Posted on by Nancy Atkinson

Massive Ice Avalanches on Iapetus

Long-runout landslides on Iapetus: A) Malun crater blocky landslide; B) Multiple lobate landslide in Engelier Basin; C) Lobate landslide in Gerin Basin. Credit: McKinnon et. al, LPSC, 2012.

We’ve seen avalanches on Mars, but now scientists have found avalanches taking place on an unlikely place in our solar system: Saturn’s walnut-shaped, two-toned moon Iapetus. And these aren’t just run-of-the-mill avalanches: they are huge inundations of debris. These events are specifically known as long-runout landslides — debris flows that have traveled unusually long distances. Just how these avalanches are occurring is somewhat of a mystery, according to Bill McKinnon from Washington University in St. Louis.

“This is really about the mystery of long-runout landslides, and no one really knows for sure what causes them,” said McKinnon, speaking at the Lunar and Planetary Science Conference this week.

These avalanches or landslides certainly have their Earthly counterparts and, as noted, similar events are found on Mars, where they are especially associated with the steep canyon walls of the Valles Marineris system. However, the large mass movements on Iapetus in the form of long-runout landslides are less common.

McKinnon said the amount of material that has been moved in all the avalanches on Iapetus that he and his team have found exceeds all the material moved in known Martian landslides (in published data), even though Mars is much bigger than Iapaetus.

“The mechanics of long-runout landslides are poorly understood, and mechanisms proposed for friction reduction are so numerous I can’t fit them all on one Powerpoint slide,” McKinnon said during his talk. Possible explanations include water (such as released groundwater), wet or saturated soil, ice, trapped or compressed air, acoustic fluidization, and more.

On Iapetus there is obviously no water or atmosphere to create conducive conditions for avalanches. But McKinnon and his team have identified over two dozen avalanche events as seen in images from the Cassini spacecraft.

Many of the landslides are seen from crater and basin walls and steep scarps. McKinnon and his team have found two types of avalanches: ‘blocky’ with rough-looking debris and smoother lobate landslides. They also see evidence that over time, multiple avalanches have likely occurred in the same location, so Iapetus must have a long history of mass wasting and landslides.

So, what allows for the huge avalanches on Iapetus? McKinnon said ice provides the best answer to that question. The low density of Iapetus indicates that it is mostly composed of ice, with only about 20% of rocky materials.

“There seems to be a necessity for a fluidization or liquid mechanism,” McKinnon said. “If ice is warmed just enough it will become slippery,” reducing the friction and cohesiveness of the crater or basin wall.

What they are seeing, especially in the lobate landslides, is consistent with ‘rheological’ flow similar to molten lava or fluid mudslides.

So, ice rubble within the rocky faces of crater and basin walls are heated just enough – either by flash heating or friction — that the surfaces become slippery. “The energetics are favorable for this mechanism on Iapetus,” McKinnon said.

Iapetus has a very slow rotation, longer than 79 days, and such a slow rotation means that the daily temperature cycle is very long — so long that the dark material can absorb heat from the Sun and warm up. Of course the dark part of Iapetus absorbs more heat than the bright icy material; therefore, McKinnon said, this is all fairly enigmatic.

Plus, saying that it “warms up” on Iapetus is a bit of an overstatement. Temperatures on the dark region’s surface are estimated to reach 130 K (-143 °C; -226 °F) at the equator and temperatures in the brighter area only reach about 100 K (-173 °C; -280 °F).

Whatever the mechanisms, the long-runout landslides on Iapetus are fairly unique when it comes to icy planetary bodies. McKinnon referenced that just two mass movements of modest scale have been detected on Callisto, and there is limited evidence of similar events on Phoebe.

These ice avalanches certainly deserve more investigation on a moon which McKinnon described as having “singularly spectacular topography,” and additional research and a more detailed paper are forthcoming.

Read the LPSC abstract: Massive Ice Avalanches on Iapetus, and the Mechanism of Friction Reduction in Long-Runout Landslides

Posted on by Jason Major

Two Moons In Passing

Animation of Tethys passing in front of Dione from Cassini's point of view. (CLICK TO PLAY)

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Saturn’s moon Tethys passes in front of its slightly larger sister Dione in this animation made from 25 raw images acquired by Cassini on March 14, 2012. Pretty cool! (Click the image to play.)

 

Tethys and Dione (NASA/JPL/SSI)

Tethys and Dione are similar in diameter, being 1,062 kilometers (660 miles) wide and 1,123 kilometers (698 miles) wide, respectively. Both are heavily cratered, ice-rich worlds.

In this view, Tethys’ enormous Odysseus crater can be seen on its northern hemisphere. 400 km (250 miles) across, Odysseus is two-fifths the diameter of Tethys itself, suggesting that it was created early in the moon’s history when it was still partially molten — or else the impact would have shattered the moon apart entirely.

The more extensively-cratered trailing side of Dione is visible here, its signature “wispy lines” rotated out of view. Since it makes sense that a moon’s leading face should be more heavily cratered, it’s thought that Dione has been spun around by an impact event in the distant past.

If you look closely, a slight rotation in Tethys can also be discerned from the first frame to the last.

Credit: NASA/JPL/SSI. Animation by Jason Major.

Posted on by Jason Major

Photo Treat: Enceladus, Titan and Saturn’s Rings

Color-composite image from Cassini raw data acquired on March 12, 2012. (NASA/JPL/SSI/J. Major)

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Little Enceladus and enormous Titan are seen on either side of Saturn’s rings in this image, a color-composite made from raw images acquired by Cassini on March 12, 2012. The original images were taken in red, green and blue color channels, and with a little Photoshop editing I combined them into a roughly true-color view of what Cassini saw as it passed within 1,045,591 km of Enceladus.

Follow along with the Cassini mission here.

Image credit: NASA/JPL/Space Science Institute. Edited by Jason Major.

Posted on by Tammy Plotner

Weekly SkyWatcher’s Forecast – March 19-25, 2012

NGC 2539 - Credit: Palomar Observatory Courtesy of Caltech

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Greetings, fellow SkyWatchers! The week starts off with new Moon and the perfect opportunity to do a Messier Marathon. The planets continue to dazzle as we not only celebrate the Vernal Equinox, but the March Geminid meteor shower as well! If that doesn’t get your pulsar racing – nothing will. It’s time to get out your binoculars and telescopes and meet me in the backyard!

Monday, March 19 – Right now the Moon is between the Earth and the Sun, and you know what that means…New Moon! Tonight we’ll start in northern Puppis and collect three more Herschel studies as we begin at Alpha Monoceros and drop about four fingerwidths southeast to 19 Puppis.

NGC 2539 (Right Ascension: 8 : 10.7 – Declination: -12 : 50) averages around 6th magnitude and is a great catch for binoculars as an elongated hazy patch with 19 Puppis on the south side. Telescopes will begin resolution on its 65 compressed members, as well as split 19 Puppis – a wide triple. Shift about 5 degrees southwest and you find NGC 2479 (Right Ascension: 7 : 55.1 – Declination: -17 : 43) directly between two finderscope stars. At magnitude 9.6 it is telescopic only and will show as a smallish area of faint stars at low power. Head another degree or so southeast and you’ll encounter NGC 2509 (Right Ascension: 8 : 00.7 – Declination: -19 : 04) – a fairly large collection of around 40 stars that can be spotted in binoculars and small telescopes.

Tuesday, March 20 – Today is Vernal Equinox, one of the two times of the year that day and night become equal in length. From this point forward, the days will become longer – and our astronomy nights shorter! To the ancients, this was a time a renewal and planting – led by the goddess Eostre. As legend has it, she saved a bird whose wings were frozen from the winter’s cold, turning it into a hare which could also lay eggs. What a way to usher in the northern spring!

With the Moon still out of the picture, let’s finish our study of the Herschel objects in Puppis. Only three remain, and we’ll begin by dropping south-southeast of Rho and center the finder on a small collection of stars to locate NGC 2489 (Right Ascension: 7 : 56.2 – Declination: -30 : 04). At magnitude 7, this bright collection is worthy of binoculars, but only the small patch of stars in the center is the cluster. Under aperture and magnification you’ll find it to be a loose collection of around two dozen stars formed in interesting chains.

The next are a north-south oriented pair around 4 degrees due east of NGC 2489. You’ll find the northernmost – NGC 2571 (Right Ascension: 8 : 18.9 – Declination: -29 : 44) – at the northeast corner of a small finderscope or binocular triangle of faint stars. At magnitude 7, it will show as a fairly bright hazy spot with a few stars beginning to resolve with around 30 mixed magnitude members revealed to aperture. Less than a degree south is NGC 2567 (Right Ascension: 8 : 18.6 – Declination: -30 : 38). At around a half magnitude less in brightness, this rich open cluster has around 50 members to offer the larger telescope, which are arranged in loops and chains.

Congratulations on completing these challenging objects!

Are you up for another challenge? Then test your ability to judge magnitude as Mars has now dimmed to approximately -1.0. Does it look slightly different in size and brightness than it did a week or so ago? Keep watching!

Wednesday, March 21 – Take your telescopes or binoculars out tonight to look just north of Xi Puppis for a celebration of starlight known as M93 (Right Ascension: 7 : 44.6 – Declination: -23 : 52). Discovered in March of 1781 by Charles Messier, this bright open cluster is a rich concentration of various magnitudes that will simply explode in sprays of stellar fireworks in the eyepiece of a large telescope. Spanning 18 light-years of space and residing more than 3400 light-years away, it contains not only blue giants, but lovely golds as well. Jewels in the night…

Thursday, March 22 – Today in 1799 Friedrich Argelander was born. He was a compiler of star catalogues, studied variable stars and created the first international astronomical organization.

Tonight let’s celebrate no Moon and have a look at an object from an alternative catalog that was written by Lacaille, and which is about two fingerwidths south of Eta Canis Majoris.

Also known as Collinder 140, Lacaille’s 1751 catalog II.2 “nebulous star cluster” is a real beauty for binoculars and very low power in telescopes. More than 50% larger than the Full Moon, it contains around 30 stars and may be as far as 1000 light-years away. When re-cataloged by Collinder in 1931, its age was determined to be around 22 million years. While Lacaille noted it as nebulous, he was using a 15mm aperture reflector, and it is doubtful that he was able to fully resolve this splendid object. For telescope users, be sure to look for easy double Dunlop 47 in the same field.

Now, kick back and enjoy a spring evening with two meteor showers. In the northern hemisphere, look for the Camelopardalids. They have no definite peak, and a screaming fall rate of only one per hour. While that’s not much, at least they are the slowest meteors – entering our atmosphere at speeds of only 7 kilometers per second!

Far more interesting to both hemispheres will be the March Geminids which peak tonight. They were first discovered and recorded in 1973 and then confirmed in 1975. With a much faster fall rate of about 40 per hour, these slower than normal meteors will be fun to watch! When you see a bright streak, trace it back to its point of origin. Did you see a Camelopardalid, or a March Geminid?

Friday, March 23 – Today in 1840, the first photograph of the Moon was taken. The daguerreotype was exposed by American astronomer and medical doctor J. W. Draper. Draper’s fascination with chemical responses to light also led him to another first – a photo of the Orion Nebula.

Our target for tonight is an object that’s better suited for southern declinations – NGC 2451 (Right Ascension: 7 : 45.4 – Declination: -37 : 58). As both a Caldwell object (Collinder 161) and a southern skies binocular challenge, this colorful 2.8 magnitude cluster was probably discovered by Hodierna. Consisting of about 40 stars, its age is believed to be around 36 million years. It is very close to us at a distance of only 850 light-years. Take the time to closely study this object – for it is believed that due to the thinness of the galactic disk in this region, we are seeing two clusters superimposed on each other.

With the Moon out of the picture early, why not get caught up in a galaxy cluster study – Abell 426. Located just 2 degrees east of Algol in Perseus, this group of 233 galaxies spread over a region of several degrees of sky is easy enough to find – but difficult to observe. Spotting Abell galaxies in Perseus can be tough in smaller instruments, but those with large aperture scopes will find it worthy of time and attention.

At magnitude 11.6, NGC 1275 (Right Ascension: 3 : 19.8 – Declination: +41 : 31) is the brightest of the group and lies physically near the core of the cluster. Glimpsed in scopes as small as 150 mm aperture, NGC 1275 is a strong radio source and an active site of rapid star formation. Images of the galaxy show a strange blend of a perfect spiral being shattered by mottled turbulence. For this reason NGC 1275 is thought to be two galaxies in collision. Depending on seeing conditions and aperture, galaxy cluster Abell 426 may reveal anywhere from 10 to 24 small galaxies as faint as magnitude 15. The core of the cluster is more than 200 million light-years away, so it’s an achievement to spot even a few!

Saturday, March 24 – Today is the birthday of Walter Baade. Born in 1893, Baade was the first to resolve the Andromeda galaxy’s individual stars using the Hooker telescope during World War II blackout times, and he also developed the concept of stellar populations. He was the first to realize that there were two types of Cepheid variables, thereby refining the cosmic distance scale. He is also well known for discovering an area towards our galactic center which is relatively free of dust, now known as “Baade’s Window.”

Just after sunset, you really need to take a look out your western window for a really beautiful bit of scenery. As the sky darkens, look for the very tender crescent Moon lit with “Earthshine”. Above it you will see bright Jupiter. Above that you will see blazing Venus. And, if that’s not enough, just a little higher will bring you to the Pleiades! What a great way to start a weekend evening!

With the Moon so near the horizon, we have only a short time to view its features. Tonight let’s start with a central feature – Langrenus – and continue further south for crater Vendelinus. Spanning 92 by 100 miles and dropping 14,700 feet below the lunar surface, Vendelinus displays a partially dark floor with a west wall crest catching the brilliant light of an early sunrise. Notice also that its northeast wall is broken by a younger crater – Lame. Head’s up! It’s an Astronomical League challenge.

Once the Moon has set, revisit M46 in Puppis – along with its mysterious planetary nebula NGC 2438. Follow up with a visit to neighboring open cluster M47 – two degrees west-northwest. M47 may actually seem quite familiar to you already. Did you possibly encounter it when originally looking for M46? If so, then it’s also possible that you met up with 6.7 magnitude open cluster NGC 2423 (Right Ascension: 7 : 37.1 – Declination: -13 : 52), about a degree northeast of M47 and even dimmer 7.9 magnitude NGC 2414 (Right Ascension: 7 : 33.3 – Declination: -15 : 27 ) as well. That’s four open clusters and a planetary nebula all within four square arc-minutes of sky. That makes this a cluster of clusters!

Let’s return to study M47. Observers with binoculars or using a finderscope will notice how much brighter, and fewer, the stars of M47 are when compared to M46. This 12 light-year diameter compact cluster is only 1600 light-years away. Even as close as it is, not more than 50 member stars have been identified. M47 has about one tenth the stellar population of larger, denser, and three times more distant, M46.

Of historical interest, M47 was “discovered” three times: first by Giovanni Batista Hodierna in the mid-17th century, then by Charles Messier some 17 years later, and finally by William Herschel 14 years after that. How is it possible that such a bright and well-placed cluster needed “re-discovery?” Hodierna’s book of observations didn’t surface until 1984, and Messier gave the cluster’s declination the wrong sign, making its identification an enigma to later observers – because no such cluster could be found where Messier said it was!

Sunday, March 25 – Today in 1655, Titan – Saturn’s largest satellite – was discovered by Christian Huygens. He also discovered Saturn’s ring system during this same year. 350 years later, the probe named for Huygens stunned the world as it reached Titan and sent back information on this distant world. How about if we visit Saturn? You’ll find the creamy yellow planet located about a fistwidth northwest of bright, white Spica! Even a small telescope will reveal Titan, but remember… it orbits well outside the ring plane, so don’t mistake it for a background star! While you’re there, look closely around the ring edges for the smaller moons. A 4.5” telescope can easily show you three of them. How about the shadow the rings on the planet’s surface? Or how about the shadow of the planet on the rings? Is the Cassini division visible? If you have a larger telescope, look for other ring divisions as well. All are part and parcel of viewing incredible Saturn!

If you missed yesterday evening’s scenic line-up, don’t despair. Just after the Sun sets tonight – and above the western horizon – you’ll find the young Moon very closely paired with Jupiter. Keep traveling eastward (up) and you’ll encounter Venus. Continue east and the next stop is M45. Watch in the days ahead as the Moon sweeps by, continuing to provide us with a show! Need more? Then check out Leo and Mars! You’ll find a great triangulation of Regulus to the west, Mars to the east and Algieba to the north. If you didn’t know better, you’d almost swear the Lion swallowed the red planet.

Tonight let’s return to our previous studies of the Moon and revisit a challenging crater. Further south than Vendelinus, look for another large, mountain-walled plain named Furnerius, located not too far from the terminator. Although it has no central peak, its walls have been broken numerous times by many smaller impacts. Look at a rather large one just north of central on the crater floor. If skies are stable, power up and search for a rima extending from the northern edge. Keep in mind as you observe that our own Earth has been pummeled just as badly as its satellite.

On this day in 1951, 21 cm wavelength radiation from atomic hydrogen in the Milky Way was first detected. 1420 MHz H I studies continue to form the basis of a major part of modern radio astronomy. If you would like to have a look at a source of radio waves known as a pulsar, then aim your binoculars slightly more than a fistwidth east of bright Procyon. The first two bright stars you encounter will belong to the constellation of Hydrus and you will find pulsar CP0 834 just above the northernmost – Delta.

Unitl next week? May all your journeys be at light speed!

Posted on by Jason Major

Saturn’s “Wispy” Moon Has An Oxygen Atmosphere

Cassini has detected molecular oxygen ions around Saturn's icy Dione

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There’s oxygen around Dione, a research team led by scientists at New Mexico’s Los Alamos National Laboratory announced on Friday. The presence of molecular oxygen around Dione creates an intriguing possibility for organic compounds — the building blocks of life — to exist on other outer planet moons.

Dione's signature "wispy lines" are actually the bright walls of long cliff faces. (NASA/JPL/SSI)

One of Saturn’s 62 known moons, Dione (pronounced DEE-oh-nee) is 698 miles (1,123 km) in diameter. It orbits Saturn at about the same distance that our Moon orbits Earth. Heavily cratered and crisscrossed by long, bright scarps, Dione is made mostly of water ice and  rock. It makes a complete orbit of Saturn every 2.7 days.

Data acquired during a flyby of the moon by the Cassini spacecraft in 2010 have been found by the Los Alamos researchers to confirm the presence of molecular oxygen high in Dione’s extremely thin atmosphere — so thin, in fact, that scientists prefer the term exosphere.

While you couldn’t take a deep breath on Dione, the presence of O2 indicates a dynamic process in action.

“The concentration of oxygen in Dione’s atmosphere is roughly similar to what you would find in Earth’s atmosphere at an altitude of about 300 miles,” said Robert Tokar, researcher at Los Alamos National Laboratory and lead author of the paper published in Geophysical Research Letters.  “It’s not enough to sustain life, but—together with similar observations of other moons around Saturn and Jupiter—these are definitive examples of a process by which a lot of oxygen can be produced in icy celestial bodies that are bombarded by charged particles or photons from the Sun or whatever light source happens to be nearby.”

On Dione the energy source is Saturn’s powerful magnetic field. As the moon orbits the giant planet, charged ions in Saturn’s magnetosphere slam into the surface of Dione, stripping oxygen from the ice on its surface and crust. This molecular oxygen (O2) flows into Dione’s exosphere, where it is then steadily blown into space by — once again — Saturn’s magnetic field.

Cassini’s instruments detected the oxygen in Dione’s wake during an April 2010 flyby.

Molecular oxygen, if present on other moons as well (say, Europa or Enceladus) could potentially bond with carbon in subsurface water to form the building blocks of life. Since there’s lots of water ice on moons in the outer solar system, as well as some very powerful magnetic fields emanating from planets like Jupiter and Saturn, there’s no reason to think there isn’t more oxygen to be found… in our solar system or elsewhere.

Read the news release from the Los Alamos National Laboratory here.

 

Image credits: NASA/JPL/Space Science Institute. Research citation: Tokar, R. L., R. E. Johnson, M. F. Thomsen, E. C. Sittler, A. J. Coates, R. J. Wilson, F. J. Crary, D. T. Young, and G. H. Jones (2012), Detection of exospheric O2+ at Saturn’s moon Dione, Geophys. Res. Lett., 39, L03105, doi:10.1029/2011GL050452.

 

Posted on by VirtualAstro

Night Sky Guide: March 2012

Special thanks to Ninian Boyle astronomyknowhow.com for information in parts of this guide.

March brings us some wonderful sights to see in the night skies for those who are armed with binoculars, telescopes or just their eyes.

The brightest object in the night sky this month (apart from the Moon) is the Planet Venus. Venus and mighty Jupiter have already been providing a treat n the western skies for naked eye observers, but by the middle of the month the two planets will inch even closer. There are other planetary conjunctions this month as well.

The stars of spring are starting to become more prominent and the mighty constellation of Orion sets earlier in the west as the nights roll on. The constellations of Leo, Coma Berenices and Virgo herald the region of the sky known as the “Realm of the Galaxies” more so as the month moves on.

We have Comet Garradd visible all night long through binoculars, as it starts to fade from 7th to 8th magnitude. You can find it near the north celestial North pole near the star Kochab or Beta Ursa Minoris (The little Bear) on the 6th, and the star Dubhe in the Plough on the 21st. Scan this region with binoculars and you should pick it up as a faint misty patch of light.

The Sun continues to become more active as it approaches “Solar Maximum” in 2013 and this is a time when we need to be on our guard for sudden bursts of activity which can result in aurora for observers in high latitudes. Some large geomagnetic storms in the past have resulted in Aurora being spotted as far south as regions near the Caribbean and Mediterranean. Will we get a show like this soon?

Planets

There are going to be some excellent conjunctions this month, as planets and even sometimes the Moon are close together and appear in the same region of the sky.

Mercury. Keep an eye out for the tiny planet Mercury. This planet (closest one to the Sun) is notoriously difficult to see. The best time to try and catch it is on the 4th, low down near the western horizon shortly after sunset. Make sure the Sun has fully set if you plan to sweep the area with binoculars. Never ever look at the sun directly with binoculars, telescopes or your naked eyes – This will damage your eyes or permanently blind you!

Mercury just after sunset - Beginning of March

Mars reaches what we call ‘opposition’ on the 3rd, when it is directly opposite the Sun in the sky from our point of view here on Earth. This is the best time to view the “Red Planet” with a telescope. Try and see if you can spot its ice caps and dark markings. It will need a clear steady sky and a good magnification to see these well, try different coloured filters and even have a go at webcam imaging this amazing Planet. On the 7th the nearly full Moon lies 10-degrees to the south of the planet Mars. You’ll know its Mars by its distinct orange/pink colour.

Mars

Venus & Jupiter bring us the highlight of the month when they appear to be very close to each other and are just separated by 3 degrees on the 15th of March. The brightest out of the pair will be Venus with Jupiter below it and the pair will be an amazing sight – like a pair of heavenly eyes staring down at us. The two planets will be close to each other either side of the 15th, so there should be plenty of picture-taking opportunities. The Moon joins the Venus and Jupiter on the 25th and 26th and the thin crescent Moon will make the show even more stunning.

Venus Jupiter 15 March

Saturn rises later in the evenings in the constellation of Virgo, the rings are now nicely tilted towards us and the planet looks stunning right throughout the month. If you have never seen Saturn through a telescope before, you must see it! It is the most beautiful of all the planets and one of the reasons so many people get interested in astronomy.

Saturn

Moon phases

  • First Quarter – 1st March
  • Full Moon – 8th March
  • Last Quarter – 15th March
  • New Moon – 22nd March

Constellations

In March Orion is getting lower in the West and setting earlier as the spring constellations of Leo, Coma Berenices and Virgo come into view; this is the “Realm of the Galaxies.”

In the month of March the Earth’s orbit around the Sun means that during the night we see out from our own galaxy the ‘Milky Way’ into the depths of deep space. Because of this, we can see many other galaxies and some similar to our own, each contains hundreds of billions of stars. You will need a good telescope to see these amazing wonders; however a good pair of binoculars will show one or two faint fuzzy patches. Some of these faint fuzzy objects are many millions of light years distant.

A few brighter examples lay in the constellation of Leo the Lion. Have a look for M 95, M96 and M105; these are not far from Mars during March. You will need a dark Moonless night to see them well.

Another trio of galaxies still in the constellation of Leo are M65, M66 and NGC 3628 otherwise known as the ‘Leo Triplet’ A small telescope and a low to medium power should show these objects in the same field of view.

The region of sky within Leo, Coma and Virgo is packed with galaxies and whatever telescope you use, you will be sure to spot something.

For those of you without a telescope, see if you can discern the asterism of the ‘Bowl of Virgo’. This is a chain of five stars in a loose semi-circle pointing towards the ‘tail’ of Leo. The brightest star in the chain is Porrima. South of Porrima lays the brightest star in the constellation, called Spica. Saturn can be found to the east of this.

Credit: Adrian West
Posted on by Jason Major

Moons Large and Small

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It may be one of the best images from Cassini yet this year! Cloud-covered Titan and tiny Prometheus (can you see it just above the rings on the right?) are literally dwarfed by their parent Saturn in an image captured on Jan. 5, 2012.

Prometheus’ pinpoint shadow can also be seen on Saturn’s cloud tops, just inside the thin, outermost F ring shadow at bottom left.

The two moons themselves couldn’t be more different; Titan, 3,200 miles (5,150 km) wide, is wrapped in a nitrogen and methane atmosphere ten times thicker than Earth’s and is covered with vast plains of dark hydrocarbon dunes and crisscrossed by rivers of liquid methane.

Prometheus imaged by Cassini in Dec. 2009.

Prometheus, on the other hand, is a potato-shaped shepherd moon 92 miles long and 53 miles wide (148 x 53 km) that orbits Saturn just inside the narrow, ropy F ring. While it doesn’t have an atmosphere, it does create some impressive effects on the icy material in the ring!

Another moon, Pandora, casts its shadow onto Saturn just outside the F ring shadow at bottom center. 50 miles (80 km) wide, Pandora shepherds the outer edge of the F ring but is itself not visible in this image. Watch an animation here.

This image was featured on the Cassini Imaging Central Laboratory for Operations (CICLOPS) website on Feb. 28, 2012. The view looks toward the southern, unilluminated side of the rings from about 1 degree below the ringplane.

Image credit: NASA / JPL / Space Science Institute.

Posted on by VirtualAstro

Night Sky Guide: February 2012

Special thanks to Ninian Boyle astronomyknowhow.com for information in parts of this guide

This month, the Solar System gives us a lot to observe and we’ll even start to see the ‘spring’ constellations appear later in the evenings. But February still has the grand constellations of winter, with mighty Orion as a centrepiece to long winter nights.

The Sun has finally started to perform as it should as it approaches “Solar Maximum.” This means we get a chance to see the northern lights (Aurora), especially if you live in such places as Scotland, Canada, Scandinavia, or Alaska or the southern light (Aurora Australis) if you live in the southern latitudes of South America, New Zealand and Australia. Over the past few weeks we have seen some fine aurora displays and will we hope to seesome in February!

We have a bit of a treat in store with a comet being this month’s favourite object with binoculars as well, so please read on to find out more about February’s night sky wonders.

You will only need your eyes to see most of the things in this simple guide, but some objects are best seen through binoculars or a small telescope.

So what sights are there in the February night sky and when and where can we see them?

Aurora

Looking north from the science operations center at Poker Fla,Alaska. Credit: Jason Ahrns.

The Aurora or Northern Lights (Aurora Borealis) have been seen from parts of Northern Europe and North America these last few weeks. This is because the Sun has been sending out huge flares of material, some of which have travelled towards us slamming into our magnetic field. The energetic particles then follow the Earth’s magnetic field lines towards the poles and meet the atoms of our atmosphere causing them to fluoresce, similar to what happens in a neon tube or strip light.

The colours of the aurora depend on the type of atom the charged particles strike. Oxygen atoms for example usually glow with a green colour, with some reds, pinks and blues. So the more active the Sun gets, the more likely we are to see the Northern (or Southern) Lights.

All you need to see aurora is your eyes, with no other equipment is needed. Many people image the aurora with exposures of just a few seconds and get fantastic results. Unfortunately auroras are “space weather” and are almost as difficult to predict as normal terrestrial weather, but thankfully we can be given the heads up of potential geomagnetic storms by satellites monitoring the Sun such as “STEREO” (Solar TErrestrial RElations Observatory).

Spaceweather.com is a great resource for aurora and other space weather phenomenon and the site has real-time information on current aurora conditions and other phenomenon.

Planets

Mercury is too close to the Sun to be seen at the beginning of the month, but will be visible very low in the south west from the 17th onwards. At the end of February Mercury will be quite bright at around mag -0.8 and will be quite a challenge. It can be seen for about 30 minutes after sunset.

Venus will improve throughout the month in the south west and will pass within half a degree of Uranus on the 9th of February. You can see this through binoculars or a small telescope. On the 25th Venus and the slender crescent Moon can be seen together a fabulous sight. At the end of month Venus closes in on Jupiter for a spectacular encounter in March.

Venus

Mars can easily be spotted with the naked eye as a salmon pink coloured “star” and starts off the month in the constellation of Virgo and moves into Leo on the 4th. Mars is at opposition on March 3rd but is also at its furthest from the Sun on the 15th February making this opposition a poor one with respect to observing due to its small apparent size. The planet will still be visually stunning throughout the month.

Mars

Jupiter starts off the month high in the south as darkness falls and is still an incredibly bright star-like object. Through good binoculars or a small telescope you can see its four Galilean moons – a fantastic sight. On the 8th at around 19:50 UT, Europa will transit Jupiter and through a telescope you will see the tiny moons shadow move across its surface. Throughout February, Jupiter moves further west for its close encounter with Venus in March.

Jupiter

Saturn rises around midnight in the constellation of Virgo and appears to be a bright yellowish star. Through a small telescope you will see the moon Titan and Saturn’s rings as well.

Saturn

Uranus is now a binocular or telescope object in the constellation of Pisces. On the 9th Uranus and the planet Venus will be within half a degree of each other.

Uranus

Neptune is not visible this month.

Comets

Comet Garradd Credit: astronomy.com

Comet Garradd is still on show early in the month — if you have binoculars — and as the month progresses the viewing should improve. You can find the comet in the constellation of Hercules not far from the globular cluster M92. It is about a half a degree away or around the same width as the full Moon. The comet is around magnitude 7 or a little fainter than the more famous globular cluster M13 also to be found in Hercules, so you will definitely need binoculars to see it. The comet is heading north over the course of the month which should mean that it will become a little easier to see. At the beginning of the month you will have to get up early to see it, the best time being around 5:30 to 6:30 GMT. By the end of the month though, it should be visible all night long.

Moon phases

  • Full Moon – 7th February
  • Last Quarter – 14th February
  • New Moon – 21st February

Constellations

In February, Orion still dominates the sky but has many interesting constellations surrounding it.

Above and to the left of Orion you will find the constellation of Gemini, dominated by the stars Castor and Pollux, representing the heads of the twins with their bodies moving down in parallel lines of stars with each other.

Legend has it that Castor and Pollux were twins conceived on the same night by the princess Leda. On the night she married the king of Sparta, wicked Zeus (disguised as a swan) invaded the bridal suite, fathering Pollux who was immortal and twin of Castor who was fathered by the king so was mortal.

Castor and Pollux were devoted to each other and Zeus decided to grant Castor immortality and placed Castor with his brother Pollux in the stars.

Gemini has a few deep sky objects such as the famous Eskimo nebula and some are a challenge to see. Get yourself a good map, Planisphere or star atlas and see what other objects you can track down.

Credit: Adrian West

 

Posted on by Amy Shira Teitel

Astronomers Find Saturn’s Possible Cosmic Doppelgänger

Credit: Michael Osadciw/University of Rochester

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By analyzing the silhouette of an exoplanet passing in front of its parent star some 420 light years from Earth, a team of astrophysicists has discovered an exoplanet that just might turn out to be Saturn’s cosmic doppelgänger. 

Assistant Professor of Physics and Astronomy at Rochester University Eric Mamajek and graduate student Mark Pecaut studied data from the international SuperWASP (Wide Angle Search for Planets) and All Sky Automated Survey (ASAS) project.

An artist's impression of a brown dwarf surrounded by a cloud of proto-planet dust. Image credit: JPL

They were looking at the star’s light pattern; periodic dimming is a telltale sign that a planet is passing in front of it. A spherical planet will dim a star’s light regularly. As seen from Earth, the star’s light will dim as the planet starts to cross it, getting darker until it reaches a point of maximum dimness – the point when the planet is directly between the Earth and the star. Then, the light will get brighter at the same pace as it previously dimmed.

But in December 2010, they noticed something odd. As they analyzed data gathered over a 54 day period in early 2007, the star 1SWASP J140747.93-394542.6 dimmed irregularly. The object passing in front of it couldn’t be a spherical planet, so what was it?

The object had an elliptical silhouette, it was blocking the star’s light in an intermittent and irregular pattern, and was obscuring a significant portion of the star’s light. At one point in the pass, 95 percent of the star’s light was obscured, most likely by dust.

“When I first saw the light curve, I knew we had found a very weird and unique object,” said Mamajek. “After we ruled out the eclipse being due to a spherical star or a circumstellar disk passing in front of the star, I realized that the only plausible explanation was some sort of dust ring system orbiting a smaller companion—basically a ‘Saturn on steroids.'” Rings were the likeliest culprit of the oscillating dimness in the star’s light.

“This marks the first time astronomers have detected an extrasolar ring system transiting a Sun-like star, and the first system of discrete, thin, dust rings detected around a very low-mass object outside of our solar system,” said Mamajek. But there are still some major questions about what exactly has been discovered.

A size comparison between the Sun, a low mass star, a brown dwarf, Jupiter, and the Earth. Image credit: NASA

It could be a very low-mass star, brown dwarf, or gas giant planet. But it’s still too early to know either way. To arrive at some answer, they will need to determine the object’s mass.

A planet that size will exert a gravitational pull on its star in the same way that Jupiter tugs on the Sun. The amount of wobbling this gravitational interaction creates can reveal the mass of the object and give astronomers a clue about what it might be. If it has a mass between 13 and 75 times that of Jupiter, it will likely be a brown dwarf. If it’s any smaller, astronomers will know that it’s likely a planet more similar to Saturn.

Two of Saturn's shepherd moons keep the planet's F ring in check. Image Credit: NASA/JPL

The object itself isn’t the only interesting part of the find; Mamajek is particularly interested in the gaps between the apparent rings that are optically similar to those around Saturn. Gaps are usually indicative of objects within the rings with enough gravitational influence to shape them, like Saturn’s shepherd moons.

But even if the rings turn out to be a cloud of dust, the discovery will be no less exciting. If the object turns out to be a brown dwarf with a cloud of dust, Mamajek thinks it’s likely his team has observed the late stages of planet formation. Or, if the object is a large planet, they may be observing the formation of moons around the giant planet.

Either way it’s an awesome discovery. As cool as finding Saturn’s twin would be, watching moons form around another planet would be equally fascinating. The team’s findings will be published in an upcoming issue of the Astronomical Journal.

Source: University of Rochester.

Posted on by Tammy Plotner

Storms And Lakes On Titan Revealed By Computer Modeling

An artist's imagination of hydrocarbon pools, icy and rocky terrain on the surface of Saturn's largest moon Titan. Image credit: Steven Hobbs (Brisbane, Queensland, Australia).

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Thanks to the Cassini mission and the Huygens probe, we’ve glimpsed a wet world when science took a look at Saturn’s moon, Titan. Its atmosphere is rich in methane and its average temperature is about -300 degrees Fahrenheit (about 90 kelvins). Although the chemical composition is different than ours, Titan still has similar features such as clouds, fog, rain and even lakes. However, the origin of these features haven’t really been well explained until now.

Researchers at the California Institute of Technology (Caltech) have been hard at work creating a computer program based on observations made by Cassini imaging and radar that could help explain Titan’s weather patterns and liquid surface deposits. One major oddity was discovered in 2009 when Oded Aharonson, Caltech professor of planetary science, and his team confirmed Titan’s lakes appeared to be gathered around its poles – more predominately in the northern hemisphere than compared to the south – yet that’s not the only curiosity. The areas around the equator were suspected to be dry, but the Huygens probe revealed areas of run-off and four years later researchers observed a storm system delivering moisture. Need more? Then check out the clouds observed by ground-based telescopes… They gather around southern middle and high latitudes during Titan’s southern hemisphere summer season.

“We can watch for years and see almost nothing happen. This is bad news for people trying to understand Titan’s meteorological cycle, as not only do things happen infrequently, but we tend to miss them when they DO happen, because nobody wants to waste time on big telescopes—which you need to study where the clouds are and what is happening to them—looking at things that don’t happen,” explains Mike Brown of the California Institute of Technology (Caltech).

Sure. The researchers have worked hard at creating models that could explain these exotic weather features, but such explanations involve way out theories, such as cryogenic volcanoes that blast out methane vapor to cause clouds. However, the latest computer renderings are much more basic – the principles of atmospheric circulation. “We have a unified explanation for many of the observed features,” says Tapio Schneider, the Frank J. Gilloon Professor of Environmental Science and Engineering. “It doesn’t require cryovolcanoes or anything esoteric.” Schneider, along with Caltech graduate student Sonja Graves, former Caltech graduate student Emily Schaller (PhD ’08), and Mike Brown, the Richard and Barbara Rosenberg Professor and professor of planetary astronomy, have published their findings in the January 5 issue of the journal Nature.

Why is this data set different than its predecessors? According the Schneider, these new simulations were able to reproduce cloud patterns which match factual observations – right down to the distribution of lakes. “Methane tends to collect in lakes around the poles because the sunlight there is weaker on average,” he explains. “Energy from the sun normally evaporates liquid methane on the surface, but since there’s generally less sunlight at the poles, it’s easier for liquid methane there to accumulate into lakes.” Because Titan has an elongated orbit, it’s a bit further away during the northern hemisphere summer allowing for a longer rainy season and thus a stronger accumulation of lakes.

So what about storms? Near the equator, Titan isn’t very exciting – or is it? Originally it was theorized the area was almost desert-like. That’s why when the Huygens probe discovered evidence of run-off, it became apparent that existing models could be wrong. Imagine the surprise when Schaller, Brown, Schneider, and then-postdoctoral scholar Henry Roe discovered storms in this supposedly arid region in 2009! No one could figure it out and the programs did little more than predict a drizzle. With the new model, heavy rains became a possibility. “It rains very rarely at low latitudes,” Schneider says. “But when it rains, it pours.”

So what else makes the new Titan weather computer model even more unique? This time it runs for 135 Titan years and links the methane lakes – and how methane is distributed – to its atmosphere. According to the research, this matches current Titan weather observations and will help to predict what could be seen in coming years. Making testable predictions is “a rare and beautiful opportunity in the planetary sciences,” Schneider says. “In a few years, we’ll know how right or wrong they are.”

“This is just the beginning,” he adds. “We now have a tool to do new science with, and there’s a lot we can do and will do.”

Original Story Source: California Institute of Technology News Release. For Further Reading: Caltech Scientists Discover Storms in the Tropics of Titan.