Alan Shepard and MESSENGER Stamps Unveiled at Kennedy Space Center Ceremony

Mercury Astronaut Scott Carpenter speaks in tribute to Alan B. Shepard, first American in Space. Carpenter spoke at the First-Day-of-Issue Stamp dedication ceremony at NASA’s Kennedy Space Center on May 4, 2011. Credit: Ken Kremer

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KENNEDY SPACE CENTER – 50 Years ago this week, Alan B. Shepard became the first American to be launched into space. Shepard blasted off on May 5, 1961 from Cape Canaveral, Florida. NASA and the US Postal Service honored Shepard’s historic achievement today (May 4) at an Official First-Day-of-Issue dedication ceremony at NASA’s Kennedy Space Center in Florida.

Alan Shepard was one of the seven Project Mercury astronauts – who will be collectively known for all eternity as – “The Original 7”.

The US Postal Service simultaneously released two new 44 cent Forever Stamps at today’s commemoration, which bookend two historic space achievements – Shepard’s inaugural manned spaceflight aboard the Mercury capsule and NASA’s unmanned MESSENGER mission which recently became the first probe from Earth to achieve orbit about the Planet Mercury.

Alan Shepard and MESSENGER First-Day-of-Issue Stamp dedication ceremony at NASA’s Kennedy Space Center on May 4, 2011. Alan Shepard is the only American astronaut to be honored with his image on a US postal stamp. Credit: Ken Kremer

Fellow Mercury Astronaut Scott Carpenter attended the ceremony and unveiled the stamps along with Steve Masse, United States Postal Service Vice President of Finance at the Rocket Garden at the KSC Visitor Complex.

Mercury Astronaut Scott Carpenter poses in front of a Mercury Atlas rocket at the Rocket Garden at KSC. Carpenter was propelled to space by the Atlas rocket as the 2nd American to orbit the Earth on May 24, 1962. Credit: Ken Kremer

“Today we celebrate the 50th anniversary of many, many important issues, among them is the first steps from the home planet that were taken by the family of man,” said Carpenter.

Although Shepards suborbital flight aboard the one man “Freedom 7” Mercury capsule lasted barely 15½ minutes, the flight ignited America’s Moon landing effort and propelled American Astronaut Neil Armstrong to become the first human to set foot on the moon on July 20, 1969 during the Apollo 11 mission – one of the crowning technological achievements of the 20th Century.

The success of “Freedom 7” emboldened President John F. Kennedy to declare that America “should commit itself to achieving the goal, before this decade is out, of landing a man on the moon and returning him safely to the Earth,” just three weeks later on May 20.

“That was largely a response to Alan’s success,” Carpenter told the crowd of assembled officials, journalists and visitors. Also on hand for the stamp dedication was Shepard’s daughter Laura Shepard Churchly; Charles Bolden, NASA Administrator and former shuttle astronaut; Bob Cabana, KSC Director and former shuttle astronaut; and Jim Adams, NASA deputy director, Planetary Science.

“A decision was made not to put 44 cents on the stamp, but it is forever,” Carpenter emphasized. “It is appropriate to the time we should honor and remember Alan B Shepard and Freedom 7.”

Alan Shepard display at the Kennedy Space Center Visitor Complex. Credit: Ken Kremer

Shepard’s tiny capsule measured just six feet by six feet, reached a maximum speed of 5,100 MPH, roughly eight times the speed of sound, and a zenith of 116 miles above the Earth. Freedom 7 was bolted atop a Redstone rocket that generated only 78,000 pounds of thrust, followed a ballistic arc and landed 300 miles down range in the ocean.

“These stamps, which will go out by the millions across this country, are a testament to the thousands of NASA men and women who shared dreams of human spaceflight and enlarging our knowledge of the universe,” said Bolden.
Shepard’s flight and MESSENGER both blasted off from launch pads quite close to one another at Cape Canaveral Air Force Station which is adjacent to the Kennedy Space Center.

Mercury Astronaut Scott Carpenter is applauded at tribute to Alan B. Shepard, first American in Space ceremony at the Rocket Garden at KSC on May 4, 2011. Credit: Ken Kremer

On Thursday May 5, watch for my on site coverage of NASA’s special ceremony marking the 50th Anniversary of Shepard’s milestone “Freedom 7” mission – and an interview with Scott Carpenter.

Shepard’s mission came barely three weeks after Cosmonaut Yuri Gagarin became the first human to orbit the Earth. The bold flights of these brave Cosmonauts and Astronauts – backed by a few insightful political leaders – began the Era of Human Spaceflight. As the shuttle program winds to a close, the future of US Human Spaceflight is very uncertain.

Read my related articles about Yuri Gagarin and the 50th Anniversary of Human Spaceflight:

Yuri Gagarin and Vostok 1 Photo Album – 50th Anniversary of Human Spaceflight
Countdown to Yuri’s Night and the 50th Anniversary of Human Spaceflight !
Stirring Video Tributes to Yuri Gagarin
Yuri Gagarin From the Earth to Mars Tribute

NASA Administrator and former shuttle astronaut Charles Bolden praises Alan Shepard at KSC stamp unveiling ceremony on May 4, 2011. Credit: Ken Kremer

USPS Commemorates Spaceflight Past and Present

Postage stamps honoring Mercury astronaut Alan Shepard, America’s first man in space, and NASA’s MESSENGER probe, the first spacecraft to orbit Mercury, will be presented on May 4th at a public event taking place at the Aviation Heritage Park in Dayton, Ohio.

Alan Shepard poses in his pressure suit before his historic flight on May 5, 1961. Credit: NASA.

The first stamp salutes NASA’s Project Mercury, America’s first manned spaceflight program, and astronaut Alan B. Shepard, Jr.’s historic sub-orbital flight on May 5, 1961 aboard the spacecraft Freedom 7.

The other stamp highlights NASA’s MESSENGER spacecraft currently exploring the planet Mercury. It successfully established orbit around the planet on March 18, 2011, the first spacecraft ever to do so.

These two historic missions frame a remarkable fifty-year period in which the U.S. has advanced space exploration through more than 1,500 manned and unmanned flights.

Both stamps were designed by professional artist Donato Giancola of Brooklyn, NY, who based the stamp designs on NASA photos and images.

Both stamps will be issued as “Forever Stamps” for use in mailing a one-ounce letter. Regardless of when the stamps are purchased and no matter how postage prices may change, these stamps will always be equal to the current First-Class Mail one-ounce price.

NASA's Mercury-Redstone 3 rocket, with Alan Shepard inside the Freedom 7 capsule, launches from Cape Canaveral on May 5, 1961. Credit: NASA.

Stamps are now available online at the US Postal Service store here.

MESSENGER Finds Where X Marks the Spot on Mercury

An unnamed crater on Mercury taken by MESSENGER's Narrow Angle Camera. Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington

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Buried treasure on Mercury? If so, I’d look here first. This image shows a currently unnamed crater with an “X” emblazoned on it. The perpendicular lines that cross the crater are secondary crater chains caused by ejecta from two primary impacts outside of the field of view, according to MESSENGER scientists. MESSENGER has been in orbit of Mercury since mid-March of this year, and its Mercury Dual Imaging System (MDIS) pivot and Narrow Angle Camera (NAC) spotted this unusual landform. MESSENGER will be mapping more than 90% of Mercury’s surface as part of a high-resolution surface morphology base map that will be created with MDIS.

See more about this image on the MESSENGER website.

Latest Images from Mercury: Bright Peaks, Swirling Craters and Weird Terrain

Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington

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The MESSENGER spacecraft is still happily orbiting Mercury since its orbit insertion in mid-March, and here are some of the latest images sent back from the first rock from the Sun. In this image, the central peaks inside a large crater named Asvaghosa show up as exceptionally bright. The MESSENGER team believes that their high reflectance appears to have been enhanced by the crater rays that cross the area, which originates from another crater. Asvaghosa is 90 km (56 mi.) in diameter, and was targeted for special, high-resolution observations, where MESSENGER’s cameras zero-in for the closest looks possible. While it is not possible to cover all of Mercury’s surface at this high of a resolution during the spacecraft’s one-year mission, several areas of high scientific interest are generally imaged in this mode each week.

See more below!

Oblique view of Bek crater on Mercury. Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington

What a unique, swirling crater — and this high-resolution view of Bek crater (32 km (20 miles) in diameter) has me trying to imagine scaling the cliffs seen in this incredible vista. The MESSENGER team says that the sharp crater rim is in contrast to its subdued surroundings, where crater ejecta scoured the surface and left behind many secondary craters.

'Weird terrain' inside the crater Petrarch on Mercury. Credit: Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington

When scientists from the Mariner 10 team first saw this region around Petrarch crater, they called it “weird terrain.” The rugged terrain has an unusual “hilly and lineated” that may have been modified by converging seismic waves and/or ejecta from the formation of the Caloris basin, which is located on the opposite side of the planet. Now, MESSENGER viewed this area under differing lighting conditions than those seen during MESSENGER’s second flyby and Mariner 10’s first pass. The large, smooth area in the upper left is the floor of Petrarch.

See more of the latest images from MESSENGER on the mission’s gallery on their website.

New Images from Mercury: Just the Beginning for MESSENGER in Orbit

Smooth plains on Mercury's northern hemisphere. Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington

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Sharing just a few of the 1,500 images the MESSENGER spacecraft has now taken from its orbital vantage point, mission scientists are understandably excited – if not overwhelmed – by the data being returned from Mercury. “The instruments are all working marvelously and returning data,” said MESSENGER Principal Investigator Sean Solomon. “The imaging system was turned on earlier this week and over 1,500 images will be acquired over a 3 day period. That is more images than were taken during any of the flybys by the spacecraft.”

Solomon said some of the first images were taken precisely 37 years after the first spacecraft flew by Mercury, Mariner 10 in 1974. “We have now closed the loop begun by Mariner 10, culminating with the first insertion of a spacecraft in orbit.”

2,430 days ago the MESSENGER lifted off from Earth, and after three flybys and a nearly 5 billion mile journey, the spacecraft’s thrusters fired for 15 minutes back on March 17, enabling the spacecraft to ease into orbit.

While already finding intriguing features – many which pose more questions than answers, Solomon reminded reporters during a press conference call today that “all the big questions about Mercury are meant to be answered in a year of observations, not just a couple of days, so we’ll look forward to what is yet to come.”

The top image shows an area of Mercury’s north polar region, revealing terrain that had not been previously seen by spacecraft. The long shadows also accentuate the topography of the surface, which includes a number of ridges, but an unusually smooth surface. Solomon said understanding the interiors of the craters in Mercury’s polar regions and any ices they may contain is one of the main science goals of the MESSENGER mission. “Radar images of Mercury that are now 20 years old suggested that water ice could be in the interiors of these craters,” Solomon said. “That is a hypothesis we’ve been aching to test for 20 years, and now we’ll be able to peer into those crater floors.”

This WAC image showing a never-before-imaged area of Mercury’s surface was taken from an altitude of ~450 km (280 miles) above Mercury. Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington

This is another region never seen before by spacecraft. “This is probably a plain deposit formed by undulating ridges and a host of secondary craters formed when a large crater was formed out of the field of view,” Solomon said. “We’re seeing that secondary craters (those formed from the ejecta of another crater) are very pervasive across the surface.”

Solomon added that they are seeing secondary craters that are larger than most secondary craters, compared to those on the Moon and other planetary bodies. “They are surprisingly large,” he said. “ A lot of questions raised by images taken so far and have a large menu of questions we’ll be pursuing over the mission.”

Beautiful bright crater on Mercury. Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington

The crater near the bottom of this image is a beautiful example of a relatively small, simple, fresh impact feature on Mercury.The bright ejecta and rays are symmetrically distributed around the crater, indicating that the body that struck Mercury to form the crater approached on a path that was not highly inclined from the vertical.

MESSENGER Systems engineer Eric Finnegan told reporters that it takes about 6 minutes for data to be relayed from the spacecraft to Earth, as Mercury (and the spacecraft) is about .71 AU away, the equivalent of about 106 million km (66 million miles). MESSENGER is in an elliptical orbit, and at its closest point in orbit (periapsis) is about 250 km away from Mercury, and at its farthest point (apoapsis) is about 1,500 km away.

Wide Angle Camera color image of Mercury. Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington

This is one of the first color images from MESSENGER in orbit. Solomon said the Wide Angle Camera is not a typical color camera. It can image in 11 colors, ranging from 430 to 1020 nm wavelength (visible through near-infrared). “We will be taking global images in at least 8 filters to get a sense of the color variation, which shows the variations in composition and depth of surface features exposed by the action of impact cratering from Mercury’s history.”

From Orbit, Looking toward Mercury's Horizon. Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington

Images like this were frequently seen during MESSENGER’s three flybys. But now that the spacecraft is in orbit of Mercury, views of Mercury’s horizon in the images will be much less common. Occasionally, however, in order to obtain images of a certain portion of Mercury’s surface, the horizon will also be visible. But Solomon said MESSENGER’s goal is to get a set of global data for the planet. “An entire global perspective is unfolding and will continue to unfold over next few months,” he said.

Bright rays, consisting of impact ejecta and secondary craters, spread across this NAC image and radiate from Debussy crater, located at the top. Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington

This is a closeup Debussy Crater, which was the object of the first image released by MESSENGER yesterday. When asked about the age of this crater, Solomon said it is difficult to give a hard age to craters on Mercury due to not having samples in hand, like to do for the Moon. “On the moon ones that are bright like this, such as Copernicus, were formed in the last 20% in the history of the planet. We see only a handful of bright craters like Debussy on Mercury.”

“When you see a crater that is so bright,” Solomon continued, “ it is because it has not gone through the process of space weathering, completely. Brightness of craters identifies them as being younger than the rest of the terrain, as it hasn’t had the time to have their characteristics altered by age, as those of us with gray hair know.”

Solomon said Debussy was likely created by in impact of an object 5-10 km across.

“Orbits of most asteroids and comets that encounter Mercury are traveling at a much higher speed than planetary bodies farther out from the Sun, and that shows in the amount of melt shown in the surface of Mercury. But still a lot we have to learn about that. Craters at different states of decay and degradation will tell us more about this.”

Altimetric profiles obtained on 29 March during the first two successive MESSENGER orbits on which the Mercury Laser Altimeter (MLA) instrument was operating. Credit: NASA/Goddard Space Flight Center/MIT/Johns Hopkins University Applied Physics Laboratory

This graph shows the first two topographic profiles that were obtained from orbit by the Mercury Laser Altimeter (MLA). “This shows rich detail that we’ve just begun to analyze,” Solomon said, “showing exquisite detail, and we’ll be able to see the topography at both scales of individual geological features and global regions.”

This plot depicts measurements of the strength of Mercury's internal magnetic field measured on 10 successive MESSENGER orbits. Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington

One big question is about Mercury’s magnetic field. This illustrates the measurements made from 10 orbits of MESSENGER’s magnetometer. In a span of 5 days, messenger has tripled the mount of observations of the planet’s magnetic field, so Solomon said the science team is quickly ramping up a much larger data set to see the geometry of Mercury’s magnetic field, which might help explain why the solar system’s smallest planet still has a magnetic field when the larger planets Mars and Venus do not.

Moreover, because of MESSENGER’s orbit, the maximum magnitude of the measured field was greater than that seen during any of the spacecraft flybys. Solomon said these observations are improving our understanding of Mercury’s magnetic field and how its magnetosphere can change over timescales of minutes, how the solar activity and interaction between the Sun and the planet affect the magnetic field.

“As the Sun’s activity ramps up, it is an exciting time to be at Mercury and have a ringside perspective,” Solomon said.

Sources: MESSENGER press conference page, Main MESSENGER website; Quotes are from press conference call.

MESSENGER’s First Image from Orbit of Mercury

MESSENGER's first image from Mercury orbit, with the bright Debussy crater visible at upper right. Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington
MESSENGER's first image from Mercury orbit, with the bright Debussy crater visible at upper right. Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington

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Here it is, the first image taken by the MESSENGER spacecraft since entering orbit around Mercury on March 17, and it includes portions of the planet not yet previously seen by spacecraft. The image was taken on today, March 29, 2011 at 5:20 am EDT by the Mercury Dual Imaging System as the spacecraft sailed high above Mercury’s south pole. The dominant rayed crater in the upper portion of the image is Debussy, and the smaller crater Matabei with unusual dark rays is visible to the west of Debussy. The bottom portion of this image near Mercury’s south pole is new territory, with MESSENGER being the first spacecraft to image this region of Mercury.


After capturing its first image, MESSENGER acquired an additional 363 images during six hours before downlinking some of the data to Earth. The MESSENGER team is currently looking over the newly returned data, which are still continuing to come down.

The image was acquired as part of the orbital commissioning phase of the MESSENGER mission. Over the next three days, the spacecraft will acquire 1,185 additional images in support of MDIS commissioning-phase activities. Continuous global mapping of Mercury will begin on April 4.

“The entire MESSENGER team is thrilled that spacecraft and instrument checkout has been proceeding according to plan,” says MESSENGER Principal Investigator Sean Solomon, of the Carnegie Institution of Washington. “The first images from orbit and the first measurements from MESSENGER’s other payload instruments are only the opening trickle of the flood of new information that we can expect over the coming year. The orbital exploration of the Solar System’s innermost planet has begun.”

Several other images will be released tomorrow, March 30, in conjunction with a media teleconference. We’ll get them posted as quickly as possible!

Source: MESSENGER website

STEREO Catches Mercury Acting Like a Comet

An image of Mercury’s tail obtained from combining a full day of data from a camera aboard the STEREO-A spacecraft. The reflected sunlight off the planet's surface results in a type of over-exposure that causes Mercury to appear much larger than its actual size. The tail-like structure extending anti-sunward from the planet is visible over several days and spans an angular size exceeding that of a full Moon in the night sky. Credit: Boston University

The STEREO mission to study the Sun also has observed some unusual comet-like features exhibited by the planet Mercury, with a coma of tenuous gas surrounding the planet and a very long tail extending away from the sun. These types of features had been seen before from telescopes on Earth, but the STEREO observations are helping scientists to understand the nature of the emissions coming from Mercury, which might be different from what was previously thought.

Another note of interest: the tail in the STEREO data was actually discovered by a fellow blogger, Ian Musgrave, who writes Astroblog. He is a medical researcher in Australia who has a strong interest in astronomy. Viewing the on-line data base of STEREO images and movies, Dr. Musgrave recognized the tail and sent news of it to a team of astronomers from Boston University to compare it with their observations.

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The STEREO mission has two satellites placed in the same orbit around the Sun that the Earth has, but at locations ahead and behind it. This configuration offers multi-directional views of the electrons and ions that make up the escaping solar wind. On occasion, the planet Mercury appears in the field of view of one or both satellites. In addition to its appearance as a bright disk of reflected sunlight, a ‘tail’ of emission can be seen in some of the images.

From Earth-based telescopes, astronomers have seen how the Sun’s radiation pressure pushes sodium atoms from Mercury’s surface away from the planet – and away from the Sun – creating a tail that extends many hundreds of times the physical size of Mercury.

Much closer to Mercury, several smaller tails composed of other gases, both neutral and ionized, have been found by NASA’s MESSENGER satellite as it flew by Mercury in its long approach to entering into a stable orbit there.

“We have observed this extended sodium tail to great distances using our telescope at the McDonald Observatory in Texas,” Boston University graduate student Carl Schmidt explained, “and now the tail can also be seen from satellites near Earth.”

“What makes the STEREO detections so interesting is that the brightness levels seem to be too strong to be from sodium,” said Boston University graduate student Carl Schmidt, lead author on a paper that was presented at European Planetary Science Congress in Rome this week.

Now, the Boston University scientists are working with the STEREO scientists to try and sort everything out.

The current focus of the team is to sort out all of the possibilities for the gases that make up the tail. Dr. Christopher Davis from the Rutherford Appleton Laboratory in Chilton, England, a member of the STEREO team is working closely with the Boston University group on refining the brightness calibration methods, and determining the precise wavelengths of light that would get through the cameras’ filters.

“The combination of our ground-based data with the new STEREO data is an exciting way to learn as much as possible about the sources and fates of gases escaping from Mercury,” said Michael Mendillo, Professor of Astronomy at Boston University and director of the Imaging Science Lab where the work is being done.

“This is precisely the type of research that makes for a terrific Ph.D. dissertation,” Mendillo added.

Read the team’s paper: “Observations of Mercury’s Escaping Sodium Atmosphere by the STEREO Spacecraft”

Sources: European Planetary Science Congress, Boston University, Astroblog,

MESSENGER Looks Back at the Earth and Moon

Earth and Moon from 114 Million Miles.Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington

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A new image to add to the family photo album! The MESSENGER spacecraft is working its way to enter orbit around Mercury in March of 2011, and while wending its way, took this image of the Earth and Moon, visible in the lower left. When the image was taken in May 2010, MESSENGER was 183 million kilometers (114 million miles) away from Earth. For context, the average separation between the Earth and the Sun is about 150 million kilometers (93 million miles). It’s a thought provoking image (every one of us is in that image!), just like other Earth-Moon photos — Fraser put together a gallery of Earth-Moon images from other worlds, and this one will have to be added. But this image was taken not just for the aesthetics.

This image was taken as part of MESSENGER’s campaign to search for vulcanoids, small rocky objects hypothesized to exist in orbits between Mercury and the Sun. Though no vulcanoids have yet been detected, the MESSENGER spacecraft is in a unique position to look for smaller and fainter vulcanoids than has ever before been possible. MESSENGER’s vulcanoid searches occur near perihelion passages, when the spacecraft’s orbit brings it closest to the Sun. August 17, 2010 was another such perihelion, so if MESSENGER was successful in finding any tiny asteroids lurking close to the Sun, we may hear about it soon.

Source: MESSENGER

Latest Look at Mercury Reveals Surprises

A double-ring basin named Rachmaninoff reveals young volcanism on Mercury. Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington

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Younger volcanoes, stronger magnetic storms and a more intriguing exosphere: three new papers from data gathered during the MESSENGER spacecraft’s third flyby of Mercury in September of last year provide new insights into the planet closest to our Sun. The new findings make the science teams even more anxious for getting the spacecraft into orbit around Mercury. “Every time we’ve encountered Mercury, we’ve discovered new phenomena,” said principal investigator Sean Solomon. “We’re learning that Mercury is an extremely dynamic planet, and it has been so throughout its history. Once MESSENGER has been safely inserted into orbit about Mercury next March, we’ll be in for a terrific show.”

The closest look ever at some of Mercury’s plains suggests the planet’s volcanic activity lasted much longer than previously thought. From new images, researchers identified a 290-kilometer-diameter peak-ring impact basin, among the youngest to be observed on the planet. Named Rachmininoff, the region is characterized by exceptionally smooth, sparsely cratered plains, which formed later than the basin itself, likely from volcanic flow.

“We interpret these plains to be the youngest volcanic deposits yet found on Mercury,” said lead author Louise Prockter, from Johns Hopkins University Applied Physics Laboratory, one of MESSENGER’s deputy project scientists. “Moreover, an irregular depression surrounded by a diffuse halo of bright material northeast of the basin marks a candidate explosive volcanic vent larger than any previously identified on Mercury.
These observations suggest that volcanism on the planet spanned a much greater duration than previously thought, perhaps extending well into the second half of solar system history.”

A depression northeast of the basin is surrounded by a halo of bright mineral deposits, which Prockter and her team propose to be the largest volcanic vent identified on Mercury so far. Both of these findings mean that volcanism continued well into the second half of our Solar System’s history.

A double-ring basin named Rachmaninoff reveals young volcanism on Mercury. Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington

During the third fly-by, the team was able to take measurements of Mercury’s magnetic field, and this happened to occur during a time when the planet was being hit by a strong solar wind. MESSENGER’s Magnetometer documented for the first time the substorm-like build-up, or “loading,” of magnetic energy in Mercury’s magnetic tail. The tail’s magnetic field increased and decreased by factors ranging from two to 3.5 during very brief periods of just two to three minutes.

“The extreme tail loading and unloading observed at Mercury implies that the relative intensity of substorms must be much larger than at Earth,” said lead author James A. Slavin, a space physicist at NASA’s Goddard Space Flight Center and a member of MESSENGER’s Science Team. “However, what is even more exciting is the correspondence between the duration of tail field enhancements and the Dungey cycle time, which describes plasma circulation through a magnetosphere.”

Substorms on Earth are powered by similar processes—except that the loading of our planet’s magnetosphere is ten times weaker and occurs over the course of a full hour. Therefore, the team said, Mercury’s substorms must release more energy than terrestrial ones.

A third paper analyzed data from specialized instruments on-board the spacecraft to gain a clearer picture of Mercury’s neutral and ionic exospheres. Mercury’s exosphere is a tenuous atmosphere of atoms and ions derived from the planet’s surface and from the solar wind. Notable in the new observations were the differences in altitude of elements like magnesium, calcium, and sodium above the planet’s north and south poles. The team said this indicates that several processes are at work and that a given process may affect each element quite differently

“A striking feature in the near-planet tail ward region is the emission from neutral calcium atoms, which exhibits an equatorial peak in the dawn direction that has been consistent in both location and intensity through all three flybys,” said lead author Ron Vervack, also at the Applied Physics Laboratory. “The exosphere of Mercury is highly variable owing to Mercury’s eccentric orbit and the effects of a constantly changing space environment. That this observed calcium distribution has remained relatively unchanged is a complete surprise.”

The results are reported in three papers published online on July 15, 2010 in the Science Express section of the website of Science magazine.

Sources: EurekAlert, Science Express, MESSENGER website

Which of the Planets is Closest to the Sun?

Mercury as Never Seen Before
Mercury as Never Seen Before

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Were you wondering which of the planets is closest to the Sun? The answer is planet Mercury. At an average distance of only 57.9 million km, Mercury orbits closer to the Sun than any other planet.

Just to give you a comparison, Venus orbits the Sun at an average distance of 108.2 million km. And Earth orbits the Sun at an average distance of 149.6 million km. So you can see that Mercury is much closer, taking only 88 days to complete an orbit around the Sun.

So, Mercury is the closest planet to the Sun. And then Venus is the second closest planet to the Sun, and Earth is the third closest planet to the Sun.

The distance of Mercury to the Sun is actually an average. Mercury follows an elliptical orbit around the Sun. Sometimes it’s much closer, and other times it’s much further. At its closest point, called perihelion, Mercury is only 46 million km from the Sun. And then at its most distant point in orbit, called aphelion, Mercury gets out to 69.8 million km from the Sun.

And just for comparison, the planet furthest from the Sun is Neptune, with an average distance of 4.5 billion km from the Sun.

We’ve written many articles about distances in the Solar System. Here’s an article about the distance to the Sun, and here’s an article about how far all the planets are from the Sun.

If you’d like more information on Mercury, check out NASA’s Solar System Exploration Guide, and here’s a link to NASA’s MESSENGER Misson Page.

We’ve also recorded an entire episode of Astronomy Cast all about Mercury. Listen here, Episode 49: Mercury.