In late May 2015, the highest volcano in the Galapagos Islands, Wolf volcano, erupted for the first time in 33 years. The wide image and closeup of Wolf was acquired on June 11, 2015, by the ASTER instrument on NASA’s Terra satellite. The false-color images combine near-infrared, red, and green light (ASTER bands 3-2-1).
In late May 2015, the highest volcano in the Galapagos Islands, Wolf volcano, erupted for the first time in 33 years. The wide image and closeup of Wolf was acquired on June 11, 2015, by the ASTER instrument on NASA’s Terra satellite. The false-color images combine near-infrared, red, and green light (ASTER bands 3-2-1).
For the last decade, astronomers have observed curious “hotspots” on Saturn’s poles. In 2008, NASA’s Cassini spacecraft beamed back close-up images of these hotspots, revealing them to be immense cyclones, each as wide as the Earth. Scientists estimate that Saturn’s cyclones may whip up 300 mph winds, and likely have been churning for years.
While cyclones on Earth are fueled by the heat and moisture of the oceans, no such bodies of water exist on Saturn. What, then, could be causing such powerful, long-lasting storms?
In a paper published today in the journal Nature Geoscience, atmospheric scientists at MIT propose a possible mechanism for Saturn’s polar cyclones: Over time, small, short-lived thunderstorms across the planet may build up angular momentum, or spin, within the atmosphere — ultimately stirring up a massive and long-lasting vortex at the poles.
The researchers developed a simple model of Saturn’s atmosphere, and simulated the effect of multiple small thunderstorms forming across the planet over time. Eventually, they observed that each thunderstorm essentially pulls air towards the poles — and together, these many small, isolated thunderstorms can accumulate enough atmospheric energy at the poles to generate a much larger and long-lived cyclone.
The team found that whether a cyclone develops depends on two parameters: the size of the planet relative to the size of an average thunderstorm on it, and how much storm-induced energy is in its atmosphere. Given these two parameters, the researchers predicted that Neptune, which bears similar polar hotspots, should generate transient polar cyclones that come and go, while Jupiter should have none.
Morgan O’Neill, the paper’s lead author and a former PhD student in MIT’s Department of Earth, Atmospheric and Planetary Sciences (EAPS), says the team’s model may eventually be used to gauge atmospheric conditions on planets outside the solar system. For instance, if scientists detect a cyclone-like hotspot on a far-off exoplanet, they may be able to estimate storm activity and general atmospheric conditions across the entire planet.
“Before it was observed, we never considered the possibility of a cyclone on a pole,” says O’Neill, who is now a postdoc at the Weizmann Institute of Science in Israel.
“Only recently did Cassini give us this huge wealth of observations that made it possible, and only recently have we had to think about why [polar cyclones] occur.”
O’Neill’s co-authors are Kerry Emanuel, the Cecil and Ida Green Professor of Earth, Atmospheric and Planetary Sciences, and Glenn Flierl, a professor of oceanography in EAPS.
Beta-drifting toward a cyclone
Polar cyclones on Saturn are a puzzling phenomenon, since the planet, known as a gas giant, lacks an essential ingredient for brewing up such storms: water on its surface.
“There’s no surface at all — it just gets denser as you get deeper,” O’Neill says. “If you lack choppy waters or a frictional surface that allows wind to converge, which is how hurricanes form on Earth, how can you possibly get something that looks similar on a gas giant?”
The answer, she found, may be something called “beta drift” — a phenomenon by which a planet’s spin causes small thunderstorms to drift toward the poles. Beta drift drives the motion of hurricanes on Earth, without requiring the presence of water. When a storm forms, it spins in one direction at the surface, and the opposite direction toward the upper atmosphere, creating a “dipole of vorticity.” (In fact, videos of hurricanes taken from space actually depict the storm’s spin as opposite to what’s observed on the ground.)
“The whole atmosphere is kind of being dragged by the planet as the planet rotates, so all this air has some ambient angular momentum,” O’Neill explains. “If you converge a bunch of that air at the base of a thunderstorm, you’re going to get a small cyclone.”
The combination of a planet’s rotation and a circulating storm generates secondary features called beta gyres that wrap around a storm and essentially split its dipole in half, tugging the top half toward the equator, and the bottom half toward the pole.
The team developed a model of Saturn’s atmosphere and ran hundreds of simulations for hundreds of days each, allowing small thunderstorms to pop up across the planet. The researchers observed that multiple thunderstorms experienced beta drift over time, and eventually accumulated enough atmospheric circulation to create a much larger cyclone at the poles.
“Each of these storms is beta-drifting a little bit before they sputter out and die,” O’Neill says. “This mechanism means that little thunderstorms — fast, abundant, but not very strong thunderstorms — over a long period of time can actually accumulate so much angular momentum right on the pole, that you get a permanent, wildly strong cyclone.”
Next stop: Jupiter
The team also explored conditions in which planets would not form polar cyclones, even though they may experience thunderstorms. The researchers found that whether a polar cyclone forms depends on two parameters: the energy within a planet’s atmosphere, or the total intensity of its thunderstorms; and the average size of its thunderstorms, relative to the size of the planet itself. Specifically, the larger an average thunderstorm compared to a planet’s size, the more likely a polar cyclone is to develop.
O’Neill applied this relationship to Saturn, Jupiter, and Neptune. In the case of Saturn, the planet’s atmospheric conditions and storm activity are within the range that would generate a large polar cyclone. In contrast, Jupiter is unlikely to host any polar cyclones, as the ratio of any storm to its overall size would be extremely small. The dimensions of Neptune suggest that polar cyclones may exist there, albeit on a fleeting basis.
“Saturn has an intense cyclone at each pole,” says Andrew Ingersoll, professor of planetary science at Caltech, who was not involved in the study. “The model successfully accounts for that. Jupiter doesn’t seem to have polar cyclones like Saturn’s, but Jupiter isn’t tipped over as much as Saturn, so we don’t get a good view of the poles. Thus the apparent absence of polar cyclones on Jupiter is still a mystery.”
The researchers are eager to see whether their predictions, particularly for Jupiter, bear out. Next summer, NASA’s Juno spacecraft is scheduled to enter into an orbit around Jupiter, kicking off a one-year mission to map and explore Jupiter’s atmosphere.
“If what we know about Jupiter currently is correct, we predict that we won’t see these wildly strong cyclones,” O’Neill says. “We’ll find out next year if our predictions are true.”
This research was funded in part by the National Science Foundation.
Viewed from above, our solar system’s planetary orbits around the sun resemble rings around a bulls-eye. Each planet, including Earth, keeps to a roughly circular path, always maintaining the same distance from the sun.
For decades, astronomers have wondered whether the solar system’s circular orbits might be a rarity in our universe. Now a new analysis suggests that such orbital regularity is instead the norm, at least for systems with planets as small as Earth.
In a paper published in the Astrophysical Journal, researchers from MIT and Aarhus University in Denmark report that 74 exoplanets, located hundreds of light-years away, orbit their respective stars in circular patterns, much like the planets of our solar system.
These 74 exoplanets, which orbit 28 stars, are about the size of Earth, and their circular trajectories stand in stark contrast to those of more massive exoplanets, some of which come extremely close to their stars before hurtling far out in highly eccentric, elongated orbits.
“Twenty years ago, we only knew about our solar system, and everything was circular and so everyone expected circular orbits everywhere,” says Vincent Van Eylen, a visiting graduate student in MIT’s Department of Physics. “Then we started finding giant exoplanets, and we found suddenly a whole range of eccentricities, so there was an open question about whether this would also hold for smaller planets. We find that for small planets, circular is probably the norm.”
Ultimately, Van Eylen says that’s good news in the search for life elsewhere. Among other requirements, for a planet to be habitable, it would have to be about the size of Earth — small and compact enough to be made of rock, not gas. If a small planet also maintained a circular orbit, it would be even more hospitable to life, as it would support a stable climate year-round. (In contrast, a planet with a more eccentric orbit might experience dramatic swings in climate as it orbited close in, then far out from its star.)
“If eccentric orbits are common for habitable planets, that would be quite a worry for life, because they would have such a large range of climate properties,” Van Eylen says. “But what we find is, probably we don’t have to worry too much because circular cases are fairly common.”
In the past, researchers have calculated the orbital eccentricities of large, “gas giant” exoplanets using radial velocity — a technique that measures a star’s movement. As a planet orbits a star, its gravitational force will tug on the star, causing it to move in a pattern that reflects the planet’s orbit. However, the technique is most successful for larger planets, as they exert enough gravitational pull to influence their stars.
Researchers commonly find smaller planets by using a transit-detecting method, in which they study the light given off by a star, in search of dips in starlight that signify when a planet crosses, or “transits,” in front of that star, momentarily diminishing its light. Ordinarily, this method only illuminates a planet’s existence, not its orbit. But Van Eylen and his colleague Simon Albrecht, of Aarhus University, devised a way to glean orbital information from stellar transit data.
They first reasoned that if they knew the mass of a planet’s star, they could calculate how long a planet would take to orbit that star, if its orbit were circular. The mass of a star determines its gravitational pull, which in turn influences how fast a planet travels around the star.
By calculating a planet’s orbital velocity in a circular orbit, they could then estimate a transit’s duration — how long a planet would take to cross in front of a star. If the calculated transit matched an actual transit, the researchers reasoned that the planet’s orbit must be circular. If the transit were longer or shorter, the orbit must be more elongated, or eccentric.
Not so eccentric
To obtain actual transit data, the team looked through data collected over the past four years by NASA’s Kepler telescope — a space observatory that surveys a slice of the sky in search of habitable planets. The telescope has monitored the brightness of over 145,000 stars, only a fraction of which have been characterized in any detail.
The team chose to concentrate on 28 stars for which mass and radius have previously been measured, using asteroseismology — a technique that measures stellar pulsations, which reflect a star’s mass and radius.
These 28 stars host multiplanet systems — 74 exoplanets in all. The researchers obtained Kepler data for each exoplanet, looking not only for the occurrence of transits, but also their duration. Given the mass and radius of the host stars, the team calculated each planet’s transit duration if its orbit were circular, then compared the estimated transit durations with actual transit durations from Kepler data.
Across the board, Van Eylen and Albrecht found the calculated and actual transit durations matched, suggesting that all 74 exoplanets maintain circular, not eccentric, orbits.
“We found that most of them matched pretty closely, which means they’re pretty close to being circular,” Van Eylen says. “We are very certain that if very high eccentricities were common, we would’ve seen that, which we don’t.”
Van Eylen says the orbital results for these smaller planets may eventually help to explain why larger planets have more extreme orbits.
“We want to understand why some exoplanets have extremely eccentric orbits, while in other cases, such as the solar system, planets orbit mostly circularly,” Van Eylen says. “This is one of the first times we’ve reliably measured the eccentricities of small planets, and it’s exciting to see they are different from the giant planets, but similar to the solar system.”
David Kipping, an astronomer at the Harvard-Smithsonian Center for Astrophysics, notes that Van Eylen’s sample of 74 exoplanets is a relatively small slice, considering the hundreds of thousands of stars in the sky.
“I think that the evidence for smaller planets having more circular orbits is presently tentative,” says Kipping, who was not involved in the research. “It prompts us to investigate this question in more detail and see whether this is indeed a universal trend, or a feature of the small sample considered.”
In regard to our own solar system, Kipping speculates that with a larger sample of planetary systems, “one might investigate eccentricity as a function of multiplicity, and see whether the solar system’s eight planets are typical or not.”
This research was funded in part by the European Research Council.
Looking up through a telescope at the contours of the moon or at Saturn with its faint yet startlingly familiar ring system can be a life changing experience. But in the age of the Internet, sensors, and the ability to connect to observing equipment across the world from a simple desktop, it was perhaps only a matter of time before the attention of MIT’s Wallace Observatory team would turn to making their suite of off-campus telescopes work remotely.
The George R. Wallace Jr. Astrophysical Observatory (WAO), in Westford, Massachusetts, is a teaching and research facility run by the Planetary Astronomy Lab in the MIT Department of Earth, Atmospheric and Planetary Sciences (EAPS). Until now, students in the MIT observing courses 12.409 (Hands-on Astronomy: Observing Stars and Planets) and 12.410 (Observational Techniques of Optical Astronomy), have had to travel the 40 miles to and from Wallace to make their observations. But no more. Two years ago Wallace’s roll-off roof-shed that houses four 14-inch Celestron C14 telescopes was retrofitted with a custom system that allows it to be operated and scripted by a standard astronomy equipment language — and can stow the telescopes safely if bad weather arrives.
One of the greatest barriers to student data in the classes had been the two-hour round-trip transit time to WAO. Between getting there and getting back, an observing evening became such an investment of time that instructors needed to be very careful about deciding which nights to go, and which to let pass because they didn’t look like they were going to be quite good enough. With the new system based in the Green Building (Building 54), students can get started almost immediately when they and their telescopes are available — and if it should suddenly cloud up, they can close down and walk back to their dorms with only half an hour lost.
“After working on it for the past two years, we’ve at last ‘perfected’ the ability to observe with the C-14s remotely, so that by the end of the fall semester, 12.410 had students using the telescopes on Monday and Wednesday evenings from campus without the need to drive out to Wallace — without anyone being out there at all, actually,” says Michael Person, a research scientist in the Planetary Astronomy Lab and director of the Wallace Observatory.
The lion’s share of the work was carried out in-house by an assortment of stellar students in the Undergraduate Research Opportunities Programs and others, coordinated by site manager Tim Brothers. Effective and reliable design and installation of the custom shed opening and closing mechanism; acquisition, installation, and testing of remote weather sensors, and nightvision capable video cameras; as well as development of appropriate firewalls to protect the systems in Westford from hackers while allowing control from the designated remote observing lab in Cambridge, all had to come together to make observing direct from Building 54 a reality.
Brothers, who also fully refurbished the vintage “orange tube” C-14s to their original specifications over this past summer, is pleased with how things are developing. He recently expressed excitement at the fact that continuing developments have allowed the beginning of automated observing — the ability to script observations from start to finish and to “wake up with tons of data waiting for us.” A recent milestone this spring was an entirely scripted observation containing two different data sets — an asteroid light curve and Pluto astrometry — on one telescope, resulting in almost eight hours’ worth of data.
Meanwhile, automation of the domes housing Wallace’s two largest telescopes — 24-inch and 16-inch Cassegrain reflectors — is still on the WAO’s to-do list. Person says, “My long-term goal is to have the entire site ready for fully remote operations, but having students able to use the shed telescopes remotely is a first big milestone.”
“We still can’t control the weather,” he adds ruefully, “but maybe someone else in the department is working on that.”
On the 100th anniversary of Einstein’s theory of relativity, scientists at the Laser Interferometer Gravitational Observatory (LIGO) anticipate new opportunities to tease out one of the remaining mysteries of relativity theory. LIGO was designed to directly observe the gravitational waves predicted by Einstein’s remarkable theory in 1915 — a feat that, despite global participation by scientists in multiple projects, has not yet been accomplished.
This fall, LIGO — which was designed and operated by Caltech and MIT, with funding from the National Science Foundation — will reach a significant milestone as its newest incarnation, the Advanced LIGO detector, comes online. To mark this achievement, a day-long dedication ceremony is being held May 19 at the LIGO Hanford Observatory in Richland, Washington. LIGO research is carried out by the LIGO Scientific Collaboration, a group of some 950 researchers at universities around the United States and the world.
Nergis Mavalvala, the Curtis and Kathleen Marble Professor of Astrophysics at MIT, is a member of the LIGO Scientific Collaboration, a group of some 950 researchers at universities around the world who are working on the LIGO project. She explains the significance of LIGO’s new phase in gravitational wave detection.
Q: Einstein’s theory of general relativity is 100 years old this year. It has been very important in applications such as GPS, and tremendously successful in understanding astrophysical systems like black holes. Is there anything left to test about general relativity?
A: Yes. Gravitational waves, which are ripples in the fabric of space and time produced by violent events in the distant universe — for example, by the collision of two black holes or by the cores of supernova explosions — were predicted by Albert Einstein in 1916 as a consequence of his general theory of relativity. Gravitational waves are emitted by accelerating masses much in the same way electromagnetic waves are produced by accelerating charges, such as radio waves radiated by electrons accelerating in antennas. As they travel to Earth, these ripples in the space-time fabric carry information about their violent origins and about the nature of gravity that cannot be obtained by traditional astronomical observations using light.
Gravitational waves have not yet been detected directly. Scientists do, however, have great confidence that they exist because their influence on a binary pulsar system (two neutron stars orbiting each other) has been measured accurately and is in excellent agreement with the predictions. Directly detecting gravitational waves will confirm Einstein’s prediction in a new regime of extreme relativistic conditions, and open a promising new window into some of the most violent and cataclysmic events in the cosmos.
Q: How do you directly detect gravitational waves?
A: According to Einstein’s theory, the relative distance between objects will change very slightly when a gravitational wave passes by. Researchers have built long L-shaped interferometers that use a laser split into two beams that travel back and forth down multi-kilometer-long arms. The interference between the beams is used to monitor the distance between precisely configured mirrors. When a gravitational wave passes through the interferometer, the distance between the mirrors changes by a distance of one-thousandth the size of a proton.
LIGO comprises two 4-km-long interferometers, one each at Hanford, Washington, and Livingston, Louisiana. The initial LIGO detectors that operated between 2000 and 2010 were sensitive enough to detect the collision and merging of two neutron stars out to the Virgo galaxy cluster, or 50 million light years away, but no detections of gravitational waves were made. Advanced LIGO, a new detector now being commissioned, is expected to be 10 times more sensitive and probe a thousand-fold greater volume of the universe.
Q: What will Advanced LIGO tell us about the universe?
A: With the 10-fold improvement in sensitivity comes a significant increase in the sensitive frequency range and the ability to tune the instrument for specific astrophysical sources. Advanced LIGO should allow scientists to observe the final death throes of pairs of neutron stars or black holes as they spiral closer to each other, coalesce into one larger black hole, and vibrate ever more faintly — a process much like two soap bubbles becoming one. Advanced LIGO will also allow scientists to zoom in on and study periodic signals from pulsars that spin as fast as a household blender, radiating gravitational waves at frequencies of many hundreds of Hertz (frequencies that correspond to high notes on an organ).
Advanced LIGO will also be used to search for the gravitational cosmic background that originated a mere 10-35 seconds after the Big Bang. Detecting the gravitational cosmic background would enable scientists to study the universe at its very inception: 400,000 years before the earliest glimmers of light — the cosmic microwave background — began to stream toward us.
Every time scientists have turned new instruments with unprecedented capabilities towards the cosmos, they have discovered amazing and unexpected things about our vast and mysterious universe. Advanced LIGO has the potential to be such a pioneering instrument, one that will allow scientists to observe the universe in a completely new way.
The U.S. Senate yesterday unanimously confirmed the appointment of MIT Professor Dava Newman as NASA deputy administrator, the agency’s number-two position. The appointment will become official when signed by President Obama.
Newman is a professor of aeronautics and astronautics and of engineering systems. On the MIT faculty since 1993, she directs the Institute’s Technology and Policy Program and MIT Portugal Program, and is co-director of the Department of Aeronautics and Astronautics’ Man Vehicle Laboratory. She is a Harvard-MIT Division of Health Sciences and Technology faculty member, and a Margaret McVicar Faculty Fellow.
Accepting the confirmation, Newman said, “It’s an enormous honor to serve at NASA in times when our country is extending humanity’s reach into space while strengthening American leadership here on Earth. I’m profoundly grateful to President Obama, the United States Senate, and Administrator Bolden — along with everyone at MIT. I can’t wait to come aboard.”
NASA Administrator Charles Bolden said, “I am delighted with the Senate confirmation of Dr. Dava Newman to be the deputy administrator of NASA. The strong bipartisan support Dr. Newman received in the Senate is a reflection of her well-earned reputation and renown as a global leader in science and technology research and policy.”
According to NASA, the deputy administrator “provides overall leadership, planning, and policy direction.” Her duties will include leading NASA governmental affairs; oversight of the agency’s offices, communications, and educational programs; and serving as the NASA representative to the multinational partnership that manages the International Space Station.
Newman received her BS from the University of Notre Dame. She earned MS degrees in aeronautics and astronautics and technology and policy in 1989 and a PhD in aerospace biomedical engineering in 1992, all from MIT.
Her research has included modeling human performance in low and micro-gravity conditions, examining the dynamics and control of astronaut motion, and the development of assisted walking devices for the physically handicapped. Perhaps her most prominent project has been development of the BioSuit, a skintight spacesuit that would give astronauts unprecedented comfort and freedom in exploration of planetary surfaces and extra-vehicular activity.
The deputy administrator position has been vacant since September 2013 when Lori Garver stepped down to accept a job with the Air Line Pilots Association.
Chancellor Cynthia Barnhart announced today that alumnus Mike Massimino SM ’88, PhD ’92 will be the first-ever guest speaker at MIT’s Investiture of Doctoral Hoods, a ceremony for PhD candidates held the day before Commencement.
“We are thrilled that Dr. Massimino has accepted the invitation to speak on June 4,” says Barnhart, who hosts the hooding ceremony. “His words will motivate and inspire our doctoral candidates as they make this significant transition from student life.”
The 2015 Investiture of Doctoral Hoods takes place Thursday, June 4, at 11:30 a.m. in the Johnson Athletics Center Ice Rink. The ceremony is open to family and friends of doctoral candidates; no tickets are required.
Last fall, on the recommendation of Eric Grimson, chancellor for academic advancement and chair of the Commencement Committee, a proposal to invite a guest speaker was brought to that committee for consideration. Consultation with doctoral students and alumni indicated keen interest in a guest speaker, with preference for an MIT PhD who could speak empathetically to candidates as they complete their doctoral studies and begin their professional careers.
Grimson extended his appreciation to all who participated in the pilot speaker selection process: “I’d like to thank the Commencement Committee, the department heads who submitted nominations, and the doctoral candidate working group for their collaboration to enhance the ceremony. We couldn’t be more delighted with the outcome.”
Massimino earned his undergraduate degree from Columbia University, where he is now professor of professional practice at the Fu Foundation School of Engineering and Applied Science; he worked as a systems engineer at IBM before coming to MIT to begin graduate work. His research as an MIT graduate student in mechanical engineering — on human operator control of space robotics systems — ultimately led to two patents.
After receiving his PhD from MIT in 1992, Massimino worked at McDonnell Douglas Aerospace in Houston as a research engineer, during which time he was also an adjunct assistant professor of mechanical engineering and material sciences at Rice University. In 1995, he became an assistant professor at Georgia Tech’s School of Industrial and Systems Engineering, where he taught human-machine systems engineering and researched human-machine interfaces for space and aircraft systems.
After joining NASA in 1996, Massimino logged more than 570 hours in space, 30 hours of which were on spacewalks; the focus of his two missions was the servicing of the Hubble Space Telescope. He spoke at MIT in 2011 as part of the Institute’s sesquicentennial celebration, and last fall as part of events marking the centennial of the Department of Aeronautics and Astronautics.
Today, Massimino is known for his efforts to make aerospace engineering accessible to the public; at present, he has 1.31 million Twitter followers and a recurring role (as himself) on the CBS sitcom “The Big Bang Theory.”
“Mike’s service to the country during his nearly 20 years at NASA is a credit to MIT and to mechanical engineers everywhere,” says Gang Chen, the Carl Richard Soderberg Professor in Power Engineering and head of the Department of Mechanical Engineering. “His commitment to public education, combined with a distinguished teaching and technical career, is the very best of ‘mens et manus.’ … It will be a great privilege to welcome Mike back to MIT.”
By News Office
Apollo 11 astronaut Michael Collins was part of the three-person crew that flew on mankind’s first mission to land on the moon, but he was the one who remained in orbit and never got to the lunar surface. In a talk at MIT yesterday as part of a class in the Department of Aeronautics and Astronautics (AeroAstro), Collins said that he probably could have had a chance to walk on the moon after all, had he chosen to remain at NASA after that epochal mission.
“What I gave up probably was the opportunity to be the last person to walk on the moon,” Collins said in response to a question from the audience. Although there was no guarantee, he said, under the rotation system for crew selection at that time, he would likely have been named as commander of the Apollo 17 mission, which turned out to be the last to visit the moon.
Instead, Collins retired from NASA and went on to other things: writing a bestselling book about his experiences, called “Carrying the Fire,” and becoming director of the Smithsonian Air and Space Museum in Washington. After the success of Apollo 11 in fulfilling President John F. Kennedy’s call to send a man to the moon and back before the end of the 1960s, Collins said, “My mindset was, ‘It’s over, we did it’.”
Collins, who also appeared at MIT last year as part of AeroAstro’s 100th anniversary celebration, was back on campus this week to speak to a class on the history of the Apollo program. The course, “Engineering Apollo,” is taught by David Mindell, the Frances and David Dibner Professor of the History of Engineering and Manufacturing and a professor in the Department of Aeronautics and Astronautics.
A hero to many
“He’s a hero to many of us who have followed the world of Apollo,” Mindell said in introducing Collins. Among the numerous honors bestowed on Collins, Mindell said, perhaps the ones that would resonate most strongly at MIT were the naming of both an asteroid and a lunar crater after him. Collins’ book, Mindell added, is widely considered the best astronaut book from that era — or maybe ever.
Before flying the Apollo 11 mission, Collins graduated from the United States Military Academy at West Point, joined the Air Force, and became a test pilot, flying a variety of fighter jets. Though he had never anticipated flying into space, when President Dwight D. Eisenhower announced that U.S. astronauts would be selected from among qualified test pilots, Collins realized he was part of a select pool of perhaps 200 people, and decided to apply.
Prior to Eisenhower’s decision, Collins said, there were “a lot of crazy ideas” about how to choose astronauts, including suggestions for selecting people “accustomed to danger, including bullfighters,” or those used to having to breathe through special equipment, such as scuba divers.
Collins’ first mission was on Gemini 10, flying a two-person capsule that he recalled fondly as a “nice little flying machine.” On that mission, he became the fourth human ever to perform an “extra-vehicular activity,” or spacewalk.
The most challenging part of that mission, Collins said, was a first attempt at a rendezvous and docking between two spacecraft in orbit — an essential part of the preparations for the eventual lunar missions. “It was the rendezvous that probably bothered us more than anything,” he said, because of the technical complexity and risks of bringing together two vehicles flying in different orbits at high speed.
To train, the astronauts spent a lot of time in simulators, which faithfully reproduced the spacecraft’s interior and controls. That was a big improvement over preparation as a test pilot, he said, where there often were no simulators for the testing of experimental craft.
“I spent probably 600 hours in one simulator” while preparing for the Gemini mission, Collins said, in addition to many hours in other simulators. Overall, he said, “We were pretty well prepared” for both the Apollo and Gemini flights.
Basketballs and dancing
Asked about MIT’s role in producing the guidance system for the Apollo program, Collins recalled meeting Charles “Doc” Draper, then head of the MIT Instrumentation Lab, who was responsible for that system. “When I think of the instrumentation lab, I think of a basketball and ballroom dancing,” he said.
The “basketball,” he explained, was the heart of the inertial guidance system — a sphere that contained a timer, three gyroscopes, and three accelerometers. “You told it what time it was, and where it was,” he said, and “it knew where you were, and where you were going. That was the heart of Apollo.”
As for the ballroom dancing, he said, that referred to Draper himself — who, despite the hectic preparations for the lunar mission, “would disappear for weekends, and come back with these trophies for ballroom dancing. I thought that was so cool!”
Collins’ talk was open to the MIT community. He was asked about contingency planning in case the other two astronauts, Neil Armstrong and Buzz Aldrin, had been unable to return from the moon’s surface — which could have happened due to any number of malfunctions.
In that event, Collins said, “I’d go home,” leaving the others behind. “They knew that, and I knew that, but it’s not something we ever talked about. What’s the point?”
As for the future of the space program, Collins was emphatic: “I think NASA should be renamed NAMA,” he said. “They ought to make [Mars] their one overriding goal and destination.”
A handful of new stars are born each year in the Milky Way, while many more blink on across the universe. But astronomers have observed that galaxies should be churning out millions more stars, based on the amount of interstellar gas available.
Now researchers from MIT, Columbia University, and Michigan State University have pieced together a theory describing how clusters of galaxies may regulate star formation. They describe their framework this week in the journal Nature.
When intracluster gas cools rapidly, it condenses, then collapses to form new stars. Scientists have long thought that something must be keeping the gas from cooling enough to generate more stars — but exactly what has remained a mystery.
For some galaxy clusters, the researchers say, the intracluster gas may simply be too hot — on the order of hundreds of millions of degrees Celsius. Even if one region experiences some cooling, the intensity of the surrounding heat would keep that region from cooling further — an effect known as conduction.
“It would be like putting an ice cube in a boiling pot of water — the average temperature is pretty much still boiling,” says Michael McDonald, a Hubble Fellow in MIT’s Kavli Institute for Astrophysics and Space Research. “At super-high temperatures, conduction smooths out the temperature distribution so you don’t get any of these cold clouds that should form stars.”
For so-called “cool core” galaxy clusters, the gas near the center may be cool enough to form some stars. However, a portion of this cooled gas may rain down into a central black hole, which then spews out hot material that serves to reheat the surroundings, preventing many stars from forming — an effect the team terms “precipitation-driven feedback.”
“Some stars will form, but before it gets too out of hand, the black hole will heat everything back up — it’s like a thermostat for the cluster,” McDonald says. “The combination of conduction and precipitation-driven feedback provides a simple, clear picture of how star formation is governed in galaxy clusters.”
Crossing a galactic threshold
Throughout the universe, there exist two main classes of galaxy clusters: cool core clusters — those that are rapidly cooling and forming stars — and non-cool core clusters — those have not had sufficient time to cool.
The Coma cluster, a non-cool cluster, is filled with gas at a scorching 100 million degrees Celsius. To form any stars, this gas would have to cool for several billion years. In contrast, the nearby Perseus cluster is a cool core cluster whose intracluster gas is a relatively mild several million degrees Celsius. New stars occasionally emerge from the cooling of this gas in the Perseus cluster, though not as many as scientists would predict.
“The amount of fuel for star formation outpaces the amount of stars 10 times, so these clusters should be really star-rich,” McDonald says. “You really need some mechanism to prevent gas from cooling, otherwise the universe would have 10 times as many stars.”
McDonald and his colleagues worked out a theoretical framework that relies on two anti-cooling mechanisms.
The group calculated the behavior of intracluster gas based on a galaxy cluster’s radius, mass, density, and temperature. The researchers found that there is a critical temperature threshold below which the cooling of gas accelerates significantly, causing gas to cool rapidly enough to form stars.
According to the group’s theory, two different mechanisms regulate star formation, depending on whether a galaxy cluster is above or below the temperature threshold. For clusters that are significantly above the threshold, conduction puts a damper on star formation: The surrounding hot gas overwhelms any pockets of cold gas that may form, keeping everything in the cluster at high temperatures.
“For these hotter clusters, they’re stuck in this hot state, and will never cool and form stars,” McDonald says. “Once you get into this very high-temperature regime, cooling is really inefficient, and they’re stuck there forever.”
For gas at temperatures closer to the lower threshold, it’s much easier to cool to form stars. However, in these clusters, precipitation-driven feedback starts to kick in to regulate star formation: While cooling gas can quickly condense into clouds of droplets that can form stars, these droplets can also rain down into a central black hole — in which case the black hole may emit hot jets of material back into the cluster, heating the surrounding gas back up to prevent further stars from forming.
“In the Perseus cluster, we see these jets acting on hot gas, with all these bubbles and ripples and shockwaves,” McDonald says. “Now we have a good sense of what triggered those jets, which was precipitating gas falling onto the black hole.”
McDonald and his colleagues compared their theoretical framework to observations of distant galaxy clusters, and found that their theory matched the observed differences between clusters. The team collected data from the Chandra X-ray Observatory and the South Pole Telescope — an observatory in Antarctica that searches for far-off massive galaxy clusters.
The researchers compared their theoretical framework with the gas cooling times of every known galaxy cluster, and found that clusters filtered into two populations — very slowly cooling clusters, and clusters that are cooling rapidly, closer to the rate predicted by the group as a critical threshold.
By using the theoretical framework, McDonald says researchers may be able to predict the evolution of galaxy clusters, and the stars they produce.
“We’ve built a track that clusters follow,” McDonald says. “The nice, simple thing about this framework is that you’re stuck in one of two modes, for a very long time, until something very catastrophic bumps you out, like a head-on collision with another cluster.”
The researchers hope to look deeper into the theory to see whether the mechanisms regulating star formation in clusters also apply to individual galaxies. Preliminary evidence, he says, suggests that is the case.
“If we can use all this information to understand why or why not stars form around us, then we’ve made a big step forward,” McDonald says.
“[These results] look very promising,” says Paul Nulsen, an astronomer at the Harvard-Smithsonian Center for Astrophysics who was not involved in this research. “More work will be needed to show conclusively that precipitation is the main source of the gas that powers feedback. Other processes in the feedback cycle also need to be understood. For example, there is still no consensus on how the gas falling into a massive black hole produces energetic jets, or how they inhibit cooling in the remaining gas. This is not the end of the story, but it is an important insight into a problem that has proved a lot more difficult than anyone ever anticipated.”
This research was funded in part by the National Science Foundation and NASA.
Meteorologists sometimes struggle to accurately predict the weather here on Earth, but now we can find out how cloudy it is on planets outside our solar system, thanks to researchers at MIT.
In a paper to be published in the Astrophysical Journal, researchers in the Department of Earth, Atmospheric, and Planetary Sciences (EAPS) at MIT describe a technique that analyzes data from NASA’s Kepler space observatory to determine the types of clouds on planets that orbit other stars, known as exoplanets.
The team, led by Kerri Cahoy, an assistant professor of aeronautics and astronautics at MIT, has already used the method to determine the properties of clouds on the exoplanet Kepler-7b. The planet is known as a “hot Jupiter,” as temperatures in its atmosphere hover at around 1,700 kelvins.
NASA’s Kepler spacecraft was designed to search for Earth-like planets orbiting other stars. It was pointed at a fixed patch of space, constantly monitoring the brightness of 145,000 stars. An orbiting exoplanet crossing in front of one of these stars causes a temporary dimming of this brightness, allowing researchers to detect its presence.
Researchers have previously shown that by studying the variations in the amount of light coming from these star systems as a planet transits, or crosses in front or behind them, they can detect the presence of clouds in that planet’s atmosphere. That is because particles within the clouds will scatter different wavelengths of light.
Modeling cloud formation
To find out if this data could be used to determine the composition of these clouds, the MIT researchers studied the light signal from Kepler-7b. They used models of the temperature and pressure of the planet’s atmosphere to determine how different types of clouds would form within it, says lead author Matthew Webber, a graduate student in Cahoy’s group at MIT.
“We then used those cloud models to determine how light would reflect off the atmosphere of the planet [for each type of cloud], and tried to match these possibilities to the actual observations from the Kepler mission itself,” Webber says. “So we ran a large set of models, to see which models fit best statistically to the observations.”
By working backward in this way, they were able to match the Kepler spacecraft data to a type of cloud made out of vaporized silicates and magnesium. The extremely high temperatures in the Kepler-7b atmosphere mean that some minerals that commonly exist as rocks on Earth’s surface instead exist as vapors high up in the planet’s atmosphere. These mineral vapors form small cloud particles as they cool and condense.
Kepler-7b is a tidally locked planet, meaning it always shows the same face to its star — just as the moon does to Earth. As a result, around half of the planet’s day side — that which constantly faces the star — is covered by these magnesium silicate clouds, the team found.
“We are really doing nothing more complicated than putting a telescope into space and staring at a star with a camera,” Cahoy says. “Then we can use what we know about the universe, in terms of temperatures and pressures, how things mix, how they stratify in an atmosphere, to try to figure out what mix of things would be causing the observations that we’re seeing from these very basic instruments,” she says.
A clue on exoplanet atmospheres
Understanding the properties of the clouds on Kepler-7b, such as their mineral composition and average particle size, tells us a lot about the underlying physical nature of the planet’s atmosphere, says team member Nikole Lewis, a postdoc in EAPS. What’s more, the method could be used to study the properties of clouds on different types of planet, Lewis says: “It’s one of the few methods out there that can help you determine if a planet even has an atmosphere, for example.”
A planet’s cloud coverage and composition also has a significant impact on how much of the energy from its star it will reflect, which in turn affects its climate and ultimately its habitability, Lewis says. “So right now we are looking at these big gas-giant planets because they give us a stronger signal,” she says. “But the same methodology could be applied to smaller planets, to help us determine if a planet is habitable or not.”
The researchers hope to use the method to analyze data from NASA’s follow-up to the Kepler mission, known as K2, which began studying different patches of space last June. They also hope to use it on data from MIT’s planned Transiting Exoplanet Survey Satellite (TESS) mission, says Cahoy.
“TESS is the follow-up to Kepler, led by principal investigator George Ricker, a senior research scientist in the MIT Kavli Institute for Astrophysics and Space Research. It will essentially be taking similar measurements to Kepler, but of different types of stars,” Cahoy says. “Kepler was tasked with staring at one group of stars, but there are a lot of stars, and TESS is going to be sampling the brightest stars across the whole sky,” she says.
This paper is the first to take circulation models including clouds and compare them with the observed distribution of clouds on Kepler-7b, says Heather Knutson, an assistant professor of planetary science at Caltech who was not involved in the research.
“Their models indicate that the clouds on this planet are most likely made from liquid rock,” Knutson says. “This may sound exotic, but this planet is a roasting hot gas-giant planet orbiting very close to its host star, and we should expect that it might look quite different than our own Jupiter.”