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Mercury science

Scientists present imagery and instrument data collected by NASA's MESSENGER spacecraft during its flyby of Mercury.

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STS-98: Destiny lab

NASA's centerpiece module of the International Space Station -- the U.S. science laboratory Destiny -- rode to orbit aboard Atlantis in February 2001.

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Earth science update

NASA leaders discuss the agency's Earth science program and preview major activities planned for 2008, including the launch of three new satellites.

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STS-97: ISS gets wings

Mounting the P6 power truss to the station and unfurling its two solar wings were the tasks for Endeavour's STS-97 mission.

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STS-92: ISS construction

The Discovery crew gives the station a new docking port and the box-like Z1 truss equipped with gyroscopes and a communications antenna.

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Expedition 17 crew

Pre-flight news briefing with the crew members to serve aboard the space station during various stages of Expedition 17.

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STS-106: Making the station a home in space

Following the Russian Zvezda service module's long-awaited launch to serve as the station's living quarters, Atlantis pays a visit in September 2000 to prepare the complex for arrival of the first resident crew.

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STS-101: ISS service call

An impromptu maintenance mission to the new space station was flown by Atlantis in May 2000. The astronauts narrate their mission highlights.

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STS-96: First ISS docking

The first shuttle mission to dock with the fledgling International Space Station came in May 1999 when Discovery linked up with the two-module orbiting outpost. The STS-96 crew tells story of the mission.

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STS-88: Building the ISS

Construction of the International Space Station commenced with Russia's Zarya module launching aboard a Proton rocket and shuttle Endeavour bringing up the American Unity connecting hub. STS-88 crew narrates highlights from the historic first steps in building the outpost.

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Mysteries and surprises found during Mercury flyby
BY STEPHEN CLARK
SPACEFLIGHT NOW

Posted: January 31, 2008

A treasure trove of data captured by NASA's Messenger probe as it zoomed past Mercury earlier this month revealed a mysterious world fraught with scars, leaving researchers with more questions about the solar system's innermost planet.


This remarkable feature has been nicknamed "The Spider" by the science team. Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington
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"I was astounded by the quality of these images, and it dawned on me after looking at these that this is a whole new planet we're looking at," said Robert Strom, a Messenger science team member from the University of Arizona.

During more than two days of near-continuous science activity, Messenger snapped 1,213 images and gathered an immense heap of data that took nearly four days to beam back to Earth. About 500 megabytes of data was stored on Messenger's solid-state recorder during the Mercury encounter.

All seven of Messenger's science instruments were turned on during the observation phase.

Mariner 10, the only other spacecraft to ever visit Mercury, flew past the planet three times in the 1970s but never entered orbit. The combined observations from the three visits only covered about 45 percent of Mercury's surface, but Messenger's Jan. 14 flyby uncovered about half of the planet's previously unexplored terrain.

Strom, who was also part of the Mariner 10 team, said he was blown away by the quality of data from Messenger.

"Every part of the planet, seen or unseen (before), is new," Strom said.

Another swing past Mercury on Oct. 6 will expose most of Mercury's remaining undiscovered surface. A final approach and flyby of Mercury is scheduled for September 2009.

Messenger is using the flybys to gradually slow its velocity enough to eventually maneuver into orbit around Mercury on March 18, 2011. Plans call for Messenger to study Mercury from orbit for at least one year.

"The best is yet to come," Strom said. "What you're seeing here is just the tip of the iceberg."

Messenger's study of Mercury closes one of the final chapters in solar system exploration after NASA spacecraft flew by seven planets between the early 1960s and 1989. Orbiters have now been dispatched to five of those planets, including Messenger's unfinished voyage to Mercury.

This month's flyby of Mercury marked "the unveiling of one of the largest pieces of unseen real estate in the solar system," said Alan Stern, associate administrator of NASA's science mission directorate.

Mercury is an "extremely dynamic planet, one where all components are strongly interacting and one where we're going to have to watch it for some time before we can say fully understand it," said Sean Solomon, Messenger principal investigator at the Carnegie Institute of Washington.

Messenger revealed surface features on Mercury that have not been seen on any other planet, according to Solomon.

"It was not the planet we expected," Solomon said.


This image shows details of the Caloris basin, one of the largest impact basins in the solar system. Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington
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The geometry of the approach to Mercury gave Messenger's suite of instruments a better view of the planet's giant Caloris impact basin. Mariner 10 only saw a portion of Caloris during its exploration three decades ago.

Messenger's images allowed scientists to revise size estimates of Caloris from a diameter of about 800 miles to 960 miles. The basin was likely carved out by the impact of a large object between 3.8 and 3.9 billion years ago, Strom said.

The collision excavated material from deep within Mercury and brought it to the surface, Solomon said.

"We expect that the walls of Caloris basin are (made of) revealing material that are from great depths," he said.

Other smaller impacts also deposited debris from inside Mercury at the surface, giving scientists access to material from the planet's primordial interior. One such crater, a peculiar 25-mile-wide feature resembling a spider near the middle of Caloris, is of particular interest to Messenger's science team.

"We have seen a number of impact basins in the solar system," said Louise Prockter, instrument scientist for Messenger's camera system at the Johns Hopkins University Applied Physics Laboratory. "We have never ever seen anything like this in the center of any of them."

Streak-like marks radiate outward from the crater for hundreds of miles across the Caloris basin. The leading theory says the radial features are troughs from the break-up of congealed materials that filled Caloris after the basin formed.

Some of the troughs could have existed prior to the crater's formation, while other fractures could have been caused by the impact itself.

"We've got a variety of natural drill cores into Mercury's interior going back to nearly four billion years ago in the history of this planet, and it's sitting there for us to unravel," Solomon said.

Scientists believe Mercury can harbor clues about the early history of the solar system, which was born roughly 4.5 billion years ago when a cloud of hot gas and cosmic debris coalesced to form the sun, planets, moons, and other smaller bodies.


Several processes have acted to sculpt Mercury's surface over time, and evidence of them is abundant in this image. This scene shows at least five different events in Mercuryıs surface history. Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington
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Messenger's $446 million mission to the barren world will help fill in the gaps in the study of the solar system's history.

Many of Mercury's surface features are as old as the solar system itself. Mercury is also the only terrestrial planet other than Earth to have an active magnetic field and magnetosphere, a protective bubble that can shield against the solar wind and radiation.

Scientists are not sure how Mercury is able to maintain its magnetic field because the planet's small size should have caused its oversized metallic core to solidify long ago. Scientists say Earth's magnetic field is generated by processes deep within the planet's molten liquid core.

"Mercury's magnetosphere is more similar to Earth's than we might have thought," said Thomas Zurbuchen, instrument scientist for Messenger's fast imaging plasma spectrometer.

A solution to this key question could help scientists determine the history and future of Earth's magnetic field. Data from Mercury may also lead to conclusions about the fate of magnetic fields on Venus and Mars, according to researchers.

Volcanism, an important piece of evidence indicating a molten interior, was present on Mercury during its early history, but not today, according to preliminary results from Messenger.

Uneven crater distributions inside the Caloris basin show fields of lava flowed across parts of the broad valley in the planet's distant history, according to Strom.

"That shows that there's been a lot of volcanic activity on Mercury," Strom said. "This cratering record that we're seeing now is going to give us a lot of clues about the geologic evolution of Mercury."

Mariner 10 provided data hinting at previous volcanic activity, but scientists were unable to reach a consensus on whether volcanism was once widespread on Mercury.

"There's (now) very little doubt in the minds of most of us on the geology team that there has been widespread volcanism on Mercury's surface," Prockter said.


Color differences on Mercury are subtle, but they reveal important information about the nature of the planet's surface material. Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington
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Despite superficial comparisons between Mercury and the moon, one of the most striking differences between the two bodies is the color variation between valleys and highlands, according to Prockter.

The Caloris basin is filled with bright material, while higher regions of the planet appear darker. This disparity is the opposite of what is found on the moon, but scientists still do not know what drives the difference, Prockter said.

Although Mercury and the moon appear similar to the naked eye, color-enhanced imagery from Messenger's spectral instruments will help reveal the chemical differences. Those images are just now being examined, Prockter said.

Messenger also turned its instruments on Mercury's tenuous atmosphere, which is so thin that its atoms rarely collide with one another. Messenger detected sodium, calcium and hydrogen emissions streaming from the feeble atmosphere in a tail stretching more than 25,000 miles behind the planet.

Messenger also turned on its radar altimeter for about 11 minutes around the time of the craft's closest approach. The altimeter mapped a narrow swath of Mercury's terrain, discovering valleys nearly 10,000 feet deep and peaks towering 16,000 feet above surrounding areas, said Maria Zuber, a Messenger science team member from the Massachusetts Institute of Technology.

Altimeter data combined with spectral and visual imagery from Messenger will help scientists create a geographical map of the planet, Zuber said.

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