Saturn’s back at dawn – follow the moon to the ring-bearer’s lair

Face southeast about an hour fifteen minutes before sunrise to see Saturn and a beautiful, thin lunar crescent this week. Source: Stellarium

While Orion’s stepping into the evening sky followed by Jupiter in Leo, the lord of the rings has returned to punctuate the dawn. It’s great to see Saturn back in view. Along with Venus, which we’ll take a look at later this week, there are now three evening planets (Mars, Jupiter, Venus) and one in the morning.

While still low in the southeast, the delicate crescent moon has a happy meeting with Saturn this Friday the 19th two nights after a conjunction with Virgo’s brightest star Spica. The rings are tilted a hair more than 24° or near the maximum of 27°. Any telescope will show the rings at 30x or higher magnification. You can even see the planet’s oval shape due to the extra girth provided by the rings in a pair of 10x binoculars.

The many ringlets that compose Saturn’s ring system are seen here projected against the planet. This angle shows how translucent they are – you can see one of the planet’s dark belt showing through the rings. Credit: NASA/JPL-Caltech

In honor of the rings, we present a recent photo of Saturn taken by the Cassini spacecraft on August 14 this year. Although Saturn’s rings look solid when viewed from Earth, they’re really translucent, composed of floating chunks of water ice in size from about 1/2-inch (1 cm) to 33 feet (10 meters). I wouldn’t put it past some future entrepreneur to gather up these smaller chunks and market them to those wishing to sip their hard liquor “on the rocks” as it were.

It wasn’t until 1859 that physicist James Clerk Maxwell demonstrated the rings must be made of many individual particles; if they were solid they’d be unstable and break into pieces. Spectroscopic studies in the 1970s, where astronomers determine the composition of an object by examining the light it reflects and absorbs with a spectroscope, proved beyond a shadow that the rings were made of mostly water ice.

One of my favorite astronomical daydreams is to imagine myself in the ring plane gently hopping from one low-gravity ice chunk to the next. Once I arrived at a piece large enough to make for a comfortable seat, I’d tether myself to it so as not to float off and then ponder the millions of small, icy world-lets tumbling across my field of view.

A lovely vision on a wintery afternoon.

Sun keeps close company with the planets / New color maps of Saturn’s moons

Although not an official conjunction, three planets and the Moon are grouped within about 10 degrees of the Sun today. Except for the Moon, which will move on into the evening sky, the planets will be near the Sun the next few days. Stellarium

Hidden by sunlight today, the New Moon and three planets parade across the sky in the constellations Libra and Scorpius. It’s a big celestial gathering and one of the reasons few planets are visible in the evening sky this month — they’re all too close to the Sun.

Hanging like a dewdrop from a blade of grass, Saturn’s moon Tethys (TEE-thiss) is about 660 miles (1062 km) across and made of mostly ice. The narrow F-ring and wider A-ring cross in front of the moon in this image released last month and taken by the Cassini spacecraft. Credit: NASA/JPL-Caltech/Space Science Institute

Mars escapes the glare and so does Jupiter, which comes up in the east like a spark yellow fire around 11 o’clock. Saturn, east of the Sun, is now in the morning sky though still lost in the solar glare. Let’s stop by that planet and its largest moons today and look at some brand new maps made with NASA’s Cassini orbiter.

Color map of Enceladus. The yellow and magenta colors show differences in the depth of surface deposits. The blue “tiger stripes” in the southern hemisphere, where the moon vents water vapor and other material as geysers, show brightly in ultraviolet light. Researchers think it might be due to large-grained ice exposures. Credit: NASA/JPL-Caltech/Space Science Institute/Lunar and Planetary Institute

With its rings and butterscotch clouds, few planets rival Saturn for beauty, but its moons are equally fascinating for their strange colors, textures and alien features. NASA recently released a series of global, color mosaics of six of its largest moons based on 10 years of images taken by NASA’s Cassini spacecraft as it orbited the Saturn system. These are the first global color maps of these moons produced from the Cassini data. The colors are broader than what the human eye sees, extending into the ultraviolet and infrared (beyond red) part of the spectrum. They’re also VERY detailed – just click on any of them for a close-up. I’ve included four of the six. To see them all, click HERE.

Iapetus (eye-APP-eh-tuss) looks very strange with one hemisphere bright and icy and the other covered in about a foot of darker material. Iapetus rotates very slowly – once every 79 days. It’s thought that an impact of a darker object long ago coated part of  its surface, causing that area to absorb more sunlight over the long day. More heat meant more ice vaporized which then re-condensed as frost/ice on the moon’s bright side, further concentrating the darker material. This expanded in a positive feedback loop that eventually led to an ever-whitening hemisphere while the other grew blacker. Credit: NASA/JPL-Caltech/Space Science Institute/Lunar and Planetary Institute

On Tethys, scientists think the dark colors of the moon’s trailing hemisphere are due to changes in ice and minerals caused by bombardment from high-speed particles and radiation in Saturn’s powerful magnetic field. The lighter-colored leading hemisphere is coated with icy dust from Saturn’s E-ring, formed from tiny particles ejected from Enceladus’ south polar geysers. The purplish equatorial band gets its color from high-energy electrons in Saturn’s magnetic field slamming into the moon. Credit: NASA/JPL-Caltech/Space Science Institute/Lunar and Planetary Institute

Meet Dione, a 698-mile-wide moon. Its color variations are believed to be caused by the same factors affecting Tethys – radiation and high-speed particles weathering the trailing hemisphere ice and the effects of icy mist spewed by Enceladus on the leading hemisphere. Credit:  NASA/JPL-Caltech/Space Science Institute/Lunar and Planetary Institute 

Planets, moon gather at dusk / Curiosity chews into Mt. Sharp

The crescent moon and Saturn twist the night away this evening September 27, 2014. Catch the pair low in the southwestern sky 1-2 hours after sunset. Further east, Mars joins Antares in conjunction. Stellarium

Space weather experts are forecasting a minor G1 geomagnetic storm with possible auroras across the northern U.S. and southern Canada this evening.

While you’re out watching for that telltale green arc in the north, take a few minutes to face the opposite direction. Low above the southwestern horizon you’ll find the crescent moon parked near the planet Saturn. It may be our last chance to see the planet with ease. Saturn’s been sinking into the west for some time. Tonight’s moon will guide you right to it.

A little more than a fist to the left or east of Saturn, Mars will be in conjunction with its colorful friend Antares (both are red-hued) only 3.1º to its north. Both star and planet shine at magnitude +1 though Mars is officially a hair brighter. Can you see the difference?

Photo from the Mars Hand Lens Imager (MAHLI) camera on Curiosity shows the first sample-collection hole drilled in Mount Sharp, the layered mountain that is the science destination of the rover’s extended mission. The hole is 0.63 inch wide and about 2.6 inches deep and photographed from 2 inches away. Click to enlarge. Credit: NASA/JPL-Caltech

This week NASA’s Mars Curiosity Rover drilled and gathered its first rock sample from the base of Mt. Sharp in Gale Crater. The target rock formation, called Confidence Hills, lies on the Pahrump Hills outcrop at the base of the mountain. The rock is a mudstone and softer than any of the rocks previously sampled by the rover.

Mudstone rock outcrop where Curiosity got its first taste of Mt. Sharp (drill hole at top), the rover’s main science target during its time on Mars. Curiosity landed on the planet in August 2012. Credit: NASA/ JPL-Caltech, colorized by Bob King

“This drilling target is at the lowest part of the base layer of the mountain, and from here we plan to examine the higher, younger layers exposed in the nearby hills,” said Curiosity Deputy Project Scientist Ashwin Vasavada of JPL. Scientists hope to get a look at the first rock to underlie Mount Sharp to get a picture of the environment at the time the mountain formed and what led to its formation. Mount Sharp is composed of layered sediments, some of which appear to have been deposited by water several billion years ago.

Fish-eye view taken with Curiosity’s front hazcam showing the drill at work on the Confidence Hills target at the base of Mount Sharp September 24, 2014. The rock surface is webbed with cracks. Click to enlarge. Credit: NASA/JPL-Caltech, colorized by Bob King

NASA will put the breaks on Curiosity now that it’s reached its prime science destination after traveling 5 miles (8 km) since touching down on Mars August 6, 2012. Next, the rover will deliver a powdered rock sample into a scoop on it arm, where the soil’s texture will be scrutinized to access whether it’s safe for further sieving, portioning and delivery into Curiosity’s internal laboratory instruments without clogging hardware.

 

Goodmorning moon / Tomorrow’s Titan flyby

Look east Monday morning around 6 a.m. to spot the goodmorning moon. Only 2.5% of the moon will be illuminated by the sun; the remainder by ghostly earthshine. Venus will be about a fist held at arm’s length to the moon’s lower left. Stellarium

Like a lot of parents, we read Goodnight Moon by Margaret Wise Brown to our kids to get them ready for bed at night. The calming words and repetition soothed child and adult alike at the end of the day.

Maybe a sequel titled “Goodmorning Moon” will be written someday about waking up to the smiling crescent in the east and getting ready for the day. Tomorrow morning we’ll see exactly that, a very thin moon, low in the eastern sky at dawn. Its delicate arc will surely make you stop and realize how much beauty nature puts on the plate for enjoyment and study every day.

Venus seekers can use the moon to make one last attempt to find the planet, now nestled very low in the east just a degree or two above the horizon 40 minutes before sunrise.

Animation showing clouds of methane moving over Ligeia Mare, a large sea of liquid methane near Titan’s north pole, between July 20 and 22, 2014 as Cassini departed the moon during the last flyby. Credit: NASA/JPL-Caltech/SSI

While we’re on the topic of planets, NASA’s Cassini spacecraft will make a close flyby of Saturn’s moon Titan tomorrow September 22nd. At 3,201 miles (5,150 km) across, Titan is the solar system’s second largest moon, only 79 miles smaller than Jupiter’s Ganymede. It’s also unique in having a very thick atmosphere – 1.5 times thicker than Earth’s – a feature usually found only on planets.

It’s still not known how Titan managed to hold onto all its air, which consists of primarily nitrogen mingled with methane and various other hydrocarbons that react in sunlight to create an orange smog that gives the moon its distinctive color. Several other moons such as Ganymede, Rhea and even our own moon have atmospheres, but they’re exceedingly thin compared to Titan’s.

In this photo taken by Cassini, Saturn’s airless, cratered moon Dione is juxtaposed with Titan. Titan appears smaller because it’s 600,000 miles farther away from the spacecraft’s perspective. To see beneath the clouds and map the surface, Cassini observes the moon in infrared light and with radar. Credit: NASA/JPL-Caltech

It’s thought that Titan maintains and replenishes its atmosphere through outgassing from its interior. The bitter cold temperatures at Saturn’s nearly billion mile distance from the sun along with Titan’s considerable gravitational pull undoubtedly help preserve and hang on to its air. Comet impacts may also contribute to the moon’s stockpile of ices and organic compounds.

Along with an atmosphere come clouds, though of methane rather than the water vapor variety found on Earth. Temperatures at the surface hover just 90 degrees above absolute zero (-290º F, -179º C), chill enough for methane clouds to form and supply at least some of the precipitation to lakes of liquid ethane, methane and propane below.

This will be Cassini’s 9th flyby of Titan this year. During a flyby, the craft zips by the moon at high speed while keeping its instruments precisely pointed at the target using either its reaction wheels or thrusters, which spin the spacecraft to track the moon as it passes by. Thrusters are also used to keep Cassini from tumbling when it experiences drag while passing through Titan’s upper atmosphere during close flybys.


Descent through Titan’s atmosphere made by the Huygens probe on January 14, 2005

On Monday, Cassini will be traveling at 13,000 mph (21,000 km/hr) and come within 870 miles of Titan’s surface as it photographs seas and lakes – including Ligeia Mars shown above – around the north pole. Another instrument will observe Titan’s southern hemisphere atmosphere in ultraviolet light by observing the dimming of Alkaid, the star at the end of the Big Dipper’s handle as its light passes through the moon’s varied atmospheric layers.

Moon, Mars, Saturn and Antares gather at dusk tonight

The crescent moon, Saturn and Mars will form a compact triangle in the southwestern sky in this evening August 31st. 3.5º separate the moon and Saturn; Mars and Saturn will be 5º apart. Antares is about two ‘fists’ to the east or left. Stellarium

Don’t miss tonight’s sweet gathering of crescent moon and evening planets. Just look to the southwest in late twilight to spot the trio.

Both Saturn and Mars happen to be exactly the same brightness, shining equally at magnitude 0.8, but each with a distinctly different hue. Can you see the contrast between rusty red Mars and vanilla-white Saturn?

Antares is a red supergiant that’s blowing a powerful stellar wind into space at the rate of several solar masses every million years. One day it’s likely to explode as a supernova. Credit: Wikimedia

All this happens in Libra, a dim zodiac constellation preceding the brighter and better known Scorpius. Scorpius brightest star, Antares, is similar to Mars in color and just a tad fainter.

Visually, this red supergiant star doesn’t even hint of its true proportions because it’s 620 light years away, too far to appear as anything more than a shifting point of light. Measuring in at three times the diameter of Earth’s orbit, if Antares were put in place of the sun, its bubbly surface extending beyond the orbit of Mars.

How Antares would appear if we could get close enough to see it based on simulations by A. Chiavassa and team. Huge convective cells of rising and sinking gas crinkle its surface. Click to read the group’s 2010 research paper on the star. Credit: A. Chiavassa et. all

Recent research shows the star dominated by enormous bubbles of incandescent hydrogen gas called convective cells. Although it has a mass some 18 times that of the sun, the star’s powerful winds – from convection and sheer radiant energy – blast away something like 3 solar masses of material into space every million years. Unless Antares slims down through mass loss, it’s destined to grow a core of iron, collapse and explode as a supernova in the future.

Mars and Saturn boogaloo with Zubenelgenubi

Mars and Saturn are now only about 7 degrees apart (a little more than three fingers) low in the southwestern sky at dusk. This view shows the sky about 90 minutes after sunset. Between the two, you can spot the dimmer star Zubenelgenubi, the brightest star in the constellation Libra the Scales. Stellarium

Evening planets Saturn and Mars are fading and dropping lower in the western sky as August ticks toward September. Remember when Mars was brighter than Arcturus this spring? Planets. They never sit still. Their light’s never constant. We love watching them change, which is why our ancient ancestors knew immediately they were different from the static stars.

From my house, I need to be vigilant to spot Saturn and Mars before they’re lost in the treetops. That means getting out about an hour after sunset in fading twilight and finding an open spot where I can look low in the southwestern sky.

You may have noticed that the two have slowly been drawing together over the past few weeks. Mars, much closer to Earth than Saturn, moves more quickly across the sky. It’s been ‘chasing’ slower Saturn for some time now.

Mars gets closer to Saturn with each passing night until August 25 when they’ll be in conjunction just 3.4 degrees apart (twice as close as tonight). Watching Mars move against much slower Saturn makes a fun and easy observing project. Stellarium

Tonight, the two planets will be 7 degrees apart on either side of Libra the Scales’ brightest star, Zubenelgenubi (zoo-BEN-el-je-NEW-bee). The name, a delight to pronounce, is pure Arabic and means ‘southern claw’. Libra’s stars used to belong to neighboring Scorpius and both it and nearby Zubeneschamali (northern claw) remind of us of times long ago when Libra belonged to Scorpius.

Zubenelgenubi (a.k.a. Alpha Librae) is a double star that observers with keen vision can split with the naked eye. Most of us will find that a pair of binoculars will make the job much easier.

Mars will soon pass its slower brother but not before the two are in conjunction and closest together on the evening of August 25th. Watching two planets pass in the night is fun and instructive – it makes us aware that everything in our solar system’s on the move.

This weekend we’ll look at another even more amazing planetary conjunction coming up very soon – Jupiter and Venus on August 18.

Crescent moon joins a planet parade / Opportunity ready for marathon run

The moon scoots by two bright stars and two bright evening planets in the next few nights. This map shows the sky facing southwest in late evening twilight. Stellarium

The moon joins a lineup of planets and bright stars hung like tiki lamps across the southwestern sky at dusk. Watch for it to pass near fading Mars Saturday evening and Saturn on Monday.

The Martian landscape photographed by on July 30, 2014. The rover is exploring south along the west rim of Endeavour Crater heading toward a notch called ‘Marathon Valley’ about 1.2 miles (2 kilometers) away. Credit: NASA/JPL

While you’re gazing at the Red Planet, know that the Opportunity rover made news this week when it set a record for the most miles ever driven off-planet, tallying a satisfying 25 miles (40 km) of Martian travels. The previous record was held by the Soviet Union’s Lunokhod 2 rover when it ambled across 24.2 miles of the moon’s surface in 1973.

Out of this world distance records compared. Credit: NASA

Opportunity surpassed that record on Monday July 28 when it registered 25.01 miles en route to a notch called Marathon Valley along the west rim of Endeavour Crater. Mission controllers would like to get a look at clay minerals there that have been spotted from orbit.

Lunokhod 2 crater photographed by Opportunity last spring. The crater’s 20 feet (6 meters) in diameter. Credit: NASA/JPL

When it reaches the Valley it will have completed 26.2 miles (42 km), the official distance of a marathon. When you consider that Opportunity and its sister probe Spirit were only intended to function for 90 days, the current record-breaking feat and upcoming marathon completion are that more remarkable.

101 geysers erupt from Enceladus’ salty deeps

At least 20 geysers blast icy particles and water vapor from cracks in the icy crust of Saturn’s moon Enceladus. Scientists recently confirmed the geyser material derives from a salty ocean beneath the moon’s surface. Credit: NASA/JPL

Future astronauts better watch where their step when exploring the south polar terrain of Saturn’s icy moon Enceladus. A geyser could pop up anywhere.

This graphic shows a 3-D model of 98 geysers whose source locations and tilts were found in a Cassini imaging survey of Enceladus’ south polar terrain by the method of triangulation. Credit: NASA/JPL-Caltech/Space Science Institute

NASA’s Cassini spacecraft have identified 101 distinct geysers erupting on Saturn’s icy moon Enceladus. Cassini has studied and photographed the moon’s intriguing ‘tiger stripe’ fractures for over 7 years and discovered that each of them coincides with a particular hot spot within a fracture.

Three competing hypotheses were put forward to explain how geysers might happen on an ice-covered moon nearly a billion miles from the warmth of the sun.

#1 – Tidal flexing: As Enceladus revolves around Saturn, the planet’s enormous gravity flexes the little moon, heating up its interior and melting ice into water which escapes as vapor through openings in the icy crust.
#2 – Frictional heating: Back-and-forth rubbing of opposing walls of the fractures generate frictional heat that turns ice into geyser-forming vapor and liquid. Same principle as rubbing your hands together to create heat.
#3 – Jaws of ice: The opening and closing of the fractures caused by Saturn’s gravitational might exposes water from below when then quickly vaporizes in the moon’s vacuum.

This artist’s rendering shows a cross-section of the ice shell immediately beneath one of Enceladus’ geyser-active fractures, illustrating how water works its way to the moon’s surface. Credit: NASA/JPL-Caltech/Space Science Institute

But a detailed study by Cassini in 2010 appears finally to have netted the correct explanation. The probe’s heat-sensing instruments matched the geysers’ locations with small-scale hot spots only a few dozen feet across - too small to be produced by frictional heating, but the right size to be the result of condensation of vapor on the near-surface walls of the fractures.

“Once we had these results in hand, we knew right away heat was not causing the geysers, but vice versa,” said Carolyn Porco, leader of the Cassini imaging team and lead author of the first scientific paper on the discovery. “It also told us the geysers are not a near-surface phenomenon, but have much deeper roots.”

Researchers concluded the only logical source of the material forming the geysers is the sea now known to exist beneath the ice shell. They also found that narrow pathways through the ice shell can remain open from the sea all the way to the surface, if filled with liquid water. This implies, at least in my mind, that liquid water might exist as pools in hot spots encircled by thick rims of ice (condensed water vapor) on the moon’s chill -330° F (-201° C) surface.

Imagine standing nearby watching fountains of vapor turn to ice crystals before your eyes and sparkling like diamond dust against the black starry sky.

Source: JPL

Rocky moon meets the ringed planet tonight

Look to the waxing gibbous moon tonight July 7 and you’ll see the planet Saturn about 1 degree above it. This map shows the sky around 10 o’clock local time. Stellarium

Forgive this ultra-brief appearance, but I’ve been exploring a virtually unknown astronomical paradise the past few days – Las Vegas! Although it seems incongruous, given Vegas’ image, the Las Vegas Astronomical Society has a very active presence here.

A recent photo posted by the Cassini spacecraft photo group shows Saturn’s magnificent rings, polar vortex and the jet stream-created polar hexagon. The hexagon, which is wider than 2 Earths, forms a six-lobed, stationary wave that wraps around the north polar regions at a latitude of roughly 77 degrees North. Credit: NASA/JPL-Caltech

The group planned a public outing for the Mars-moon conjunction on July 5 but were clouded out. Maybe tonight their members will get a clear sky for the Saturn-moon conjunction. I’ll be in a plane at 35,000 feet for the event crossing my fingers I get a window seat on the ‘right’ side.

Celestial fireworks light up the sky on the Fifth of July

The crescent moon shines in the southwestern sky tonight July 2 not far from Leo’s brightest star Regulus. It’s headed for two fine conjunctions later this week. Stellarium

We celebrate Independence Day this Friday the 4th with parades and good food topped off with colorful fireworks. Consider that the opening act. Festivities continue into the weekend with two spectacular conjunctions of the moon and planets.

Saturday evening July 5 allow your gaze to wander up to the first quarter moon. Levitating above it will be a bright red light – the planet Mars! They’ll be close. From most of the central and eastern U.S. and Canada the two are separated by just a half degree or one moon diameter. Look a short distance to the left of moon and you’ll also spot Virgo’s brightest star Spica.

The first quarter moon pays a close visit to Mars on Saturday July 5 and then passes Saturn two nights later. The views show the scene from the central U.S. around the start of nightfall. Stellarium

If you live farther south, the moon will inch closer to Mars. From sizzling Miami, the duo’s only a 1/3 of a moon apart, while the moon will completely cover or occult Mars for up to an hour across a wide swath of South America. Click HERE for a map and times showing where and when the occultation will occur.

Though Mars isn’t quite as bright as it was at opposition in April, it’s still brighter than its color rival Betelgeuse in Orion. With haze-free skies and a pair of binoculars you might be able to see it atop the moon a short time before sunset. Certainly worth a try.

Everybody loves an encore after a great performance, and the moon’s happy to oblige. Two nights later on July 7 it glides about a degree (two diameters) directly below Saturn. Once again, the moon will occult the planet as seen from the southern half of South America. While these sky events aren’t exactly stars exploding before our very eyes, their quiet beauty is worth our admiration.