SASTIND via Weibo / UMSF

China's Chang'e-2 probe took multiple images of the asteroid Toutatis during its Dec. 13 flyby.

China's official news agency is reporting that the country's Chang'e 2 deep-space probe made an amazing flyby of the asteroid Toutatis this week, snapping a series of pictures as it passed by at a distance of just 2 miles. The achievement signals China's entry into yet another exclusive space club.

Only four of the world's space efforts have managed close encounters with asteroids: NASA (with NEAR Shoemaker and Dawn, for example), the European Space Agency (with Rosetta), Japan (with Hayabusa) — and now China with Toutatis.

The official Xinhua news agency quoted officials at the State Administration of Science, Technology and Industry for National Defense, or SASTIND, as saying that Chang'e 2 buzzed past the 3-mile-long (5-kilometer-long) asteroid at a relative speed of 24,000 mph (10.73 kilometers per second).

Chang'e 2 was launched in 2010 primarily to serve as a lunar orbiter, but after a successful mission at the moon, the $132 million spacecraft was repurposed as a deep-space explorer. The encounter with Toutatis had been planned for months, but Chinese media kept mum about the results until Saturday.

Aficionados of planetary science hailed China's success.

"Oh my goodness, did they succeed. This is awesome," the Planetary Society's Emily Lakdawalla said in a blog post passing along the news. On the Unmanned Spaceflight discussion forum, Ted Stryk wrote, "Welcome to the interplanetary club, China."

Toutatis is a near-Earth object that's big enough to cause a mass extinction if it were to hit our planet — but fortunately, it isn't projected to come all that near in the foreseeable future. This week it passed by Earth at a minimum distance of 4.3 million miles (7 million kilometers). That provided scientists with an opportunity to study the peanut-shaped space mountain at a relatively close but totally safe distance.

NASA's Jet Propulsion Laboratory conducted a series of radar observations using the Goldstone radio antenna in California, and on Friday, JPL released a grainy time-lapse video showing Toutatis' rotation.

The insights gleaned from such observations could conceivably help scientists figure out how asteroids came into existence early in the solar system's history, how to mine asteroids for valuable resources, or how to divert asteroids that have the potential to threaten Earth.

Lakdawalla noted that the radar readings, combined with China's up-close images, made Toutatis one of the "best-studied asteroids in the solar system." That sounds like a bold statement, considering that NASA studied the asteroid Eros with NEAR Shoemaker for more than a year, and had Dawn in orbit around the asteroid Vesta for a year as well. But the fact that Toutatis has gotten so much attention in the past week from multiple space efforts certainly suggests that scientists see "minor planets" as a major interest.

Still more asteroid encounters are on the agenda in coming years — including Dawn's arrival at the dwarf planet Ceres in 2015, a potential sequel to Japan's Hayabusa mission, and the crewed mission that NASA wants to send to a near-Earth asteroid in the mid-2020s.

And let's not forget China. Chang'e 2 isn't finished just yet. Xinhua quoted sources as saying that the probe "is continuing its deep space travel and will reach a distance of more than 10 million kilometers away from Earth in January next year."

More about asteroids:

• More study urged for asteroid heading near Earth
• Save the earth: Hit killer asteroids with spaceships
• Flash interactive: Close encounters of the asteroid kind

Alan Boyle is NBCNews.com's science editor. Connect with the Cosmic Log community by "liking" the log's Facebook page, following @b0yle on Twitter and adding the Cosmic Log page to your Google+ presence. To keep up with Cosmic Log as well as NBCNews.com's other stories about science and space, sign up for the Tech & Science newsletter, delivered to your email in-box every weekday. You can also check out "The Case for Pluto," my book about the controversial dwarf planet and the search for new worlds.

NASA / JPL-Caltech

It turns out that Eris, shown in this artist's conception, may be Pluto's denser twin.

It's been almost a year since astronomers suggested that Eris, the icy world whose discovery prompted Pluto's controversial reclassification in 2006, wasn't as big as they originally thought. Now the official word has leaked out unofficially: Pluto just might be the largest dwarf planet after all — although Eris is still seen as more massive.

The latest measurements were reported last week in Nantes, France, at a joint meeting of the American Astronomical Society's Division of Planetary Sciences and the European Planetary Science Congress. But as the Planetary Society's Emily Lakdawalla explains, it took a while for the report to become public, due to worries about the journal Nature's rules on embargoes and confidentiality.

Here are the statistics: Based on measurements made last November during the dwarf planet's occultation of a faraway star, Eris' diameter is estimated at 2,326 kilometers (1,445 miles). A similar set of measurements, published in 2009. estimated that Pluto was at least 2,338 kilometers (1,453 miles). When you include the margin of error, Pluto is essentially Eris' equal in size.

"It could be smaller, it could be larger; basically, it is a twin," Lakdawalla quoted Paris Observatory astronomer Bruno Sicardy, the lead researcher for the Eris measurements, as saying at the conference.

Lakdawalla held back from reporting what Sicardy said because she was asked to. The research paper about the measurements is under consideration for publication in Nature, and Sicardy said the journal's editors told him he could discuss the results only if he instructed his audience not to report them publicly. The implication was that Sicardy's paper would be tossed out if his team's findings appeared in the press.

The audience was all abuzz about the findings, of course, but Lakdawalla said she wouldn't "break anything until somebody else breaks it."

She did, however, refer to the zipped-lip situation in a Twitter message to Embargo Watch's Ivan Oransky. Long story short, Oransky checked with Nature and was told that "researchers with papers in submission at a Nature journal can certainly present at a scientific meeting but shouldn't court the press." Oransky blogs about the back-and-forth today on Embargo Watch, but the bottom line is that Sicardy needn't have feared having his paper rejected, as long as he confined his public remarks to the presentation.

If Nature sticks to the reported publication plan, the paper will be published on Oct. 26. Today, a lot of the details came out not only on Lakdawalla's blog, but also on Scientific American's Observations blog — which is interesting, because Scientific American is part of the Nature Publishing Group. (SciAm's John Matson helpfully included a link to Sicardy's conference report.)

So what else do Sicardy and his colleagues say? Although Pluto and Eris are roughly the same size, Eris is more massive, which implies it's "mainly composed of rocky material, with a relatively thin ice mantle," the astronomers say. They suggest that Eris once had a thicker layer of ice, most of which was "blasted away" as the result of a catastrophic cosmic collision.

Sicardy and his colleagues also note that when you factor in Eris' distance, its observed brightness and its relatively small size, the dwarf planet stands out as one of the brightest bodies in the solar system, after the Saturnian moons Tethys and Enceladus. They suggest that the dwarf planet is so bright because it has a surface layer of nitrogen or methane frost, due to the freezing-out of its atmosphere.

A similar freeze-out might well happen on Pluto as it heads out to the farthest point of its orbit around the sun. Eris, meanwhile, is coming closer to the sun — and at some point the nitrogen or methane might thaw back into the atmosphere.

The two worlds seem destined to stand in the planetary pantheon as separated twins — in possession of moons, seasons, their own distinctive geologies and potentially some kind of cryovolcanic activity. Should they really be regarded as non-planets, or is it better to see them as a different class of planets? I argue for the latter in my book, "The Case for Pluto," but I'd love to hear what you think. Please feel free to add your comments below.

More about dwarfs and other planets:

• Pluto debate is about more than one little world
• Interactive: The new solar system
• Eris looks a lot like Pluto
• Eight decades of Pluto
• The Pluto files on msnbc.com

Connect with the Cosmic Log community by "liking" the log's Facebook page, following @b0yle on Twitter or adding me to your Google+ circle.

It seems that the world was shocked to learn this week that astrology no longer reflects astronomical realities. But such shifts are merely part of the routine in a changing universe. They don't always come to our attention, but they can make more of a difference in your daily life than your horoscope.

Parke Kunkle, an astronomer who teaches at Minneapolis Community and Technical College, set off an Internet-wide viral buzz when the Star-Tribune published his observation that the constellations don't match the traditional astrological signs. Back in the days of Babylonian soothsayers, the sun might have been in the constellation Capricorn at this time of year. But due to the changing tilt of Earth's axis, it's actually in Sagittarius right now.

Today, Kunkle told MSNBC that his phone has been ringing off the hook — and he doesn't know why this has turned into such a big deal. "What we've been doing is just a standard astronomy lesson that we talk about in every astronomy class," he said.

Over the course of thousands of years, Earth's axis wobbles like a top, and as a result the apparent position of the sun against the constellations varies. The boundaries of the constellations have become more sharply defined as well, which means the sun doesn't spend equal amounts of time in each of the zodiacal "signs." In fact, the sun passes through a 13th constellation — Ophiuchus the serpent bearer — which throws off the whole traditional 12-house system that astrologers swear by.

Of course, most people don't give any credence to astrology, with or without Ophiuchus. A 2005 Gallup Poll found that only about a quarter of Americans believe that the position of stars or planets can affect their lives. And even if you are a believer, the planetary shift doesn't magically transform you from a Virgo to a Leo. "This doesn't change your chart at all," Shelly Ackerman, an astrologer and spokeswoman for the American Federation of Astrologers, told The Associated Press.

The same advice holds for other astrological systems. For example, it's still the Chinese Year of the Tiger (well, at least until February). The fact is that the practice of astrology is separate from the modern science of astronomy, even though ancient cultures spent so much effort on astronomy mainly so that astrologers could do their job better.

Earth's cosmic shifts have had other effects as well. Just for luck, here are seven examples:

Changing pole star: Another effect of Earth's wobbling axis is that different stars have served as the guide star for our planet's geographical north pole throughout history. During the heyday of the Egyptian pharaohs, for example, other stars took on the role of the pole star, an "undying" star that never set. This is thought to be the reason why the Great Pyramid of Khufu was built with a passageway that pointed to the star Thuban in the constellation Draco, which was the star closest to the north pole when Khufu died, around 2566 B.C. Later on, the pole stars were  Kochab and Pherkad in the constellation Ursa Minor. Today it's Polaris, but the bright star Vega had its turn around 12,000 B.C. and will be the pole star once again in the year 13,727 or so.

Changing magnetic poles: Last week's big geophysical story had to do with the gradual shift of Earth's magnetic north pole away from Canada and toward Russia. The poles move because of the changing flow of molten iron in Earth's core, which drives the planet's huge magnetic dynamo. This doesn't affect Earth's spin or geographical north, but it does cause the structure of the magnetic field to shift, which affects compasses. Although a lot of navigation nowadays is done using GPS systems, the Federal Aviation Administration wants to make sure that aviators can still find their way to a safe landing using magnetic compasses — and that's why it requires airports to revise their runway designations periodically to reflect the magnetic shift.

Shifting continents: Earth's continents are on the move as well, and over the course of millions of years, that has affected the course of evolution. "The continents are drifting at about the same rate that your fingernails are growing," Phil Plait, the astronomer who presides over the Bad Astronomy blog, told me. If you go back 180 million years or so, nearly all of Earth's land mass was united in one large continent called Pangea, which meant land-based organisms could spread far and wide. Since then, the continents have drifted apart, separating populations and leading to the rise of new species. The breakup of Pangea helps explain why kangaroos thrived in Australia but not America.

Uneven gravity: Just as Earth's magnetic field has its variations, so does Earth's gravitational field. Readings from the European Space Agency's GOCE satellite have plotted the subtle differences in our planet's mass distribution, on land and in the oceans. "You'd think gravity is the same everywhere, until you start delving really deep into it," said Alice Enevoldsen, planetarium supervisor at the Pacific Science Center in Seattle (and the blogger behind Alice's Astro Info). Variations in Earth's mass could help explain how ocean circulation works and lead to better climate prediction models.

Inconstant sun: Speaking of climate, the variations in solar irradiance play a significant role in the warming and cooling trends experienced on our planet as well as on others. Some suggest that the sun is a bigger factor than human industrial activity when it comes to global climate change. Most climate scientists say greenhouse-gas emissions have been playing a more significant role lately, but variations in the amount of solar radiation hitting the planet are definitely a factor as well. Last year, one study found that the amount of solar energy reaching Earth increased even though the sun was at the low point in its 11-year activity cycle. And just today, scientists reported that the solar energy levels were actually lower than previously thought.

Lengthening day: If it seems as if each day is longer than the last, you're right. But that's just because Earth is slowing down ever so slightly every day. Gravitational tugs from other celestial bodies (principally the moon and the sun) are causing the "great slowdown," as my colleague David Ropeik explained back in 2001. It's thought that when the moon formed, billions of years ago, a full day was six hours long, and that the day lasted less than 23 hours when dinosaurs ruled the earth. Nowadays, leap seconds are periodically added to keep atomic clocks in sync — most recently at the end of 2008.

Galactic tides: Our solar system's path through the Milky Way galaxy is subject to shifts as well. Scientists have noted that Earth's biodiversity seems to dip every 60 million years or so, at just about the time when the solar system bobs up through the average plane of the Milky Way's disk. Last month, researchers suggested that the rise through the galactic plane exposed the solar system to a surge of cosmic rays, dealing a damaging blow to life on Earth. Some scientists have also wondered whether the solar system's galactic oscillations might periodically send more comets into the solar system (killing off, let's say, the dinosaurs). This definitely sounds like a bad thing, and depending on who's doing the talking, we're either "very close" to the next risky period, or 10 million years away.

That puts this whole question over whether you're a Virgo or a Leo in perspective, doesn't it?

Update for 2:30 p.m. ET Jan. 15: I initially wrote that astrology is "totally divorced" from modern astronomy, but that's an overstatement. Astrologers still depend on accurate determinations of celestial bodies' positions in the sky, as seen from Earth. They incorporate astronomical advances as well, such as the discovery of additional dwarf planets. But the way they interpret that information is different from how astronomers would interpret it.

Take the constellations, for example: Some commenters have noted that when an astrologer says the sun is "in the house of Aries," that doesn't mean the sun is actually in the astronomical constellation of Aries. In astrology, the sun enters Aries at the time of the March equinox, as explained here by EarthSky. The sky is then divided into 12 houses (named after constellations) that take up equal amounts of angular distance around the celestial equator. Thus, the astrological signs do not correspond precisely with the astronomical constellations as they're defined today, and they never did.

In ancient times, the "first point of Aries" occurred when the sun was actually in the astronomical constellation of Aries. No more. Now the sun is in the constellation of Pisces for the March equinox, and by the time Earth wobbles its way to the year 2600 it will be in Aquarius for the start of northern spring. For astronomers, that will be the true dawning of the age of Aquarius, although some astrologers (and songwriters) argue that the Aquarian age has already begun.

Astrologers borrow quite a bit from astronomy, but generally speaking, the only professional interest that astronomers take in astrology is historical — since, as noted above, the roots of astronomy go back to ancient beliefs about the connections between the cosmos and our destinies. It's a natural human yearning. I'll bet that at least one or two young astronomers have checked their "love signs" at some point, even if they haven't written a research paper about it.

More on scientific paradigm shifts:

• Technolog: How Twitter snowballed the zodiac 
• Vote: Has your opinion of astrology changed?
• Scientists give the periodic table a makeover
• Earth's timeline: How continents clashed
• Scientists question fundamental laws

Connect with the Cosmic Log community by "liking" our Facebook page, or by following msnbc.com's science editor, Alan Boyle, on Twitter (@boyle).  

A. Schaller / STScI

New observations suggest that the dwarf planet Eris, shown in this artist's conception, isn't as big as scientists thought it was.

Everyone knows that the solar system is no longer seen as a nine-planet set. When you count the dwarfs, there could be scores or hundreds of planets out there -- as I write in my book, "The Case for Pluto." But a case could be made that Pluto is once again the ninth-largest planet orbiting the sun, based on observations reported over the weekend.

Pluto was ousted from the No. 9 spot five years ago, after the discovery of another dwarf planet on the solar system's icy frontier, known today as Eris. It was Eris' apparent status as an object slightly bigger than Pluto that brought the controversy over the definition of a planet to a head. If Pluto was an honest-to-goodness planet, shouldn't Eris be one as well?

In 2006, the International Astronomical Union approved a definition that established a new class of objects, called dwarf planets, which were big enough to be basically round but not gravitationally dominant enough to "clear out the neighborhood of their orbit." What's more, the IAU ruled that dwarf planets were not really planets.

My book delves into the questions raised about that definition, particularly in light of what we've been learning about planetary systems since then. Now there's a new question: Is Eris bigger than Pluto after all? Based on observations of Eris' occultation of a faraway star in the constellation Cetus, the answer could well be no.

Sky & Telescope's Kelly Beatty reports that the latest observations suggest Eris is actually slightly smaller than Pluto. He quotes the Paris Observatory's Bruno Sicardy as saying Eris is "almost certainly" no wider than 1,454 miles (2,340 kilometers), compared with Pluto's estimated width of 1,456.5 miles, plus or minus 6.5 miles (2,344 kilometers, plus or minus 10 kilometers).

"If the early results hold up, this time it's the dwarf planet Eris' turn to be demoted, and Pluto might have just regained its status as the largest object in the Kuiper Belt," Beatty writes. The Kuiper Belt is the broad zone of icy objects that lie beyond Neptune's orbit.

Gathering the data for the measurements was a grand astronomical feat: Three teams of scientists watched the distant star disappear when Eris crossed in front of it. By analyzing how long the star was covered over, as seen from three vantage points in Chile, the astronomers could calculate how wide Eris' round disk was. Previous estimates were based on indirect data, such as Eris' brightness.

Further observations will be required to reduce the uncertainties surrounding the two worlds' widths. The current estimates are so close that Caltech astronomer Mike Brown, whose team discovered Eris and two other dwarf planets, can justifiably say Eris and Pluto are "more or less the same size." And when you rank the two by mass rather than size, Eris clearly comes out on top. That implies that Eris' interior is denser and thus rockier than Pluto's.

"How could Eris and Pluto look so similar in size and exterior composition yet be totally unalike on the inside?" Brown writes. "As of today I have absolutely no idea. ... Something is going on in the outer solar system, and I don’t know what."

Whether Pluto is bigger or smaller than Eris really doesn't affect its status as a dwarf planet. But it does illustrate that small celestial objects can deliver some big scientific surprises -- and that it's a huge mistake to write off the little guys of the solar system.

Correction for 6:50 a.m. ET Nov. 8: I originally wrote that Pluto might be the ninth-widest object in the solar system, neglecting to take into account that some moons are wider than Pluto (and in fact wider than Mercury). Thanks to Stevesliva for pointing that out.

More on dwarf planets:

• Pluto debate is about more than one little world
• Interactive: Guide to the new solar system
• Pluto maps raise new questions
• 80 years of Pluto

Connect with the Cosmic Log community by "liking" the log's Facebook page or following @b0yle on Twitter. You can also check out "The Case for Pluto," Alan's book about the controversial dwarf planet and the search for new worlds.