NASA Selects Material For Orion Spacecraft Heat Shield

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ScienceDaily (Apr. 10, 2009) — NASA has chosen the material for a heat shield that will protect a new generation of space explorers when they return from the moon. After extensive study, NASA has selected the Avcoat ablator system for the Orion crew module.

Orion is part of the Constellation Program that is developing the country's next-generation spacecraft system for human exploration of the moon and further destinations in the solar system. The Orion crew module, which will launch atop an Ares I rocket, is targeted to begin carrying astronauts to the International Space Station in 2015 and to the moon in 2020.
Orion will face extreme conditions during its voyage to the moon and on the journey home. On the blistering return through Earth's atmosphere, the module will encounter temperatures as high as 5,000 degrees Fahrenheit. Heating rates may be up to five times more extreme than rates for missions returning from the International Space Station. Orion's heat shield, the dish-shaped thermal protection system at the base of the spacecraft, will endure the most heat and will erode, or "ablate," in a controlled fashion, transporting heat away from the crew module during its descent through the atmosphere.
To protect the spacecraft and its crew from such severe conditions, the Orion Project Office at NASA's Johnson Space Center in Houston identified a team to develop the thermal protection system, or TPS, heat shield. For more than three years, NASA's Orion Thermal Protection System Advanced Development Project considered eight different candidate materials, including the two final candidates, Avcoat and Phenolic Impregnated Carbon Ablator, or PICA, both of which have proven successful in previous space missions.
Avcoat was used for the Apollo capsule heat shield and on select regions of the space shuttle orbiter in its earliest flights. It was put back into production for the study. It is made of silica fibers with an epoxy-novalic resin filled in a fiberglass-phenolic honeycomb and is manufactured directly onto the heat shield substructure and attached as a unit to the crew module during spacecraft assembly. PICA, which is manufactured in blocks and attached to the vehicle after fabrication, was used on Stardust, NASA's first robotic space mission dedicated solely to exploring a comet, and the first sample return mission since Apollo.
"NASA made a significant technology development effort, conducted thousands of tests, and tapped into the facilities, talents and resources across the agency to understand how these materials would perform on Orion's five-meter wide heat shield," said James Reuther, the project manager of the study at NASA's Ames Research Center at Moffett Field, Calif. "We manufactured full-scale demonstrations to prove they could be efficiently and reliably produced for Orion."
Ames led the study in cooperation with experts from across the agency. Engineers performed rigorous thermal, structural and environmental testing on both candidate materials. The team then compared the materials based on mass, thermal and structural performance, life cycle costs, manufacturability, reliability and certification challenges. NASA, working with Orion prime contractor Lockheed Martin, recommended Avcoat as the more robust, reliable and mature system.
"The biggest challenge with Avcoat has been reviving the technology to manufacture the material such that its performance is similar to what was demonstrated during the Apollo missions," said John Kowal, Orion's thermal protection system manager at Johnson. "Once that had been accomplished, the system evaluations clearly indicated that Avcoat was the preferred system."
In partnership with the material subcontractor, Textron Defense Systems of Wilmington, Mass., Lockheed Martin will continue development of the material for Orion. While Avcoat was selected as the better of the two candidates, more research is needed to integrate it completely into Orion's design.
For more information about the Orion crew module, visit: http://www.nasa.gov/orion
For more information about the Constellation Program, visit: http://www.nasa.gov/constellation
Adapted from materials provided by NASA.

James Webb Space Telescope First Flight Mirror Completes Cryogenic Testing

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ScienceDaily (Apr. 10, 2009) — The first mirror segment that will fly on the James Webb Space Telescope, built by Northrop Grumman Corporation, has completed its first series of cryogenic temperature tests in the X-ray and Cryogenic Facility at the Marshall Space Flight Center in Huntsville, Ala.

"We’re excited that we can support the James Webb Space Telescope with our world class cryogenic and x-ray telescope test facility," said Helen Cole, project manager for the Webb Telescope activities at NASA's Marshall Space Flight Center, Huntsville, Ala. "The test performed here are crucial to the success of the program since they’ll ensure the mirrors and components will be able to withstand the extreme cold temperatures of space."
The mirror segment is the first of 18 flight mirror segments that will be joined to make a giant, 6.5-meter diameter (21.3 ft.) hexagonal mirror. The segments will be subject to temperatures of -414 degrees Fahrenheit in a 7,600 cubic-foot helium-cooled vacuum chamber at NASA Marshall.
Engineers will measure how the mirror changes shape going from room temperature to cryogenic (frigid) temperatures, as the metal expands and contracts. They can model these changes to some extent, but not perfectly. The mirrors will be polished to about 100 nanometers (a human hair is approximately 60,000 to 120,000 nanometers) accuracy at room temperature, based on the expected changes. Then it will be cooled down to cryogenic temperatures and engineers will measure the mirror's surface, creating a "hit map" of unexpected changes.
"This is what we have done so far with the first flight mirror segment," said Jonathan Gardner, Webb Telescope Deputy Project Scientist at NASA Goddard Space Flight Center, Greenbelt, Md. "Now, engineers will warm it up and polish out the "hit map" areas to get the mirror to 20 nanometer accuracy - a process which will take months. The mirrors will then be brought back down to cryogenic temperatures to verify the increased accuracy." In addition to this testing, engineers also did some "cryo cycling." That means going up and down in temperature (without polishing in between) to test the repeatability of the changes.
Since there are 18 mirror segments, each measuring about 1.5 meters (4.9 ft.) in diameter, they will be tested in batches of six and chilled to cryogenic temperatures four times in a six-week time span. It takes approximately five days to cool a mirror segment to cryogenic temperatures. All flight mirror tests are expected to be completed in June 2011. The Webb telescope is scheduled for launch in 2013.
Northrop Grumman is the prime contractor for the Webb telescope, leading a design and development team under contract to NASA’s Goddard Space Flight Center.
"It has taken years of intense effort for the Webb Telescope team to begin flight mirror cryotesting and we’re gratified that testing was successful," said Martin Mohan, Webb telescope program manager for Northrop Grumman’s Aerospace Systems sector, Redondo Beach, Calif. "Along the way, we’ve had to invent entire manufacturing and measurement processes because no one has ever built a telescope this large that has to operate at temperatures this extreme."
The James Webb Space Telescope is the next-generation premier space observatory, exploring deep space phenomena from distant galaxies to nearby planets and stars. The Webb Telescope will give scientists clues about the formation of the universe and the evolution of our own solar system, from the first light after the Big Bang to the formation of star systems capable of supporting life on planets like Earth.
Adapted from materials provided by NASA/Goddard Space Flight Center.

High-resolution Image Of The Brightest Orion Trapezium Star

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ScienceDaily (Apr. 12, 2009) — Astronomy & Astrophysics is publishing the first high-resolution image of the young binary system Theta1 Orionis C, located in the Orion Trapezium cluster.

The binary star Theta1 Ori C is the brightest of the four Trapezium stars in the Orion nebula. The Orion Trapezium cluster is the nearest region where massive stars are forming, located at about 1350 light-years from us. It provides a unique laboratory for studying the formation process of massive stars in detail. The intense radiation of Theta1 Ori C ionizes the whole Orion nebula. Its strong wind also shapes the famous Orion proplyds, young stars that are still surrounded by their protoplanetary dust disks.
This image was obtained by a team of astronomers led by Stefan Kraus and Gerd Weigelt (MPIfR, Bonn, Germany), using the AMBER instrument installed at the ESO/Very Large Telescope Interferometer (VLTI). AMBER is an interferometer beam combiner for the VLT, sensitive in the near-infrared wavelength range (from 1 to 2.5 microns).
Theta1 Ori C is a bright, naked-eye star, but its companion is so close (20 milli-arcseconds) that it was not detected before 1999. Thus, high-angular resolution is needed for an in-depth study of the system. The new image has a sharpness of 2 milli-arcseconds, which corresponds to the apparent size of an automobile on the surface of the Moon. Combining AMBER observations with position measurements of the system over the past 12 years, the team was able to compute the orbital period of the system (11 years).
Using Kepler's third law, they also derived the masses of the two stars (38 and 9 solar masses). Finally, they estimated the distance to the system, hence to the center of the Orion star-forming region (1350 light-years). These various measurements are essential for improving theoretical models of massive star formation.
Journal reference:
S. Kraus, G. Weigelt, Y. Y. Balega, J. A. Docobo, K.-H. Hofmann, T. Preibisch, D. Schertl, V. S. Tamazian, T. Driebe, K. Ohnaka, R. Petrov, M. Schoeller, and M. Smith. Tracing the young massive high-eccentricity binary system Theta1 Orionis C through periastron passage. Astronomy & Astrophysics, 2009, vol. 497, p. 195
Adapted from materials provided by Astronomy & Astrophysics.

Some Massive Galaxies May Be Relatively New: Discovery Challenges Galaxy Formation Theories

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ScienceDaily (Apr. 11, 2009) — A team led by an Indiana University astronomer has found a sample of massive galaxies with properties that suggest they may have formed relatively recently. This would run counter to the widely-held belief that massive, luminous galaxies (like our own Milky Way Galaxy) began their formation and evolution shortly after the Big Bang, some 13 billion years ago.

Further research into the nature of these objects could open new windows into the study of the origin and early evolution of galaxies.
John Salzer, principal investigator for the study published in Astrophysical Journal Letters, said that the 15 galaxies in the sample exhibit luminosities (a measure of their total light output) that indicate that they are massive systems like the Milky Way and other so-called "giant" galaxies. However, these particular galaxies are unusual because they have chemical abundances that suggest very little stellar evolution has taken place within them. Their relatively low abundances of "heavy" elements (elements heavier than helium, called "metals" by astronomers) imply the galaxies are cosmologically young and may have formed recently.
The chemical abundances of the galaxies, combined with some simple assumptions about how stellar evolution and chemical enrichment progress in galaxies in general, suggest that they may only be 3 or 4 billion years old, and therefore formed 9 to 10 billion years after the Big Bang. Most theories of galaxy formation predict that massive, luminous systems like these should have formed much earlier.
If this overall interpretation proves correct, the galaxies may allow astronomers to investigate phases of the galaxy formation and evolution process that have been difficult to study because they normally occur at such early times in the Universe, and therefore at very large distances from us.
"These objects may represent a unique window on the process of galaxy formation, allowing us to study relatively nearby systems that are undergoing a phase in their evolution that is analogous to the types of events that, for most galaxies, typically occurred much earlier in the history of the Universe," Salzer said.
The discoveries are the result of a multi-year survey of more than 2,400 star-forming galaxies called the Kitt Peak National Observatory International Spectroscopic Survey (KISS). The survey was designed to collect basic observational data for a large number of extragalactic emission-line sources. Additional rounds of follow-up spectroscopy for the sources discovered in the initial survey led to the discovery of the 15 luminous, low-abundance systems.
"The reason we found these types of galaxies has to do with the unique properties of the KISS survey method," Salzer said. "Galaxies were selected via their strong emission lines, which is the only way to detect these specific galaxies."
Previous surveys done by others have largely missed finding these unusual galaxies.
While the hypothesis that these galaxies are cosmologically young is provocative, it is not the only possible explanation for these enigmatic systems. An alternative explanation proposes that the galaxies are the result of a recent merger between two smaller galaxies. Such a model might explain these objects, since the two-fold result of such a merger might be the reduction of metal abundances due to dilution from unprocessed gas and a brief but large increase in luminosity caused by rampant star formation. As a way to distinguish between these two scenarios, Salzer and his team intend to request observing time on NASA's Hubble Space Telescope to use high-resolution imaging to determine whether or not the systems might be products of merging.
A National Science Foundation Presidential Faculty Award to Salzer, as well as continued NSF support cumulatively totaling $1.2 million, funded the KISS survey and supporting work.
Also contributing to the Astrophysical Journal Letters paper were astronomers Anna Williams of Wesleyan University in Middletown, Conn. and Caryl Gronwall of Pennsylvania State University. Salzer is at IU while on leave from his position of professor of astronomy at Wesleyan, but expects to formally join the faculty at IU in the coming year. The authors also recognized KISS team members Gary Wegner, Drew Phillips, Jessica Werk, Laura Chomiuk, Kerrie McKinstry, Robin Ciardullo, Jeffrey Van Duyne and Vicki Sarajedini for their participation in the follow-up spectroscopic observations over the past several years.
Adapted from materials provided by Indiana University.

Cool Stars Have Different Mix Of Life-Forming Chemicals

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ScienceDaily (Apr. 10, 2009) — Life on Earth is thought to have arisen from a hot soup of chemicals. Does this same soup exist on planets around other stars? A new study from NASA's Spitzer Space Telescope hints that planets around stars cooler than our sun might possess a different mix of potentially life-forming, or "prebiotic," chemicals.

Astronomers used Spitzer to look for a prebiotic chemical, called hydrogen cyanide, in the planet-forming material swirling around different types of stars. Hydrogen cyanide is a component of adenine, which is a basic element of DNA. DNA can be found in every living organism on Earth.
The researchers detected hydrogen cyanide molecules in disks circling yellow stars like our sun -- but found none around cooler and smaller stars, such as the reddish-colored "M-dwarfs" and "brown dwarfs" common throughout the universe.
"Prebiotic chemistry may unfold differently on planets around cool stars," said Ilaria Pascucci, lead author of the new study from Johns Hopkins University, Baltimore, Md. The study will appear in the April 10 issue of the Astrophysical Journal.
Young stars are born inside cocoons of dust and gas, which eventually flatten to disks. Dust and gas in the disks provide the raw material from which planets form. Scientists think the molecules making up the primordial ooze of life on Earth might have formed in such a disk. Prebiotic molecules, such as adenine, are thought to have rained down to our young planet via meteorites that crashed on the surface.
"It is plausible that life on Earth was kick-started by a rich supply of molecules delivered from space," said Pascucci.
Could the same life-generating steps take place around other stars? Pascucci and her colleagues addressed this question by examining the planet-forming disks around 17 cool and 44 sun-like stars using Spitzer's infrared spectrograph, an instrument that breaks light apart, revealing signatures of chemicals. The stars are all about one to three million years old, an age when planets are thought to be growing. The astronomers specifically looked for ratios of hydrogen cyanide to a baseline molecule, acetylene.
They found that the cool stars, both the M-dwarf stars and brown dwarfs, showed no hydrogen cyanide at all, while 30 percent of the sun-like stars did. "Perhaps ultraviolet light, which is much stronger around the sun-like stars, may drive a higher production of the hydrogen cyanide," said Pascucci.
The team did detect their baseline molecule, acetylene, around the cool stars, demonstrating that the experiment worked. This is the first time that any kind of molecule has been spotted in the disks around cool stars.
The findings have implications for planets that have recently been discovered around M-dwarf stars. Some of these planets are thought to be large versions of Earth, the so-called super Earths, but so far none of them are believed to orbit in the habitable zone, where water would be liquid. If such a planet is discovered, could it sustain life?
Astronomers aren't sure. M-dwarfs have extreme magnetic outbursts that could be disruptive to developing life. But, with the new Spitzer results, they have another piece of data to consider: these planets might be deficient in hydrogen cyanide, a molecule thought to have eventually become a part of us.
Said Douglas Hudgins, the Spitzer program scientist at NASA Headquarters, Washington, "Although scientists have long been aware that the tumultuous nature of many cool stars might present a significant challenge for the development of life, this result begs an even more fundamental question: Do cool star systems even contain the necessary ingredients for the formation of life? If the answer is no then questions about life around cool stars become moot."
Other authors include Daniel Apai of the Space Telescope Science Institute, Baltimore, Md.; Kevin Luhman of Pennsylvania State University, University Park; Thomas Henning and Jeroen Bouwman of the Max Planck Institute for Astronomy, Germany; Michael Meyer of the University of Arizona, Tucson; Fred Lahuis of the SRON Netherlands Institute for Space Research, the Netherlands; and Antonella Natta of the Arcetri Astrophysical Observatory, Italy.
Journal reference:
A. Juhász, Th. Henning, J. Bouwman, C. P. Dullemond, I. Pascucci, and D. Apai. Do We Really Know the Dust? Systematics and Uncertainties of the Mid-Infrared Spectral Analysis Methods. The Astrophysical Journal, 2009; 695 (2): 1024 DOI: 10.1088/0004-637X/695/2/1024
Adapted from materials provided by NASA/Jet Propulsion Laboratory.

Astronomers Help Solve Mystery Of Starlight's Origins Using A Telescope And Huge Balloon

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ScienceDaily (Apr. 9, 2009) — Scientists from the University of Toronto and the University of British Columbia have helped unveil the birthplaces of ancient stars using a two-tonne telescope carried by a balloon the size of a 33-storey building.

After two years spent analyzing data from the Balloon-borne Large-Aperture Sub-millimeter Telescope (BLAST) project, an international group of astronomers and astrophysicists from Canada, the U.S. and the U.K. reveals April 8 in the journal Nature that half of the starlight of the Universe comes from young, star-forming galaxies several billion light years away.
"While those familiar optical images of the night sky contain many fascinating and beautiful objects, they are missing half of the picture in describing the cosmic history of star formation," says UBC Astronomy Prof. Douglas Scott.
"Stars are born in clouds of gas and dust," says Barth Netterfield, a cosmologist in the Department of Astronomy & Astrophysics at U of T. "The dust absorbs the starlight, hiding the young stars from view. The brightest stars in the Universe are also the shortest lived and many never leave their stellar nursery. However, the warmed dust emits light at far-infrared and submillimetre wavelengths – invisible to the human eye, but visible to the sensitive thermo-detectors on BLAST."
"The history of star formation in the universe is written out in our data. It is beautiful. And it is just a taste of things to come," says UBC Prof. Mark Halpern, part of the UBC team that also includes post-doctoral fellows Ed Chapin and Gaelen Marsden.
In the 1990s, NASA's COBE satellite discovered a nearly uniform glow of submillimetre light, known as the Far Infrared Background. It had been expected that this radiation was coming from warmed dust enshrouding bright young stars, but the nature of the galaxies which contain the dust had remained a mystery.
The Nature study combines BLAST submillimetre observations at wavelengths around 0.3 mm – between infrared and microwave wavelengths – with data at much shorter infrared wavelengths from NASA's Spitzer Space Telescope to confirm that all of the Far Infrared Background comes from individual distant galaxies, answering a decade-old question of the radiation's origin.
In addition to leading the data analysis, the Canadian scientists also constructed much of the hardware that made BLAST a reality. The aluminum gondola was designed to protect the telescope, the onboard computers and data upon landing. The motorized pointing system controlled the 2,000 kilogram payload with its two-metre-in-diameter telescope – the largest of its kind – to one one-hundredth of a degree in precision. The complex electronics monitored and recorded nearly 1,000 sensors while the software – nearly 300,000 lines of code – controlled the payload during its long flight 39 kilometres above the Earth.
Flying the telescope above much of the atmosphere allowed the BLAST team to peer out into the distant Universe at wavelengths nearly unattainable from the ground, and uncover dust-enshrouded galaxies that hide about half of the starlight in the Universe.
"Over the last decade, submillimetre telescopes on the ground have produced several 'black and white' images no larger than the size of a fingernail at the end of your outstretched arm," says Chapin. "In a single 11-day flight BLAST has taken a huge leap forward, producing colour images the size of your hand."
BLAST has acted as a pathfinder for the SPIRE (Spectral and Photometric Imaging Receiver) instrument on the upcoming Herschel satellite, in which Canadians are also involved. Using the same detectors as SPIRE, BLAST has provided an invaluable first look at the submillimetre sky.
"BLAST has given us a new view of the Universe," says Netterfield, whose U of T colleagues on the project include department chair Peter G. Martin and graduate students Marco P. Viero, Donald V. Wiebe (now a post-doc at UBC) and Enzo Pascale (now a faculty member at Cardiff University). "The data we collected enable us to make discoveries in topics ranging from the formation of stars to the evolution of distant galaxies."
BLAST is also uniquely capable of studying the earliest stages of star formation locally, in the Milky Way Galaxy. The BLAST collaboration is also releasing a study, submitted to the Astrophysical Journal, of the largest survey to date of the earliest stages of star formation. This study documents the existence of a large population of cold clouds of gas and dust, many of which have cooled to less than -260 C. These cold cores, which exist for millions of years, are the birthplaces of stars.
"Over the last nine years, I've followed BLAST from Vancouver to Toronto, Philadelphia, New Mexico, Texas, northern Sweden and Antarctica, and it feels great for us to finally announce the results," says Marsden. "These results are a very big step forward in submillimetre astronomy."
"The world-leading scientific success of Canadian graduate students and post-docs working on BLAST has been very impressive and, speaking as an educator, very gratifying," says Halpern.
Collaborators on the BLAST project include: Mark Devlin, Jeff Klein, Marie Rex, Christopher Semisch and Matthew D. P. Truch (University of Pennsylvania); Mark Halpern, Edward L. Chapin, Gaelen Marsden, Henry Ngo and Douglas Scott (University of British Columbia); C. Barth Netterfield, Peter G. Martin, Marco P. Viero, Donald V. Wiebe (University of Toronto); Enzo Pascale, Peter A. R. Ade, Matthew Griffin, Peter C. Hargrave, Philip Mauskopf, Lorenzo Moncelsi and Carole Tucker (Cardiff University); James J. Bock (Jet Propulsion Laboratory); Gregory S. Tucker (Brown University); Itziar Aretxaga and David H. Hughes (Instituto Nacional de Astrofısica Optica y Electronica, Mexico); Joshua O. Gundersen and Nicholas Thomas (University of Miami); Luca Olmi (University of Puerto Rico, Rio Piedras Campus and the INAF), and Guillaume Patanchon (Laboratoire APC, Paris).
The BLAST experiment has been supported by funding from the National Aeronautics and Space Administration, the National Science Foundation Office of Polar Programs, the Canadian Space Agency, the Natural Sciences and Engineering Research Council of Canada, and the UK Science and Technology Facilities Council, and with assistance from Benjamin Magnelli, WestGrid computing resources and the SIMBAD and NASA/IPAC databases, the Columbia Scientific Balloon Facility, Ken Borek Air Ltd., and the mountaineers of McMurdo Station, Antarctica.
Journal reference:
Devlin et al. Over half of the far-infrared background light comes from galaxies at z greater than or equal to 1.2. Nature, 2009; 458 (7239): 737 DOI: 10.1038/nature07918
Adapted from materials provided by University of British Columbia.

Twin Spacecraft To Explore Gravitational 'Parking Lots' That May Hold Secret Of Moon's Origin

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ScienceDaily (Apr. 10, 2009) — Two places on opposite sides of Earth may hold the secret to how the moon was born. NASA's twin Solar Terrestrial Relations Observatory (STEREO) spacecraft are about to enter these zones, known as the L4 and L5 Lagrangian points, each centered about 93 million miles away along Earth's orbit.

As rare as free parking in New York City, L4 and L5 are among the special points in our solar system around which spacecraft and other objects can loiter. They are where the gravitational pull of a nearby planet or the sun balances the forces from the object's orbital motion. Such points closer to Earth are sometimes used as spaceship "parking lots", like the L1 point a million miles away in the direction of the sun. They are officially called Libration points or Lagrangian points after Joseph-Louis Lagrange, an Italian-French mathematician who helped discover them.
L4 and L5 are where an object's motion can be balanced by the combined gravity of the sun and Earth. "These places may hold small asteroids, which could be leftovers from a Mars-sized planet that formed billions of years ago," said Michael Kaiser, Project Scientist for STEREO at NASA's Goddard Space Flight Center in Greenbelt, Md. "According to Edward Belbruno and Richard Gott at Princeton University, about 4.5 billion years ago when the planets were still growing, this hypothetical world, called Theia, may have been nudged out of L4 or L5 by the increasing gravity of the other developing planets like Venus and sent on a collision course with Earth. The resulting impact blasted the outer layers of Theia and Earth into orbit, which eventually coalesced under their own gravity to form the moon."
This theory is a modification of the "giant impact" theory of the moon's origin, which has become the dominant theory because it explains some puzzling properties of the moon, such as its relatively small iron core. According to giant impact, at the time of the collision, the two planets were large enough to be molten, so heavier elements, like iron, sank to their centers to form their cores.
The impact stripped away the outer layers of the two worlds, which contained mostly lighter elements, like silicon. Since the moon formed from this material, it is iron-poor.
STEREO will look for asteroids with a wide-field-of-view telescope that's part of the Sun Earth Connection Coronal and Heliospheric Investigation instrument. Any asteroid will probably appear as just a point of light. Like a picky person circling the mall for the perfect parking space, the asteroids orbit the L4 or L5 points. The team will be able to tell if a dot is an asteroid because it will shift its position against stars in the background as it moves in its orbit. The team is inviting the public to participate in the search by viewing the data and filing a report at: >
Kaiser said, "If we discover the asteroids have the same composition as the Earth and moon, it will support Belbruno and Gott's version of the giant impact theory. The asteroids themselves could well be left-over from the formation of the solar system. Also, the L4/L5 regions might be the home of future Earth-impacting asteroids."
Analyses of lunar rocks brought to Earth by the Apollo missions reveal that they have the same isotopes (heavier versions of an element) as terrestrial rocks. Scientists believe that the sun and the worlds of our solar system formed out of a cloud of gas and dust that collapsed under its gravity. The composition of this primordial cloud changed with temperature. Since the temperature decreased with distance from the sun, whatever created the moon must have formed in the same orbital location as Earth in order for them to have the same isotope composition.
In a planetary version of "the rich get richer", Earth's gravity should have swept up most of the material in its orbit, leaving too little to create our large moon or another planet like Theia. "However, computer models by Belbruno and Gott indicate that Theia could have grown large enough to produce the moon if it formed in the L4 or L5 regions, where the balance of forces allowed enough material to accumulate," said Kaiser.
The STEREO spacecraft are designed to give 3D views of space weather by observing the sun from two points of view and combining the images in the same way your eyes work together to give a 3D view of the world. STEREO "A" is moving slightly ahead of Earth and will pass through L4, and STEREO "B" is moving slightly behind Earth and will pass through L5. "Taking the time to observe L4 and L5 is kind of cool because it's free. We're going through there anyway -- we're moving too fast to get stuck," said Kaiser. "In fact, after we pass through these regions, we will see them all the time because our instruments will be looking back through them to observe the sun – they will just happen to be in our field of view."
Although L4 and L5 are just points mathematically, their region of influence is huge – about 50 million miles along the direction of Earth's orbit, and 10 million miles along the direction of the sun. It will take several months for STEREO to pass through them, with STEREO A making its closest pass to L4 in September, and STEREO B making its closest pass to L5 in October.
"L4 or L5 are excellent places to observe space weather. With both the sun and Earth in view, we could track solar storms and watch them evolve as they move toward Earth. Also, since we could see sides of the sun not visible from Earth, we would have a few days warning before stormy regions on the solar surface rotate to become directed at Earth," said Kaiser.
Adapted from materials provided by NASA/Goddard Space Flight Center.