Aurora borealis is a natural light spectacle in the Polar Regions. It is caused by the interaction between charged particles from the Sun and the Earth’s magnetic field. However, aurora borealis is not limited to Earth; it can also be observed on other planets in our solar system and exoplanets beyond our solar system.
This article will explore beautiful skies of exoplanets and the science behind their auroras.
What are Exoplanets?
Exoplanets are planets that orbit stars other than our Sun. Since the first exoplanet discovery in 1995, thousands of exoplanets have been found, and they come in various sizes and compositions. Some exoplanets are rocky, like Earth, while others are gas giants like Jupiter. Exoplanets also come in different distances from their host star; some are located in the habitable zone, where liquid water could exist.
What Causes Auroras on Exoplanets?
Like on Earth, auroras on exoplanets are caused by the interaction between charged particles and the planet’s magnetic field. However, the source of charged particles can vary. On Earth, charged particles come from the solar wind, a stream of charged particles that constantly flows from the Sun. On exoplanets, charged particles can come from the planet’s atmosphere, its host star, or even from its moons if they have one.
The strength and shape of the planet’s magnetic field also play a crucial role in determining the aurora’s characteristics. A strong magnetic field can trap charged particles, causing them to spiral along the magnetic field lines and collide with atoms in the atmosphere, resulting in an aurora. On the other hand, a weak magnetic field would allow charged particles to escape and interact with the planet’s atmosphere, resulting in a different type of aurora.
Auroras on Exoplanets
So far, auroras have been observed on several planets in our solar system, including Jupiter, Saturn, Uranus, and Neptune. Each of these planets has its unique aurora, shaped by its magnetic field, atmosphere, and the source of charged particles.
Scientists have also detected aurora-like signals on exoplanets outside of our solar system in recent years. In 2015, the Hubble Space Telescope detected a strong aurora on a gas giant exoplanet called HD 189733b. This planet is located about 63 light-years away from Earth and is roughly the size of Jupiter. The aurora on HD 189733b was caused by charged particles from the planet’s atmosphere, which were ionized by the planet’s intense ultraviolet radiation.
In 2020, scientists used the Hubble Space Telescope to study the atmosphere of an exoplanet called WASP-79b, located about 780 light-years from Earth. The researchers detected a bright, pulsating signal that could be an aurora caused by charged particles from the planet’s host star. However, more observations are needed to confirm whether this signal is an aurora.
Auroras on Venus
There is no magnetic field on Venus. But it doesn’t imply the aurora borealis doesn’t exist there! Its radiance, reminiscent of the aurora borealis, is currently thought to be caused by the impact of solar wind particles on Venus’s atmosphere. Astronomers have noticed strange lights on Earth’s dark side for a long time, and such observations have generally corresponded with times of increased solar activity.
Auroras on Venus are not restricted to the planet’s poles like their Earthly counterparts. Spots are bright and hazy clusters of varying shapes and intensities that can spread across the planet’s disk. Yet, the auroras can only be seen from outer space since Venus’s atmosphere is so thickly clouded.
Northern Lights on Mars
Long ago, Mars had its magnetic field. There are still magnetic regions in the Earth’s crust from that time. This means that the equatorial parts of Mars are just as likely as the polar regions to have auroras.
Whether or not future Martian explorers can witness the Red Planet’s auroras is a topic of debate between experts. The vast majority of their rays are really in the UV spectrum. Other research suggests that they may still be seen with the naked eye under specific situations. Most Martian auroras are predicted to be blue, with some red and green dots.
Large-Planet Auroras
Weak compared to the big planets of our solar system, their magnetic fields are nonetheless rather significant. This is why their auroras are so much more impressive than Earth’s. Nevertheless, we can only view the planets’ day sides since they are “external” to Earth. Hence the auroras are hidden by the reflected sunshine.
Saturn’s Northern Lights
Astronomers, therefore, must use infrared and ultraviolet wavelengths to investigate the auroras of the large planets. Several unexpected developments resulted from these investigations. According to observations, Saturn has the brightest aurora borealis in the solar system. At the height of 1200 miles, it begins to take shape.
Uranus is unique because its geographical and magnetic poles are not remotely aligned. Hence, the skies above the poles of Uranus are illuminated by the brilliant aurora borealis. They drop from the equator into the southern hemisphere, stretching from the north to the south.
Jupiter’s auroras are strangers. Bright aurora borealis regions are created in the gas giant’s magnetosphere, which is directly influenced by the satellites of the big planets. Io’s volcanic emissions are a key factor in this process.
Last but not least, Ganymede is significant. It’s the only planet-orbiting body in the Solar System to possess its magnetic field. Galileo and Juno’s data suggest that the planet’s poles occasionally emit light.
