football—not the football that most of the world knows as soccer. However, its odd shape isn't the reason it's considered dangerous. The real threat comes from the exoplanet’s extreme proximity to its star.
WASP-121b orbits so close to its star that temperatures reach around 2,540 degrees Celsius (4,600 °F). This heat is so intense that nothing can remain solid or liquid; everything stays in a gaseous state. The exoplanet’s atmosphere, which contains iron and magnesium gases, is also in this gaseous form. To make matters worse, it’s losing this atmosphere to its star, much like KELT-9b.
Interestingly, the close proximity to its star is also why WASP-121b is stretching out of shape. The star exerts a powerful gravitational force on the exoplanet, which doesn’t have enough gravitational strength to fully resist it. As a result, the exoplanet distorts and bends under the star’s influence.
6. Upsilon Andromedae b
Upsilon Andromedae b is a peculiar exoplanet that orbits the star Upsilon Andromedae A, located 44 light-years from Earth. The exoplanet is dangerously close to its sun, completing an orbit in just 4.6 days. This suggests that Upsilon Andromedae b is tidally locked, with one side constantly facing the sun and becoming incredibly hot.
Strangely, the hottest area, known as the 'warm spot,' is not the side facing the star. Instead, it’s found on the side that is perpetually in the dark. This baffling discovery left astronomers scratching their heads, as the sun-facing side should be the hottest. The explanation seems to lie in the way wind transfers the heated air to the side that never sees the sun.
Here’s one possible explanation for how this works: the heat from Upsilon Andromedae warms the side of the exoplanet facing the star, causing the air to heat up. Once the air becomes sufficiently warm, wind carries it to the opposite side of the exoplanet.
Meanwhile, the cooler air from the dark side is transported to the sun-facing side. This cycle continues, ensuring that the side shielded from the sun constantly receives a flow of hot air, while the side exposed to the sun remains much cooler.
5. OGLE-2005-BLG-390Lb
OGLE-2005-BLG-390Lb is a rocky exoplanet with a very thin atmosphere, situated right in the heart of our Milky Way. When it was first discovered, astronomers speculated that it might harbor life, but they now believe it does not, due to its incredibly low temperature.
The surface temperature of OGLE-2005-BLG-390Lb is approximately -220 degrees Celsius (-364 °F), far too cold to support any known form of life. For context, the lowest temperature ever recorded on Earth is -97.8 degrees Celsius (-144 °F), in an area of frozen Antarctica that has never been touched by sunlight. Breathing in that frigid air would be fatal, destroying our lungs instantly.
4. TrES-2b
TrES-2b is the darkest known planet in the universe. Its blackness is so intense that coal would appear brighter if placed next to it. This exoplanet, the size of Jupiter, is located 750 light-years away in the Draco constellation, orbiting a star almost identical to our Sun, GSC 03549-02811.
TrES-2b’s darkness is due to its atmosphere, which absorbs more than 99 percent of the light from its star. Astronomers believe the planet reflects so little light because its atmosphere contains vaporized sodium, potassium, and possibly gaseous titanium oxide.
Despite its pitch-black appearance, TrES-2b is far from cold. Its atmospheric temperatures soar above 980 degrees Celsius (1,800 °F), causing some parts of the planet to glow red, similar to burning coal or electric stove coils. Astronomers also suspect that TrES-2b may be tidally locked to its star due to their close proximity.
3. Proxima b
Proxima b initially seemed promising when it was discovered. It orbits Proxima Centauri, a red dwarf star located just 4.24 light-years away from Earth. Astronomers were intrigued by its potential to harbor water and exhibit Earthlike characteristics. However, further investigations revealed that those assumptions were incorrect.
Proxima b is in such close proximity to Proxima Centauri that it completes an orbit in just 11.2 days. The exoplanet is also tidally locked, with one side being unbearably hot, while the other is bitterly cold and frozen. Between these extremes lies a narrow temperate zone, but it is unlikely to support life due to the harsh conditions of Proxima Centauri.
As noted earlier, Proxima Centauri is a red dwarf star. One notable feature of such stars is their frequent emission of solar flares every two to three months, which strike the nearby planets. These flares can strip away ozone layers, leaving the planets exposed to harmful ultraviolet radiation from the star.
On March 24, 2017, we observed a solar flare released by Proxima Centauri toward Proxima b. The flare was so powerful that the star's brightness surged by 1,000 times in just 10 seconds. As a result, Proxima b received 4,000 times the amount of radiation that Earth typically experiences from solar flares. This intense radiation would be detrimental to any life on the exoplanet.
2. Venus
Deadly planets aren’t just confined to distant corners of the universe; one resides right in our own solar system. Venus takes the crown as the most dangerous planet in our solar system, mainly due to its clouds laden with sulfur dioxide. These clouds block the sunlight from reaching Venus' surface and prevent deadly carbon dioxide from escaping into space.
Venus' surface is dotted with volcanoes that emit huge quantities of heat and carbon dioxide. The abundant carbon dioxide makes Venus toxic to humans. The thick cloud cover traps heat and gases, rendering the planet unbearably hot. Temperatures soar to a staggering 467 degrees Celsius (872 °F).
This extreme heat is constant across the entire planet, even at the poles. Unlike other hot planets, Venus doesn’t cool down at its poles. The scorching temperatures persist year-round, and even at night, Venus remains as hot as during the day. Scientists believe Venus would be much like Mercury if it weren’t for its suffocating cloud cover.
Interestingly, Venus experiences both rain and snow, but it's nothing like what we see on Earth. Instead of liquid water, the snow on Venus is made of metals like galena and bismuthinite. The rain consists of deadly sulfuric acid. However, the planet's scorching temperatures ensure that the rain never reaches the ground. Instead, it evaporates midway, only to form more clouds.
1. OGLE-TR-56b
OGLE-TR-56b is located in the Sagittarius constellation, about 5,000 light-years from Earth. It is one of the infamous 'hot Jupiters' that we mentioned earlier. These planets usually form farther away from their stars before gradually moving closer to them.
OGLE-TR-56b has drifted so close to its star that a year on the exoplanet lasts just 29 hours, and its surface temperature reaches a searing 2,000 kelvins. The clouds on this planet aren't made of water, but of vaporized iron, and the rain falls as molten liquid iron.
