A View of Mercury’s Far Side

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Images and data are arriving from MESSENGER’s recent flyby of Mercury. Scientists from NASA and the Johns Hopkins Applied Physics Lab are pouring over high resolution images of the side of the planet that has never before been imaged by a spacecraft. From these images, planetary geologists can study the processes that have shaped Mercury’s surface over the past 4 billion years. Let’s take a look at some of the images snapped by MESSENGER on January 14:

This image was taken just 21 minutes after MESSENGER’s closest approach to Mercury, at a distance of only 5,000 kilometers (3600 miles). It shows a region about 170 km (100 miles) across. Visible are a variety of surface features, including craters as small as about 300 meters (about 300 yards) across. But the most striking part of the image is one of the highest and longest cliffs yet seen on Mercury. About 80 km (50 miles) long, it curves from the bottom center up across the right side of this image. Scientists say that great forces in Mercury’s crust must have thrust the terrain occupying the left two-thirds of the picture up and over the terrain to the right. An impact crater has subsequently destroyed a small part of the cliff near the top of the image.

MESSENGER at Mercury.  Image Credit:  Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington
This image shows a previously unseen crater with distinctive bright rays of ejected material from the impact extending outward, providing a look at minerals from beneath Mercury’s surface. A chain of craters nearby is also visible. Studying impact craters provides insight into the history and composition of Mercury. The width of the image is about 370 kilometers (about 230 miles), and was taken about 37 minutes after MESSENGER’s closest approach. This image is the 98th in a set of 99 images that were taken to create a large, high-resolution mosaic of this region of Mercury. Hopefully this anticipated mosaic will be released at a planned press conference on January 30.

MESSENGER at Mercury.  Image Credit:  Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington
As MESSENGER approached Mercury on January 14, 2008, about 56 minutes before the spacecraft’s closest encounter, the Narrow-Angle Camera captured this view of the planet’s rugged, cratered landscape illuminated by the Sun. Although this crater has been imaged before by Mariner 10, MESSENGER’s modern camera has revealed detail that was not well seen by Mariner including the broad ancient depression overlapped by the lower-left part of the Vivaldi crater. Its outer ring has a diameter of about 200 kilometers (about 125 miles). The image shows an area about 500 km 9300 miles) across and craters as small as 1 kilometer (0.6 mile) can be seen. It was taken from a distance of about 18,000 km (11,000 miles.)

The MESSENGER (Mercury Surface Space Environment Geochemistry and Ranging) Science Team has begun analyzing these high-resolution images to unravel the history of Mercury, as well as the history of our solar system.

Original News Source: MESSENGER Website

A Winged MESSENGER Flies By Mercury

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On January 14 the MESSENGER spacecraft skimmed just 200 kilometers (124 miles) above the surface of Mercury in the first of three flybys of the planet. Today (Jan. 15) the spacecraft will turn back towards the Earth to start down-linking the on-board stored science data it acquired during the flyby. The probe’s equipment gathered data on the mineral and chemical composition of Mercury’s surface, its magnetic field, its surface topography and its interactions with the solar wind. “This was fantastic,” said Michael Paul, a mission engineer. “We were closer to the surface of Mercury than the International Space Station is to the Earth.”

The closest approach was on the planet’s night side, the side facing away from the sun, and the spacecraft flew in the region along the equator. The scientific results will be available for the public at the end of January.

“The engineers and operators pulled off a tremendous feat, acquiring and locking onto the downlink signal from the spacecraft within seconds, providing the necessary Doppler measurements for the Radio Science team.” said MESSENGER Mission Systems Engineer Eric Finnegan, of the Applied Physics Lab in Laurel, Maryland. “The spacecraft is continuing to collect imagery and other scientific measurements from the planet as we now depart Mercury from the illuminated side, documenting for the first time the previously unseen surface of the planet.”

The signal from the spacecraft is tracked by the Deep Space Network, an international network of antennas that supports space missions.

In addition to Monday’s rendezvous, MESSENGER is scheduled to pass Mercury again this October and in September 2009, using the pull of the planet’s gravity to guide it into position to begin a planned yearlong orbit of the planet in March 2011. By the time the mission is completed, scientists also hope to get answers on why Mercury is so dense, as well as determine its geological history and the structure of its iron-rich core and other issues.

MESSENGER stands for Mercury Surface, Space Environment, Geochemistry and Ranging. Launched in 2004, it already has flown past Venus twice and Earth once on its way to Mercury.

Only one spacecraft has previously visited Mercury. Mariner 10 flew past the planet three times in 1974 and 1975, and mapped about 45 percent of its surface.

With Pluto now considered a dwarf planet, Mercury is the solar system’s smallest planet, with a diameter of 3,032 miles, about a third that of Earth.

A surface feature of great interest to scientists is the Caloris basin, an impact crater about 800 miles in diameter, one of the biggest such craters in our solar system. It likely was caused when an asteroid hit Mercury long ago. Scientists hope to learn about the subsurface of the planet from studying this crater.

True to its name, temperatures on the closest plant to the sun are quite “mercurial,” as Mercury experiences the largest swing in surface temperatures in our solar system. When its surface faces the sun, temperatures hit about 800 degrees Fahrenheit (425 Celsius), but when its faces away from the sun they can plummet to minus-300 Fahrenheit (minus-185 Celsius).

Original News Source: Reuters

Comet, Cometary Dust Formed in Different Parts of Solar System

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Scientists studying the particles of comet dust brought to Earth by the Stardust spacecraft have uncovered a bit of a mystery. Research on the particles seem to indicate that while the comet formed in the icy fringes of the solar system, the dust appears to have been formed close to the sun and was bombarded by intense radiation before being flung out beyond Neptune and trapped in the comet. The finding opens the question of what was going on in the early life of the solar system to subject the dust to such intense radiation and hurl them hundreds of millions of miles from their birthplace.

The Stardust spacecraft flew to Comet Wild-2 in 2004, coming approximately 150 miles from the comet’s nucleus, and captured particles of dust and gases from the comet’s coma and then returned those particles to Earth in 2006.

Researchers from the University of Minnesota and Nancy University in France analyzed gases locked in the tiny dust grains, which are about a quarter of a billionth of a gram in weight. They were looking for helium and neon, two noble gases that don’t combine chemically with other elements, and therefore would be in the same condition as when the comet dust formed.

The analysis of the helium and neon isotopes suggests that some of the Stardust grains match a special type of carbonaceous material found in meteorites. The gases most likely came from a hot environment exposed to magnetic flares that must have been close to the young sun.

About 10 percent of the mass of Wild 2 is estimated to be from particles transported out from hot inner zones to the cold zone where Wild 2 formed. Earlier research showed that the comet formed in the Kuiper Belt, outside the orbit of Neptune, and only recently entered the inner regions of the solar system.

“Somehow these little high-temperature particles were transported out very early in the life of the solar system,” said Bob Pepin from the University of Minnesota. “The particles probably came from the first million years or even less, of the solar system’s existence.” That would be close to 4.6 billion years ago. If our middle-aged sun were 50 years old, then the particles were born in the first four days of its life.

The studies of cometary dust are part of a larger effort to trace the history of our celestial neighborhood.
“We want to establish what the solar system looked like in the very early stages,” said Pepin. “If we establish the starting conditions, we can tell what happened in between then and now.”

Stardust launched in February 1999, began collecting interstellar dust in 2000 and met up with Wild-2 in January 2004. It’s tennis raquet-sized collector made of an ultra-light material called aerogel, trapped aggregates of fine particles that hit at 13,000 miles per hour and split on impact. It is the first spacecraft to bring cometary dust particles back to Earth.

This study also has relevance in learning about the history of our own planet. “Because some scientists have proposed that comets have contributed these gases to the atmospheres of Earth, Venus and Mars, learning about them in comets would be fascinating,” Pepin said.

The research appears in the Jan. 4 issue of the journal Science

Original News Sources: University of Minnesota Press Release, Lawrence Livermore National Laboratory Press Release

Landing Sites for Mars Science Lab Narrowed to Six

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Where should the next spacecraft land on Mars? The Mars Science Laboratory (MSL) rover is scheduled to launch in the fall of 2009. MSL is a long-range rover that will explore a region on Mars with the goal of determining if Mars has or ever had conditions capable of supporting microbial life. Over fifty landing sites have been proposed by various planetary scientists, and recently, the selection committee narrowed the field down to six possible sites. The final site and a backup will be selected in September of 2008. Here’s a look at the six final candidates:

Mawrth Vallis: Location:Northern Plains, east of Pathfinder rover site (24.65°N, 340.10°E)
Mars Global Surveyor MOLA Instrument
This is an ancient channel carved by catastrophic floods. Spectrometers on the Mars Reconnaissance Orbiter (MRO) have detected clay minerals which contain water, and may also preserve organic materials, so there is great interest in studying these deposits to understand past environments that could have supported life. Images from the MRO HiRise camera show hills with several layers and intriguing boulders.

Nili Fossae Trough: Location: Near Isidis Planitia, and near the Beagle 2 intended landing site. (21°N, 74.2°E)
Nilli Fossae Trough.  Image Credit:  Mars Global Surveyor MOLA Instrument
This region has one of the largest and most diverse exposures of clays minerals that have been detected from orbit. Again, clay minerals contain water, and possibly organic materials. The area is a linear depression about 25 km wide that was created from tectonic activity.

Holden Crater: Location: South of Vallis Marineris (26.4°S, 325.3°E)
Holden Crater.  Image Credit:  Mars Global Surveyor MOLA Instrument
This crater contains deep gullies carved by running water as well as examples of what are assumed to be lake beds and sediments deposited by streams. These deposits are more than three billion years old, which dates back to a wetter period on Mars. Scientists believe Holden Crater once was a lake, and when the water disappeared, wind eroded the surface and formed the ripples and dunes that have been imaged by the HiRise instrument.

Eberswalde Crater: Location: South of Vallis Marineris (23.20°S, 326.75°E)
Eberswalde Delta.  Image Credit:  Mars Global Surveyor MOLA Instrument
The Eberswalde delta is the most convincing evidence on Mars for the persistent flow of a river into a standing body of water. HiRise images show many channels within the delta that have become inverted, which occurs as sediments deposited by flowing water solidify over time and become resistant to erosion. High resolution HiRise images show individual boulders breaking off from the channel deposits.

Miyamoto Crater: Location: Merdiani Planum, near Opportunity Rover site. (1.7°S, 352.4°E)
Miyamato Crater.  Image Credit:  Mars Global Surveyor MOLA Instrument
Located along the western boundary of Meridiani Planum, this 150-km crater has hematite and sulfate-bearing minerals, possibly created from lakes or groundwater. The southwestern part of the crater floor has been stripped by erosion, revealing clay minerals.

Northern Meridiani: Location: Meridiani Planum,2.34°N, 6.69°E
Meridiani.  Image Credit:  Mars Global Surveyor MOLA Instrument
This is the same area that the Opportunity rover has studied. By landing here, the MSL rover could increase our knowledge of the Meridiani region, which Opportunity has revealed to have a complex geologic history that involves flowing water, groundwater, lakes and wind. If chosen as a landing site, the MSL rover would study the smooth plains before driving to the ridged plains to the north.

MSL will arrive on Mars in 2010. Once on the surface, the rover will be able to roll over obstacles up to 75 centimeters (29 inches) high and travel up to 90 meters (295 feet) per hour. On average, the rover is expected to travel about 30 meters (98 feet) per hour, based on power levels, slippage, steepness of the terrain, visibility, and other variables. The science instruments on board include cameras, spectrometers, radiation detectors and environmental sensors.

Original News Source: HiRise Blog

A Submarine for Europa

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Many planetary scientists believe that Jupiter’s moon Europa is our solar system’s best contender to share Earth’s distinction of harboring life. Evidence gathered by the Voyager and Galileo spacecrafts suggests Europa contains a deep, possibly warm ocean of salty water under an outer shell of fissured ice. In a paper published in the July 2007 Journal of Aerospace Engineering a British mechanical engineer proposes sending a submarine to explore Europa’s oceans.

Carl T. F. Ross, a professor at the University of Portsmouth in England offers an abstract design of an underwater craft built of a metal matrix composite. He also provides suggestions for suitable power supplies, communication techniques and propulsion systems for such a vessel in his paper, “Conceptual Design of a Submarine to Explore Europa’s Oceans.”

Ross’s paper weighs the options for constructing a submarine capable of withstanding the undoubtedly high pressure within Europa’s deep oceans. Scientists believe that this moon’s oceans could be up to 100 kilometers deep, more than ten times deeper than Earth’s oceans. Ross proposes a 3 meter long cylindrical sub with an internal diameter of 1 meter. He believes that steel or titanium, while strong enough to withstand the hydrostatic pressure, would be unsuitable as the vessel would have no reserve buoyancy. Therefore, the sub would sink like a rock to the bottom of the ocean. A metal matrix or ceramic composite would offer the best combination of strength and buoyancy.

Ross favors a fuel cell for power, which will be needed for propulsion, communications and scientific equipment, but notes that technological advances in the ensuing years may provide better sources for power.

Ross concedes that a submarine mission to Europa won’t occur for at least 15-20 years. Planetary scientist William B. McKinnon agrees.
Artist illustration of a Europa probe. Image credit: NASA/JPL
“It is difficult enough, and expensive, to get back to Europa with an orbiter, much less imagine a landing or an ocean entry,” said McKinnon, professor of Earth and Planetary Sciences at Washington University in St. Louis, Missouri. “Sometime in the future, and after we have determined the ice shell thickness, we can begin to seriously address the engineering challenges. For now, it might be best to search for those places where the ocean has come to us. That is, sites of recent eruptions on Europa’s surface, whose compositions can be determined from orbit.”

The Jet Propulsion Laboratory is currently working on a concept called the Europa Explorer which would deliver a low orbit spacecraft to determine the presence (or absence) of a liquid water ocean under Europa’s ice surface. It would also map the distribution of compounds of interest for pre-biotic chemistry, and characterize the surface and subsurface for future exploration. “This type of mission,” says McKinnon, “would really allow us to get the hard proof we would all like that the ocean is really there, and determine the thickness of the ice shell and find thin spots if they exist.”

McKinnon added that an orbiter could find “hot spots” that indicate recent geological or even volcanic activity and obtain high-resolution images of the surface. The latter would be needed to plan any successful landing.

Slightly smaller than Earth’s moon, Europa has an exterior that is nearly craterless, meaning a relatively “young” surface. Data from the Galileo spacecraft shows evidence of near-surface melting and movements of large blocks of icy crust, similar to ice bergs or ice rafts on Earth.

While Europa’s midday surface temperatures hover around 130 K (-142 C, -225 degrees F), interior temperatures could be warm enough for liquid water to exist underneath the ice crust. This internal warmth comes from tidal heating caused by the gravitational forces of Jupiter and Jupiter’s other moons which pull Europa’s interior in different directions. Scientists believe similar tidal heating drives the volcanoes on another Jovian moon, Io. Seafloor hydrothermal vents have also been suggested as another possible energy source on Europa. On Earth, undersea volcanoes and hydrothermal vents create environments that sustain colonies of microbes. If similar systems are active on Europa, scientists reason that life might be present there too.

Among scientists there is a big push to get a mission to Europa underway. However this type of mission is competing for funding against NASA’s goal of returning to our own moon with human missions. The proposed Jupiter Icy Moon Orbiter (JIMO) a nuclear powered mission to study three of Jupiter’s moons, fell victim to cuts in science missions in NASA’s Fiscal Year 2007 Budget.

Ross has been designing and improving submarines for over 40 years, but this is the first time he’s designed a craft for use anywhere but on Earth.

“The biggest problem that I see with the robot submarine is being able to drill or melt its way through a maximum of 6 km of the ice, which is covering the surface,” said Ross. “However, the ice may be much thinner in some places. It may be that we will require a nuclear pressurized water reactor on board the robot submarine to give us the necessary power and energy to achieve this”

While Ross proposes using parachutes to bring the submarine to Europa’s surface, McKinnon points out that parachutes would not work in Europa’s almost airless atmosphere.

Ross has received very positive responses to his paper from friends and colleagues, he says, including notable British astronomer Sir Patrick Moore. Ross says his life has revolved around submarines since 1959 and he finds this new concept of a submarine on Europa to be very exciting.

McKinnon classifies the exploration of Europa as “extremely important.”

“Europa is a place is where we are pretty sure we have abundant liquid water, energy sources, and biogenic elements such as carbon, nitrogen, sulfur, phosphorus, etc,” he said. “Is there life, any kind of life, in Europa’s ocean? Questions don’t get much more profound.”

Written by Nancy Atkinson

New Horizons Prepares to Zoom to Pluto

Artist impression of the New Horizons spacecraft sweeping past Pluto. Image credit: JHUAPL/SwRI. Click to enlarge.

If all goes well, the first mission to the farthest known planet in our Solar System will launch in early 2006, and give us our first detailed views of Pluto, its moon Charon, and the Kuiper Belt Region, while completing NASA’s reconnaissance of all the planets in our Solar System.

“We’re going to a planet that we’ve never been to before,” said Dr. Alan Stern, Principal Investigator for the New Horizons mission to Pluto. “This is like something out of a NASA storybook, like in the 60’s and 70’s with all the new missions that were happening then. But this is exploration for a new century; it’s something bold and different. Being the first mission to the last planet really ‘revs’ me. There’s something special about going to a new frontier, about

Pluto is so far away (5 billion km or 3.1 billion miles when New Horizons reaches it) that no telescope, not even the Hubble Space Telescope, has been able to provide a good image of the planet, and so Pluto is a real mystery world. The existence of Pluto has only been known for 75 years, and the debate continues about its classification as a planet, although most planetary scientists classify it in the new class of planets called Ice Dwarfs. Pluto is a large, ice-rock world, born in the Kuiper Belt area of our solar system. Its moon, Charon, is large enough that some astronomers refer to the two as a binary planet. Pluto undergoes seasonal change and has an elongated and enormous 248-year orbit which causes the planet’s atmosphere to cyclically dissipate and freeze out, but later be replenished when the planet returns closer to the sun.

New Horizons will provide the first close-up look at Pluto and the surrounding region. The grand piano-sized spacecraft will map and analyze the surface of Pluto and Charon, study Pluto’s escaping atmosphere, look for an atmosphere around Charon, and perform similar explorations of one or more Kuiper Belt Objects.

The spacecraft, built at the Johns Hopkins Applied Physics Laboratory, is currently being flight tested at the Goddard Space Flight Center. Dr. Stern has been planning a mission to Pluto for quite some time, surviving through the various on-again, off-again potential missions to the outer solar system.

“I’m feeling very good about the mission,” he said in an interview from his office at the Southwest Research Institute in Boulder, Colorado. “I’ve been working on this project for about 15 years, and the first 10 years we couldn’t even get it out of the starting blocks. Now we’ve not only managed to get it funded, but we have built it and we are really looking forward to flying the mission soon if all continues to go well.”

Of the hurdles remaining to be cleared before launch, one looms rather large. New Horizons’ systems are powered by a Radioisotope Thermoelectric Generator (RTG), where heat released from the decay of radioactive materials is converted into energy. This type of power system is essential for a mission going far from the Sun like New Horizons where solar power is not an option, but it has to be approved by both NASA and the White House. The 45-day public comment period ended in April 2005, so the project now awaits final, official approval. Meanwhile, the New Horizons mission teams prepare for launch.

“We still have a lot of work in front of us,” Stern said. “All this summer we’re testing and checking out the spacecraft and the components, getting all the bugs out, and making sure its launch ready, and flight ready. That will take us through September and in October we hope to bring the spacecraft to the Cape.”

The month-long launch window for New Horizons opens on January 11, 2006.

New Horizons will be the fastest spacecraft ever launched. The launch vehicle combines an Atlas V first stage, a Centaur second stage, and a STAR 48B solid rocket third stage.

“We built the smallest spacecraft we could get away with that has all the things it needs: power, communication, computers, science equipment and redundancy of all systems, and put it on the biggest possible launch vehicle,” said Stern. “That combination is ferocious in terms of the speed we reach in deep space.”

At best speed, the spacecraft will be traveling at 50 km/second (36 miles/second), or the equivalent of Mach 85.

Stern compared the Atlas rocket to other launch vehicles. “The Saturn V took the Apollo astronauts to the moon in 3 days,” he said. “Our rocket will take New Horizons past the moon in 9 hours. It took Cassini 3 years to get to Jupiter, but New Horizons will pass Jupiter in just 13 months.”

Still, it will take 9 years and 5 months to cross our huge Solar System. A gravity assist from Jupiter is essential in maintaining the 2015 arrival date. Not being able to get off the ground early in the launch window would have big consequences later on.

“We launch in January of 2006 and arrive at Pluto in July of 2015, best case scenario,” said Stern. “If we don’t launch early in the launch window, the arrival date slips because Jupiter won’t be in as good a position to give us a good gravity assist.”

New Horizons has 18 days to launch in January 2006 to attain a 2015 arrival. After that, Jupiter’s position moves so that for every 4 or 5 days delay in launch means arriving at Pluto year later. By February 14 the window closes for a 2020 arrival. New Horizons can try to launch again in early 2007, but then the best case arrival year is 2019.

New Horizons will be carrying seven science instruments:

  • Ralph: The main imager with both visible and infrared capabilities that will provide color, composition and thermal maps of Pluto, Charon, and Kuiper Belt Objects.
  • Alice: An ultraviolet spectrometer capable of analyzing Pluto’s atmospheric structure and composition.
  • REX: The Radio Science Experiment that measures atmospheric composition and surface temperature with a passive radiometer. REX also measures the masses of objects New Horizons flies by.
  • LORRI: The Long Range Reconnaissance Imager has a telescopic camera that will map Pluto?s far side and provide geologic data.
  • PEPSSI: The Pluto Energetic Particle Spectrometer Science Investigation that will measure the composition and density of the ions escaping from Pluto’s atmosphere.
  • SWAP: Solar Wind Around Pluto, which will measure the escape rate of Pluto?s atmosphere and determine how the solar wind affects Pluto.
  • SDC: The Student Dust Counter will measure the amount of space dust the spacecraft encounters on the voyage. This instrument was designed and will be operated by students at the University of Colorado in Boulder.

Stern says the first part of the flight will keep the mission teams busy, as they need to check out the entire spacecraft, and execute the Jupiter fly-by at 13 months.

“The middle years will be long and probably — and hopefully — pretty boring,” he said, but will include yearly spacecraft and instrument checkouts, trajectory corrections, instrument calibrations and rehearsals the main mission. During the last three years of the interplanetary cruise mission teams will be writing, testing and uploading the highly detailed command script for the Pluto/Charon encounter, and the mission begins in earnest approximately a year before the spacecraft arrives at Pluto, as it begins to photograph the region.

A mission to Pluto has been a long time coming, and is popular with a wide variety of people. Children seem to have an affinity for the planet with the cartoon character name, while the National Academy of Sciences ranked a mission to Pluto as the highest priority for this decade. In 2002, when it looked as though NASA would have to scrap a mission to Pluto for budgetary reasons, the Planetary Society, among others, lobbied strongly to Congress to keep the mission alive.

Stern said the mission’s website received over a million hits the first month it was active, and the hit rate hasn’t diminished. Stern writes a monthly column on the website, http://pluto.jhuapl.edu , where you can learn more details about the mission and sign-up to have your name sent to Pluto along with the spacecraft.

While Stern is understandably excited about this mission, he says that any chance to explore is a great opportunity.

“Exploration always opens our eyes,” he said. “No one expected to find river valleys on Mars, or a volcano on Io, or rivers on Titan. What do I think we’ll find at Pluto-Charon? I think we’ll find something wonderful, and we expect to be surprised.”