Summary
Scientists used one of the world’s most powerful telescopes to hunt for the glowing auroras on two distant ‘hot Jupiter’ planets. But the search came up empty, creating a cosmic mystery about these strange and stormy worlds.
Quick Facts
Scientists were looking for auroras on two 'hot Jupiters' named WASP-80b and WASP-69b.
Instead of visible light, they searched for an infrared 'glow' from a molecule called H3+.
This H3+ molecule is the main source of auroras on Jupiter, Saturn, and Uranus in our own solar system.
They used the powerful Keck/NIRSPEC instrument in Hawaii to search for the signal.
Despite the advanced search, no auroras were detected on either planet.
The Discovery: The Search for a Cosmic Glow
Imagine a planet bigger than Jupiter, orbiting so close to its star that its year lasts only a few days. These are ‘hot Jupiters’, and scientists believe they should have spectacular auroras, far more powerful than Earth’s Northern Lights. Researchers aimed the giant Keck telescope at two of these worlds, WASP-80b and WASP-69b, hoping to catch the tell-tale infrared glow of a special molecule called H3+. This molecule is created when energetic particles from the star slam into the planet’s atmosphere, guided by a magnetic field. Finding this glow would be a huge discovery, but after hours of staring into the cosmos, the light just wasn’t there.
The Science Explained Simply
On Earth, auroras happen when solar wind particles hit oxygen and nitrogen, making them glow green and red. But on gas giants like Jupiter, the atmosphere is mostly hydrogen. When charged particles funnel down the planet’s powerful magnetic field lines and crash into the hydrogen gas, they create a new, energized molecule called H3+ (pronounced ‘H-three-plus’). This molecule is unstable and quickly releases its extra energy as infrared light—light that is invisible to our eyes but can be seen by special telescopes. Scientists call H3+ the ‘thermostat’ of Jupiter’s upper atmosphere because this process is the main way the planet cools itself down. Finding this specific infrared light on an exoplanet is the best way to confirm an aurora is happening.
The Aurora Connection
Auroras aren’t just pretty light shows; they are giant signposts in space. The single most important thing an aurora tells us is that a planet has a magnetic field. A magnetic field acts like a planetary shield, deflecting harmful radiation and stopping the star’s wind from blowing the atmosphere away. Finding a magnetic field on an exoplanet would be a first, and it would give us vital clues about the planet’s interior and its potential to hold onto an atmosphere over billions of years. Studying these distant auroras also helps us understand the ‘space weather’ created by the host star, giving us a window into the violent interactions between stars and their planets.
Observations of auroras on exoplanets would provide numerous insights into planet-star systems, including potential detections of the planetary magnetic fields.
— Richey-Yowell et al. (2025)
A Peek Inside the Research
Finding a faint aurora from trillions of miles away is like trying to hear a whisper in a rock concert. The planet’s light is completely overwhelmed by its star. To find the signal, astronomers used high-resolution spectroscopy, a technique that splits the incoming light into thousands of different shades of color. Then, they used a powerful data-sifting method called cross-correlation. They created a computer model of what the H3+ aurora ‘fingerprint’ should look like, with all its dozens of individual light lines. They then compared this model to the real data, shifting it around to match the planet’s velocity as it orbited its star. If a real signal was hidden in the noise, it would pop out when it lined up perfectly with the model. But even with this clever trick, no signal appeared.
Key Takeaways
Finding auroras on exoplanets would be the first proof of magnetic fields on worlds outside our solar system.
Magnetic fields are crucial because they can protect a planet's atmosphere from being stripped away by its star.
Scientists used a clever technique called 'cross-correlation' to hunt for the faint signal, like using a template to find a hidden image.
This research set the strictest limits yet on how bright these auroras can be, meaning if they exist, they are very faint.
The mystery continues: are the auroras just too weak to see, or is the H3+ molecule being destroyed in the planet's hot atmosphere?
Sources & Further Reading
Frequently Asked Questions
Q: Does this mean these planets have no auroras or magnetic fields?
A: Not necessarily. It just means that any auroras they have are too faint for our current telescopes to see. The magnetic fields might be weaker than expected, or something else in the atmosphere could be interfering with the aurora’s glow.
Q: Why can’t we just take a picture of the auroras like we do on Earth?
A: These planets are incredibly far away and extremely faint compared to their bright host stars. We can’t resolve them into a picture; all we receive is a single point of light that contains the combined light of the star and the planet, which we must then carefully separate using techniques like spectroscopy.
Q: What is a ‘hot Jupiter’?
A: A hot Jupiter is a type of gas giant exoplanet, similar in size to our own Jupiter, but that orbits extremely close to its star. This makes them incredibly hot, with temperatures reaching thousands of degrees, and gives them very short orbital periods (a ‘year’ can be just a few Earth days).
Q: What’s the next step in the search for alien auroras?
A: The next step is to use even more powerful observatories, like the upcoming class of Extremely Large Telescopes (ELTs). With their giant mirrors, they will be sensitive enough to either finally detect these faint auroras or confirm that they are truly absent, deepening the mystery.
