With a mixture of emotions, I'm signing off from my blog. A few weeks ago I accepted an offer to work as the senior science writer in the Astrophysics Science Division at NASA's Goddard Space Flight Center, located in Greenbelt, Maryland, just outside Washington, DC. Today is my final day at Sky & Telescope, and I will be leaving the Boston metro area on Monday. I start my new job in early February. I will be working to promote many of NASA's current and planned space-science missions, such as Swift, WMAP, GALEX, RXTE, GLAST, JWST, Constellation-X, LISA, and many others. These orbiting observatories are advancing human knowledge of our universe by leaps and bounds (or they will do so if launched), and I'm excited that I will be part of the effort to inform you about what they're doing.

It has been a rewarding and enriching experience working at S&T for the past 3-plus years. Those of you who have visited our offices already know this, but for those of you who have not, the staff of this publication has an enormous commitment to accuracy and integrity — a commitment that cannot be surpassed — only equaled. We don't make many mistakes in print, and when we do, unlike other publications covering astronomy and the sciences, we fess up to it. Whenever I made an error that would appear in print (even a relatively minor error, such as putting an obscure galaxy in the wrong constellation), it would gnaw at me for days, because I would feel like I let my colleagues down.

I have many people to thank at S&T, but I particularly want to thank editor-in-chief Rick Fienberg for giving me the opportunity to return home. I say "home" because my science-writing career started here back in 1991, when I worked as an editorial intern at S&T while finishing my master's degree across the river at Boston University. I also want to thank Dave Tytell, Alan MacRobert, and Joshua Roth for stimulating conversations about science, journalism, and other subjects, and for helping me get up to speed when I returned home in November 2003. And I can't say enough about how much I have enjoyed working with our outstanding designers and illustrators (and I congratulate Pat Coppola for her recent promotion to Design Director of S&T).

I want to thank all of you who wrote comments to my blog over the past few months. I really appreciate hearing from you, even if you disagreed with what I wrote. Blogs are supposed to be about expressing opinions and sometimes taking unpopular stances, so I tried not to be bashful about what was on my mind. I apologize that because I was busy helping to produce a magazine, I did not have time to post all the comments that were sent.

Last but not least, as much as I enjoyed writing my blog, and as much as I read other blogs and articles on the Internet, this entire medium gives me great concern about the future. The very nature of the Internet puts tremendous pressure on journalists to write their stories fast, and to be the first to post a story about a particular result. The result is often shoddy and incomplete reporting, and many times the media hypes a purported "discovery" that is unlikely to hold up upon further scrutiny. I saw this in action just a few weeks ago at the American Astronomical Society conference in Seattle, with stories such as "NASA Discovers and Then Kills Martian Life." While I was not immune to this affliction, S&T's priority has always been to get the story right, not necessarily to be the first to go on record. So as you read stories about astronomy on the Internet, please bear in mind the possibility that what you're reading might not be true, or might not be a good result. Ultimately, the great questions of science are not going to be resolved on the Internet or who shouts first or the loudest, they will be resolved by the scientific method and in the scientific literature.

The conflict between science and religion has recently become a hot-button topic in the media. Several prominent books on this subject have been published in the past few months, and a recent Time magazine cover story featured a debate between evolutionary biologist Richard Dawkins (an atheist) and geneticist Francis Collins (a Christian).

This controversy led me to imagine a trip to a car dealership. The salesman shows me a model that has sleek lines, gets great gas mileage, has a 5-year warranty, and fits my budget. Everything about the car is perfect, except for one thing: The engine contains a part called a kanootin valve that occasionally breaks down. And when it does, the engine explodes. When I ask what good the kanootin valve does for the car, the salesman replies, "Oh, it does nothing at all. You only know about it when it fails." I respond, "Hmmm… this vehicle does not seem to be designed particularly intelligently. I think I'll buy another model."

No auto manufacturer would design a car in such a way. And yet that is how the human body is "designed." We have an organ called the appendix that does nothing positive for us, and yet it can kill us if it becomes inflamed. And when it breaks down, only human physicians, using their scientific training, can save our lives.

The existence of the appendix is powerful evidence that the human body is the product of random mutations and natural selection operating over immense timescales, and that intelligent design is pure bunk. The fact that we share about 99.7 percent of our genes with chimpanzees is overwhelming evidence that humans and chimps evolved from a common ancestor. The progression of species in the fossil record unveiled by paleontologists over the past few centuries gives irrefutable evidence that lifeforms on Earth have evolved. Evolution is a well-established fact, not an opinion.

Intelligent design basically says that whenever scientists can’t solve a particular mystery about the natural world, then we should invoke some kind of mystical being, the so-called intelligent designer, to answer the question (and let's be honest, everyone knows we're talking about god here, and preferably one in the Judeo-Christian tradition). If humans had been adopting that philosophy for the past few thousand years, we'd still be living as hunter-gatherers. We'd still believe that lighting reflects the wrath of angry gods, and we'd still be using shamans and priests to address our medical needs. Intelligent design basically tells us to stop investigating the natural world, because when we hit a brick wall in our knowledge, we can find the answers in god.

I’m not saying whether or not you should believe in god, because that's not for me to decide. But invoking supreme beings and divine interventions has done nothing to advance human knowledge about the natural world. Our knowledge of the universe has advanced in leaps in bounds the past few centuries because of science: the formulation of hypotheses and the testing of those hypotheses through experiment and observation, and having the courage to ask the most penetrating questions about the natural world. Intelligent design, on the other hand, stifles our perseverance because it says that answers to the great questions have already been handed to us on a silver platter. It's the mindset that says that maybe we should buy the car with the kanootin valve.

Quick: name the astronauts currently on board the International Space Station.

If you couldn't answer this question off the top of your head, don't feel bad. You have plenty of company, perhaps 99 percent of the American public.

I can't think of a single person not connected directly with the program itself who feels the slightest bit of excitement about the Station. And one doesn't have to be a rocket scientist to understand why. As Carl Sagan once stated, NASA can't pretend it's exploring space when it sends astronauts to low-Earth orbit. Humans have been up there since Yuri Gagarin's flight in 1961. Been there, done that.

According to several recent articles, young people are having a difficult time mustering much enthusiasm not only for the Station, but also for the program to land humans on the Moon and Mars. Given that lunar landings are at least a decade away, and a Mars landing will occur who-knows-when, the payoff is so far in the future it would be difficult for even the most genius marketer to drum up much excitement in today's Internet/video-game/media-saturated world.

Last January in Washington, DC, NASA administrator Michael Griffin delivered a tepidly received speech to the American Astronomical Society. With several thousand people in attendance, it was probably the largest gathering of astronomers in one room in human history. Griffin told the assembled scientists that NASA won't be doing "boring" things in the future, which seemed to be a not-so-thinly veiled reference to space-science missions.

But if the Station isn't "boring," and it's hard to imagine a space project costing tens of billions of dollars being met with greater public indifference, then what is boring? Given all the T-shirts and posters I've seen over the years with Hubble Space Telescope pictures, large segments of the public certainly don't find HST boring (and this probably explains Griffin's decision to fly another shuttle servicing mission). I can't think of anyone who finds the Mars rovers boring, and they cost a tiny amount compared to the Station. And if NASA could shift a relatively small amount of money away from the Moon/Mars program and divert it to a space telescope that could find life-bearing planets around nearby stars, the public certainly wouldn't find that boring. Or how about sending a glider to Mars, or an instrument-laden balloon to Titan? Or perhaps an X-ray mission that could watch matter spiraling into black holes? And if we consider human spaceflight, sending a mission to a near-Earth asteroid would certainly generate a huge amount of excitement and attention.

Yes, NASA probably can do a better job of promoting its various missions and programs, which overall have a remarkable track record of success. But the key, as Griffin implied, is to develop missions that will generate excitement by their very nature — in which the media will latch on because the objective is so compelling that they have no choice. Better education and marketing will help, but we need to think of exciting missions that will automatically inspire the next generation of would-be scientists and engineers. I'd like to know what kind of missions (humans and robots, planetary spacecraft and space telescopes) you'd like to see NASA fly. Let your imaginations run wild, but try to think of projects that would be affordable, and that could be realized with current or near-term technology.

Today many Internet sites are reporting a "news" story that I first reported in a SkyandTelescope.com article on August 15th, and which is written up on page 26 of the December 2006 S&T (currently on newsstands). These stories are about the detection earlier this year by NASA's Swift satellite of two bizarre gamma-ray bursts (GRBs). Surprisingly, neither of these GRBs was associated with a supernova. As I'll explain below, these are important results, but the significance remains far from clear.

GRBs are extraordinary outbursts of gamma rays from deep space that generally last less than a second to several minutes. Since gamma rays are the most energetic form of light in the electromagnetic spectrum, astronomers have been well aware for quite some time that these cosmic cataclysms release staggering amounts of energy. Previously, GRBs fell into two broad categories: short and long. The dividing line between the two classes is about 2 to 3 seconds. Conventional wisdom says that most short GRBs come from merging neutron stars, while their longer counterparts are produced by the explosions of massive stars.

On May 5 and June 14, 2006, Swift picked up GRBs that lasted 4 and 100 seconds, respectively. This puts them in the category of "long GRBs." Both GRBs occurred in galaxies that are relatively close to Earth, "close" meaning within a couple billion light-years. In the past, when astronomers could localize a long burst’s host galaxy and see that it was within 1 or 2 billion light-years, they always saw an associated supernova. This firmly established a link between GRBs and the explosive deaths of massive stars. So far, so good. But in the May 5 and June 14 bursts, follow-up studies by large telescopes failed to see any hint of a supernova, even though the galaxies were close enough that large telescopes should have been able to see one.

Therein lies the conundrum. The media is instantly leaping to the most sensational interpretation, that these events represent a new type of stellar death. This interpretation may, in fact, turn out to be correct. But it's too early to say. Right now, astronomers don't really know what happened in these two bursts.

University of California, Santa Cruz astrophysicist Stan Woosley, who along with Andrew MacFadyen developed the leading collapsar model for long GRBs in the early 1990s, has predicted that sometimes the mechanism that blows up stars as supernovae fails to do its job, leading to a failed supernova. In this case, a dying massive star can produce a GRB but no supernova. But in other cases, the supernova might not produce the right kind of radioactive isotopes that cause it to light up. The supernova still happens, but it would be too dark to see at a distance of 1 or 2 billion light-years. Alternatively, one or both of these events might represent entirely new kinds of events, such as the explosion of a highly magnetized white dwarf, or the merger of a black hole and white dwarf.

Woosley points out that the GRB and supernovae, though often related, have different origins. The GRB comes from material in a disk accreting onto the black hole or neutron star that results from the gravitational collapse of the stellar core. The supernova comes from pressure exerted by a wind emanating from the disk. In other words, a dying star can produce a supernova but no GRB, or vice-versa.

GRBs have one thing in common with other cosmic phenomena: they are turning out to be much more diverse (and thus more interesting) when studied in large numbers and in greater detail. It will probably take years for astronomers to sort through all the evidence and figure out exactly what’s going on.

Last Friday I wrote a blog entry about NASA's plans for a lunar base, and whether the US would be able to afford such a massive enterprise given its soaring national debt. I received many interesting comments, and I apologize that I could only post a small minority of them. But I thank everyone who wrote in.

Most of the comments were either favorable or did not object to the entire premise of my essay. But several readers complained about my discussion of politics in an essay about lunar bases. As I responded briefly to some of these commentators, politics cannot be divorced from space exploration. I really wish it could, but it can't. Somebody has to pay for the missions, and unfortunately, it costs an enormous amount of money to send people into space with a decent chance of coming home alive. The farther we send them, and the longer they have to stay there, the more expensive the program. Building permanently occupied bases on the Moon will cost hundreds of billions of dollars, which will be far beyond the means of private enterprise for a long, long time.

The bottom line is that if people are going to live on the Moon for extended stays, perhaps starting in the 2020s as NASA proposes, governments are going to have to pony up for the vast majority of the cost. Only governments will be able to muster the enormous resources of money, technology, and human talent to make it happen. And as soon as we're talking about governments, we're talking about politics. There's no way around it. If you want to see lunar bases in your lifetime, and particularly ones operated by Americans and our allies, don't complain about my blog essay. Write your Congressional representatives and tell them to quit wasting enormous amounts of your tax dollars on pork and destructive endeavors, and tell them to bring the federal budget into balance. And while you're at it, tell them to increase their support for NASA and space science.

Earlier this week, without the great deal of fanfare one might expect, NASA announced its new plans for a permanently settled lunar base. Forgive me for failing to muster much enthusiasm.

One of my favorite insights (I think it was from Isaac Asimov) was his statement that the most amazing aspect of the Apollo 11 mission was not the landing itself, since sci-fi writers had predicted that humans would one day walk on the Moon. The most amazing thing about it was that a billion people watched it live on TV.

Something else that would have been amazing to Jules Verne or H.G. Wells is the fact that the nation that could muster the economic and technological resources to send people to the Moon would, at the same time, be fighting a war that it would ultimately lose.

That's one of many reasons why I find the current talk about lunar missions and permanent bases somewhat bizarre. As the Baker-Hamilton Commission Report makes perfectly clear, and what was already obvious to most people around the world, the US is not exactly faring well in Iraq. In addition to the tragic loss of life, the war has cost American taxpayers nearly $350 billion so far. This comes at a time when the US national debt is approaching $8.7 trillion. We're talking real money, given that the debt averages out to about $29,000 per US citizen (the nation's population just passed 300 million).

Perhaps things will change once the Democrats take charge, but the US Congress shows no appetite for reducing spending or bringing the budget into balance. In all likelihood, the debt will continue to soar to stratospheric levels, and American taxpayers will owe increasingly large amounts of money to investors in Japan, China, and elsewhere. Can a nation with such a staggering level of debt actually afford to set up bases on the Moon? NASA won't even tell us how much it's going to cost. Given the fiscal reality of a national debt that will easily surpass $10 trillion in the next few years, will Congress a decade hence be willing to fork over the Big Bucks when funding for lunar exploration will have to ramp up to meet NASA's timetable?

My crystal ball is a bit hazy, but NASA has always been a popular target for Congressional cost-cutters. My gut feeling is that the lunar program as currently conceived will never come to fruition, or at best, the grandiose plans will be postponed for many years.

Sure, sending people back to the Moon and setting up permanent bases would be extremely exciting, but to pay for this program, NASA is sacrificing many relatively low-cost but equally exciting robotic space-science missions. These include observatories such as Terrestrial Planet Finder (which could identify life-bearing planets around other stars) and Constellation-X (which would greatly improve our understanding of black holes and other exotic objects). In other words, the lunar program is sacrificing exciting near-term science for a very nebulous distant future. To me, this is not a satisfying trade-off, but I'd like to know what you think.

In my line of work, I have become quite accustomed to writing about exoplanets, Mars rovers, black holes, cosmology, and other astronomical topics. It never gets boring, but every once in a while, I come across a story that really perks me up. Yesterday I wrote a web article about one of those stories: an ancient Greek astronomical computer that was so far ahead of its time that it would be like someone from the future traveling through a time warp to modern-day Earth with a teleportation device (or, more likely, some amazing invention that nobody has even imagined).

The results announced yesterday by an international team of scientists show unequivocally that the Greek device, known as the Antikythera Mechanism, used a complex series of gears to accurately predict the movements of the Sun, Moon, and planets. It was built sometime between 150 and 100 BC. The people who constructed this machine were geniuses on the order of those who design and build spacecraft today. And like their modern-day counterparts, these ancient Greek astronomers and engineers probably didn't require help from space aliens.

The Antikythera Mechanism was found in the Mediterranean by sponge divers in 1900, near a Roman shipwreck. Nothing like it has ever been discovered, which makes one wonder if it was a one-of-a-kind device, or whether others were built and have either not survived to our era, or are awaiting discovery. But why was such a sophisticated machine not copied during its day and spread widely throughout the Mediterranean world? We may never know. It was a technology that had to be reinvented about 1,000 years later. We can only speculate how astronomy may have progressed had the device not been lost to history. Astronomy in the Western world advanced very little between the time of the Greeks and the early Renaissance. Would the widespread distribution of a sophisticated astronomical computer have helped some genius discover and perhaps prove the Sun-centered solar system centuries before Copernicus? And if so, where would science and astronomy be today?

The situation reminds me of the ancient Minoan civilization, which was thriving on Crete around 1500 BC until it was devastated by tsunamis and volcanic ash spawned by the horrific eruption of the volcano on the island of Santorini. The Minoans, almost certainly the inspiration of the Homeric tales of Atlantis, had indoor plumbing, written language, and architecture that would not be equaled in the European world until the Greeks a millennium later. If it had not been for the Santorini catastrophe, would humans have walked on the Moon a thousand years ago? And if so, what would the world be like today?

Today we heard news from NASA that confirms what we had feared for the past few weeks: Mars Global Surveyor appears to be dead. The agency hasn't communicated with the spacecraft since November 2nd. The mission team is not giving up all hope on its intrepid orbiter, but it does not expect to re-establish contact.

I hope major newspapers, magazines, and websites emphasize the spectacular success of the mission, and don't convey the impression that this is yet another NASA failure. Just like the Mars rovers Spirit and Opportunity, MGS was not supposed to live this long, and it has exceeded its minimum design lifetime five times over. And oh by the way, the MGS mission revolutionized our view of Mars.

I would develop carpal tunnel syndrome if I had to list all of MGS's accomplishments, so to save my fingers and wrists, let me name just a few. The high-resolution camera has greatly added to our knowledge of Mars's geologic and climate history by returning spectacular images from all over the planet, showing layered polar deposits, volcanic structures, and narrow features carved by water. The infrared spectrometer has monitored the global climate and found evidence for deposits of the mineral hematite (which forms in liquid water on Earth) in the Meridiani Planum region, paving the way for Opportunity’s great discoveries. The magnetometer found indications that the Red Planet had plate tectonics and a global magnetic field in its early history. The laser altimeter mapped the entire planet to a vertical resolution of less than a meter, meaning we have a far better topographic map for Mars than we do for Earth (the ocean floors have not been mapped to such high resolution).

For obvious reasons, orbiters have less "sex appeal" than landers and rovers. So MGS has been quietly conducting science operations from Mars orbit for 9 years while the rovers basked in the limelight. Fortunately, the loss of MGS does not herald the loss of science from Mars orbit. NASA's Mars Odyssey and Mars Reconnaissance Orbiter are returning impressive images and data, and the European Space Agency's Mars Express continues to dazzle with its high-quality spectral data and 3-D color images.

The entire MGS mission cost American taxpayers only $377 million. When divided by 300 million people and the 10 years that the mission flew in space, that works out to an average of about 12.5 cents per year per US citizen. I think it's safe to say we got our money's worth.

Just a few minutes before I wrote this blog entry, NASA concluded a press conference to announce further evidence for dark energy — the mysterious whatever-it-is that is causing cosmic expansion to accelerate.

A team of astronomers using the Hubble Space Telescope has found a couple dozen additional Type Ia supernovae, explosions of white-dwarf stars that have relatively similar characteristics. Scientists use these extremely luminous events to look backward in time to map the universe's expansion history. The new supernovae were seen so far back in time that astronomers could map how fast the universe was expanding in it is youth.

There are a lot of things out there in the universe that the human mind has a difficult time grasping. Based on conversations with many amateur astronomers and S&T readers, dark energy is probably near the top of the confusion scale. I get the sense that many astronomy aficionados don't really understand it (the same could be said for many scientists!), and are by no means convinced that it actually exists.

But anyone interested in how the universe works should give the current cosmological paradigm a fair hearing. For example, the results announced today are exactly what astronomers expected, and to be honest, they didn't really tell us anything that scientists didn't already know, or what S&T hasn't covered in recent issues (such as Anthony Aguirre's cover story in the December 2006 issue). But they add one more link in the solid chain of impressive evidence built up over the past few decades that the universe experienced an explosive growth spurt in its youth, then began decelerating due to the gravitational attraction of matter, and is now in a second (and perhaps permanent) epoch of accelerated expansion because there is an unidentified energy source, called dark energy, that is acting like an antigravity force.

This standard cosmological model is extremely well supported by high-quality observations from many independent techniques: mapping the hot and cold spots in the cosmic microwave background, seeing how galaxies cluster together on large scales, observing the X-ray properties of galaxy clusters at different distances, and observing Type Ia supernovae. All of these results are consistent with one another and they tell a consistent and compelling story. The theory behind them continually makes accurate predictions of future observations. That's the hallmark of a mature science, and it's this self-consistency that explains why the overwhelming majority of cosmologists embrace this picture.

This is not necessarily the universe that scientists wanted to uncover, and I don't get the impression it's what the public wanted either. But science has taught us over and over again that the universe is under no obligation to conform to human expectations or desires. Heck, I would prefer not to have shared a common ancestor with a gorilla, but the evidence is overwhelming that I do, so I accept it and marvel at nature's ingenuity and creative force operating over enormous timescales. The universe is what it is, and it's science's job to figure it out, whether we like the results or not.

Astronomy is not a static enterprise. To continue the advancement of human knowledge about our universe, we need to continue developing new and better telescopes, instruments, technologies, and facilities. And while astronomers should respect and cherish their history, astronomy is about the future, not the past. Astronomers are also keenly aware that building new observatories costs money, and that they do not have unlimited resources with which to accomplish all of their dreams.

It was probably with these thoughts in mind that the National Science Foundation (NSF), in October 2005, established a Senior Review Committee of 13 prominent astronomers in diverse fields. The NSF is an independent government agency and a major funding source for national ground-based observatories. It charged the Senior Review with the task of coming up with recommendations for redistributing 15% of the NSF's annual $200 million astronomy budget in the coming years, when researchers' aspirations will far outpace the level of federal funding.

The committee, chaired by Roger Blandford (Stanford University), has spent the past year reviewing the costs and scientific productivity of current observatories and consulting with the community to see how assets can be freed for next-generation telescopes. On November 3, 2006, the Senior Review released its report, which is available at the NSF website.

The report calls for big changes and inevitable sacrifices. Among them are recommendations to curtail or discontinue future NSF support for several astronomical powerhouses, including the radio telescopes of the Arecibo Observatory and Very Long Baseline Array, and almost all of the solar telescopes on Kitt Peak and Sacramento Peak. If these recommendations are followed, major facilities will eventually be shut down unless new funding partners emerge. The Senior Review also calls for staff reductions and improved efficiencies in several areas of research.

I have read the report, listened to a press conference about it, and interviewed NSF astronomy director Wayne Van Citters. I have also read numerous press statements issued by groups within the astronomical community who will be significantly affected if the committee's recommendations are implemented.

While I am not an expert in the politics of astronomy funding, I applaud the Senior Review for a thorough analysis, and for engaging in a thoughtful and ongoing dialog with the astronomical community. From what I can see, this was done the right way, even if not everyone is happy with all of the committee's recommendations. I would hate to see facilities such as Arecibo closed down, and I hope new funding partners emerge if the NSF moves its support to new facilities. For example, Arecibo has made an immeasurable contribution to astronomy through its discoveries of pulsars, pulsar planets, interstellar molecules … this list could go on and on.

But I am even more excited about the future, and want to see money freed up to build observatories such as the Square Kilometre Array, the Expanded Very Large Array, and the Giant Segmented Mirror Telescope, to name just a few. The discovery potential of these instruments is breathtaking, and they will keep astronomy alive and well deep into the 21st century. Let's hope that someday these observatories will have to be shut down to build even better instruments, since that's what astronomy is all about.

As my colleague Stuart Goldman reported last week on his blog, Sky & Telescope has changed locations for the first time in 50 years. We are now located at 90 Sherman Street in Cambridge, Massachusetts, about a kilometer (half mile) from our previous Bay State Road location. We are still unpacking boxes and crates, but we're starting to assume an air of normalcy and we're actually working on the next issues of S&T and Night Sky.

We also heard some very encouraging news today. NASA administrator Michael Griffin has given the green light to service the Hubble Space Telescope sometime in 2008. Citing safety concerns after the Columbia tragedy, previous administrator Sean O'Keefe had canceled the mission, which would have meant the death knell of the facility before this decade was out. But ever since Griffin assumed the reigns of NASA in 2005, he had given positive vibes about a fifth and final servicing mission, and barring catastrophe on an upcoming shuttle flight, I think it's extremely likely that it will happen.

The mission will give Hubble a new lease on life by installing new gyroscopes and batteries, which will probably extend the mission to about 2013. Better yet, the astronauts will install two new instruments that will enable entirely new science: the Cosmic Origins Spectrograph and the Wide Field Camera 3.

While I applaud Griffin's decision, this was a no-brainer. Independent studies have shown that flying to Hubble is only slightly more dangerous than flying to the International Space Station (ISS). But Hubble is vastly cheaper, and its scientific productivity has outstripped ISS to such a huge extent that comparing the two is about as competitive as a baseball game between the World Series champion St. Louis Cardinals and the S&T all stars. Flying this servicing mission is the cheapest way to add the equivalent of a new Great Observatory. And given the fact that there are no big space observatory launches on the horizon until the James Webb Space Telescope in 2014 or thereabouts, this announcement will come as particularly welcome news to most research astronomers. The fact that Hubble is still oversubscribed by a factor of 7 to 1 means it is nowhere near the end of its scientific productivity, even if no new instruments were being added. Most of all, Hubble is too important a scientific asset to let die in orbit while it remains a cutting-edge discovery machine.

Today's Hubble announcement overshadows another important development. NASA has just selected three low-cost Discovery missions for concept studies. These spacecraft, if funded to completion, will return a sample from an asteroid, study the chemistry of Venus's atmosphere, and map the Moon in detail to reveal its internal structure. These are exciting missions, so stay tuned!

First off, I apologize for not having posted a blog entry for several weeks. I was on vacation, and have just caught up with things after returning last week.

Yesterday, several colleagues and I caught wind of some rumors over the Internet that the SETI Institute was going to make a "major announcement" today. While Sky & Telescope editors are quite used to possible big stories that turn out to be letdowns, my ears perked up briefly, until I heard that there would be no announcement that humanity has picked up a signal from ET. And that got me to thinking about the age-old question of whether or not we're alone in the universe. The only intellectually honest answer to that question is "We don't know." But that should not stop us from trying to make educated guesses.

While I applaud the efforts of privately funded SETI programs and the multifaceted research conducted by SETI Institute scientists, and support SETI through my membership in the Planetary Society, the admittedly limited evidence at our disposal indicates that technological civilizations are extremely rare, and it wouldn't surprise me if we're the only one in our galaxy right now. (I certainly do not think we’re alone in our visible universe.)

Both ET optimists and pessimists agree that the term L (the average lifetime of a communicating civilization) in the Drake equation is crucial. If L is a low number relative to the age of our galaxy, then no matter what values one assigns to the other terms in the equation, N (the number of communicating civilizations) will be very small. Given the 13-billion-year history of our Milky Way Galaxy, if L is small, it means (to paraphrase Arthur C. Clarke) that civilizations are flickering in and out of existence like fireflies in the night. Unless some civilizations endure for millions of years, only one civilization will exist in our galaxy at a given time.

So let's assume that the Milky Way Galaxy is teeming with civilizations right now, which necessarily implies that some of them have existed for a very long time. It is shockingly naive to think they're all going to sit around in their home system for millions of years beaming radio waves into space, as many SETI proponents would have us believe. As UCLA astronomer Ben Zuckerman has effectively argued, intelligent beings are going to go out and remake the universe around them. At least some technological civilizations are going to build giant space interferometers to identify all the life-bearing planets within several hundred light-years, and when they find them, they'll have an insatiable desire to explore them up close, and once they get there, they might as well remain there. They'll build large-scale astro-engineering projects. With millions of years at their disposal, and technology beyond our wildest imaginations, they'll figure out how to traverse interstellar distances. After all, we've already launched five probes (Pioneers 10 and 11, Voyagers 1 and 2, and New Horizons) that will leave our planetary system, and we've only been able to fly in our own atmosphere for about 100 years — a pitiful timespan with respect to the age of our galaxy.

In fact, the ability to travel vast distances, and establish multi-planet societies, is probably a requirement to guarantee that a civilization (and its offshoots) will be long-lived. For L to be large, civilizations will need to secure themselves against local disasters and the evolution of their host stars. If there are large numbers of civilizations out there, does anyone seriously think that Earth would have escaped colonization long ago, especially given that it's hosted life for at least 3.5 billion years and resides in a planetary system with vast resources and a stable star? Yet there's not a shred of credible evidence that our planet or solar system has ever been visited.

The Fermi paradox (i.e. the question "Where are they?"), the nondetection of radio signals, the lack of any evidence of astro-engineering projects — all of this is admittedly limited and inconclusive, but it's the only direct evidence we have that bears on the question. And all of it is indicating that technologically capable life is extremely rare.

Another important point is that if all the SETI programs were to be shut off (something I would not support!), that doesn't mean our search for ET will come to an end. Many of the great discoveries in astronomy were made serendipitously: the Galilean moons of Jupiter, Uranus, quasars, the cosmic microwave background, pulsars, gamma-ray bursts, the first extrasolar planets (which orbit a pulsar, not 51 Pegasi)…the list goes on and on. The history of astronomy suggests that if we ever do find evidence for extraterrestrial civilizations, it will not come through a directed SETI program, but from a telescope built for another purpose that passed some critical threshold that makes alien civilizations detectable. I hope to live to see that day, but I'm not holding my breath.

Several readers wrote here a few weeks ago asking for my own definition of a "planet." Since I have been critical of the IAU's definition, it's only fair that I stick out my neck. So here's my definition and reasoning. To be honest, I'm not completely satisfied with it. The rancorous debate shows that it's not an easy problem, and there's no obvious "correct" solution. If a perfect definition existed, astronomers would have agreed upon it long ago.

Here's how I see things. In our galaxy we see large clouds of gas and dust. They collapse gravitationally and form dense cores — pockets of gas that go on to form either a single star or a multiple-star system. Most of the material ends up in the star, but since the cloud was probably rotating to begin with, some of the material settles into a disk of gas and dust around the forming star. To make a long story short, material starts clumping together inside the disk, and eventually forms objects ranging in size from pebbles to bodies the mass of Jupiter or larger. Since formation is a rather important process in determining an object's ultimate physical nature, planets are objects that form from material in these disks. But where does one set the upper and lower boundaries?

If an object contains between about 13 and 75 Jupiter masses, theorists calculate that it can fuse the trace amounts of deuterium (a heavy isotope of hydrogen) in its core for a few million years. Astronomers call such an object a "brown dwarf." Anything above 75 Jupiter masses is a star, which fuses ordinary hydrogen. Almost all astronomers agree that the 13-Jupiter-mass deuterium-fusion threshold sets a very natural upper boundary for planets. Anything above that limit is a brown dwarf, and not a planet.

Nature forms objects in a continuum of sizes, so any lower limit to a "planet" will be somewhat arbitrary, and this is the cause of the controversy and hoopla surrounding Pluto. Where should one draw that boundary?

I don't like the IAU's "clearing the neighborhood" definition, for several reasons. First, it's easy for an object to clear its neighborhood or control its region of space if it's close to the star, but it's a lot harder if it's farther out, where the volume of space is much larger and orbital periods are much longer. For example, Mercury controls its region of space, but even Earth, which is 18 times more massive than Mercury, would not be able to clear out the Kuiper Belt or control that region if it were moved to Pluto's distance. So the IAU's planet definition is, in my view, unfairly biased toward objects near their host stars.

Second, astronomers will almost certainly find Mercury-sized or even larger objects in the distant reaches of the solar system. At that point, the IAU's definition will face even more criticism than it does now.

Third, it's very likely exoplanet hunters will eventually find two massive planets sharing the same orbit in a "Trojan" configuration. Under the IAU's definition, neither body clears its neighborhood, or even controls its region of space. But everyone would know that such objects are indeed planets.

So I think we need a definition that's based on size, not dynamics. Several planetary scientists have expressed this view to me in the past few weeks. I'm not claiming this is a perfect solution, but the least-arbitrary lower physical boundary is established by the concept of hydrostatic equilibrium. Admittedly, there will be fuzzy objects around the boundary, but at a certain composition and mass, the self-gravity of an object will overcome the material strength of the object and fashion it more or less into a sphere (which can be flattened somewhat by rotation). The IAU's definition of both "planet" and "dwarf planet," and the original proposal of the IAU committee chaired by Owen Gingerich, incorporated this concept.

One reason I think it makes sense is the vast differences in size, mass, composition, and orbit between two of the IAU’s eight "official" solar-system planets: Mercury and Jupiter. About the only thing they have in common is that they orbit a star and are roughly spherical due to hydrostatic equilibrium. Therefore, if both are considered planets, common sense dictates that any object that shares these characteristics should also be considered a planet.

So my definition is as follows (drum roll please):

"A planet is an object that formed from material in a disk around a star, whose shape is roughly spherical due to its self-gravity, and which never experienced or will experience nuclear fusion in its core." This would be the definition I'd tell the public. I'd come up with a more long-winded technical definition for the scientific community.

If you've been patient enough to stick with me so far, you're probably thinking, "By this definition, lots of moons are also planets." Correct. Remember that the two largest satellites in the solar system, Ganymede and Titan, are not only larger than Pluto, they're also larger than Mercury. The only difference is that these worlds directly orbit another planet, not the Sun.

To take location into account, I would subdivide planets into three categories: Primary planets orbit a star directly. Satellites (or "secondary planets") orbit a primary planet directly. Ejected (or unbound) planets were thrown out of their system and are now free-floating in interstellar space. But all of these objects are still "planets."

Further categories can be adopted to describe the physical nature of the planet. Gas giants, for example, would be large bodies such as Jupiter or Saturn whose mass is dominated by hydrogen and helium. Ice giants are large worlds such as Uranus and Neptune whose mass is dominated by ices. Terrestrial planets, or rock dwarfs, would be objects like Mercury, Venus, Earth, and Mars, whose relatively low masses are dominated by heavy elements. Ice dwarfs, such as Pluto and the larger trans-Neptunian objects, are small bodies whose masses are dominated by various forms of ice. New categories can be added for new types of extrasolar planets as they are discovered and characterized (hot Jupiters, for example). But just as dwarf stars are still stars, and dwarf galaxies are still galaxies, all of these objects are still "planets" as long as they meet the criteria described in the definition above.

I think my definition is self-consistent and flexible — that is, it can easily accommodate new discoveries inside and outside the solar system — and the rules are simple and easy to interpret in the vast majority of cases. A lot of researchers will object because they don't like the idea of basing the definition on formation. They would argue, correctly, that in certain cases, observations won't be able to distinguish whether, say, a 7-Jupiter-mass free-floating body formed from a collapsing gas cloud or inside a disk from which it was later ejected. While acknowledging that argument, I would counter that we can put these objects in their own category until future advances clarify their origin.

Others would say that my definition would mean too many solar-system planets, perhaps devaluing the entire concept of "planet." Such criticisms are also legitimate. But we don't ask students to memorize the name of every city, just the major ones. I would have students learn the eight official IAU planets, Pluto (for historical reasons), the major satellites (our Moon, Io, Europa, Ganymede, Callisto, Titan, and Triton), and any new very large bodies that astronomers find way out there in the trans-Neptunian region. That's not too many, is it?

I never said my definition was perfect, and I welcome comments and criticism. Fire away!

I promised in my Tuesday blog entry that I would not discuss Pluto today, and since I'm a journalist rather than a politician, I'm gonna stick to my promise! But since several readers suggested that I propose my own planet definition, I plan to unveil one next Tuesday.

I'd like to say a few words about Star Trek, even though I missed the official 40-year anniversary by six days. I must confess that I have watched practically every episode of all five series, and I own every episode of the original series, Next Generation, and Deep Space 9 on DVD (but I got good deals by buying them as used box sets on the web). I also own most of the movies on DVD. However, I have never attended a Star Trek convention, I have never dressed up as a Star Trek character, and I don't speak Klingon. I'm not sure if I qualify as a bona fide Trekkie …err… Trekker.

I enjoy Star Trek for what it is: science fantasy, not science fiction. Other than an occasional episode, the writers break practically every known law of physics. Staying within the bounds of plausibility is what separates science fiction and science fantasy. From a purely intellectual and scientific point of view, Star Trek doesn't even begin to rise to the level of truly great science fiction, such as the novels and short stories of Stanislaw Lem and Arthur C. Clarke (my two favorites). And personally, I find real science a lot more interesting and exciting than science fiction. If Star Trek had never been created, I'm pretty sure I’d still be doing what I'm doing.

Here's an example of how Star Trek gets it all wrong. In the TV episodes and films, we see starships zipping around our Galaxy at warp speed — supposedly much faster than the speed of light. Yet when the Federation and Klingons duke it out, they're firing phasers and photon torpedoes at each other (shouldn't a warp-capable starship easily be able to outrun a photon torpedo?). I have a better strategy. If the Federation wants to wipe out the Klingons' home world, all it needs to do is take an object with the mass of a coffee table, and accelerate it to 99.99999% the speed of light, and slam it into the planet. Given the Federation's advanced technology, that would be a trivial matter. The energy of the impact would be stupendous. The Klingon world will be toast, literally, and every inhabitant will be dead. Do this to the Klingon home planet and their major colonies, and the Klingon Empire is past tense.

For me, Star Trek is pure entertainment, and nothing more. The various TV series and movies have featured compelling characters such as Mr. Spock and Data, some very good stories, and occasionally some interesting concepts. Claims have been made that Star Trek stimulated developments of certain technologies, and that it brilliantly anticipated future discoveries. Such claims are wildly exaggerated, and I can barely contain my contempt for the title of a recent TV program on the Discovery Channel: "How William Shatner Changed the World." Many of the episodes in recent years have been little more than soap operas in space with mediocre characters and acting, and after watching them, I'd say to myself, "Well, I just wasted an hour of my life."

Yet there's something about the franchise that keeps drawing me back, and I can't explain what it is. Given the fact that the last few movies were lousy, I'm almost horrified to hear that a new film is being produced. I won't see it on opening night because of the crowds. But I'll be in the theater the following day.

Probably like many of you, I'm growing a bit weary of the Pluto controversy. I was originally planning to drop the discussion from this blog. But before I turn to another topic on Thursday (and I promise I will!), I wanted to point out that I have had several very interesting private discussions this past week with planetary scientists about the Pluto controversy. They have convinced me that the International Astronomical Union (IAU) vote to downgrade Pluto to dwarf-planet status, despite being made by only a few hundred people, was indeed representative of the professional astronomical community as a whole, that it followed established procedures, and that it was based on sound scientific reasoning. I also agree with their contention that the IAU is the only proper forum to address these issues.

But I still think that for a variety of reasons that I have discussed ad nauseum, the IAU definition is flawed on a number of accounts, and it needs to be improved regardless of what one thinks about Pluto's status. And even though several scientists and readers have raised very strong arguments in favor of the IAU's decision to downgrade Pluto, I still have not found any of them to be satisfying from a strictly scientific perspective. I'm comfortable with the IAU's decision that Pluto is a "dwarf planet," but just as a "dwarf star" is still a "star," and a "dwarf galaxy" is still a "galaxy" in conventional astronomical usage, I think the majority of voters at the IAU General Assembly made a scientific and public-relations error by deliberately specifying that a "dwarf planet" is not a "planet."

So, where do we go from here? There is a great deal of acrimony within the astronomical community right now. Scientific debate is healthy and enables human knowledge to advance. But the degree of bitterness and anger that currently exists within the community is probably not a good thing, and goes beyond typical and appropriate standards of scientific debate. I continue to be utterly amazed at the passion that is stirred by a relatively small ice world in the distant reaches of the solar system.

I am going to paraphrase one of the e-mail messages sent me last week, from the distinguished astronomer Keith Noll of the Space Telescope Science Institute. I agree totally that this is the way to move forward. We need a calmer scientific discussion that seeks to broaden the definition of "planet" to include extrasolar planetary systems, that deals explicitly with binary objects in the solar system (dozens of binary asteroids and trans-Neptunian objects are known), and that includes planet-sized satellites such as Ganymede, Titan, and Earth's Moon. (One could make a very strong case that these objects should also be considered "planets," with the appropriate terminology to indicate their dynamical status.) He would also like any broadened definition to address the very interesting issue of free-floating planetary-mass objects that are being found in increasingly large numbers in interstellar space. Dr. Noll concludes, "When that happens, Pluto may make a reappearance as an ice dwarf planet that is still a planet."

Before I close, I want to thank everyone who has written to this blog to express his or her thoughts on the Pluto/planet controversy. I wish I had time to respond individually to everyone's comments and questions. But as you know, we also have a magazine to produce! :-)