As we on Earth prepare for the best time in 2012 to view Saturn, the Cassini spacecraft – cruising in orbit around Saturn since 2004, studying its rings and moons – has returned this beautiful image. It’s Saturn’s moon Enceladus in a crescent phase, with Saturn’s rings in the bckground. The image was taken with Cassini’s narrow-angle camera on January 4, 2012 at a distance of 181,000 miles (291,000 km) from Enceladus. Image scale is about 2 km per pixel.

Best view of Saturn starts with retrograde on February 8

Saturn’s moon rains water onto Saturn

Image Credit: NASA/JPL–Caltech/Space Science Institute

Click here to expand image above

The famous and mystifying jets of water ice emanating from the south polar region of Enceladus are faintly visible in the image above.

Enceladus and its jets.

In the image above, the jets appear as a small white blur below Enceladus’ dark pole, down and to the right of the illuminated part of the moon’s surface. You can see it better if you click to enlarge. Scientists at the European Space Agency enhanced the image’s contrast to increase the jets’ visibility.

The image on the right also shows this amazing feature on Saturn’s moon.

The sunlit terrain seen here is on the trailing hemisphere of Enceladus, whose diameter is 313 miles (504 km). North is up in the image above. This view looks toward the northern, sunlit side of the rings from just above the ringplane.

Bottom line: The Cassini spacecraft returned a beautiful image of Saturn’s moon Enceladus, with Saturn’s ring, on January 4, 2012. The image faintly shows the jets spewing water from Enceladus onto Saturn. Meanwhile, the best time to view Saturn in the night sky is upon us.

Via European Space Agency

Give me 5 minutes, and I’ll give you Saturn in 2012

The European Space Agency (ESA) reported today (February 6, 2012) that its Mars Express spacecraft has strong evidence for an ocean once covering part of Mars.

The spacecraft used radar to detect sediments reminiscent of an ocean floor within the boundaries of previously identified, ancient shorelines on Mars.

A former ocean on Mars? Image Credit: ESA, C. Carreau

Jérémie Mouginot, Institut de Planétologie et d’Astrophysique de Grenoble (IPAG) and the University of California, Irvine, and colleagues have analysed more than two years of data and found that the northern plains are covered in low-density material. Dr. Mouginot said:

Mars Express studies Mars with radar

We interpret these as sedimentary deposits, maybe ice-rich. It is a strong new indication that there was once an ocean here.

The existence of oceans on ancient Mars has been suspected before and features reminiscent of shorelines have been tentatively identified in images from various spacecraft.

But a Mars ocean remains a controversial issue.

Read more from ESA

Not all Martian gullies formed by flowing water

Space Exploration Technologies Corporation (SpaceX) is aiming to complete the first launch of a commercially built craft to the International Space Station (ISS) on March 20, 2012. But the launch might be pushed back to early April, 2012, ISS program manager Mike Suffredini announced in a press briefing on February 2. The original launch date was set for February 7, but the schedule proved to be too tight. These announcements come about a year after SpaceX’s historic first recovery of a commercial craft from orbit, after their Dragon spacecraft successfully orbited Earth two times in late 2010.

SpaceX Dragon craft

The first SpaceX flight to ISS will be a demonstration flight, launching out of Cape Canaveral in Florida. During the briefing, Suffredini said:

I don’t think they’re going to make March 20. I think it will be early April. We won’t fly until we’re ready . . . . There is not much margin in their schedule and on a new vehicle schedules without margins tend to move to the right.

SpaceX’s Dragon craft is capable of carrying cargo and, eventually, crew to the ISS, a pressing need for the United States now that the shuttle program has ended. The Dragon is designed to be reusable, as the shuttles were. The company is also aiming to to develop the first-ever reusable launch vehicle. Dragon will be launched on SpaceX’s Falcon 9 rocket. It was the Falcon 9 that launched SpaceX’s Dragon craft on December 8, 2010, for its successful two orbits of Earth and history-making first commercial recovery of a craft from orbit.

Dragon is lifted inside a processing hangar at Cape Canaveral. Credit: NASA/Kim Shiflett

Though development of the ISS launch is behind schedule, Suffredini expressed confidence in the way things are proceeding. And on February 1, SpaceX successfully test fired its SuperDraco engine, an advanced version of the Draco engine currently used on Dragon. The SuperDraco is part of Dragon’s launch-escape system, and, because it is not jettisoned like other escape systems, allows astronauts to escape to safety at any point during a launch, not just the first few minutes.

Falcon 9 lifts off for its first flight. Credit: SpaceX/Chris Thompson

SpaceX currently has a $1.6 billion contract with NASA’s Commercial Orbital Transportation Services (COTS) program, representing 12 flights to the ISS. More flights can be added and the contract can be increased to up to $3.1 billion. The company’s current launch manifest calls for two launches to resupply the ISS in 2012, two in 2013, three in 2014, and five in 2015. SpaceX is also planning to use Dragon to conduct in-orbit science independent of NASA, in a program called Dragon Lab.

Bottom line: Space Exploration Technologies Corporation (SpaceX) hopes to launch the first commercially built craft to the International Space Station (ISS) on March 20, 2012. But the launch might be pushed back to early April, 2012. These announcements come about a year after SpaceX’s historic first recovery of a commercial craft from orbit, after their Dragon spacecraft successfully orbited Earth two times in late 2010. Dragon will be launched to ISS on SpaceX’s Falcon 9 rocket. A new launch-escape system and SuperDraco engine are being developed for future missions.

NASA released the first video from GRAIL, its newest moon mission, yesterday (February 1, 2012). GRAIL stands for Gravity Recover and Interior Laboratory. It consists of two robotic probes – once called GRAIL-A and GRAIL-B, but now officially named Ebb and Flow – that are orbiting the moon in tandem, using minute variations in the radio signals between them to help scientists to study the moon’s gravity. The overall goal of the mission is to learn more about the formation of our solar system. In the meantime, GRAIL has released its first video, showing the mysterious far side of the moon. You can view it below.

The video, taken by Ebb as part of a January 19 test, images the far side of the moon, a rugged, crater-laden place that never faces the Earth.

It begins at the moon’s north pole, flies over the 560-mile-wide Mare Oriental impact crater and then makes its way to the lunar south pole, finishing up with the 93-mile-wide Drygalski crater, inside of which is visible a star-shaped central peak created by an impact millions of years ago.

A view of the moon's south pole.

The GRAIL probes were given their new names as recently as January 2012 after a class from Emily Dickinson Elementary School in Bozeman, Montana won a nationwide naming contest. Hence Ebb and Flow.

The mission is the first robotic planetary mission to carry equipment whose sole purpose is education and outreach. They each carry a MoonKAM (Moon Knowledge Acquired by Middle school students), which will allow students across the U.S. to study specific parts of the moon.

Students in the MoonKAM program will send requests for images of specific areas to the Mission Operations Center in San Diego, which will then send the schools the images. So far, more than 2,500 participants have signed up. They’ll begin using pictures in mid-March 2012, which is when Ebb and Flow’s science phase will begin. Scientists plan on testing Flow’s MoonKAM at a later date.

NASA says the MoonKAM program is designed to inspire students to consider careers in science and engineering. In a press release, Maria Zuber, GRAIL principle investigator, who narrates the clip, said:

The quality of the video is excellent and should energize our MoonKAM students as they prepare to explore the moon.

GRAIL spacecraft at moon. Image Credit: NASA

Bottom line: The first video from NASA’s Gravity Recover and Interior Laboratory (GRAIL) mission was released February 1, 2012. The two spacecraft in the GRAIL mission, named Ebb and Flow by school children in January 2012, are now orbiting the moon with the goal of studying the moon’s gravity. Ebb captured this first video, showing the moon’s far side. In March 2012, students in the MoonKAM program will begin using images from GRAIL.

 NASA announces winners of student contest to name GRAIL spacecraft

GRAIL spacecraft will use lunar gravity to peer inside moon

In early 2012, astronomers announced that the Kepler satellite has found two additional gas giant planets – which they’ve labeled Kepler-34b and Kepler-35b – orbiting binary or double star systems. The planets are approximately Saturn-sized. Only one other planet orbiting a double star – Kepler-16b – was previously observed; its discovery was announced in September, 2011. The Kepler collaboration reported the two most recent planets of double stars on January 11, 2012, in the journal Nature.

Kepler-35 system. Artist: Lynette Cook / extrasolar.spaceart.org

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Kepler-34b orbits its two sun-like stars every 289 days, and the stars orbit one another every 28 days. Kepler-35b orbits its smaller and cooler host stars every 131 days, and the stellar pair orbit each other every 21 days. The planets reside too close to their parent stars to be in the “habitable zone”- the region where liquid water could exist on a planet’s surface.

Planets orbiting double stars were formerly the stuff of Issac Asimov novels and George Lucas films. But the authors of the Nature article estimate that for short-period binary systems – where two stars orbit each other on timescales similar to those mentioned above – at least 1% of them will host planets. This amounts to millions of systems, at least, not to mention the longer period double systems (some double stars take many years to orbit each other once) which the Nature article does not analyze.

Kepler 34b, Courtesy of W. Wilson et al.

As of this report, the Kepler satellite has currently located 2,326 candidate exoplanets, or planets orbiting stars other than our sun, but – other than the three planets mentioned above – all of these planets orbit single stars. Meanwhile, roughly one-third of all the star systems in the Milky Way are believed to be binary systems, where two gravitationally bound stars orbit each other. Only a handful of other systems are believed to be comprised of more than two stars, by the way. The star Castor in the constellation Gemini is believed to be a sextuple star system: three orbiting pairs of binaries!

The Kepler satellite, named in honor of the 17th century astronomer Johannes Kepler, was launched in 2009 with the precise mandate of locating Earth-like exoplanets, planets orbiting other stars. Prior to Kepler, while a few exoplanets had been discovered in the past, they were all very massive planets like Jupiter. Very massive planets, while relatively easy to detect, do not offer the possibility of Earth-like life. The Kepler satellite has offered us a look at the diverse planet landscape our galaxy offers.

The artist's rendering depicts the multiple planet systems discovered by NASA's Kepler mission. Out of hundreds of candidate planetary systems, scientists had previously verified six systems with multiple transiting planets (denoted here in red). Now, Kepler observations have verified planets (shown here in green) in 11 new planetary systems. Many of these systems contain additional planet candidates that are yet to be verified (shown here in dark purple). For reference, the eight planets of the solar system are shown in blue. Credit: NASA Ames/Jason Steffen, Fermilab Center for Particle Astrophysics

Click here to expand image above

The Kepler satellite is also looking particularly close at double star systems to see what types of planets they host. These findings will provide important clues to how these systems form. Are double star systems formed through collisions of separate star systems, or do these binaries form from the same ‘star stuff’ simultaneously? Are double star systems more likely to host planets than single star systems? Kepler hopes to begin answering many of these questions.

Astronomers detect binary star systems in a number of different ways. Some binaries are close enough to be resolved optically through telescopes. We can actually see the two separate stars! For star systems farther away, more clever methods must be employed.

Measuring the luminosity, or brightness, of distant points of light provides clues as to whether not not they might actually be double stars. The system Algol, the Demon Star, found in the constellation Perseus, was noticed by early stargazers to have a varying luminosity. It wasn’t until 1783 that early scientists recorded its brightness varying in a repetitive pattern, dimming about every three days for 10 hours. They proposed that Algol was actually a binary system with one star eclipsing the other for those 10 hours.

The frequencies of the emitted light from a star system are also utilized to determine the nature of the system. Stars, as our sun, produce electromagnetic radiation over a range of frequencies, or colors. Our sun actually produces mostly visible light, but also infrared and radio waves in the low frequency side of the spectrum, as well as ultraviolet and x-ray radiation in the upper frequency bands. These electromagnetic waves behave similarly to the sound waves we’re more familiar with. We’ve all noticed the Doppler effect as vehicles with sirens have passed us: the sound waves moving towards us become higher pitched, or higher frequency, the sound waves moving away from us become lower pitched. The same effect happens with the electromagnetic waves that are light. Astronomers can measure the light from these binary systems simultaneously become repetitively higher and lower ‘pitched,’ allowing us to ascertain that that there are in fact two stars simultaneously moving towards and away from us.

The Kepler satellite, planet-hunter extraordinaire. Image Credit: NASA

Nowadays, once astronomers find a double star system, the task may turn to detecting any possible planets in the system. The Kepler satellite utilizes a very similar method to the aforementioned luminosity measurement. Kepler maintains its camera on a particular section of the sky, towards the constellations Cygnus, Lyra, and Draco. It then patiently waits until one of the stars momentarily dip in luminosity. This is the signal of an exoplanet. This dimming is interpreted as a planet transiting across the face of the star. By measuring the amount of dimming and the frequency of occurrence, the characteristics of the planet, such as size and mass, can be ascertained. With this little bit of information, it is possible to determine if the planet is Earthlike or more similar to the giant gaseous planets in the outer reaches of our solar system, such as Jupiter.

Though its recent discovery of Earthlike planets as well as planets orbiting double stars, the Kepler satellite is offering us an unparalleled view into the diverse solar landscape.

Kepler satellite homepage

Milky Way has 100 billion planets, astronomers say

Earthlike moons in habitable zones of double suns

Hello asteroid 433 Eros … and goodbye. We got a slightly panic-y sounding comment from a Facebook friend yesterday about asteroid 433 Eros, which will be making its closest approach to Earth since 1975 today (January 31, 2012). Afterwards, I saw a few misleading headlines about this event. Yes, Eros is passing closer on Tuesday than it has in some decades. In fact, although I had a tough time finding the information, its perigee – or closest point to Earth – appears to be January 31 at around 11 UTC – or 5 a.m. CST – which means it has already passed closest. The closest point of Eros was not very close. At its closest, it was about 16,608,000 miles (26,729,000 km) away – some 70 times the moon’s average distance. It was some 80 times farther than the closest point of a much smaller body that passed safely within the moon’s orbit on November 8, 2011. That object was called 2005 YU55. So there was – and is – absolutely no danger at all from 433 Eros at this 2012 passage.

Asteroid Eros on January 31, 2012

Even though it is closer than since 1975 – and even though it won’t come this close again until 2056 – Eros won’t be close enough to view with the eye alone. But amateur astronomers with backyard telescopes have been watching it and will continue to observe it for probably another week or so at least.

Skyandtelescope.com has information on an Eros Parallax Project, a chance for amateur gazers to contribute to science. In fact, Eros helped astronomers pin down the exact distance to the sun in the 20th century, first with a worldwide program of observations of Eros as a passage much like today’s in 1900-1901, then with even greater exactitude at another close passage in 1930–1931. As skyandtel says on its website:

A similar close pass of Eros in 1931 allowed professional astronomers to refine the true scale of the solar system, starting with the Earth-Sun distance (the astronomical unit). This was the last great improvement in the scale of the solar system until interplanetary radar began making direct distance measurements in the 1960s.

If you have a small telescope, and want to try to observe Eros, you’ll find a finder chart and article from skyandtelescope.com.

Asteroid 433 Eros

The NEAR Shoemaker spacecraft captured this movie of Eros on December 3-4, 2000, while in orbit 125 miles (200 km) from the center of this asteroid. Image Credit: NASA / Johns Hopkins University Applied Physics Laboratory

Those of us without small telescopes will not see 433 Eros. It’s too faint to be seen with the eye alone. Eros is a near-Earth asteroid (NEA). It’s about 21 miles (34 km) wide. It was discovered in 1898 by astronomers Carl Gustav Witt in Berlin and Auguste Charlois in Nice.

Eros also made history in 2000, when NASA’s NEAR Shoemaker probe approached it, went into orbit around it and even made a soft landing on its surface. This was the first such orbit of an asteroid. NEAR took over 160,000 images of Eros’ surface and helped researchers conclude that this asteroid is a solid object rather than a “flying rubble pile” as some had previously thought.

Bottom line: Asteroid 433 Eros made its closest approach to Earth since 1975 on January 31, 2012 at 11 UTC (5 a.m. CST). At its closest, it was be about 16.6 million miles (26.7 million km) away – some 70 times the moon’s average distance. There is absolutely no danger at all.

Astronomer Judy Cheng of the University of California, Santa Cruz was part of a science team that used a giant survey of stars to reveal something new about how our Milky Way galaxy formed. The team found evidence that the inner disk of the Milky Way grew organically from the inside out, like the rings of a tree. The surrounding outer disk, according to Cheng, likely formed all at once. EarthSky’s Jorge Salazar spoke to Cheng this week at the 219th meeting of the American Astronomical Society held in Austin, Texas, January 9-12, 2012.

Astronomer Judy Cheng of UC Santa Cruz.

Cheng’s study looked at data from the Sloan Extension for Galactic Understanding and Exploration 2 (SEGUE-2), which is part of the Sloan Digital Sky Survey-III project, operating from the Apache Point Observatory in New Mexico. The star survey collected starlight of more than 118,000 stars to measure their motions and inner chemistry.

The first generation of stars in the Milky Way are thought to have consisted entirely of the elements hydrogen and helium. Over time, those early stars turned some of their hydrogen and helium into heavier elements, like calcium or iron. When those stars died, the heavier elements they produced became part of the next generation of stars. As new stars were born and the Milky Way disk grew, each generation had more calcium, iron, and other heavy elements. Thus, scientists can learn which parts of our galaxy have seen several generations of stars come and go, simply by looking at the metal content of stars in that part of the galaxy. Judy Cheng told EarthSky:

The thick and thin of it. Disks of our Milky Way Galaxy.

What we did was, we looked at the elemental abundances of stars at different positions in the disk of the Milky Way. The disk is what you normally see when you go out on a clear night and you see a bright band of stars across the sky. That’s the Milky Way disk. What we looked at was how the amount of metals in the stars varied as you looked at different positions in the galaxy.

Stars in the plane of our galaxy showed a drop off in metals the further out from center; not so for stars away from the galactic plane.

Cheng’s team looked at different parts of the entire galactic disk. That disk can be divided into two components. There’s a thin disk, which is the milky band of stars what one can actually see in the sky on a clear night. Then there’s a surrounding thick disk, which is not visible from the Earth but is made up of much older stars, according to Cheng. Those stars can go very far from the plane of the galaxy, which is why it’s called a thick disk. Cheng told EarthSky what she found:

What we are finding is that when we look at how the metals vary as a function of distance from the center of the galaxy, when we looked at the thin disk, we see that there are more metals in the inner part of the galaxy than in the outer parts. And that tells us that the thin disk of the galaxy formed from the inside out. But when we look at the thick disk of the galaxy, we don’t see any change in the metals as you look farther from the center of the disk. So that tells us either that the thick disk all formed at once, and so that all of the metals in the disk accumulated the metal content at the same rate. Or it could also be that the thick disk formed inside out, like the thin disk, but things have gotten mixed around so well over time that we don’t see any change in the metal content farther from the center of the galaxy.

The 2.5-meter Sloan telescope at Apache Point Observatory, which did the SEGUE-2 star survey.

Cheng explaineed that one goal of the SEGUE surveys is to understand how the Milky Way got assembled. In a sense, how all the pieces of the puzzle of our galaxy came together. Cheng told EarthSky:

The idea behind SEGUE is to use the stars that we observe and study their chemical compositions, look at their motions and also their positions in the galaxy to understand how the stars got there, when they were born, and how they fit into our picture of the galaxy as having this thin disk, and a thick disk. And there’s also different components of the galaxy as well. There’s a halo that goes out farther and is made up of even older stars. And by looking at all of these types of stars in SEGUE, we can try to put together a picture of how these stars got to where we see them today.

Bottom line: Astronomer Judy Cheng of UC Santa Cruz led a survey of stars called SEGUE-2 that found the thin disk of our Milky Way galaxy grew differently than its thick disk.

Milky Way has 100 billion planets, astronomers say

Doomed gas cloud stretched as nears Milky Way black hole

Previously I wrote a blog called Ten things you may not know about the solar system, from a list by my friend Dr. Victor Anderson of the Community College of Aurora (Colorado). This time I blog my own list of interesting facts about stars:

10) Every star you see in the night sky is bigger and brighter than our Sun
Of the 5,000 or so stars brighter than magnitude 6, only a handful of very faint stars are approximately the same size and brightness of our Sun and the rest are all bigger and brighter. Of the 500 or so that are brighter than 4th magnitude (which includes essentially every star visible to the unaided eye from a urban location), all are intrinsically bigger and brighter than our Sun, many by a large percentage. Of the brightest 50 stars visible to the human eye from Earth, the least intrinsically bright is Alpha Centauri, which is still more than 1.5 times more luminous than our Sun, and cannot be easily seen from most of the Northern Hemisphere.

9) You can’t see millions of stars on a dark night
Despite what you may hear in TV commercials, poems and songs, you cannot see a million stars … anywhere. There simply are not enough close enough and bright enough. On a really exceptional night, with no Moon and far from any source of lights, a person with very good eyesight may be able to see 2000-2500 stars at any one time. (Counting even this small number still would be difficult.). So the next time you hear someone claim to have seen a million stars in the sky, just appreciate it as artistic license or exuberant exaggeration – because it isn’t true!

8) Red hot and cool ice blue – NOT!
We are accustomed to referring to things that are red as hot and those that are blue as cool. This is not entirely unreasonable, since a red, glowing fireplace poker is hot and ice, especially in glaciers and polar regions, can have a bluish cast. But we say that only because our everyday experience is limited. In fact, heated objects change color as their temperature changes, and red represents the lowest temperature at which a heated object can glow in visible light. As it gets hotter, the color changes to white and ultimately to blue. So the red stars you see in the sky are the “coolest” (least hot), and the blue stars are the hottest!

7) Stars are black bodies
A black body is an object that absorbs 100 percent of all electromagnetic radiation (that is, light, radio waves and so on) that falls on it. A common image here is that of a brick oven with the interior painted black and the only opening a small window. All light that shines through the window is absorbed by the interior of the oven and none is reflected outside the oven. It is a perfect absorber. As it turns out, this definition of being perfect absorbers suits stars very well! However, this just says that a blackbody absorbs all the radiant energy that hits it, but does not forbid it from re-emitting the energy. In the case of a star, it absorbs all radiation that falls on it, but it also radiates back into space much more than it absorbs. Thus a star is a black body that glows with great brilliance! (An even more perfect black body is a black hole, but of course, it appears truly black, and radiates no light.)

6) There are no green stars
Although there are scattered claims for stars that appear green, including Beta Librae (Zuben Eschamali), most observers do not see green in any stars except as an optical effect from their telescopes, or else an idiosyncratic quirk of personal vision and contrast. Stars emit a spectrum (“rainbow”) of colors, including green, but the human eye-brain connection mixes the colors together in a manner that rarely if ever comes out green. One color can dominate the radiation, but within the range of wavelengths and intensities found in stars, greens get mixed with other colors, and the star appears white. For stars, the general colors are, from lower to higher temperatures, red, orange, yellow, white and blue. So as far as the human eye can tell, there are no green stars.

5) The Sun is a green star
That being said, the Sun is a “green” star, or more specifically, a green-blue star, whose peak wavelength lies clearly in the transition area on the spectrum between blue and green.  This is not just an idle fact, but is important because the temperature of a star is related to the color of its most predominate wavelength of emission. (Whew!) In the Sun’s case, the surface temperature is about 5,800 K, or 500 nanometers, a green-blue. However, as indicated above, when the human eye factors in the other colors around it, the Sun’s apparent color comes out a white or even a yellowish white.

4) The Sun is a “dwarf” star
We are accustomed to think of the Sun as a “normal” star, and in many respects, it is. But did you know that it is a “dwarf” star? You may have heard of a “white dwarf,” but that is not a regular star at all, but the corpse of a dead star. Technically, as far as “normal” stars go (that is, astronomical objects that produce their own energy through sustained and stable hydrogen fusion), there are only “dwarfs,” “giants” and “supergiants.” The giants and supergiants represent the terminal (old age) stages of stars, but the vast majority of stars, those in the long, mature stage of evolution (Main Sequence) are all called “dwarfs.” There is quite a bit of range in size here, but they are all much smaller than the giants and supergiants. So technically, the Sun is a dwarf star, sometimes called “Yellow Dwarf” in contradiction to the entry above!

3) Stars don’t twinkle
Stars appear to twinkle (“scintillate”), especially when they are near the horizon. One star, Sirius, twinkles, sparkles and flashes so much some times that people actually report it as a UFO. But in fact, the twinkling is not a property of the stars, but of Earth’s turbulent atmosphere. As the light from a star passes through the atmosphere, especially when the star appears near the horizon, it must pass through many layers of often rapidly differing density. This has the effect of deflecting the light slightly as it were a ball in a pinball machine. The light eventually gets to your eyes, but every deflection causes it to change slightly in color and intensity. The result is “twinkling.” Above the Earth’s atmosphere, stars do not twinkle.

2) You can see 20 quadrillion miles, at least
On a good night, you can see about 19,000,000,000,000,000 miles, easily. That’s 19 quadrillion miles, the approximate distance to the bright star Deneb in Cygnus. which is prominent in the evening skies of Fall and Winter. Deneb is bright enough to be seen virtually anywhere in the Northern hemisphere, and in fact from almost anywhere in the inhabited world. There is another star, Eta Carina, that is a little more than twice as far away, or about 44 quadrillion miles. But Eta Carina is faint, and not well placed for observers in most of the Northern hemisphere. Those are stars, but both the Andromeda Galaxy and the Triangulum Galaxy are also visible under certain conditions, and are roughly 15 and 18 quintillion miles away! (One quintillion is 10^18!)

1) Black holes don’t “suck”
Many writers frequently describe black holes as “sucking” in everything around them. And it is a common worry among the ill-informed that the so-far hypothetical “mini” black holes that may be produced by the Large Hadron Collider would suck in everything around them in an ever increasing vortex that would consume the Earth! “Say it ain’t so, Joe!” Well, I am not Shoeless Joe Jackson, but it ain’t so. In the case of the LHC, it isn’t true for a number of reasons, but black holes in general do not “suck.”

This not just a semantic distinction, but one of process and consequence as well. The word “suck” via suction, as in the way vacuum cleaners work, is not how black holes attract matter. In a vacuum cleaner, the fan produces a partial vacuum (really, just a slightly lower pressure) at the floor end of the vacuum, and regular air pressure outside, being greater, pushes the air into it, carrying along loose dirt and dust.

In the case of black holes, there is no suction involved. Instead, matter is pulled into the black hole by a very strong gravitational attraction. In one way of visualizing it, it really is a bit like falling into a hole, but not like being hoovered into it. Gravity is a fundamental force of Nature, and all matter has it. When something is pulled into a black hole, the process is more like being pulled into like a fish being reeled in by an angler, rather than being pushed along like a rafter inexorably being dragged over a waterfall.

The difference may seem trivial, but from a physical standpoint it is fundamental.

So black holes don’t suck, but they are very cool. Actually, they are cold. Very, very cold. But that’s a story for another time.

(P.S. The image of a green Sun above is actually a satellite image from the SOHO project, and in fact is an image taken in the extreme ultraviolet range of the spectrum. The human eye cannot see at this wavelength at all. The green color was added just to make it visible. Credit: SOHO, ESA, NASA)

A young astrophysicist, Sukanya Chakrabarti, assistant professor of physics at the Charles E. Schmidt College of Science at Florida Atlantic University, has developed a way to discover and map the dark matter halos of distant galaxies, using gravitational ripples caused by the passing of their dim satellite galaxies. She spoke with EarthSky at the January 2012 meeting of the American Astronomical Society in Austin, TX, where she was announcing the results of her research. She told us:

Sukanya Chakrabarti. Image Credit: Harvard-Smithsonian Center for Astrophysics

Dark matter is dark because it doesn’t emit any electromagnetic radiation. But it is massive. So that means that it will interact gravitationally with whatever else.

Chakrabarti mapped the ripples in gigantic clouds of gas that surround spiral galaxies. Those ripples, said Chakrabarti, are made by dark matter. She told EarthSky:

The cold gas is a great tracer because it’s very responsive. It’s basically like dropping pebbles into a pond and looking at the ripples in the pond, trying to figure out how massive was the pebble. If you sort of understood the physics of that well enough you might be able to do it, even if you didn’t see the pebble fall in.

Projected density of a dark matter halo from a distant galaxy. The visible part of the galaxy (not shown in the image) would lie at the dense center of the halo. Satellite galaxies each would have their own subhalos, visible as a region of high dark matter density in the image. Image Credit: Wikimedia Commons

Chakrabarti first demonstrated her method of mapping dark matter with the Whirlpool Galaxy, about 23 million light years away. She said:

I think the hunt for dark matter has a lot in common with the hunt for planets, back in the 1800s. There’s a lot of potential to understand dark matter from its gravitational effects on other things. I think that’s a very promising thing, similar in spirit to the way Neptune was discovered. It’s a kind of indirect means of hunting for this thing that we can’t see. And if these kind of methods turn out to be successful, it gives us a way of hunting for dim things, kind of like looking for you car in a fog. If you kind of know approximately where to look, you’re going to do much better than if you have to do a completely blind search.

Chakrabarti’s paper – “A New Probe of the Distribution of Dark Matter in Galaxies” – is published online.

The galaxies we see around us in space have extended gas disks that are very fragile and respond easily to the gravitational pull of passing satellites, Chakrabarti said. She added that the ripples in the outer gas disks of spiral galaxies act like a mirror of the potential depth of the dark matter halo in the primary galaxy.

Thus, even though the dark matter halo cannot be seen directly, scientists can essentially map a galaxy’s dark matter, using this method.

Chakrabarti previously developed a mathematical method called tidal analysis to find unseen satellite galaxies by analyzing the ripples in the hydrogen gas distribution of large spiral galaxies. Many dwarf galaxies are very dim, so it is useful to have a way of finding them that does not rely on their optical light, she said.

The Whirlpool Galaxy and its satellite, left. Image Credit: Todd Boroson (NOAO), AURA, NOAO, NSF

Earlier, she applied the method to the nearby Whirlpool Galaxy, which has an optically visible satellite, to infer the mass and location of the satellite. She found these values to be observationally corroborated, thus proving her method.

Listen to the 8-minute and 90-second EarthSky interviews with Sukanya Chakrabarti on mapping the distribution of mass in the unseen dark matter halo of a galaxy, using gravitational ripples caused by passing satellite galaxies (at top of page).

Last week (January 23, 2012), space scientists released a montage of images of dune fields on Saturn’s large moon Titan. The images are the result of a new analysis of radar data from NASA’s Cassini mission to Saturn. The scientists say these images give new clues about the climate and geology of Titan, which is our solar system’s second-largest moon, the only moon with an atmosphere, and which has a bigger volume than the planet Mercury (although it is only half as dense).

Radar images of wind-driven sand dunes in different places on Saturn's moon Titan, acquired by the Cassini spacecraft. Image credit: NASA/JPL-Caltech, and NASA/GSFC/METI/ERSDAC/JAROS and U.S./Japan ASTER Science Team

Click here to expand image above

Dune fields cover about 13 percent of Titan, or roughly the surface area of the United States. Scientists say Titan’s dunes are similar to the some found in the earthly Republic of Namibia, which is in southwestern Africa. Namibia has some giant dunes – some reaching nearly 1,000 feet (300 meters) in height. Titan has some giant dunes as well. Even the average sized ones are 300 feet (100 meters) high, and the longitudinal (or linear) dunes, which are always aligned with average wind direction, can stretch hundreds of miles across the surface of this alien moon.

Yes, Titan has wind and rain of liquid methane, and, in addition to sand dunes, it has rivers, lakes and seas (probably of liquid methane or ethane) and shorelines. It has seasons and seasonal weather patterns. All of this is amazing news of recent years, since Titan’s surface cannot be seen directly. It is hidden by this moon’s dense atmosphere. But Cassini is equipped with radar, and that’s where we get these images, and much of what we know of Titan.

Give me 5 minutes, and I’ll give you Saturn in 2012

Best images of sand dunes on planet Mars

Scientists are now saying that the size and spacing of dunes on Titan has given them clues as to how the dunes formed and evolved. For example, the size of Titan’s dunes appears to be controlled by at least two factors: latitude and altitude. Sand dunes on Titan are confined to low latitudes – in a band between 30 degrees south latitude and 30 degrees north latitude, with fewer dunes toward the north. Meanwhile, dunes at higher altitudes on Titan tend to be thinner and more widely separated, possibly with a thinner covering of sand.

Earthly sand dunes, not unlike the dunes on Titan. These are in Namibia, in southwestern Africa, where winds blowing in off the Atlantic Ocean create the tallest sand dunes on Earth. Image Credit: NASA

The dunes in the image above aren’t on Titan. They’re on Earth, in Namibia in southwestern Africa, in the Namib-Naukluft National Park, an ecological preserve in Namibia’s vast Namib Desert. Earthly winds, blowing in from the Atlantic Ocean, create the tallest sand dunes on Earth here. They look similar, yes? That’s because nature works the same way throughout space. If it didn’t, by the way, we’d be at a loss to understand anything about what’s around us in the cosmos. You’ll find more information about this image here.

There’s more to the Titan dune story, too, from NASA, which you can read here.

Smog-enshrouded Titan in the background, with Saturn's small moon Epimetheus, plus Saturn's F ring, in the foreground. Beneath Titan's dense atmosphere, wind blows and a rain of liquid methane falls. There are sand dunes, rivers, lakes and seas (probably of liquid methane or ethane) and shorelines. Titan also has seasons and seasonal weather patterns. Image via Cassini spacecraft.

Click here to expand image above

By the way, the Cassini orbiter has been weaving in and around Saturn and its moon since 2004. It has now far surpassed its original mission and is scheduled to remain in orbit until 2017.

Bottom line: On January 23, 2012, space scientists released a montage of images of dune fields on Saturn’s large moon Titan. The images are the result of a new analysis of radar data from NASA’s Cassini mission to Saturn. The scientists say these images give new clues about the climate and geology of Titan.

Lakes and storms on Saturn’s moon Titan explained