The search for planets outside our solar system has revolutionized astronomy. Among the most intriguing systems, we discovered the so-called WASP exoplanets, a family of worlds that continue to surprise the scientific community. Their study is changing our understanding of planetary formation, atmospheric chemistry, and the extreme conditions that can occur elsewhere in the universe.
In this article, we take you on an in-depth look at the WASP exoplanets that have been the subject of some of the most mind-blowing discoveries in recent years. You'll see how these gas giants, plagued by unusual phenomena, have forced us to rethink theories and raised new questions about the diversity and evolution of planets in the galaxy.
What are WASP exoplanets and how were they detected?
The WASP exoplanets take their name from the international project Wide Angle Search for Planets, a collaboration that uses automated observatories in both hemispheres to monitor millions of stars. These observatories detect periodic drops in the brightness of stars, which usually indicate the passage of a planet in front of its star.
Since its launch, the WASP project has detected thousands of candidates and confirmed a large number of exoplanets, some of which stand out for having radically different properties from the planets that exist in our solar system. These discoveries have been made possible through techniques such as transit photometry and radial velocity measurements of host stars.
WASP-193b: The planet lighter than cotton candy
One of the biggest recent stirs has been caused by the discovery of WASP-193bImagine a colossal planet, 50% larger than Jupiter, but with a much smaller mass: only a tenth of that of our solar system's giant.
The result? An absurd density by planetary standards: just 0,059 grams per cubic centimeter. To give you an idea, it's practically like cotton candy floating in space! In fact, only Kepler-51d surpasses WASP-193b in low density, even though it is much smaller.
Discovering such an oddity led scientists to doubt their own measurements. Was it a mistake, an instrumental failure, or were they really looking at such a spongy planet? After repeating the processes and validating the data with different methods and observatories, the team confirmed that the measurements were real.
Why is WASP-193b so rare? Standard planetary physics cannot explain how a planet can inflate to that extent without becoming unstable or dispersing. It is suspected to have a vast atmosphere composed primarily of hydrogen and helium, extending far beyond that of any known gas giant.
This discovery calls for more detailed observations with instruments like the James Webb Telescope, as studying its atmosphere can shed light on phenomena of planetary evolution that we do not yet understand.
How to confirm such an unusual exoplanet
Confirming the existence and characteristics of such an unusual planet required combining observations from multiple telescopes and spectrographs. The process began with the detection of periodic transits by WASP-South. The planet's size was verified by analyzing how much the host star's light dimmed during each transit, and its mass was subsequently calculated using radial velocity spectroscopy.
This rigorous methodology ruled out alternative explanations and confirmed that the dips in brightness were caused by a real planet and not by other stellar phenomena.
In addition, the collaboration benefited from Chilean observatories such as TRAPPIST-South and SPECULOOS-South to maintain detailed monitoring, which is essential for validating such extreme exoplanets.
The atmosphere and composition of WASP-193b
The mystery of WASP-193b goes even beyond its density. The atmosphere, which is vast and composed primarily of hydrogen and helium, raises enormous questions about how it can remain stable and what mechanism inflated it so much.
Current models of planet formation fail to describe such an object. Even if the absence of a planetary core were assumed, the resulting density would still be inexplicably low. For now, Scientists point out that much more detail will be needed about its atmosphere to unravel its history and evolution.
Furthermore, the researchers emphasize that the existence of WASP-193b challenges the limits of what we understand as giant planets, and opens the door to the possibility that there are many more such strange worlds yet to be discovered in our galaxy.
WASP-127b: unprecedented supersonic winds and atmospheric dynamics
Turning to another of the protagonists of the WASP system, we find WASP-127bIt's a so-called "hot Jupiter," a gas giant planet comparable in size to Jupiter, but less massive and with a much closer orbit to its star, which pushes temperatures to over 1.000°C.
This exoplanet has astounded astronomers thanks to its unprecedented atmospheric conditions. While part of its atmosphere moves closer to Earth, the rest moves away at unprecedented speeds, creating a supersonic equatorial jet stream that spins at about 33.000 kilometers per hour.
To give you an idea of the magnitude, the fastest winds on Saturn barely reach 1.800 km/h, and on Earth, Cyclone Olivia in 1996 holds the record at 408 km/h.
Spectroscopic analysis confirmed the presence of water vapor and carbon monoxide in the atmosphere, which are essential for deciphering the chemistry and origin of this planet. The discovery was made possible thanks to instruments such as CRIRES+ on the VLT, allowing these phenomena to be observed despite the bright glare of the host star.
A unique opportunity to study the dynamics of exoplanets
WASP-127b represents a natural laboratory for investigating the most extreme face of planetary atmospheres. Mapping supersonic winds and temperature and composition variations at different latitudes and atmospheric depths has opened up new avenues of research.
Even the most subtle details, such as weaker signals from the poles—indicating colder regions compared to the equator—have been identified, something that until very recently was unthinkable on planets located more than 500 light-years from Earth.
This advance in precision helps us better understand how heat, elements, and chemical compounds circulate on gas giant planets, testing our models and enriching our understanding of our own solar system.
WASP-121b: Climatology Beyond Science Fiction
Technological advances, such as ESO's Very Large Telescope (VLT), have made it possible to analyse the atmosphere of WASP-121b in three dimensions, revealing weather patterns that look like something out of a science fiction novel.
This planet, also known as Tylos, orbits just 900 light-years away and is considered an "ultra-hot Jupiter" given its proximity to the star. A year on WASP-121b lasts only 30 Earth hours and has a huge temperature difference between its star-facing hemisphere and its nighttime hemisphere.
Atmospheric mapping has revealed complex jet streams and flows separated into various layers, transporting material from the warm side to the cold side. Elements such as iron, titanium, sodium, and hydrogen reveal the intricate structure and dynamics of the atmosphere.
Surprisingly, some elements, such as titanium, have only been detected in deep layers beneath the jet stream, hinting at an even richer atmospheric chemistry than anticipated. This underscores the potential for future research with even more powerful telescopes like the Extremely Large Telescope (ELT) which is under construction.
WASP-39b: The James Webb Telescope's Molecular and Chemical Catalog
The James Webb Space Telescope (JWST) has opened a new frontier in the study of exoplanets, and WASP-39b has been one of the first to benefit. This planet, the size of Saturn but with an orbit much closer to its star, has been imaged in unprecedented detail.
The JWST has identified a multitude of molecules and elements in its atmosphere, including water, sulfur dioxide, carbon monoxide, sodium, potassium, and fragmented cloudsFor the first time, sulfur dioxide has been detected as a result of chemical reactions triggered by starlight, a direct sign of photochemistry in action, something that on Earth is associated with the formation of ozone.
The comprehensive list of chemical ingredients allows scientists to deduce details about WASP-39b's formation and evolutionary history. Precise analysis of the abundances of different elements supports the hypothesis that the planet formed far from its star, capturing oxygen-rich materials in its youth.
These findings demonstrate the power of JWST to explore the atmospheric diversity of exoplanets, and mark the beginning of a new era in the exploration of smaller, rocky worlds in the near future.
Other fascinating cases: exoplanets with tails and escaping atmospheres
As if that were not enough, the WASP family includes even more extravagant phenomena, such as the case of WASP-69b. This planet is not only a gas giant similar to Jupiter, but it loses its atmosphere in the form of a hydrogen and helium tail up to 563.000 km long, driven by extreme stellar winds and intense radiation from its star.
WASP-69b is one of the clearest examples of how stellar environments affect planets, giving rise to phenomena such as the photoevaporation and losing mass at a rate of hundreds of thousands of tons per second.
Detailed studies of their tails are also allowing these exoplanets to be used as indicators of the activity and stellar winds of their host stars, valuable tools for understanding both the planets and the stars themselves.
