Mercury Is Shrinking, Scientists Say

mercuryMercury, the closest planet to the Sun and the smallest in the solar system, is shrinking, scientists say. In nearly four billion years – 3.8 billion, to be exact –the planet has lost 8.6 miles (14km) in diameter. Scientists say the reason Mercury is losing girth is because the planet is cooling.

Images produced by NASA, which have provided scientists with the first images of the rocky geology that encapsulates Mercury, is contracting and transforming the surface into wrinkled ridges and edged cliffs known as lobate scarps. “It is Mercury’s version of a mountain belt,” said Paul Byrne, lead author of the study in Nature Geoscience and planetary geologist at the Carnegie Institution in Washington, D.C.

Byrne explains that all planets in the solar system are cooling and shedding miles of planetary diameter, and Mercury is no exception. After all, the sun is much cooler than it was during the formation of the solar system, eons ago. However, despite being closer to the sun, Mercury’s process has progressed further than its celestial counterparts.


The shrinking process has taken a toll on its observable geology. On its already cratered complexion, cliffs have formed from sprouting mountainous peaks that can reach heights of over two miles (3km) high – almost as tall as Mount St. Helens in Washington State. There are long chains of ridges running across the surface of the planet. One formation, known as the Enterprise Ruples, extends up to 1,050 miles (1,700 km), nearly half as long as the eastern seaboard of the United States.

Charting this newly formed geography by foot on a manned mission will be impossible in the near future. Surface temperatures can reach upwards of 800 degrees Fahrenheit (430 Celsius), which would quickly melt any military and aerospace heat-resistant material currently in use. Instead, scientists observe the surface of Mercury from images sent to NASA from the MESSENGER spacecraft, a sun-shielded craft that has been orbiting the swift, first planet since 2011.

William McKinnon, professor at Washington University in the Department of Earth and Planetary Sciences, said that Mercury’s landscape is “literally crumpling up.” He says that gigantic slabs of rock are moving and sliding across one another. The movement of the surface geology is similar to the movement of tectonic plates on Earth that constantly alter both surface and subterranean geology.

The surface faulting shows that seismic activity carved out the landscape, which is still progressing. McKinnon explains that if NASA, or any other space agency, could land seismometers on Mercury, without them being destroyed by the intense heat and radiation, scientists would be able to observe and document further seismic movement on the surface.


With these recent findings, the documentation and observation of Mercury’s surface for study have resulted in unfinished business. The only other spacecraft to come near the planet was Mariner 10, sent by NASA. The Mariner craft completed three fly bys of Mercury between 1974 and 1975. Although this was an astronomical achievement, only 45 percent of the surface was photographed.

The incomplete data has baffled scientists for decades. Mariner’s original findings suggested that Mercury had only shrunk by 1.25 to 3.75 miles (2-6 km) in diameter since its inception nearly four billion years ago. However, thermal history models of the interior of Mercury predicted that the planetary contraction should have amounted to more than 10 times the previous amount.

Byrne states that scientists have a full picture now. His findings demonstrate that Mercury has seen a radial contraction between 2.5 and 4.3 miles (4-7 km), which makes the modern radial measurement around 1,516 miles (2,440 km).

Similar peaks and ridges on Mercury can be observed on Mars and the Moon, but there is one significant difference. Byrne explains that Mercury is an anomaly; it seems to have shrunk more in diameter than both Mars and the moon. With newer and better photographs and findings using the MESSENGER craft, which documented 5,900 landforms created by the contraction, scientists have a more complete portrait with which they can tackle new questions. These questions include why Mercury is shrinking when the deformation of the surface began, the extent of the seismic activity, and how fast the diameter has contracted.

Centuries ago, scientists believed the Earth was shrinking. After much deliberation and scientific observation, that notion was ruled out. Our planet was changing form due to the constant shifting of tectonic plates that makes the land rise and fall. In regard to the previous notion, it seems it was a case of right theory, wrong planet. Even though Mercury’s surface geography is changing, plate tectonics are not to blame. Unless scientists find out exactly why the planet is becoming more deformed, Mercury is shrinking.

By Alex Lemieux


National Geographic

Universe Today

BBC News

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