TIME space

Watch a Black Hole Get Evicted From a Galaxy

A dramatic study—and an equally dramatic video simulation—reveal a cataclysmic cosmic event

A couple of years ago, astronomer Michael Koss was searching the heavens for active galactic nuclei (AGN). In plain English, those are giant black holes, lurking in the cores of galaxies, which swallow matter so voraciously that the gas they gobble heats up to an incandescence visible billions of light-years away. And he wasn’t looking for just any AGN; he was looking for twin AGNs, which occur when two AGN-bearing galaxies merge into one.

Then, says Koss, “I found this thing.”

The thing was just a single spot of light, labeled SDSS1133, nestled in a dwarf galaxy called Markarian 177, located in the bowl of the Big Dipper, about 90 million light-years from Earth. It looked just like an AGN—except it wasn’t in the galaxy’s core. It was off-center by about 2,600 light-years. So maybe it wasn’t an AGN after all, but an unusual type of exploding star.

But when Koss went back to earlier observations, some made by NASA’s Swift satellite, the bright spot was there, at least as far back as the 1950′s. Since stars don’t usually take a half-century to explode, Koss and several colleagues were forced to consider a much stranger possibility: the mystery object could be an AGN after all, but one that was somehow booted from the center of its galaxy. Their report appears in the November 21 Monthly Notices of the Royal Astronomical Society.

You might imagine it would be touch difficult to boot a black hole anywhere, especially one that weighs millions of times as much as a star. There is, however, one thing that could do the job: a second black hole. Sort of. “We suspect we’re seeing the aftermath of a merger of two small galaxies and their central black holes,” said co-author Laura Blecha, of the University of Maryland, in a statement.

The idea goes like this. Astronomers know that galaxies that wander too close to each other get trapped by their mutual gravity, and merge into one; it happens all the time, in fact. Since virtually all galaxies have huge black holes inside, the new, combined galaxy ends up with twin black holes in their cores (some of which turn into the double AGN’s Koss was looking for in the first place).

But the black holes themselves can merge as well. When that happens, the cataclysm sends gravitational waves rippling across the universe. If the black holes have different masses and different spins, those waves can shoot out more powerfully in one direction than another—and that can kick the new, single black hole right out of the galaxy’s core. “That’s our most plausible case,” Koss says.

It’s not the only case, however: the scientists haven’t ruled out the idea that the bright spot is an exploding star after all. If so, the light seen in earlier images from the 1950s could have come from violent eruptions on the star, which culminated in an explosion back in 2001, when SDSS1133 brightened visibly. It’s not unheard of: a nearby star in our own galaxy, Eta Carinae, is erupting in what astronomers think could be a prelude to a full-fledged supernova explosion.

But SDSS1133 shines brightly in ultraviolet as well as visible light, even though the ultraviolet light from supernovas tends to fade quickly. Followup observations with the Hubble Space Telescope a year or so from now could clear up the question for good.

In the meantime, it’s natural to wonder whether SDSS1133 will eventually fly out of its host galaxy entirely and begin to roam the universe as a naked black hole. The answer, says Koss, is “it’s hard to say.” The galaxy itself is small, so it doesn’t have a lot of gravity to hold SDSS1133 back. But the original kick wasn’t all that hard, so the black hole might not have reached escape velocity.

In short, we’ll know one way or another whether SDSS is a black hole within the year. To learn whether it will escape Markarian 177—well, that’ll take a couple million.

TIME space

Strange Visitors From the Edge of the Solar System

Sometimes a comet isn't a comet
Sometimes a comet isn't a comet Art Montes De Oca; Getty Images

A pair of sort-of comets pose a puzzle for astronomers

The term “Oort Cloud” may be obscure for many people, but it’s familiar terrain for astronomy buffs. It’s a giant spherical swarm of trillions of proto-comets, lurking at the outer fringes of the Solar System, so far away that it may stretch a quarter of the way to the nearest star. They’re proto because they’re not technically comets unless they get knocked out of orbit and fall toward the heat of the Sun, whose warmth turns their long-frozen ices into a halo of dusty gas and, sometimes, a tail as well.

A pair of very unusual objects announced at last week’s Planetary Science Meeting in Tucson, however, have complicated this seemingly straightforward story. The first, found in 2013, has an orbit that clearly shows it came from the Oort Cloud—but while it resembles a comet in some ways, it didn’t light up like one even after it warmed. The second, found just this past September, also came from the fringes of the Solar System. This one doesn’t even resemble a comet, let alone act like one: it looks more like a rocky asteroid.

Except asteroids aren’t supposed to live in the Oort Cloud—and that creates just the sort of mystery scientists love. “We’re all very excited,” admits Karen Meech, of the University of Hawaii, who led the discovery team. But while both objects surprised researchers, both turn out to confirm two pieces of cosmic wisdom, one from a half-century ago and the other much more recent.

The old wisdom comes from Jan Oort himself, the mid-20th-century Dutch astronomer the Oort cloud is named for. He theorized that long-period comets, with highly elongated orbits lasting more than 200 years, came from a distant, spherical cloud that surrounds the Solar System. “He figured this out based on just 13 comets,” says Meech. “It’s really amazing.”

The idea is that the comets formed closer in, along with the rest of the Solar System, but that many were flung outward in gravitational interactions with Neptune and other giant planets. That notion was reinforced long after Oort’s time, when planetary scientists realized that the giant planets might have changed their orbits significantly soon after they were born; that motion would have ejected icy bodies in vast numbers.

Oort also suggested that the objects that eventually fell in again would be especially bright the first time around, since they’d have lots of ice on their surfaces—precisely what happened when Comet Hale-Bopp showed up in 1997. “On their very first passage through the inner Solar System,” says Meech, “all of that sublimates away, so after that you just don’t see them.”

The object discovered in 2013, she says, which is known as (deep breath) C/2013 P2 Pan-STARRS, fits the profile of what an Oort cloud comet should look like on a second or later return to the inner Solar System, and, says Meech “it may be proof at last that Oort was correct.”

Even as the astronomers were trying to figure out what they were seeing, though, the second object, C/2014 S3 Pan-STARRS, showed up (in both cases, the objects were found by the Pan-STARRS1 telescope, atop Mauna Kea, in Hawaii). It didn’t act like a comet either, but unlike the first object, it also didn’t much resemble one, as a close look at its composition revealed.

And that seems to support an idea advanced back in 2011 by Kevin Walsh, of the Southwest Research Institute, along with several colleagues. Their computer models of the newborn Solar System found that the giant planets should indeed have migrated from their original positions, moving first in toward the Sun, then out to where they are today. As they moved out, says Meech, “they would have dragged about fourteen Earth masses worth of material with them and thrown it outward.”

That material, in the form of asteroids, could have ended up in the Oort Cloud along with the proto-comets. Even as recently as a decade ago, this theory would have seemed crazy. Now—as so often happens—the very old solar system is teaching us something very new.

TIME space

Since You Wondered, Here’s Why Jupiter’s Great Red Spot Isn’t White

NASA says it's likely "a sunburn, not a blush"

The giant cyclonic storm that swallowed Alaska last week has nothing on Jupiter’s Great Red Spot. The GRS is a cyclone, too, but one so immense it could gulp down the Earth in one shot and still have room for Mars. It’s been swirling for centuries, at the very least, and while it’s smaller than it used to be, nobody thinks it’s going away.

All of this is pretty well known to planetary scientists. What they don’t know is the answer to a very simple question: Why is the Red Spot, well, red? “There are some other places on Jupiter that are reddish,” says Kevin Baines of NASA’s Jet Propulsion Laboratory (JPL), “although they’re more of a reddish-brown.” The spot’s color, however, is pretty much unique and thus pretty mysterious. In fact, Baines adds, “back in the 1970′s, when we were trying to sell the Galileo mission to Congress, it really resonated that we were going to try and answer that question.”

Now Baines and two JPL colleagues may have finally done it — not with data from Galileo, which orbited Jupiter and its moons from 1995 to 2003, but from the Cassini probe, which took a few snapshots en route to Saturn. Those images, supplemented by laboratory experiments, suggest that the red color is just a thin dusting on the very top of swirling clouds that are otherwise white. “I call it the creme brulee model,” Baines says, “or the strawberry frosting model.”

Cassini was essential to solving the mystery because its instruments were sensitive to a broader range of light wavelengths than Galileo’s, and could thus show that the very center of the Red Spot is redder than the rest. The center is also at the highest altitude of what’s already an unusually high-altitude feature. “It reaches something like 50,000 feet higher than the surrounding clouds,” says Baines.

That exposes the swirling clouds to more intense ultraviolet light from the sun than most of Jupiter’s clouds. And when the JPL scientists did lab experiments to test the effects of ultraviolet rays on chemicals such as ammonia, acetylene and various hydrocarbons, which are abundant in Jupiter’s atmosphere, they got the same red colors seen on the giant planet itself. (They did eventually, anyway. At first, they did their tests with ammonium hydrosulfide, another chemical abundant on Jupiter, and recreated what Baines calls the “Great Green Spot. We were faked out,” he says.)

This isn’t the only evidence that the Spot’s red is created from above rather than coming from reddish gases upwelling from below, which is the leading alternate theory: There actually are some other tiny spots of red dotted around Jupiter, and they also coincide with clouds of unusually high altitude.

The Red Spot, in short, as a JPL press release cutely puts it, represents “a sunburn, not a blush,” on the face of the Solar System’s largest planet.

TIME astronomy

Rogue Stars Are Everywhere You Look

A recent study found that as many as half the stars in the entire universe live outside galaxies

Astronomy 101 tells us that galaxies are massive collections of stars, gas and dust—”island universes,” early 20th-century stargazers used to call them–glowing with the light of hundreds of billions of stars, surrounded by darkness. Sure, the occasional star manages to escape the gravitational bonds of its galactic home, but that’s a rare event.

That’s what astronomers thought, anyway. But two new discoveries have made it startlingly clear that stellar liberation isn’t even remotely uncommon. Last week, a paper in the Astrophysical Journal reported that as many as 200 billion stars are roaming free in a cluster of galaxies known as Abell 2744 some four billion light-years from Earth.

But that pales next to a study just published in Science. An international team of astronomers has found that as many as half the stars in the entire universe live outside galaxies. “It is remarkable that such a major component of the universe could be hiding in plain sight,” writes S.H. Moseley, of the Laboratory for Observational Cosmology at NASA’s Goddard Space Flight Center in Maryland in an accompanying commentary.

“Remarkable” is probably the understatement of the year. But in fact, those billions of quintillions of orphan stars really have been visible all along—in a sense, anyway. Astronomers have had evidence for at least a half a decade, thanks to the Spitzer Space Telescope, that the cosmos is suffused with a faint glow of infrared light whose sources are too faint to identify. Some of it presumably comes from the very first galaxies that lit up after the Big Bang, too small to see individually but producing an overall haze of infrared light.

But that’s just a presumption, and, says James Bock, an astronomer at Caltech and a co-author of the paper, “I was kind of skeptical about the the Spitzer results anyway.” so a group of astronomers led by Caltech’s Michael Zemcov, at Caltech, decided to find out what’s actually going on. They couldn’t make their observations from the ground because the atmosphere itself glows with infraed light. “It’s pretty horrible,” says team member and co-author James Bock, also at Caltech. “So we need to get above the atmosphere—but not for a long time.”

So they sent their instruments up on a sounding rocket, which shot up to about 200 miles in altitude, then parachuted back down. Their goal was not to find the sources of infrared light directly, but rather to see how the intensity of the light varied across a relatively wide swath of sky.

It turned out to vary significantly, with brighter patches spanning 20 times the area of the full Moon. “They’re associated with clusters of galaxies,” Bock says, “but we calculated how much infrared light could be coming from the clusters themselves, and it wasn’t enough.”

Instead, they concluded, it must be coming from stars completely outside the galactic clusters, flung into intergalactic space as galaxies collided, their clashing gravitational fields whipping stars in all directions. The same process presumably send stars flying around within Abell 2744, the cluster described in last week’s announcement—but on a much vaster scale.

The discovery of huge numbers of stars nobody knew about doesn’t necessarily alter our overall view of the cosmos. It doesn’t refute the existence dark matter, or of dark energy, or the Big Bang itself. But it does give astronomers a whole new collection of objects to think about. “If you want to understand the global process of star formation,” says Bock, “you can’t just look at galaxies.” If you do, he says, “you’ll miss all the action.”

TIME space

New Mesmerizing Image of a Young Star

ALMA image of the protoplanetary disc around HL Tauri
This is the sharpest image ever taken by ALMA ALMA (ESO/NAOJ/NRAO)

The detail in the image is far greater than anything even the Hubble could achieve

If someone had been around to see it, this is what our Solar System probably looked like when it was only a million years old (for the record, it’s nearly 4.6 billion now, and counting). This image was taken by the giant ALMA telescope, located in the high desert of northern Chile, which sees in radio wavelengths. The detail here is far greater than anything even the Hubble could achieve.

The glowing disk is dust and gas whirling around the young star, known as HL Tauri, located about 450 light-years from Earth in the constellation Taurus. The dark gaps are almost certainly places where the gravity of newly forming planets has swept the dust clean — exactly as Earth, Mars and the other planets in our mature Solar System did long ago. It’s a strong clue that our theories of how planets form are very much on the right track.


Explaining Your Thesis Topic the Hard Way

You’ll probably never have occasion to explain how tornadoes might disrupt the biological relationships between tree seedlings and soil organisms. But if you do, you almost certainly won’t do it by swinging from a trapeze as friends and acquaintances writhe around on the floor below.

But then, you’re not Uma Nagendra, a doctoral candidate in plant biology at the University of Georgia. By choreographing and performing a piece called “Plant-soil feedbacks after severe tornado damage,” Nagendra has just snagged first place in the seventh annual international Dance your Ph.D. contest, sponsored by the American Association for the Advancement of Science, Science magazine and HighWire Press.

The curmudgeons among us might be tempted to smirk—especially when they find out one of the runners-up was honored for his interpretive dance titled “Reduced-fat mayonnaise: Can’t maintain its stability.”

A conversation with Nagendra, however, will nip that impulse in the bud. “Lots of people are looking for ways to communicate science better, since we haven’t done so well in the past,” she says. “For me, the value of incorporating dance into science communication is that it can help illustrate complex ideas.” For anyone who relies on photos, graphics or illustrations to help us understand scientific concepts—which is to say, just about everyone—this should make all sorts of sense.

Nagendra, first heard about the contest a few years ago. She has no formal training in dance (“I dabble in different social dance forms,” she says, which means she likes go dancing for fun) but she knew immediately that she wanted to enter someday. She had some friends who were exploring trapeze as a kind dance medium—think Cirque du Soleil—and when she began taking trapeze classes herself, she was hooked. “The choreography took a while,” Nagendra says. “I had to do it in bits and pieces, since I couldn’t exactly practice in my living room.”

The other trapeze performers who appear in the piece are from the class, but most of the people playing soil pathogens on the ground are “grad students or friends of friends who thought it would be fun to roll around on the floor and pretend to be a fungus.” (She recruited some of them on Facebook, with a post that urged interested parties to, “unleash your inner nematode.”)

For winning the contest, Nagendra will get a $1000 prize and an all-expenses-paid trip to Stanford University next may for a screening of all the winning entries (you can read about all 12 finalists here, and read the official announcement at the Science website).

TIME space

Asteroid in a Bag? Bag it, Says MIT Space Scientist

Bad trip? Solar electric propulsion would help redirect an asteroid to lunar orbit
Bad trip? Solar electric propulsion would help redirect an asteroid to lunar orbit NASA

NASA's next great manned mission has always sounded like something of a fever dream. There may be a better way to do the same work.

MIT planetary scientist Richard Binzel calls himself an “asteroid guy.” He’s been studying the rocky planetoids for decades now, so you might think he’d be thrilled with NASA’s plan to snag a very small asteroid in a very large bag and tow it into lunar orbit for astronauts to visit.

In fact, he’s anything but. At a talk last summer, Binzel called the Asteroid Return Mission (or ARM) “the emperor with no clothes, or at best with very thin cloth.” And now he’s written a commentary in the latest issue of Nature laying out his objections in greater detail, but also proposing an alternative. Instead of bringing one of the solar system’s uncounted asteroids to us, he says, we should send astronauts to visit them in a program that could ultimately lead to the goal people have been looking toward since the Space Age began: sending astronauts to Mars.

“In fairness,” Binzel says, “NASA doesn’t really know what to do with its hardware.” That’s never a good thing. Back in 2010, President Obama officially killed the plan to send astronauts back to the Moon and began pushing instead for a visit to an asteroid by 2025. “NASA took that as a mandate,” says Binzel. When they realized they couldn’t pull it off by then with the available budget, he says, they came up with ARM, which quickly became known as “Asteroid in a Bag”—a term that suggests the space community didn’t exactly take it seriously.

But asteroids are whizzing by Earth all the time, and we don’t know about most of them. “The ones we’ve detected so far,” says Binzel, “aren’t the tip of the iceberg. They’re the snowflake on the tip of iceberg.” An asteroid a few miles across can cause the sort of planetwide catastrophe that played a big part in ending the dinosaurs’ dominance of the Earth. And even a smallish one, like the 60-foot rock that fell near Chelyabinsk, Russia last year (and which Binzel helped investigate) can do plenty of damage.

The first part of Binzel’s proposed three-part program, therefore, is to mount an exhaustive telescopic search for Near-Earth Asteroids, or NEO’s, ten meters (33 ft.) across or bigger. He estimates there are about ten million of them—so many, he says, that “at least one passes by as close as the Moon every week (NASA is searching for them already, but there are still plenty of rocks going undetected).

ID’ing the NEO’s that pose a threat is a good thing on its own merits, but these are also the ones that would be easiest for astronauts to visit. The idea, says Binzel: spot a likely candidate as it approaches the Earth and send astronauts out to match its orbit—something like the way relay runners start sprinting before their partner arrives so they’re going at the same speed at the point of baton handoff. “They’d go out and greet it,” he says, “and follow alongside for a few days.” Then the astronauts would peel off and circle back to Earth.

While hanging out with the asteroid, astronauts could do all sorts of exploration. They couldn’t land themselves, because a small asteroid has too little gravity to keep a human from floating off, but they could use robotic landers to beam back all sorts of information, bring samples back for study in Earthly labs, and even prospect for minerals. Astronauts could also test deflection technologies that could someday be used to push a killer asteroid off course to keep Earth safe.

Best of all, says Binzel, a series of asteroid missions of longer and longer durations means you don’t have to jump to Mars all at once without practicing long-distance and long-duration spaceflight first. NASA can flex its exploratory muscles bit by bit, preparing for that ultimate leap. The image he keeps returning to is that of the Gateway Arch, in St. Louis—the great portal to America’s West. When Lewis and Clark returned with their maps of the vast spaces of still untouched mountains and prairies, says Binzel, who has a painting of the adventurers in his MIT office, “it triggered an enormous wave of exploration. Imagine,” he says, “that we knew of a thousand or even thousands of objects that were readily accessible to human spaceflight.” Retrieval gets you one object; a survey will find thousands at a fraction of the cost. What’s not to like?

Read next: Watch This Pilot’s Dramatic Midair Video of the Antares Rocket Explosion

TIME Sex/Relationships

Manly Men Are Not Always the Best Choice, Study Says

Man with weights
Getty Images

It’s a Hollywood stereotype: Men prefer to partner up with feminine-looking women, and women favor masculine men. But even when you allow for same-gender couples and variations in personal preference, plenty of research suggests that the proposition is generally true. “It’s been replicated many times across different cultures,” says Isabel Scott, a psychologist at Brunel University in Uxbridge, on the outskirts of London, “so people tend to assume it’s universal.” A new study in Proceedings of the National Academy of Sciences challenges that thinking, however.

Historically, human studies have shown that women with more feminine faces tend to have higher estrogen levels, which are in turn associated with reproductive health. In men, the argument is that masculine-looking faces are associated with stronger immune systems—always a good thing in a mate, especially if that trait is passed on to the kids. Masculine appearance may also a sign of a dominant and aggressive personality, but our distant female ancestors might plausibly have gravitated toward these men anyway, for the sake of their children’s health.

These theories fall under the rubric of evolutionary psychology—the idea that many of our fundamental behaviors have evolved, just as our bodies did, to maximize reproductive success. But as in many cases with evolutionary psychology, it’s easier to come up with a plausible explanation than to demonstrate that it’s correct. In this case, says Scott, “the assumptions people were making weren’t crazy. They just weren’t fully tested.”

To correct that, Scott and the 21 colleagues who put together the new study used computer simulations to merge photos of men’s and women’s faces into composite, “average” faces of five different ethnicities. Then they twirled some virtual dials to make more and less masculine-looking male faces and more or less feminine female versions. (“More masculine” in this case means that they calculated the specific differences between the average man’s face and the average woman’s for each ethnicity, then exaggerated the differences. “Less masculine” means they minimized the differences. Same goes, in reverse, for the women’s faces.)

Then they showed the images to city-dwellers in several countries and also to rural populations in Malaysia, Fiji, Ecuador, Central America, Central Asia and more—a total of 962 subjects. “We asked, ‘What face is the most attractive’ and ‘What face is the most aggressive looking,’” says Scott.

The answers from urban subjects more or less confirmed the scientists’ expectations, but the others were all over the place. “This came as a big surprise to us,” Scott says. “In South America,” for example, “women preferred feminine-looking men. It was quite unexpected.”

If these preferences had an evolutionary basis, you’d expect them to be strongest in societies most similar to the ones early humans lived in. “These are clearly modern preferences, though,” Scott says, which raises the question of why they arose.

One idea, which she calls “extremely speculative at this point,” is that when you pack lots of people together, as you do in a city, stereotyping of facial characteristics might be a way of making snap judgements. “In urban settings,” she says, “you encounter far more strangers, so you have a stronger motive to figure out their personalities on zero acquaintance.”

Read next: Wide-Faced Men: Good Guys or Bad?

TIME space

What’s Cooler Than One Comet? A Storm of Them

Nifty alright. Now imagine 500 of these babies.
Nifty alright. Now imagine 500 of these babies. Art Montes De Oca; Getty Images

A stunning sighting around a nearby star offers a glimpse of our own solar system billions of years ago

With some 2,000 planets now known to orbit stars beyond the Sun and thousands more in the can waiting for confirmation, the once-exotic term “exoplanet” is so commonplace it requires no definition for many people. The term “exocomet,” by contrast, is a bit more obscure. Astronomers have known for years that comets orbit other stars—in particular, the relatively nearby star β Pictoris, which lies about 63 light-years from Earth, in the constellation Pictor.

But a new paper in Nature is more than a little mindblowing nevertheless. A team of astronomers is reporting the detection of nearly 500 individual comets that passed in front of β Pictoris between 2003 and 2011. And that’s not even remotely a complete sample. “We had only a couple of nights of observing time per year,” says lead author Flavien Kiefer, now at the University of Tel Aviv. “If we’d been looking constantly, we would have seen many thousands.”

There are a lot of reasons all of this seems slightly crazy. To start with, there’s the notion that you can see something as relatively tiny as a comet from nearly 300 trillion miles away. And in fact, you can’t. But when comets approach the heat of a star, some of their substance boils off to form an enormous cloud of gas and dust, and sometimes a tail as well. And when that cloud moves in front of the star, it distorts the starlight in ways you can see with sufficiently powerful instruments.

In this case, the scientists used the High-Accuracy Radial-Velocity Planet Searcher (HARPS), located at the European Southern Observatory, in Chile. As the name implies, it was designed to find planets—and it has. HARPS does so by looking for subtle changes in starlight created as the star wobbles in response to an orbiting planet’s gravitational tug. The distortions caused by an intervening comet are different, but HARPS can find those too.

The technique isn’t easy, says Aki Roberge, an astronomer with NASA’s Goddard Spaceflight Center, in Maryland who has studied β Pictoris as well, and who wrote a commentary in Nature on the new results, but it clearly works. “We always knew this would be a powerful technique,” she says, “They’ve done a really amazing job.”

The sheer number of comets also seems unlikely at first, until you realize that β Pictoris is extremely young—about 22 million years old compared with the Sun’s 4.6 billion. If we could see our own Solar System at that age, it wouldn’t look all that much different: a thick disk of gas and dust surrounding the central star, with planets just assembling themselves out of chunks of rock and ice. In fact, β Pictoris has at least one young planet already, but there’s still an awful lot of debris flying around.

And that’s what makes this discovery so important, not just as a technical tour de force, but also scientifically. “We can now begin to study a newly forming solar system in detail,” says Kiefer, “and perhaps get an understanding of how our own Solar System was born.”

It probably won’t be the last chance to do so, either. Roberge has her eye on a star called 49 Ceti, which she says is very similar to β Pic in many ways. Kiefer, meanwhile, is conducting preliminary surveys of no fewer than 30 promising stars. With powerful instruments like HARPS on the case, the word “exocomet” could become a lot more familiar before long.

TIME space

Ice Spotted on Mercury—Yes, We Know It Sounds Nuts

"This is making a lot of people happy"

At high noon on Mercury, the temperature can soar to 800°F—and no wonder. The Solar System’s smallest planet (as of 2006, anyway) averages only 36 million miles from the Sun, which is right next door compared with Earth’s 93 million. You’d be justified in thinking that ice couldn’t possibly exist on such a scorching world.

But you’d be wrong. Scientists using the MESSENGER space probe are reporting in the journal Geology that they’ve taken images of that reveal what they call “the morphology of frozen volatiles” in permanently shadowed crater floors near the planet’s north pole. That’s ice, in plain English. “This is making a lot of people happy,” said Nancy Chabot of the Applied Physics Laboratory at Johns Hopkins, lead author of the report.

It’s good news because the discovery confirms circumstantial evidence for ice on Mercury that’s been mounting for decades—first from radar observations with powerful radio telescopes on Earth that showed high reflectivity from the polar region, then from MESSENGER’s neutron spectrometer, which picked up the atomic signal of hydrogen in the same area. That pointed to H2O, almost certainly in the form if ice, especially since the high precision topographic maps made by MESSENGER have shown planetary scientists just how deeply shadowed, and thus how perpetually frigid, some of the craters really are.

All of that made a strong case for ice, and the fact that the same thing occurs on the Moon is further confirmation that it’s possible

These are the first optical images, and nobody is entirely sure how the ice got there. One idea is that it was released from water-bearing rock in Mercury’s crust. But the leading theory suggests it arrived instead in the form of impacts from icy comets, which may well be the same way Earth got its oceans. “It’s a fair amount of ice,” Chabot said, “about equivalent to the water in Lake Ontario, so if it was one comet, it was a pretty sizable one.” More likely, she said, it would have been a series of smaller comets, falling over billions of years.

Either way, the comets would have disintegrated on impact, and while some of the resulting water vapor would have escaped into space, some would have found itself at the poles, where chilly temperatures in the craters’ shadows would have allowed it to freeze out and drop to the crater floors.

Another hint that comets may have been the source of Mercury’s ice: Some of the frozen stuff is partially covered with unusually dark material, which could be organic compounds, also found on comets in abundance. The dark, ice-concealing patches have sharp edges, suggesting that whatever created them happened relatively recently, just hundreds of millions of years ago at most. That supports the idea that comet impacts could be happening all the time (in the geologic sense, anyway).

Excited as the scientists are to see the presence of ice on Mercury confirmed, they’re even more excited by the prospect of what’s to come. Messenger’s orbit is bringing the probe to within about 120 miles above the planet’s surface on its closest approach, which is why it’s able to take such high-resolution images.

By next spring, however, the probe will be zipping just 12 miles above the surface, before the mission ends with a planned crash. At that distance, no one knows what surprises MESSENGER’s cameras are going to reveal. “It’s going to be interesting, to say the least,” Chabot said.


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