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.

I am the senior editor at Sky & Telescope with the last name that nobody can pronounce (it's NOY-uh, like "paranoia"). I've been working at S&T for nearly 3 years, although I also did a 6-month internship at the magazine back in 1991, while attending the science journalism graduate program at Boston University. I later worked on the editorial staffs of Discover and Astronomy magazines, and I served as editor of Mercury magazine for three years.

My job at S&T is to write and edit science articles, both news stories and features. I previously authored two books on astronomy and have won several awards for my astronomy journalism and outreach activities. I am the proud owner of 5 telescopes, although my amateur activities are limited to eyeball-to-eyepiece astronomy.

My interests in astronomy are diverse. I've covered stories ranging from planetary science to cosmology, and everything in between. Since I started my career in science journalism in the early 1990s, I have written about topics such as extrasolar planets, the various missions to Mars and the other planets, the Kuiper Belt, the shocking realization that our universe's expansion is accelerating, and the breakthroughs in our understanding of gamma-ray bursts (check out my feature article on GRBs in the August 2006 S&T). If it's above our atmosphere, chances are that it's interesting. The really boring and depressing things seem to be here on Earth.

My main goal with this blog is to inform you of interesting new developments in astronomy and space, particularly stories that the mainstream press ignores. I'll also help you separate truth from fiction, and reality from myth. I will highlight the truly important results and provide an antidote for the bogus and overhyped claims that permeate Cyberspace.

For example, a particularly egregious example occurred yesterday with all the articles claiming that the distance scale of the universe might have to be revised because of one group's measurement of the distance to the galaxy M33. Many groups of distinguished astronomers working with independent techniques over many years have painstakingly established the extragalactic distance scale, and they have come up with consistent, reliable results. To convey the impression that all of this work might have to be overthrown because of one group's distance measurement to a single galaxy is an example of the irresponsible journalism that is all too common these days.

Besides highlighting good science while debunking the bad, I'll discuss interesting and controversial subjects, such as NASA funding, the possibility of extraterrestrial life and alien visitations, sending humans to the Moon and Mars, alternative cosmology, "intelligent design," and so on. I've been covering this stuff for years, and I care deeply about it. I'll probably ruffle a few feathers, but I won't be bashful about my opinions. When you write back, don't be bashful about yours. If there's something you want me to write about, let me know. If you agree with me, let me know. If you disagree, let me know (but also tell me why). This blog is a two-way street, and I want it to be fun and stimulating. I'll be back on Thursday to weigh in on the issue of whether Pluto should be considered a planet, and I'll explain why a resolution to this debate may soon be at hand.

The latest news from the International Astronomical Union’s General Assembly in Prague is that a revised proposed definition for “planet” is under consideration, and that the debate has been rancorous. If Oliver Stone were to direct a movie about the deliberations, he might give it the title Astronomers Behaving Badly. The IAU is scheduled to take an official vote on Thursday, and at this point, I would not want to hazard a prediction on what the members will decide, if they decide anything at all.

I have made my views on Pluto crystal clear on this blog: its physical characteristics (spherical shape, three moons, atmosphere, etc.) clearly place it within the family of planets. I also call on the IAU members to accept an official definition that will accommodate new discoveries both inside and outside the solar system, although that now seems unlikely. But right now, my main hope is that the IAU decides something. This Pluto/planet-definition controversy has been simmering for years, and the IAU fiasco has turned into an embarrassing spectacle. For decades, the public has been told that the solar system has 9 planets. Then people heard last week that the total will be upped to 12. And later this week, they might wake up to the news that it has dropped to 8. Surely, this affair could have been handled more discreetly, generating less confusion among the public at large.

Yes, the debate has given the public a glimpse into the scientific process, and layfolk have received a demonstration that science is a dynamic process in which conclusions change with new discoveries. And it’s almost always good for astronomy when it makes the news. But there are several important reasons to resolve this Pluto/planet issue. First, astronomical researchers need to know what to call Pluto and other borderline objects in their communications to one another. Perhaps more important, how are we to convince people that they should abandon outmoded concepts such as creationism and intelligent design if astronomers can’t even reach a consensus on something as seemingly basic as the number of planets in our solar system? Science opponents are always looking for cracks in the scientific establishment, and astronomers have handed them a dream example on a silver platter. It’s time to resolve this issue and move on, and that’s more important than what astronomers decide to call Pluto.

So I hope that the IAU this week accepts one of the proposed definitions, even if it means Pluto is booted from the family of planets. Future discoveries may force revisions to whatever planet definition is accepted, so it won’t necessarily be the end of the story. And of course, whatever definition is accepted won’t change our understanding of Pluto’s origin and context within the solar system. But sweeping the definition problem under a rug until the next IAU General Assembly convenes in 2009 is hardly an acceptable outcome. Once the IAU renders its verdict, then it’s the task of researchers, educators, amateur astronomers, and media outlets like S&T to communicate the result to the public, and explain the rationale for the decision. At that point, astronomy aficionados of all types will have an opportunity to turn a negative into a positive.

I want to thank everyone who has responded to my postings. I’m new at this game, and I’m very pleased to see people writing to the blog with such interesting and insightful comments. Writing magazine articles is essentially a one-way street, with the flow of information and interpretation going from the author to the reader. I really enjoy this blog format, since I can express myself more freely and less formally, but more important, I am receiving quick and valuable feedback from readers.

My original plan for today’s blog installment was to discuss your Pluto comments, and point out that the committee’s proposed definition of a “planet” will be released to the public tomorrow morning. I have seen the press release announcing the definition, but it is embargoed by the International Astronomical Union until 2:00am EDT Wednesday, so I’m not supposed to say anything about it. I can tell you, however, that Pluto aficionados will probably be happy. But check our Web site tomorrow morning for more details.

My plans for today’s posting changed when I saw the new papers posted on Astro-ph last night. Astro-ph is an Internet site where astronomers post their research papers before they actually appear in printed journals. This Web site is a great way for astronomers to disseminate their work quickly to the entire professional community. Last night, I saw a paper that totally blew me away, and it’s so exciting that I want to tell you about it. It suggests that there is a new type of mega-explosion process operating in our universe. Scientifically, this is much, much, much more important than the Pluto/planet debate.

The paper, written by a large group of distinguished astronomers with Avishay Gal-Yam of Caltech as lead author, reports the detection and subsequent observation of a relatively nearby gamma-ray burst (GRB) on June 14, 2006. GRBs are extraordinarily violent and bizarre events. For those of you who have been following the GRB story, including my feature in the August 2006 S&T, you probably recall that GRBs come in two classes: long-duration bursts (lasting several seconds to several minutes) that come from exploding massive stars, and short bursts (lasting a fraction of a second to perhaps 2 or 3 seconds) that originate from a variety of processes, including merging neutron stars. As my August 2006 article explains, astronomers have accumulated compelling evidence that long bursts are powered by massive stars collapsing to form black holes or neutron stars, and in the process they generate high-speed jets that punch through the dying star. Colliding blobs of material within these jets probably trigger the actual burst of gamma rays.

One of the key pieces of evidence in favor of this scenario is the fact that whenever astronomers have pinpointed the location of a long GRB relatively close to Earth, astronomers have always seen a supernova. This association unambiguously links long GRBs to the explosion of massive stars, in line with theoretical predictions. But in this new paper, Gal-Yam and his colleagues report that the relatively nearby long GRB detected by NASA’s Swift satellite on June14th is not associated with a supernova. In other words, the GRB was close enough to Earth (about 1.7 billion light-years) that a supernova should have been visible. Yet when astronomers looked for a supernova with the Hubble Space Telescope and other instruments, they only saw evidence for an afterglow — the interaction of the jets with the surrounding interstellar gas. Either there was no supernova, or it was too faint to be detected, which means it was the lowest-luminosity supernova on record.

Another group, led by Johan Fynbo (University of Copenhagen, Denmark), is just about to come out with a paper reporting a second long GRB without an underlying supernova. This burst was detected by Swift on May 5, 2006. Fynbo's group also failed to find any evidence of a supernova accompanying the June 14th burst.

Theorists are just coming to grips with these discoveries, and it might take months or years for a consensus to emerge. Right now, my speculation as an armchair theorist is that astronomers might have seen two events in which the core of a dying star collapsed to form a black hole, and a supernova either failed to occur or was smothered by inrushing stellar material. Many theorists have predicted that such “failed supernovae” should exist.

But it’s also possible that there is a range of supernova luminosities, and these two events just happen to fall at the low end. In this scenario, the collapsing stellar core initially formed a neutron star, but it later accreted enough infalling stellar gas to form a black hole. Computer models suggest that the subsequent explosion will fail to eject large quantities of nickel-56, the radioactive isotope that is responsible for most of a supernova's early luminosity.

A third possibility is that these events are an extreme version of short bursts, which are not associated with supernovae. But that raises the question of why these bursts lasted so long — about 2 minutes for the June 14th GRB — which is much longer than other short GRBs. Perhaps we’re seeing a powerful and previously unknown explosion process.

Right now, astronomers have more questions than answers. Just when scientists thought they were beginning to understand GRBs, Mother Nature found a way to stay one step ahead of the curve. No doubt about it, the planet controversy will dominate the media spotlight over the next few days. But ultimately, these GRB observations will tell us a lot more about how the universe works than what a committee of astronomers decides to call Pluto.

Last weekend I attended the Astronomer’s Conjunction, an annual amateur event held in western Massachusetts. After listening to two teams of well-informed amateurs debate the Pluto-planet question, I asked the following hypothetical question: Let’s pretend that we wake up on Monday morning to the following exciting news. Astronomers using the Keck Telescope announce that they took a series of deep images of Proxima Centauri, the nearest star to the Sun. The pictures revealed an orbiting body that is well above the threshold to be spherical, it has three moons, and a spectrum shows that it has an atmosphere. Should we call it a planet? After nobody in the audience objected to this designation, I added, “Actually, I was just describing Pluto.”

We heard the news today that after 76 years, less than 400 members of the International Astronomical Union decided to boot Pluto out of the family of planets. This was an unfortunate decision for a number of reasons, not the least being the bad PR that such a tiny minority of self-appointed elites is ramming its arbitrary decision down the throats of the entire astronomical community. I predict that some of the members who voted for the new definition of “planet” will come to regret it, because it will fail to accommodate future discoveries. But I’m pleased that the IAU made a decision, and that the new official definition of “planet” is well motivated and based on sound scientific reasoning. Nobody is going to die or lose their life savings because Pluto will no longer be considered a full-fledged planet.

But there are several gaping holes in the IAU’s definition, including one that is so immediately obvious that it boggles my mind that intelligent people could actually vote for it. The definition is anti-Copernican in the sense that it defines planets as objects orbiting the Sun. In other words, only solar-system objects can be considered true planets. Excuse me, but even under the most liberal definition for “planet” that one could seriously propose, we know of about 50 planets in our solar system right now. We already know of more than 200 planets outside the solar system. And if the official definition were extended to include planets around other stars, the total in our Milky Way Galaxy alone must be something on the order of 100 billion to a trillion. In other words, the IAU definition completely ignores 99.99999999999 percent of the planets that exist in our galaxy. Huh?

Maybe this was prudent, because adding extrasolar planets to the resolution would have made it even harder to reach a verdict. Maybe a bunch of astronomers thought, “We need to learn more about planets outside the solar system before we can come up with a sensible definition.” But something inside of me says that the IAU wimped out, and that it might end up sweeping this problem under the rug for a very long time, just as it did with the Pluto question.

Perhaps certain members of the IAU leadership, who were responsible for the exoplanet omission, felt concern that future discoveries could throw a monkey wrench into the official definition. If that’s what they thought, their concern was justified. For example, one of the criteria is that a planet “has cleared the neighborhood around its orbit.” Not only is this statement rather vague when applied to our solar system, but I predict that in the next few years, we’ll find systems around other stars where it fails miserably. Astronomers who simulate the evolution of planetary systems on computers have shown that in some circumstances, interacting planets can leave behind a system with two Jupiter-mass planets that share the same orbit, with one 60 degrees ahead of the other. Such a “Trojan” configuration is stable for billions of years, so it almost certainly exists in nature. It’s only a matter of time until planet hunters such as Geoff Marcy and Paul Butler uncover this kind of system (it’s possible that several have already been found!). So if the IAU definition is applied to other stars, two very massive planets sharing an orbit would not be true planets, because neither one has cleared out its neighborhood.

Astronomers have also found that at least half of very young stars are surrounded by disks, and there’s good reason to think that many of these disks will spawn planets. It will take tens of millions of years for these planets to clear out their regions of space. Does that mean that a newborn 5-Earth-mass object that has not had time to clear out its zone is not a planet?

I also suspect we’ll find systems that through some kind of freak dynamical evolution, have left planet-mass objects in zones of rubble. Heck, even Earth shares its region of space with tens of thousands of asteroids of various sizes. One could counter that these bodies are in unstable orbits. But both Jupiter and Neptune harbor vast populations of Trojan asteroids that will remain in their orbits for billions of years. And even many trans-Neptunian bodies, such as Pluto, cross Neptune’s orbit. Under the IAU’s vague new rules, we could rule out Earth, Jupiter, and Neptune, and perhaps other planets as well.

And by not setting a specific size or mass requirement, the IAU has left itself wide open for criticism as soon as astronomers find Mercury-, Mars-, and perhaps even Earth-sized bodies in the distant solar system. Such discoveries are only a matter of time, given the limited nature of surveys to date.

I know it was really, really hard to come up with the definition that the IAU accepted today, and I also know it was impossible to come up with one that would satisfy everyone. The definition that was accepted could have been much worse. And while I hope the passage of this new definition calms down the debate for awhile, we have not heard the end of this story.

I grew up in Hershey, Pennsylvania, just a few miles downwind from Three Mile Island. When I was studying math in the 1970s, Hershey was not known for the quality of its public schools. The local school board seemed to think that the kids needed to know just enough to work in the chocolate factory. But when I learned that 9 + 1 = 10, I was apparently taught correctly. I confirmed this fact when I went to college.

Yet amazingly, some of the most learned professional astronomers, and even some of my esteemed S&T colleagues, think that 9 + 1 = 8. They argue that because of last summer's announcement of a new Kuiper Belt object (KBO) larger than Pluto (2003 UB₃₁₃), the solar system now has 8 major planets. In other words, astronomers have been saying since 1930 that the solar system has 9 planets, then they find another planet, then all of a sudden we have 8 planets. Am I missing something here?

The campaign to drum Pluto out of the category of "major planets" has actually been gathering steam since the early 1990s, when David Jewitt and Jane Luu discovered the first KBO besides Pluto and its moon Charon. The argument goes something like this: With a diameter of just 2,300 kilometers (1,400 miles), Pluto is just too much of a pipsqueak to deserve membership in the exclusive club of major planets. It's merely the largest known member of the Kuiper Belt, several of whose members are half to two-thirds Pluto's diameter. If we count Pluto as a major planet, we should also count all of these other KBOs, and pretty soon we’ll have more planets than Elvis impersonators.

Admittedly, the critics' contentions have considerable merit. Until last year, Pluto really was just the largest known member of the Kuiper Belt. I also have to concede their point that if Pluto had been discovered in 2006 instead of 1930, few astronomers would call it a major planet.

But that's not the whole story.

For every argument against Pluto being a planet, Pluto's defenders can summon an equally legitimate counterargument. When critics say Pluto is small, defenders can point out that it's easily big enough so that gravity can pull it into a sphere, and that astronomers from Jupiter might consider Earth to be an overgrown asteroid. When critics say Pluto has a highly elongated orbit, defenders can point out that many of the 200 known extrasolar planets have even more eccentric orbits. When critics say Pluto shares its region of space with zillions of other KBOs, defenders can point out that Earth shares its orbit with thousands of asteroids (and even mighty Jupiter and Neptune share their orbits with swarms of Trojan asteroids).

The bottom line is that Pluto is big enough to be round, it has an atmosphere for at least part of its orbit, and it has at least three satellites. It might even have rings. While asteroids and moons share some of these characteristics, we don't know of any that have the whole kit and kaboodle. And since these are all traits one normally associates with "planets," it's not at all obvious that Pluto should be booted from the realm of planethood.

What is clear is that because Mother Nature makes objects in a continuum of sizes, wherever you draw the line that distinguishes a major planet from a minor planet, your boundary will be arbitrary. Astronomers have been calling Pluto a major planet since 1930, and they haven't been saying that just to kids, they've been saying it to each other in their books and research papers. The simplest thing to do is to simply grandfather Pluto into the planet club, and set its 2,300-km diameter as the minimum size for a major planet.

The debate has festered because there is no official definition of what constitutes a "planet." For years, the organization that resolves these nomenclature matters, the International Astronomical Union (IAU), has sidestepped the controversy. But Mike Brown's announcement last summer of 2003 UB₃₁₃ forced the issue. The IAU has to give this object an official name, and that name will depend on whether it's a major planet, or just another KBO. And since 2003 UB₃₁₃ is only slightly larger than Pluto, once the IAU decides its official status, it will resolve Pluto's as well.

The IAU has appointed a committee, chaired by the eminent astronomy historian Owen Gingerich, to come up with a definition of "planet." Gingerich's committee, which includes members on all sides of the Pluto debate, has reached a consensus after a period of intense discussion, and National Public Radio reported today that the definition will include Pluto. However, the report was based on what 5 committee members thought before the committee even met, and S&T has learned that some of the "facts" that NPR reported are wrong — but we don't know which ones! According to the NPR report, the definition will establish several classes of planets, such as terrestrial planets (Mercury, Venus, Earth, and Mars), giant planets (Jupiter, Saturn, Uranus, and Neptune), and dwarf planets (Pluto and the larger KBOs, and perhaps several main-belt asteroids). In other words, if the IAU adopts this classification scheme, we might have dozens of objects that fall under the term "planets."

This scheme makes sense scientifically in terms of our solar system, but I predict that as we learn more about planets around other stars, we'll find plenty that don't fit neatly into these categories. The history of science tells us time and time again that Mother Nature refuses to conform to human expectations and nomenclature systems. I also predict that a lot of people in the general public would find such a classification scheme confusing and dissatisfying.

The committee will present its definition at the IAU's General Assembly in Prague next week, and a vote by the full membership is expected around August 25th. S&T editor in chief Rick Fienberg will be at the conference to cover this unfolding story, and SkyandTelescope.com will keep you posted with accurate and authoritative coverage. I have great confidence that whatever it decides, the IAU will eventually come to a sensible conclusion that will lay the controversy to rest. While I enjoy discussing the Pluto debate, ultimately the science is more important than the semantics, and it's time to move on. When it comes to the solar system, the world needs to know whether 9 + 1 = 10, or whether we need to learn New Math.

Gosh, am I glad I was not a member of the International Astronomical Union committee tasked with the thankless job of proposing a definition for “planet.” These seven unfortunate souls were inserted between the proverbial rock and hard place. Given the wide range of objects in our solar system, and the many different opinions within the astronomical community and general public, there was no chance that they could come up with a definition that would satisfy everybody.

So I don’t want to sound overly critical of the proposal, which has since been strongly endorsed by the American Astronomical Society’s Division for Planetary Sciences. The committee’s proposal essentially defines “planets” as nearly round objects that orbit stars. I don’t have a strong opinion as to whether the IAU General Assembly should vote “yes” or “no” to this proposal on August 24th (I bet it will pass by a large margin). The committee deserves credit for coming up with a definition based on physical principles that can be applied to objects inside and outside the solar system. But there are several glaring inconsistencies in the proposed definition that will open up a can of worms if approved.

For example, what exactly is meant by “nearly round?” The committee defines it as an object in “hydrostatic equilibrium” (i.e. its mass is sufficient for gravitational compression to overcome its material strength and force it into a nearly round shape). But where does one draw the line between an object that is in hydrostatic equilibrium and one that is just slightly out of hydrostatic equilibrium? If they haven't done so already, astronomers will find borderline cases, so the decision whether or not to include certain objects as planets will be arbitrary.

Making matters worse, the committee is including Pluto’s largest satellite Charon as a planet, because the system’s center of gravity is located in the space between the two objects. In other words, the committee members are saying that Pluto and Charon form a double-planet system.

That sounds clean cut, but it’s not, because the location of a system’s center of gravity depends both on the objects’ masses and their physical separation. At the moment, the Earth–Moon system’s center of gravity is inside Earth. But tidal interactions cause the Moon to recede from Earth by about 4 centimeters per year. In many billions of years, the center of mass will reside in outer space. Does this mean that future astronomers will suddenly have to change the Moon’s status from satellite to planet? This flies in the face of common sense. Given that Pluto is 7 times more massive than Charon (which means the system’s center of gravity is much closer to Pluto), a lot of folks will think it’s patently obvious that Charon should be considered a satellite rather than a planet.

For those who bemoan this new definition because it includes Pluto, I ask the following: what should we do when astronomers find a body, either in the outer solar system or around another star, that is halfway or two-thirds of the way between Pluto and Mercury in size? Such a discovery is just a matter of time. As I wrote in my essay last Thursday, wherever one draws the line that distinguishes planets from non-planets, it will be arbitrary.

And for astronomers who want to divide planets into various subclasses, like giant planets, terrestrial planets, and ice dwarfs (and the proposed definition recognizes Pluto-like objects as “plutons”), Mother Nature will always create objects that don’t fit cleanly into the categories. We already know of several extrasolar planets that would not fit into any classification scheme based on our solar system, and there are tens of billions of planets in our galaxy alone. These planets are going to display a bewildering variety of sizes, masses, orbits, physical characteristics, and so forth. And even if you count all the known round asteroids and Kuiper Belt objects in the solar system, we still know of many more planets outside our solar system than within it. Any sensible definition of “planet” must take them into account.

So despite all the arguments I have heard over the past few days, my position remains unchanged. The simplest way to define “planet” is to use Pluto as the minimum size of a planet, and state that any body found orbiting a star (or brown dwarf!) the size of Pluto or larger is a planet. And despite the fact that astronomy does not operate in a cultural vacuum, my conclusion is not based on sentiment or history, or the desire to prevent kids from having to memorize the names of dozens of planets. It’s based on the fact that Pluto has many characteristics that we commonly associate with planets: a respectable diameter that’s well above the minimum size to be spherical, an atmosphere, a multiplicity of moons, and probably rings. I freely admit that my definition is arbitrary, but I challenge anyone to come up with a less-arbitrary scheme.

Finally, most of the public’s attention has been focused on the low end of the planetary size regime. But the controversy extends to the upper end as well, and the proposed definition fails to address this problem in a satisfying manner. Basically, this issue boils down to the question of how astronomers should draw the line between planets and brown dwarfs. Currently, objects between about 13 and 75 Jupiter masses are generally considered brown dwarfs, because they briefly fuse deuterium in their cores (anything above 75 Jupiters is a star). But there are many gray areas. Should it matter whether an object orbits a star or another brown dwarf, or how it formed?

For example, Geoff Marcy and Paul Butler’s group found a star that has 7- and 17-Jupiter mass objects that are coplanar, meaning they probably formed in a disk. Should the 17-Jupiter-mass object be considered a planet because of its origin, or since it's above the deuterium-fusion threshold, should it be termed a brown dwarf? What about the dozens of known free-floating objects (not bound to stars) that have less than 13 Jupiter masses? Should we call them planets because of their low mass, do we call them sub-brown dwarfs since they probably formed in stellar-like processes, or do we have to adopt the horrible acronym PMOs or planemos, short for “planetary-mass objects”? What about the 5-Jupiter-mass object that orbits at a very far distance from the 25-Jupiter-mass brown dwarf 2M 1207? That system probably formed like a very-low-mass binary star, but the 5-Jupiter-mass bugger is well below the deuterium threshold. The proposed planet definition either fails to clarify many of these ambiguities, or it leaves us with unpleasant outcomes.

I want to make it clear that I don’t have a strong disagreement with the proposed definition, but it’s an imperfect solution to a complex problem. Don’t be surprised if there are modifications down the road.

One of the reasons I am so passionate about astronomy is that it is almost always associated with something positive. This can take the form of looking at a beautiful object through the eyepiece of a telescope, or learning of a fascinating discovery about a planet, star, or galaxy. So it saddens me when I see so few young people at amateur astronomy events and read articles about the lack of American university students who are majoring in science, math, and engineering.

There are probably many reasons for these trends, and not being an expert in sociology, I can only offer a few speculations. These days kids have so many things competing for their time and attention — a zillion TV stations, the Internet, video games, sporting events, etc. etc. — that they have little time for hobbies like astronomy. Also, in our celebrity-obsessed contemporary culture, science and astronomy are not “cool,” and interested students risk being branded as “geeks” and “nerds” by their peers. I think another big problem is that most kids in urban and suburban areas never really experience a truly dark night sky. The washed-out, light-polluted sky they see contains so few stars that it hardly inspires the sense of awe and wonder that inspired the generations of yesteryear.

I know that amateur astronomers are trying to reach out to children in a big way. I’m a proud member of the Amateur Telescope Makers of Boston (ATMoB), the largest club in the Boston area. The club holds so many school star parties that any new school that wants to sign up must schedule its party in the winter. ATMoB members are maxed out, and I can’t imagine them being able to do any more than they are already doing to reach out to young people. Yet at a monthly meeting a year ago, several members lamented that the school star parties didn’t seem to have the intended effect of attracting young members. I suspect that other clubs share similar experiences.

These concerns were on my mind as I traveled to a remote mountainous area in West Virginia this past weekend to attend the Almost Heaven Star Party (AHSP), organized by the Northern Virginia Astronomy Club. Even though we didn’t enjoy crystal clear skies Friday and Saturday night, I had a great time and met a lot of wonderful people. Best of all, I was delighted to see quite a few young people in attendance, and they seemed genuinely interested in astronomy, and happy to be there.

In particular, I met a high-school-age girl named Esther who attended my presentation about NASA’s Cassini mission. I saw her furiously taking notes the entire time I was speaking. Afterward, she peppered me with questions about astronomy and other areas of science, taking notes as I replied. She was like a sponge, constantly soaking up knowledge. Later that evening, while watching a gentle rain come down, I met a 12-year-old boy named Ian who says his goal in life is to become a radio astronomer who studies pulsars and quasars. As Ian, his father, and I discussed astronomy, I was totally blown away by his advanced state of astronomical knowledge. How many 12-year-olds know what a magnetar is? Ian knew all about them.

So I came away from AHSP with renewed optimism about the future of astronomy. Yes, there are kids out there who feel intense passion for astronomy, and they need to be nurtured and encouraged, so they know that no matter what anyone else says, astronomy is “cool” (make that very cool) because it touches on the deepest questions about humanity’s relationship to the universe. Maybe we’ll lose some of these kids to peer pressure as they go through high school and college. But I bet we’ll get a lot of them back later in life.

I wanted to use today’s blog entry to tell you about an innovative Web site that enables anybody with an Internet connection to engage in exciting, cutting-edge scientific research.

While astronomers continue to debate the definition of “planet” for objects inside the solar system, this Internet site allows you to join the hunt for planets around other stars. As he explains in S&T’s October 2006 issue, University of California, Santa Cruz, astronomer Greg Laughlin and his colleagues have developed the Systemic Project Web site, which allows users to search for extrasolar planets using published radial-velocity data taken by the California/Carnegie group led by Geoff Marcy, Paul Butler, and Debra Fischer, and the Geneva team led by Michel Mayor.

This is no joke. If you’re willing to invest some time and brainpower at this site, there is a distinct possibility that you could discover an actual planet orbiting another star. Since you’re reading this blog article, it means you have everything you need to participate: access to a computer and the Internet, and an interest in astronomy. No telescope or other instruments are required.

Greg and his colleagues have developed a console that allows participants to search for planets by moving banks of sliders (like one would find in an audio mixing board) to adjust for different possible planet masses, orbital periods, etc. to see if one can match up a model radial-velocity curve to the host star’s measured radial velocities. The Systemic team has also developed special tools to enable users to dig out planets in complex systems with multiple worlds. All of this is described in a user-friendly tutorial that can have a typical participant up and running in one hour.

How is this possible, you might ask? There are so many interesting planetary systems out there waiting to be deciphered, and the amount of computation is so extensive, that the professionals who are conducting these searches simply don’t have the time to analyze all of the data they are collecting. They have done the technically difficult job of obtaining the radial-velocity data (which can reveal the gravitational influence of orbiting planets), and they have generously published it in publicly accessible journals. Greg and his Systemic colleagues have combined some of these data sets for the first time, enabling users to find planets that are ripe for the picking.

The 4-planet configurations around the stars 55 Cancri and Mu Arae are of particular interest. Greg points out that the orbital solutions published in the professional literature for each star are not the end of the story. The data suggest that there are additional planets in these systems that a dedicated amateur could uncover.

In the months ahead, Greg and his Systemic team will allow participants to search for “synthetic planets” in simulated data sets, which will allow the professionals to learn about potential biases and other problems that might plague the real data sets. Starting this Sunday and running until the end of September, the Systemic team will post a synthetic “Star of the Week” on its Web site. The first person to successfully crack each week’s system will win a copy of our Millennium Star Atlas. To see the contest URL, pick up a copy of the October 2006 S&T and turn to page 41. If you’re not a subscriber, the issue will be on newsstands no later than next Tuesday.

Of course, the International Astronomical Union last week approved a poorly conceived definition of "planet," which applies only to bodies around the Sun. So according to the IAU, none of these worlds around other stars are “official” planets. But putting that bit of IAU absurdity aside, please note that the lion’s share of the credit for any discovery made through the Systemic project should and will go to the astronomers who took the data. But imagine the life-long satisfaction you’ll receive if you play a direct role in finding a planet around a distant star. Give it a whirl!

The short answer to this potentially explosive question is "I don't know." I wasn’t in Prague for the International Astronomical Union’s decisive vote to downgrade Pluto to "dwarf planet" status. And like the rest of humanity, I flunked Mind Reading 101. But because these perceptions seem to be spreading in the American planetary-science community, I think we have to face the possibility that the Pluto/planet controversy will be dragged through the mud of international geopolitics.

While there is no proof for the accusation in the title above, three leading American planetary scientists told me last week that they keenly sensed a strong anti-American component in the IAU vote. Two of the three attended at least part of the IAU General Assembly in Prague, and one was present for the decisive vote. These astronomers, who do not wish to be named for fear of backlash, charge that at least some of the astronomers used the Pluto vote as a way to "stick it" to the United States for its perceived domination of the IAU in past years, and to protest the invasion of Iraq.

But another distinguished American planetary scientist who was also in Prague adamantly denied the anti-American accusation when I spoke to him last week, and he expressed confidence that the assembled astronomers based their votes on the merits of the scientific arguments. He suggests that some of astronomers in the pro-Pluto camp are using this claim of anti-American bias to further their agenda. It should also be noted that some of the astronomers who have led the effort to downgrade Pluto’s planetary status were Americans, perhaps the most outspoken being Neil deGrasse Tyson of New York’s Rose Center for Earth and Space.

It’s no secret that Pluto was discovered by an American astronomer, and the same can be said for 2003 UB313 (informally known as Xena), the trans-Neptunian object (TNO) that is larger than Pluto. Most of the deep surveys that will turn up additional TNOs are being conducted by US-based astronomers, so if more planet-size bodies are discovered in the outer solar system, they will be found mostly by Americans. The majority of astronomers who study Pluto also happen to be Americans, and the New Horizons mission to explore Pluto is a NASA mission with mostly Americans on its science team.

For these reasons, it can safely be said that American astronomers have a lot more at stake than many of their international counterparts in maintaining Pluto’s status as a full-fledged planet. For those who think these nomenclature issues are meaningless, consider the following. The decision what to call Pluto and other large TNOs could very well affect future funding for planetary research. (I personally am very glad that the decision to downgrade Pluto was made after the launch of New Horizons.) I suspect that a lot of astronomers who study Pluto also feel that their peers in the IAU have devalued their research. Perhaps most important of all, Pluto’s status will affect what future generations of children are taught in schools and planetariums, and that will shape their perceptions of the solar system. So this controversy goes way beyond trivial issues relating to nomenclature, particularly for scientists whose careers are based on studying Pluto and the outer solar system.

Seen in that context, it’s not a surprise that the American Astronomical Society’s Division for Planetary Sciences (DPS) strongly endorsed the original proposed definition for "planet," which would have maintained Pluto’s status while also adding Ceres, Charon, and Xena. In going against the DPS endorsement, the IAU essentially delivered a slap in the face to the largest organization of planetary sciences in the world — whose membership happens to be predominantly American. A petition that circulated last week among a partial list of DPS members, and which calls for a revised definition of "planet," attracted more than 300 signatures. But I was struck by the fact that only a handful came from scientists outside the US.

Regardless of what one thinks of Pluto, the wording (and not necessarily the intent) of the IAU’s accepted definition is deeply flawed, as I pointed out in my blog entry on August 24th. It boggles my mind that hundreds of intelligent, well-informed astronomers actually voted for it. It deliberately excludes extrasolar planets, and because it specifies that a planet is a celestial body that "has cleared the neighborhood around its orbit," a literal interpretation would boot out Earth, Mars, Jupiter, and Neptune. Moreover, as New Horizons’ lead scientist Alan Stern (Southwest Research Institute, Colorado) has pointed out, astronomical objects have historically been classified according to their properties, not according to what they are near. Stern and other leading planetary scientists are calling for an international conference to devise a better definition, with the hope that most textbook publishers, educators, and museums will simply ignore the current vague definition until the IAU accepts an improved version at its 2009 General Assembly in Brazil.

Science is supposed to be an objective method for investigating nature. But anyone who follows it closely realizes that like every other human endeavor, politics and personalities always come into play. So don’t be surprised if the Pluto/planet debate becomes deeply politicized, and it could get very, very ugly. This may damage the public's perception of astronomy, and it’s particularly unfortunate that we’re having this debate at a time when US astronomy funding, especially for space missions, is being cut back drastically.

By their very nature, blogs are intended to address controversial issues and stimulate discussion, so I really appreciate everyone who has written so far to share their thoughts. If had to venture a guess, I suspect that the large majority (and perhaps all) of the several hundred astronomers at the IAU who voted to exclude Pluto based their decision strictly on scientific reasoning. But given the tense and changing international climate, and how the US government is perceived around the world, I can understand why some American astronomers at the IAU might have genuinely perceived an anti-American bias whether or not such a bias actually existed.

Pluto advocates are being accused of misrepresenting the IAU's planet definition in order to advance their agenda. But I can understand why they are upset with the IAU's definition. Among other reasons, the definition went against astronomical precedent by including a clause pertaining to whether an object can clear out its neighborhood. Here's why I think that was a mistake, and why I don't think Pluto should suffer the ignominy of having the word "dwarf" officially and permanently attached to its status.

Clearly, Pluto is a different type of object than the 8 solar system planets in the official IAU definition. But if we look at those 8, we see an extreme range of diversity as well. Mercury and Jupiter differ in mass by a factor of 5,750, and in volume by 25,000. Their compositions could hardly be more different. Jupiter's composition is more like that of a star; it's a giant ball of mostly hydrogen and helium. It also has a family of at least 63 moons, and several tenuous rings. In contrast, Mercury is a ball made of heavy elements, with no appreciable atmosphere and zero moons. Mercury is more than 13 times closer to the Sun. About all that Jupiter and Mercury have in common is that they are spherical objects orbiting the Sun. So if astronomers are comfortable lumping Jupiter and Mercury into the same category, it's not at all obvious that Pluto should be excluded from this club.

Yes, Pluto is embedded in the Kuiper Belt, and it certainly does not dominate its region of space, but its spherical shape, multiplicity of moons, and an atmosphere are properties that give it some commonality with the official 8 solar system planets. Let's consider three other classes of astronomical objects — galaxies, stars, and black holes — and we'll see an even greater diversity of characteristics, and we will see that these categories are not based on an object's location or gravitational influence.

First, let's examine galaxies. On one extreme, we see enormous elliptical-shaped galaxies that are much larger than our Milky Way, such as M87, which anchors the giant Virgo Cluster. Some of these assemblages contain trillions of stars, and have converted almost all of their gas into stars. Astronomers also see stately spirals like the Milky Way and Andromeda, which contain hundreds of billions of stars, and which are still actively churning out new stars. At the bottom end, astronomers studying Sloan Digital Sky Survey data have found about 10 new dwarf galaxies orbiting the Milky Way. These galaxies contain only a few tens of millions of stars, and appear to be even more dominated by dark matter than larger galaxies. Almost all of these dwarfs are destined to be tidally shredded and devoured by the Milky Way. But despite their vast range in sizes, shapes, stellar populations, and locations, astronomers have no problem lumping all of these objects together under the term "galaxies" because they share certain properties — they are collections of large numbers of stars that are spread out over a very large volume of space. We might call a small galaxy a "dwarf galaxy," but it's still a "galaxy."

Stars range in mass from blazing beacons such as Eta Carinae, which contains roughly 100 solar masses and shines with the luminosity of about 5 million Suns, to red dwarfs, which have only about one-twelfth of a solar mass and shine with the feeble glow of about 1/100,000th of a Sun. Some stars are only the size of Jupiter, others have swelled to such enormous diameters that their outer envelopes would extend to the orbit of Jupiter if they replaced the Sun. Some stars are located in dense star clusters, and others have been flung out of their parent galaxies into the lonely depths of intergalactic space. Some stars are solitary, but many others reside in binary or higher-order multiple systems. But despite their extraordinary wide range of sizes, masses, luminosities, and locations, astronomers lump them together because all of these objects fuse lighter elements into heavier elements in their cores. So a red-dwarf star is still a "star." (For the sake of brevity and simplicity, I’m leaving out collapsed stars such as neutron stars and white dwarfs, and brown dwarfs.)

Black holes exhibit an even wider range of masses, about as extreme as it gets in the universe. At the center of large galaxies such as M87 are monsters that pack a billion or more solar masses into a volume of space no larger than our solar system. Some of these monsters accrete matter at such furious rates that they become incredibly active, producing jets of particles traveling at near light-speed across thousands of light-years of space. These black holes are expected to live for 10¹⁰⁰ years, a span of time so immense that no human mind can fully grasp its meaning. At the other extreme, many physicists think that tiny black holes were forged in the very early universe, and some might be created even today when ultrahigh-energy cosmic rays slam into Earth's atmosphere. These black holes have the mass of a heavy atomic nucleus, and live for a minuscule fraction of a second before exploding into a shower of subatomic particles and radiation (the so-called Hawking radiation). Yet because all of these objects share similar properties (the presence of event horizons and singularities), astronomers call all of them "black holes."

Seen in this context, it makes perfect sense to call all spherical objects (from hydrostatic equilibrium) that directly orbit stars "planets," and this is close to the position that the world's largest body of planetary scientists strongly endorsed a few weeks ago. If astronomers don't make a distinction based on location, mass, and size for galaxies, stars, and black holes, why should planets be different? Why should it matter whether a spherical object orbiting a star can clear out its zone of space? A galaxy is a galaxy whether it dominates its cluster or is being devoured by a bigger galaxy. A star is a star whether it's alone, inside a cluster, or part of a binary. Just because a 50-solar-mass star can't eject a red-dwarf binary companion doesn't mean that we stop calling it a star! As described above, astronomers have historically categorized almost all classes of objects by their properties, not their locations. So if Mercury and Jupiter are considered similar enough to fall under the same category, it's not crazy or unscientific to think that Pluto should also be included, especially since Pluto shares the same properties with Jupiter and Mercury that give these two objects their commonality. And Pluto is in no danger of exploding or being devoured. Sure, call Pluto a "dwarf planet," but it should still be considered a "planet" with no officially mandated qualifiers. From Jupiter's perspective, Mercury and Earth are dwarf planets as well.

The astronomers who voted at the IAU to boot out Pluto were basing their decision on legitimate scientific principles that have considerable merit. But those on the other side have equally strong arguments. That’s why this issue is so contentious. By creating objects with a continuum of sizes and other properties, Mother Nature didn't make it easy for astronomers, and both sides can summon reasonable and valid arguments. So let's all take a deep breath and appreciate Mother Nature's wondrous diversity, and take time to understand and respect other peoples' points of view.

Update on September 7: Pluto has been assigned the number 134340 from the Minor Planet Center. The trans-Neptunian object announced last year that is even larger than Pluto, 2003 UB313 (informally known as Xena), has been assigned the number 136199.