samedi 4 novembre 2017
Asteroid Watch logo.
November 4, 2017
An international team of astronomers led by NASA scientists successfully completed the first global exercise using a real asteroid to test global response capabilities.
Planning for the so-called "TC4 Observation Campaign" started in April, under the sponsorship of NASA's Planetary Defense Coordination Office. The exercise commenced in earnest in late July, when the European Southern Observatory's Very Large Telescope recovered the asteroid. The finale was a close approach to Earth in mid-October. The goal: to recover, track and characterize a real asteroid as a potential impactor -- and to test the International Asteroid Warning Network for hazardous asteroid observations, modeling, prediction and communication.
Animation above: Asteroid 2012 TC4 glides across a field of background stars in this animation taken on Oct. 11, 2017, by the 3.3-foot (1.0-meter) Kiso Schmidt telescope in Nagano, Japan. Animation Credits: Kiso Observatory, University of Tokyo.
The target of the exercise was asteroid 2012 TC4 -- a small asteroid originally estimated to be between 30 and 100 feet (10 and 30 meters) in size, which was known to be on a very close approach to Earth. On Oct. 12, TC4 safely passed Earth at a distance of only about 27,200 miles (43,780 kilometers) above Earth's surface. In the months leading up to the flyby, astronomers from the U.S., Canada, Colombia, Germany, Israel, Italy, Japan, the Netherlands, Russia and South Africa all tracked TC4 from ground- and space-based telescopes to study its orbit, shape, rotation and composition.
"This campaign was an excellent test of a real threat case. I learned that in many cases we are already well-prepared; communication and the openness of the community was fantastic," said Detlef Koschny, co-manager of the near-Earth object (NEO) segment in the European Space Agency (ESA)'s Space Situational Awareness program. "I personally was not prepared enough for the high response from the public and media -- I was positively surprised by that! It shows that what we are doing is relevant."
Image above: Asteroid 2012 TC4 appears as a dot at the center of this composite of 37 individual 50-second exposures obtained on Aug. 6, 2017 by the European Southern Observatory's Very Large Telescope located in the Atacama Desert region of Chile. The asteroid is marked with a circle for a better identification. The individual images have been shifted to compensate for the motion of the asteroid, so that the background stars and galaxies appear as bright trails. Image Credit: ESO.
"The 2012 TC4 campaign was a superb opportunity for researchers to demonstrate willingness and readiness to participate in serious international cooperation in addressing the potential hazard to Earth posed by NEOs," said Boris Shustov, science director for the Institute of Astronomy at the Russian Academy of Sciences. "I am pleased to see how scientists from different countries effectively and enthusiastically worked together toward a common goal, and that the Russian-Ukrainian observatory in Terskol was able to contribute to the effort." Shustov added, "In the future I am confident that such international observing campaigns will become common practice."
Using the observations collected during the campaign, scientists at NASA's Center for Near-Earth Object Studies (CNEOS) at the Jet Propulsion Laboratory in Pasadena, California were able to precisely calculate TC4's orbit, predict its flyby distance on Oct. 12, and look for any possibility of a future impact. "The high-quality observations from optical and radar telescopes have enabled us to rule out any future impacts between the Earth and 2012 TC4," said Davide Farnocchia from CNEOS, who led the orbit determination effort. "These observations also help us understand subtle effects such as solar radiation pressure that can gently nudge the orbit of small asteroids."
Image above: 2012 TC4's heliocentric orbit has changed due to the 2012 and 2017 close encounters with Earth. The cyan color shows the trajectory before the 2012 flyby, the magenta shows the trajectory after the 2012 flyby, and yellow shows the trajectory after the 2017 flyby. The orbital changes were primarily in semi-major axis and eccentricity, although there were also slight changes in the inclination. Image credits: NASA/JPL-Caltech.
A network of optical telescopes also worked together to study how fast TC4 rotates. Given that TC4 is small, astronomers expected it to be rotating fast, but were surprised when they found that TC4 was not only spinning once every 12 minutes, it was also tumbling. "The rotational campaign was a true international effort. We had astronomers from several countries working together as one team to study TC4's tumbling behavior," said Eileen Ryan, director of the Magdalena Ridge Observatory. Her team tracked TC4 for about 2 months using the 7.9-foot (2.4-meter) telescope in Socorro, New Mexico.
The observations that revealed the shape and confirmed the composition of the asteroid came from astronomers using NASA's Goldstone Deep Space Network antenna in California and the National Radio Astronomy Observatory's 330-foot (100-meter) Green Bank Telescope in West Virginia. "TC4 is a very elongated asteroid that's about 50 feet (15 meters) long and roughly 25 feet (8 meters) wide," said Marina Brozovic, a member of the asteroid radar team at JPL.
Image above: The Terksol Observatory is located in the Northern Caucasus Mountains and operated jointly by the Russian Academy of Sciences and the National Academy of Sciences of the Ukraine. The 2-meter telescope provided follow-up astrometry of asteroid 2012 TC4. Image credit: INASAN.
Finding out what TC4 is made of turned out to be more challenging. Due to adverse weather conditions, traditional NASA assets studying asteroid composition -- such as the NASA Infrared Telescope Facility (IRTF) at the Mauna Kea Observatory in Hawaii -- were unable to narrow down what TC4 was made of: either dark, carbon-rich or bright igneous material.
"Radar has the ability to identify asteroids with surfaces made of highly reflective rocky or metallic materials," said Lance Benner, who led the radar observations at JPL. "We were able to show that radar scattering properties are consistent with a bright rocky surface, similar to a particular class of meteorites that reflect as much as 50 percent of the light falling on them."
In addition to the observation campaign, NASA used this exercise to test communications between the many observers and also to test internal U.S. government messaging and communications up through the executive branch and across government agencies, as it would during an actual predicted impact emergency.
Image above: The 2.4-meter telescope facility at Magdalena Ridge Observatory provided astrometric and photometric observations for two months during the 2012 TC4 campaign. Image credits: Magdalena Ridge Observatory, New Mexico Tech.
"We demonstrated that we could organize a large, worldwide observing campaign on a short timeline, and communicate results efficiently," said Vishnu Reddy of the University of Arizona's Lunar and Planetary Laboratory in Tucson, who led the observation campaign. Michael Kelley, TC4 exercise lead at NASA Headquarters in Washington added, "We are much better prepared today to deal with the threat of a potentially hazardous asteroid than we were before the TC4 campaign."
NASA's Planetary Defense Coordination Office administers the Near-Earth Object Observations Program and is responsible for finding, tracking and characterizing potentially hazardous asteroids and comets coming near Earth, issuing warnings about possible impacts, and assisting coordination of U.S. government response planning, should there be an actual impact threat.
NASA's Planetary Defense Coordination Office: https://www.nasa.gov/planetarydefense/overview
International Asteroid Warning Network: http://iawn.net/frequently-asked-questions/
Animation (mentioned), Images (mentioned), Text, Credits: NASA/Dwayne Brown/Laurie Cantillo/JPL/DC Agle.
Publié par Orbiter.ch à 09:23
vendredi 3 novembre 2017
NASA & ESA - SOHO Mission patch / NASA - STEREO Mission logo.
Nov. 3, 2017
The ESA (European Space Agency) and NASA mission SOHO — short for Solar and Heliospheric Observatory — got a visit from an old friend this week when comet 96P entered its field of view on Oct. 25, 2017. The comet entered the lower right corner of SOHO’s view, and skirted up and around the right edge before leaving on Oct. 30. SOHO also spotted comet 96P in 1996, 2002, 2007 and 2012, making it the spacecraft’s most frequent cometary visitor.
Animation above: The comet entered the lower right corner of SOHO’s view, and skirted up and around the right edge before leaving on Oct. 30. Jupiter can be seen passing left-to-right behind the solid central disk — called an occulting disk — that blocks sunlight and allows SOHO to see the solar atmosphere, planets and comets. Animation Credits: ESA/NASA’s Goddard Space Flight Center/SOHO/NRL/Karl Battams/Joy Ng.
At the same time, comet 96P passed through a second NASA mission’s view: STEREO — short for Solar and Terrestrial Relations Observatory — also watched the comet between Oct. 26-28, from the opposite side of Earth’s orbit. It is extremely rare for comets to be seen simultaneously from two different locations in space, and these are the most comprehensive parallel observations of comet 96P yet. Scientists are eager to use these combined observations to learn more about the comet’s composition, as well as its interaction with the solar wind, the constant flow of charged particles from the Sun.
Animation above: The comet entered the bottom of STEREO’s view and crossed it diagonally before leaving on Oct. 28. Most of the corona has been suppressed in order to bring out the comet, leaving only the dynamic flow of the solar wind. Animation Credits: NASA’s Goddard Space Flight Center/STEREO/Bill Thompson/Joy Ng.
Both missions gathered polarization measurements of the comet; these are measurements of sunlight in which all the light waves become oriented the same way after passing through a medium — in this case, particles in the tail of the comet. By pooling the polarization data together, scientists can extract details on the particles that the light passed through.
“Polarization is a strong function of the viewing geometry, and getting multiple measurements at the same time could potentially give useful information about the composition and size distribution of the tail particles,” said William Thompson, STEREO chief observer at NASA’s Goddard Space Flight Center in Greenbelt, Maryland.
Comet 96P — also known as comet Machholz, for amateur astronomer Dan Machholz’s 1986 discovery of the comet — completes an orbit around the Sun every 5.24 years. It makes its closest approach to the Sun at a toasty 11 million miles — a very close distance for a comet.
When comet 96P appeared in SOHO’s view in 2012, amateur astronomers studying the SOHO data discovered two tiny comet fragments some distance ahead of the main body, signaling the comet was actively changing. This time around they have detected a third fragment — another breadcrumb in the trail that indicates the comet is still evolving.
Image above: Observations of a third fragment indicate comet 96P is still evolving. Image Credits: ESA/NASA’s Goddard Space Flight Center/SOHO/Steele Hill.
Scientists find comet 96P interesting because it has an unusual composition and is the parent of a large, diverse family, referring to a group of comets sharing a common orbit and originating from a much larger parent comet that over millennia, broke up into smaller fragments. Comet 96P is the parent of two separate comet groups, both of which were discovered by citizen scientists studying SOHO data, as well as a number of Earth-crossing meteor streams. By studying the comet’s ongoing evolution, scientists can learn more about the nature and origins of this complex family.
NASA's SOHO (Solar and Heliospheric Observatory): http://www.nasa.gov/mission_pages/soho/index.html
ESA's SOHO (Solar and Heliospheric Observatory): http://sci.esa.int/soho/
STEREO (Solar TErrestrial RElations Observatory): http://www.nasa.gov/mission_pages/stereo/main/index.html
Animations (mentioned), Image (mentioned), Text, Credits: NASA/Rob Garner/Goddard Space Flight Center, by Lina Tran.
Publié par Orbiter.ch à 15:21
NASA / Orbital ATK - OA-8 Commercial Resupply Services patch.
Nov. 3, 2017
Image above: NASA will host a media teleconference to discuss select science investigations and technology demonstrations launching on the next Orbital ATK commercial resupply flight to the International Space Station. Image Credit: NASA.
Orbital ATK will launch its Cygnus spacecraft into orbit to the International Space Station, targeted for November 11, 2017, from Wallops Flight Facility in Virginia. Cygnus will launch on an Antares rocket carrying crew supplies, equipment and scientific research to crewmembers aboard the station. The spacecraft, named the S.S. Gene Cernan after former NASA astronaut Eugene “Gene” Cernan, who is the last person to have walked on the moon, will deliver scientific investigations including those that will study communication and navigation, microbiology, animal biology and plant biology.
Here are some highlights of research that will be delivered to the station:
Investigation tests bacterial antibiotic resistance in microgravity
Antibiotic resistance could pose a danger to astronauts, especially since microgravity has been shown to weaken human immune response. E. coli AntiMicrobial Satellite (EcAMSat) will study microgravity’s effect on bacterial antibiotic resistance. The experiment will expose two strains of E. coli, one with a resistance gene, the other without, to three different doses of antibiotics, then examine the viability of each group. Results from this investigation could contribute to determining appropriate antibiotic dosages to protect astronaut health during long-duration human spaceflight and help us understand how antibiotic effectiveness may change as a function of stress on Earth.
Image above: EcAMSAT, undergoes thermal vacuum power management testing at NASA Ames. The test simulates the thermal vacuum and power environment of space and is an element of the spacecraft's flight validation testing program. Image Credit: NASA.
CubeSat used as a laser communication technology testbed
Traditional laser communication systems use transmitters that are far too large for small spacecraft. The Optical Communication Sensor Demonstration (OCSD) tests the functionality of laser-based communications using CubeSats that provide a compact version of the technology. Results from OCSD could lead to significantly enhanced communication speeds between space and Earth and a better understanding of laser communication between small satellites in low-Earth orbit.
Image above: The Optical Communications and Sensor Demonstration (OCSD) project uses CubeSats to test new types of technology in Earth's orbit. This work was funded by NASA’s Small Spacecraft Technology Program under the Space Technology Mission Directorate. Image Credits: NASA/Ames Research Center.
Hybrid solar antenna seeks solution to long distance communications in space
As space exploration increases, so will the need for improved power and communication technologies. The Integrated Solar Array and Reflectarray Antenna (ISARA), a hybrid solar power panel and communication solar antenna that can send and receive messages, tests the use of this technology in CubeSat-based environmental monitoring. ISARA may provide a solution for sending and receiving information to and from faraway destinations, both on Earth and in space.
Nitrogen fixation process tested in microgravity environment
The Biological Nitrogen Fixation in Microgravity via Rhizobium-Legume Symbiosis (Biological Nitrogen Fixation) investigation examines how low-gravity conditions affect the nitrogen fixation process of Microclover, a resilient and drought tolerant legume. The nitrogen fixation process, a process by which nitrogen in the atmosphere is converted into a usable form for living organisms, is a crucial element of any ecosystem necessary for most types of plant growth. This investigation could provide information on the space viability of the legume’s ability to use and recycle nutrients and give researchers a better understanding of this plant’s potential uses on Earth.
Life cycle of alternative protein source studied
Mealworms are high in nutrients and one of the most common sources of alternative protein in developing countries. The Effects of Microgravity on the Life Cycle of Tenebrio Molitor (Tenebrio Molitor) investigation studies how the microgravity environment affects the mealworm life cycle. In addition to alternative protein research, this investigation will provide information about animal growth under unique conditions.
Investigation studies advances in plant and crop growth in space
The Life Cycle of Arabidopsis thaliana in Microgravity investigation studies the formation and functionality of the Arabidopsis thaliana, a mustard plant with a well-known genome that makes it ideal for research, in microgravity conditions. The results from this investigation will contribute to an understanding of plant and crop growth in space, a vital aspect to long-term spaceflight missions.
The Biological Nitrogen Fixation and Tenebrio Molitor are student investigations in the Go for Launch! - Higher Orbits program and sponsored by Space Tango and the ISS National Lab, which is managed by the Center for the Advancement of Science in Space (CASIS). The Arabidopsis thaliana investigation, also a student investigation, is a part of the Magnitude.io program, sponsored by Space Tango and CASIS.
OA-8 marks Orbital ATK’s eighth cargo delivery mission to the space station, and the research on board will join many other investigations currently happening aboard the orbiting laboratory. Follow https://twitter.com/ISS_Research for more information about the science happening on station.
E. coli AntiMicrobial Satellite (EcAMSat): http://www.nasa.gov/centers/ames/engineering/projects/ecamsat
Optical Communication Sensor Demonstration (OCSD): http://www.nasa.gov/directorates/spacetech/small_spacecraft/ocsd_project.html
Solar Array and Reflectarray Antenna (ISARA): http://www.jpl.nasa.gov/cubesat/isara.php
Biological Nitrogen Fixation in Microgravity via Rhizobium-Legume Symbiosis (Biological Nitrogen Fixation): http://www.nasa.gov/mission_pages/station/research/experiments/2717.html
Tenebrio Molitor (Tenebrio Molitor): http://www.nasa.gov/mission_pages/station/research/experiments/2718.html
Life Cycle of Arabidopsis thaliana in Microgravity: https://www.nasa.gov/mission_pages/station/research/experiments/2719.html
Go for Launch! - Higher Orbits program: http://higherorbits.org/
Space Tango: http://www.spacetango.com/
Center for the Advancement of Science in Space (CASIS): http://www.iss-casis.org/
Commercial Resupply: http://www.nasa.gov/mission_pages/station/structure/launch/index.html
Space Station Research and Technology: https://www.nasa.gov/mission_pages/station/research/index.html
International Space Station (ISS): https://www.nasa.gov/mission_pages/station/main/index.html
Images (mentioned), Text, Credits: NASA/Michael Johnson/JSC/International Space Station Program Science Office/Jenny Howard.
Best regards, Orbiter.ch
Publié par Orbiter.ch à 14:59
ALMA - Atacama Large Millimeter/submillimeter Array logo.
3 November 2017
Artist’s impression of the dust belts around Proxima Centauri
The ALMA Observatory in Chile has detected dust around the closest star to the Solar System, Proxima Centauri. These new observations reveal the glow coming from cold dust in a region between one to four times as far from Proxima Centauri as the Earth is from the Sun. The data also hint at the presence of an even cooler outer dust belt and may indicate the presence of an elaborate planetary system. These structures are similar to the much larger belts in the Solar System and are also expected to be made from particles of rock and ice that failed to form planets.
Proxima Centauri is the closest star to the Sun. It is a faint red dwarf lying just four light-years away in the southern constellation of Centaurus (The Centaur). It is orbited by the Earth-sized temperate world Proxima b, discovered in 2016 and the closest planet to the Solar System. But there is more to this system than just a single planet. The new ALMA observations reveal emission from clouds of cold cosmic dust surrounding the star.
Proxima Centauri in the southern constellation of Centaurus
The lead author of the new study, Guillem Anglada , from the Instituto de Astrofísica de Andalucía (CSIC), Granada, Spain, explains the significance of this find: “The dust around Proxima is important because, following the discovery of the terrestrial planet Proxima b, it’s the first indication of the presence of an elaborate planetary system, and not just a single planet, around the star closest to our Sun.”
Dust belts are the remains of material that did not form into larger bodies such as planets. The particles of rock and ice in these belts vary in size from the tiniest dust grain, smaller than a millimetre across, up to asteroid-like bodies many kilometres in diameter .
The location of Proxima Centauri in the southern skies
Dust appears to lie in a belt that extends a few hundred million kilometres from Proxima Centauri and has a total mass of about one hundredth of the Earth’s mass. This belt is estimated to have a temperature of about –230 degrees Celsius, as cold as that of the Kuiper Belt in the outer Solar System.
There are also hints in the ALMA data of another belt of even colder dust about ten times further out. If confirmed, the nature of an outer belt is intriguing, given its very cold environment far from a star that is cooler and fainter than the Sun. Both belts are much further from Proxima Centauri than the planet Proxima b, which orbits at just four million kilometres from its parent star .
The sky around Alpha Centauri and Proxima Centauri (annotated)
Guillem Anglada explains the implications of the discovery: “This result suggests that Proxima Centauri may have a multiple planet system with a rich history of interactions that resulted in the formation of a dust belt. Further study may also provide information that might point to the locations of as yet unidentified additional planets.”
Proxima Centauri's planetary system is also particularly interesting because there are plans — the Starshot project — for future direct exploration of the system with microprobes attached to laser-driven sails. A knowledge of the dust environment around the star is essential for planning such a mission.
Artist’s impression of the dust belts around Proxima Centauri
Co-author Pedro Amado, also from the Instituto de Astrofísica de Andalucía, explains that this observation is just the start: “These first results show that ALMA can detect dust structures orbiting around Proxima. Further observations will give us a more detailed picture of Proxima's planetary system. In combination with the study of protoplanetary discs around young stars, many of the details of the processes that led to the formation of the Earth and the Solar System about 4600 million years ago will be unveiled. What we are seeing now is just the appetiser compared to what is coming!”
 In a cosmic coincidence, the lead author of the study, Guillem Anglada shares his name with the astronomer who led the team that discovered Proxima Centauri b, Guillem Anglada-Escudé, himself a co-author of the paper in which this research is published, although the two are not related.
 Proxima Centauri is quite an old star, of similar age to the Solar System. The dusty belts around it are probably similar to the residual dust in the Kuiper Belt and the asteroid belt in the Solar System and the dust that creates the Zodiacal Light. The spectacular discs that ALMA has imaged around much younger stars, such as HL Tauri, contain much more material that is in the process of forming planets.
 The apparent shape of the very faint outer belt, if confirmed, would give astronomers a way to estimate the inclination of the Proxima Centauri planetary system. It would appear elliptical due to the tilt of what is assumed to be in reality a circular ring. This would in turn allow a better determination of the mass of the Proxima b planet, which is currently known only as a lower limit.
This research was presented in a paper entitled “ALMA Discovery of Dust Belts Around Proxima Centauri”, by Guillem Anglada et al., to appear in Astrophysical Journal Letters.
The team is composed of Guillem Anglada (Instituto de Astrofísica de Andalucía (CSIC), Granada, Spain [IAA-CSIC]), Pedro J. Amado (IAA-CSIC), Jose L. Ortiz (IAA-CSIC), José F. Gómez (IAA-CSIC), Enrique Macías (Boston University, Massachusetts, USA), Antxon Alberdi (IAA-CSIC), Mayra Osorio (IAA-CSIC), José L. Gómez (IAA-CSIC), Itziar de Gregorio-Monsalvo (ESO, Santiago, Chile; Joint ALMA Observatory, Santiago, Chile), Miguel A. Pérez-Torres (IAA-CSIC; Universidad de Zaragoza, Zaragoza, Spain), Guillem Anglada-Escudé (Queen Mary University of London, London, United Kingdom), Zaira M. Berdiñas (Universidad de Chile, Santiago, Chile; IAA-CSIC), James S. Jenkins (Universidad de Chile, Santiago, Chile), Izaskun Jimenez-Serra (Queen Mary University of London, London, United Kingdom), Luisa M. Lara (IAA-CSIC), Maria J. López-González (IAA-CSIC), Manuel López-Puertas (IAA-CSIC), Nicolas Morales (IAA-CSIC), Ignasi Ribas (Institut de Ciències de l’Espai (IEEC-CSIC), Bellaterra, Spain), Anita M. S. Richards (JBCA, University of Manchester, Manchester, United Kingdom), Cristina Rodríguez-López (IAA-CSIC) and Eloy Rodríguez (IAA-CSIC).
ESO is the foremost intergovernmental astronomy organisation in Europe and the world’s most productive ground-based astronomical observatory by far. It is supported by 16 countries: Austria, Belgium, Brazil, the Czech Republic, Denmark, France, Finland, Germany, Italy, the Netherlands, Poland, Portugal, Spain, Sweden, Switzerland and the United Kingdom, along with the host state of Chile and by Australia as a strategic partner. ESO carries out an ambitious programme focused on the design, construction and operation of powerful ground-based observing facilities enabling astronomers to make important scientific discoveries. ESO also plays a leading role in promoting and organising cooperation in astronomical research. ESO operates three unique world-class observing sites in Chile: La Silla, Paranal and Chajnantor. At Paranal, ESO operates the Very Large Telescope and its world-leading Very Large Telescope Interferometer as well as two survey telescopes, VISTA working in the infrared and the visible-light VLT Survey Telescope. ESO is also a major partner in two facilities on Chajnantor, APEX and ALMA, the largest astronomical project in existence. And on Cerro Armazones, close to Paranal, ESO is building the 39-metre Extremely Large Telescope, the ELT, which will become “the world’s biggest eye on the sky”.
ESOcast 136 Light: ALMA Discovers Cold Dust Around Nearest Star: http://www.eso.org/public/videos/eso1735a/
Starshot project: https://breakthroughinitiatives.org/Initiative/3
Research paper: https://www.eso.org/public/archives/releases/sciencepapers/eso1735/eso1735a.pdf
Photos of ALMA: http://eso.org/public/images/archive/category/alma/
Press release about Proxima b discovery: http://www.eso.org/public/news/eso1629/
Images, Text, Credits: ESO/Richard Hook/M. Kornmesser/ALMA/Itziar de Gregorio-Monsalvo/Boston University/Enrique Macias/Instituto de Astrofísica de Andalucía (CSIC)/Antxon Alberdi/Pedro J. Amado/Guillem Anglada/IAU and Sky & Telescope/ESA/NASA/M. Zamani/Digitized Sky Survey 2/Acknowledgement: Davide De Martin/Mahdi Zamani/Video: ESO/M. Kornmesser.
Best regards, Orbiter.ch
Publié par Orbiter.ch à 14:06
jeudi 2 novembre 2017
NASA - EOS Aura Mission patch / NASA-NOAA Suomi NPP Mission logo.
Nov. 2, 2017
Measurements from satellites this year showed the hole in Earth’s ozone layer that forms over Antarctica each September was the smallest observed since 1988, scientists from NASA and NOAA announced today.
Warm Winter Air Makes for a Small Ozone Hole
Video above: This year’s ozone hole was similar in area to the hole in 1988, about 1 million miles smaller than in 2016. Although scientists predict the ozone hole will continue to shrink, this year’s smaller ozone hole had more to do with weather conditions than human intervention. Image Credits: NASA's Goddard Space Flight Center/Kathryn Mersmann.
According to NASA, the ozone hole reached its peak extent on Sept. 11, covering an area about two and a half times the size of the United States – 7.6 million square miles in extent - and then declined through the remainder of September and into October. NOAA ground- and balloon-based measurements also showed the least amount of ozone depletion above the continent during the peak of the ozone depletion cycle since 1988. NOAA and NASA collaborate to monitor the growth and recovery of the ozone hole every year.
“The Antarctic ozone hole was exceptionally weak this year,” said Paul A. Newman, chief scientist for Earth Sciences at NASA's Goddard Space Flight Center in Greenbelt, Maryland. “This is what we would expect to see given the weather conditions in the Antarctic stratosphere.”
The smaller ozone hole in 2017 was strongly influenced by an unstable and warmer Antarctic vortex – the stratospheric low pressure system that rotates clockwise in the atmosphere above Antarctica. This helped minimize polar stratospheric cloud formation in the lower stratosphere. The formation and persistence of these clouds are important first steps leading to the chlorine- and bromine-catalyzed reactions that destroy ozone, scientists said. These Antarctic conditions resemble those found in the Arctic, where ozone depletion is much less severe.
In 2016, warmer stratospheric temperatures also constrained the growth of the ozone hole. Last year, the ozone hole reached a maximum 8.9 million square miles, 2 million square miles less than in 2015. The average area of these daily ozone hole maximums observed since 1991 has been roughly 10 million square miles.
Although warmer-than-average stratospheric weather conditions have reduced ozone depletion during the past two years, the current ozone hole area is still large because levels of ozone-depleting substances like chlorine and bromine remain high enough to produce significant ozone loss.
Animation above: Ozone depletion occurs in cold temperatures, so the ozone hole reaches its annual maximum in September or October, at the end of winter in the Southern Hemisphere. Animation Credits: NASA/NASA Ozone Watch/Katy Mersmann.
Scientists said the smaller ozone hole extent in 2016 and 2017 is due to natural variability and not a signal of rapid healing.
First detected in 1985, the Antarctic ozone hole forms during the Southern Hemisphere’s late winter as the returning sun’s rays catalyze reactions involving man-made, chemically active forms of chlorine and bromine. These reactions destroy ozone molecules.
Thirty years ago, the international community signed the Montreal Protocol on Substances that Deplete the Ozone Layer and began regulating ozone-depleting compounds. The ozone hole over Antarctica is expected to gradually become less severe as chlorofluorocarbons—chlorine-containing synthetic compounds once frequently used as refrigerants – continue to decline. Scientists expect the Antarctic ozone hole to recover back to 1980 levels around 2070.
Ozone is a molecule comprised of three oxygen atoms that occurs naturally in small amounts. In the stratosphere, roughly 7 to 25 miles above Earth’s surface, the ozone layer acts like sunscreen, shielding the planet from potentially harmful ultraviolet radiation that can cause skin cancer and cataracts, suppress immune systems and also damage plants. Closer to the ground, ozone can also be created by photochemical reactions between the sun and pollution from vehicle emissions and other sources, forming harmful smog.
Although warmer-than-average stratospheric weather conditions have reduced ozone depletion during the past two years, the current ozone hole area is still large compared to the 1980s, when the depletion of the ozone layer above Antarctica was first detected. This is because levels of ozone-depleting substances like chlorine and bromine remain high enough to produce significant ozone loss.
Image above: At its peak on Sept. 11, 2016, the ozone hole extended across an area nearly two and a half times the size of the continental United States. The purple and blue colors are areas with the least ozone. Image Credits: NASA/NASA Ozone Watch/Katy Mersmann.
NASA and NOAA monitor the ozone hole via three complementary instrumental methods. Satellites, like NASA’s Aura satellite and NASA-NOAA Suomi National Polar-orbiting Partnership satellite measure ozone from space. The Aura satellite’s Microwave Limb Sounder also measures certain chlorine-containing gases, providing estimates of total chlorine levels.
NOAA scientists monitor the thickness of the ozone layer and its vertical distribution above the South Pole station by regularly releasing weather balloons carrying ozone-measuring “sondes” up to 21 miles in altitude, and with a ground-based instrument called a Dobson spectrophotometer.
The Dobson spectrophotometer measures the total amount of ozone in a column extending from Earth’s surface to the edge of space in Dobson Units, defined as the number of ozone molecules that would be required to create a layer of pure ozone 0.01 millimeters thick at a temperature of 32 degrees Fahrenheit at an atmospheric pressure equivalent to Earth’s surface.
This year, the ozone concentration reached a minimum over the South Pole of 136 Dobson Units on September 25— the highest minimum seen since 1988. During the 1960s, before the Antarctic ozone hole occurred, average ozone concentrations above the South Pole ranged from 250 to 350 Dobson units. Earth's ozone layer averages 300 to 500 Dobson units, which is equivalent to about 3 millimeters, or about the same as two pennies stacked one on top of the other.
"In the past, we've always seen ozone at some stratospheric altitudes go to zero by the end of September," said Bryan Johnson, NOAA atmospheric chemist. "This year our balloon measurements showed the ozone loss rate stalled by the middle of September and ozone levels never reached zero."
NASA’s Aura satellite: https://aura.gsfc.nasa.gov/
Aura satellite’s Microwave Limb Sounder: http://mls.jpl.nasa.gov/
NASA-NOAA Suomi National Polar-orbiting Partnership satellite: http://www.nasa.gov/mission_pages/NPP/main/index.html
Dobson spectrophotometer: http://www.ozonelayer.noaa.gov/action/dobson.htm
Animation (mentioned), Image (mentioned), Video (mentioned), Text, Credits: NASA/Sara Blumberg/Earth Science News Team/Katy Mersmann/NOAA Office of Oceanic and Atmospheric Research/Theo Stein.
Publié par Orbiter.ch à 18:11
NASA - Hubble Space Telescope patch.
Nov. 2, 2017
Like rude relatives who jump in front of your vacation snapshots of landscapes, some of our solar system's asteroids have photobombed deep images of the universe taken by NASA's Hubble Space Telescope. These asteroids reside, on average, only about 160 million miles from Earth — right around the corner in astronomical terms. Yet they've horned their way into this picture of thousands of galaxies scattered across space and time at inconceivably farther distances.
This Hubble photo of a random patch of sky is part of a survey called Frontier Fields. The colorful image contains thousands of galaxies, including massive yellowish ellipticals and majestic blue spirals. Much smaller, fragmentary blue galaxies are sprinkled throughout the field. The reddest objects are most likely the farthest galaxies, whose light has been stretched into the red part of the spectrum by the expansion of space.
Image above: This Hubble photo of a random patch of sky is part of a survey called Frontier Fields. It contains thousands of galaxies, including massive yellowish ellipticals and majestic blue spirals. Much smaller, fragmentary blue galaxies are sprinkled throughout the field. The reddest objects are most likely the farthest galaxies. Asteroid trails appear as curved or S-shaped streaks. Asteroids appear in multiple Hubble exposures that have been combined into one image. Of the 20 total asteroid sightings for this field, seven are unique objects. Image Credits: NASA, ESA, and B. Sunnquist and J. Mack (STScI).
Intruding across the picture are asteroid trails that appear as curved or S-shaped streaks. Rather than leaving one long trail, the asteroids appear in multiple Hubble exposures that have been combined into one image. Of the 20 total asteroid sightings for this field, seven are unique objects. Of these seven asteroids, only two were earlier identified. The others were too faint to be seen previously.
The trails look curved due to an observational effect called parallax. As Hubble orbits around Earth, an asteroid will appear to move along an arc with respect to the vastly more distant background stars and galaxies.
Hubble Space Telescope (HST). Animation Credits: NASA/ESA
This parallax effect is somewhat similar to the effect you see from a moving car, in which trees by the side of the road appear to be passing by much more rapidly than background objects at much larger distances. The motion of Earth around the Sun, and the motion of the asteroids along their orbits, are other contributing factors to the apparent skewing of asteroid paths.
All the asteroids were found manually, the majority by "blinking" consecutive exposures to capture apparent asteroid motion. Astronomers found a unique asteroid for every 10 to 20 hours of exposure time.
Image above: Galaxy cluster Abell 370 contains several hundred galaxies tied together by the mutual pull of gravity. It is located approximately 4 billion light-years away in the constellation Cetus, the Sea Monster. The thin, white trails that look like curved or S-shaped streaks are from asteroids that reside, on average, only about 160 million miles from Earth. The trails appear in multiple Hubble exposures that have been combined into one image. Of the 22 total asteroid sightings for this field, five are unique objects. These asteroids are so faint that they were not previously identified. Image Credits: NASA, ESA, and STScI.
The Frontier Fields program is a collaboration among NASA's Great Observatories and other telescopes to study six massive galaxy clusters and their effects. Using a different camera, pointing in a slightly different direction, Hubble photographed six so-called "parallel fields" at the same time it photographed the massive galaxy clusters. This maximized Hubble's observational efficiency in doing deep space exposures. These parallel fields are similar in depth to the famous Hubble Deep Field, and include galaxies about four-billion times fainter than can be seen by the human eye.
This picture is of the parallel field for the galaxy cluster Abell 370. It was assembled from images taken in visible and infrared light. The field's position on the sky is near the ecliptic, the plane of our solar system. This is the zone in which most asteroids reside, which is why Hubble astronomers saw so many crossings. Hubble deep-sky observations taken along a line-of-sight near the plane of our solar system commonly record asteroid trails.
The Hubble Space Telescope is a project of international cooperation between NASA and ESA (European Space Agency). NASA's Goddard Space Flight Center in Greenbelt, Maryland, manages the telescope. The Space Telescope Science Institute (STScI) in Baltimore conducts Hubble science operations. STScI is operated for NASA by the Association of Universities for Research in Astronomy, Inc., in Washington, D.C.
For additional imagery, visit: http://hubblesite.org/news_release/news/2017-33
For more information about Hubble, visit: http://www.nasa.gov/hubble or http://hubblesite.org/
For the Hubble Frontier Fields Program, visit: http://www.frontierfields.org/
Animation (mentioned), Images (mentioned), Text, Credits: NASA/Karl Hille/Space Telescope Science Institute/Ann Jenkins/Ray Villard.
Best regards, Orbiter.ch
Publié par Orbiter.ch à 16:39
NASA - JUNO Mission logo.
Nov. 2, 2017
Data returned Tuesday, Oct. 31, indicate that NASA’s Juno spacecraft successfully completed its eighth science flyby over Jupiter's mysterious cloud tops on Tuesday, Oct. 24. The confirmation was delayed by several days due to solar conjunction at Jupiter, which affected communications during the days prior to and after the flyby.
Image above: This illustration depicts NASA's Juno spacecraft soaring over Jupiter’s south pole. Image Credits: NASA/JPL-Caltech.
Solar conjunction is the period when the path of communication between Earth and Jupiter comes into close proximity with the Sun. During solar conjunction, no attempts are made to send new instructions or receive information from Juno, as it is impossible to predict what information might be corrupted due to interference from charged particles from the Sun. Instead, a transmission moratorium is put into place; engineers send instructions prior to the start of solar conjunction and store data on board for transmission back to Earth following the event.
“All the science collected during the flyby was carried in Juno’s memory until yesterday, when Jupiter came out of solar conjunction,” said the new Juno project manager, Ed Hirst, from NASA’s Jet Propulsion Laboratory in Pasadena, California. “All science instruments and the spacecraft's JunoCam were operating, and the new data are now being transmitted to Earth and being delivered into the hands of our science team.”
Hirst has worked on Juno since its preliminary design phase, through launch in 2011 and arrival at Jupiter in 2016. He previously worked on NASA’s Galileo, Stardust and Genesis missions. Born in Guatemala City, Guatemala, he earned a B.S. in Aerospace Engineering from the University of Texas at Austin and joined JPL in 1993. Hirst succeeds Rick Nybakken, who was recently appointed deputy director for JPL’s Office of Safety and Mission Success.
“We couldn’t be happier for Rick and know he will continue to do great things to further NASA’s leadership in space exploration,” said Scott Bolton, Juno’s principal investigator from the Southwest Research Institute in San Antonio. “Similarly, we are pleased with Ed’s promotion to project manager. He has been a critical part of Juno for many years and we know he’ll hit the ground running.”
Image above: Juno’s new project manager is Ed Hirst of NASA's Jet Propulsion Laboratory, Pasadena, California. Image Credits: NASA/JPL-Caltech.
Juno's next close flyby of Jupiter will occur on Dec. 16.
“There is no more exciting place to be than in orbit around Jupiter and no team I’d rather be with than the Juno team,” said Hirst. “Our spacecraft is in great shape, and the team is looking forward to many more flybys of the solar system’s largest planet.”
Juno launched on Aug. 5, 2011, from Cape Canaveral, Florida, and arrived in orbit around Jupiter on July 4, 2016. During its mission of exploration, Juno soars low over the planet's cloud tops -- as close as about 2,100 miles (3,400 kilometers). During these flybys, Juno is probing beneath the obscuring cloud cover of Jupiter and studying its auroras to learn more about the planet's origins, structure, atmosphere and magnetosphere.
JPL manages the Juno mission for the principal investigator, Scott Bolton, of Southwest Research Institute in San Antonio. The Juno mission is part of the New Frontiers Program managed by NASA's Marshall Space Flight Center in Huntsville, Alabama, for the Science Mission Directorate. Lockheed Martin Space Systems, Denver, built the spacecraft. JPL is a division of Caltech in Pasadena, California.
More information on the Juno mission is available at:
The public can follow the mission on Facebook and Twitter at:
Images (mentioned), Text, Credits: NASA/Dwayne Brown/Laurie Cantillo/Tony Greicius/JPL/DC Agle.
Publié par Orbiter.ch à 16:20
NASA - Spitzer Space Telescope patch.
November 2, 2017
Image above: Artist concept of an exoplanet and debris disk orbiting a polluted white dwarf. Image Credits: NASA/JPL-Caltech.
Beneath an elegant office building with a Spanish-style red tiled roof in Pasadena, California, three timeworn storerooms safeguard more than a century of astronomy. Down the stairs and to the right is a basement of wonder. There are countless wooden drawers and boxes, stacked floor to ceiling, with telescope plates, sunspot drawings and other records. A faint ammonia-like smell, reminiscent of old film, fills the air.
Image above: A storeroom at Carnegie Observatories in Pasadena, California, holding archives from the Mount Wilson telescopes and other astronomical records. Image Credits: NASA/JPL-Caltech.
Guarding one storeroom is a short black door with a sign saying "This door to be kept closed."
Image above: The door to a storeroom at Carnegie Observatories. Image Credits: NASA/JPL-Caltech.
Carnegie Observatories hosts 250,000 photographic plates taken at Mount Wilson, Palomar and Las Campanas observatories, spanning more than 100 years. In their heydays, the Mount Wilson 60-inch and 100-inch telescopes -- the bigger saw its first light on Nov. 1, 1917 -- were the most powerful instruments of their kind. Each indelibly changed humanity's understanding of our place in the cosmos. But these technological marvels were ahead of their time -- in one case, capturing signs of distant worlds that wouldn't be recognized for a century.
Image above: The Mount Wilson 60-inch and 100-inch telescopes. Image Credits: Image courtesy of the Observatories of the Carnegie Institution for Science Collection at the Huntington Library.
Mount Wilson is the site where some of the key discoveries about our galaxy and universe were made in the early 20th century. This is where Edwin Hubble realized that the Milky Way cannot be the extent of our universe, because Andromeda (or M31) is farther away than the most distant reaches of our galaxy. The photographic plate from the 100-inch Hooker Telescope from 1923, which captured this monumental realization, is blown up as a huge poster outside the Carnegie storerooms.
Image above: The plate showing Andromeda (or M31) must be a different galaxy. Image Credits: Carnegie Observatories.
Hubble and Milton Humason, whose Mount Wilson career began as a janitor, worked together to explore the expanding nature of the universe. Using the legendary telescopes, as well as data from Lowell Observatory in Flagstaff, Arizona, they recognized that clusters of galaxies are traveling away from each other -- and the more distant galaxies move away from each other at greater speeds.
Image above: Edwin Hubble. Image Credits: Image courtesy of the Observatories of the Carnegie Institution for Science Collection at the Huntington Library.
Image above: Milton Humason. Image Credits: Image courtesy of the Observatories of the Carnegie Institution for Science Collection at the Huntington Library.
But there is a far lesser known, 100-year-old discovery from Mount Wilson, one that was unidentified and unappreciated until recently. It's actually: The first evidence of exoplanets.
A detective story
It started with Ben Zuckerman, professor emeritus of astronomy at the University of California, Los Angeles. He was preparing a talk about the compositions of planets and smaller rocky bodies outside our solar system for a July 2014 symposium at the invitation of Jay Farihi, whom he had helped supervise when Farihi was a graduate student at UCLA. Farihi had suggested that Zuckerman talk about the pollution of white dwarfs, which are faint, dead stars composed of mainly hydrogen and helium. By "pollution," astronomers mean heavy elements invading the photospheres -- the outer atmospheres -- of these stars. The thing is, all those extra elements shouldn't be there -- the strong gravity of the white dwarf should pull the elements into the star's interior, and out of sight.
The first polluted white dwarf identified is called van Maanen's Star (or "van Maanen 2" in the scientific literature), after its discoverer Adriaan van Maanen. Van Maanen found this object in 1917 by spotting its subtle motion relative to other stars between 1914 and 1917. Astronomer Walter Sydney Adams, who would later become director of Mount Wilson, captured the spectrum -- a chemical fingerprint -- of van Maanen's Star on a small glass plate using Mount Wilson's 60-inch telescope. Adams interpreted the spectrum to be of an F-type star, presumably based on the presence and strength of calcium and other heavy-element absorption features, with a temperature somewhat higher than our Sun. In 1919, van Maanen called it a "very faint star."
Today, we know that van Maanen's Star, which is about 14 light-years away, is the closest white dwarf to Earth that is not part of a binary system.
"This star is an icon," Farihi said recently. "It is the first of its type. It's really the proto-prototype."
While preparing his talk, Zuckerman had what he later called a "true 'eureka' moment." Van Maanen's Star, unbeknownst to the astronomers who studied it in 1917 and those who thought about it for decades after, must be the first observational evidence that exoplanets exist.
What does this have to do with exoplanets?
Heavy elements in the star's outermost layer could not have been produced inside the star, because they would immediately sink due to the white dwarf's intense gravitational field. As more white dwarfs with heavy elements in their photospheres were discovered in the 20th century, scientists came to believe that the exotic materials must have come from the interstellar medium -- in other words, elements floating in the space between the stars.
But in 1987, more than 70 years after the Mount Wilson spectrum of van Maanen's Star, Zuckerman and his colleague Eric Becklin reported an excess of infrared light around a white dwarf, which they thought might come from a faint "failed star" called a brown dwarf. This was, in 1990, interpreted to be a hot, dusty disk orbiting a white dwarf. By the early 2000s, a new theory of polluted white dwarfs had emerged: Exoplanets could push small rocky bodies toward the star, whose powerful gravity would pulverize them into dust. That dust, containing heavy elements from the torn-apart body, would then fall on the star.
"The bottom line is: if you're an asteroid or comet, you can't just change your address. You need something to move you," Farihi said. "By far, the greatest candidates are planets to do that."
NASA's Spitzer Space Telescope has been instrumental in expanding the field of polluted white dwarfs orbited by hot, dusty disks. Since launch in 2004, Spitzer has confirmed about 40 of these special stars. Another space telescope, NASA's Wide-field Infrared Survey Explorer, also detected a handful, bringing the total up to about four dozen known today. Because these objects are so faint, infrared light is crucial to identifying them.
"We can't measure the exact amount of infrared light coming from these objects using telescopes on the ground," Farihi said. "Spitzer, specifically, just burst this wide open."
Image above: NASA's Spitzer Space Telescope. Image Credits: NASA/JPL-Caltech.
Supporting the new "dusty disk" theory of pulled white dwarfs, in 2007, Zuckerman and colleagues published observations of a white dwarf atmosphere with 17 elements -- materials similar to those found in the Earth-Moon system. (The late UCLA professor Michael Jura, who made crucial contributions to the study of polluted white dwarfs, was part of this team.) This was further evidence that at least one small, rocky body -- or even a planet -- had been torn apart by the gravity of a white dwarf. Scientists now generally agree that a single white dwarf star with heavy elements in its spectrum likely has at least one rocky debris belt -- the remnants of bodies that collided violently and never formed planets -- and probably at least one major planet.
So, heavy elements that happened to be floating in the interstellar medium could not account for the observations. "About 90 years after van Maanen's discovery, astronomers said, 'Whoa, this interstellar accretion model can't possibly be right,'" Zuckerman said.
Chasing the spectrum
Inspired by Zuckerman, Farihi became enamored with the idea that someone had taken a spectrum with the first evidence of exoplanets in 1917, and that a record must exist of that observation. "I got my teeth in the question and I wouldn't let go," he said.
Farihi reached out to the Carnegie Observatories, which owns the Mount Wilson telescopes and safeguards their archives. Carnegie Director John Mulchaey put volunteer Dan Kohne on the case. Kohne dug through the archives and, two days later, Mulchaey sent Farihi an image of the spectrum.
"I can't say I was shocked, frankly, but I was pleasantly blown out of my seat to see that the signature was there, and could be seen even with the human eye," Farihi said.
Image above: Drawers hosting records at Carnegie Observatories. Image Credits: NASA/JPL-Caltech.
The spectrum of van Maanen's Star that Farihi had requested is now located in a small archival sleeve, labeled with the handwritten date "1917 Oct 24" and a modern yellow sticky note: "possibly 1st record of an exoplanet."
Image above: The current location of the spectrum of van Maanen's Star, taken Oct. 24, 1917. Image Credits: NASA/JPL-Caltech.
Cynthia Hunt, an astronomer who serves as chair of Carnegie's history committee, took the glass plate out of the envelope and placed it onto a viewer that lit it up. The spectrum itself just about 1/6th of an inch, or a bit over 0.4 centimeters.
Image above: The spectrum of van Maanen's Star. Image Credits: Dan Kohne / Carnegie Observatories.
Though the plate seems unremarkable at first glance, Farihi saw two obvious "fangs" representing dips in the spectrum. To him, this was the smoking gun: Two absorption lines from the same calcium ion, meaning there were heavy elements in the photosphere of the white dwarf -- indicating it likely has at least one exoplanet. He wrote about it in 2016 in New Astronomy Reviews.
Image above: Close-up of spectrum of van Maanen's Star. Image Credits: Carnegie Institution for Science.
Exoplanets and debris disks
Scientists have long thought the gravity of giant planets could be keeping debris belts in place, especially in young planetary systems. A recent study in The Astrophysical Journal showed that young stars with disks of dust and debris are more likely to have giant planets orbiting at great distance from their parent star than those without disks.
A white dwarf is not a young star -- on the contrary, it forms when a low-to-medium-mass star has already burned all of the fuel in its interior. But the principle is the same: The gravitational pull of giant exoplanets could throw small, rocky bodies into the white dwarfs.
Our own Sun will become a red giant in about 5 billion years, expanding so much it may even swallow Earth before it blows off its outer layers and becomes a white dwarf. At that point, Jupiter's large gravitational influence may be more disruptive to the asteroid belt, flinging objects toward our much-dimmer Sun. This kind of scenario could explain the heavy elements at van Maanen's Star.
Spitzer's observations of van Maanen's Star have not found any planets there so far. In fact, to date, no exoplanets have been confirmed orbiting white dwarfs, although one does have an object thought to be a massive planet. Other compelling evidence has emerged just in the last couple of years. Using the W. M. Keck Observatory in Hawaii, scientists, including Zuckerman, recently announced that they had found evidence of a Kuiper-Belt-like object having been eaten by a white dwarf.
Scientists are still exploring polluted white dwarfs and looking for the exoplanets they may host. About 30 percent of all white dwarfs we know about are polluted, but their debris disks are harder to spot. Jura put forward that with lots of asteroids coming in and colliding with debris, dust may be converted into gas, which would not have the same highly detectable infrared signal as dust.
Farihi was thrilled about how his Mount Wilson archive detective work turned out. In 2016, he described the historical find in the context of a review paper about polluted white dwarfs, arguing that white dwarfs are "compelling targets for exoplanetary system research."
Who knows what other overlooked treasures await discovery in the archives of great observatories -- the sky-watching records of a cosmos rich in subtlety. Surely, other clues will be found by those motivated by curiosity who ask the right questions.
"It's personal interaction with data that can really spur us to get invested in the questions that we're asking," Farihi said.
Image above: Happy 100th anniversary to the 100-inch Hooker Telescope! Image Credits: NASA/JPL-Caltech.
Exoplanet: a planet orbiting a star other than the Sun.
White dwarf: a dim, dense, compact star -- the remnant core that remains after intermediate-mass stars (similar to the Sun) exhaust their nuclear fuel and blow off their outer layers. They are dominated by oxygen and carbon, but often have thin layers of hydrogen and helium.
F-type star: a main sequence star that is somewhat hotter, more massive, and more luminous than our Sun.
Main asteroid belt: the region between Mars and Jupiter populated by millions of small, rocky bodies. The largest member of this belt is dwarf planet Ceres.
Kuiper belt: a disk-shaped region of icy bodies beyond Neptune, whose largest known members include dwarf planets Pluto, Haumea, and Makemake.
New Astronomy Reviews: https://arxiv.org/abs/1604.03092
The Astrophysical Journal: https://www.nasa.gov/feature/jpl/giant-exoplanet-hunters-look-for-debris-disks
For more information about Spitzer, visit http://spitzer.caltech.edu and http://www.nasa.gov/spitzer.
Images (mentioned), Text, Credits: NASA/JPL/Elizabeth Landau.
Best regards, Orbiter.ch
Publié par Orbiter.ch à 12:04
mercredi 1 novembre 2017
NASA - Mars Science Laboratory (MSL) patch.
Nov. 1, 2017
Image above: This pair of images from the Mast Camera (Mastcam) on NASA's Curiosity rover illustrates how special filters are used to scout terrain ahead for variations in the local bedrock. Image Credits: NASA/JPL-Caltech/MSSS/ASU.
Color-discerning capabilities that NASA's Curiosity rover has been using on Mars since 2012 are proving particularly helpful on a mountainside ridge the rover is now climbing.
These capabilities go beyond the thousands of full-color images Curiosity takes every year: The rover can look at Mars with special filters helpful for identifying some minerals, and also with a spectrometer that sorts light into thousands of wavelengths, extending beyond visible-light colors into infrared and ultraviolet. These observations aid decisions about where to drive and investigations of chosen targets.
One of these methods for discerning targets' colors uses the Mast Camera (Mastcam); the other uses the Chemistry and Camera instrument (ChemCam).
Each of the Mastcam's two eyes -- one telephoto and one wider angle -- has several science filters that can be changed from one image to the next to assess how brightly a rock reflects light of specific colors. By design, some of the filters are for diagnostic wavelengths that certain minerals absorb, rather than reflect. Hematite, one iron-oxide mineral detectable with Mastcam's science filters, is a mineral of prime interest as the rover examines "Vera Rubin Ridge."
Image above: This Sept. 16, 2017, image from the Mars Hand Lens Imager (MAHLI) camera on NASA's Curiosity Mars rover shows effects of using the rover's wire-bristled Dust Removal Tool on a rock target called "Christmas Cove." Removal of dust revealed purplish rock that may contain the mineral hematite. Image Credits: NASA/JPL-Caltech/MSSS.
"We're in an area where this capability of Curiosity has a chance to shine," said Abigail Fraeman of NASA's Jet Propulsion Laboratory, Pasadena, California, who leads planning for the mission's investigation of Vera Rubin Ridge.
This ridge on lower Mount Sharp became a planned destination for Curiosity before the rover landed five years ago. Spectrometer observations from orbit revealed hematite here. Most hematite forms in the presence of water, and the mission focuses on clues about wet environments in Mars' ancient past. It found evidence during the first year after landing that some ancient Martian environments offered conditions favorable for life. As the mission continues, it is studying how those conditions varied and changed.
Curiosity's ChemCam is best known for zapping rocks with a laser to identify chemical elements in them, but it also can examine targets near and far without use of the laser. It does this by measuring sunlight reflected by the targets in thousands of wavelengths. Some patterns in this spectral data can identify hematite or other minerals.
"The colors of the rocks on the ridge are more interesting and more variable than what we saw earlier in Curiosity's traverse," said science team member Jeffrey Johnson of the Johns Hopkins University Applied Physics Laboratory, Laurel, Maryland. He uses both Mastcam and ChemCam data for analyzing rocks.
Image above: This false-color image shows how special filters of the Curiosity Mars rover's Mastcam can help reveal certain minerals in target rocks. It is a composite of images taken Sept. 17, 2017, through three "science" filters chosen to make hematite, an iron-oxide mineral, stand out as exaggerated purple. Image Credits: NASA/JPL-Caltech/MSSS.
Image above: On "Vera Rubin Ridge," to determine whether dust coatings are hiding rocks' hematite content, the Mastcam on NASA's Curiosity Mars rover took this Sept. 17, 2017, image of a rock surface that had been brushed with the rover's Dust Removal Tool. The purplish tint may indicate fine-grained hematite. Image Credits: NASA/JPL-Caltech/MSSS.
Hematite occurs at sufficiently small grain sizes in rocks found at this part of Mars to preferentially absorb some wavelengths of green light. This gives it a purplish tint in standard color images from Curiosity, due to more reflection of redder and bluer light than reflection of the green wavelengths. The additional color-discerning capabilities of Mastcam and ChemCam show hematite even more clearly.
Johnson said, "We're using these multi-spectral and hyper-spectral capabilities for examining rocks right in front of the rover and also for reconnaissance -- looking ahead to help with choosing where to drive for closer inspection."
Image above: The ChemCam on NASA's Curiosity Mars rover examined a brushed area on target rock "Christmas Cove" on Sept. 17, 2017, and found spectral evidence of hematite, an iron-oxide mineral. Five lines on the graph of brightness at different wavelengths correspond to the labeled points in the inset image. Image Credits: NASA/JPL-Caltech/LANL/CNES/IRAP/LPGNantes/CNRS/IAS.
For example, a false-color Sept. 12 panorama combining Mastcam images taken through three special filters provided a map of where hematite could be seen in a region a few days' drive away. The hematite is most apparent in zones around fractured bedrock. The team drove Curiosity to a site in that scene to check the possible link between fracture zones and hematite. Investigation with Mastcam, ChemCam and other tools, including a camera and brush on the rover's arm, revealed that hematite is also in bedrock farther from the fractures once an obscuring layer of tan dust is brushed away. The dust doesn't coat the fractured rock as thoroughly.
That finding suggests that dust and fractures cause the hematite to appear more patchy than it actually is. If the hematite is broadly distributed, its origin likely was early, rather than in a later period of fluids moving through fractures in the rock.
"As we approached the ridge and now as we're climbing it, we've been trying to tie what was detected from orbit to what we can learn on the ground," said Curiosity science team member Danika Wellington of Arizona State University, Tempe. "It's still very much a work in progress. The extent to which iron-bearing minerals here are oxidized relates to the history of interactions between water and rock."
The U.S. Department of Energy's Los Alamos National Laboratory in Los Alamos, New Mexico, developed ChemCam in partnership with scientists and engineers funded by the French national space agency (CNES). Mastcam was built by Malin Space Science Systems, San Diego. JPL, a division of Caltech in Pasadena, California, manages the Mars Science Laboratory Project for NASA's Science Mission Directorate, Washington, and built the project's Curiosity rover. For more information about Curiosity, visit: https://mars.jpl.nasa.gov/msl
Mast Camera (Mastcam): https://mars.jpl.nasa.gov/msl/mission/instruments/cameras/mastcam/
Chemistry and Camera instrument (ChemCam): https://mars.jpl.nasa.gov/msl/mission/instruments/spectrometers/chemcam/
Images (mentioned), Text, Credits: NASA/Laurie Cantillo/Dwayne Brown/Tony Greicius/JPL/Guy Webster.
Best regards, Orbiter.ch
Publié par Orbiter.ch à 19:53