NASA's WISE Finds Mysterious Centaurs May Be Comets

The true identity of centaurs, the small celestial bodies orbiting the sun between Jupiter and Neptune, is one of the enduring mysteries of astrophysics. Are they asteroids or comets? A new study of observations from NASA's Wide-field Infrared Survey Explorer (WISE) finds most centaurs are comets.

Until now, astronomers were not certain whether centaurs are asteroids flung out from the inner solar system or comets traveling in toward the sun from afar. Because of their dual nature, they take their name from the creature in Greek mythology whose head and torso are human and legs are those of a horse.

"Just like the mythical creatures, the centaur objects seem to have a double life," said James Bauer of NASA's Jet Propulsion Laboratory in Pasadena, Calif. Bauer is lead author of a paper published online July 22 in the Astrophysical Journal. "Our data point to a cometary origin for most of the objects, suggesting they are coming from deeper out in the solar system."

"Cometary origin" means an object likely is made from the same material as a comet, may have been an active comet in the past, and may be active again in the future.
The findings come from the largest infrared survey to date of centaurs and their more distant cousins, called scattered disk objects. NEOWISE, the asteroid-hunting portion of the WISE mission, gathered infrared images of 52 centaurs and scattered disk objects. Fifteen of the 52 are new discoveries. Centaurs and scattered disk objects orbit in an unstable belt. Ultimately, gravity from the giant planets will fling them either closer to the sun or farther away from their current locations.

Although astronomers previously observed some centaurs with dusty halos, a common feature of outgassing comets, and NASA's Spitzer Space Telescope also found some evidence for comets in the group, they had not been able to estimate the numbers of comets and asteroids.

Infrared data from NEOWISE provided information on the objects' albedos, or reflectivity, to help astronomers sort the population. NEOWISE can tell whether a centaur has a matte and dark surface or a shiny one that reflects more light. The puzzle pieces fell into place when astronomers combined the albedo information with what was already known about the colors of the objects. Visible-light observations have shown centaurs generally to be either blue-gray or reddish in hue. A blue-gray object could be an asteroid or comet. NEOWISE showed that most of the blue-gray objects are dark, a telltale sign of comets. A reddish object is more likely to be an asteroid.

"Comets have a dark, soot-like coating on their icy surfaces, making them darker than most asteroids," said the study's co-author, Tommy Grav of the Planetary Science Institute in Tucson, Ariz. "Comet surfaces tend to be more like charcoal, while asteroids are usually shinier like the moon."

The results indicate that roughly two-thirds of the centaur population are comets, which come from the frigid outer reaches of our solar system. It is not clear whether the rest are asteroids. The centaur bodies have not lost their mystique entirely, but future research from NEOWISE may reveal their secrets further.

Tropical Ecosystems Boost Carbon Dioxide as Temperatures Rise

NASA scientists and an international team of researchers have found tropical ecosystems can generate significant carbon dioxide when temperatures rise, unlike ecosystems in other parts of the world.

The researchers discovered a temperature increase of just 1 degree Celsius in near-surface air temperatures in the tropics leads to an average annual growth rate of atmospheric carbon dioxide equivalent to one-third of the annual global emissions from combustion of fossil fuels and deforestation combined. In tropical ecosystems carbon uptake is reduced at higher temperatures. This finding provides scientists with a key diagnostic tool to better understand the global carbon cycle.

"What we learned is that in spite of droughts, floods, volcano eruptions, El Niño and other events, the Earth system has been remarkably consistent in regulating the year-to-year variations in atmospheric carbon dioxide levels," said Weile Wang, a research scientist at NASA's Ames Research Center in Moffett Field, Calif., and lead author of a paper published Wednesday, July 24, in the Proceedings of the National Academy of Sciences.

The study provides support for the "carbon-climate feedback" hypothesis proposed by many scientists. This hypothesis asserts a warming climate will lead to accelerated carbon dioxide growth in the atmosphere from vegetation and soils. Multiple Earth system processes, such as droughts and floods, also contribute to changes in the atmospheric carbon dioxide growth rate. The new finding demonstrates observed temperature changes are a more important factor than rainfall changes in the tropics.

The team used a state-of-the-art, high-performance computing and data access facility called NASA Earth Exchange (NEX) at Ames to investigate the mechanisms underlying the relationship between carbon dioxide levels and increased temperatures. The NEX facility allowed scientists to analyze widely available data of atmospheric carbon dioxide concentrations and global air temperatures between 1959 and 2011, while studying outputs from several global dynamic vegetation models.

"Climate warming is what we know with certainty will happen under climate change in the tropics,," said Josep G. Canadell, executive director of the Global Carbon Project in Canberra, Australia, and co-author on the paper. This implies that the release of carbon dioxide from the tropical ecosystems will very likely be accelerated with future warming.

Events that can temporarily influence climate, such as volcanic eruptions, may disturb the strength of the relationship between annual temperature and carbon dioxide growth for a few years, but the coupling always recovers after such events.

"The study really highlights the importance of long-term Earth observations for improving our understanding of the Earth system," said Rama Nemani, principal scientist at Ames for the NEX project." Conclusions drawn from analysis of shorter records could be misleading."

Reports Detail Mars Rover Clues to Atmosphere's Past

PASADENA, Calif. – A pair of new papers report measurements of the Martian atmosphere's composition by NASA's Curiosity rover, providing evidence about loss of much of Mars' original atmosphere.

Curiosity's Sample Analysis at Mars (SAM) suite of laboratory instruments inside the rover has measured the abundances of different gases and different isotopes in several samples of Martian atmosphere. Isotopes are variants of the same chemical element with different atomic weights due to having different numbers of neutrons, such as the most common carbon isotope, carbon-12, and a heavier stable isotope, carbon-13.

SAM checked ratios of heavier to lighter isotopes of carbon and oxygen in the carbon dioxide that makes up most of the planet's atmosphere. Heavy isotopes of carbon and oxygen are both enriched in today's thin Martian atmosphere compared with the proportions in the raw material that formed Mars, as deduced from proportions in the sun and other parts of the solar system. This provides not only supportive evidence for the loss of much of the planet's original atmosphere, but also a clue to how the loss occurred.

"As atmosphere was lost, the signature of the process was embedded in the isotopic ratio," said Paul Mahaffy of NASA Goddard Space Flight Center, Greenbelt, Md.  He is the principal investigator for SAM and lead author of one of the two papers about Curiosity results in the July 19 issue of the journal Science.
Other factors also suggest Mars once had a much thicker atmosphere, such as evidence of persistent presence of liquid water on the planet's surface long ago even though the atmosphere is too scant for liquid water to persist on the surface now. The enrichment of heavier isotopes measured in the dominant carbon-dioxide gas points to a process of loss from the top of the atmosphere -- favoring loss of lighter isotopes -- rather than a process of the lower atmosphere interacting with the ground.

Curiosity measured the same pattern in isotopes of hydrogen, as well as carbon and oxygen, consistent with a loss of a substantial fraction of Mars' original atmosphere. Enrichment in heavier isotopes in the Martian atmosphere has previously been measured on Mars and in gas bubbles inside meteorites from Mars. Meteorite measurements indicate much of the atmospheric loss may have occurred during the first billion years of the planet's 4.6-billion-year history. The Curiosity measurements reported this week provide more precise measurements to compare with meteorite studies and with models of atmospheric loss.

The Curiosity measurements do not directly measure the current rate of atmospheric escape, but NASA's next mission to Mars, the Mars Atmosphere and Volatile Evolution Mission (MAVEN), will do so. "The current pace of the loss is exactly what the MAVEN mission now scheduled to launch in November of this year is designed to determine," Mahaffy said.
The new reports describe analysis of Martian atmosphere samples with two different SAM instruments during the initial 16 weeks of the rover's mission on Mars, which is now in its 50th week. SAM's mass spectrometer and tunable laser spectrometer independently measured virtually identical ratios of carbon-13 to carbon-12. SAM also includes a gas chromatograph and uses all three instruments to analyze rocks and soil, as well as atmosphere.

"Getting the same result with two very different techniques increased our confidence that there's no unknown systematic error underlying the measurements," said Chris Webster of NASA's Jet Propulsion Laboratory, Pasadena, Calif. He is the lead scientist for the tunable laser spectrometer and the lead author for one of the two papers. "The accuracy in these new measurements improves the basis for understanding the atmosphere's history."

Curiosity landed inside Mars' Gale Crater on Aug. 6, 2012 Universal Time (on Aug. 5 PDT). The rover this month began a drive of many months from an area where it found evidence for a past environment favorable for microbial life, toward a layered mound, Mount Sharp, where researchers will seek evidence about how the environment changed. 

Hubble Sees Stars That go out with a Whimper

This NASA/ESA Hubble Space Telescope image shows the planetary nebula IC 289, located in the northern constellation of Cassiopeia. Formerly a star like our sun, it is now just a cloud of ionized gas being pushed out into space by the remnants of the star’s core, visible as a small bright dot in the middle of the cloud.

Weirdly enough, planetary nebulae have nothing to do with planets. Early observers, when looking through small telescopes, could only see undefined, smoky forms that looked like gaseous planets — hence the name. The term has stuck even though modern telescopes like Hubble have made it clear that these objects are not planets at all, but the outer layers of dying stars being thrown off into space.

Stars shine as a result of nuclear fusion reactions in their cores, converting hydrogen to helium. All stars are stable, balancing the inward push caused by their gravity with the outwards thrust from the inner fusion reactions in their cores. When all the hydrogen is consumed the equilibrium is broken; the gravitational forces become more powerful than the outward pressure from the fusion process and the core starts to collapse, heating up as it does so.

When the hot, shrinking core gets hot enough, the helium nuclei begin to fuse into carbon and oxygen and the collapse stops. However, this helium-burning phase is highly unstable and huge pulsations build up, eventually becoming large enough to blow the whole star’s atmosphere away.

A Beautiful End to a Star’s Life

Stars like the Sun can become remarkably photogenic at the end of their life. A good example is NGC 2392, which is located about 4,200 light years from Earth. NGC 2392, nicknamed the "Eskimo Nebula", is what astronomers call a planetary nebula. This designation, however, is deceiving because planetary nebulas actually have nothing to do with planets. The term is simply a historic relic since these objects looked like planetary disks to astronomers in earlier times looking through small optical telescopes.

Instead, planetary nebulas form when a star uses up all of the hydrogen in its core -- an event our Sun will go through in about five billion years. When this happens, the star begins to cool and expand, increasing its radius by tens to hundreds of times its original size. Eventually, the outer layers of the star are carried away by a thick 50,000 kilometer per hour wind, leaving behind a hot core. This hot core has a surface temperature of about 50,000 degrees Celsius, and is ejecting its outer layers in a much faster wind traveling six million kilometers per hour. The radiation from the hot star and the interaction of its fast wind with the slower wind creates the complex and filamentary shell of a planetary nebula. Eventually the remnant star will collapse to form a white dwarf star.

Now days, astronomers using space-based telescopes are able to observe planetary nebulas such as NGC 2392 in ways their scientific ancestors probably could never imagine. This composite image of NGC 2392 contains X-ray data from NASA's Chandra X-ray Observatory in purple showing the location of million-degree gas near the center of the planetary nebula. Data from the Hubble Space Telescope show – colored red, green, and blue – the intricate pattern of the outer layers of the star that have been ejected. The comet-shaped filaments form when the faster wind and radiation from the central star interact with cooler shells of dust and gas that were already ejected by the star.

The observations of NGC 2392 were part of a study of three planetary nebulas with hot gas in their center. The Chandra data show that NGC 2392 has unusually high levels of X-ray emission compared to the other two. This leads researchers to deduce that there is an unseen companion to the hot central star in NGC 2392. The interaction between a pair of binary stars could explain the elevated X-ray emission found there. Meanwhile, the fainter X-ray emission observed in the two other planetary nebulas in the sample – IC 418 and NGC 6826 – is likely produced by shock fronts (like sonic booms) in the wind from the central star. A composite image of NGC 6826 was included in a gallery of planetary nebulas released in 2012.

A paper describing these results is available online and was published in the April 10th, 2013 issue of The Astrophysical Journal. The first author is Nieves Ruiz of the Instituto de Astrofísica de Andalucía (IAA-CSIC) in Granada, Spain, and the other authors are You-Hua Chu, and Robert Gruendl from the University of Illinois, Urbana; Martín Guerrero from the Instituto de Astrofísica de Andalucía (IAA-CSIC) in Granada, Spain, and Ralf Jacob, Detlef Schönberner and Matthias Steffen from the Leibniz-Institut Für Astrophysik in Potsdam (AIP), Germany.

NASA's Marshall Space Flight Center in Huntsville, Ala., manages the Chandra program for NASA's Science Mission Directorate in Washington. The Smithsonian Astrophysical Observatory controls Chandra's science and flight operations from Cambridge, Mass.

First Testing of Orion Launch Abort System Flight Hardware

NASA engineers and contractors have begun tests on NASA’s Launch Abort System (LAS) Fairing Assembly, flight hardware that will be used to cover and protect the Orion crew module during Exploration Flight Test-1 (EFT-1), scheduled for September 2014.

Similar to the material of a graphite tennis racquet, the LAS fairing is a lightweight composite structure weighing 3,000 pounds that protects the capsule from the environment around it, whether it's heat, wind or acoustics.

“The fairing surface interacts with the atmosphere as we launch through it,” explains Kevin Rivers, LAS project manager at NASA’s Langley Research Center in Hampton, Va. “It plays a significant role in the EFT-1 launch. It’s got to maintain structural integrity and protect the spacecraft.”

During static loads testing of the LAS fairing, the structure is placed into a large steel frame and loaded by 10 hydraulic actuators – simulating aerodynamic pressures and bending loads experienced during flight.

Approximately 36 strain gauges and 26 displacement sensors are placed on the structure to measure the way it handles various loads and stresses. Testing makes certain that the structure will work during flight and helps to better understand how well the engineering analysis predicts real flight vehicle behavior.

“This test helps to verify that the structure can withstand the worst case flight loads by testing to even higher levels,” said Gary Keyser, Lockheed Martin LAS lead system engineer. “Testing like this gives us confidence in our analysis and the workmanship of the actual flight hardware.”

During EFT-1, Orion will travel to an altitude 3,600 miles above Earth’s surface. It will return at a speed over 20,000 mph for a landing in the Pacific Ocean. If an emergency were to occur on the pad or initial ascent during EFT-1 or future Orion flights, the LAS would jettison the crew module away from the launch vehicle.

Lockheed Martin, the prime contractor for Orion, is conducting the tests at the company's Sunnyvale, Calif., facility, along with several other tests for components of Orion this summer. The actual flight hardware will be exposed to loads and pressures greater than those expected during launch.

Traveling beyond low Earth orbit requires comprehensive life support systems capable of sustaining humans for long duration missions. Orion is adaptable to multiple destinations throughout the solar system.

“Traveling to deep space is an exponentially more difficult process than flying to low Earth orbit because we have to carry everything that we need for those missions with us, and the life support systems must be robust and account for contingencies,” said Rivers. “As we travel farther away from Earth, there are more difficult challenges with radiation exposure, communications, and life support for long duration missions. We have to have emergency systems – it is significantly more complex.”

“We are blazing a trail – going to new places –doing what NASA does best.”
NASA is also developing the Space Launch System (SLS), a heavy-lift launch vehicle capable of sending humans in Orion and other payloads to deep space. Orion will first launch on SLS in 2017 on Exploration Mission-1, an uncrewed mission around the moon.

Inseparable Galactic Twins

Looking towards the constellation of Triangulum (The Triangle), in the northern sky, lies the galaxy pair MRK 1034. The two very similar galaxies, named PGC 9074 and PGC 9071, are close enough to one another to be bound together by gravity, although no gravitational disturbance can yet be seen in the image. These objects are probably only just beginning to interact gravitationally.

Both are spiral galaxies, and are presented to our eyes face-on, so we are able to appreciate their distinctive shapes. On the left of the image, spiral galaxy PGC 9074 shows a bright bulge and two spiral arms tightly wound around the nucleus, features which have led scientists to classify it as a type Sa galaxy. Close by, PGC 9071 — a type Sb galaxy — although very similar and almost the same size as its neighbor, has a fainter bulge and a slightly different structure to its arms: their coils are further apart.

The spiral arms of both objects clearly show dark patches of dust obscuring the light of the stars lying behind, mixed with bright blue clusters of hot, recently-formed stars. Older, cooler stars can be found in the glowing, compact yellowish bulge towards the center of the galaxy. The whole structure of each galaxy is surrounded by a much fainter round halo of old stars, some residing in globular clusters.

Gradually, these two neighbors will attract each other, the process of star formation will be increased and tidal forces will throw out long tails of stars and gas. Eventually, after maybe hundreds of millions of years, the structures of the interacting galaxies will merge together into a new, larger galaxy.