Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Mercury not like other planets MESSENGER finds

30.09.2011
Only six months into its Mercury orbit, the tiny MESSENGER spacecraft has shown scientists that Mercury doesn't conform to theory.

Its surface material composition differs in important ways from both those of the other terrestrial planets and expectations prior to the MESSENGER mission, calling into question current theories for Mercury's formation. Its magnetic field is unlike any other in the Solar System, and there are huge expanses of volcanic plains surrounding the north polar region of the planet and cover more than 6% of Mercury's surface. These findings and other surprises are revealed in seven papers in a special section of the September 30, 2011, issue of Science.

Surface Surprises

Two of the seven papers indicate that the surface material is more like that expected if Mercury formed from similar, but less oxidized, building blocks than those that formed its terrestrial cousins, perhaps reflecting a variable proportion of ice in the initial accretionary stages of the planets. Measurements of Mercury's surface by MESSENGER's X-Ray and Gamma-Ray Spectrometers also reveal substantially higher abundances of sulfur and potassium than previously predicted. Both elements vaporize at relatively low temperatures, and their abundances thus rule out several popular scenarios in which Mercury experienced extreme high-temperature events early in its history.

"Theorists need to go back to the drawing board on Mercury's formation," remarked the lead author of one of the papers, Carnegie's Larry Nittler. "Most previous ideas about Mercury's chemistry are inconsistent with what we have actually measured on the planet's surface."

Volcanism

For decades scientists had puzzled over whether Mercury had volcanic deposits on its surface. MESSENGER's three flybys answered that question in the affirmative, but the global distribution of volcanic materials was not well constrained. New data from orbit show a huge expanse of volcanic plains surrounding the north polar region of Mercury. These continuous smooth plains cover more than 6% of the total surface of Mercury.

Another lead author, James Head of Brown University, said that the deposits appear typical of flood lavas, like those found in the few-million-year-old Columbia River Basalt Group on Earth. "Those on Mercury appear to have poured out from long, linear vents and covered the surrounding areas, flooding them to great depths and burying their source vents,"

Scientists have also discovered vents, measuring up to 25 kilometers (km) (15.5 miles) in length, that appear to be the source of some of the tremendous volumes of very hot lava that have rushed out over the surface of Mercury and eroded the substrate, carving valleys and creating teardrop-shaped ridges in the underlying terrain.

New landforms

MESSENGER revealed an unexpected class of landform on Mercury and suggest that a previously unrecognized geological process is responsible for its formation. Images collected during the Mariner 10 and MESSENGER flybys of Mercury showed that the floors and central mountain peaks of some impact craters are very bright and have a blue color relative to other areas of Mercury. These deposits were considered to be unusual because no craters with similar characteristics are found on the Moon. But without higher-resolution images, the bright crater deposits remained a curiosity.

Now MESSENGER's orbital mission has provided close-up, targeted views of many of these craters. The bright areas are composed of small, shallow, irregularly shaped depressions that are often found in clusters said David T. Blewett, a planetary scientist at the Johns Hopkins University Applied Physics Laboratory (APL) and lead author of one of the Science reports. "The science team adopted the term 'hollows' for these features to distinguish them from other types of pits that are found on Mercury."

Hollows have been found over a wide range of latitudes and longitudes, suggesting that they are fairly common across Mercury. Many of the depressions have bright interiors and halos, and Blewett says the ones detected so far have a fresh appearance and have not accumulated small impact craters, indicating that they are relatively young.

"Analysis of the images and estimates of the rate at which the hollows may be growing lead to the conclusion that they are actively forming today," Blewett says. "The old conventional wisdom was that 'Mercury is just like the Moon.' But from its vantage point in orbit, MESSENGER is showing us that Mercury is radically different from the Moon in just about every way we can measure."

Magnetic Field

Earth, Mercury, Jupiter, Saturn, Uranus, and Neptune all have intrinsic magnetic fields, but MESSENGER found that Mercury's weak field is different. So too are particle acceleration processes in Mercury's magnetosphere, as described in a paper by lead author George Ho of APL. MESSENGER's observations of energetic electrons indicated that their distribution is not consistent with what are known as Van Allen radiation belts. These belts are bands of charged particles that interact with the magnetic field and surround the planets.

Mercury's magnetic equator is also well to the north of the planet's geographic equator. The best-fitting internal dipole magnetic field is located about 480 km (298 miles), northward of the planet's center.

The team found that sodium is the most important plasma ion contributed by the planet to the magnetosphere. "We had previously observed neutral sodium from ground observations, but up close we've discovered that charged sodium particles are concentrated near Mercury's polar regions where they are likely liberated by solar wind ion sputtering, effectively knocking sodium atoms off Mercury's surface" notes the University of Michigan's Thomas Zurbuchen, author of one of the Science reports. "We were able to observe the formation process of these ions, one that is comparable to the manner by which auroras are generated in the Earth atmosphere near polar regions."

MESSENGER's Fast Imaging Plasma Spectrometer detected helium ions throughout the entire volume of Mercury's magnetosphere. "Helium must be generated through surface interactions with the solar wind," says Zurbuchen. "We surmise that the helium was delivered from the Sun by the solar wind, implanted on the surface of Mercury, and then fanned out in all directions."

"Our results tell us is that Mercury's weak magnetosphere provides very little protection of the planet from the solar wind," he continued. "Extreme space weather must be a continuing activity at the surface of the planet closest to the Sun."

"In the history of exploration of our planetary system, the first spacecraft to orbit a planet has always yielded stunning surprises, and MESSENGER has been true to that pattern," notes Carnegie's Sean Solomon, MESSENGER Principal Investigator. "Our first good views of the polar regions, our first high-resolution images, our first continuous observations of the exosphere and magnetosphere, and our first opportunity to collect time-consuming measurements of surface composition have all returned unexpected results. Mercury is not the planet described in the textbooks. Although a true sibling of Venus, Mars, and Earth, the innermost planet has had a much more exciting life than anyone predicted."

MESSENGER (MErcury Surface, Space ENvironment, GEochemistry, and Ranging) is a NASA-sponsored scientific investigation of the planet Mercury and the first space mission designed to orbit the planet closest to the Sun. The MESSENGER spacecraft launched on August 3, 2004, and entered orbit about Mercury on March 18, 2011, to begin a one-year study of its target planet. Dr. Sean C. Solomon, of the Carnegie Institution of Washington, leads the mission as Principal Investigator. The Johns Hopkins University Applied Physics Laboratory built and operates the MESSENGER spacecraft and manages this Discovery-class mission for NASA.

The Carnegie Institution for Science (carnegiescience.edu) is a private, nonprofit organization headquartered in Washington, D.C., with six research departments throughout the U.S. Since its founding in 1902, the Carnegie Institution has been a pioneering force in basic scientific research. Carnegie scientists are leaders in plant biology, developmental biology, astronomy, materials science, global ecology, and Earth and planetary science.

Sean Solomon | EurekAlert!
Further information:
http://www.ciw.edu

More articles from Physics and Astronomy:

nachricht Meteoritic stardust unlocks timing of supernova dust formation
19.01.2018 | Carnegie Institution for Science

nachricht Artificial agent designs quantum experiments
19.01.2018 | Universität Innsbruck

All articles from Physics and Astronomy >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: Artificial agent designs quantum experiments

On the way to an intelligent laboratory, physicists from Innsbruck and Vienna present an artificial agent that autonomously designs quantum experiments. In initial experiments, the system has independently (re)discovered experimental techniques that are nowadays standard in modern quantum optical laboratories. This shows how machines could play a more creative role in research in the future.

We carry smartphones in our pockets, the streets are dotted with semi-autonomous cars, but in the research laboratory experiments are still being designed by...

Im Focus: Scientists decipher key principle behind reaction of metalloenzymes

So-called pre-distorted states accelerate photochemical reactions too

What enables electrons to be transferred swiftly, for example during photosynthesis? An interdisciplinary team of researchers has worked out the details of how...

Im Focus: The first precise measurement of a single molecule's effective charge

For the first time, scientists have precisely measured the effective electrical charge of a single molecule in solution. This fundamental insight of an SNSF Professor could also pave the way for future medical diagnostics.

Electrical charge is one of the key properties that allows molecules to interact. Life itself depends on this phenomenon: many biological processes involve...

Im Focus: Paradigm shift in Paris: Encouraging an holistic view of laser machining

At the JEC World Composite Show in Paris in March 2018, the Fraunhofer Institute for Laser Technology ILT will be focusing on the latest trends and innovations in laser machining of composites. Among other things, researchers at the booth shared with the Aachen Center for Integrative Lightweight Production (AZL) will demonstrate how lasers can be used for joining, structuring, cutting and drilling composite materials.

No other industry has attracted as much public attention to composite materials as the automotive industry, which along with the aerospace industry is a driver...

Im Focus: Room-temperature multiferroic thin films and their properties

Scientists at Tokyo Institute of Technology (Tokyo Tech) and Tohoku University have developed high-quality GFO epitaxial films and systematically investigated their ferroelectric and ferromagnetic properties. They also demonstrated the room-temperature magnetocapacitance effects of these GFO thin films.

Multiferroic materials show magnetically driven ferroelectricity. They are attracting increasing attention because of their fascinating properties such as...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

10th International Symposium: “Advanced Battery Power – Kraftwerk Batterie” Münster, 10-11 April 2018

08.01.2018 | Event News

See, understand and experience the work of the future

11.12.2017 | Event News

Innovative strategies to tackle parasitic worms

08.12.2017 | Event News

 
Latest News

Let the good tubes roll

19.01.2018 | Materials Sciences

How cancer metastasis happens: Researchers reveal a key mechanism

19.01.2018 | Health and Medicine

Meteoritic stardust unlocks timing of supernova dust formation

19.01.2018 | Physics and Astronomy

VideoLinks
B2B-VideoLinks
More VideoLinks >>>