September 20, 2006 2:50

Baby Lucy

The most exciting discoveries in human paleontology usually involve finding a brand-new species of ancient ancestor--but a paper in Nature today breaks that mold. Paleontologists announced that they'd excavated the partial skeleton of a three-year-old girl who lived in what is now Ethiopia about 3.3 million years ago. She's of the same species as the famous Lucy--Australopithecus afarensis--a type of pre-human that for decades reigned as the oldest known hominid.

But while the primitive child isn't the first of her species, the remarkable condition of the skeleton, including an essentially complete skull, firms up what paleontologists had concluded from Lucy herself: A. afarensis was a strange amalgam of human and apelike features. The human part was the lower body, whose bone structure made it clear that this species was capable of walking fully upright, where true apes spend most of their time walking on all fours. The apelike part was above the waist, including the skull--more like a chimp in size than a human--and the arms, with rounded shoulders and long, curving figures, well adapted to climbing, although it isn't clear whether they actually did climb at this point, or merely retained a more primitive feature.

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September 14, 2006 5:39

Planetary Christening

It's official: the object formerly known as 2003 UB313, just a bit bigger than Pluto and, for a week or so last month, on the verge of becoming a full-fledged planet, has been named by the International Astronomical Union. Until now, it was known informally as Xena, after the Warrior Princess of TV fame, but now the icy body will be called Eris, after the Greek goddess of discord.

Nice choice, since Xena's discovery by Caltech astronomer Mike Brown and his colleagues brought the long-simmering controversy over Pluto's own planethood to a head a year ago. If Pluto was a planet, then Xena--I mean, Eris--had to be too, since it was larger. But then, what kept smaller objects like Sedna and Quaoar from being planets? The IAU voted last month, in a very controversial ballot, to call the newly named Eris a dwarf planet, put Pluto into that new category, and add Ceres, the biggest asteroid. That has set off a revolt among planetary scientists who hate the new category--but in the meantime, 2003 UB313, or Xena, will henceforth be known as Eris. Its moon, in another nice touch, will be called Dysnomia Eris's daughter and the demon goddess of lawlessness.

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September 14, 2006 5:02

Puffy Planet

One of the fun facts astronomers love to trot out about Saturn is that its density is less than that of water; unlike any other planet, Saturn would float (if you could find an ocean big enough for it, that is).

But if the Guinness Book ever starts a floating-planet category, Saturn won't be in it, because a team of observers just announced the discovery of a new planet, orbiting a star about 450 light-years from Earth, in the constellation Lacerta. Like many of the more than 200 extrasolar planets found since 1995, this one zips around its parent star in an orbit that once would have been thought impossible--so close in that its "year" is only a four and a half days long.

Unlike anything ever seen to date, though, its density is only about 1/4 that of water (Saturn's is more like 3/4)--about the equivalent of cork. The new planet, known as  HAT-P-1, orbits one star in a double-star system (another situation thought until recently to be impossible). It was found by a relatively new technique: instead of measuring the gravitational wobble a planet imposes as it circles a star, astronomers using the Hungarian Automated Telescope network  measured the almost imperceptible dimming of the star as the planet crossed in front of it.

Just as a piece of popcorn is less dense and also bigger than an unpopped kernel, this planet is not only low in density: it's physically larger than any planet ever found--nearly 1.4 times the size of Jupiter (other planets are more massive, but they're also more compressed by their own gravity).

As for what could explain this bizarre object...well, nobody really knows. And that's not surprising, really; from the moment astronomers began finding planets around other stars, after literally thousands of years of speculation, these other worlds have turned to be endlessly astonishing. Theorists who were pretty sure they understood what a solar system should look like, based on our own, have turned out to be quite wrong--and it will take them a while to catch up.

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September 8, 2006 12:50

Is She Brain-Dead or Not?

That was more or less the question everyone asked about Terri Schiavo, but the answers were all more or less informed opinion until her autopsy, in which it became clear that her brain had atrophied so badly no mental function of any sort was going on.

But a new case described in the current issue of Science makes clear that in at least one case, being in what appears to be a complete vegetative state doesn't necessarily mean there's nothing going on inside. A British woman who'd been in a car accident and suffered severe brain damage was put in a functional MRI machine, which can show which parts of the brain become active under different circumstances. In this experiment the circumstances were doctors speaking to the woman. They were astonished to see that her brain responded to conversation in an almost normal way--lighting up in one way when they asked her to imagine physical activities, in another when they used complex sentence structure and so on.

So was the woman really understanding, even though she couldn't communicate in any way? Was she aware of her surroundings, trapped inside a damaged body? What must it be like to be in a state like that--like being buried alive? Worse?

Alas, these are questions nobody can possibly answer at this point. Scientists' understanding of what consciousness is and what awareness means is so rudimentary that there's no way to know precisely what a given pattern of brain activity means. It's perfectly conceivable that you have to be fully conscious to be aware; we have the sense of awareness when we're dreaming, but there's no proof that this isn't retrospective--that we aren't really aware of dreaming until we wake up and recall it. There's simply no way to get inside another person's brain to figure out what he or she is actually experiencing. Indeed, the sort of philosophical question that keeps college students arguing long into the night--"when you see red, is it really the same color I see when I see red?" has yet to be fully answered.

No one knows, either, whether this woman's responses are typical of people in her state, or whether she's the only case that will ever be found. It matters, of course, because if she has even minimal consciousness, that can raise hope that she might recover further--which in fact has subsequently happened in this case, but might not happen with others. So, the scientists caution, while this is a remarkable study, it carries the danger that friends and loved ones will now assume anyone in an evident vegetative state knows what's going on and might recover. And as we learned with Terri Schiavo, it's not always the case.

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September 7, 2006 4:01

Would You Rather Die of Cancer, or Old Age?

Increasing the human age span and preventing cancer are two of the most intriguing areas in medical research, and now a series of papers in Nature has shown how they may be intimately related--in a way that isn't necessarily the best news for either camp. It turns out that, in mice at least, adult stem cells--cells specific to the brain, heart and other organs that help replenish those body tissues--are gradually turned off as an organism age, losing their ability to divide  indefinitely.

The reason is that indefinite division is the process behind cancer; the mammalian body has evolved a tumor-suppression gene, known as p16-Ink4a to help defend against such uncontrolled growth in cells in general. But by shutting down stem cells as well, believe researchers from the University of North Carolina, Harvard and the University of Michigan, p16-Ink4a allows organs to age and ultimately fail.

Indeed, three different labs looked at three different stem-cell systems, in mice genetically engineered to be lacking p16-Ink4a--brain, bone marrow (which makes blood cells) and the pancreas; in each one, the lack of the gene allowed organs to remain youthful long after they'd be expected to start aging. But the mice were more prone to cancer.

All of which means that scientists will have to be very careful about tinkering with lifespan extension. They'll also have to consider that using adult stem-cells rather than embryonic stem cells for therapeutic purposes might not work after all. An adult stem cell has presumably been affected by p16-Ink4a already, so using it to repair a damaged heart, say, could backfire. An embryonic stem cell, by contrast, is inherently youthful, and can presumably live for decades.

That doesn't help the arguments of those who insist adult stem cells are every bit as useful as embryonic ones--arguments that were already based not on actual knowledge, but on hope, tied to a moral revulsion against "destroying human life." And it also doesn't suggest with any finality that adult stem cells are useless. Anyone who makes either argument is talking politics, not science.

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September 5, 2006 3:02

Since When are Stingrays Dangerous?

I have to admit something: when headlines began popping up about the tragic death of Steve Irwin, my first reaction was "who's Steve Irwin?" Yes, I'm a science guy who'd never heard of him. Now I have, and I realize why people are so surprised: here's a man who jokes with killer crocodiles, handles lethal snakes and wrestles with Komodo dragons, and he's done in by a stingray? Aren't those the scary-looking creatures we're always reminded by aquarium guides are really quite docile and unaggressive?

In fact, they are. A stingray will do everything it can to  try and get away when it feels threatened, and certainly never attacks unprovoked. That's why only a couple of dozen deaths by ray have ever been documented, and many of those not by the sting itself but by the venom that coats its surface. The most common way to trigger a sting is to step on the ray's back as it rests on the sea bottom. which makes its stinger-tipped tail flip up in a reflex reaction.

Bur Irwin didn't step on the ray that killed him, and by all accounts he wasn't threatening it--he was just snorkeling above it. The catch is that a ray doesn't have to be threatened, just feel that way. So when two large animals floated overhead--Irwin's cameraman was right there as well--the ray presumably felt it might be eaten and couldn't get away, and lashed out. If it had been one of the smaller stingray species that are found in pretty much every tropical ocean, he might have simply suffered a lot of pain.

But  Irwin was jabbed by a bull ray, the biggest species in the world, and one that is common on the Continental shelves of countries in and near the Indian Ocean. This one was a 200-pounder (they can grow up to 3 times that size), and by even worse luck its 8-in. barbed stinger tore directly into Irwin's heart; when he yanked it out, the barbs ripped the hole even bigger. Whether it was the shock and blood loss that killed him or an allergic reaction to the venom, he was dead in seconds.

A poet or a philosopher would undoubtedly find something deep to say about a man who laughed in the presence of vicious, deadly animals and was ultimately killed by an utterly placid one. But I'm just a science guy, so all I can say is that they're all wild animals--which means anyone who thinks he knows for sure how they'll act is probably kidding himself.

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September 1, 2006 9:31

And You Thought the Pluto Problem was Solved...

Here's a riddle: what do the International Astronomical Union (IAU) and the International Star Registry have in common? Not much, you'd think, aside from their similarly official-sounding names. The former is an association of professional astronomers which, among other things, bestows names on heavenly objects. If you discovery a comet or an asteroid or a new planet, it's the IAU that formally recognizes the discovery. The Registry, by contrast, is a private company that will name a star after anyone you like, for a fee--but it's completely unofficial. It's pretty much guaranteed that no professional astronomer will use or even know about the name, and you won't be seeing it in Sky and Telescope magazine

And that, it turns out, is what the two groups may suddenly have in common in the case of Pluto. Last week, IAU members at the group's annual conference voted on the first formal definition of "planet" in modern history--a definition that demoted Pluto to the status of "dwarf planet," leaving just eight full-fledged planets in our Solar System and leaving many schoolchildren, and many former schoolchildren, grieving for poor little Pluto.

But another shoe has now dropped. Last weekend, without much fuss, planetary scientist Alan Stern, of the Southwest Research Institute, and a few colleagues circulated a petition among fellow astronomers, which stated:

“We, as planetary scientists and astronomers, do not agree with the IAU’s definition of a planet, nor will we use it. A better definition is needed.”

Within a couple of days, with 300 signatures from some very prominent scientists at very prominent institutions, they shut down the process, figuring the point had been made. "The IAU can also declare that the sky is green," Stern told me last night, "but that doesn't make it so."

The problem, he says, is that the new definition states that to be a planet, an object must have "cleared its neighborhood" of other objects--that is, flung them out of orbit through gravity. Pluto hasn't, so it's no planet. "The definition is awful," says Stern. "It's pedagogically impossible to explain, and it's technically flawed."

Why? Because several of the eight remaining planets haven't "cleared their neighborhoods" either. Plenty of asteroids share Jupiter's orbit. Some cross Earth's orbit. And Pluto crosses Neptune's orbit. Does that mean Neptune really isn't a planet either? One counter-argument might be that while Jupiter, Neptune and Earth all share their orbits, it's with much much smaller objects, and relatively few of them. Pluto, by contrast, is smaller than our Moon to begin with, and swims in a sea of so-called Kuiper Belt Objects, icy bodies that have a wide range of sizes. So Pluto hasn't cleared its neighborhood as completely.

Not a good argument, says Stern. If Earth were out where Pluto is, it wouldn't have cleared the neighborhood either: Pluto's orbit is so much bigger than Earth's that it has a much bigger neighborhood, and Earth couldn't have cleared it out yet even after 4 billion years or so of existence. "Which means," says Stern, "that whether something is a planet or not depends on where it is, not on its intrinsic properties. That makes science looks arbitrary."

Not only that: the IAU's definition of "planet" specifically says the object has to be orbiting the Sun--not "a star," but the Sun. Which means it only applies to our Solar System. Given that astronomers have found 200 or so planets around other stars already, that's just a bit parochial. It's as though you defined "mountain," but it only counted in North America. The Himalayas wouldn't be included. One reason the IAU may have done it this way is that there's a controversy over how big a planet can get before you have to call it something else--and some of the objects around other stars are already ten times the size of Jupiter.

Finally, Stern and his colleagues are upset because while the IAU has some 10,000 members, only a couple of thousand attended the meeting in Prague, and by the time the vote on planets came, on the last day, most had left (Stern had to take his daughter to college, so he couldn't stick around). As a result, fewer than 500 members of a 10,000-member organization voted on the resolution. "They wouldn't allow electronic voting," says Stern. "And here I thought astronomy was a high-tech field."

The upshot is that the controversy over what is and what isn't a planet is far from over; indeed, next week, says Stern, a few other shoes are going to drop, though he can't reveal them yet. Stay tuned.

P.S. I made a dumb mistake in my cover story this week on the First Stars. Jacqueline Hewitt is at MIT's Kavli Institute for Astrophysics & Space Research. I left of the "Kavli," which is especially unfortunate because the Kavli Foundation is a major supporter of basic research in physics, astrophysics, neuroscience and more. So now you know.

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