Teachers in Space

I will never forget the morning I entered my seventh grade science class and our teacher, Mr. Harshfield, quietly played a video recording of that morning's launch of the Space Shuttle Challenger. It was the 28th of January 1986, and 73 seconds after liftoff the classroom fell into a stunned silence as we witnessed the disaster that claimed the lives of seven astronauts, including Christa McAuliffe who would have been the first teacher launched into orbit under a new NASA program. The tragedy was later traced to a design flaw in the "O-ring" seal on one of the solid rocket boosters, leading to a fuel leak which ultimately broke up the entire shuttle.

The dream of sending a teacher safely into space was finally realized last week, when the Space Shuttle Endeavour successfully returned home after 13 days in orbit. Former elementary school teacher Barbara Morgan, who served as NASA's backup astronaut to McAuliffe for the ill-fated Challenger mission in 1986, said "the flight was absolutely wonderful" and "the shuttle program gets an A-plus". There were initially some concerns about the safety of the crew after a small gouge was discovered in the protective heat shield on the underside of the shuttle. The gash was apparently caused by a collision during liftoff with a baseball-sized chunk of insulating foam from the external fuel tank, similar to the damage that caused the Space Shuttle Columbia to disintegrate during re-entry in February 2003, but considerably less severe and in a less vulnerable location on the spacecraft.

Engineers from NASA determined that the risk posed by the gouge was not significant enough to justify an unrehearsed spacewalk to repair the damage from the International Space Station, where the shuttle was docked for most of the mission. Given the tragic potential of the damage, as exemplified by the Columbia disaster, it must have been a difficult decision for the engineers to make and for the astronauts to accept. But knowing the extreme risks of an impromptu spacewalk to the underside of the shuttle -- a procedure that has never been attempted before, and one that would normally require extensive training and practice in enormous dive tanks to simulate the weightless environment -- and considering the unknown effectiveness of the proposed repair work, NASA's decision is understandable.

Thankfully, it all worked out in the end. The space agency is now planning to implement several modifications to the foam-covered fuel tanks to prevent future damage to the shuttle's heat shield. These modifications are expected to be complete in time for the next mission to the International Space Station, in April 2008.

Cosmic Fireworks

This weekend, one of the best annual displays of shooting stars will light up the night sky. The Perseid meteor shower has its peak activity during August 11-12 every year, but it promises to be a particularly good show this year since it coincides with new moon -- ensuring dark skies if you're away from the city lights.

Contrary to their name, "shooting stars" aren't stars at all -- they are tiny pieces of dust from outer space that run into the Earth's atmosphere and burn up from the friction of moving at thousands of miles per hour. Most of the streaks of light that we see are caused by particles no larger than a grain of sand. When they burn up in the atmosphere, somewhere between 30 and 80 miles above the surface of the Earth, scientists call them "meteoroids". Only the very rare chunks of rock that are larger than a car have any chance of striking the ground, and these so-called "meteorites" are typically no bigger than your fist by the time they hit the surface. On average, only about 8000 meteorites weighing more than a few ounces make it to the ground every year (with another 16000 falling into the oceans). That's a little more than 1 per day for an area the size of the continental United States.

Meteors are streaking through the sky all the time, but sometimes the Earth moves through a dense cloud of dust that was left behind by a comet and we have a "meteor shower". Meteor showers are named for the constellation where all of the streaks of light appear to originate, which is roughly the direction that the Earth is moving in its orbit around the Sun as we intersect a particular cloud of comet dust. During the Perseid meteor shower you can trace most of the shooting stars back to the constellation Perseus, which rises in the northeast sky after sunset. Comet Swift-Tuttle, named after the astronomers who discovered it in 1862, is the source of the Perseid meteor shower. It orbits the Sun every 130 years, and most recently crossed the orbit of the Earth in 1992 -- leaving behind fresh debris for our viewing pleasure every August.

So find a spot away from the city lights, spread out a blanket or set up your reclining lawn chairs facing the northeast, and just look up. Give your eyes about 30 minutes to adjust to the dark, and keep your flashlights off or covered in red plastic. You can expect to see a Perseid meteor shoot across the sky about once or twice minute, with the show getting better and better after midnight when you are on the side of the Earth that is blasting through the dust cloud. Happy skywatching!

Water Worlds

Earlier this month, astronomers announced the first clear detection of water in the atmosphere of an alien world orbiting a distant star in the constellation Vulpecula, "the Fox". The star is formally known as HD 189733, and the planet -- which is slightly larger than the planet Jupiter in our solar system -- is affectionately called HD 189733b. Like the detection earlier this year of an extrasolar planet not much larger than the Earth, finding evidence of water from a distance of 63 light years is a landmark in the search for habitable worlds outside of our solar system.

This particular planet is special -- the alignment of its orbit causes it to pass directly in front of its parent star as seen from the Earth. As a consequence, the planet causes a tiny eclipse during each orbit as it blocks a few percent of the starlight from reaching us. How much starlight it blocks depends on the size of the planet, including its atmosphere. That atmosphere acts as a kind of filter -- allowing some colors of light through easily, while blocking some others. The scientists exploited this fact, along with the known absorption properties of water, to measure the size of the planet in several different colors of infrared light. The pattern of absorption in these colors matched the pattern expected for water, and could not be explained by any other common atmospheric molecule.

After the planet stops blocking any starlight, it swings around to the back side of the star. During this segment of its orbit, the planet exhibits phases just like the moon -- showing a crescent until it reaches the largest separation, and then gradually becoming fully illuminated before it slides out of view behind the star. Although astronomers cannot observe the phases directly, they can monitor the tiny changes in reflected light during this part of the orbit. In this way, it was also recently possible to reconstruct a map of the temperature difference between the day and night sides of HD 189733b. The day side of the atmosphere turned out to be more than 200 C degrees hotter than the night side, and the hottest spot actually occurred slightly before noon local time on the planet.

The ultimate goal of such research is to find water and other possible signs of life on a distant Earth-like planet, motivated by the age old question: "Are we alone in the Universe?". With the demonstration of these powerful techniques to study the atmospheres of alien worlds, we are on our way to finding the answer.

The Would-Be 10th Planet

Today, astronomers at the California Institute of Technology announced new measurements of a Pluto-like object in the outer solar system, which under different circumstances could have been identified as the 10th planet. The object, officially named Eris, belongs to the new class of "dwarf planets" that now includes Pluto. Earlier measurements had securely determined that Eris was physically larger than Pluto, which was one factor in the decision to demote Pluto from planethood and create the new category. The new observations show that Eris is also 27 percent more massive than Pluto -- making the would-be 10th planet the currently undisputed king of the dwarf planets.

In 2005, a tiny moon called Dysnomia was discovered in orbit around Eris. Using both the Hubble Space Telescope and the largest telescope in the world on top of Mauna Kea in Hawaii, the scientists measured the position of Dysnomia on six different nights as it traveled around Eris in a 15-day orbit. There is a simple relation between the size of a moon's orbit and the mass of the planet it circles, formulated in the 16th century by Johannes Kepler. This allowed the CalTech astronomers to calculate the mass of Eris directly from the observations.

This discovery adds further support to the reclassification of objects like Pluto and Eris as "dwarf planets" instead of traditional planets like the other 8 in our solar system. Without the new definitions, there would probably already be 8 Pluto-like planets for school children to memorize in the sequence after Neptune, with hundreds of others likely to be discovered in the coming years. Pluto has made its mark in history, but 50 years from now it will be as anonymous as a random chunk of rock in the asteroid belt.

Images of Distant Stars

Last week, astronomers from the University of Michigan announced that they have successfully obtained the first image of a distant Sun-like star. Using a technique known as optical interferometry, the scientists combined the light from a group of four small telescopes scattered across the top of a mountain in California -- effectively creating one huge telescope more than 200 meters across. The resulting image is about 100 times sharper than the view from the Hubble Space Telescope.

Astronomers have been making images of the nearest star (our Sun) since the time of Galileo, but other stars are so far away that even the most powerful telescopes see them as single points of light. In 1995, the Hubble Space Telescope obtained the first direct image of a distant star -- the supergiant Betelgeuse in the constellation Orion, which is so enormous that it would span the orbit of Jupiter in our solar system. The technique of interferometry -- combining the signals from many individual telescopes to produce a sharper image -- has been used in radio astronomy for a long time, most famously in New Mexico at the Very Large Array that was featured in the movie Contact, with Jodie Foster. Recent advances in technology have now made it possible to do a similar thing with optical telescopes.

The target of the University of Michigan study was Altair, the brightest star in the constellation Aquila, which is about 80% more massive than the Sun and spins about 60 times faster. It's rotation is so fast -- more than 600,000 miles per hour at the equator -- that Altair bulges out around the middle. The new image not only reveals this flattened shape, it also shows that the star is much cooler around the equator than near the pole. Although this feature was expected, the predictions do not match the observations exactly -- suggesting that astronomers may need to improve the theory.

There are several arrays of telescopes around the world that are designed for this type of imaging. As the technology continues to improve, imaging of distant Sun-like stars will become routine. This is just the beginning of an exciting era for interferometry.

Book Review

"Survival Skills for Scientists" by Federico Rosei and Tudor Johnston is the best career guide to be published since Peter Feibelman's "A Ph.D. Is Not Enough!". Because the authors work in an academic environment, as opposed to a government laboratory, they offer a different perspective of the optimal career path. By co-authoring the work, they combine the time-tested wisdom of a senior researcher (Johnston) with the more recent experience of a junior faculty member (Rosei) who has direct knowledge of the current job climate. Drawing from their own interactions in Europe, North America, and Asia, they also provide a more international outlook.

The authors begin with the First Law of Scientific Survival, which is "Know thyself". Their simple recommendation is that you figure out what kind of scientist you want to be by carefully considering the kind of person you actually are. Obviously this includes an assessment of your strengths and weaknesses, but it also means understanding what role you want to play in research, and how you want to spend your time on a day to day basis. They don't try to conceal their preference for an academic career, and this could slightly alienate the reader who prefers another path. But everyone can benefit from the self-reflection that the authors promote by asking the right questions.

The bulk of the book is devoted to the Second Law: "Know your tradecraft". This begins with a very honest and pragmatic critique of postdoctoral experience, and outlines the essential factors to consider when choosing a position at various stages of your career. While admitting that intelligence and hard work are the foundation of a successful career in science, they go on to summarize other advantageous character traits that anyone can develop over time. They continue with a broad overview of the landscape of the science profession, and the metrics that will be used throughout your career to judge your productivity. Among the many unique themes that emerge from the text is the concept of being your own "agent", boosting your prospects for a successful career. The authors point out that publications in scholarly journals are the primary way other scientists learn about your research, and that generously citing the work of others will help get their attention. They finish by detailing all of the ways you communicate your work to others, including specific advice about journal papers, your thesis and curriculum vitae, as well as conference talks and posters.

The book closes with the Third Law: "Know thy neighbor". Unlike Feibelman's book, which begins with a series of anecdotes to illustrate how a scientific career can be derailed, Rosei and Johnston place this section in the back of their book. The authors also try to keep it positive by including success stories in addition to the failures.

Overall, this book fills a niche that nicely complements the material contained in other popular career guides. It is logically organized, and is filled to the brim with candid advice that you are unlikely to find anywhere else. Some readers may be frustrated by the many parenthetical remarks, footnotes, and clearly labeled "diversions" that make the text less concise than it could be. To others, these features will simply add humor, depth, and humanity to an otherwise serious discussion. "Survival Skills for Scientists" may not replace your copy of Feibelman's "A Ph.D. Is Not Enough!", but it certainly deserves to sit alongside it on your bookshelf.

Sister Earth?

Last week, a group of European astronomers announced that they had discovered the "most Earth-like planet yet" around a star in the constellation Libra. The planet, known as GL581c, is the first of more than 200 planets discovered outside our solar system that is apparently in the so-called "habitable zone" of its star -- the range of orbital distances where liquid water can theoretically exist. In this sense, the discovery is a landmark in the search for life elsewhere in the Universe.

But if you examine the details more closely, you will discover a planet that is very different from the Earth. First of all, it is at least 5 times the mass of the Earth -- and it orbits the star every 13 days (instead of our leisurely 365 days), at less than 1/5 the distance from the Sun to the sweltering planet Mercury. The only reason the planet isn't burnt to a crisp is that its parent star is much cooler than the Sun -- a tiny red dwarf. As a consequence, it is likely that the surface of this planet has the right temperature for liquid water to exist.

But I wouldn't want to live there, even if I could breath whatever atmosphere might exist. Red dwarf stars give off most of their radiation in the form of infrared light -- basically heat, like what you see with night vision goggles -- and almost no visible light. So it might be warm, but it would always be dark to human eyes. Finally, although it is among the 100 nearest stars to the Sun, even the fastest spacecraft ever built by humans would take more than 90,000 years to get there. So don't count on this planet offering us a safe haven in case we wreck our own.

It's an exciting discovery -- and one that we will undoubtedly see more of in the near future. As technology improves and allows astronomers to find ever-smaller planets around other stars, we will eventually find a true Sister Earth, and maybe even life. But we're not there yet.

Sustainable Planet

A report issued Friday from the UN-sponsored Intergovernmental Panel on Climate Change (IPCC) has once again prompted debate about how to respond to global warming. Perhaps one of the biggest obstacles to meaningful progress on this issue comes from the perception that changing our consumption levels will drastically reduce our standard of living. This kind of hysteria is fueled by the commonly quoted phrase: "if everyone consumed like North Americans, we'd need five planets to support us". But if you consider the natural resources, population, and consumption patterns of the U.S. by itself, how unsustainable are we, really?

This is similar to the question raised by popular "ecological footprint" calculators, but it takes into account the fact that our nation has more natural resources and a lower population density than most of the rest of the world. So in a sense, it's more fair. Basically, "sustainability" is a careful balance of three factors: (1) the available natural resources, often lumped into a quantity called "biocapacity", (2) the average consumption level of those natural resources, known as our "footprint", and (3) the total size of the population. Since total biocapacity is fairly constant, any increase in population erodes the available footprint per person. So if we want to maintain a certain standard of living, we need to either control population growth or decrease our footprint over time.

As you can imagine, the average footprint in the U.S. is actually growing slowly over time, mostly from energy use (the inability of the environment to absorb all of the carbon dioxide we release). The last time we were in balance with the available resources was around 1969. As it stands today, the average footprint is about twice the available biocapacity per person. So we only need two planets to be sustainable as a nation, not five. The reason is simple: it's harder for Africa to be locally sustainable because they don't have enough arable land, and it's harder for China because they have too many people. We should certainly help them address these problems, but those challenges are distinct from the challenge of sustainability at home.

Even so, the average footprint in the U.S. is still twice as high as it needs to be if we want to live a sustainable lifestyle. So you might ask: when in history was the standard of living in the U.S. half of what it is today? Even if you use a traditional economic measure of the standard of living, like "real GDP per capita" (which is adjusted for inflation and population growth), you find that to be sustainable we would need to adopt the lifestyle of the mid-1960's. That doesn't seem like such a sacrifice, and it's close to the "1969" balance mentioned above because improvements in (agricultural and energy) efficiency have basically made up for all of the population growth since then.

The average U.S. footprint is currently about 24 acres, while the locally sustainable level is around 12. Something to shoot for.

Blaming the Sun for Global Warming

In recent weeks, skeptics of the notion that global warming is caused by humans have been promoting alternative theories. One of the most plausible explanations asserts that global warming is part of a natural cycle caused by changes in the temperature of the Sun. It's undeniable that the Earth experiences natural variations in climate due to the Sun and other factors, but the warming over the past 100 years has a fundamentally different character, and is unprecedented in the 600,000 year climate history that scientists have reconstructed from ice cores and tree rings.

One way to quantify the relative importance of natural variations compared to those caused by people is to calculate the climate "forcing" of each factor individually. In this way, scientists have shown that changes in the concentration of carbon dioxide (CO2) in the Earth's atmosphere are at least 5 times more important to global warming than any changes in the Sun. The skeptics argue that the atmospheric CO2 concentration is changing because of temperature changes on the Earth, rather than the other way around. In fact, scientists have shown that changes in the Earth's orbit over thousands of years lead to natural changes in global temperature (periodic ice ages) that also cause natural changes in the CO2 concentration. But this predictable effect cannot explain the extraordinary warming that the Earth has experienced in recent times.

Another point raised by skeptics is that for several decades after 1945, global temperatures were falling even though the atmospheric CO2 concentration was rising. This is true, but there is a very simple explanation: in addition to the warming effect of CO2, common pollution in the form of particulate matter called "aerosols" has a cooling effect on the climate. Prior to the clean-air legislation enacted in the 1960's and 1970's, the cooling from aerosols overwhelmed the warming from additional CO2. As developing countries such as China and India adopt similar clean-air measures, this may actually accelerate global warming in the future.

By raising plausible doubts about the responsibility of humans for global warming in modern times, skeptics are trying to confuse the public into inaction. If climate scientists successfully communicate these subtle effects to the public, the skeptics will ultimately fail.

The Magnetic Sun

This week, the recently launched "Hinode" satellite returned some stunning new photos and video of our Sun. Focusing near the edge of our star, the space telescope documents the turbulent boiling of the solar surface in exquisite detail. But look a little closer and you will notice that as the hot material flows away from the surface, it does not simply stream off in any direction. It follows the invisible lines of a pervasive and dynamic magnetic field.

Galileo was the first to point a telescope at the Sun, revealing the dark spots that litter the surface. We now know that these "sunspots" are areas where the magnetic field is stronger, inhibiting the boiling motion and keeping the surface cooler -- and thus darker -- than its surroundings. Each spot is enormous, typically the size of our entire planet. But sunspots are only the beginning of the story of our magnetic Sun.

If you watched the Sun closely over many years, and you counted the total number of sunspots regularly, you might notice an interesting pattern. Every 11 years, the Sun seems to show a few sunspots, then many more, and then fewer again. What's more, when there are only a few spots they seem to show up in two bands, about halfway between the Sun's equator and poles. Over the course of this 11 year "solar cycle" they increase in number, migrate toward equator, and gradually fade away.

As the decades go by, you would notice that some of the cycles are stronger than others -- generating far more sunspots during the peak. Best of all, you would undoubtedly notice the huge explosions on the Sun's surface that eject hot gas out into space, sometimes directly at the Earth. When there are many sunspots, these explosions are more frequent and more dangerous. They are powerful enough to threaten astronauts and orbiting satellites, disrupt our communications systems, and occasionally bring down electricity grids.

With this new eye in the sky, astronomers will study the underlying order in these patterns -- eventually helping us predict the explosions and protect ourselves from the boiling magnetic Sun.

Astronomer Surplus

This week, as part of my work with the American Astronomical Society's Committee on Employment, I've been digging up statistics on the relative rates of training and employment of young astronomers. As in many sciences, the production rate of new Ph.D. astronomers by universities is completely decoupled from the global demand for trained scientists. This has created a huge surplus of young astronomers -- there are now about 3 new Ph.D. recipients annually for every new tenure-track job in astronomy.

The job market has responded by creating more and more temporary (2-3 year) "postdoctoral" positions -- a sort of holding pattern for young scientists who are seeking an academic or research career. In the long term, there appears to be no easy solution to the problem, since the incentive of the university system is to use as many graduate students as possible for cheap skilled labor, without regard to their long-term job prospects. Essentially, overproduction appears to be built into the system -- making the mathematical formulation of surplus production of astronomers similar to that for industrial pollution models, an unintended side-effect of the production process.

What I found in the numbers surprised me. Although the current situation is clearly unsustainable, it was much worse a decade ago -- with nearly 7 times as many Ph.D. recipients in 1995 than new tenure-track jobs. While the number of new "permanent" positions steadily increased throughout the late-1990's, the number of new Ph.D. astronomers gradually declined. After the turn of the century, something else happened. The number of new astronomers being produced by the system leveled off, but new postdoctoral positions grew dramatically. With fewer graduate students around, all of those new university professors had to hire postdocs to get the work done.

Of course this only tells part of the story. There has also been recent growth in the number of non-tenure-track lecturer, research, and support positions. This is just one example of the larger cultural shift to temporary employment that is happening throughout society -- it is not unique to astronomy. It may not be in the best interests of science, but there it is.

Pluto and Planethood

Today NASA's "New Horizons" mission, launched just over 13 months ago, will fly past Jupiter on its way to Pluto. The giant planet will provide a gravitational boost to the spacecraft, helping it reach the edge of our solar system by 2015. Over the past few decades, NASA satellites have visited Mercury, Venus, Mars, Jupiter, Saturn, Uranus, and Neptune -- but this is the first mission ever to visit Pluto. Meanwhile, astronomers have decided that Pluto should no longer be considered a planet.

To the average person, it probably seemed ridiculous when the International Astronomical Union announced last August that Pluto would henceforth be known as a "dwarf planet" -- the prototype of a new class of objects in the outer solar system. It even led to a satirical headline reading "NASA Launches Probe To Inform Pluto Of Demotion". However, there were legitimate scientific developments that compelled astronomers to adopt a new definition of planet -- it was just unfortunate that this new definition removed Pluto from the list.

Starting in 1992, astronomers began to discover many small icy objects outside the orbit of Neptune that appeared similar to comets, but which never came close enough to the Sun to evaporate and develop tails. As time went by and the technologies for detecting these objects improved, surveys began to identify some larger examples. In the last few years, astronomers found several that are comparable in size to Pluto -- and even one that is larger! Theories suggested that there were likely to be hundreds or thousands of such objects in the outer solar system, so classifying them all as new planets could create real problems for school children trying to remember them all.

Since Pluto appeared to be just one of the larger members of this class of objects, it fell victim to the new classification scheme. Like many political decisions, the available choices were limited to bad (define planet in a way that excludes Pluto) or worse (bestow the title of planet on hundreds of new objects). Conspicuously absent was an alternative proposal to adopt a new definition of planet that would avoid such proliferation, while honoring the historical status of Pluto as an exception to the new rule. When the IAU meets again 3 years from now, I suspect that such an alternative will be considered by the astronomers -- with plenty of time to spare before "New Horizons" reaches its final destination.