Life on an aquaplanet

Nearly 2,000 planets beyond our solar system have been identified to date. Whether any of these exoplanets are hospitable to life depends on a number of criteria. Among these, scientists have thought, is a planet’s obliquity — the angle of its axis relative to its orbit around a star.

Earth, for instance, has a relatively low obliquity, rotating around an axis that is nearly perpendicular to the plane of its orbit around the sun. Scientists suspect, however, that exoplanets may exhibit a host of obliquities, resembling anything from a vertical spinning top to a horizontal rotisserie. The more extreme the tilt, the less habitable a planet may be — or so the thinking has gone.

Now scientists at MIT have found that even a high-obliquity planet, with a nearly horizontal axis, could potentially support life, so long as the planet were completely covered by an ocean. In fact, even a shallow ocean, about 50 meters deep, would be enough to keep such a planet at relatively comfortable temperatures, averaging around 60 degrees Fahrenheit year-round.  

David Ferreira, a former research scientist in MIT’s Department of Earth, Atmospheric and Planetary Sciences (EAPS), says that on the face of it, a planet with high obliquity would appear rather extreme: Tilted on its side, its north pole would experience daylight continuously for six months, and then darkness for six months, as the planet revolves around its star.

“The expectation was that such a planet would not be habitable: It would basically boil, and freeze, which would be really tough for life,” says Ferreira, who is now a lecturer at the University of Reading, in the United Kingdom. “We found that the ocean stores heat during summer and gives it back in winter, so the climate is still pretty mild, even in the heart of the cold polar night. So in the search for habitable exoplanets, we’re saying, don’t discount high-obliquity ones as unsuitable for life.”

Details of the group’s analysis are published in the journal Icarus. The paper’s co-authors are Ferreira; Sara Seager, the Class of 1941 Professor in EAPS and MIT’s Department of Physics; John Marshall, the Cecil and Ida Green Professor in Earth and Planetary Sciences; and Paul O’Gorman, an associate professor in EAPS.

Tilting toward a habitable exoplanet

Ferreira and his colleagues used a model developed at MIT to simulate a high-obliquity “aquaplanet” — an Earth-sized planet, at a similar distance from its sun, covered entirely in water. The three-dimensional model is designed to simulate circulations among the atmosphere, ocean, and sea ice, taking into the account the effects of winds and heat in driving a 3000-meter deep ocean. For comparison, the researchers also coupled the atmospheric model with simplified, motionless “swamp” oceans of various depths: 200 meters, 50 meters, and 10 meters.

The researchers used the detailed model to simulate a planet at three obliquities: 23 degrees (representing an Earth-like tilt), 54 degrees, and 90 degrees.

For a planet with an extreme, 90-degree tilt, they found that a global ocean — even one as shallow as 50 meters — would absorb enough solar energy throughout the polar summer and release it back into the atmosphere in winter to maintain a rather mild climate. As a result, the planet as a whole would experience spring-like temperatures year round.

“We were expecting that if you put an ocean on the planet, it might be a bit more habitable, but not to this point,” Ferreira says. “It’s really surprising that the temperatures at the poles are still habitable.”

A runaway “snowball Earth”

In general, the team observed that life could thrive on a highly tilted aquaplanet, but only to a point. In simulations with a shallower ocean, Ferreira found that waters 10 meters deep would not be sufficient to regulate a high-obliquity planet’s climate. Instead, the planet would experience a runaway effect: As soon as a bit of ice forms, it would quickly spread across the dark side of the planet. Even when this side turns toward the sun, according to Ferreira, it would be too late: Massive ice sheets would reflect the sun’s rays, allowing the ice to spread further into the newly darkened side, and eventually encase the planet.

“Some people have thought that a planet with a very large obliquity could have ice just around the equator, and the poles would be warm,” Ferreira says. “But we find that there is no intermediate state. If there’s too little ocean, the planet may collapse into a snowball. Then it wouldn’t be habitable, obviously.”

Darren Williams, a professor of physics and astronomy at Pennsylvania State University, says past climate modeling has shown that a wide range of climate scenarios are possible on extremely tilted planets, depending on the sizes of their oceans and landmasses. Ferreira’s results, he says, reach similar conclusions, but with more detail.

“There are one or two terrestrial-sized exoplanets out of a thousand that appear to have densities comparable to water, so the probability of an all-water planet is at least 0.1 percent,” Williams says. “The upshot of all this is that exoplanets at high obliquity are not necessarily devoid of life, and are therefore just as interesting and important to the astrobiology community.”

By Jennifer Chu | MIT News Office

Image of the Day: Thor’s Helmet

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This image of Thor’s Helmet, or formally NGC2359, was obtained with the wide-field view of the Mosaic camera on the KPNO 0.9m-meter telescope at Kitt Peak National Observatory. Thor’s Helmet is a giant bubble that is being blown off of the Wolf-Rayet star HD 56925. Wolf-Rayet stars are extremely massive stars that are very hot and luminous. Their intense energy blows off the outer layers, causing the bubble shape seen here. The complex shape of the bubble is due to its interaction with dust and gas in which the star is embedded.

Image credit: T.A. Rector (University of Alaska Anchorage) and NOAO/AURA/NSF

Life on an aquaplanet

Nearly 2,000 planets beyond our solar system have been identified to date. Whether any of these exoplanets are hospitable to life depends on a number of criteria. Among these, scientists have thought, is a planet’s obliquity — the angle of its axis relative to its orbit around a star.

Earth, for instance, has a relatively low obliquity, rotating around an axis that is nearly perpendicular to the plane of its orbit around the sun. Scientists suspect, however, that exoplanets may exhibit a host of obliquities, resembling anything from a vertical spinning top to a horizontal rotisserie. The more extreme the tilt, the less habitable a planet may be — or so the thinking has gone.

Now scientists at MIT have found that even a high-obliquity planet, with a nearly horizontal axis, could potentially support life, so long as the planet were completely covered by an ocean. In fact, even a shallow ocean, about 50 meters deep, would be enough to keep such a planet at relatively comfortable temperatures, averaging around 60 degrees Fahrenheit year-round.  

David Ferreira, a former research scientist in MIT’s Department of Earth, Atmospheric and Planetary Sciences (EAPS), says that on the face of it, a planet with high obliquity would appear rather extreme: Tilted on its side, its north pole would experience daylight continuously for six months, and then darkness for six months, as the planet revolves around its star.

“The expectation was that such a planet would not be habitable: It would basically boil, and freeze, which would be really tough for life,” says Ferreira, who is now a lecturer at the University of Reading, in the United Kingdom. “We found that the ocean stores heat during summer and gives it back in winter, so the climate is still pretty mild, even in the heart of the cold polar night. So in the search for habitable exoplanets, we’re saying, don’t discount high-obliquity ones as unsuitable for life.”

Details of the group’s analysis are published in the journal Icarus. The paper’s co-authors are Ferreira; Sara Seager, the Class of 1941 Professor in EAPS and MIT’s Department of Physics; John Marshall, the Cecil and Ida Green Professor in Earth and Planetary Sciences; and Paul O’Gorman, an associate professor in EAPS.

Tilting toward a habitable exoplanet

Ferreira and his colleagues used a model developed at MIT to simulate a high-obliquity “aquaplanet” — an Earth-sized planet, at a similar distance from its sun, covered entirely in water. The three-dimensional model is designed to simulate circulations among the atmosphere, ocean, and sea ice, taking into the account the effects of winds and heat in driving a 3000-meter deep ocean. For comparison, the researchers also coupled the atmospheric model with simplified, motionless “swamp” oceans of various depths: 200 meters, 50 meters, and 10 meters.

The researchers used the detailed model to simulate a planet at three obliquities: 23 degrees (representing an Earth-like tilt), 54 degrees, and 90 degrees.

For a planet with an extreme, 90-degree tilt, they found that a global ocean — even one as shallow as 50 meters — would absorb enough solar energy throughout the polar summer and release it back into the atmosphere in winter to maintain a rather mild climate. As a result, the planet as a whole would experience spring-like temperatures year round.

“We were expecting that if you put an ocean on the planet, it might be a bit more habitable, but not to this point,” Ferreira says. “It’s really surprising that the temperatures at the poles are still habitable.”

A runaway “snowball Earth”

In general, the team observed that life could thrive on a highly tilted aquaplanet, but only to a point. In simulations with a shallower ocean, Ferreira found that waters 10 meters deep would not be sufficient to regulate a high-obliquity planet’s climate. Instead, the planet would experience a runaway effect: As soon as a bit of ice forms, it would quickly spread across the dark side of the planet. Even when this side turns toward the sun, according to Ferreira, it would be too late: Massive ice sheets would reflect the sun’s rays, allowing the ice to spread further into the newly darkened side, and eventually encase the planet.

“Some people have thought that a planet with a very large obliquity could have ice just around the equator, and the poles would be warm,” Ferreira says. “But we find that there is no intermediate state. If there’s too little ocean, the planet may collapse into a snowball. Then it wouldn’t be habitable, obviously.”

Darren Williams, a professor of physics and astronomy at Pennsylvania State University, says past climate modeling has shown that a wide range of climate scenarios are possible on extremely tilted planets, depending on the sizes of their oceans and landmasses. Ferreira’s results, he says, reach similar conclusions, but with more detail.

“There are one or two terrestrial-sized exoplanets out of a thousand that appear to have densities comparable to water, so the probability of an all-water planet is at least 0.1 percent,” Williams says. “The upshot of all this is that exoplanets at high obliquity are not necessarily devoid of life, and are therefore just as interesting and important to the astrobiology community.”

By Jennifer Chu | MIT News Office

Image of the Day: Galaxy evolution modeled

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An interstellar mystery of why stars form has been solved thanks to the most realistic supercomputer simulations of galaxies yet made. Galaxy simulations were tested on the Stampede supercomputer of the Texas Advanced Computing Center (TACC), an Extreme Science and Engineering Discovery Environment-allocated resource funded by the National Science Foundation.

Image credit: Philip Hopkins/Caltech

Tracking what students grasp

As a teaching assistant at the MIT Sloan School of Management in 2010, Amit Maimon MBA ’11 witnessed the origins of a technological phenomenon: Smartphones and tablets had started creeping into the classroom in the hands of students.

But instead of dismissing these devices as distractions, Maimon saw a way to leverage them to help teachers get a better idea of what students grasp during lectures.

That year, Maimon co-developed Socrative, an app that lets teachers design or select premade quizzes for students to answer, publicly or anonymously, on personal mobile devices during lectures. The app is now being used by about 1.1 million teachers and millions of students across the globe.

The idea is that students respond better to quizzes deployed via mobile devices — “which they’re already staring at,” Maimon says — and many feel more comfortable answering questions anonymously. For the teacher, the accumulated data gives immediate feedback on student comprehension — allowing tailoring of lectures to address problematic material — and tracks student or class progress over time.

“Teachers benefit tremendously by having knowledge of what their students find easy or difficult, what they’re understanding or not, in the moment, in class,” says Maimon, who co-founded a startup, also called Socrative, to commercialize the app. “Teachers [with Socrative] can see how well the class is doing in a very detailed way, and see who’s struggling more, what the class doesn’t understand, and even which students can help others.”

Quizzes can be designed, using a “teacher” app, on any mobile device — either as one-off questions or as a series of true-or-false, multiple-choice, or open-ended questions. In the classroom, students can punch in a class’s identification number on their “student” apps and answer away. Color-coded results for each student and question pop up instantly in the teacher app in rows and columns, with green boxes indicating correct responses, and red boxes indicating incorrect responses.

Importantly, the app is a time-saver — grading is automatic, and there’s a growing database of premade quizzes designed and shared by teachers — which has contributed to its wide adoption, Maimon says. In June, after accumulating 750,000 teacher users worldwide, Socrative sold for $5 million in stock and cash to MasteryConnect, a company that provides digital student-assessment tools to around 85 percent of U.S. school districts.

Current Socrative employees — including two co-founders, Benjamin Berte and Michael West — are further developing the app under MasteryConnect. (After the acquisition, Maimon is no longer part of the company.)

From classroom to classroom

Socrative was conceived and trialed in course 15.060 (Data, Models, Decisions), where Maimon served as a teaching assistant. Frequently, after lectures, students would pose questions about certain aspects of material that were not fully addressed in class, reflecting an understanding that was very different from what he might have expected.

Back then, the only real-time student-response systems were “clickers” — remote-control-like devices with buttons students can press to answer questions or vote in class. But teachers usually rent those systems, which can be expensive, and the systems are difficult to implement.

Seeing the inevitability of mobile devices in the classroom, Maimon recruited fellow MIT Sloan students — Slava Menn MBA ’11, Puneet Newaskar SM ’03, MBA ’11, Karan Singh MBA ’11, Tal Snir MBA ’11, and Jaime Contreras MBA ’11 — to help build an early prototype for an app that would send out a few multiple-choice questions on material he taught during class.

When he used the app in class a few days later, Maimon saw the potential power of gathering anonymous, real-time data. First, his students voted on answers to lesson-based questions by a show of hands. Then the students weighed in anonymously on the same questions on the prototype app. Maimon saw that certain answers received more votes anonymously than by a show of hands. One reason, he posits: Students may be uncomfortable admitting they don’t understand, so they don’t ask for clarification.

“That’s when the power of real-time anonymity came in, which is fantastic because it changes the social layout,” he says. “If you’re afraid of asking a question because you think you’re the only one who doesn’t understand it, and then suddenly you remove that barrier, you see many others don’t understand as well, and it changes people’s comfort levels.”

In 2010, Maimon recruited Berte and West, and turned to mentors in MIT’s Venture Mentoring Service and Martin Trust Center for MIT Entrepreneurship for advice on marketing and financing, among other things. In 2011, they joined the Imagine K-12 startup accelerator in Palo Alto, Calif., and grew out their team.

“It was internal and external momentum,” Maimon says. “The more we saw people being excited about it from the outside, and the more we brought in team members who were excited about carrying this forward internally, the more we realized this is turning into an actual company.”

That momentum carried Socrative through to the 2012-13 academic year, when the app saw 278,000 quizzes created and shared by more than 3 million teachers and students worldwide, with more than 1,000 teacher users joining per day.

The experience of teachers

Today, other companies have released similar student-response tools. But what sets Socrative apart, Maimon says, is a core focus on K-12 teachers, which informs its simple design.

The app, for instance, has dedicated K-12 features, making it accessible to a broad audience, Maimon says. Apart from quizzes, a “space race” feature lets students compete for the most correct responses; “exit tickets” let students weigh in on what they learned — and what they’d like to learn — as they’re leaving the class.

This simplicity is especially important for teachers trying to educate dozens of students — sometimes very young — without disrupting class. “The experience of the teachers in the class became core to everything we do: making sure that it’s seamless. We knew that if we can’t make it simple enough for core users, we aren’t going to intro more teachers into our system,” Maimon says.

Today, testimonials on the company’s website — and countless online reviews from K-12 teachers of all disciplines — laud the app for its simplicity, as well as for saving time, helping students better understand material, and providing clear data analysis on student progress.

Having reached so many teachers, Socrative is expanding its mission — such as by using data to improve and personalize K-12 education. For instance, Maimon says, should some students learn by video or by lecture? What lessons should be taught by hands-on, experiential methods? Overall, how can we provide better tools for teachers to help every student based on individual needs?

“We need a body of data that is available to start deriving meaningful insights about how to tailor learning methods to students,” Maimon says. “That’s the lofty objective.”

By Rob Matheson | MIT News Office

Image of the Day: Pink-footed Adelie

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Pink feet and a white belly mean this Adelie penguin has just been in the icy cold ocean. His feet turn pink due to the blood circulating to keep them warm while in the water. A few minutes after leaving the water his feet will lose the pinkish tone.

Image credit: Elaine Hood, National Science Foundation

What really killed the dinosaurs?

Sixty-six million years ago, an asteroid more than five miles wide smashed into the Earth at 70,000 miles per hour, instantly vaporizing upon impact. The strike obliterated most terrestrial life, including the dinosaurs, in a geological instant: Heavy dust blocked out the sun, setting off a cataclysmic chain of events from the bottom of the food chain to the top, killing off more than three-quarters of Earth’s species — or so the popular theory goes.

But now scientists at MIT and elsewhere have found evidence that a major volcanic eruption began just before the impact, possibly also playing a role in the extinction.

The team precisely dated rocks from the Deccan Traps — a region of west-central India that preserves remnants of one of the largest volcanic eruptions on Earth. Based on their analysis, the researchers determined that the eruption began 250,000 years before the asteroid strike and continued for 500,000 years after the giant impact, spewing a total of 1.5 million square kilometers of lava. 

The immense and long-lasting volcanism may have released dangerous levels of volatile chemicals into the air, poisoning the atmosphere and oceans.

“If models of volatile release are correct, we’re talking about something similar to what’s happening today: lots of carbon dioxide being emitted into the atmosphere very rapidly,” says Michael Eddy, a graduate student in MIT’s Department of Earth, Atmospheric and Planetary Sciences (EAPS). “Ultimately what that can do is lead to ocean acidification, killing a significant portion of plankton — the base of the food chain. If you wipe them out, then you’d have catastrophic effects.”

Based on the new, more precise dates for the Deccan Traps, the researchers believe the massive eruptions may have played a significant role in extinguishing the dinosaurs — although the exact kill mechanism may never be known.

“I don’t think the debate will ever go away,” says Sam Bowring, the Robert R. Shrock Professor of Earth and Planetary Sciences at MIT. “The [asteroid] impact may have caused the extinction. But perhaps its effect was enhanced because things were softened up a bit by the eruption of these volcanoes.”

Bowring and Eddy are authors of a paper published in Science, along with colleagues at Princeton University, the University of Lausanne in Switzerland, and Amravati University in India.

A one-two punch

Prior to 1980, the exact cause of dinosaurs’ demise was unknown; one hypothesis proposed that they were killed off by massive volcanic eruptions. (Similar episodes have subsequently been shown to have played a role in two other mass extinctions, the end-Permian and end-Triassic.) But the 1980 discovery in Italy of iridium, a rare element primarily found in extraterrestrial materials, suggested otherwise.

“They eventually found a crater in the early ’90s, so the smoking gun of the story seemed to be perfect: An asteroid caused the mass extinction,” Eddy says. “In fact, a few people have suggested that there is evidence for environmental degradation before the impact.”

It’s long been known that a major eruption occurred in India around the time of the end-Cretaceous extinction, but this event had never been precisely dated. The MIT and Princeton researchers used high-precision geochronology to determine the age of rocks in the Deccan Traps, to evaluate whether the eruptions began before the extinction — a necessity, if volcanism was indeed the cause.

“The story that is emerging is that perhaps both might have been involved,” Bowring says. “Perhaps the end of the dinosaurs was caused by a one-two punch.”

Dating from the bottom up

In December 2013, the team made an expedition to the Deccan Traps, east of Mumbai, a region known for its expansive, step-like topology. (The term “traps” is Swedish for “stairs.”)

For two weeks, the researchers looked for volcanic rocks that might contain zircon — a uranium-containing mineral that forms in magma shortly after an eruption, and that can be used as a very precise clock for determining the age of rocks; the mineral typically crystallizes in magma containing high amounts of silica and zirconium.

The researchers collected more than 50 samples of rocks from the region representing the largest pulse of volcanism. Fortunately, samples from both the bottom and top of this volcanic layer contained zircon, allowing the team to pinpoint the timing of the beginning and end of the Deccan Traps eruptions.

The researchers analyzed the rocks separately at Princeton and MIT to make sure the dates determined in one lab could be replicated in another lab. In both laboratories, the scientists pulverized rocks and separated out millimeter-length grains of zircon. To determine the age of zircon, and the rock from which it came, the teams measured the ratio of uranium to lead isotopes.

The group’s analysis indicates that the region of the Deccan Traps started erupting 250,000 years before the asteroid strike, continuing for another 500,000 years after the impact.

“We have 750,000 years as the duration for the main pulse of volcanism, but it’d be nice to know whether that time represents a constant flux of magma, or if pulses of magmatism were erupted over an even shorter period of time,” Eddy says. “Can we pick things apart at the 10,000-year level and see correlations between an individual pulse of volcanism and environmental change? That’s where we need to go with this study.”

Adds Bowring: “We’re getting better and better at dating mass-extinction events, but we’re not having a comparable improvement in our understanding of what caused them. Now that the timing is so well-resolved, I think there will be people coming back to think about the cause with new vigor.”

This research was funded in part by the National Science Foundation.

By Jennifer Chu | MIT News Office

Tomasz Mrowka named head of the Department of Mathematics

Tomasz S. Mrowka, the Singer Professor of Mathematics, has been named head of the Department of Mathematics, effective immediately. 

“Mathematics holds a unique place at MIT,” Mrowka said. “Much of the community uses it on a daily basis and in an ever-growing and sophisticated manner. The Mathematics department is the nexus of this activity. Its health and strength are crucial for MIT’s future.”

Mrowka has served as the interim department head since June 2014. Mrowka takes over the role from Michael Sipser, the Barton L. Weller Professor of Mathematics. Sipser was named Dean of the School of Science after serving since last December as interim dean and since 2004 as head of the Department of Mathematics.

“I am delighted that Tom has agreed to be head of mathematics,” said Sipser. “From working with him closely for many of the past 10 years while I was in that role, I know of his deep dedication to the department, to mathematics, and to MIT. He is a stellar mathematician and we are fortunate to have him in this position of leadership.”

Mrowka brings substantial experience as a researcher, educator, and administrator to his role as department head. A 1983 graduate of MIT, he received a PhD from the University of California at Berkeley in 1988 under the direction of Clifford Taubes and Robin Kirby. He taught at Stanford University, Caltech, and Harvard University before returning to MIT in 1996. He served as chair of the Graduate Student Committee from 1999 to 2002 and has chaired the Pure Mathematics Committee since 2004, with a one-year pause in 2009-2010.

Mrowka’s work combines analysis, geometry, and topology, specializing in the use of partial differential equations such as the Yang-Mills equations from particle physics to analyze low-dimensional mathematical objects. Among his results is the discovery (jointly with Robert Gompf of the University of Texas at Austin) of surprising four-dimensional models of space-time topology, going far beyond the expected examples envisaged by Kodaira and others.

In joint work with Peter Kronheimer of Harvard, Mrowka settled many long-standing conjectures, including ones posed by John Milnor on the complexity of knots in three space and another due to Rene Thom on surfaces in four space. Mrowka and Kronheimer also revealed a deep structure underlying the Donaldson invariants of four-dimensional manifolds, which was an avatar of the Seiberg-Witten invariants. In further recent work with Kronheimer, Mrowka used these tools to show that a certain subtle combinatorially-defined knot invariant introduced by Mikhail Khovanov can detect “knottedness.” 

Mrowka’s joint work with Kronheimer has been honored by the American Mathematical Society with the 2007 Oswald Veblen Prize in Geometry as well as the 2010 Joseph L. Doob Prize for their monograph, “Monopoles and Three-Manifolds” (Cambridge University Press, 2007). In addition, Mrowka was elected a fellow of the American Academy of Arts and Sciences in 2007 and was named a Guggenheim fellow in 2010 and Fellow of the Radcliffe Institute for Advanced Studies in 2013.

By Bendta Schroeder | School of Science

Image of the Day: Storm cloud and lightning

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Cloud-to-ground lightning is joined by intra-cloud lightning in a nighttime thunderstorm. When a cumulus cloud becomes exceptionally dense and vertically developed, with a dark base from which rain could fall, it is called a cumulonimbus, or thunderstorm, cloud. Toward the cold top of the cloud are ice crystals, and swift winds at these higher altitudes, together with the outflowing air from the storm’s updraft, can sculpt the cloud into the shape of a huge flattened anvil.

Image credit: University Corporation for Atmospheric Research

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