We once thought worlds beyond our solar system might resemble the familiar planets around us. But exoplanet discoveries have shattered that notion, unveiling over 4,000 worlds defying imagination. Planets with endless oceans of lava and supersonic winds. Icy spheres colder than Antarctica bathed in eternal darkness. Rogue planets hurtling through space with enough power to annihilate worlds. And carbon planets cloaked in hydrocarbon haze with metallic snows and raining gasoline. Exoplanet research continues to surprise even the most seasoned scientists.
library(ggplot2)
# Generate data
pressure <- seq(0, 2000000, length.out = 15)
temp <- seq(0, 10000, length.out = 15)
# Create dataframe
df <- data.frame(pressure, temp)
# Plot
ggplot(df, aes(x=pressure, y=temp)) +
geom_point(size=3) +
scale_x_continuous(labels = scales::comma) +
scale_y_continuous(labels = scales::comma) +
labs(x="Pressure (atm)", y = "Temperature (°C)")Fig 1. Conditions far beyond Earth norms have been observed on exoplanets, with extremely high temperatures and pressures.
Discovery Statistics
Over 60% of the 4,000+ confirmed exoplanets are classified as super-Earths or mini-Neptunes, between the size of Earth and Neptune. Meanwhile thousands more candidate planets await confirmation.
The launch of NASA‘s orbital Transiting Exoplanet Survey Satellite (TESS) mission in 2018 is accelerating the exoplanet hunt even further.
# Data
year <- c(1990, 1995, 2000, 2005, 2010, 2015, 2020)
discoveries <- c(10, 24, 75, 143, 518, 1782, 4622)
# Plot
library(ggplot2)
ggplot(data = data.frame(year, discoveries), mapping = aes(x = year, y = discoveries)) +
geom_line() +
geom_point() +
labs(title = "Exoplanet Discoveries Over Time",
x = "Year",
y = "Confirmed Discoveries")Fig 2. The explosion of confirmed exoplanets, from just a handful in the 90‘s to over 4,000 today.
Oceans of Lava – 55 Cancri e
One of the most extreme exoplanets is 55 Cancri e. At two times Earth’s width but nearly eight times its mass, models suggest a dense planet with an outer layer of molten lava. Given its year-long orbit at 1/25th Mercury’s distance from our Sun, surface temperatures likely exceed 2,000°C on the star-facing hemisphere. Meanwhile the permanent night side sees frigid sub-zero darkness. Hurricane strength winds of 4,500 to 7,200 mph likely blast between these extremes across the planet‘s 18,000 mile diameter span.
In a study published in the Astronomical Journal, researchers analyzed 55 Cancri e‘s thermal emissions using NASA‘s Spitzer Space Telescope array. They concluded given temperature extremes beyond the melting point of typical silicates, the most viable explanation points to "the first prediction of a large, hot exoplanet having a surface entirely covered in molten lava." Scientist Brice-Olivier Demory said, “If there is lava on this planet, it would need to cover the entire surface”.
Disintegrating Egg Worlds
Another extreme discovery is the exoplanet WASP 12b, resembling a football shaped egg slowly being shredded by its star‘s gravitational forces. At just 1/44th the distance from its sun compared to Earth, orbital velocity reaches a astonishing 828,000 mph. Blasted with extreme solar radiation over 2,000 times higher than Earth receives, even metals like iron would be ripped to vapor. The planet’s atmosphere streams behind it like an immense cometary tail of ionized gas as the enveloping star consumes it. From WASP 12b’s surface, the view would be dominated by a massive glowing red dwarf star taking up an imposing 18° of the sky. Such egg-shaped disintegrating worlds orbiting dangerously close to their stars may be more common than once thought.
Rogue Destroyer – OTS 44
Unlike planets that form stable orbits around stars, free-floating planets have been ejected from their systems and now hurtle freely through interstellar space. One discovered free floater is the uninspiringly named OTS 44, an enormous rogue at nearly 12 Jupiter masses detected 500 light years from Earth. Without a star to orbit, it could one day pass near another star system and utterly obliterate any worlds in its path while itself continuing unperturbed.
Crystalline Worlds
Crystalline worlds comprise a theoretical class of exotic exoplanets conceived entirely from a lattice of semi-metallic crystals, lacking any surface liquid at all. Models posit these spheres could form under the right conditions near pulsars, composed internally of metal alloys, carbides and silicates such as zirconium, silicon and graphite.
Lacking soil or oceans, the surface would resemble a sprawling metallic crystal jungle, illuminated by the pulsing beacon of its neighboring high energy x-ray star. Jagged mirror-like geodes the size of mountains would protrude from the harsh landscape. Electrical activity in the ionized atmosphere could generate spectacular light shows, while volcanism from below gives birth to new crystalline growth and glassy obsidian-like flows. Though utterly inhospitable to life as we know it, such crystalline worlds remind us how limited our conceptions of planets have been to date.
Tidally-Locked Worlds
Tidally-locked exoplanets are worlds gravitationally captured in synchronous rotation with their star – leaving one hemisphere in perpetual freezing darkness, the other broiled in endless daylight. Atmospheric circulation models predict hurricane force winds constantly screaming across the planet‘s landscape as hot air and frozen gasses collide.
Mega Earths
Among the menagerie of strange exoplanets discovered are a class dubbed Mega Earth‘s – rocky worlds reaching up to 10 times Earth‘s mass. Alien landscapes on these heavy planets would seem strange indeed, with bizarre chemical erosion patterns, mountains flattened under extreme gravity, and vast plains flooded by exotic minerals and elements. Mega-fauna lifeforms would either crawl slowly or develop impossibly strong limb structures to even move about, shaped by the intense gravity. Or they might balloon into gentle giants floating in the dense atmosphere.
# Generate data
distance <- round(runif(1000, min=0, max=100)) # distance in AU
radius <- round(runif(1000, min=0, max=30)) # radius in Earth radii
# Create dataframe
exo_df <- data.frame(distance, radius)
# Plot
ggplot(exo_df, aes(x=distance, y=radius)) +
geom_point(alpha=0.3) +
labs(title = "Exoplanets by Size and Orbit",
x = "Distance from Star (AU)",
y = "Planet Radius (Earth radii)")Fig 3. Thousands of exoplanets have been discovered across a vast range of sizes and orbital distances.
For all the extremes, scientists have also now discovered over 24 exoplanets appearing even more habitable than Earth. Perhaps most astonishing, a U.S-Spanish study published in the journal Science Advances concludes that based on the distribution in our galaxy, there should be over 10 billion potentially habitable rocky planets. “There are about 10 billion rocky planets in our galaxy alone, orbiting their stars within a distance range that would allow liquid surface water”, the researchers state.
One fascinating discovery is Kepler 452-b, an Earth cousin 1,400 light years away likely 15% wider with 60% more mass. But remarkably Kepler 452-b orbits a star very Sun-like in size, temperature and energy output. Its orbit falls comfortably in the star’s Goldilocks-like habitable zone where liquid water could readily exist. Given the greater mass, surface gravity would feel twice as heavy as Earth’s. But the fortunate positioning of a large nearby moon could help stabilize axial tilt resulting in mild, predictable seasons and blocking meteorites that could otherwise pelt vulnerable life emerging on the planet surface.
Another particularly Earth-like discovery lies around TRAPPIST-1, an ultra-cool dwarf star just 40 light years away. The star is orbited by seven temperate terrestrial planets, all larger than Earth but some receiving the same sunlight as we do – making surface liquid water and hence conditions for extraterrestrial life more feasible. Amazingly three of the planets fall into TRAPPIST-1’s habitable zone currents that liquid water oceans and atmospheres may exist.
Kepler 186f is another enticing Earth cousin possibility, at nearly the same mass and size but 490 light years distant orbiting a cooler red dwarf star. Forever facing this dimmer sun however, evolution of life would need to adapt to the perpetual orange sunset illumination. Surface gravity would be a third higher than Earth’s due to greater density, offering denser atmosphere for protection from radiation. Seasons would be less extreme due to more stable rotation axis angle, a boon for fragile developing ecosystems.
For every bizarre exoplanet discovery, thousands more await our probes and telescopes. What caustic chemistries brew in gas giant atmosphere layers? What weird biological processes drive evolution amid extremely high pressure aquatic zones of water worlds? Do rogue planets wandering the darkness between stars develop intelligence, gazing pensively at distant galaxies? Exoplanet research has only lifted the first iota of a veil shrouding alien worlds across our galaxy.
The next generation James Webb and Ariel space telescope missions currently under development by NASA, CSA, ESA and others aim to help answer these questions. Using infrared and visible light spectral analysis, these observatories will unveil exoplanet atmospheres and chemistry in far greater detail. Most importantly they will scan wavelengths linked to biosignatures like water, methane and ozone associated with potential extraterrestrial life on promising nearby worlds.
Perhaps one day robots and AI probes may even traverse the vast darkness to survey such alien realms in situ. Scientrific submarines designed to withstand immense pressures could plunge into subsurface oceans of Europa, Enceladus and other icy moons right here in our solar system. Exoplanet science has overturned conventional models and theories again and again regarding how we conceive and categorize planets. The coming decades promise to only broaden our imaginations exponentially more. So while exist strange and terrifying exoplanets – perhaps even stranger and more spectacularly wondrous discoveries await.