Light Echoes Used to Study Protoplanetary Disks

A new study published in the Astrophysical Journal uses data from NASA's Spitzer Space Telescope and four ground-based telescopes to determine the distance from a star to the inner rim of its surrounding protoplanetary disk. Researchers used a method called "photo-reverberation," also known as "light echoes." When the central star brightens, some of the light hits the surrounding disk, causing a delayed “echo.” Scientists measured the time it took for light coming directly from the star to reach Earth, then waited for its echo to arrive.

The Spitzer study marks the first time the light echo method was used in the context of protoplanetary disks.

This illustration shows a star surrounded by a protoplanetary disk. Material from the thick disk flows along the star’s magnetic field lines and is deposited onto the star’s surface. When material hits the star, it lights up brightly
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The Soyuz TMA-20M rocket launches from the Baikonur Cosmodrome in Kazakhstan

The Soyuz TMA-20M rocket launches from the Baikonur Cosmodrome in Kazakhstan on Saturday, March 19, 2016 (Friday, March 18, in the U.S.), carrying Expedition 47 Soyuz Commander Alexey Ovchinin of Roscosmos, Flight Engineer Jeff Williams of NASA, and Flight Engineer Oleg Skripochka of Roscosmos into orbit to begin their five and a half month mission on the International Space Station.

Credit: NASA/Aubrey Gemignani

W pattern in northern constellation Cassiopeia

A familiar, zigzag, W pattern in northern constellation Cassiopeia is traced by five bright stars in this colorful and broad mosaic. Stretching about 15 degrees across rich starfields, the celestial scene includes dark clouds, bright nebulae, and star clusters along the Milky Way. In yellow-orange hues Cassiopeia's alpha star Shedar is a standout though. The yellowish giant star is cooler than the Sun, over 40 times the solar diameter, and so luminous it shines brightly in Earth's night from 230 light-years away. A massive, rapidly rotating star at the center of the W, bright Gamma Cas is about 550 light-years distant. Bluish Gamma Cas is much hotter than the Sun. Its intense, invisible ultraviolet radiation ionizes hydrogen atoms in nearby interstellar clouds to produce visible red H-alpha emission as the atoms recombine with electrons. Of course, night skygazers in the Alpha Centauri star system would also see the recognizable outline traced by Cassiopeia's bright stars. But from their perspective a mere 4.3 light-years away they would see our Sun as a sixth bright star in Cassiopeia, extending the zigzag pattern just beyond the left edge of this frame.


The W in Cassiopeia
Image Credit & Copyright: Rogelio Bernal Andreo (Deep Sky Colors) 
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One Year Crew Back On Mother Earth

NASA astronaut and Expedition 46 Commander Scott Kelly and his Russian counterpart Mikhail Kornienko returned to Earth Tuesday after a historic 340-day mission aboard the International Space Station. They landed in Kazakhstan at 11:26 p.m. EST (10:26 a.m. March 2 Kazakhstan time).

Joining their return trip aboard a Soyuz TMA-18M spacecraft was Sergey Volkov, also of the Russian space agency Roscosmos, who arrived on the station Sept. 4, 2015. The crew touched down southeast of the remote town of Dzhezkazgan.

“Scott Kelly’s one-year mission aboard the International Space Station has helped to advance deep space exploration and America’s Journey to Mars,” said NASA Administrator Charles Bolden. “Scott has become the first American astronaut to spend a year in space, and in so doing, helped us take one giant leap toward putting boots on Mars.”

During the record-setting One-Year mission, the station crew conducted almost 400 investigations to advance NASA’s mission and benefit all of humanity. Kelly and Kornienko specifically participated in a number of studies to inform NASA’s Journey to Mars, including research into how the human body adjusts to weightlessness, isolation, radiation and the stress of long-duration spaceflight. Kelly’s identical twin brother, former NASA astronaut Mark Kelly, participated in parallel twin studies on Earth to help scientists compare the effects of space on the body and mind down to the cellular level.

One particular research project examined fluid shifts that occur when bodily fluids move into the upper body during weightlessness. These shifts may be associated with visual changes and a possible increase in intracranial pressure, which are significant challenges that must be understood before humans expand exploration beyond Earth’s orbit. The study uses the Russian Chibis device to draw fluids back into the legs while the subject’s eyes are measured to track any changes. NASA and Roscosmos already are looking at continuing the Fluid Shifts investigation with future space station crews.

The crew took advantage of the unique vantage point of the space station, with an orbital path that covers more than 90 percent of Earth’s population, to monitor and capture images of our planet. They also welcomed the arrival of a new instrument to study the signature of dark matter and conducted technology demonstrations that continue to drive innovation, including a test of network capabilities for operating swarms of spacecraft.

Kelly and Kornienko saw the arrival of six resupply spacecraft during their mission. Kelly was involved in the robotic capture of two NASA-contracted cargo flights -- SpaceX’s Dragon during the company’s sixth commercial resupply mission and Orbital ATK’s Cygnus during the company’s fourth commercial resupply mission. A Japanese cargo craft and three Russian resupply ships also delivered several tons of supplies to the station.

Kelly ventured outside the confines of the space station for three spacewalks during his mission. The first included a variety of station upgrade and maintenance tasks, including routing cables to prepare for new docking ports for U.S. commercial crew spacecraft. On a second spacewalk, he assisted in the successful reconfiguration of an ammonia cooling system and restoration of the station to full solar power-generating capability. The third spacewalk was to restore functionality to the station’s Mobile Transporter system.

Including crewmate Gennady Padalka, with whom Kelly and Kornienko launched on March 27, 2015, 10 astronauts and cosmonauts representing six different nations (the United States, Russia, Japan, Denmark, Kazakhstan and England) lived aboard the space station during the yearlong mission.

With the end of this mission, Kelly now has spent 520 days in space, the most among U.S. astronauts. Kornienko has accumulated 516 days across two flights, and Volkov has 548 days on three flights.

Expedition 47 continues operating the station, with NASA astronaut Tim Kopra in command. Kopra, Tim Peake of ESA (European Space Agency) and Yuri Malenchenko of Roscosmos will operate the station until the arrival of three new crew members in about two weeks. NASA astronaut Jeff Williams and Russian cosmonauts Alexey Ovchinin and Oleg Skripochka are scheduled to launch from Baikonur, Kazakhstan, on March 18.

The International Space Station is a convergence of science, technology and human innovation that enables us to demonstrate new technologies and make research breakthroughs not possible on Earth. It has been continuously occupied since November 2000 and, since then, has been visited by more than 200 people and a variety of international and commercial spacecraft. The space station remains the springboard to NASA's next giant leap in exploration, including future missions to an asteroid and Mars.

NASA’s IBEX Observations Pin Down Interstellar Magnetic Field

Immediately after its 2008 launch, NASA’s Interstellar Boundary Explorer, or IBEX, spotted a curiosity in a thin slice of space: More particles streamed in through a long, skinny swath in the sky than anywhere else. The origin of the so-called IBEX ribbon was unknown – but its very existence opened doors to observing what lies outside our solar system, the way drops of rain on a window tell you more about the weather outside.

Now, a new study uses IBEX data and simulations of the interstellar boundary – which lies at the very edge of the giant magnetic bubble surrounding our solar system called the heliosphere – to better describe space in our galactic neighborhood. The paper, published Feb. 8, 2016, in The Astrophysical Journal Letters, precisely determines the strength and direction of the magnetic field outside the heliosphere. Such information gives us a peek into the magnetic forces that dominate the galaxy beyond, teaching us more about our home in space.

(Artist concept) Far beyond the orbit of Neptune, the solar wind and the interstellar medium interact to create a region known as the inner heliosheath, bounded on the inside by the termination shock, and on the outside by the heliopause.

Credits: NASA/IBEX/Adler Planetarium

The new paper is based on one particular theory of the origin of the IBEX ribbon, in which the particles streaming in from the ribbon are actually solar material reflected back at us after a long journey to the edges of the sun’s magnetic boundaries. A giant bubble, known as the heliosphere, exists around the sun and is filled with what’s called solar wind, the sun’s constant outflow of ionized gas, known as plasma. When these particles reach the edges of the heliosphere, their motion becomes more complicated. 

“The theory says that some solar wind protons are sent flying back towards the sun as neutral atoms after a complex series of charge exchanges, creating the IBEX ribbon,” said Eric Zirnstein, a space scientist at the Southwest Research Institute in San Antonio, Texas, and lead author on the study. “Simulations and IBEX observations pinpoint this process – which takes anywhere from three to six years on average – as the most likely origin of the IBEX ribbon.”Outside the heliosphere lies the interstellar medium, with plasma that has different speed, density, and temperature than solar wind plasma, as well as neutral gases. These materials interact at the heliosphere’s edge to create a region known as the inner heliosheath, bounded on the inside by the termination shock – which is more than twice as far from us as the orbit of Pluto – and on the outside by the heliopause, the boundary between the solar wind and the comparatively dense interstellar medium.  

Some solar wind protons that flow out from the sun to this boundary region will gain an electron, making them neutral and allowing them to cross the heliopause. Once in the interstellar medium, they can lose that electron again, making them gyrate around the interstellar magnetic field. If those particles pick up another electron at the right place and time, they can be fired back into the heliosphere, travel all the way back toward Earth, and collide with IBEX’s detector. The particles carry information about all that interaction with the interstellar magnetic field, and as they  hit the detector they can give us unprecedented insight into the characteristics of that region of space.

“Only Voyager 1 has ever made direct observations of the interstellar magnetic field, and those are close to the heliopause, where it’s distorted,” said Zirnstein. “But this analysis provides a nice determination of its strength and direction farther out.”

The directions of different ribbon particles shooting back toward Earth are determined by the characteristics of the interstellar magnetic field. For instance, simulations show that the most energetic particles come from a different region of space than the least energetic particles, which gives clues as to how the interstellar magnetic field interacts with the heliosphere.

For the recent study, such observations were used to seed simulations of the ribbon’s origin. Not only do these simulations correctly predict the locations of neutral ribbon particles at different energies, but the deduced interstellar magnetic field agrees with Voyager 1 measurements, the deflection of interstellar neutral gases, and observations of distant polarized starlight.

However, some early simulations of the interstellar magnetic field don’t quite line up. Those pre-IBEX estimates were based largely on two data points – the distances at which Voyagers 1 and 2 crossed the termination shock.  

“Voyager 1 crossed the termination shock at 94 astronomical units, or AU, from the sun, and Voyager 2 at 84 AU,” said Zirnstein. One AU is equal to about 93 million miles, the average distance between Earth and the sun. “That difference of almost 930 million miles was mostly explained by a strong, very tilted interstellar magnetic field pushing on the heliosphere.” 

But that difference may be accounted for by considering a stronger influence from the solar cycle, which can lead to changes in the strength of the solar wind and thus change the distance to the termination shock in the directions of Voyager 1 and 2. The two Voyager spacecraft made their measurements almost three years apart, giving plenty of time for the variable solar wind to change the distance of the termination shock.

“Scientists in the field are developing more sophisticated models of the time-dependent solar wind,” said Zirnstein.

The simulations generally jibe well with the Voyager data.

The IBEX ribbon is a relatively narrow strip of particles flying in towards the sun from outside the heliosphere. A new study corroborates the idea that particles from outside the heliosphere that form the IBEX ribbon actually originate at the sun – and reveals information about the distant interstellar magnetic field.

Credits: SwRI

“The new findings can be used to better understand how our space environment interacts with the interstellar environment beyond the heliopause,” said Eric Christian, IBEX program scientist at NASA’s Goddard Space Flight Center in Greenbelt, Maryland, who was not involved in this study. “In turn, understanding that interaction could help explain the mystery of what causes the IBEX ribbon once and for all.”

The Southwest Research Institute leads IBEX with teams of national and international partners. NASA Goddard manages the Explorers Program for the agency’s Heliophysics Division within the Science Mission Directorate in Washington.

Courtesy of NASA

NASA's Spitzer, Hubble Find "Twins" of Superstar Eta Carinae in Other Galaxies

Eta Carinae, the most luminous and massive stellar system within 10,000 light-years, is best known for an enormous eruption seen in the mid-19th century that hurled at least 10 times the sun's mass into space. This expanding veil of gas and dust, which still shrouds Eta Carinae, makes it the only object of its kind known in our galaxy. Now a study using archival data from NASA's Spitzer and Hubble space telescopes has found five objects with similar properties in other galaxies for the first time.  

"The most massive stars are always rare, but they have tremendous impact on the chemical and physical evolution of their host galaxy," said lead scientist Rubab Khan, a postdoctoral researcher at NASA's Goddard Space Flight Center in Greenbelt, Maryland. These stars produce and distribute large amounts of the chemical elements vital to life and eventually explode as supernovae.

Located about 7,500 light-years away in the southern constellation of Carina, Eta Carinae outshines our sun by 5 million times. The binary system consists of two massive stars in a tight 5.5-year orbit. Astronomers estimate that the more massive star has about 90 times the sun’s mass, while the smaller companion may exceed 30 solar masses.

As one of the nearest laboratories for studying high-mass stars, Eta Carinae has been a unique astronomical touchstone since its eruption in the 1840s. To understand why the eruption occurred and how it relates to the evolution of massive stars, astronomers needed additional examples. Catching rare stars during the short-lived aftermath of a major outburst approaches needle-and-haystack levels of difficulty, and nothing matching Eta Carinae had been found prior to Khan's study.

"We knew others were out there," said co-investigator Krzysztof Stanek, a professor of astronomy at Ohio State University in Columbus. "It was really a matter of figuring out what to look for and of being persistent."

Working with Scott Adams and Christopher Kochanek at Ohio State and George Sonneborn at Goddard, Khan developed a kind of optical and infrared fingerprint for identifying possible Eta Carinae twins, or "Eta twins" for short.

Dust forms in gas ejected by a massive star. This dust dims the star’s ultraviolet and visible light, but it absorbs and reradiates this energy as heat at longer mid-infrared wavelengths. "With Spitzer we see a steady increase in brightness starting at around 3 microns and peaking between 8 and 24 microns," explained Khan. "By comparing this emission to the dimming we see in Hubble's optical images, we could determine how much dust was present and compare it to the amount we see around Eta Carinae."

An initial survey of seven galaxies from 2012 to 2014 didn't turn up any Eta twins, underscoring their rarity. It did, however, identify a class of less massive and less luminous stars of scientific interest, demonstrating the search was sensitive enough to find Eta Carinae-like stars had they been present.


The nearby spiral galaxy M83 is currently the only one known to host two potential Eta Carinae twins. This composite of images from the Hubble Space Telescope's Wide Field Camera 3 instrument shows a galaxy ablaze with newly formed stars. A high rate of star formation increases the chances of finding massive stars that have recently undergone an Eta Carinae-like outburst. Bottom: Insets zoom into Hubble data to show the locations of M83's Eta twins.
Credits: NASA, ESA, the Hubble Heritage Team (STScI/AURA) and R. Khan (GSFC and ORAU)

In a follow-on survey in 2015, the team found two candidate Eta twins in the galaxy M83, located 15 million light-years away, and one each in NGC 6946, M101 and M51, located between 18 and 26 million light-years away. These five objects mimic the optical and infrared properties of Eta Carinae, indicating that each very likely contains a high mass star buried in five to 10 solar masses of gas and dust. Further study will let astronomers more precisely determine their physical properties. The findings were published in the Dec. 20 edition of The Astrophysical Journal Letters.
Researchers found likely Eta twins in four galaxies by comparing the infrared and optical brightness of each candidate source. Infrared images from NASA's Spitzer Space Telescope revealed the presence of warm dust surrounding the stars. Comparing this information with the brightness of each source at optical and near-infrared wavelengths as measured by instruments on Hubble, the team was able to identify candidate Eta Carinae-like objects. Top: 3.6-micron images of candidate Eta twins from Spitzer's IRAC instrument. Bottom: 800-nanometer images of the same sources from various Hubble instruments.
Credits: NASA, ESA, and R. Khan (GSFC and ORAU)

NASA's James Webb Space Telescope, set to launch in late 2018, carries an instrument ideally suited for further study of these stars. The Mid-Infrared Instrument (MIRI) has 10 times the angular resolution of instruments aboard Spitzer and is most sensitive at the wavelengths where Eta twins shine brightest. "Combined with Webb's larger primary mirror, MIRI will enable astronomers to better study these rare stellar laboratories and to find additional sources in this fascinating phase of stellar evolution," said Sonneborn, NASA's project scientist for Webb telescope operations. It will take Webb observations to confirm the Eta twins as true relatives of Eta Carinae.

The Spitzer Space Telescope is managed by NASA's Jet Propulsion Laboratory in Pasadena, California. The Spitzer Science Center at the California Institute of Technology in Pasadena conducts science operations.

The Hubble Space Telescope is a project of international cooperation between NASA and the European Space Agency. NASA's Goddard Space Flight Center manages the telescope. The Space Telescope Science Institute (STScI) in Baltimore, Maryland, conducts Hubble science operations. STScI is operated for NASA by the Association of Universities for Research in Astronomy in Washington, D.C.

For more information about Spitzer, visit:

http://www.nasa.gov/spitzer

For more information about Hubble, visit:

http://www.nasa.gov/hubble

Courtesy of NASA, Goddard Space Flight Center

First British Astronaut to the ISS, American, Russian and Briton Join International Space Station Crew

Hatches between the International Space Station and an arriving Soyuz spacecraft opened at 2:58 p.m. EST Tuesday, signaling the arrival of three new crew members, including NASA astronaut Tim Kopra. They will join other residents on the station to continue important research that advances NASA's journey to Mars, while making discoveries that can benefit all of humanity.
Kopra, Russian Federal Space Agency (Roscosmos) cosmonaut Yuri Malenchenko and ESA (European Space Agency) astronaut Tim Peake launched from the Baikonur Cosmodrome in Kazakhstan at 6:03 a.m. (5:03 p.m. in Baikonur) and, after orbiting Earth four times, manually docked to the station at 12:33 p.m.

The arrival of Kopra, Malenchenko and Peake returns the station's crew complement to six. The three join Expedition 46 Commander Scott Kelly of NASA and Flight Engineers Sergey Volkov and Mikhail Kornienko of Roscosmos. During more than five months on humanity’s only microgravity laboratory, the Expedition 46 crew members will conduct more than 250 science investigation in fields including biology, Earth science, human research, physical sciences and technology development.


Kopra, Malenchenko and Peake will remain aboard the station until early June 2016. Kelly and Kornienko will return to Earth at the conclusion of their one-year mission on March 1, 2016, along with Volkov. The pair will have spent 340 consecutive days living and working in space to advance understanding of the medical, psychological and biomedical challenges astronauts face during long duration spaceflight, in addition to developing countermeasures to reverse those effects.

Ongoing station research also includes the Microbial Payload Tracking Series project, which uses microbial analysis techniques to establish a census of the microorganisms living on surfaces and in the atmosphere of the space station. Along with crew members and experimental payloads, the space station is home to a variety of microbes, which are a cleaning nuisance and potentially threatening to crew health and station equipment. Analyzing these microbes can help determine whether some are more virulent in space, and which genetic changes might be involved in this response. Results from the investigation can be used to evaluate cleaning strategies, and to mitigate microbe-related risks to crew health and spacecraft system performance.

The crew members are scheduled to receive several cargo spacecraft -- including multiple U.S. commercial resupply vehicles from SpaceX and Orbital ATK -- each delivering tons of food, fuel, supplies and research.

SpaceX will deliver on its eighth commercial resupply services mission an important technology project that could help drive future exploration. Developed under a public-private partnership, the Bigelow Expandable Activity Module (BEAM) is an expandable habitat technology demonstration for the International Space Station. Expandable habitats can greatly decrease the amount of transport volume for future space missions, weighing less and taking up less room on a rocket. These habitats have the potential to provide a comfortable area for astronauts to live and work, as well as a varying degree of protection from solar and cosmic radiation, space debris and other elements of the space environment. Highly reliable habitation systems will be essential to keep future crews healthy and productive in the deep-space environment during missions in lunar orbit where the systems will be validated for future missions to Mars that could last as long as 1,100 days.

For 15 years, humans have been living continuously aboard the station to advance scientific knowledge and demonstrate new technologies, making research breakthroughs not possible on Earth that also will enable long-duration human and robotic exploration into deep space. A truly global endeavor, more than 200 people from 15 countries have visited the unique microgravity laboratory that has hosted more than 1,700 research investigations from researchers in more than 80 countries.