Category: Mercury

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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.

With Mercury fading in MESSENGER’s rear view mirror, scientists are just starting to pore through the torrent of images sent back. And as you can probably guess, the new mysteries are piling up fast and furious. The planet is much less like the Moon than scientists previously thought.

MESSENGER made its closest approach to Mercury on January 14, passing just a few hundred kilometres above its surface. During the flyby it captured a total of 1,213 images.

One of the most unique features discovered by MESSENGER has been dubbed “The Spider” by scientists. And that’s what it looks like. The feature has a central crater surrounded by more than a hundred narrow, flat-floored troughs (called graben) radiating away.

Unlike the Moon, Mercury has huge cliffs or scarps, which can snake hundreds of kilometres across the planet’s surface. They trace the lines of old volcanic faults, from when the planet was still geologically active.

Because of its small size and high density, Mercury has a surprisingly large pull of gravity. Astronauts walking around its surface would experience 38% of the Earth’s gravity. This higher gravity means that the impact craters look different. Material doesn’t splash out from the impact craters so far, and there are many more secondary crater chains.

“We have seen new craters along the terminator on the side of the planet viewed by Mariner 10 where the illumination of the MESSENGER images revealed very subtle features. Technological advances that have been incorporated in MESSENGER are effectively revealing an entirely new planet from what we saw over 30 years ago,� said Science Team Co-Investigator Robert Strom, professor emeritus at the University of Arizona and the only member of both the MESSENGER and Mariner 10 science teams.

MESSENGER wasn’t just taking pictures. It also had a suite of scientific instruments measuring many features of the planet. Perhaps the most puzzling of these is its magnetic field. Even though Mercury cooled down and solidified eons ago, it still has an magnetic field. This was first detected by Mariner 10, and MESSENGER confirmed it.

This is just the beginning. MESSENGER will return to Mercury on October 6, 2008 to make a second flyby, and then a third on September 29, 2009. The spacecraft make its final return to the planet on March 18, 2011 when it’ll begin a year-long orbital mission.

Original Source: MESSENGER News Release

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Even though the Mercury flyby happened earlier this week, you can look forward to days and days of images. I’m nowhere near finished being amazed and entertained by the deluge of images captured by MESSENGER.

This latest image was captured when MESSENGER was about 20 minutes from its closest approach – at a range of 5,000 km (3,100 miles) of the tiny planet. The image is so crisp and clear that features as small as 400 metres (0.25 miles) across can be distinguished.

The large crater is located near Mercury’s equator on the side of the planet newly imaged by MESSENGER. I’m guessing it has no name, since it’s never been seen before! Around the crater are hundreds of smaller, secondary impactors. Some of these create long linear chains that look like machine gun fire. These occur when an asteroid or comet is torn apart by gravity, and then rain down on the planet in a straight line.

By counting craters that sit on top of the large crater’s ejecta blanket, and then comparing this count to the ones inside the crater, scientists will be able to calculate how old the crater is, and when it was formed.

Mission controllers also announced that they’ve received all 500 megabytes of data captured by MESSENGER as part of the flyby. The spacecraft has sent back a total of 1,213 images from its Mercury Dual Imaging System cameras.

They also revealed details about the flyby. According to their calculations, the spacecraft missed the targeted aim point by about 8.25 km (5.12 miles). This still give MESSENGER the gravity assisted speed boost it needs to meet up with the planet again and eventually go into orbit.

Original Source: MESSENGER News Release

Even though spacecraft have visited Mercury in the past, the same hemisphere was always in sunlight for every encounter. One side was photographed, and the other side was a complete and total mystery. There could be a big smiley face there, and we’d never know it. Well, the mystery’s over. MESSENGER flew past Mercury on January 14th, 2008, and revealed the planet’s hidden side… mostly.

Mariner 10 was the first spacecraft to zip past the planet Mercury, making three flybys in 1974 and 1975. Because the same hemisphere was in sunlight, the spacecraft was only able to image half the planet.

On January 14th, 2008, NASA’s MESSENGER spacecraft captured this image of Mercury when it was about 27,000 km (17,000 miles) away from the planet. During this flyby, it filled in about half of the hemisphere missed by Mariner 10. So that means that there are still some parts hidden – waiting to be revealed in future flybys.

And so, did it see a smiley face? Nope. The hidden hemisphere was pretty much like the rest of Mercury revealed so far: craters, ridges, bright and dark regions. At the upper right is the giant Caloris basin; its western regions haven’t been seen by spacecraft before.

If you’re hoping for more photos, don’t worry. This is just a quick black-and-white image captured by MESSENGER. NASA is planning to release more detailed images, including colour photographs over the next few days, so stay tuned.

We’ll keep posting them as they’re released.

Original Source: MESSENGER News Release