Mercury’s Bright Streaks May Reveal a Big Secret

Mercury, the smallest planet in the Solar System, could be concealing an enormous secret.

Unusual bright streaks traced across Mercury’s craters and slopes may point to extremely recent geological activity, new modelling indicates.

The results imply that Mercury is not as ‘dead’ or uninteresting as astronomers previously believed.

Rather, the surface of our neighbouring planet - a geological ‘hellscape’ - appears to be active after all, at least in geological terms.

Mercury’s bright streaks and geological activity

Until not long ago, researchers had identified only a small number of Mercury’s bright streaks, formally called lineae.

Astronomer Valentin Bickel of the University of Bern in Germany, working with colleagues at Italy’s Astronomical Observatory of Padova, has now compiled a catalogue of 402 such features.

By examining these bright markings, the researchers have produced a very different picture of Mercury: one that is unexpectedly changeable for a small, atmosphere-free planet that has spent 4.5 billion years cooling down.

Machine learning reveals Mercury lineae patterns

The team applied machine learning to 100,000 high-resolution photographs of the planet captured from 2011 to 2015.

Their analysis shows that Mercury’s elongated bright lines commonly gather on the Sun-facing sides of crater slopes, though they do not invariably seem to begin at hollows.

On other worlds, lineae are believed to wear away rapidly. The authors therefore propose that Mercury’s streaks may still be developing and changing today. That would make them evidence not of a violent ancient history, but of an unsettled present driven by heat and volatile substances, such as sulphur, rising from beneath the surface.

“Volatile material could reach the surface from deeper layers through networks of cracks in the rock caused by the preceding impact,” explains Bickel.

“Most of the streaks appear to originate from bright depressions, so-called ‘hollows.’ These hollows are probably also formed by the outgassing of volatile material and are usually located in the shallow interior or along the edges of large impact craters.”

New Mercury mission images could test the theory

The researchers hope that fresh images of Mercury from European Space Agency (ESA) and Japan Aerospace Exploration Agency (JAXA) missions will confirm their hypothesis.

If Mercury’s surface remains active, a more detailed view may be available soon.

The study appeared in Nature Communications Earth & Environment.