Bright Streaks on Mercury Suggest That It's Not a Dead Planet, but Geologically Active 

Mercury’s barren surface has led to the planet being labeled as "dead," but signs of geological activity say otherwise. Bright streaks known as “lineae,” which can be seen on slopes across the planet, may be the key to proving that reports of the planet’s death have been greatly exaggerated.

A new study published in Communications Earth & Environment has compiled an inventory of around 400 lineae on Mercury; these streaks may signal that material continues to be pushed up to the surface from deep within the planet. While it may seem like there’s not much action on Mercury, a closer look reveals the potential for active geological processes underneath its surface.

Read More: What Do Astronomers Mean When They Say Mercury Is In Retrograde?

Mercury's Lost Volcanoes

Mercury, the smallest planet and the closest to the sun, has a variety of intriguing features despite being seen as dead in the past. The planet’s surface appears similar to the moon, riddled with many impact craters that were caused by meteoroid collisions.

Mercury was once volcanically active, but activity stopped around 3.5 billion years ago. This happened because the planet was undergoing global contraction, shrinking as it cooled. And unlike Earth, which is covered in multiple moving plates, Mercury’s crust is just one big plate that envelops a molten core, according to a report from NC State University.

Mercury’s global contraction sealed off all volcanism, making it so that lava couldn’t reach the surface.

While Mercury doesn’t have active volcanoes anymore, it’s far from being dead. NASA’s MESSENGER space probe, which orbited Mercury from 2011 to 2015, found scarps (or massive cliffs) on the planet that indicated tectonic activity.

The Origin of Streaks on Mercury

The new study has curated data from MESSENGER, analyzing around 100,000 high-resolution images taken by the probe. Researchers focused on the distribution and morphological properties of 402 lineae on Mercury.

"Until now, lineae on Mercury had not been systematically mapped and studied; only a small handful of streaks were known. With the image analysis, we were able to create the first census, i.e., a systematic inventory, of slope streaks on Mercury," said first author Valentin Bickel, a researcher from the Center for Space and Habitability at the University of Bern, Switzerland, in a statement.

After using machine learning to organize the images, the researchers conducted a statistical analysis of the various lineae. They concluded that the lineae mostly occur on sun-facing slopes of young impact craters that penetrated volcanic material. Volatile material (such as sulfur or other light elements) from within Mercury could potentially slip through the cracks in the craters and reach the surface.

Continued Changes

The lineae also appear to be linked to hollows, another bizarre surface feature. These depressions, surrounded by haloes of bright material, were likely formed by a similar escape of volatile material from within Mercury. Both lineae and hollows hint at geological activity on Mercury that was never observed in such detail.

"Our findings paint a completely different, dynamic picture of the supposedly dead, dry, and boring planet Mercury," said Bickel.

These findings indicate that Mercury's surface could still be gradually changing today.

"Our results suggest that Mercury not only has a turbulent past but is still subject to modification today. As the streaks on Mercury are presumably caused by the outgassing of volatile material, they could be a promising indicator of Mercury's 'volatile budget', i.e., how much volatile material the planet is continuously losing," said Bickel.

The extent of Mercury's current geological activity will be further revealed by future missions, including the BepiColombo mission, a joint mission between the European Space Agency and the Japan Aerospace Exploration Agency that has sent two satellites into space, which will reach Mercury's orbit in November 2026.

The BepiColombo mission will create a 3D model of Mercury's topography, and with this, researchers hope to look for new streaks that have emerged since the MESSENGER mission's end over a decade ago.

Read More: Dramatic Flyby Confirms That Mercury's Radioactive Aurora Touches the Ground

Article Sources

Our writers at Discovermagazine.com use peer-reviewed studies and high-quality sources for our articles, and our editors review for scientific accuracy and editorial standards. Review the sources used below for this article:

• This article references information from a recent study published in Communications Earth & Environment: Slope lineae as potential indicators of recent volatile loss on Mercury
• This article references information from NASA: Tectonically Active Planet Mercury
• This article references information from NC State University: Mercury’s Volcanic Activity – or Lack of it – Could Help Us Find Other Earth-like Worlds