Peking University

Peking University, Beijing, China (May 25, 2016)

Peking University is the top higher learning institution in mainland China. It is also the first modern national university established in the country, founded in 1898 replacing the old imperial academy.

KIAA at Peking University

As I mentioned before, the purpose of my trip to China was to participate to a scientific meeting. The meeting was not in the University, but was organized by the Kavli Institute for Astronomy and Astrophysics (KIAA), which is located in the campus of Peking University. The institute occupies a modern building made in a traditional style (photo on the left), situated next to the pond in the photo above. The University campus is on the former site of the Qing Dynasty imperial gardens, and is an attraction in itself with the numerous traditional style buildings, pagodas and manicured gardens. The central Weiming lake is very beautiful, and is surrounded by many walking paths, smaller gardens and ponds, and there are several museums that are worth the visit. The campus is very popular, and there is a permanent line of tourists at its main gate during the security check before entering the grounds . If you want to visit the gardens in your next visit to Beijing it is well worth it, but remember to bring along your documents to gain access (that is true for all touristic attractions, including the Forbidden City and the National Museum). 

Peking University

I actually managed to avoid the line at the entrance since I was accompanied by a colleague of mine that works at KIAA, one of the organizers of the conference. He is from the Netherlands and a few years back found a new scientific home in the institute. He was not the only person I visited on campus: the fellow with me in the photo on the right was one of my office-mates when I was in graduate school in Trieste (Italy). After graduating he worked for a while in Sweden (his interest are theoretical calculations about black hole mergers) and then returned to China where he is now chair of the department. I was very happy to meet him after so many years. He was a very gracious host and walked me around the campus, showing me the architecture and the landscaping, and telling me about the history of the university. We also had some time to talk about his experience of getting back to China after having lived and worked for a long time in Europe. The government is investing a lot in science, and his department is expanding significantly, with new hiring and the development of state-of-the art astronomical facilities. This is something I gathered also from other sources, and that is true in other fields of physics (e.g. particle physics), where both the quantity and quality of Chinese scientific production has greatly improved in recent years (I see that also in my own department faculty and graduate students coming from China).

I sometime get asked why somebody would want to move from a more free country (e.g. the Netherlands) to a place with a less democratic form of government. I am in no position to judge: people make their own choice based on their own circumstances, priorities, family constraints. We don't chose the place where we go to live and work in abstract terms: there are many factors that influence our decisions. Both my friends are happy to live in Beijing and work in the university: the place definitely shows the kind of dynamism that physics and space science had in the US in the 50s, at the heigh of time when the american government believed and strongly supported science. In other fields it may be different. I heard from some sources that humanities are suffering under a more strict ideological control that is being exerted by the current leadership, in a change with respect to the more laissez-fare attitude of the previous government. Science however appears to still have little central oversight, and a lot of support and funding in today's China.

Weiming Lake and the Boya Pagoda, Peking University, Beijing, China (May 25, 2016)

Did We Found the Aliens?

Artistic impression of a swarm of comet-like fragments transiting in front of KIC 8462852. The debris tails left behind each fragment could be responsible for the observed dimming of the star (source: NASA/JPL-Caltech). The inset shows the image of the star as observed at infrared wavelength with NASA's Spitzer Space telescope (Marengo et al. 2015)

Well, most likely not. But before addressing the alien situation, let me first take a step back.

It all started with the Kepler SpaceTelescope, NASA’s facility tasked with finding worlds orbiting other stars. The spacecraft worked beautifully: since its 2009 launch it has already found 1041 extrasolar planets, with thousands more waiting for confirmation. Even after surviving a near-death experience due to the failure of its reaction wheels (the crucial devices that maintain its precise pointing), Kepler is still churning out top science, discovering new planets and characterizing their stars.

It is not one of the planets discovered by Kepler, however, that has astronomers around the world furiously scratching their head. It is a star, one of the 160,000 stars that Kepler monitored continuously for over 4 years during its main mission, that gave us the biggest surprise. It turns out that this star, with the uninspiring name KIC 8462852^[1] has been undergoing a “dimming” behavior so unique to start a veritable firestorm of speculations among the scientific community, and the public as well.

The reason why this otherwise ordinary star is so special is that KIC 8462852 during  some of its dimming episodes decreased its brightness by as much as 20%. This kind of behavior is normally associated to events where an opaque body (e.g. a planet) transits in front of its star, partially blocking its light. When that happens, however, the dimming is usually less than one percent, it repeats periodically, and has a very well defined ingress and egress profile. Whatever obscured the light from KIC 8462852, however, did it in a very disorderly fashion, managing to occult as much as 1/5 of the disk of the star. This is unprecedented, rising the intriguing possibility that the culprit could be some gigantic artificial structure being built around of the star with the purpose of intercepting its light and use it as the ultimate energy source. Such structures, known as “Dyson Spheres”, have been described as the next step of an alien civilization that, having outgrown its home planet, expands to occupy its entire planetary system. In this view the dimming episodes observed around KIC 8462852 would be caused by the elements of an incomplete Dyson sphere transiting in front of the star, as the structure is still being assembled.

But, is this what is really happening around KIC 8462852?

Spitzer Space telescope (artist's impression)
and our spectrum of KIC 8462852.

As advanced as an alien civilization could be, it must still satisfy the fundamental laws of physics. And among such laws, are the principles of thermodynamics: if a Dyson sphere is intercepting a large fraction of the light from the star it surrounds, it must be heated in the process, and it must dissipate vast amounts of residual heat in the form of thermal radiation. To test this hypothesis, and to search for natural explanations for the unusual behavior of KIC 8462852, together with my students I have analyzed archival data from another NASA facility, the Spitzer Space telescope, designed to observe the cosmos in infrared light. Spitzer happened to observe this star several months after the last dimming episode detected by Kepler, offering the perfect opportunity to check for evidences of waste thermal emission from any structure closely orbiting the star. As shown in the analysis we published in the November issue of The Astrophysical Journal Letters, we didn’t find any sign of infrared radiation in excess of the light from the star. Whatever caused the anomalous dimming of KIC 8462852 is not anymore orbiting the star up close, but must have receded to the frigid outskirts of the system, where any leakage radiation would be tuned to a wavelength much longer than the infrared radiation to which Spitzer is sensitive. This is hardly the behavior expected from a Dyson sphere closely encircling a star. Furthermore, an extensive search for extraterrestrial intelligence (SETI) transmission has so far failed to detect any signal coming from this system (the gamma-ray astronomy group in our department has also been involved in this search).

If not aliens, what is then happening on the doorstep of KIC 8462852? We still don’t know for sure. The leading hypothesis is that the dimming was caused by the fragments of some small planetary body (a large asteroid or a dwarf planet) that had the misfortune to break-up along a highly eccentric orbit circling the star (such breakup events are rare, but not unprecedented). As the fragments approached their orbit’s periastron the furious radiation from the star could have caused ablation and sublimation of volatile elements from the surface of the fragments, leading to the formation of enormous and opaque streams of left-behind debris, capable to partially obscure the star. This process is not different from the mechanism in which Solar System comets form their dusty tails as they sweep around the Sun; it is just on a vastly more massive scale. By the time Spitzer trained its optics toward KIC 8462852 the fragments and debris tails would have had enough time to travel along their orbit to the outskirt of the system, where not even the sensitive infrared detectors of Spitzer could have detected their residual heat.

We still don’t know if this hypothesis will hold true: more data is needed to confirm or rule out this scenario. For this reason, we have launched an international effort to monitor the star from space and from the ground, hoping to catch a future dimming episode and perhaps detect the elusive thermal radiation that must be associated with it. In the meantime, KIC 8462852 remains one of the most mysterious stars in our Galaxy, a puzzle that has stimulated the curiosity of scientist and public alike, and that we hope will soon reveal its wondrous secrets.

---

^[1] KIC stands for “Kepler Input Catalog” and the index code, despite appearances, is not a telephone number, although it does answers a landline in Pleasantville, IA (don’t try this at home).

and that we hope will soon reveal its wondrous secrets.

This article was first published on the 2016 issue of "Quanta and Cosmos", the Alumni Newsletter of the Iowa State University Department of Physics and Astronomy.

This image is unrelated to the topic of the post but hey, this is my photoblog so I want to have a photo shot by me in it. Las Campanas Observatory, Chile. Note that KIC 8462852 is in the Kepler Field (in between the Cygnus and Lyra constellations), so it is not visible from the southern hemisphere.

Back Trails Among the Dunes

Crane Beach, MA (June 13, 2004)

When the main road becomes too crowded, it is time to hit the back trails. The secret ones hidden behind the last turn, narrow, uneven, full of mosquitos. The one that you don't need the map, because they are not in the map, anyway. The one where you cannot get lost, because you didn't know where you were going in the first place. Where each step is a new adventure.

Among the Dunes

Crane beach has its own back trails. They are not hidden, however, and in fact you can see them well marked on the brochure you can get at the entrance of the reservation. If you look closely at the map of the area, Crane beach is on the ocean side of a very long peninsula, with the opposite side facing the Essex Bay and the Castle Neck River. In the middle, it is an expanse of sand dunes, shrub forest and marshes. All criss-crossed by a network of trails where, while is difficult to get lost, you can easily be devoured by hordes of ferocious green flies and mosquitos. If you can survive that, however, the back trails offer a welcomed change of scenery from the crowded summer beach. It also offers the chance of seeing in action a successful project of sand dune restoration, one of the many across the world aimed to protect a unique ecosystem that is our first line of defense against the destroying force of the ocean.

Animal Footprints

Dune restoration projects are common all over the world, and consist in a number of measures aimed to recreate the coastal ecosystem that too often has been degraded by human activity. The cornerstone of these projects is the reintroduction of native grass in the remaining dunes. This is not your common lawn grass: the tall grasses that live in the dunes are hardy species capable of dealing with the salty environment, and surviving being buried under the sand, of submerged under the waves during the occasional storms. Each location has its own kind of grass, evolved to adapt to the local environment. When New Zealand started its own coastal restoration project, it planted a fast growing variety of beach grass called Marram grass. As the grass spread it trapped new sand forming steep and tall dunes that were ill suited to resist to the strong southern ocean storms. The project backfired, and the grass had to be removed, and replaced with native species (Pingao and Spinifex) that are better suited to the New Zealand coastal climate; the Marram grass is now considered a pest. On the side of Crane beach, and along the back trails carefully traced among the dunes, you can still see recently planted areas, as well as more established grasses, like the beautiful green expanse in the panoramic photo below.

Crane Beach, MA (August 25, 2007)

Patterns in the Sand

Crane Beach, MA (June 17, 2006)

One thing that I like of the beach environment is how water, wind and sand collude together to create infinite magical miniature worlds. Grain by grain, as in a real-life game of minecraft, the water and the wind draw intricate patterns in the sand. Valleys, mountains, dunes, a fantastic topography replicating on a tiny scale geological features etched on Earth's continents. Walking on the beach on the line where the sea meet the sand is like flying over a Martian landscape imaged by a NASA probe.

A miniature river delta

Making a sand castle

Looking at the patterns in the sand of a beach we are faced with the fractal nature of the world. Shapes repeat across scales, self-similar, in an intricate game of russian dolls. This similitude of patterns, however, betrays the actual complexity in the physics of sand. While the forces of nature act equally on a multitude of scales, their effects are scale dependent. Even objects that are made of the same substance, such as a grain of sand and a large block of sandstone, will react to external forces in different ways, because the effect of these forces will depend differently on a combination of their size, surface area and weight. This is why the slightest of breeze can blow away the tiny grains of a dry sand beach, but you won't be able to move a pebble made with the same material by blowing on it with all the strength of your lungs. At the small scales of a grain of sand, physics becomes very complicated. Sand particles are in fact subjected to forces that have no parallel in the macroscopic world, and that in some conditions make them stick together like a solid, while in others make them flow like a liquid. This is why, during earthquakes, solid ground can sometimes suddenly liquefy. Given the obliquity of granular materials in our everyday world, one would think that by now we would have figured out the peculiarities of the physics of sand. Not so; these phenomena remain among the most baffling problems in material science. Which fortunately doesn't prevent us to admire and enjoy the beautiful miniature landscapes produced in mysterious ways by the wind and the water on our favorite beach.

Crane Beach, MA (June 17, 2006)

Yellow Sea

Crane Beach, MA (June 12, 2005)

And I mean it literally. Yellow. The color of a lemon. And this is not the body of water off the coast of China, yellow because of the particles of sand blown by the wind from the Gobi desert.

Pollen in the water

More pollen

This is another photo of Crane beach, my favorite spot in the North Shore in Massachusetts. This phenomenon happens every year in late spring, and is due to the pollen released from the pine forest in the nearby Castle Neck. And when it happens, it is quite massive, albeit the concentration reached in the water shown in the 2005 photos of this post is something that I never saw repeated with such intensity in the decade I lived in the area. Pollen is a strong allergen, so I rather not imagine what would mean to walk in the pine forest when this humongous amount of pollen is released in the air, even though some concentration caused by the coastal currents could have played a factor in this case.  Good thing that fishes and the famous North Shore lobsters are not allergic to pollen...

Crane Beach, MA (June 12, 2005)

The Next Maunder Minimum Will Not Freeze Your A**

Crane Beach, MA (Aug 25, 2007)

For most Bostonians, Crane beach is the place to cool off during hot summer days, taking advantage of the cool waters of the Atlantic ocean, just a short drive from town. During this time, the sandy expanse is a temple for the worshippers of the Sun, and its warming rays. I was thinking about this as I remembered a flurry of articles that appeared on the tabloids a couple of weeks ago, making apocalyptic predictions about how the Sun is on the verge of triggering a new ice age. This impending cataclysm will supposedly nullify global warming, and herald years of freezing winters followed by the absence of summer. As expected, these articles were immediately picked up by the usual climate change deniers communities. But is this really true? Are we really headed towards a new ice age?

Bi-color Crane beach

The last glacial period (ice age) lasted for over 100,000 years, and ended about 12,000 years ago. During that period the polar ice sheet reached its maximum extension, covering large areas of northern Europe, Asia and America. That was the time when the mammoths were roaming the frozen steppes of Siberia. Most of humanity lived at the edge of the ice, at more temperate latitudes, while only our cousins the Neanderthals were well adapted to the colder central European climate. This was just the last of a long succession of glacial periods in the last 2.6 million years, triggered by small changes in the orientation of Earth's orbit, with a periodic pattern called Milankovitch cycle. If we ignore the effect of anthropogenic climate change (which is instead warming the planet), we are indeed directed towards a phase of the next Milankovitch cycle that will lead to a new glaciation: this will not happen, however, for the next 50,000 years.

The ice age mentioned in last week news, however, has nothing to do with the Milankovitch cycle. It refers instead to the little ice age that hit Europe 400 years ago. This time was characterized by bitter winters in northern Europe, and is roughly coincident with a period of low solar activity, which is called Maunder Minimum. Discovered by Annie and Walter Maunder by analyzing historical counts of sunspots, the Maunder Minimum stands out as a period between 1672 and 1699 during which the Sun was almost completely devoid of sunspots. Since sunspots are the consequence of the changing magnetic activity of the Sun, counting the sunspots is a good proxy to estimate the overall activity of the Sun, with no-sunspots indicating a very quiet Sun. During the Maunder Minimum, the Sun was at its quietest of all recorded history. Why that happened is still a mystery, since there is no current physical theory capable to predict the long term ebbs and flows of the solar cycle, or tell us if and when a new minimum will occur. It is in this context that a new study announced at a meeting of the Royal Astronomical Society has triggered the media storm related to an impending new age. The authors of this study claim to have developed a complex model of solar activity capable to predict the occurrence of the next Maunder minimum, that will start in the decade between 2030 and 2040. This was enough to trigger the media storm about an imminent new ice age, that will balance the effects of anthropogenic climate change, and plunge the world into a deep freeze.

Ice age at Crane beach

The reality, unfortunately, is not so convenient. Despite the coincidence in time between the Maunder Minimum and the little ice age, there is little scientific evidence that the two phenomena are related. During the little ice age the global climate didn't change very much, with only northern Europe (and Greenland) experiencing colder than usual winters. Summers temperatures were however normal. Some line of evidence point towards the cold winters being caused not by the low activity of the Sun, but rather by concomitant massive volcanic eruptions in Indonesia and Vanuatu, releasing vast amount of ashes and sulfuric acid particles in the atmosphere, blocking the Sun and cooling the Earth. Despite the lack of evidence, the Maunder Minimum is still often mentioned as a possible cause for the little ice age in Europe. That's why, even though the original press release doesn't make any claim about an impending ice age, the press and the climate-change denier community jumped on chance of minimizing the impact of human activity on the climate, by placing the Sun in the driver's seat. But so is not: even if a little ice age could be caused by an imminent Maunder Minimum, the effect on the climate would be minuscule, dwarfed by the much larger increase caused by the greenhouse gases that we recklessly pump in the atmosphere. We unfortunately cannot count on whimsical ice ages to save us from our own foolishness.

[Edit: an earlier version of this post mentioned that the research presented at the Royal Astronomical Society meeting was not peer review. There is in fact a 2014 paper that present the model described in the press release. The research makes predictions for the near future solar activity, but does not address in any way its effect on climate.]

Crane Beach, MA (Aug 17, 2008)

The Nomadic Life of a Scientist to Be

Crane Beach, MA (Aug 7, 2004)

The most accurate adjective to describe the life of scientists is "nomadic". At precisely the time when most people find their first permanent job and settle down to build a family, aspiring scientists go to graduate school. For a subsistence salary, graduate students cross continents and oceans. They find their temporary place in some university around the world, where they learn the basic tools of the trade, and discover that science is based less on strokes of genius, than it is on persistence and hard work.

Graduate school lasts for 4 to 6 years, after which the newly minted Ph.D.s are on the road again, on to their first decently paid gig, as a postdoctoral research scientist, or postdoc for short. As postdocs, the young scientists learn to work independently, and build their portfolio of publications which is required, one day, to attain a permanent position. This chimera is however rarely found at the end of the first postdoctoral experience: typically two or more postdocs are required until a university, or a lab, will offer a permanent position. An all consuming tenure track position that will finally allow, six years later, to finally settle. All in all, from the day the aspiring scientists begin their undergraduate degree, to the time when they are tenured in a permanent job, it can pass more than two decades. During this period, every few years the scientists and their family uproot themselves, leave friends behind, adapt to a new life in a new city, in a new continent, a new culture, maybe a new language.

This happened to all of us, the few lucky ones that never looked at the abyss opening under our feet, and managed to hop ahead from step to step, school to school, job to job. It was quite an adventure, but not without casualties: all the friendships that were left behind, or that left us pursuing their own adventures, in some faraway corner of the world.

The photo above shows my friend Elena, when she visited us in Boston, and we went to Crane beach on the North Shore. We graduated together in Physics in Torino, then we did graduate school again together, in the same institute in Trieste. She is a biophysicist studying the electrical properties of brain cells. After her Ph.D. she went to work as a postdoc in Israel, then Paris. When she was in Paris I managed to visit her from time to time, when my own work was bringing me to the French capital. We have not seen each other since she moved to the University of Bordeaux where she has now a permanent job.

Of my graduate school classmates, not a single one still lives in Italy.

Crane Beach, MA (Aug 7, 2004)

Observing with SOFIA

SOFIA at Palmdale, CA (Jan 28, 2015)

Once we agree that the Moon is not made of swiss cheese, it becomes pretty clear that something violent must have happened in the lunar past. Many of the craters that pepper the surface of our satellite were formed when the Earth-Moon system was less than 800 million years old, in a cataclysmic event called the Late Heavy Bombardment. During that phase the celestial spheres skipped a beat and the sky, quite literally, fell: icy comets and asteroids were swung towards the rocky bodies orbiting the inner Solar System, bringing destruction but also drenching their parched surfaces with water. The same event that transformed the Moon into a block of Emmental cheese was the harbinger of life on Earth.

. . .

At first sight, it may not seem like a practical idea. Taking a big airplane, opening a huge hole in the back, bolting a large telescope into it, and then flying with the door open? Why would anybody dream anything like that?

The answer can be condensed in one word: water. Or, rather, the lack of it.

Water may be the elixir of life, but astronomers, as it turns out, are not very fond of it. And this is not because of the many squalls guilty of ruining countless observing nights. It’s because water molecules are naturally tuned to absorb infrared light, that part of the electromagnetic spectrum discovered by William Herschel beyond the deepest reds in the rainbow. And astronomers love infrared radiation, because it gives us the unique chance of studying the most elusive subjects in cutting-edge astrophysics research: planets and planetary debris surrounding the Sun and other stars, newborn protostars still hidden in their natal cocoons, dying stars enshrouded by their dusty winds. While these objects are often too dim to detect in visible light, they are copious emitters of thermal radiation, carried through space in the form of infrared light. It is to reveal the hidden secrets of these infrared sources that astronomers place their telescopes in the driest locations on Earth, blessed by unhindered access to the infrared photons coming from the heavens. The high deserts of Chile and the american Southwest, and the summit of volcanic mountains in the middle of Earth’s oceans, offer the best compromise between the needs of infrared astronomy and practical accessibility. The ice dome of Antarctica (9,000 ft thick at the South Pole) is even dryer (all water vapor is frozen), but is challenged by prohibitive environmental conditions. Deep space is the ideal location for parking infrared telescopes, but the size and weight of their mirrors, as well the possibility of repairs after launch, are limited by current technology and cost.

Inside SOFIA

Enters SOFIA, NASA’s Stratospheric Observatory For Infrared Astronomy. A wide-body Boeing 747 cargo aircraft, SOFIA serves as the flying platform for a 2.5-meters primary mirror telescope, designed to capture the infrared sky from the stratosphere. SOFIA’s cruising altitude tops at 45,000 ft, significantly higher than even long-haul transoceanic flights (typically flying at 35,000 ft, and only rarely climbing to 40,000 ft). At that height the air is very thin and, with a water vapor column reduced by 99% with respect to the ground, almost transparent to infrared radiation. This allows infrared observations at wavelengths that cannot be reached from the surface of Earth, or even from the icy deserts of Antarctica. From SOFIA’s stratospheric platform the “infrared window” is wide open up to a wavelength of 240 microns: ground-based telescopes rarely achieve observations beyond 20 microns. Its suite of 7 scientific instruments is designed to collect images and spectra in space-like conditions, but with the advantage of flying home at the end of each night, where they can be repaired and upgraded as necessary. This ability to continuously servicing the system is one of the main selling points of SOFIA with respect to space telescopes of equivalent capabilities. A human crew servicing SOFIA’s telescope and instrumentation has only to climb a ladder in the aircraft hangar. Compare that with servicing the Hubble Space Telescope that, when the Space Shuttle was still available, required the work of several astronauts in dangerous extravehicular activities, at costs approaching a billion dollar per mission. Hubble successor, the James Webb Space Telescope, will be not serviceable at all.

Despite being a plane, and not a spacecraft, SOFIA is managed by NASA with the feel of a mission to outer space. I got a taste of this in January 2015, when I briefly escaped the sub-freezing temperatures of Iowa’s winter to meet my University of Arizona collaborator Kate Su in Palmdale, at the border of the Mojave desert, where the plane is based. SOFIA is housed in the huge building 703 at the Neil A. Armstrong Flight Research Center (formerly known as “Dryden”), located inside the Edwards Air Force base. This is a legendary place in the human quest to conquer the heavens. It is from Edwards that “Chuck” Yeager became the first human to exceed the speed of sound with its Bullet-shaped Bell X-1 experimental aircraft. The base had also a prominent role during the moon race, leading the testing of essential technologies, including the Lunar Landing Prototype Vehicle that almost killed Neil Armstrong when it tipped over and crashed in a ball of fire (Armstrong ejected at the last minute). During the Shuttle era Edwards was the alternate landing site for the spacecraft, and building 703 in Dryden housed the two specially modified 747s used to ferry the orbiter back to its launching site at the Kennedy Space Center in Florida. Since the Shuttle retirement, one of the huge Shuttle Carrier Aircrafts has been moved in front of building 703, where it greets the visitors approaching the center from the south entrance. Building 703 is now shared by SOFIA and other NASA aircrafts, including two high altitude jets capable of flying at over 70,000 ft, instrumented to collect atmospheric data at the edge of space.

SOFIA's flight plan

Planning observations with SOFIA is a logistic ordeal. Since the observing chamber opens on the port side of the aircraft, the telescope can only point to the part of the sky directly on the left side of the plane. The only way to steer the telescope is to turn the whole aircraft. The typical 10-hours observing night looks then like a seemingly random-walk through the American and Pacific skies, with each leg chosen to match the orientation of one of the targets in the observing list. At the end of the night the plane must return to base, which further constrains the choice and order of the sources that can be observed. The flight plan for my trip brought us all the way down to Mexico, almost to the edge of the Intertropical Convergence Zone, where the moist air from the equator rises up to the stratosphere, an insuperable barrier in our quest for dry skies. All this was shown to us in the pre-flight briefing, where we (the two observers, the instrument scientists, telescope operators and flight support crew —— over 25 people in total) all assembled in preparation for the flight. This briefing is what you would expect for the typical NASA operation, with our mission director (Karina Leppik, a charismatic Antartica winter-over veteran) calling each sub-team for a “go”/“no go” status. At the end of the role-call we were a “go”, ready for our trip to the stratosphere.

Flying on SOFIA is nothing like flying commercial: we were reminded of that in the hour-long safety training we had to complete before boarding the plane. After all, SOFIA flies higher than a regular jet, and a sudden loss of pressurization would make you pass-out within less than 15 seconds. We were instructed to always carry with us our Emergency Portable Oxygen System (the EPOS, a sort of smoke hood with its own oxygen supply), when walking around in the plane. Stripped of all the furnishing and insulation of regular airplanes, the main cabin of SOFIA is cold and noisy, requiring to wear noise-canceling headphones connected to an internal PA system. A cumbersome system, but necessary to communicate with the telescope and camera operators during science time, and with the added bonus of allowing to overhear the cool chatter between pilots and ground traffic control during take-off and landing (pilots talk a lot, really). 

. . . 

Our program was scheduled in the second half of the night, during the northbound leg of the flight, as SOFIA returned to its base in California. The target of our observations was ε Eridani, one of the nearest neighbors of the Sun. The goal of our program was to probe the present of ε Eridani’s young planetary system, as a proxy to study the violent past of our own Solar System. Remember that dramatic event that bombarded the Moon into a maze of craters? It’s everyday news on ε Eridani, where the local “production” of the Late Heavy Bombardment “show”, is being re-enacted as you are reading these lines. By studying the drama happening today on the stage of ε Eridani, we can peer in the remote past of Earth’s history, at the age when life first appeared in the depths of its newly-formed oceans.

Specifically, we boarded SOFIA with the mission of resolving a long-standing controversy about the exact configuration of the swarming comets and asteroids that are circling ε Eridani and are responsible for its meteor bombardment. In a paper based on observations we performed a decade ago with NASA’s Spitzer space telescope (the infrared cousin of Hubble), we determined that this star possesses three separate circumstellar belts. Two inner rings are analogous to the Solar System’s asteroid belt. On the outside, a broader icy disk is instead similar to the Sun’s Kuiper belt, but on steroids: a massive version of the far-out belt that exists in the Solar System beyond the orbit of Neptune, the realm of comets and icy worlds ruled by Pluto and other dwarf planets. A key result in our work was to postulate the presence of clearly defined gaps between these three belts, a telltale sign that a whole family of planets are actively carving the humongous disk of ε Eridani into separate rings. Our conjecture, however, was not based on an actual image of the belts with their gaps, but rather on the spectral energy distribution of the infrared light emanated by the source. Spitzer lacked the visual acuity for imaging the details of ε Eridani’s disk, but possessed the sensitivity to map the thermal radiation of its emission, from which we estimated the rough distance of its components as they are heated by the central star. Our inference, however, was cast into doubts within a few years from publication, as an independent group derived a new fit of our data with a gapless (and planet-less) disk. A sure way to resolve the controversy was to obtain a true image of the gaps, in case they exist. SOFIA, with its much larger telescope, and its ability to observe infrared radiation at just the right wavelength where a gapless disk would be brightest, is the perfect tool to answer this puzzle. This was a convincing case for NASA, and we boarded the plane to find out.

. . .

Looking at ε Eridani images
(photo by B. J. Andersson)

In the stereotypical sci-fi Hollywood drama, discoveries follow experiments in real time. It takes just a few seconds for the scientists to look at the elaborate display on huge screens to declare triumphantly that the mystery is solved (and that humanity is inevitably saved by some impending cataclysm). In the real world, however, science works at a slower pace. As we huddled around the laptop of Andrew Helton, one of SOFIA's staff scientists, the image of ε Eridani captured by the FORCAST camera slowly came to life during the three hour-long exposure. Promisingly, it looked like a star, a featureless point in the sky without the extended ring of infrared emission to be expected if the gaps in the disk were filled-in, with no separation between the belts. Encouraging, but astronomy is a hard science, and as tantalizing as one single image could be, the answer for this puzzle will have to wait for the tremendous number-crunching that our computers will perform, once all the data are calibrated and merged with all other available evidence. In an age of data-intensive astrophysics, the quality and sophistication of the observations demand complex models for their full interpretation. Our few hours of telescope time, as glamorous as a trip to the stratosphere could be, will now be followed by months of gritty analysis work. The images we collected will be stacked against detailed physical models of the two competing hypothesis; hard numbers will tell us the results, and their statistical significance.

As we descended SOFIA’s ladder, heading back to building 703 in the twilight of a new day, we carried with us not just a night worth of data, but a valuable experience in how SOFIA is operated. This will be crucial for the work ahead, because it will allow us to fully appreciate the subtleties of our data, and push our analysis to its finer details. The prize at the end of this road is to understand the true structure of ε Eridani’s out-of-this-world disk, and its interactions with the cohort of planets likely inhabiting its system. SOFIA, by its unique ability of capturing infrared light in the dry stratospheric sky, is the closest we have to a time machine, revealing a glimpse of Earth’s ancient past by observing the present of a nearby young sun.

This story was first published on the Iowa State University Physics and Astronomy Department 'Quanta and Cosmos" Newsletter, June 2015 issue.