The planet Mercury has many mysteries of which the spacecraft MESSENGER helped to solve, but one of those mysteries is of particular interest to scientists. There are many eccentric features of the small planet closest to the Sun, but one theory suggests that the planet is shrinking. Slowly contracting in on itself as its core freezes, the planet Mercury appears to be indeed getting smaller.
This theory was based on pictures taken from the only spacecraft to visit Mercury, NASA’s Mariner 10, which visited the planet in the 1970s and took photos of approximately 40% of the planet’s surface. The pictures show places where the surface of the planet appears to have buckled from within, leaving randomly strewn scarps across half of the planet. Scientists hoped that new images from the MESSENGER mission would shed new light on the surface as well as the core of this rocky planet. Scientists and researchers looked for more signs of buckling on the surface where the Mariner 10 was not able to get photos. Also, surface samples were meant to be collected to examine composition data on material that may have once come from the interior of Mercury.
The MESSENGER named as such for Mercury Surface, Space Environment, and Geochemistry and Ranging, launched its mission on August 3rd, 2010 and planned to reach Mercury in March of 2011. MESSENGER passed the planet three times before entering orbit. MESSENGER ultimately crashed and probably created a large crater in the surface of the planet.
One of the scarps discovered on the surface of Mercury that helped scientists discover Mercury’s shrinkage is Discovery Rupes, which cuts a mile into the crust of the rocky planet as it weaves across the planet’s surface. Scarps such as this one would resemble features like fault lines on Earth. However, on Mercury, these lines are randomly distributed and donâ€™t appear to have formed due to the filling in processes similar to what can be found on the surface of the Moon.
The theory behind Mercury’s shrinkage comes from scientists’ belief that Mercury’s crust was formed over a gigantic molten core. The core cooled and that is what led to the volume change in the planet. As Mercury’s core cooled and condensed, the surface buckled and broke, giving scientists the view of those large scarps on the outer crust. Most materials, including those on Mercury’s outer layers, contract as they cool; this is unlike water, which expands. Scientists have estimated that the dense and rocky planet has actually shrunk inward anywhere between less than one kilometer and three kilometers, which is not insignificant.
The lack of understanding and information about Mercury’s core is part of the reason scientists can only speculate about what is happening on Mercury. They know that the planet has a very high uncompressed density for its size and that it has a large metallic, most likely iron core, but what is unknown is far greater. Researchers don’t know precisely how large the core is, or whether any of it is molten. They also don’t know if it rotates to power Mercury’s strong magnetic field.
MESSENGER gave scientists and researchers a better view, which should conform, or at least strengthen their shrinking theories. Unlike the Mariner 10’s 45 % scan of Mercury, MESSENGER spent a year mapping the entire planet. The clarity of this scan will show enormous amounts of detail previously unseen with the former mission to the tiny planet. The sophisticated cameras on MESSENGER show details down to 60 feet across, compared to one mile with Mariner10.
To help determine the state and composition of the core, the spacecraft has a Mercury Laser Altimeter instrument that can track how the planet wobbles on its axis. Also, tools will be used to scan the surface and test the composition of Mercury’s ancient lava flows, which will help scientists determine the structure of the mantle.
Mercury: The Possible Result of a Hit-and-Run
According to one theory, Mercury was created after a giant asteroid collided with an even more massive object about 4.5 billion years ago. This collision formed the planet now known as Mercury and also shot a large amount of debris into space.
This idea that Mercury was the result of a collision was stemmed from the fact that the rocky planet has an unusual amount of metal for its size. Apparently, after the impact, the outer layers were stripped off, and very little of those outer layers reattached, thus creating a fragile shell and a dense core. Scientists have examined the apparent collision with the aid of computers and looked at the anatomy of the crash, as well as how some of the impact debris ended up on Venus and Earth. Earth’s moon was also the result of an impact, as was Pluto and its moons.
After examining the computer simulation, scientists were able to able to follow the formation of Mercury and determine the composition of the two colliding bodies, as well as follow the fragments that were the result of the collision for millions of years until they either came into contact with a planet, the sun, or were ejected from the inner solar system. This is how they were able to determine that some of the ejected material landed on Earth as well as Venus. The simulation also discovered that it would take 4 million years for only half the particles to land back on Mercury if they all fell back, but by that time the debris would have been carried off by solar radiation which explains why Mercury didn’t keep much material on its outer shell.
Many planets and articles in space were created as a result of collisions. Dust in the early solar system became rock and eventually the planets we know today. Scientists believe many objects collided and became one more massive object, while others were disintegrated or became dramatically altered after as much as a glancing blow. Planets may lose their crust, or atmosphere, or can be ripped apart to form smaller objects or moons to other worlds. These impacts create fragments that could become the space rocks that land on Earth today. The moon was thought to have been created when a Mars-sized object slammed into our planet.
The solar system was created shortly after the Sun’s formation about 4.6 billion years ago. Scientists believe that the dust and gas that orbited the Sun gathered to form rocks. Those rocks collided and joined to form comets and asteroids, and eventually planets. Scientists believe there may have been as few as 100 or so objects no more substantial than the Moon or Mars responsible for forming our planets, but their cosmic collisions would have created dramatic results. When gravitational forces are taken into account with massive objects even passing near each other, extreme changes to both bodies can take place. Each object can be decompressed, melted, lose material, or also destroyed. The smaller object’s gravity could easily depressurize in the presence of a more massive object causing the smaller of the two to break apart. This can cause the formation of asteroids and meteorites.
What’s left of Mercury after this apparent hit-and-run collision is a large and dense core surrounded by a fragile mantle and crust; however, scientists still don’t fully understand the complexities of this theory and are still examining it with the help of computer models and simulations.
The hit-and-run theory may, however, explain the extremely diverse composition of asteroids, including pieces that fall to Earth as meteorites. Some resemble the rocky surfaces of planets, but others are filled with iron, which is much more like the core of a world. This diversity would account for the theory that all space rock was not formed in the same disk of debris; instead, it has been created as a result of many different collisions in space and therefore contains different types of material.