Mercury, our closest neighboring planet to our Sun, experiences extreme daytime temperatures that make its surface scorchingly hot. Craters and basins dot its surface, from small bowl-shaped cavities to multiringed impact craters hundreds of kilometers across.
Craters on Mercury are surrounded by massive scarps or cliffs that soar over one mile high, as predicted by models that assume expansion of its surface over time.
It’s Psychedelic Blue
Mercury is an extremely small planet, less than half as wide as Earth and is the closest rocky planet to our Sun, its surface heavily cratered from years of bombardment by solar radiation. Mercury alternately bakes and freezes as it orbits our star.
Astronomers and planetary geologists remain baffled by the mysterious blue streaks dotting planet Earth’s surface. These streaks could be the result of chemical reactions occurring within unexplored craters; their color may even come from volatile elements like sulfur.
NASA’s Messenger spacecraft captured this stunning color image as part of a mosaic taken during its orbit around Mercury. It displays part of the planet’s surface in an intense blue hue with light blue and white streaks extending from impact craters, while an enormous circular feature in the upper right of this picture known as Caloris basin formed when an impactor came near early in Mercury’s history.
Scientists suspect the mysterious blue streaks on Mercury could be produced by the same process responsible for producing rainbows. Furthermore, scientists are studying mysterious “hollows” dotted across its surface which seem to contain sulfides like depressions on Mars’ carbon dioxide ice surface.
As they explore these unusual features, astronomers will use the MESSENGER probe to gain more insight into Mercury’s peculiar magnetic field. Compared with most planets’ magnetic fields, Mercury’s is considerably weak – only 1/10th as strong as Earth’s. Scientists remain uncertain why Mercury has such a weak field; they’re eager to better understand what forces cause it.
On Thursday (August 24), those lucky enough to witness clear skies may witness Mercury transit the Sun as it passes directly in front of it on August 24. You’ll likely see what looks like a small, moving spot of light across its face – online sky maps provide details as to the timing and location of this transit event in both eastern and western skies; to observe safely you will require either binoculars with solar filters or telescopes fitted with them for observation purposes.
It’s Covered in Craters
Mercury’s surface is covered with craters of all sizes, reflecting its long history of extreme bombardment by NASA’s Mariner 10 and later MESSENGER probes. Their small satellites captured images of this greyish-brown planet with scarps (cliffs) up to one mile high; some may be the remnants of impact basins, while others contain smaller fragments that reflect light more efficiently than larger pieces of intact material.
Craters play an invaluable role in helping scientists estimate the age of surfaces. Craters that formed early are indicative of older surfaces while later-formed craters are indicative of younger bodies such as Mercury. Because it lacks significant tectonic activity, its craters have not been recycled by more recent impacts and remain visible on its surface.
Small craters tend to be older, while larger ones with well-defined rims and ejecta blankets appear relatively young. Many larger craters have been partially or fully submerged by subsequent impacts that left smooth plains in their place.
Contrasting with cratered plains, there are flat areas with scattered craters and an exaggerated yellow hue in exaggerated images that resemble volcanic plains created during heavy bombardments that destroyed older impact basins. Scientists suspect these may be areas where volcanic activity took place as part of heavy bombardments to form these plains – some even include arcuate scarps to define them further.
Other parts of the surface feature contractional fault scarps. Lobate scarps feature steep scarp faces with gently dipping back slopes while wrinkle ridges are flatter and appear like folded paper. Both types can be found throughout smooth plains but not only here.
The MESSENGER probes captured images of not only craters but also of mysterious “rays”, which sometimes appeared brighter than others. These bright streaks are known as crater rays; these form when an asteroid or comet hits the Earth with enough force to dig a crater as well as crush and scatter fine-grained fragments far from its point of impact – these “rays” tend to reflect more strongly than surrounding terrain and appear brighter in certain imaging modes due to higher concentration of fine-grained material than other craters do.
Mercury resembles the Moon in its cratered terrain, yet is much denser due to a vast, iron-rich core comprising more than half its volume. Scientists speculate that at one point in its past it once boasted a silicate mantle but was later destroyed by an enormous impact event.
Mercury remains a mystery to scientists for one key reason: It has no moons! Scientists think this could be because its outer layer, approximately the thickness of an NFL football, contains very little liquid water due to solar heat heating up buried minerals causing chemical reactions that produced hydrogen gas that interacted with other elements and formed ice crystals before eventually turning into frozen water molecules.
Sol-wind-borne molecules would have been transported by Mercury’s surface wind to form water clouds that may have fallen and frozen upon contact with the ground, although any accumulation would likely have been so minimal it couldn’t even be detected by spectrometers.
Mercury may have experienced water formation by melting its subsurface mantle, however this would likely involve highly reactive reactions with oxygen in the atmosphere and possible explosion. One possible scenario would be for enough of Mercury’s mantle water to have been melted through by sunlight to be pulled up through crust into surface waters via rising pressures from below and to eventually form as surface waters.
Astronomers were astounded when the MESSENGER probe made its first flybys of Mercury in 2008. Images taken by this probe revealed deposits of pyroclastic ash — evidence of volcanic eruptions — scattered throughout its surface.
Since dating effusive volcanic deposits (those formed from flowing magma) is key to understanding planetary geology, scientists wanted to locate where on Mercury volcanic activity took place. Their attention turned towards impact basin rims where at least 51 sites suspected of pyroclastic volcanism dating from 3.5-1 billion years ago had been discovered.
Ever since MESSENGER launched into orbit around Mercury in 2011–and even prior to Mariner 10’s flyby in 1974–scientists have attempted to determine what causes Mercury’s unique dark spots. Thanks to MESSENGER’s final months of mission, scientists have confirmed that these spots are indeed composed of graphite–the same material found in pencil leads! MESSENGER collected data as it passed close by Mercury and used this knowledge as it flew past.
Mercury’s dark spots, similar to those on Mars and the Moon, have long been assumed to be due to volcanic activity and carbon delivered from comet impacts. However, according to research led by Patrick Peplowski of Johns Hopkins University Applied Physics Laboratory suggests otherwise: they could actually be remnants of Mercury’s original crust–graphite that floated on top of an expansive magma ocean when the planet first formed.
To demonstrate this point, MESSENGER used its measurement capabilities to track escaping particles created when high-energy cosmic rays hit planet surfaces with great intensity. Neutrons released by such cosmic rays reveal information about what type of material a planet consists of; iron releases less neutrons than carbon does for instance. By employing this approach MESSENGER discovered large numbers of neutrons coming off Mercury’s dark patches–indicating its thick layer of carbon cover.
Scientists have made the groundbreaking discovery that Mercury’s surface contains carbon. This new insight may help scientists gain a greater understanding of how and why this planet formed, along with any additional secrets hidden under its outer layer. Scientists will continue their analysis on low-reflectance material present on Mercury to learn what other minerals might exist there, while investigating more about its mysterious core, thought to account for 42% of its mass.