Wednesday, January 25, 2012

Durable NASA Rover Beginning Ninth Year of Mars Work

Eight years after landing on Mars for what was planned as a three-month mission, NASA's enduring Mars Exploration Rover Opportunity is working on what essentially became a new mission five months ago.

Opportunity reached a multi-year driving destination, Endeavour Crater, in August 2011. At Endeavour's rim, it has gained access to geological deposits from an earlier period of Martian history than anything it examined during its first seven years. It also has begun an investigation of the planet's deep interior that takes advantage of staying in one place for the Martian winter.

Opportunity landed in Eagle Crater on Mars on Jan. 25, 2004, Universal Time and EST (Jan. 24, PST), three weeks after its rover twin, Spirit, landed halfway around the planet. In backyard-size Eagle Crater, Opportunity found evidence of an ancient wet environment. The mission met all its goals within the originally planned span of three months. During most of the next four years, it explored successively larger and deeper craters, adding evidence about wet and dry periods from the same era as the Eagle Crater deposits.

In mid-2008, researchers drove Opportunity out of Victoria Crater, half a mile (800 meters) in diameter, and set course for Endeavour Crater, 14 miles (22 kilometers) in diameter.

"Endeavour is a window further into Mars' past," said Mars Exploration Rover Program Manager John Callas, of NASA's Jet Propulsion Laboratory, Pasadena, Calif.

The trek took three years. In a push to finish it, Opportunity drove farther during its eighth year on Mars -- 4.8 miles (7.7 kilometers) -- than in any prior year, bringing its total driving distance to 21.4 miles (34.4 kilometers).

The "Cape York" segment of Endeavour's rim, where Opportunity has been working since August 2011, has already validated the choice of Endeavour as a long-term goal. "It's like starting a new mission, and we hit pay dirt right out of the gate," Callas said.

The first outcrop that Opportunity examined on Cape York differs from any the rover had seen previously. Its high zinc content suggests effects of water. Weeks later, at the edge of Cape York, a bright mineral vein identified as hydrated calcium sulfate provided what the mission's principal investigator, Steve Squyres of Cornell University, Ithaca, N.Y., calls "the clearest evidence for liquid water on Mars that we have found in our eight years on the planet."

Mars years last nearly twice as long as Earth years. Entering its ninth Earth year on Mars, Opportunity is also heading into its fifth Martian winter. Its solar panels have accumulated so much dust since Martian winds last cleaned them -- more than in previous winters -- the rover needs to stay on a sun-facing slope to have enough energy to keep active through the winter.

The rover team has not had to use this strategy with Opportunity in past winters, though it did so with Spirit, farther from the equator, for the three Martian winters that Spirit survived. By the beginning of the rovers' fourth Martian winter, drive motors in two of Spirit's six wheels had ceased working, long past their design lifespan. The impaired mobility kept the rover from maneuvering to an energy-favorable slope. Spirit stopped communicating in March 2010.

All six of Opportunity's wheels are still useful for driving, but the rover will stay on an outcrop called "Greeley Haven" until mid-2012 to take advantage of the outcrop's favorable slope and targets of scientific interest during the Martian winter. After the winter, or earlier if wind cleans dust off the solar panels, researchers plan to drive Opportunity in search of clay minerals that a Mars orbiter's observations indicate lie on Endeavour's rim.

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Thursday, January 19, 2012

2011 was ninth-warmest year since 1880: NASA

The global average temperature last year was the ninth-warmest in the modern meteorological record, continuing a trend linked to greenhouse gases that saw nine of the 10 hottest years occurring since the year 2000, NASA scientists said on Thursday.

A separate report from the US National Oceanic and Atmospheric Administration (NOAA) said the average temperature for the United States in 2011 as the 23rd warmest year on record.

The global average surface temperature for 2011 was 0.92 degrees F (0.51 degrees C) warmer than the mid-20th century baseline temperature, researchers at NASA's Goddard Institute for Space Studies said in a statement. The institute's temperature record began in 1880.

The first 11 years of the new century were notably hotter than the middle and late 20th century, according to institute director James Hansen. The only year from the 20th century that was among the top 10 warmest years was 1998.

These high global temperatures come even with the cooling effects of a strong La Nina ocean temperature pattern and low solar activity for the past several years, said Hansen, who has long campaigned against human-spurred climate change.

The NASA statement said the current higher temperatures are largely sustained by increased concentrations of greenhouse gases in the atmosphere, especially carbon dioxide. Carbon dioxide is emitted by various human activities, from coal-fired power plants to fossil-fueled vehicles to human breath.

Current levels of carbon dioxide in the atmosphere exceed 390 parts per million, compared with 285 ppm in 1880 and 315 by 1960, NASA said.

Last year was also a year of record-breaking climate extremes in the United States, which contributed to 14 weather and climate disasters with economic impact of $1 billion or more each, according to NOAA . This number does not count a pre-Halloween snowstorm in the Northeast, which is still being analyzed.

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Tuesday, January 17, 2012

NASA’s Hubble Space Telescope Solves Mystery on Source of Supernova in Nearby Galaxy

Baltimore, MD – Using NASA’s Hubble Space Telescope, astronomers have solved a longstanding mystery on the type of star, or so-called progenitor, which caused a supernova seen in a nearby galaxy. The finding yields new observational data for pinpointing one of several scenarios that trigger such outbursts.

Based on previous observations from ground-based telescopes, astronomers knew the supernova class, called a Type Ia, created a remnant named SNR 0509-67.5, which lies 170,000 light-years away in the Large Magellanic Cloud galaxy.

Theoretically, this kind of supernova explosion is caused by a star spilling material onto a white dwarf companion, the compact remnant of a normal star, until it sets off one of the most powerful explosions in the universe.

Astronomers failed to find any remnant of the companion star, however, and concluded that the common scenario did not apply in this case, although it is still a viable theory for other Type Ia supernovae.

“We know Hubble has the sensitivity necessary to detect the faintest white dwarf remnants that could have caused such explosions,” said lead investigator Bradley Schaefer of Louisiana State University (LSU) in Baton Rouge. “The logic here is the same as the famous quote from Sherlock Holmes: ‘when you have eliminated the impossible, whatever remains, however improbable, must be the truth.’”

The cause of SNR 0509-67.5 can be explained best by two tightly orbiting white dwarf stars spiraling closer and closer until they collided and exploded.

For four decades, the search for Type Ia supernovae progenitors has been a key question in astrophysics. The problem has taken on special importance during the last decade with Type Ia supernovae being the premier tools for measuring the accelerating universe.

Type Ia supernovae release tremendous energy, in which the light produced is often brighter than an entire galaxy of stars. The problem has been to identify the type of star system that pushes the white dwarf’s mass over the edge and triggers this type of explosion. Many possibilities have been suggested, but most require that a companion star near the exploding white dwarf be left behind after the explosion.

Therefore, a possible way to distinguish between the various progenitor models has been to look deep in the center of an old supernova remnant to search for the ex-companion star.

In 2010, Schaefer and Ashley Pagnotta of LSU were preparing a proposal to look for any faint ex-companion stars in the center of four supernova remnants in the Large Magellanic Cloud when they discovered the Hubble Space Telescope already had taken the desired image of one of their target remnants, SNR 0509-67.5, for the Hubble Heritage program, which collects images of especially photogenic astronomical targets.

In analyzing the central region, they found it to be completely empty of stars down to the limit of the faintest objects Hubble can detect in the photos. Schaefer suggests the best explanation left is the so-called “double degenerate model” in which two white dwarfs collide.

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Thursday, January 12, 2012

NASA’s Chandra Finds Largest Galaxy Cluster in Early Universe

An exceptional galaxy cluster, the largest seen in the distant universe, has been found using NASA’s Chandra X-ray Observatory and the National Science Foundation-funded Atacama Cosmology Telescope (ACT) in Chile.

Officially known as ACT-CL J0102-4915, the galaxy cluster has been nicknamed “El Gordo” (“the big one” or “the fat one” in Spanish) by the researchers who discovered it. The name, in a nod to the Chilean connection, describes just one of the remarkable qualities of the cluster, which is located more than 7 billion light years from Earth. This large distance means it is being observed at a young age.

“This cluster is the most massive, the hottest, and gives off the most X-rays of any known cluster at this distance or beyond,” said Felipe Menanteau of Rutgers University in New Brunswick, N.J., who led the study.

Galaxy clusters, the largest objects in the universe that are held together by gravity, form through the merger of smaller groups or sub-clusters of galaxies. Because the formation process depends on the amount of dark matter and dark energy in the universe, clusters can be used to study these mysterious phenomena.

Dark matter is material that can be inferred to exist through its gravitational effects, but does not emit and absorb detectable amounts of light. Dark energy is a hypothetical form of energy that permeates all space and exerts a negative pressure that causes the universe to expand at an ever-increasing rate.

“Gigantic galaxy clusters like this are just what we were aiming to find,” said team member Jack Hughes, also of Rutgers. “We want to see if we can understand how these extreme objects form using the best models of cosmology that are currently available.”

Although a cluster of El Gordo’s size and distance is extremely rare, it is likely that its formation can be understood in terms of the standard Big Bang model of cosmology. In this model, the universe is composed predominantly of dark matter and dark energy, and began with a Big Bang about 13.7 billion years ago.

The team of scientists found El Gordo using ACT thanks to the Sunyaev-Zeldovich effect. In this phenomenon, photons in the cosmic microwave background interact with electrons in the hot gas that pervades these enormous galaxy clusters. The photons acquire energy from this interaction, which distorts the signal from the microwave background in the direction of the clusters. The magnitude of this distortion depends on the density and temperature of the hot electrons and the physical size of the cluster.

X-ray data from Chandra and the European Southern Observatory’s Very Large Telescope, an 8-meter optical observatory in Chile, show El Gordo is, in fact, the site of two galaxy clusters colliding at several million miles per hour. This and other characteristics make El Gordo akin to the well-known object called the Bullet Cluster, which is located almost 4 billion light years closer to Earth.

Tuesday, January 03, 2012

NASA's Twin Grail Spacecraft Reunite in Lunar Orbit

PASADENA, Calif. -- The second of NASA's two Gravity Recovery And Interior Laboratory (GRAIL) spacecraft has successfully completed its planned main engine burn and is now in lunar orbit. Working together, GRAIL-A and GRAIL-B will study the moon as never before.

"NASA greets the new year with a new mission of exploration," said NASA Administrator Charles Bolden. "The twin GRAIL spacecraft will vastly expand our knowledge of our moon and the evolution of our own planet. We begin this year reminding people around the world that NASA does big, bold things in order to reach for new heights and reveal the unknown."

GRAIL-B achieved lunar orbit at 2:43 p.m. PST (5:43 p.m. EST) today. GRAIL-A successfully completed its burn yesterday at 2 p.m. PST (5 p.m. EST). The insertion maneuvers placed the spacecraft into a near-polar, elliptical orbit with an orbital period of approximately 11.5 hours. Over the coming weeks, the GRAIL team will execute a series of burns with each spacecraft to reduce their orbital period to just under two hours. At the start of the science phase in March 2012, the two GRAILs will be in a near-polar, near-circular orbit with an altitude of about 34 miles (55 kilometers).

During GRAIL's science mission, the two spacecraft will transmit radio signals precisely defining the distance between them. As they fly over areas of greater and lesser gravity caused by visible features such as mountains and craters, and masses hidden beneath the lunar surface, the distance between the two spacecraft will change slightly.

Scientists will translate this information into a high-resolution map of the moon's gravitational field. The data will allow scientists to understand what goes on below the lunar surface. This information will increase knowledge of how Earth and its rocky neighbors in the inner solar system developed into the diverse worlds we see today.

Each spacecraft carries a small camera called GRAIL MoonKAM (Moon Knowledge Acquired by Middle school students) with the sole purpose of education and public outreach. The MoonKAM program is led by Sally Ride, America's first woman in space, and her team at Sally Ride Science in collaboration with undergraduate students at the University of California in San Diego.

GRAIL MoonKAM will engage middle schools across the country in the GRAIL mission and lunar exploration. Thousands of fifth- to eighth-grade students will select target areas on the lunar surface and send requests to the GRAIL MoonKAM Mission Operations Center in San Diego. Photos of the target areas will be sent back by the GRAIL satellites for students to study.

A student contest that began in October 2011 also will choose new names for the spacecraft. The new names are scheduled to be announced in January 2012. Ride and Maria Zuber, the mission's principal investigator at the Massachusetts Institute of Technology in Cambridge, chaired the final round of judging.

NASA's Jet Propulsion Laboratory in Pasadena, Calif., manages the GRAIL mission for NASA's Science Mission Directorate, Washington. The GRAIL mission is part of the Discovery Program managed at NASA's Marshall Space Flight Center in Huntsville, Ala. Lockheed Martin Space Systems in Denver built the spacecraft. JPL is a division of the Çalifornia Institute of Technology in Pasadena.