TIME space

See the 50 Best Images Taken by Hubble

After a quarter of a century on the job, the Hubble Space Telescope has returned some of the most extraordinary cosmic images ever captured

The best space machines reveal their purpose with a single glance. The gangly, leggy lunar module could only have been a crude contraption designed to land on another world. A rocket, any rocket, could only be a machine designed to fly—fast, high and violently.

And so it is with the Hubble Space Telescope—a bright silver, 43 ft. (13 m) long, 14 ft. (4.2 m) diameter cylinder, with a wide open eye at one end and a flap-like eyelid that, for practical purposes never, ever closes. Since shortly after its launch on April 24, 1990, that eye has stared and stared and stared into the deep, and in the 25 years it’s been on watch, it has revealed that deep to be richer, lovelier and more complex than science ever imagined.

Hubble started off sickly, a long-awaited, breathlessly touted, $1.5 billion machine that was supposed to change astronomy forever from almost the moment it went into space, and might have too if its celebrated 94.5 in. (2.4 m) primary mirror that had been polished to tolerances of just 10 nanometers—or 10 one-billionths of a meter—hadn’t turned out to be nearsighted, warped by the equivalent of 1/50th the thickness of a sheet of paper. It would be three and a half years before a fix could be devised and built and flown to orbit and shuttle astronauts could set the myopic mirror right. And then, on January 13, 1994, the newly sharpened eye blinked open, the cosmos appeared before it and the first of one million observations the telescope has made since then began pouring back to Earth.

Some of Hubble’s images have become cultural icons—Pillars of Creation, the Horsehead Nebula. Some have thrilled only scientists. All have been mile-markers in the always-maturing field of astronomy. The fifty images that follow are just a sampling of the telescope’s vast body of work. Hubble still has close to a decade of life left to it. That means a great deal more work and a great many more images—before the metal eyelid closes forever.

TIME Science

How NASA Finds ‘Super Earths’ Where Alien Life Might Flourish

NASA's Kepler mission recently announced the discovery of three earth-like planets existing in a star's "Goldilocks zone."

Since 2009 NASA’s Kepler Mission has been exploring the Milky Way using an extraordinary powerful space telescope. Their mission is to discover “exoplanets” or Earth-like planets that could, in theory, be habitable for human life.

But what makes a planet habitable?

Scientists say habitable planets should be in an area round the star known as the “Goldilocks zone,” where it isn’t too hot or cold for water to exist on the surface in liquid form. Thus far, the mission has confirmed many such candidates, including a significant discovery of three planets announced in January 2015.

Jeffrey Kluger explains the significance of this newest discovery and the importance for humanity to continue space exploration.

TIME astronomy

There May Be ‘Super Earths’ at the Edge of Our Solar System

This discovery, if accurate, could completely redraw the map of the Solar System

The reason Pluto was demoted from the ranks of the planets back in 2006 was that astronomers had lately discovered it wasn’t alone out there. A whole assortment of Pluto-like objects is circling out beyond Neptune—too many, said the International Astronomical Union, for schoolchildren to memorize. (Seriously.) So despite a general public outcry that continues today, Pluto was demoted to “dwarf planet,” and the Solar System was left with a tidy eight.

But scientists think planets much bigger than Pluto could be orbiting beyond the reach of our most powerful telescopes. They probably aren’t as big as Saturn and Jupiter—but the unusual orbit of a tiny world called 2012 VP113, discovered last spring, hinted at the presence of something bigger than Earth. And now a pair of papers published in Monthly Notices of the Royal Astronomical Society suggests the evidence is even stronger.

“We have unpublished calculations,” says lead author Carlos de la Fuente Marcos, of the Complutense University of Madrid, “that suggest that there could be two planets with between two and 15 times the mass of the Earth.”

As with last year’s discovery, the evidence for the two planets is indirect. “We would like to emphasize that we have not discovered any new objects,” de la Fuente Marcos says. What they’ve done instead is to look at the orbits of 13 small bodies, including 2012 VP113, that follow elongated orbits in the distant reaches of the solar system.

In particular, they’ve looked at an orbital parameter known, in a quaint throwback to the early days of astronomy, as the “argument of perihelion”—that is, the point at which their tilted orbits cross the plane in which the other planets circle the Sun. What de la Fuente Marcos and his team find is that these points are suspiciously similar for all 13, which implies that the gravity of some massive object or objects, still unseen, is herding them. (It involves the Kozai mechanism, since you’re undoubtedly wondering).

These Super Earths would be located about four times as far away as the outer limit of Pluto’s orbit—and that’s a bit of a problem, since current models of the Solar System’s formation have a tough time putting a big planet out at that distance, especially today. “They may have existed in the past, but at very low probability,” says Ramon Brasser, of the Cote d’Azur Observatory, in France. Brasser also argues that more than half of the objects de la Fuente Marcos and his co-authors cites as evidence come close to Neptune, whose own gravity skews the results.

De la Fuente Marcos disagrees on the second point. “In general,” he says, “these objects are weakly perturbed by Neptune if they are perturbed at all. He agrees on the former, but with a caveat. “If we assume that our models of Solar System formation are correct, the objection is valid. But what if our models are incorrect?”

Even if the models are correct, however and a super Earth can’t be orbiting where de la Fuente Marcos suggests, that doesn’t mean there’s nothing big out there. “It’s possible,” says Brasser, “but the planet would have to be much farther away and much more massive in order to have the same effect. This scenario,” he says, “is currently being investigated.”

But the investigations are still purely indirect. “If large planets do exist,” says de la Fuente Marcos, “these objects must be very dark … and they are very far away from the Sun.” There won’t be a prayer of spotting them until the James Webb Space Telescope, or one of the new giant ground-based telescopes now under construction, is up and running toward the end of this decade.

But for a discovery that could completely redraw the map of the solar system yet again, that’s not too awfully long to wait.



TIME space

NASA Spacecraft Wakes Up as It Approaches Pluto

NASA's New Horizon spacecraft awakens for meeting with Pluto
NASA/EPA An undated artist's concept shows the New Horizons spacecraft as it approaches Pluto and its largest moon, Charon.

New Horizons will come closest to the dwarf planet on July 14

A NASA spacecraft has emerged from hibernation in preparation for completing its nine-year, 2.9-billion mile journey to observe Pluto from up close, the space agency said.

Sending its signal at the speed of light, the New Horizons ship beamed a report down to Earth that it was back in active mode as of Dec. 6.

“Technically, this was routine, since the wake-up was a procedure that we’d done many times before,” said Glen Fountain, the mission’s project manager. “Symbolically, however, this is a big deal. It means the start of our pre-encounter operations.”

After tests early next year, the spacecraft will collect data and images about Pluto and its surrounding moons. It will come closest to the dwarf planet on July 14.

TIME space

Why the First Comet Landing Matters

This mission may be our most informative one yet

Philae lander touched down Wednesday on the comet Churyumov-Gerasimenko, also known as 67p, after a 10 year journey that cost as much as $1.3 billion. You might be wondering why the European Space Agency spends so much time and resources on a frozen lump of ice millions of miles away. But this mission, which successfully landed the first ever probe onto our solar system’s most primitive material, will give us valuable information about the origins of our solar system and how it evolved.

TIME astronomy

The Mystery of the Solar System’s Weirdest Moon, Explained

NASA High-resolution image of the surface of Miranda, one of Uranus' largest moons, taken from the Voyager 2 spacecraft

We already knew Miranda, one of Uranus' five major moons, has "one of the strangest and most varied landscapes among extraterrestrial bodies." Now, we (probably) know why

The first and only space probe ever to visit the planet Uranus timed its encounter very badly from a public-relations perspective. Voyager 2 zipped past the solar system’s seventh planet on Jan. 24, 1986; four days later, the shuttle Challenger exploded in flames. And suddenly, far-off Uranus and its retinue of moons didn’t seem so important anymore.

Yet the images Voyager took during that overshadowed encounter have continued to intrigue planetary scientists ever since — and that’s especially true when it comes to Miranda, one of the planet’s five main moons. Its surface, U.S. Geological Survey astrogeologist Laurence Soderblom told TIME shortly after the encounter, “is a bizarre hybrid,” while NASA describes Miranda as having “one of the strangest and most varied landscapes among extraterrestrial bodies.”

Perhaps the strangest features of all are Miranda’s three visible “coronae” — relatively crater-free regions marked by ridges and valleys and slapped onto the surface “like mismatched patches on a moth-eaten coat,” in NASA’s words. But now, nearly three decades after they were found, Miranda’s coronae may have an explanation at last. Writing in the journal Geology, Brown University planetary scientists Noah Hammond and Amy Barr argue that these odd scraps of terrain come from ancient hot spots in the moon’s 100-mile-thick crust of ice. “Despite being incredible cold,” says Hammond, ” there’s a lot of geologic activity on this moon.”

Geology on the frigid moons of the outer solar system itself isn’t such big news these days. Scientists have spotted volcanoes on Jupiter’s moon Io, ice geysers on Saturn’s moon Enceladus, lakes on Titan, plate tectonics on Europa and more. But to have geology, you need some source of heat, and there just doesn’t seem to be one for Miranda, which is deep-frozen to about –350°F.

There’s no heat source now, anyway. But Miranda’s orbit is unusually tilted with respect to Uranus’ equator — its “inclination,” as astronomers call it, is about 10 times greater than that of the planet’s other major moons. One way that could have come about is if Miranda’s orbit was originally very eccentric, or elongated. That would have brought it into close encounters with other moons, which could have relocated into a tilted orbit.

If Miranda’s orbit really was elongated, the moon would have been squeezed and stretched by the tidal effect of Uranus’ gravity, and, just like a rubber ball squeezed in your hand, it would have heated up a bit. And that rising heat would have made the ice itself flow very, very slowly upward — a process physicists call convection. Hammond and Barr created a computer model of that flow, and sure enough, he says, “we were able to show that if shell is convecting, it naturally produces four upwellings.” Since it’s just a model, it can’t simulate the actual moon precisely, but it’s definitely in the ballpark of what Voyager saw.

Each upwelling of ice would have tried to spread as it reached the surface, and crinkled, accordion-fashion, into the ridges and valleys that characterize the coronae. The fact that these regions are relatively crater-free fits right in: new ice flowing out from the interior would have to sit on the surface for a long time to match the cratering of the surrounding areas.

The coronae can’t be more than a few hundred million years old — peanuts compared with the rest of the surface, which dates back billions of years, and consistent, Hammond says, with the fact that Miranda probably gained its tilt and lost its heat generation about that long ago.

It all hangs together — but since it’s based on a handful of images taken nearly 29 years ago that only show Miranda’s southern hemisphere, it may be hard to be proved definitively. Planetary scientists have a far richer set of observations for the moons of Jupiter and Saturn, where the Galileo and Cassini probes respectively stuck around snapping photos for years rather than flying by (and Cassini is still going strong).

Unfortunately, while scientists are contemplating return missions to Jupiter and Saturn, nobody’s got plans to revisit Uranus. Which leaves Hammond and Barr’s theory of where the coronae came from in the “convincing but not definitive” realm.

Hammond is absolutely definitive about one thing, however. “Miranda,” he says, “is a really cool moon.”

TIME planets

Researchers Discover Traces of the Planet That Helped Create the Moon

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.”



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
NASA/ESA, R. Soummer, Ann Feild (STScI) 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

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

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.

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