Category: Mercury

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Even though Mercury looks like the Moon at first glance, scientists from the MESSENGER mission say it’s becoming apparent that Mercury is an amazingly dynamic planet, and is actually more like Mars. For example, before this mission, scientists weren’t sure if volcanism even existed on Mercury, but from the spacecraft’s two flybys, they now know it is a very important part of the planet’s history. Additional new findings from the second flyby of Mercury in October 2008 show that the planet’s atmosphere, magnetosphere, and geological past are all characterized by much greater levels of activity than scientists first suspected.

And by the way, isn’t this a stunning picture of an impact basin? It’s one of the new discoveries from MESSENGER.

One of the most exciting results from the second flyby of Mercury is the discovery of a previously unknown large impact basin. The Rembrandt basin is more than 700 kilometers (430 miles) in diameter, and actually, to see the entire basin, it took combined images from both the first and second flyby to create the stunning picture above. Rembrandt is a relatively young impact basin, and forming about 3.9 billion years ago, is younger than any other known impact region on the planet. It shows pristine terrain on the outer portion of the crater, as well as unusual tectonic fault features, not found in any other big crater.

“This is the first time we’ve seen terrain exposed on the floor of an impact basin on Mercury that is preserved from when it formed” says MESSENGER scientist Thomas Watters. “Landforms such as those revealed on the floor of Rembrandt are usually completely buried by volcanic flows. We know that after Rembrandt formed, the planet was still contracting, so it is an exciting and unique new member of planetary craters we can study.”

MESSENGER’s Mercury Atmospheric and Surface Composition Spectrometer, or MASCS, detected significant amounts of magnesium clumped in the planet’s tenuous atmosphere, called the exosphere. Scientists had suspected magnesium would be present, but were surprised at its distribution and abundance.

“Detecting magnesium was not too surprising, but what is surprising is the distribution and amounts of magnesium that was recorded,” said Bill McClintock, a MESSENGER co- investigator.
The instrument also measured other exospheric constituents during the October 6 flyby, including calcium and sodium, and he suspects that additional metallic elements from the surface including aluminum, iron, and silicon also contribute to the exosphere.

MESSENGER observed a radically different magnetosphere at Mercury during its second flyby, compared with its earlier January 14, 2008 encounter. In the first flyby, no dynamic features were found. But the second flyby was a totally different situation, said James Slavin, MESSENGER Co-Investigator.

“MESSENGER measured large magnetic flux leakage through the dayside magnetopause, about a factor of 10 greater than even what is observed at the Earth during its most active intervals. The high rate of solar wind energy input was evident in the great amplitude of the plasma waves and the large magnetic structures measured by the Magnetometer throughout the encounter.”

Slavin said Mercury’s magnetic field bears a marked resemblance to what we have at earth, but it is about 100 times weaker, which implies interior of Mercury is in part molten. “There is a dynamo action that is ongoing which regenerates and maintains the planetary magnetic field,” he said.

Scientists are also learning more abour Mercury’s crustal evolution, and have now mapped about 90% of the planet’s surface. About 40% is covered by smooth plains which are now known to be of volcanic origna. “These plains are globally distributed (in contrast with the Moon, which has a nearside/farside asymmetry in the abundance of volcanic plains),” said Brett Denevi, MESSENGER team member.

Data shows an enhanced iron- and titanium content in an ancient basin studied by MESSENGER, which are exposed on the surface only through impact events, and may formed when dense minerals settled out as they crystallized from a cooling magma. “There are a complex series of events going on here, but we see it everywhere, so this is a microcosm of the entire planet” said Denevi.

These discoveries are more clues to the mystery of the creation of the rocky, bizarre planet that resides closest to the sun.

Source: NASA Press conference, MESSNEGER press release

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Scientists from the MESSENGER mission to Mercury discussed today the results from the spacecraft’s October 6 flyby of the closest planet to the sun. The probe has produced several science firsts and is returning hundreds of new photos and measurements of the planet’s surface, atmosphere and magnetic field. The images show a battered surface, and we now have pictures and data of parts of Mercury’s surface that have never been examined by a spacecraft. “The region of Mercury’s surface that we viewed at close range for the first time this month is bigger than the land area of South America,” said Sean Solomon, principal investigator and director of the Department of Terrestrial Magnetism at the Carnegie Institution of Washington. “When combined with data from our first flyby and from Mariner 10, our latest coverage means that we have now seen about 95 percent of the planet.”

The MErcury Surface, Space ENvironment, GEochemistry, and Ranging, or MESSENGER, spacecraft flew by Mercury shortly after 4:40 a.m. EDT, on Oct. 6. It completed a critical gravity assist to keep it on course to orbit Mercury in 2011 and unveiled 30 percent of Mercury’s surface never before seen by a spacecraft.

The spacecraft’s science instruments operated throughout the flyby. Cameras snapped more than 1,200 pictures of the surface, while topography beneath the spacecraft was profiled with a laser altimeter. The comparison of magnetosphere observations from the spacecraft’s first flyby in January with data from the probe’s second pass has provided key new insight into the nature of Mercury’s internal magnetic field and revealed new features of its magnetosphere. The magnetosphere is the volume surrounding Mercury that is controlled by the planet’s magnetic field.

It was discovered that the planet’s magnetic field is highly symmetric.

The probe’s Mercury Laser Altimeter, or MLA, measured the planet’s topography, allowing scientists, for the first time, to correlate high-resolution topography measurements with high-resolution images.

“The MLA collected altimetry in regions where images from MESSENGER and Mariner 10 data are available, and new images were obtained of the region sampled by the altimeter in January,” said Maria Zuber, co-investigator and head of the Department of Earth, Atmospheric, and Planetary Sciences at the Massachusetts Institute of Technology. “These topographic measurements now improve considerably the ability to interpret surface geology.”

The Mercury Atmospheric and Surface Composition Spectrometer observed Mercury’s thin atmosphere, known as an exosphere. The instrument searched for emissions from sodium, calcium, magnesium, and hydrogen atoms. Observations of magnesium are the first detection of this chemical in Mercury’s exosphere. Preliminary analysis suggests that the spatial distributions of sodium, calcium, and magnesium are different. Simultaneous observations of these spatial distributions, also a first for the spacecraft, have opened an unprecedented window into the interaction of Mercury’s surface and exosphere.

Spacecraft images also are revealing for the first time vast geologic differences on the surface.

“Now that MESSENGER’s cameras have imaged more than 80 percent of Mercury, it is clear that, unlike the moon and Mars, Mercury’s surface is more homogeneously ancient and heavily cratered, with large extents of younger volcanic plains lying within and between giant impact basins,” said co-investigator Mark Robinson of Arizona State University in Tempe.

Source: NASA

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Here’s the first image from MESSENGER’s flyby of Mercury on Monday. The bright crater just south of the center of the image is Kuiper, which has been seen before on images from the Mariner 10 mission in the 1970s. But most of this image, to the east, or right of Kuiper, toward the limb of Mercury is new territory for human eyes – at least in optical views. The image was taken by the Wide Angle Camera as MESSENGER was departing from the planet, and are among the first spacecraft views of that portion of Mercury’s surface. Most striking are the large pattern of rays that extend from north to south, almost along the entire face of Mercury. Amazing! This extensive ray system appears to emanate from a relatively young crater newly imaged by MESSENGER, providing a view of the planet distinctly unique from that obtained during MESSENGER’s first flyby.

2nd Update: (9:40 am CDT) More images!

Update: (8:50 am CDT) See 2nd image released below:

Above is the 3rd image released from the second flyby, a spectacular close-up of Mercury, as seen by the MESSENGER as it approached the planet, at about 17,100 kilometers (10,600 miles) altitude. The features in the foreground, near the right side of the image, are close to the terminator, the line between the sunlit dayside and dark night side of the planet, so shadows are long and prominent. The MESSENGER team has only had a few hours to examine these intriguing features, and, currently, more images from the flyby are still streaming back to Earth.

Here’s the second image released from the flyby. This is a close-up image taken 9 minutes and 14 seconds after MESSENGER’s closest approach to Mercury, when the spacecraft was moving at 6.1 kilometers/second (3.8 miles/second). The largest impact feature at the top of the image is about 133 kilometers (83 miles) in diameter and is named Polygnotus. This area was imaged previously by Mariner 10.

More on the first image: Data from the flyby started coming back to Earth early this morning, at about 1:50 am EDT. This spectacular image is one of the first to be returned and was taken about 90 minutes after the spacecraft’s closest approach to Mercury. This young, extensively rayed crater, along with the prominent rayed crater to the southeast of Kuiper, near the limb of the planet, were both seen in Earth-based radar images of Mercury but not previously imaged by spacecraft. As the MESSENGER team is busy examining this newly obtained view that is only a few hours old, data from the flyby continue to stream down to Earth, including higher resolution close-up images of this previously unseen terrain.

MESSENGER completed the flyby on Oct. 6 at 4:40 am EDT.

We’ll add more images as they become available.

Source: MESSENGER Gallery

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This morning at 4:40 am EDT, the MESSENGER spacecraft passed only 200 kilometers (124 miles) above Mercury’s surface as it made its second flyby of the mission. Now, the spacecraft is speeding away from Mercury, continuing its science observations for about 20 hours following closest approach. This flyby should provide the first global perspective of Mercury, as, if all went well, we should have images in total covering about 95 percent of the planet. “This second flyby will show us a completely new area of Mercury’s surface, opposite from the side of the planet we saw during the first,” said Louise M. Prockter, scientist for the mission.

If you’re looking for images and data from the flyby here, sorry to disappoint, but data will be transmitted to Earth only after the completion of all science observations. So, for now, even the MESSENGER science team has to wait. But scientists are already eagerly exploring the optical navigation images acquired just prior to the flyby. Shown here is a Narrow Angle Camera (NAC) image from the eighth and final optical navigation image set, taken about 14.5 hours before the flyby’s closest approach.

As in the earlier seven sets, Mercury appears as a thin sunlit crescent. Though much of Mercury is in darkness in this image, the visible portion had never been seen by spacecraft before. This portion of Mercury’s surface was not viewed during any of Mariner 10’s three flybys or during MESSENGER’s first flyby earlier this year. The newly imaged terrain shows a wide range of geologic features, and scientists have marked them on the image. Near the northern limb of the planet, extensive smooth plains, possibly volcanic in origin, are identified. A nearby crater is the brightest feature visible in the image, suggesting a relatively young age. In the southern region, a large basin is seen with a smooth floor, likely also a product of volcanism. A large scarp that appears to cut through this basin may have formed as Mercury cooled and contracted.

For this flyby, MESSENGER was a “green” spacecraft – meaning it didn’t require the firing of its thrusters to fly precisely where the scientists wanted to make observations. Instead, engineers used a type of “solar sailing,” to guide the spacecraft. “There are no refueling station in interplanetary space, so we’re stuck with the amount of fuel we had at launch,” said principal investigator Sean Solomon during a press conference last week. “Some of that fuel is required to get us into orbit (of Mercury in 2011). By not using fuel on some smaller maneuvers makes the mission more reliable and saves propellant, and allows us to have it in our back pocket when we need it for contingencies.” This is the first spacecraft to use this technique with such precision. Planetary flyby has been described as a complex ‘threading of a needle,’ and the MESSENGER team is getting better and better. The spacecraft’s first flyby was in January 2008, and a third will take place on Sept. 29, 2009. Orbit insertion will be on March 18, 2011.

We’ll post the MESSENGER images from this second flyby as soon as they’re available.

Source: MESSENGER website

Scientists from the MESSENGER mission continue to analyze the data from the spacecraft’s first flyby of Mercury on January 14, 2008. Initial data about the planet’s gravity field grabbed the science team’s attention, as the actual gravity data differed from predictions based on the Mariner 10 flyby in 1975. Any unknowns in Mercury’s gravity will provide challenges for the spacecraft’s navigation during the next flyby in October, and especially when MESSENGER goes into orbit of Mercury in 2011. This in turn could affect quality and detail of science observations. “There indeed are residuals that we have not yet been able to explain fully,” said Ralph McNutt, MESSENGER Project Scientist. “While we believe we have resolved possible extraneous effects, we continue to work those as well.”

The new data about Mercury’s internal structure is different from what the scientists expected. McNutt said that while it was surprising that the tracking data did not fit all of their preconceived notions from Mariner 10, MESSENGER went much closer to Mercury than did Mariner, which could account for the differences in data. Scientists believe there may be a large concentration of mass (mascons) under Mercury’s surface about 10 degrees south of the equator at about 60 degrees longitude. A presentation by team member David Smith at the Lunar and Planetary conference in March showed that they were able to account for about 95% of the problem deviation using a single mass anomaly at that location.

“This also leads into the most important thing on flyby 2,” said McNutt, “as we will have closest approach on the other side of the planet, we will then be able to obtain a much better separation of global versus local (mascon) signatures. So we expect major advances in our understanding of the gravity field from the 2nd flyby as it will complement the information gleaned from the first.”

From MESSENGER Navigation Team Chief Ken Williams’ perspective, any new information and understanding of this issue is important. “We’re following very closely any developments in understanding the gravity field,” said Williams. “As we encounter Mercury each time, we’re trying to build up our knowledge of what the gravity field is going to be. It’s not critical that we know it in fine detail right now, but obviously when we settle into orbit we’re going to want to know a lot more about it because that will affect the design of the orbit trim maneuvers that we’ll have to do.”

McNutt said the initial the command loads for the second flyby are being delivered to Mission Operations this week.

But Williams said the first flyby provided good news as far as knowing Mercury’s actual location in space. “While we had a pretty good idea of Mercury’s ephemeris, that fact that it hadn’t been visited by a spacecraft for a long time, there was a chance it would be different than we thought,” said Williams. “We did some things with optical navigation as we were flying by and it confirmed that it was only 2 km away at most from the ephemerides that JPL publishes. That was a great relief. That takes away the uncertainty for future encounters.”

MESSENGER’s orbit around Mercury will be affected by another perturbation, known as third body gravity, from the Sun’s gravity field. At first this effect will draw MESSENGER away from Mercury, but later in the mission it will force the spacecraft towards the planet. Williams said one navigation analyst estimated that if the mission ended in 2012 and no further maneuvers were done by the spacecraft, MESSENGER would impact Mercury sometime in 2016.

McNutt was clearly pleased with the data from the first flyby, and looks forward to the second. “The first flyby provided humanity’s first closeup of 21% of Mercury’s surface as well as an amazing set of data on the Caloris basin. We have also made major advances in our understanding of Mercury’s exosphere, magnetosphere, and surface mineralogy. The second flyby will provide a similar close-up of another 33% of terra incognita, and only ~1% of Mercury will not have been viewed by a spacecraft when we enter orbit in 2011.”

No, not that kind of snow, but scientists say deep inside the planet Mercury, iron “snow” forms and falls toward the center of the planet, much like snowflakes form in Earth’s atmosphere and fall to the ground. The movement of this iron snow could be responsible for Mercury’s mysterious magnetic field, and Mercury may be the only body in our solar system where this occurs.

Mercury and Earth are the only local terrestrial planets that possess a global magnetic field. But Mercury’s is about 100 times weaker than Earth’s, which scientists have been unable to explain.

Made mostly of iron, Mercury’s core is also thought to contain sulfur, which lowers the melting point of iron and plays an important role in producing the planet’s magnetic field.

To better understand the physical state of Mercury’s core, the researchers in a lab recreated the conditions believed to exist at Mercury’s core, and melted an iron-sulfur mixture at high pressures and high temperatures.

In each experiment, an iron-sulfur sample was compressed to a specific pressure and heated to a specific temperature. The sample was then quenched, cut in two, and analyzed with a scanning electron microscope and an electron probe microanalyzer.

As the molten, iron-sulfur mixture in the outer core slowly cools, iron atoms condense into cubic “flakes” that fall toward the planet’s center, said Bin Chen, University of Illinois graduate student and lead author of a paper published in the April issue of Geophysical Research Letters. As the iron snow sinks and the lighter, sulfur-rich liquid rises, convection currents are created that power the dynamo and produce the planet’s weak magnetic field.

The researchers say their findings provide a new context for the data that will be obtained from NASA’s MESSENGER spacecraft, which will flyby Mercury for a second time on October 6, 2008. It will pass by the planet again in September of 2009, and go into orbit in March of 2011.

Original News Source: Eureka Alert

Here are some interesting facts about Mercury.