The Pale Green Dot: Alien Auroras

Scientists predict that Proxima Centauri b, our closest exoplanet neighbor, could have auroras 100 times stronger than Earth’s. Detecting this ‘pale green dot’ would be a revolutionary way to confirm its atmosphere and learn about its potential for life.

What if we could spot an exoplanet not by the starlight it blocks, but by its own atmospheric light? That’s the incredible idea behind the ‘Pale Green Dot’ concept. Researchers led by Rodrigo Luger focused on Proxima Centauri b, our nearest exoplanetary neighbor. They knew its host star is an active red dwarf, constantly blasting the planet with a ferocious stellar wind. If Proxima b has an Earth-like magnetic field and atmosphere, it should produce auroras. Because the planet is so close to its star—about 20 times closer than Earth is to the Sun—these auroras wouldn’t just be a minor flicker. The scientists calculated they would be at least 100 times more powerful than Earth’s Northern Lights. During a solar storm, that power could jump by thousands of times, making the planet briefly glow in a specific shade of green light from excited oxygen atoms.

Read the original research paper: ‘The Pale Green Dot: A Method to Characterize Proxima Centauri b Using Exo-Aurorae’

This method would yield an independent confirmation of the planet’s existence and constrain the presence and composition of its atmosphere.
— Rodrigo Luger, Lead Author

Auroras are like giant neon signs in a planet’s sky, and they work the same way everywhere. First, a star spews out a stream of charged particles called the stellar wind. If a planet has a magnetic field, this field acts like a shield, deflecting most of the particles. However, some get trapped and funneled down toward the magnetic poles. These high-energy particles then slam into atoms and molecules in the planet’s atmosphere. This collision excites the atoms, and when they calm down, they release that extra energy as light. On Earth, when particles hit oxygen high up, we get the famous green glow. The researchers predict the same thing would happen on Proxima b. The key difference is the intensity. Proxima b is getting hit by a stellar wind that’s more like a fire hose than a sprinkler, leading to a much more intense and constant light show.

Here at NorthernLightsIceland.com, we know that auroras are more than just a pretty sight—they are the visible signature of a planet’s protective shield. The same magnetic field that creates auroras is essential for life, as it deflects harmful stellar radiation and prevents the star’s wind from stripping the atmosphere away into space. For a planet like Proxima b orbiting an angry red dwarf, this protection is even more critical. Detecting an aurora there would be monumental. It wouldn’t just confirm an atmosphere; it would prove the existence of a magnetic shield strong enough to help that atmosphere survive. It would tell us that this nearby world has two of the key ingredients necessary for potential habitability: a blanket of air and a planetary force field. The pale green dot is a beacon of hope for finding a protected, and possibly living, world right next door.

Detection of aurorae would constrain the presence of an atmosphere… a crucial step in assessing habitability.
— NorthernLightsIceland.com Science Team

So, how do you find a tiny green glow from 4.2 light-years away? The team first looked at existing data from the HARPS instrument, a high-precision spectrograph that originally helped discover Proxima b. They scanned the data for the specific wavelength of green light from oxygen (5577 Ångströms), but found no signal. This wasn’t a failure; it confirmed the aurora wasn’t ridiculously bright and set a baseline. Next, they calculated what it would take for future telescopes to succeed. Their models showed that an Extremely Large Telescope (ELT), paired with a sophisticated coronagraph to block the star’s glare, could detect a powerful aurora from a stellar storm in just a few hours. Detecting the fainter, steady-state aurora would be a bigger challenge, requiring an advanced, nearly noiseless telescope to stare at the system for several nights. This research provides a roadmap for the next generation of planet hunters.

Q: So Proxima b has auroras just like Earth?
A: The physics would be the same, but the show would be far more intense! Scientists predict its auroras would be at least 100 times stronger than ours on a normal day, and potentially thousands of times stronger during a stellar storm from its very active host star.

Q: What color would the auroras be?
A: If Proxima b has an Earth-like atmosphere, the dominant color would be green. This is because the 5577 Ångström emission from excited oxygen atoms is one of the strongest and most common auroral lines we know of.

Q: Can we see these alien auroras with a telescope right now?
A: Unfortunately, no. The signal is far too faint and buried in the glare of the host star. The paper shows that even our best current telescopes aren’t sensitive enough, but the next generation of 30-meter class telescopes might just be able to spot them.

Q: Does this mean there’s life on Proxima b?
A: Not necessarily, but it’s a very positive sign! Detecting an aurora would confirm the planet has an atmosphere and a magnetic field. These two features are crucial for protecting a planet’s surface and are considered essential ingredients for a world to be habitable.