The sands of time are running out for the central star of this the Hourglass Nebula. With its nuclear fuel exhausted, this brief, spectacular, closing phase of a sun-like star's life occurs as its outer layers are ejected and its core becomes a cooling, fading white dwarf. In 1995, astronomers used the Hubble Space Telescope to make a series of images of planetary nebulae, including the one above. Here, delicate rings of colorful glowing gas (nitrogen-red, hydrogen-green, and oxygen-blue) outline the tenuous walls of the 'hourglass.' The unprecedented sharpness of Hubble's images revealed surprising details of the nebula ejection process and may resolve the outstanding mystery of the variety of complex shapes and symmetries of planetary nebulae. Image Credit: NASA, WFPC2, HST, R. Sahai and J. Trauger (JPL) Read more...
Plans for Orion — the capsule that resembles the Apollo program’s spacecraft and was supposed to send humans to the moon by 2020 as part of NASA’s Constellation program — were changed in February when President Obama canceled Constellation, and then announced two months later that NASA would continue to develop Orion as an escape vehicle to be docked at the International Space Station for emergencies.
While it appears that Orion will eventually take flight, NASA continues to struggle with one crucial aspect of its design: minimizing the violent impact that astronauts would experience during landing. Although NASA initially designed Orion’s crew seats to be mounted onto a stiff structure supported by shock absorbers — essentially the same technology used to cushion Apollo’s water landings — this 1,100-pound structure would be too heavy to cushion astronauts if the vehicle landed on land. Whereas the Apollo capsule was designed to land in water, and Orion would likely do the same, NASA wants to make sure that Orion can land on land in case of an emergency.
A graduate student in MIT’s Department of Aeronautics and Astronautics has helped design a smaller alternative: a reusable, 700-pound air-bag system that could inflate during launch and landing, deflate for storage purposes, and partially inflate to provide seating while the vehicle is in space. Not only would the system be lighter than the one NASA originally proposed, but it would also be entirely mechanical, meaning not controlled by computers.
This is important because “the vast majority of accidents and failures in engineering systems” can be traced to computers misinterpreting situations, says Sydney Do, who helped design the air-bag system and spent several weeks in August testing a full-sized prototype designed to protect one astronaut. “Our goal was to see if it was possible to design a landing system that was purely mechanical.”
According to a paper presented at the American Institute of Aeronautics and Astronautics Space 2009 conference by Do and his thesis adviser, Olivier de Weck, an associate professor of aeronautics and astronautics and engineering systems, the air-bag system was inspired by the structure of seeds. Just as a fluid surrounds the embryo in seeds to provide protection as the seed is distributed, the Orion air-bag system would surround each astronaut in “a personal cushion of air,” according to current NASA astronaut Charlie Camarda, who seeks to develop more innovative space-engineering concepts that veer from the traditional. In 2008, Camarda helped organize a group of students from Pennsylvania State University and MIT, including Do, to explore how the physics of seeds could be applied to engineering principles. Do’s design for an Orion air-bag system, Camarda says, represents “a very novel” approach to mechanical design that could inspire more biological-based solutions in engineering. Valve analysis
NASA’s Engineering and Safety Center agreed to fund the study by the Penn State and MIT students to explore the feasibility of an air-bag system that Orion astronauts could inflate before reentering Earth’s atmosphere. The students’ first step was to conduct tests to observe how the inflated bags behave when they are dropped from increasing one-foot increments while supporting an object that weighs about the same as an average male head — such drops simulate the impact velocity that an astronaut would feel upon landing.
These tests revealed how important timing is in terms of releasing gas from an air bag. Unlike car air bags, which inflate when hot gas is injected into them upon impact, the inflated Orion air bags already contain gas upon impact. If the air bags are either not big enough or don’t have enough air in them, the astronaut’s seat will directly impact the ground. Alternatively, if there is enough gas inside the bag, but it’s not released before the seat hits the ground, the impact will cause the seat to bounce upward, which could injure the astronaut. That’s because as an astronaut falls into the bag during the landing, the kinetic energy created from this motion is combined with the energy of the gas molecules moving inside the bags. This increases the pressure of the gas inside the bag, which could cause bouncing.
To prevent this bounce, enough gas needs to be vented between the point at which the floor of Orion impacts the ground and the point at which the seat and the astronaut impact the ground so that the kinetic energy caused by the falling seat and occupant have been removed. But even after some of this gas is vented, there still needs to be enough gas remaining in the bags to prevent direct impact between the seat and the ground. To get this balance right, the students decided to design valves that are triggered to open at a low pressure, which would allow gas to vent as soon as Orion’s floor comes to rest, but before the seat can impact the ground.
This clip shows several views of a “drop test” of an air-bag system being designed for a space capsule. During the test, a dummy attached to the air-bag system is raised and then dropped, simulating the velocity an astronaut would experience during landing. Video courtesy of Sydney Do
Drop-test survival
When NASA decided to fund the research for another year last spring, Do took over the research for his master’s thesis and began testing a valve for the system. He then developed a computer model to analyze how certain variables, such as air-bag size, would affect the risk of astronaut injury upon impact. This helped him configure a prototype seat that would have four air bags — each about one foot long by two feet wide — containing two rectangular valves about six inches wide. Do then built the air bags from vectran, a high-strength material that was used to make the air bags for several rovers that landed on Mars.
Earlier this month, he tested the prototype through a series of drop tests conducted from as high as 10 feet involving a crash dummy that measured the acceleration of each drop. While Do still needs to analyze those results before presenting his final design to NASA later this fall, he says that the fact that the system survived dozens of drops suggests that certain variables he chose for the prototype, such as the material and manufacturing of the air bags, are adequate for an Orion landing. According to Camarda, future research could explore ways to ensure “a robust and fail-safe” system in the event that a valve malfunctions.
Do cautions that the air-bag system has one drawback: It’s likely only effective for vertical drops, meaning that the air bags could tip over if Orion descended at a sideways angle. But he says this might not be an issue if Orion is designed to land vertically. Although whatever NASA decides to do with Do’s research ultimately depends on the future of human spaceflight, he is hopeful that even if Orion never takes flight, his research could be used to guide designs of similar capsule-type spacecraft that commercial companies might be interested in building.
A hop, skip and a jump on the moon — and beyond »»
Although unmanned, wheeled rovers have explored the surfaces of the moon and Mars for decades, these vehicles have limits — they can’t crawl inside craters, scale cliffs or travel long distances.
For more than two years, a team of students led by Professor of the Practice of Astronautics and former NASA astronaut Jeffrey Hoffman in MIT’s Department of Aeronautics and Astronautics has been collaborating with engineers from the Charles Stark Draper Laboratory to design and build a prototype for a new type of robotic explorer that would hop over, rather than traverse, a planetary surface. Hopping, they believe, would make it easier for an explorer to access tricky sites and travel greater distances, and thus collect more data during a mission.
Known as the Terrestrial Artificial Lunar and Reduced Gravity Simulator, or Talaris, the three-foot-wide vehicle is a prototype of a larger hopper that would be used in space. The team that built it wants to use Talaris on Earth to test guidance, navigation and control (GNC) software developed by Draper that would then be used to navigate the space-based hopper autonomously. Several graduate students involved with the project will present the latest details about the prototype later this month at the American Institute of Aeronautics and Astronautics Space 2010 conference in California.
The prototype is an outgrowth of MIT’s effort to win the Google Lunar X Prize, a $20 million competition to become the first team to send a privately funded spacecraft to the moon, travel 500 meters across its surface, and transmit video and images back to Earth. Both MIT and Draper are members of Next Giant Leap, one of about 20 teams registered in the competition.
Building Talaris to test the hopper waters
Talaris uses two propulsion systems. The main system consists of four downward-pointing electric ducted fans that provide lift to counter the vehicle’s weight and simulate the gravity environments of different planetary bodies. The second system uses compressed nitrogen gas to maneuver the vehicle as it operates in the simulated gravity conditions. With this setup, the researchers can repeatedly test different navigation algorithms on Earth to perfect the control software.
What distinguishes Talaris from other explorer prototypes is its ability to test how a hopper functions in different gravity scenarios before sending one into space, according to Seamus Tuohy, director of space systems at Draper, which is funding Talaris. “Other organizations had developed little lander prototypes, but the drawback was that they were essentially Earth landers,” Tuohy says. “MIT and Draper wanted to do better — to be able to say that we have the GNC expertise to do hopping in other environments, and that we have demonstrated it with Talaris.”
Although Talaris began with the goal of hopping across the moon, the Talaris team is pushing for hoppers to be used to explore any body in the solar system that has enough gravity to make hopping feasible, including asteroids. “There are limits to the terrain you can access on wheels, and with a hopper, you simply hop in, collect data and hop out,” Hoffman says, noting that hoppers can be used to explore deep craters on the moon that are thought to contain water, measure the magnetism of steep cliffs or set up a network of seismometers by placing sensors at multiple locations.
The ability of hoppers to travel long distances and visit multiple sites is also valuable. Whereas the rovers that have been used to explore Mars since the late 1990s traveled several kilometers over several years, hoppers could travel hundreds of kilometers per hop, depending on their size.
Hopper technology could even enable a human mission to Mars where astronauts orbiting the planet could use a high-bandwidth signal to tele-operate hoppers on the Martian surface, according to Phillip Cunio, an AeroAstro doctorate student who is working with Hoffman to lead the student group working on Talaris. “This would enable direct human oversight of exploration — with all the decision-making capability and flexibility that implies — without the risks of sending human bodies to the surface of Mars,” he says.
Filling the toolkit of planetary exploration
But hoppers do have one drawback: their engines require fuel. Electric rovers, in contrast, only need to recharge their batteries to run their wheels. Given that a hopper is limited to a certain number of hops, the Talaris researchers stress that hoppers should be thought of as an additional tool to complement rovers. Even so, Cunio says, engineers could design hoppers that could be useful even after their fuel runs out. For instance, they might act as solar array-powered rovers, or make fuel from local materials.
For now, the Talaris team is focused on finalizing the construction of Talaris. Although each component has been built and tested individually, the group has yet to test the entire system, which Cunio estimates will weigh about 110 pounds. The team hopes to complete a test hop — Talaris will hop about 20 meters by hovering, moving horizontally and descending — by the end of the calendar year. The researchers predict that if Next Giant Leap is able to secure funding, a large-scale planetary surface hopper explorer could take flight by the end of 2014, the deadline for contestants in the Google Lunar X Prize competition to complete a trip to the moon.
Many students learn about the Doppler effect in physics class, typically as part of a discussion of why the pitch of a siren is higher as an ambulance approaches and then lower as the ambulance passes by. The effect is useful in a variety of different scientific disciplines, including planetary science: Astronomers rely on the Doppler effect to detect planets outside of our solar system, or exoplanets. To date, 442 of the 473 known exoplanets have been detected using the Doppler effect, which also helps planetary scientists glean details about the newly found planets.
The Doppler effect, or Doppler shift, describes the changes in frequency of any kind of sound or light wave produced by a moving source with respect to an observer. Waves emitted by an object traveling toward an observer get compressed — prompting a higher frequency — as the source approaches the observer. In contrast, waves emitted by a source traveling away from an observer get stretched out.
In astronomy, that source can be a star that emits electromagnetic waves; from our vantage point, Doppler shifts occur as the star orbits around its own center of mass and moves toward or away from Earth. These wavelength shifts can be seen in the form of subtle changes in its spectrum, the rainbow of colors emitted in light. When a star moves toward us, its wavelengths get compressed, and its spectrum becomes slightly bluer. When the star moves away from us, its spectrum looks slightly redder.
To observe the so-called red shifts and blue shifts over time, planetary scientists use a high-resolution prism-like instrument known as a spectrograph that separates incoming light waves into different colors. In every star’s outer layer, there are atoms that absorb light at specific wavelengths, and this absorption appears as dark lines in the different colors of the star’s spectrum that are recorded from the light emanating from the star. Researchers use the shifts in these lines as convenient markers by which to measure the size of the Doppler shift.
If the star exists by itself — that is, if there is no exoplanet or companion star in its stellar system — then there will be no change in the pattern of its Doppler shifts over time. But if there is a planet or companion star in the system, the gravitational pull of this unseen body or star will perturb the host star’s movement at certain parts of its orbit, producing a noticeable change in the overall pattern and size of Doppler shifts over time. In other words, the pattern of a star’s Doppler shifts can change over time as a result of gravity affecting the star’s motion. “If this shift is large, then it must be caused by another star pulling it, but if this shift is small, then it is likely caused by a low-mass body like an exoplanet,” explains Joshua Winn, an assistant professor in MIT’s Department of Physics. As part of his work at MIT’s Kavli Institute for Astrophysics and Space Research, Winn studies the relationship between an exoplanet’s orbit and its parent star’s rotation for clues about how the planet may have formed.
How a planet’s Doppler shift changes over time can also shed light on the planet’s orbital period (the length of its “year”), the shape of its orbit and its minimum possible mass. Recently, Kavli postdoc Simon Albrecht used the Doppler effect to detect color shifts in the light absorbed by an exoplanet, which indicated strong winds in the planet’s atmosphere.
Doppler shifts are used in many fields besides astronomy. By sending radar beams into the atmosphere and studying the changes in the wavelengths of the beams that come back, meteorologists use the Doppler effect to detect water in the atmosphere. The Doppler phenomenon is also used in healthcare with echocardiograms that send ultrasound beams through a body to measure changes in blood flow to make sure that a heart valve is working properly or to diagnose vascular diseases. Police also rely on the Doppler effect when they use a radar gun to bounce radio beams off of your car; the change in frequency between the directed and reflected beams provides a measure of your car’s speed.
The 2010 Grote Reber Gold Medal for outstanding and innovative contributions to radio astronomy was presented this month to Alan Rogers, a research affiliate at MIT’s Haystack Observatory. The award recognizes Rogers’ many pioneering developments in radio and radar interferometry, radio spectroscopy, and for his application of radio astronomy techniques to society.
Rogers received his BSc degree in mathematics and physics from the University College of Rhodesia in 1962, and his SM and PhD degrees in electrical engineering from MIT in 1964 and 1967, respectively. Following a year as a lecturer at the University of Zimbabwe in 1968, he worked at the Haystack Observatory until his retirement in 2006.
Rogers is best known for his contributions over many decades to the techniques of very long baseline interferometry. More recently, he developed an innovative radio array that he successfully used to detect the 327 MHz line of interstellar deuterium, capping a 40-year quest for this important astrophysical atomic gas. Currently, Rogers is searching for the low-frequency signature characteristic of the cosmic epoch of reionization using a digital spectrometer and a compact broadband dipole. He was also the leader of a program to apply radio astronomy techniques to locate emergency calls from mobile telephones.
"Alan Rogers not only changed the course of radio astronomy but, unlike most research scientists, he devoted considerable time and his unique skills to making life a bit safer for all of us," said Ken Kellermann of the National Radio Astronomy Observatory.
The 2010 Reber Medal was presented to Alan Rogers during the annual meeting of the Astronomical Society of Australia earlier this month. The Reber Medal was established by the Trustees of the Grote Reber Foundation to honor the achievements of pioneering radio astronomer Grote Reber; the award is administered by the Queen Victoria Museum in Launceston, Tasmania.
3 Questions: Richard Binzel on astronomers’ powerful new tool »»
Last month, it was announced that the first Pan-STARRS (Panoramic Survey Telescope & Rapid Response System) telescope, PS1, is fully operational. The system is designed to search for “killer” asteroids and comets by mapping large portions of the sky each night to look for moving objects in our solar system. Based in Hawaii, Pan-STARRS features the world’s largest digital camera — a 1,400-megapixel device designed by researchers at MIT Lincoln Laboratory. Follow-up observations based on those images will allow astronomers to track moving objects and calculate their orbits to determine any potential threats to Earth. Richard Binzel, professor of planetary sciences in MIT’s Department of Earth, Atmospheric and Planetary Sciences, discusses Pan-STARRs with MIT News. A member of NASA’s Task Force for Planetary Defense, Binzel believes that Pan-STARRS’ “constant watch” will not only rule out possible threats from near-Earth objects (NEOs) over time, but will also reveal unknown galaxies and details about faraway planets.
Q. How does the technology of Pan-STARRS compare to that of the Hubble Space Telescope that was launched into orbit in 1990 to study objects in space?
A. Pan-STARRS and Hubble are about as different as different can be in the way they go about their space studies. Hubble is designed to focus intensely on a very small piece of the sky to unravel the physical mysteries of very carefully pre-selected targets. Pan-STARRS is designed to see as much of the sky as possible as quickly as possible by imaging a huge chunk of the sky every 30 seconds before moving on to a different chunk of the sky. By repeating the image of each part of the sky every few minutes and then comparing those images, Pan-STARRS is designed to detect rapid changes that could indicate a moving object.
It is not known in advance what each Pan-STARRS image will reveal, but there is always something to be discovered with each new look. In most cases, these discoveries will be moving objects — small bodies in our solar system that are following their own orbital paths around the sun. Most are asteroids in the main belt between Mars and Jupiter. Some are in the outer solar system in the new zone of bodies now known to reside beyond Neptune called the Kuiper Belt. Small solar system bodies that are found to be moving the fastest — because they are closer to both the sun and Earth — are the so-called “near-Earth objects” (NEOs). These bodies can be both asteroids and comets whose orbits bring them within the vicinity of Earth, and some have the potential to be on collision course with Earth. By repeatedly imaging these objects over several hours and many nights, their orbital paths can be determined with increasing precision. Fortunately, almost all NEOs can be immediately ruled out for having any potential hazard to Earth. But for those that do show some remaining chance of a future collision, dedicated follow-up tracking by Pan-STARRS or other telescopes can find out for sure. So far, no object with a certain impact having hazardous consequences has been discovered or is known.
Q. What are the limitations of this telescope? Can it be used to find exoplanets — planets that orbit a star other than the sun — or other objects outside our solar system?
A. Pan-STARRS is most strongly specialized toward finding changes in the sky, but unraveling the cause of those changes will largely fall to specialized telescopes to analyze light from different parts of the spectrum or with much higher resolution. Pan-STARRS’ strength is being sensitive to any changes it sees anywhere in its field of view, and that, of course, also includes distant stars and galaxies beyond our solar system. While our sun is a very stable light source, many stars pulsate in their brightness in the early and late stages of their lives. Pan-STARRS will be the most sensitive survey ever performed to detect these changes over very short (minutes to hours) to very long (days and years) intervals of time. Pan-STARRS can also detect abrupt, but regularly spaced drops in the brightness of stars that can be a telltale sign of exoplanets. These drops occur when the orbit of the planet happens to carry the planet into the line of sight between us and its own star. Even though we cannot see the planet directly, we can tell that it is there, allowing follow-up observations by Pan-STARRS and other telescopes to learn more about these newly discovered exoplanets. Even farther away, enormous stellar explosions called supernovae can sometimes bring faint galaxies into view that may have never before been seen. All told, the universe is a bizarre and dramatic place, and with the constant watch that Pan-STARRS is giving us, there are plenty of unexpected surprises ahead.
Q. Even with technology like that used in Pan-STARRS, is it possible that we could fail to detect potentially dangerous asteroids or comets?
A. No single system is complete and can be sure to catch every object that is out there. Pan-STARRS’ task is to reduce risk by cataloging as many potentially hazardous asteroids and comets as possible. As Pan-STARRS starts out, nearly every discovered asteroid and comet will be a new object that has never before been seen or catalogued. As the survey continues for many years or even a decade, it will begin to “rediscover” objects that are already in the catalog. When Pan-STARRS reaches the point where 90 percent of the asteroids and comets it detects are already in its catalog, we can estimate that about 90 percent of potentially hazardous asteroids and comets have been found. This allows us to know with certainty that the overall risk to Earth is reduced because most objects that we could not know for sure whether they might be hazardous will be safely ruled out. Most importantly, specific objects that might pose a future risk will be positively identified, and resources to fully assess that risk can be focused on these objects to determine whether they are “friend or foe.” The odds favor that nearly all will be ruled out as foes, but in identifying them as friends, these objects with the near-Earth orbits have the possibility to be very easily reached for scientific exploration by robotic or human space missions.
Just how much warmer Earth will become as a result of greenhouse-gas emissions — and how much it has warmed since preindustrial times — is much debated. In a 2007 report, the Intergovernmental Panel on Climate Change, an agency formed by the United Nations to assess climate change, said that the planet’s average surface temperature will rise by between 2 and 11.5 degrees Fahrenheit by 2100, with a best estimate at between 3.2 to 7.2 degrees F. However, the IPCC’s computer models have a record of overestimating warming: If the IPCC models were right, the planet should now be hotter than it is.
The IPCC attributes the discrepancy to aerosols — microscopic particles in the atmosphere that are created by both nature (dust blown by desert winds) and human activity (liquid droplets created from fuel combustion). Because aerosols help cloud droplets form into icy particles and reflect sunlight back into space, they help to cool Earth and possibly mitigate warming caused by emissions. But Richard Lindzen, the Alfred P. Sloan Professor of Meteorology in MIT’s Department of Earth, Atmospheric and Planetary Sciences, is among those who question the accuracy of the IPCC models, and he has been critical of the aerosols argument.
In a paper published last month in the Proceedings of the National Academy of Sciences Lindzen and his former postdoctoral researcher, Yong-Sang Choi, suggest that aerosols not only cool the Earth-atmosphere system — the system by which the atmosphere and oceans interact and affect the global climate — but also heat it. By describing the potential dual effects of aerosols, the research questions the IPCC’s models.
“Current climate models generally overpredict current warming and assume that the excessive warming is cancelled by aerosols,” the researchers say in their paper. “[Our research] offers a potentially important example of where the secondary effect is to warm, thus reducing the ability of aerosols to compensate for excessive warming in current models.” That is, the degree to which aerosols can compensate for model over-prediction of warming remains open, the research suggests.
While Thomas Stocker, co-chair of the IPCC’s Working Group I that is examining the physical scientific aspects of the climate system and climate change, declined to comment on the study, he says Lindzen and Choi’s research is part of relevant peer-reviewed work that the group will assess in its Fifth Assessment Report about climate change to be published in 2013. Pinning down aerosols
In their research, Lindzen and Choi analyzed data about cloud formation and dust aerosols, or tiny particles of sand and silicate in the atmosphere, that were collected by NASA’s Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO) satellite from June 2006 through May 2007. Their analysis revealed that there were about 20 percent fewer “super-cooled” cloud particles — droplets that are a mixture of water and ice, but reflect more sunlight than ice — in regions that had dust aerosols. Such a difference, Lindzen and Choi suggest, could warm the atmosphere in those regions.
According to the researchers, the decrease in super-cooled particles occurs when aerosols travel to a layer of the atmosphere where the temperature is around minus 20 degrees Celsius, and they “effectively kill” super-cooled cloud droplets by causing them to form into ice. Fewer super-cooled cloud droplets would mean that clouds reflect less sunlight, which could have a warming effect on the climate. That effect, the researchers believe, needs to be incorporated into climate-change models. “The IPCC assumed that all the secondary effects of aerosols would be to increase reflectivity, so it has left out a very important factor that could lead to the opposite effect,” Lindzen says.
The work is important to the global-warming debate because it sheds light on the uncertainties of climate sensitivity, which is the term the IPCC uses to describe the change that a doubling of carbon dioxide would have on global average temperatures (the IPCC’s 2007 report estimates that change to be between 3.6 and 8.1 degrees F by the end of the century, with a best estimate of about 5.4 degrees F). According to Yale climate scientist Trude Storelvmo, “aerosol effects on climate, particularly via their influence on clouds, currently represent the most uncertain forcing of climate change.” Although the IPCC models assume that aerosols cool the Earth-atmosphere system, she cautions that “unless we can quantify this supposed aerosol cooling counteracting the warming due to increasing greenhouse gases, we cannot say what the climate sensitivity of the Earth-atmosphere system is.”
Because satellite data can be limited, she suggests that future research should include measurements of aerosol and cloud properties taken by instruments onboard aircraft that travel to the upper atmosphere. She thinks this combination could help address one question that remains unanswered in the paper: why few super-cooled clouds were detected over South America even though the satellite didn’t detect dust or carbon aerosols over that region.
Lindzen agrees that climate scientists can’t rely solely on remote sensing techniques to get “solid, incontrovertible data” about aerosols and clouds. Even so, he is eager for the launch of better satellites and instruments so that he and his colleagues can gather as much data as possible about how clouds evolve “so that we can better pin down what aerosols do.” Until scientists figure out that missing piece of the climate change puzzle, it will be difficult to predict the effects of future warming.
In a first, astronomers detect strong winds on an exoplanet »»
Since the first exoplanet — a planet outside our solar system — was discovered in 1995, more than 460 others have been found. While astronomers have been able to measure the size, orbital characteristics, and even some of the molecules that make up the atmospheres of some exoplanets, many mysteries about their formation and evolution remain.
A team of astronomers, including a researcher from MIT’s Kavli Institute for Astrophysics and Space Research, has become the first to measure wind in the atmosphere of an exoplanet. By detecting heavy winds on HD209458b, a huge exoplanet located 150 light years away that is slightly more than half the mass of Jupiter, the researchers could then measure the movement of the planet as it orbited its host star — also another first for exoplanetary research.
The work, which is detailed in a paper published June 24 in Nature, will guide future research on exoplanets, since understanding the properties of a planet’s atmosphere is a critical first step for characterizing how that planet formed and evolved.
Measuring the planet’s orbital movement is also important because the velocity of that movement can be used with Newton’s law of universal gravitation to get a more precise estimate of the mass of both the planet and its parent star. Before now, astronomers had to rely on complex mathematical models, as well as the changes in light that occurred when an exoplanet’s host star wobbled in response to the exoplanet’s gravitational pull, to determine the exoplanet’s mass. Thanks to a new technique that the researchers used to study HD209458b, astronomers should now be able to refine their estimates of the mass of some exoplanets and their stars.
One way that astronomers can learn a lot about an exoplanet is by observing it as it passes in front of its host star as seen from Earth. By measuring the light obscured by an exoplanet during this event, which is known as a transit, astronomers can learn details about the planet, such as its size and what kinds of molecules exist in its atmosphere. Of the 463 exoplanets discovered to date, more than 80 are known to be transiting planets. (HD209458b, identified in 1999, was the first transiting exoplanet discovered.)
Researchers detected the heavy winds in HD209458b’s atmosphere by studying carbon monoxide. According to co-author and Kavli postdoc Simon Albrecht, who collaborated with researchers from Leiden University and the Netherlands Institute for Space Research (SRON), the results are “among the many small steps the astronomy community is taking toward being able to, at some point, measure atmospheric conditions on exoplanets that are twins to our Earth.”
Doable from the ground
What makes the work, partly funded by the Netherlands Organisation for Scientific Research, “potentially groundbreaking” is the ground-based technique that was used to detect the winds and orbital movement of HD209458b, according to Adam Showman, a planetary scientist at the University of Arizona. “Just the fact this is even doable from the ground is spectacular,” he said.
Instead of using a space-based instrument like NASA’s Spitzer Space Telescope to study the faraway planet, the researchers used a ground-based, high-resolution spectrograph at the European Southern Observatory in Chile that can detect subtle changes in the wavelength of light when a planet transits its star. As HD209458b transited last August, its parent star left what lead author Ignas Snellen from the Leiden Observatory in the Netherlands described as “a fingerprint” of light that filtered through the planet’s atmosphere. The researchers then used the spectrograph to analyze that imprint of light to detect carbon monoxide molecules in the atmosphere. “It seems that H209458b is actually as carbon-rich as Jupiter and Saturn, and this could indicate that it was formed in the same way,” Snellen said.
The researchers then spent several months analyzing spectrographic measurements of the movement of the carbon monoxide thanks to the Doppler shift, a phenomenon that creates subtle color changes in wavelengths of light when something moves. When an object moves toward us, it looks slightly bluer, and when it moves away, it looks slightly redder. The spectrograph revealed color shifts in the light absorbed by the exoplanet, which indicated that something was moving the gas. That something, the researchers believe, is heavy wind that is blowing carbon monoxide in the planet’s atmosphere up to 10,000 kilometers per hour (the fastest winds ever detected on another planet in our solar system were blowing at up to 2,000 kilometers per hour on Neptune, according to previous research). By tracking the movement of the carbon monoxide, the astronomers could then measure the movement of the planet as it orbited its host star.
While the results are notable, future research must address what might be causing the heavy winds, said Showman. Right now, the spectrograph simply does not have enough spectral resolution to distinguish that level of detail.
As the team continues to refine the ground-based technique used in this research, Albrecht said that he and his colleagues must do “a better job” of analyzing exoplanetary atmospheres for molecules that have fainter spectral signals than carbon monoxide, such as water. Their next step is to measure the atmospheres of exoplanets that are located slightly farther away from their host stars to see how this distance affects detectable concentrations of carbon monoxide and other molecules.
Far beyond the orbit of Neptune in a region of the outer solar system known as the Kuiper Belt float thousands of icy, moon-sized bodies called Kuiper Belt objects (KBOs). Astronomers think they are the remnants of the bodies that slammed together to form the planets more than 4 billion years ago. Unlike Earth, which has been continually eroded by wind and water since it was formed, KBOs haven’t changed much over time and may hold clues about the early solar system and planet formation.
Until now, astronomers have used telescopes to find KBOs and obtain their spectra to determine what types of ices are on their surface. They have also used thermal-imaging techniques to get a rough idea of the size of KBOs, but other details have been difficult to glean. While astronomers think there are about 70,000 KBOs that are larger than 100 kilometers in diameter, the objects’ relatively small size and location make it hard to study them in detail. One method that has been has been proposed for studying KBOs is to observe one as it passes briefly in front of a bright star; such events, known as stellar occultations, have yielded useful information about other planets in the solar system. By monitoring the changes in starlight that occur during an occultation, astronomers can determine the object’s size and temperature, whether it has any companion objects and if it has an atmosphere.
The trick is to know enough about the orbit of a KBO to be able to predict its path and observe it as it passes in front of a star. This was done successfully for the first time last October when a team of 18 astronomy groups led by James Elliot, a professor of planetary astronomy in MIT’s Department of Earth, Atmospheric and Planetary Sciences, observed an occultation by an object named “KBO 55636.”
As Elliot and his colleagues report in a paper published June 17 in Nature, the occultation provided enough data to determine the KBO’s size and albedo, or how strongly it reflects light. The surface of 55636 turns out to be as reflective as snow and ice, which surprised the researchers because ancient objects in space usually have weathered, dull surfaces. The high albedo suggests that the KBO’s surface is made of reflective water-ice particles, and that would support a theory about how the KBO formed. Many researchers believe there was a collision that occurred one billion years ago between a dwarf planet in the Kuiper Belt known as Haumea and another object that caused Haumea’s icy mantle to break into a dozen or so smaller bodies, including 55636.
More importantly, the research demonstrates that astronomers can predict occultations accurately enough to contribute to a new NASA mission known as the Stratospheric Observatory For Infrared Astronomy (SOFIA) that completed its first in-flight observations in May. A Boeing 747SP aircraft that has a large telescope mounted in its rear fuselage, SOFIA can record infrared measurements of celestial objects that are not possible from the ground. Elliot hopes his research will help guide future flights of SOFIA to observe stellar occultations in detail.
Betting on an occultation
Elliot, who has been studying 55636’s orbit for five years, thought it would most likely pass in front of an unnamed star on Oct. 9, 2009. But the KBO’s small size made it difficult to predict exactly where the object would travel, and so, to be on the safe side, he and his colleagues assembled a network of 18 observation stations along a 5,900-kilometer stretch of the Earth’s surface that corresponded to the KBO’s predicted shadow path. Such a strategy “covered our uncertainty about where the path would go, both to the north and to the south,” Elliot explains. “It was our way of hedging our bets.”
While some of the stations couldn’t observe because of weather, and others simply didn’t detect the occultation, two stations in Hawaii captured data on the changes in starlight that occurred during the roughly 10-second occultation. After measuring the exact amount of time that the star was blocked from view, as well as the velocity with which the shadow of 55636 moved across Earth, the researchers calculated that the KBO has a radius of about 143 kilometers. Knowing this, they could then calculate the object’s albedo.
The highly reflective surface of 55636 is perplexing because the surfaces of celestial bodies in the outer solar system are supposed to darken over time as a result of dust accumulation and exposure to solar radiation. John Stansberry, an astronomer at the University of Arizona, says that if Elliot’s “solid piece of work” can be confirmed in follow-up research, then the results show that 55636 is “an extremely unique” KBO because similarly sized KBOs are thought to have significantly smaller albedos. “The result suggests that it would be worthwhile to try to measure the albedos of other Haumea family members to see if they are also very high,” says Stansberry.
Although other highly reflective bodies in the solar system, such as the dwarf planet Pluto and Saturn's moon Enceladus, have their surfaces continuously renewed with fresh ice from the condensation of atmospheric gases or by volcanic activity that spews water instead of lava, 55636 is too small for these mechanisms to be at work, says Elliot. He has no plans to investigate the cause of the high albedo but will continue to collect data about the orbits and positions of the largest KBOs in order to predict future occultations with enough accuracy that he doesn’t have to rely on a vast network of observers.
As an orthopedic oncologist who studies bone that has been damaged by cancer, Robert “Bobby” Satcher ’86, PhD ’93, HST MD ’94 is also interested in the effects of microgravity on the human body. He got the chance to experience those effects firsthand when he became the first orthopedic surgeon to venture into space in November 2009.
Satcher was one of six astronauts who spent 11 days aboard the recently retired shuttle Atlantis as part of NASA’s STS-129 Space Shuttle mission to deliver 14 tons of spare parts to the International Space Station (ISS). During the mission, he completed two spacewalks to attach hardware to the exterior of the ISS that will help keep the research facility running until 2015.
“It’s definitely the most physically demanding thing we do as astronauts,” Satcher, speaking at a talk at MIT on Tuesday hosted by the Harvard-MIT Division of Health Sciences and Technology (HST), said about his spacewalk experience. “It’s really kind of a sensory overload.”
If anyone could handle the physical and mental stress of that task, it would be Satcher, according to Joseph R. Madsen, an associate professor of neurosurgery at Harvard Medical School and president of the HST Alumni Association. “Dr. Satcher demonstrates the core idea of the HST program — combining a deep understanding of human biology with a deep understanding of engineering and science to accomplish things that can hardly be imagined,” he said. Space surgery
Satcher has been on leave as an assistant professor of orthopedic surgery at the Northwestern University Feinberg School of Medicine since 2004, when he was selected to be an astronaut. Prior to the launch of STS-129, Satcher underwent 18 months of rigorous mission training that included land- and water-survival classes and learning about the technical aspects of the space shuttle and orbital mechanics.
Despite that intensive astronaut training, it was actually Satcher’s medical background that proved to be the most valuable during the mission. Satcher said that his surgical experience helped prepare him for using highly sophisticated instruments during the two spacewalks he completed that totaled more than 12 hours. During the first spacewalk, he helped attach a spare antenna to the ISS and perform maintenance work on a robotic arm, and during his second spacewalk, he helped install a new high-pressure oxygen tank.
Satcher, who holds a doctorate in chemical engineering from MIT, said he was most intrigued with the scientific aspects of the mission, including conducting short-term experiments and delivering equipment for ongoing experiments on the ISS.
He was particularly interested in the orthopedic experiments, such as measuring how the astronauts’ heights increased in space as a result of the absence of gravity, or microgravity, and delivering mice that over-express a gene related to osteogenesis, or the process of bone formation, to the ISS. The mice will be brought back during a later mission to see how their skeletons develop in space and whether they experience bone loss.
As an orthopedic surgeon, Satcher is also interested in the negative side effects of microgravity. Although scientists have known for decades that microgravity causes bone to lose essential minerals, muscles to atrophy and the cardiovascular system to weaken, they are still experimenting with different countermeasures to pinpoint the best way to keep astronauts healthy.
Satcher was eager to test various resistive exercises, including doing squats or running attached to a treadmill, that he believes are “very effective” countermeasures to offset the effects of microgravity. “We know exercise works,” he said, adding that it still took several days for his muscles and sense of balance to readjust when he returned to Earth.
Because the space shuttle program is scheduled to end later this year, Satcher said that he would have to fly aboard a Russian spacecraft if he wanted to return to space before 2020. Even so, he remained positive about NASA’s future under President Obama’s new space policy, which would boost NASA’s budget by $6 billion over the next five years. “NASA has done a tremendous amount with very little,” he said, adding that American taxpayers pay more each year for Halloween activities ($25) than they do to send people into space ($20).
In a lecture on Monday at MIT, NASA Administrator Charles F. Bolden Jr. defended President Barack Obama’s controversial plans for the U.S. space agency’s future and touted the president’s plan to invest billions of dollars in basic science research.
Some in Congress have criticized Obama’s proposal to cancel the Constellation program, which would have sent humans to the moon by 2020, saying such a move will effectively cede U.S. space leadership to other nations. But Bolden noted that the White House’s plan would also invest an additional $6 billion in NASA over the next five years, including a 60-percent increase in earth sciences research funding, as well as a 20-percent increase in planetary sciences research. Such an expansion could revitalize NASA’s ties with institutions like MIT, which has played an instrumental role in the agency since NASA was founded in 1958.
“The frustration for me is that we always talk about the cancellation of Constellation,” former astronaut Bolden said of his appearances before Congress and interviews with the media, in which he has been grilled over the president’s plan. “But we are adding an incredible amount of money for research.”
Bolden was at MIT to deliver the 20th annual Massachusetts Space Grant Consortium (MSGC) public lecture, titled “Looking Ahead to the Future of NASA.” Headquartered at MIT, the MSGC’s primary goal is to represent NASA in Massachusetts by supporting space exploration and research by the state’s students and teachers.
David Mindell, the Frances and David Dibner Professor of the History of Engineering and Manufacturing and director of MIT’s Program in Science, Technology, and Society, said that Bolden’s defense of Obama’s proposal wasn’t surprising, given that it’s his job to do so. “But the proposal does recommend a fresh approach that, though risky, could reinvigorate human spaceflight in the U.S. and restart research — at MIT and many other places — that had been sacrificed for the Constellation program,” he said.
Professor of Aeronautics and Astronautics and Engineering Systems Dava Newman agreed, saying that the proposal would strengthen — not weaken — U.S. leadership in space. “The budget for science, engineering and technology development, testbeds and flight experiments is extraordinary, and if realized, will help NASA once again become the agency to realize exploration (both human and robotic) and major technological breakthroughs both in space and here on Earth,” Newman said. “It's very exciting to think of this future investment in science, engineering and technology and to think that MIT students and faculty will be part of the community to shape NASA's future and to realize this vision.
Looking ahead
During his talk, Bolden said NASA was going through what he called a “difficult, but very interesting” period. As a former astronaut who completed four space flights, Bolden expressed sadness about the prospect of ending NASA’s space-shuttle fleet, admitting he is “emotionally attached” to the shuttle program. But he insisted that NASA is “committed” to Obama’s new era of space exploration, which calls for a flexible path approach for NASA to gain progressively more experience, such as a lunar fly-by or exploration of asteroids, before making a trip to Mars. The plan also calls for developing a “heavy-lift” system to launch spacecraft into deep space, as well as technologies to protect humans from long-term radiation. In the future, NASA would lease vehicles from private companies to ferry astronauts to and from the International Space Station.
“The president, with my full agreement, made a change — a big change,” Bolden said of Obama’s decision to undertake a new direction for NASA, adding that the agency’s fundamental goal “to boldly advance the human presence beyond the cradle of Earth,” has not changed, and that Mars remains an “especially compelling target.”
Bolden outlined several tracks that NASA has proposed to achieve its goals, such as developing robotic technologies to scout new targets and test precision landings. He said the agency remains focused on using the International Space Station to learn more about human health issues, referring to ongoing work by ISS researchers to develop a salmonella vaccine.
He pledged NASA’s commitment to develop a commercial launch industry for carrying humans into low Earth orbit, but said that the agency was still fine-tuning specific operations details, such as whether a crew would be trained at NASA facilities. He also said the agency was honoring Obama’s request to collaborate with other countries like Saudi Arabia to foster science research.
When pressed to name a timetable for a manned mission to Mars, Bolden said it was “pretty vague,” but that if NASA started to develop the architecture for a heavy-lift launch vehicle right now, it could be as soon as the early 2020s that a spacecraft orbits the moon, and maybe 2025 for a spacecraft or robot to land on an asteroid. Those advances could make travel to Mars a reality by 2030, he said.
Regardless of a timetable, Bolden insisted that NASA’s future must include increased collaboration with research institutions like MIT, noting that, “we can’t carry out this work without engaging the public.”
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Science Podcast, 19 July 2010 -- Special: HIV Prevention Progress »»
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Galaxy Zoo and the whole Zooniverse will be well represented at the upcoming Citizen Cyberscience Summit. This event, held at King’s College London on 2-3 September 2010, has been organised in order to showcase recent examples of online citizen science and provide a forum for discussing the impact, potential and future directions of such [...] Read more...
There have been several new starters at the Zooniverse in the past few months. Myself and Stuart were remarking the other day that we have still not met the Zooites in person. Although we have come to know several of you via email, we thought it was time to rectify the situation.
We have organised a [...] Read more...
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Greetings from the sunny town of Tucson, Arizona! I’m here this week doing some observing. We are hunting Voorwerp! I left the UK on Saturday lunchtime and, in a strange convergence of fate (or more accurately time zones), arrived in the US at approximately the same time! Following a delayed flight from Denver to [...] Read more...
We just updated Supernovae Zoo with some changes. First of all notifications are now live, every day snzoo will rummage through its database and find out how many new candidates there are. If there are more than 80 it will drop everyone who has signed up for a notification a friendly email. We have tested [...] Read more...
So I don’t know about you but Moon Zoo Live is completely destroying my productivity. It’s mesmerizing watching people all around the world explore the Moon. Every so often someone pops up in a totally cool place! Here at the Zooniverse we try to do everything to feed your addiction to citizen science, so we [...] Read more...
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Astronomy Photographer of the Year Guest Gallery »»
Hey all
Just a quick heads up to advertise a great project run by Greenwich Royal Observatory. The astronomy photographer of the year competition invites members of the public to submit their images of the night sky.
This year they are asking guest astronomers to curate flicker galleries of their favourite entries and have asked me to [...] Read more...
