TIME space

Here are the Most Heart-Stopping Photos of Saturn from the Cassini Mission

As the spacecraft completes its final flyby of Saturn's moon Dione, TIME reflects on the most spectacular images from the mission thus far

TIME space

See a Newly-Released Image of Saturn’s Moon Dione

Saturn Moon Dione Cassini Farewell
NASA/JPL-Caltech/Space Science Institute/EPA A visible light image of Saturn's moon Dione captured with the Cassini spacecraft narrow-angle camera on April 11, 2015 and released on Aug. 17, 2015.

Despite the high-resolution images Cassini sent back, Dione remains a mystery to scientists

NASA released this never-before-seen image of Saturn’s moon Dione as the Cassini spacecraft said goodbye to it on August 17. Photos of the final encounter are expected to reach Earth in the next few days.

Cassini was the first spacecraft to enter Saturn’s orbit, and for the last 11 years, it’s been studying the planet and its many satellites including Dione, Titan and Rhea. Cassini will now make a series of close moon flybys until late 2015, at which time it will begin a year-long setup of the mission’s daring finale, NASA said, when it will repeatedly dive through the space between Saturn and its rings.

In the meantime, NASA’s scientists will await the final high-resolution images from Dione to come in, especially those the spacecraft will take of the moon’s north pole. They hope to find out if Dione has geological activity. “Dione has been an enigma, giving hints of active geologic processes, including a transient atmosphere and evidence of ice volcanoes,” says Bonnie Buratti, a Cassini science team member at NASA’s Jet Propulsion Laboratory in Pasadena, California. “But we’ve never found the smoking gun. The fifth flyby of Dione [was] our last chance.”

TIME Science

Why Pluto Still Deserves Our Love

Pluto is a reminder that there are many worlds out there beyond our own

One of my first memories as a child in the in the 1950s was a discussion I had with my brother in our tiny bedroom in the family house in Bethlehem, Pennsylvania. We had heard in school about a planet called Pluto.

Pluto was the farthest, coldest, and darkest thing a child could imagine. We guessed how long it would take to die if we stood on the surface of such a frozen place wearing only the clothes we had on. We tried to figure out how much colder Pluto was than Antarctica, or than the coldest day we had ever experienced in Pennsylvania. Did the surface of Pluto have mountains, frozen ponds like the ones we loved to skate on, or acres of snow to play in and build snowmen?

Pluto—which famously was demoted from a “major planet” to a “dwarf planet” in 2006—captured our imagination in a way that even Mars (a possible abode of life) and glorious, ringed Saturn couldn’t. It was a mystery that could complete our picture of what it was like at the most remote corners of our solar system.

Pluto’s underdog discovery story is part of what makes it so compelling. Clyde Tombaugh was a Kansas farm boy who built telescopes out of spare auto parts, old farm equipment, and self-ground lenses. In 1928, he sent drawings of Jupiter and Mars to Lowell Observatory, a premier observatory in Flagstaff, Arizona, to ask for a job as an assistant. At first, the observatory rejected his request, but Clyde showed persistence, and eventually got a job.

The observatory’s founder, the astronomer Percival Lowell, believed there existed a planet beyond the orbit of Neptune, so Tombaugh’s task was to search among millions of stars for a moving point of light. He used a device called a blink comparator, which compared two photographs of the sky taken at different times, so that a moving target, such as a planet, could be seen flitting back and forth against a background of fixed stars.

On February 18, 1930, Tombaugh found Pluto. It was the first planet discovered by an American, and represented a moment of light in the midst of the Great Depression’s dark encroachment. The planet’s name, referencing the Greek god of the underworld, was suggested by an 11-year old British girl. (The cartoon dog was named later.)

For decades, Pluto thrived in its role as the ninth major planet of our solar system, even though it was tiny compared to the others (just one-fifth the diameter of Earth) and so far away (on average, about 3.6 billion miles from the sun and 1 billion miles from Neptune, its closest planetary “neighbor”).

But then, in 1992, two astronomers discovered another planet-like object beyond the orbit of Neptune. Six months later, they discovered a third object. It looked like Pluto might actually be a member of a sort of asteroid belt, similar to but way beyond one we’ve known about for a long time between the orbits of Mars and Jupiter.

At this point, the scientific community began to wonder whether the tiniest planet was going to keep its rarefied title. Would it suffer the same fate as Ceres, the first and largest asteroid discovered in 1801, which reigned as a planet for decades before it was demoted? Despite this concern, a core group of scientists and engineers, me included, was working on convincing NASA to send a probe to our solar system’s last unexplored planet.

By the turn of the millennium, dozens more objects beyond Neptune like Pluto had been discovered, including one that might even be larger than Pluto. So, in August 2006, the International Astronomical Union elected to demote the planet. It now shares its dwarf planet designation with Ceres and three other of the 1,200 bodies that have been located beyond Neptune, collectively known as “Kuiper Belt Objects.”

This demotion came just seven months after we’d successfully launched the NASA New Horizons spacecraft. When I heard this sad announcement, I felt as if I’d lost an old childhood friend.

But Pluto’s scientific interest to those of us on the New Horizons team didn’t diminish. The Kuiper Belt is still an interesting place: It’s populated by icy bodies that are remnants of the solar system’s formation 4.6 billion years ago. These are the building blocks of planets, and they are still around for us to examine.

The few clues scientists have been able to gather about Pluto so far are tantalizing. We know its surface contains ices composed of methane, nitrogen, carbon monoxide, and other compounds familiar to us. It has some very dark regions, but it also seems to have a bright polar cap, like on Earth. Its atmosphere is very thin, but it’s composed largely of nitrogen, like our own. And we believe Pluto’s largest moon, Charon, was formed the same way as our moon, by coalescing from the debris left over from a massive impact by a rogue body.

So, all of us scientists are hoping that the close-up looks we are finally getting now of this dwarf planet can tell us how the chaos that reigned at the beginning of the solar system could have created objects so similar and yet so foreign as Earth and Pluto.

It’s taken nine years of travel, but we’ll finally get within 7,800 miles of Pluto Tuesday. Our spacecraft will enable us to see features as small as a football field. I’ve been painstakingly observing Pluto through a large telescope for over 15 years, seeing what I think is frost moving around on its surface with the seasons. I hope to see it more clearly as the data come in.

As we bear down on Pluto, all of us scientists are just as curious as I was in my childhood bedroom, wondering what Pluto is like. Is its surface old and cratered, or does it have shifting polar caps like the Earth’s that indicate recent activity? Does it have volcanoes like Jupiter’s moon Io, plumes like Neptune’s moon Triton, or water geysers like Saturn’s moon Enceladus? Will it just be like the objects around it, or will it have some unique quality that earns back the special place it once had in everyone’s hearts?

Pluto is much more than something that is not a planet. It’s an underdog we’re still cheering for. It’s a reminder that there are many worlds out there beyond our own—that the sky isn’t the limit at all. We don’t know what kinds of fantastic variations on a theme nature is capable of making until we get out there to look.

Bonnie Buratti is a principal scientist at NASA’s Jet Propulsion Laboratory and a member of the New Horizons science team. She divides her time between New Horizons and Cassini, a mission currently in orbit around Saturn.

TIME Innovation

See Why NASA Is Dying to Visit Jupiter’s Moon Europa

"The time has come to seek answers"

A new mission to see if water or life exists beneath the icy surface of Jupiter’s moon Europa has moved from concept to development, NASA announced this week.

“Observations of Europa have provided us with tantalizing clues over the last two decades, and the time has come to seek answers to one of humanity’s most profound questions,” John Grunsfeld, associate administrator for NASA’s Science Mission Directorate, said in a public statement.

An observational spacecraft is slated to launch by the late 2020’s. After several years, the craft will enter Jupiter’s orbit, offering upwards of 45 opportunities to fly within shutter range of Europa, collecting images of the planet’s surface and possibly “tasting” spumes from massive geysers erupting into space. However, the craft won’t actually land on the Europa’s surface.

The spacecraft will have to take only a glancing look, given the intense levels of radiation. “Any mission that goes in the vicinity of Europa gets cooked pretty quickly,” says Europa mission project scientist Robert Pappalardo.

Europa first captivated NASA scientists in the late 1990’s, when the Hubble telescope returned images of the planet’s icy crust. Scientists theorized that an ocean might lay beneath the crust, holding twice as much water as large as all of Earth’s oceans combined. NASA hopes to gain a deep enough understanding of the water’s composition to see if it contains signs of life or life-sustaining nutrients.

“That would mean the origin of life must be pretty easy throughout the galaxy and beyond,” Pappalardo says.

TIME space

The Mystery of Saturn’s Earth-Sized Cyclone, Explained

How a whole lot of little storms converge to produce one of the largest tempests in the solar system

Correction appended, 6/17/15

There’s one big difference between Earth and Saturn—OK, there are a lot of big differences between Earth and Saturn, including size, chemistry, temperature, distance from the sun and number of moons (one for Earth, up to 62 for Saturn). But the difference that may be most important concerns their atmospheres: Earth has one, Saturn essentially is one, part of the solar system’s quartet of gas giants that also includes Jupiter, Uranus and Neptune.

With a vastly larger atmosphere than Earth’s, Saturn also has vastly larger storms—and none is as impressive as the huge cyclones that spin at its north pole, each as big around as the entire Earth, with winds that whip at 300 mph (483 k/h). The storms, first photographed by the Cassini spacecraft, which has been orbiting Saturn since 2004, have always been a mystery. But now, a paper published in Nature Geoscience by a team of researchers headed by planetary scientist Morgan O’Neill of MIT may explain things.

One thing O’Neill and her colleagues knew was that understanding cyclones on Earth would provide only limited help in understanding them on Saturn. The Earthly storms can’t form without a fixed surface beneath them—especially a wet, fixed surface, which provides the friction that allows winds to drag and converge and the warm water that serves as the storms’ rocket fuel.

MORE: See The Trailer For TIME’s Unprecedented New Series: A Year In Space

To understand how things work on Saturn, the researchers had to develop a computer model that recreated the planet’s gassier, drier, deeper and more turbulent atmosphere. They then ran hundreds of simulations over the course of days to try to see how cyclones could form at all and why they would converge into one super storm at the top of the planet. The computer delivered the goods.

Around the planet, the models showed, small vortices develop as a result of temperature differences in the atmosphere interacting with condensed water and ammonium hydrosulphide. The storms spin in two directions at once, with the bottom half moving one way—either clockwise or counterclockwise—and the top half moving the other. The rotation of the planet drags the storms toward the poles, in a process called beta drift. A second process, called beta gyre, surrounds each mini-cyclone, tearing it in two, with the upper half of each moving toward the equator, where they have room to disperse, and the top half continuing toward the poles, where they converge. The result: lots of mini-storms producing one massive, long-lived one at the top of the planet.

Why does any of this matter—aside from the fact that it’s an exceedingly elegant solution to an exceedingly stubborn riddle about Saturn’s behavior? For one thing, it provides some rules that help explain atmospheric behavior on other worlds. Exceedingly large planets like Jupiter are unlikely to have suprcyclones at their poles because the size of the individual storms is too small relative to the size of the overall world. Smaller gas giants like Neptune could well have polar cyclones. All that, in turn, could lead to greater understanding of exoplanets—those orbiting other stars.

Oh, and finally there’s this: Saturn’s atmosphere is just hypnotically beautiful, as this gallery of pictures suggests. Understanding how it works doesn’t increase that beauty any, but it does help you appreciate it more.

The original version of this story misidentified the gender of lead researcher Morgan O’Neill. She is a woman.

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.

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