TIME planets

Researchers Discover Traces of the Planet That Helped Create the Moon

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Getty Images

Researchers believe that a planet, named Theia, collided with Earth 4.5 billion years ago, creating the moon from floating debris

Analysis of moon rocks brought back by Apollo astronauts has revealed remnants of Theia, the planet that researchers believe collided with Earth to create the moon 4.5 billion years ago.

Researchers have long hypothesized that Theia — named after the Greek goddess who was the mother of Selene, the goddess of the moon — collided with Earth and was destroyed upon impact. Remains of the colliding planet and debris from Earth were thought to have joined together, eventually forming the moon. The moon’s thin core suggests that it was created with the help of two other planets, but no hard evidence has been found to confirm the theory until now.

According to the study published in the journal Science, an analysis of different varieties of oxygen, called isotopes, in the lunar rocks reveals equal traces of both the moon and the colliding planet. The moon rocks also contain a rare material called enstatite chondrite, which is not found on earth, also suggesting that the moon was formed by planetary coalescing.

The team, led by Dr. Daniel Herwartz from the University of Goettingen, wrote to Science that previous analysis of the rocks showed little difference in isotopes, but that the recent analysis “supports the view that the Moon was formed by a giant collision of the proto-Earth with [an impactor].”

Despite the new discoveries, some scientists are still not convinced that the minor differences in isotopes confirm the big-impact hypothesis. Dr. Mahesh Anand from the Open University told BBC that the rocks shouldn’t be used to represent the entire moon and that “further analysis of a variety of lunar rocks is required for further confirmation.”

[Science]

 

TIME space

Window on Infinity: Pictures from Space

From Martian vistas to NASA's #GlobalSelfie, here are the month's best photographs from space

TIME space

CSI NASA: Using Old Space Images to Find New Planets

Images of planetary disks from Hubble
The two images at top reveal debris disks around young stars uncovered in archival images taken by NASA’s Hubble Space Telescope. The illustration beneath each image depicts the orientation of the debris disks NASA/ESA, R. Soummer, Ann Feild (STScI)

A team of scientists from the Space Telescope Science Institute is using image-recognition software and new algorithms to re-analyze existing Hubble images of space in the hopes of finding new stars and planets

When detectives use DNA to crack a cold case, or when defense attorneys use it to free the wrongly convicted, the evidence itself can date back years—in some cases, to a time before DNA forensics had even been invented. No police officer imagined when they took hair or blood or tissue samples years ago that such tests would ever be invented.

Now something similar is happening in astronomy. A team of scientists from the Space Telescope Science Institute has re-analyzed old Hubble images with new software algorithms to reveal disks of dusty material around five young stars—an indirect hint that unseen planets are lurking there as well. “We had evidence that these disks might exist,” says Rémi Soummer, the institute astronomer who led the project, “but we had no idea about their size or structure.”

Some of that evidence dates all the way back to the early 1980s, when a satellite known as IRAS detected excess infrared radiation coming from a number of nearby stars. The best bet was that it was coming from orbiting dust particles, created when rocky asteroids smashed into each other—an early hint that the building blocks of planets were common around other stars. In 1984, astronomers using ground-based telescopes even managed to take images of a disk-shaped dust cloud swirling around the star Beta Pictoris.

But for more distant stars, it’s proven very tough to take images of dusty disks, even with the powerful Near Infrared Camera and Multi-Object Spectrometer (NICMOS), installed on Hubble during a 1997 shuttle mission. Like blood samples preserved in police evidence room, however, those images have been sitting in electronic storage in the Mikulsko Archive for Space Telescope database. (It’s named for Hubble-friendly Senator Barbara Mikulski, who represents Maryland, where the space telescope institute is located.)

In 2011, Soummer plunged back into that archive with a newly developed image-processing algorithm similar to those used in face-recognition software, and “discovered” three planets orbiting a star called HR 8799, about 130 light-years from Earth. The planets had already been found with ground-based telescopes between 2007 and 2010, but the pictures Soummer analyzed dated all the way back to 1998. (University of Montreal astronomer David Lafreniere found a fourth planet in the same system with similar image-processing techniques in 2009).

“It was great that we could see the planets in these old images,” Soummer says, but it was even better that they could now note the planets’ positions. Comparing them with the newer images, he says, “we could see a bit of orbital motion.” That’s crucial in understanding the dynamics of this distant solar system, but also in proving that the tiny dots of light hugging the star aren’t actually background stars that happen to lie along the same line of sight.

That success inspired Soummer and his colleagues to scrutinize archived NICMOS images of 400 additional stars. “Once we knew we could find planets that were already known,” he says, “we knew we could apply our technique to find entirely new stuff.”

They developed a new, faster algorithm, which turned out to be better at finding diffuse objects than it was at finding pointlike planets. They focused on stars that showed excess infrared light, figuring that this is where they’d likely find planet-forming dust disks—and ultimately, they discovered five, along with hints about their structure. In one case, the dust disk has a sharply defined inner edge, hinting at a still unseen planet “shepherding” the dust with its gravity. In another, the star in question, known as HD 141943, is an almost exact twin of our Sun. It’s only about 30 million years old, though, which puts it right at the age when the planets in our own Solar System formed. It’s like looking at a baby picture of the Sun and its newborn family.

And that’s just the start. “We’re only halfway through our observing program,” says Soummer. “We’re hoping to find new planets and new disks around many of these stars.” They’re also hoping to apply their algorithm to images from the James Webb Space Telescope, which will be far more powerful and sensitive than even the Hubble once it’s operational in 2018. The Webb has every prospect of revolutionizing scientists’ understanding of how planets form, around what kinds of stars, out of what raw materials—and unlike the Hubble, it presumably won’t have to leave its images sitting in an evidence locker, waiting for someone to figure out how to process them.

 

TIME space

Almost Earth: A Newly Discovered Planet Could Be a Lot Like Ours

An artist's conception of Kepler 186f, with its reddish sun setting over its maybe-ocean
An artist's conception of Kepler 186f, with its reddish sun setting over its maybe-ocean. Danielle Futselaar

The best place to look for extraterrestrial life would be on worlds with a size and composition like our own. Astronomers have now discovered what may be the Earthiest planet yet—and there are surely more out there

When a faulty aiming device crippled the Kepler space telescope last year, NASA officials reluctantly declared the orbiting observatory’s planet-hunting days over—but they also said that Kepler would keep finding planets. That’s not as crazy as it sounds: the probe had made so many observations since its launch in 2009 that scientists hadn’t come close to processing them all. There were sure to be spectatcular discoveries still lurking in those terabytes of stored data, said Kepler’s founding father, William Borucki, of the NASA Ames Research Center.

Turns out he was right: a team of astronomers has just announced the discovery of a planet almost identical in size to Earth, orbiting in the habitable zone of its star—the region where water in liquid form, an essential ingredient for life as we know it, could plausibly exist. Kepler has found Earth-size planets before, and habitable-zone planets, but nobody has ever found a single planet that falls into both of these crucial categories.

“We’ve had a handful of candidates that looked good in the past,” says Elisa Quintana, of NASA Ames, lead author of the paper describing the discovery, which appears in Science. “But we always took them with a grain of salt.” That’s because false-positive detections are always possible in the planet-hunting game. Kepler finds planets by watching for the almost imperceptible dimming of stars as an orbiting world passes in front of them. But other things can cause a very similar signal. The star itself might flicker, or a dark sunspot might slide across its face. Another possibility: a pair of mutually orbiting stars could be sitting almost directly behind the target star, increasing the total amount of starlight that reaches Kepler. When one of these background stars moves in front of the other, the collective incoming light dips—just as it would if a planet eclipsed a single star.

Every candidate planet goes through tests to rule out these possibilities, and in the end, all of those possible habitable-zone Earth-size planets failed. But this planet, called Kepler 186f, passed with honors. “Statistically,” says Quintana, “we’re 99.98% certain that this is in fact a planet.”

They’re also reasonably sure, although not quite as certain, that the planet is made mostly of rock, just like the actual Earth. It wasn’t possible to conduct the definitive observations that would make this a slam-dunk—that is, measuring how much the planet’s gravity makes the star wobble back and forth with each full orbit. If the astronomers could do that, they’d know the planet’s mass, not just its size. Dividing mass by size would have given them Kepler 186f’s density, and thus its composition.

At nearly 500 light-years away, however, Kepler 186f is too distant for that sort of measurement. Still, the best available planet-formation models suggest that the new world is too small to be made of anything but rock. The discovery last fall of Kepler 78b, a somewhat bigger planet that is close enough for the wobble test and is definitively rocky, lends credence to the idea that 186f is too.

Still, there’s one thing about the new planet that’s decidedly non-Earthlike: it orbits an M-dwarf, a dim, reddish star with only about half the mass of the Sun. As recently as a decade ago, few astronomers would have considered such a star a good place to look for life-friendly planets. One reason is that M-dwarfs tend to have lots of violent flares and magnetic storms that spew charged particles out into space. And because these small stars put out less energy than the Sun, their habitable zones are much closer in, exposing planets to a more severe bath of radiation (Kepler 186f, for example, has a “year” that lasts just 130 days, putting it closer to its star than Venus is to our Sun).

Those closer orbits can also place M-dwarf planets at risk of becoming tidally locked to their stars, just as the Moon is to Earth. That means they’ll always show one face to the star; the bright side can therefore be far warmer than the dark side, which could create violent weather that would make life hard to sustain.

But planet hunters have been rethinking all of these factors, and new theoretical studies suggest they might not necessarily deal-breakers. And in this case, they may not even apply: the star that is home to Kepler 186f is relatively massive and bright for an M-dwarf, putting a habitable-zone planet far enough away to be outside the danger zone. Plus, says Quintana, the star has relatively little flare activity. The true measure of Earthiness, of course, would be if Kepler 186f has water on its surface, and more than that, if the water has helped give rise to life. But there’s no way of knowing that from the current observations.

The good news is that there are ridiculous numbers of M-dwarfs in the Milky Way—far more than there are Sun-like stars. There are so many, in fact, that a study concluded last year that if only six percent of them had an Earthlike planet, and if they were spread evenly through the galaxy, that would put the nearest one a mere 13 light-years away. “Astronomically speaking,” said the study’s lead author Courtney Dressing, of the Harvard-Smithsonian Center for Astrophysics, at the time that study came out, “this is like a stroll across the park.”

The even better news is that a newly approved mission called the Transiting Exoplanet Survey Satellite, scheduled for a 2017 launch, could find such nearby planets in droves—and the James Webb Space Telescope, which could go up as early as 2018, could follow up by probing their atmospheres, looking for the chemical byproducts of living organisms.

Kepler scientists, meanwhile, are still looking for a more elusive quarry: a true Mirror Earth, the size and composition of our own planet, orbiting in the habitable zone of a Sun-like star. “Kepler 186f,” says Quintana, “is more of an Earth cousin than an Earth twin.” While scientists can theorize all day about whether life might be possible in the reddish light of an M-dwarf, they know for certain it’s possible on a world like Earth bathed by yellow-white light. “We’re still working hard to find one,” Quintana says. And the fact that Kepler died nearly a year ago isn’t slowing them down even a little bit.

TIME space

Window on Infinity: Star Trails Over Yosemite and a Supermassive Black Hole

From a Soyuz launch in Kazakhstan to a new image of a crescent Saturn, here are the most impressive space photos from the month of March.

TIME space

Space Discovery Suggests Unknown Planet At Solar System’s Fringe

2012 VP113, also known as "Biden," because of the VP in the provisional name.
2012 VP113, also known as "Biden," because of the VP in the provisional name. Scott Sheppard and Chad Trujillo—Carnegie Institution for Science

Astronomers found a new dwarf planet beyond Pluto they say could signal the existence of a much bigger planet further out in our solar system, a potentially groundbreaking discovery that could change the way we look at our cosmic neighborhood

Science teachers, get ready, you may soon have to come up with a new mnemonic device for the planets.

Astronomers announced Wednesday the discovery of a new dwarf planet at the outer edge of our solar system. While that’s interesting on its own, the scientists also believe something far more fascinating: that the dwarf planet’s far-out position suggests there may be a much larger planet beyond it.

The dwarf planet—named 2012 VP113, and nicknamed “Biden” for obvious reasons—was found near another tiny, icy planet named Sedna that was first discovered ten years ago, National Geographic reports. Scientists involved in the new discovery believe the two objects may have been pulled so far out in the solar system by the gravity of a much larger planet hulking still farther out in our solar system.

“A rogue planet could have been ejected from our solar system and perturbed their orbits,” says Scott Sheppard, a co-author of the report. “Definitely, it could still be out there.”

Harold Levison, an astronomer who was not part of the study, said Biden’s discovery “suggests something interesting.” However, Levison advised caution about the theory put forth by the study’s authors — that a giant mystery planet lurking in the outer reaches of the solar system is responsible for the location of the cluster.

“There may be another explanation we just haven’t seen yet,” he said.

[National Geographic]

TIME planets

The Hunt for Super Pluto Comes Up Empty—For Now

A pair of small moons orbiting pluto discovered by NASA's Hubble Space Telescope.
A pair of small moons orbiting pluto discovered by NASA's Hubble Space Telescope. Universal History Archive—UIG via Getty Images

An exhaustive sky survey reveals no sign of a fabled Planet X, but plenty of other cool discoveries

Back in 2011, a couple of astronomers presented circumstantial evidence of a giant, undiscovered planet they named Tyche, for the Greek goddess of good fortune, lurking at the outer edges of the Solar System. This faraway world would be at least as big as Jupiter, but hundreds of times more distant than Pluto, so it could easily have escaped the notice of nearly all of the world’s most powerful telescopes.

NASA’s orbiting Wide-field Infrared Survey Explorer (WISE) should have been able to spot it, though—and if Tyche really existed, the proof would already be stored somewhere in the telescope’s vast database of observations. If so, said WISE principal investigator and UCLA astrophysicist Ned Wright at the time, “we might be able to tell you something in a year or two.”

That year or two has now come and gone, and the answer is…better luck next time. An exhaustive look through the database, chronicled in two separate papers in the Astrophysical Journal, has turned up all sorts of unexpected objects, including thousands of previously unknown dim stars and hundreds of the bigger-than-a-planet-smaller-than-a-star objects known as brown dwarfs. But the WISE data also ruled out anything as big as Saturn out to 250 times Pluto’s distance, and anything as big as Jupiter to about one light-year away—a quarter of the distance to the nearest star.

That doesn’t mean it was crazy to guess there might be a big planet out there. The evidence offered by Daniel Whitmire and John Matese, of the University of Louisiana, was based on a suspiciously large number of long-period comets coming from a particular part of the sky. In theory, such comets originate in a vast comet reservoir known as the Oort Cloud, which forms a kind of spherical halo around the Solar System.

If that’s true, then comets from the cloud should fall in toward us from all directions in an equal distribution. If they were coming in from one direction more than others, Matese and Whitmire argued, then the gravity of some large object must be diverting them. Wright called the evidence “kind of flimsy” at the time, but didn’t dismiss it entirely.

Still, few people thought the odds of finding the mysterious body were terribly high, mostly because the kind of gravitational reasoning on which the hunt was based has produced more duds than discoveries. One example of the latter: astronomers in the 1800’s noticed that Uranus was moving in ways that didn’t make sense unless some other object was pulling on it. They calculated where this unknown planet should be—and there, it turned out, was Neptune. In the 1920’s, it was Neptune that seemed to be moving strangely. A young Clyde Tombaugh looked where calculations said something should be—and there was Pluto.

Except Pluto was far too small to affect Neptune’s orbit, and Neptune, it turned out on closer examination, hadn’t been orbiting strangely in the first place. The fact that Pluto was where “Planet X” was supposed to be turned out to be a concidence. In the 1980’s, Berkeley astrophysicist Richard Muller and several colleagues proposed the existence not of a planet, but a dim companion star to the Sun they called Nemesis. Their reasoning: catastrophic extinctions, like the one that killed the dinosaurs, seemed to come with a regular rhythm. Maybe Nemesis was knocking big comets out of their orbits whenever it came around, sending them to smash into Earth. But again, extensive searches turned up nothing (and WISE has just re-confirmed the non-existence of Nemesis).

Nonetheless, the new results from WISE have revealed plenty of other cosmic bodies, including a pair of brown dwarfs orbiting each other just six or so light-years from Earth and several dim stars not all that much further away. “We think there are even more stars out there left to find with WISE,” said Wright in a statement. “We don’t know our own Sun’s backyard as well as you might think.” That’s good news for planet-hunters, who now think dim red M-dwarf stars, which are far more plentiful than Sun-like stars in the Milky Way, are prime places to look for habitable worlds.

And there could be even better news still to come. WISE was put into hibernation in 2011, when its primary mission ended. But last fall, it was dusted off for a new assignment, to look for the sort of near-earth asteroids that could someday threaten our planet. In doing so, it will be covering the same enormous swath of space it already scanned twice during its first incarnation, adding six more all-sky surveys to the two it has in the can. Anything that changes position from one survey to the next—or from the 2010-2011 batch to the current round—is something in motion.

Most of what WISE will see moving will indeed be asteroids (as was the case did in its first two rounds), but it will also see comets, brown dwarfs, M-dwarfs—and it just might see Tyche after all. “We didn’t actually rule it out with 100 percent certainty. If there’s a Jupiter-mass object within a light-year,” says project scientist Peter Eisenhardt, “there’s still a very slim chance we could have missed it.” When it comes to space, never say never.

TIME space

Galileo’s Planetary Puzzle Has Finally Been Solved

Facing Venus-Jupiter Close Conjunction
Galileo's Planetary Puzzle Has Finally Been Solved Laurent Laveder

It only took 400 years to explain why Venus looks bigger than Jupiter

Venus looks bigger than Jupiter, so long as you’re looking at them with your naked eye, but when observed through a telescope the planets seem to swap sizes: Jupiter looks bigger than Venus. Italian physicist, mathematician and astronomer Galileo Galilei puzzled over this mysterious switcheroo some 400 years ago and speculated it had something to with an “impediment of our eye.”

According to The Independent, scientists now have a more thorough explanation. Our perception of light, as it passes through the eye, tends to enlarge radiant objects set against a dark background. Venus, with its “radiant crown” outshines the less-than-lustrous Jupiter, and therefore appears eight to ten times larger to our deceptive peepers. Turns out the legendary 16th century scientist wasn’t far off.

[The Independent]

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