Universe Today

December 15, 2014March 1, 2017 by Fraser Cain

Why Is Space Black?

Since there are stars and galaxies in all directions, why is space black? Shouldn’t there be a star in every direction we look?

Imagine you’re in space. Just the floating part, not the peeing into a vacuum hose or eating that funky “ice cream” from foil bags part. If you looked at the Sun, it would be bright and your retinas would crisp up. The rest of the sky would be a soothing black, decorated with tiny little less burny points of light.

If you’ve done your homework, you know that space is huge. It even be infinite, which is much bigger than huge. If it is infinite you can imagine looking out into space in any direction and there being a star. Stars would litter everything. Dumb stars everywhere wrecking the view. It’s stars all the way down, people.

So, shouldn’t the entire sky be as bright as a star, since there’s a star in every possible minute direction you could ever look in? If you’ve ever asked yourself this question, you probably won’t be surprised to know you’re not the first. Also, at this point you can tell people you were wondering about it and they’ll never know you just watched it here and then you can sound wicked smart and impress all those dudes.

This question was famously asked by the German astronomer Heinrich Wilhelm Olbers who described it in 1823. We now call this Olbers’ Paradox after him. Here let me give you a little coaching, you’ll start your conversation at the party with “So, the other day, I was contemplating Olbers’ Paradox… Oh what’s that? You don’t know what it is… oh that’s so sweet!”. The paradox goes like this: if the Universe is infinite, static and has existed forever, then everywhere you look should eventually hit a star.

Our experiences tell us this isn’t the case. So by proposing this paradox, Olbers knew the Universe couldn’t be infinite, static and timeless. It could be a couple of these, but not all three. In the 1920s, debonair man about town, Edwin Hubble discovered that the Universe isn’t static. In fact, galaxies are speeding away from us in all directions like we have the cooties.

This led to the theory of the Big Bang, that the Universe was once gathered into a single point in time and space, and then, expanded rapidly. Our Universe has proven to not be static or timeless. And so, PARADOX SOLVED!

Here’s the short version. We don’t see stars in every direction because many of the stars haven’t been around long enough for their light to get to us. Which I hope tickles your brain in the way it does mine. Not only do we have this incomprehensibly massive size of our Universe, but the scale of time we’re talking about when we do these thought experiments is absolutely boggling. So, PARADOX SOLVED!

Well, not exactly. Shortly after the Big Bang, the entire Universe was hot and dense, like the core of a star. A few hundred thousand years after the Big Bang, when the first light was able to leap out into space, everything, in every direction was as bright as the surface of a star.

Cosmic microwave background. Image credit: WMAP

So, in all directions, we should still be seeing the brightness of a star.. and yet we don’t. As the Universe expanded, the wavelengths of that initial visible light were stretched out and out and dragged to the wide end of the electromagnetic spectrum until they became microwaves. This is Cosmic Microwave Background Radiation, and you guessed it, we can detect it in every direction we can look in.

So Olbers’ instinct was right. If you look in every direction, you’re seeing a spot as bright as a star, it’s just that the expansion of the Universe stretched out the wavelengths so that the light is invisible to our eyes. But if you could see the Universe with microwave detecting eyes, you’d see this: brightness in every direction.

Did you come up with Olbers’ Paradox too? What other paradoxes have puzzled you?

December 15, 2014December 23, 2015 by Elizabeth Howell

Martian Teardrop: Here’s How The Sun Moves Over A Red Planet Year

The Opportunity rover captured this analemma showing the Sun's movements over one Martian year. Images taken every third sol (Martian day) between July, 16, 2006 and June 2, 2008. Credit: NASA/JPL/Cornell/ASU/TAMU

Stand in the same spot every day. Take a picture of the Sun. What happens? Slowly, you see our closest star shifting positions in the sky. That motion over an entire year is called an analemma. The Opportunity rover on Mars even captured one on the Red Planet, which you can see above, and it’s a different shape than what you’ll find on Earth.

An April Astronomy Picture of the Day post (highlighted this weekend on Reddit) explains that Earth’s analemma of the Sun is figure-8-shaped, while that on Mars looks somewhat like a pear (or a teardrop, we think.) The Earth and Mars each have about the same tilt in their orbit — that same tilt that produces the seasons — but the orbit of Mars is more elliptical (oval) than that of Earth.

An analemma of the Sun, taken from Budapest, Hungary over a one year span. (Courtesy of György Soponyai, used with permission).

“When Mars is farther from the Sun, the Sun progresses slowly in the martian sky creating the pointy top of the curve,” the APOD post stated. “When close to the Sun and moving quickly, the apparent solar motion is stretched into the rounded bottom. For several sols some of the frames are missing due to rover operations and dust storms.”

The picture you see at the top of the post was taken every third sol (or Martian day, which is 24 hours and 37 minutes) between July 2006 and June 2008. The landscape surrounding the analemma is from Victoria Crater, where Opportunity was roaming at that time. (The rover is now on the rim of Endeavour Crater, still trucking after nearly 11 full years on the surface.)

In 2006, APOD also published a simulated analemma from Sagan Memorial Station, the landing site of the Sojourner spacecraft and tiny Pathfinder rover. In this case, the simulation showed the Sun’s movements every 30 sols. A Martian year is 668 sols.

You can read more details about analemmae in this past Universe Today post by David Dickinson, which relates the phenomenon to the passage of time.

December 15, 2014December 23, 2015 by Elizabeth Howell

Could Mercury Get A Meteor Shower From Comet Encke?

Artist's concept of the planet Mercury orbiting through a debris trail from Comet Encke that may cause a meteor shower. Credit: NASA's Goddard Space Flight Center

We’re sure going to miss the MESSENGER spacecraft at Mercury when it concludes its mission in 2015, because it keeps bringing us really unexpected news about the Sun’s closest planet. Here’s the latest: Mercury may get a periodic meteor shower when it passes through the debris trail of Comet Encke.

Why do scientists suspect this? It’s not from patiently watching for shooting stars. Instead, they believe the signature of calcium in Mercury’s tenuous atmosphere may be pointing to a pattern.

MESSENGER (which stands for MErcury Surface, Space ENvironment, GEochemistry, and Ranging) has been orbiting the planet for three Earth years and sees regular “surges” in calcium abundance on a predictable schedule. The researchers suspect it’s because of bits of dust colliding with Mercury and ricocheting bits of calcium up from the surface.

Mercury also picks up bits of dust from interplanetary debris, but the scientists say it’s not enough to account for the amounts of calcium they see. Extrapolating, the researchers suspect it must occur as the planet passes through debris left behind from a comet or asteroid. There are a small number of such small bodies that do this, and the scientists narrowed it down to Encke.

Illustration of MESSENGER in orbit around Mercury (NASA/JPL/APL)

Computer simulations of the comet’s debris showed a slight difference from what researchers predicted, but they believe it’s because of variations in Mercury’s orbit as it gets tugged by larger planets, particularly Jupiter. Encke itself takes about 3.3 years to do one lap around the Sun, and has been photographed by MESSENGER in the past.

“The possible discovery of a meteor shower at Mercury is really exciting and especially important because the plasma and dust environment around Mercury is relatively unexplored,” stated lead author Rosemary Killen, a planetary scientist at NASA’s Goddard Space Flight Center in Maryland.

MESSENGER, meanwhile, is burning off the last of its fuel to stay in orbit; the final engine maneuver is expected for Jan. 21. Once that’s finished, the spacecraft will slowly spiral down towards the planet for an expected impact in March, ending the mission.

Source: NASA

December 15, 2014December 23, 2015 by Elizabeth Howell

How NASA Filmed Humans Last Leaving The Moon, 42 Years Ago

Still of the Apollo 17 spacecraft leaving the moon on Dec. 14, 1972. Credit: NASA/YouTube (screenshot)

When Apollo 17 lifted off from the moon, a camera captured the movements of the spacecraft — even though nobody was left behind to, say, establish a lunar base. How was that possible? With a camera on the lunar rover that could be controlled — or even programmed — from Earth.

Pretty impressive technology for the takeoff 42 years ago yesterday (Dec. 14) in 1972, although it took three tries to get the technique right.

As the Smithsonian National Air and Space Museum explains in a 2011 blog post, the camera was available on Apollos 15, 16 and 17. The television camera communicated from Earth using a high-gain antenna on the rover, but there was a slight time delay for the radio waves to travel (a couple of seconds) between the Earth and the Moon.

So the engineers suggested moving the rover a certain distance from the lunar module and setting the camera to automatically tilt to show the lunar liftoff when commanded from Earth.

That was the plan, at least. On Apollo 15, the tilt mechanism malfunctioned and the camera never moved upwards, allowing the lunar module to slip out of sight. And while the attempt on Apollo 16 gave a longer view of the lunar module rising up, the astronauts actually parked the rover too close to it, which threw off the calculations and timing of the tilt upwards so it left view just a few moments into the flight.

Ed Fendall was the person doing the controlling. In an oral history for NASA done in 2000, he recalled how complex the procedure was.

Now, the way that worked was this. Harley Weyer, who worked for me, sat down and figured what the trajectory would be and where the lunar rover would be each second as it moved out, and what your settings would go to. That picture you see was taken without looking at it [the liftoff] at all. There was no watching it and doing anything with that picture. As the crew counted down, that’s a [Apollo] 17 picture you see, as [Eugene] Cernan counted down and he knew he had to park in the right place because I was going to kill him, he didn’t — and Gene and I are good friends, he’ll tell you that — I actually sent the first command at liftoff minus three seconds. And each command was scripted, and all I was doing was looking at a clock, sending commands. I was not looking at the television. I really didn’t see it until it was over with and played back. Those were just pre-set commands that were just punched out via time. That’s the way it was followed.

December 15, 2014December 23, 2015 by Vanessa Janek

New Signal May Be Evidence of Dark Matter, Say Researchers

Dark Matter Halo and dwarf galaxies — All galaxies are thought to have a dark matter halo. This image shows the distribution of dark matter surrounding our very own Milky Way. Image credit: J. Diemand, M. Kuhlen and P. Madau (UCSC)

Dark matter is the architect of large-scale cosmic structure and the engine behind proper rotation of galaxies. It’s an indispensable part of the physics of our Universe – and yet scientists still don’t know what it’s made of. The latest data from Planck suggest that the mysterious substance comprises 26.2% of the cosmos, making it nearly five and a half times more prevalent than normal, everyday matter. Now, four European researchers have hinted that they may have a discovery on their hands: a signal in x-ray light that has no known cause, and may be evidence of a long sought-after interaction between particles – namely, the annihilation of dark matter.

When astronomers want to study an object in the night sky, such as a star or galaxy, they begin by analyzing its light across all wavelengths. This allows them to visualize narrow dark lines in the object’s spectrum, called absorption lines. Absorption lines occur because a star’s or galaxy’s component elements soak up light at certain wavelengths, preventing most photons with those energies from reaching Earth. Similarly, interacting particles can also leave emission lines in a star’s or galaxy’s spectrum, bright lines that are created when excess photons are emitted via subatomic processes such as excitement and decay. By looking closely at these emission lines, scientists can usually paint a robust picture of the physics going on elsewhere in the cosmos.

But sometimes, scientists find an emission line that is more puzzling. Earlier this year, researchers at the Laboratory of Particle Physics and Cosmology (LPPC) in Switzerland and Leiden University in the Netherlands identified an excess bump of energy in x-ray light coming from both the Andromeda galaxy and the Perseus star cluster: an emission line with an energy around 3.5keV. No known process can account for this line; however, it is consistent with models of the theoretical sterile neutrino – a particle that many scientists believe is a prime candidate for dark matter.

The researchers believe that this strange emission line could result from the annihilation, or decay, of these dark matter particles, a process that is thought to release x-ray photons. In fact, the signal appeared to be strongest in the most dense regions of Andromeda and Perseus and increasingly more diffuse away from the center, a distribution that is also characteristic of dark matter. Additionally, the signal was absent from the team’s observations of deep, empty space, implying that it is real and not just instrumental artifact.

In a pre-print of their paper, the researchers are careful to stress that the signal itself is weak by scientific standards. That is, they can only be 99.994% sure that it is a true result and not just a rogue statistical fluctuation, a level of confidence that is known as 4σ. (The gold standard for a discovery in science is 5σ: a result that can be declared “true” with 99.9999% confidence) Other scientists are not so sure that dark matter is such a good explanation after all. According to predictions made based on measurements of the Lyman-alpha forest – that is, the spectral pattern of hydrogen absorption and photon emission within very distant, very old gas clouds – any particle purporting to be dark matter should have an energy above 10keV – more than twice the energy of this most recent signal.

As always, the study of cosmology is fraught with mysteries. Whether this particular emission line turns out to be evidence of a sterile neutrino (and thus of dark matter) or not, it does appear to be a signal of some physical process that scientists do not yet understand. If future observations can increase the certainty of this discovery to the 5σ level, astrophysicists will have yet another phenomena to account for – an exciting prospect, regardless of the final result.

The team’s research has been accepted to Physical Review Letters and will be published in an upcoming issue.

December 15, 2014December 23, 2015 by Matt Williams

Just in Time for the Holidays – Galactic Encounter Puts on Stunning Display

That's the case with NGC 2207 and IC 2163, which are located about 130 million light-years from Earth, in the constellation of Canis Major. Image credit: NASA/CXC/SAO/STScI/JPL-Caltech

At this time of year, festive displays of light are to be expected. This tradition has clearly not been lost on the galaxies NHC 2207 and IC 2163. Just in time for the holidays, these colliding galaxies, which are located within the Canis Major constellation (some 130 million light-years from Earth,) were seen putting on a spectacular lights display for us folks here on Earth!

And while this galaxy has been known to produce a lot of intense light over the years, the image above is especially luminous. A composite using data from the Chandra Observatory and the Hubble and Spitzer Space Telescopes, it shows the combination of visible, x-ray, and infrared light coming from the galactic pair.

In the past fifteen years, NGC 2207 and IC 2163 have hosted three supernova explosions and produced one of the largest collections of super bright X-ray lights in the known universe. These special objects – known as “ultraluminous X-ray sources” (ULXs) – have been found using data from NASA’s Chandra X-ray Observatory.

While the true nature of ULXs is still being debated, it is believed that they are a peculiar type of star X-ray binary. These consist of a star in a tight orbit around either a neutron star or a black hole. The strong gravity of the neutron star or black hole pulls matter from the companion star, and as this matter falls toward the neutron star or black hole, it is heated to millions of degrees and generates X-rays.

the core of galaxy Messier 82 (M82), where two ultraluminous X-ray sources, or ULXs, reside (X-1 and X-2). Credit: NASA — *The core of galaxy Messier 82 (M82), where two ultraluminous X-ray sources, or ULXs, reside (X-1 and X-2). Credit: NASA*

Data obtained from Chandra has determined that – much like the Milky Way Galaxy – NGC 2207 and IC 2163 are sprinkled with many star X-ray binaries. In the new Chandra image, this x-ray data is shown in pink, which shows the sheer prevalence of x-ray sources within both galaxies.

Meanwhile, optical light data from the Hubble Space Telescope is rendered in red, green, and blue (also appearing as blue, white, orange, and brown due to color combinations,) and infrared data from the Spitzer Space Telescope is shown in red.

The Chandra observatory spent far more time observing these galaxies than any previous ULX study, roughly five times as much. As a result, the study team – which consisted of researchers from Harvard University, MIT, and Sam Houston State University – were able to confirm the existence of 28 ULXs between NGC 2207 and IC 2163, seven of which had never before been seen.

In addition, the Chandra data allowed the team of scientists to observe the correlation between X-ray sources in different regions of the galaxy and the rate at which stars are forming in those same regions.

Galaxy mergers, such as the Mice Galaxies will be part of Galaxy Zoo's newest project. Credit: Hubble Space Telescope — *The Mice galaxies, seen here well into the process of merging. Credit: Hubble Space Telescope*

As the new Chandra image shows, the spiral arms of the galaxies – where large amounts of star formation is known to be occurring – show the heaviest concentrations of ULXs, optical light, and infrared. This correlation also suggests that the companion star in the star X-ray binaries is young and massive.

This in turn presents another possibility which has to do with star formation during galactic mergers. When galaxies come together, they produce shock waves that cause clouds of gas within them to collapse, leading to periods of intense star formation and the creation of star clusters.

The fact that the ULXs and the companion stars are young (the researchers estimate that they are only 10 million years old) would seem to confirm that they are the result of NGC 2207 and IC 2163 coming together. This seem a likely explanation since the merger between these two galaxies is still in its infancy, which is attested to by the fact that the galaxies are still separate.

They are expected to collide soon, a process which will make them look more like the Mice Galaxies (pictured above). In about one billion years time, they are expected to finish the process, forming a spiral galaxy that would no doubt resemble our own.

A paper describing the study was recently published on online with The Astrophysical Journal.

Further Reading: NASA/JPL, Chandra, arXiv Astrophysics

December 13, 2014December 23, 2015 by Ken Kremer

Amazing Up Close Videos Capture Orion’s Final Descent, Splashdown and Ocean Recovery

The Orion crew module was recovered Dec. 5, 2014 after splashdown in the Pacific Ocean about 600 miles off the coast of San Diego, California. Credit: U.S. Navy

Video Caption: Last moments of Orion descent as viewed from the recovery ship USS Anchorage. Credit: NASA/US Navy

Relive the final moments of the first test flight of NASA’s Orion spacecraft on Dec. 5, 2014, through this amazing series of up close videos showing the spacecraft plummeting back to Earth through the rollicking ocean recovery by dive teams from the US Navy and the USS Anchorage amphibious ship.

The two orbit, 4.5 hour flight maiden test flight of Orion on the Exploration Flight Test-1 (EFT-1) mission was a complete success.

It was brought back to land to the US Naval Base San Diego, California.

Orion’s test flight began with a flawless launch on Dec. 5 as it roared to orbit atop the fiery fury of a 242 foot tall United Launch Alliance Delta IV Heavy rocket – the world’s most powerful booster – at 7:05 a.m. EST from Space Launch Complex 37 (SLC-37) at Cape Canaveral Air Force Station in Florida.

The unpiloted test flight of Orion on the EFT-1 mission ignited NASA’s roadmap to send Humans to Mars by the 2030s by carrying the capsule farther away from Earth than any spacecraft designed for astronauts has traveled in more than four decades.

Humans have not ventured beyond low Earth orbit since the launch of Apollo 17 on NASA’s final moon landing mission on Dec. 7, 1972.

Video Caption: NASA TV covers the final moments of Orion spacecraft descent and splashdown in the Pacific Ocean approximately 600 miles southwest of San Diego on Dec. 5, 2014, as viewed live from the Ikhana airborne drone. Credit: NASA TV

The spacecraft was loaded with over 1200 sensors to collect critical performance data from numerous systems throughout the mission for evaluation by engineers.

EFT-1 tested the rocket, second stage, and jettison mechanisms as well as avionics, attitude control, computers, environmental controls, and electronic systems inside the Orion spacecraft and ocean recovery operations.

It also tested the effects of intense radiation by traveling twice through the Van Allen radiation belt.

After successfully accomplishing all its orbital flight test objectives, the capsule fired its thrusters and began the rapid fire 10 minute plummet back to Earth.

During the high speed atmospheric reentry, it approached speeds of 20,000 mph (32,000 kph), approximating 85% of the reentry velocity for astronauts returning from voyages to the Red Planet.

The capsule endured scorching temperatures near 4,000 degrees Fahrenheit in a critical and successful test of the 16.5-foot-wide heat shield and thermal protection tiles.

The entire system of reentry hardware, commands, and 11 drogue and main parachutes performed flawlessly.

Finally, Orion descended on a trio of massive red and white main parachutes to achieve a statistical bulls-eye splashdown in the Pacific Ocean, 600 miles southwest of San Diego, at 11:29 a.m. EST.

It splashed down within one mile of the touchdown spot predicted by mission controllers after returning from an altitude of over 3600 miles above Earth.

The three main parachutes slowed Orion to about 17 mph (27 kph).

Here’s a magnificent up close and personal view direct from the US Navy teams that recovered Orion on Dec. 5, 2014.

Video Caption: Just released footage of the Orion Spacecraft landing and recovery! See all the sights and sounds, gurgling, and more from onboard the Zodiac boats with the dive teams on Dec. 5, 2014. See the initial recovery operations, including safing the crew module and towing it into the well deck of the USS Anchorage, a landing platform-dock ship. Credit: US Navy

Navy teams in Zodiac boats had attached a collar and winch line to Orion at sea and then safely towed it into the flooded well deck of the USS Anchorage and positioned it over rubber “speed bumps.”

Next they secured Orion inside its recovery cradle and transported it back to US Naval Base San Diego where it was off-loaded from the USS Anchorage.

The Orion EFT-1 spacecraft was recovered by a combined team from NASA, the U.S. Navy, and Orion prime contractor Lockheed Martin.

Orion has been offloaded from the USS Anchorage and moved about a mile to the “Mole Pier” where Lockheed Martin technicians have conducted the first test inspection of the crew module and collected test data.

It will soon be hauled on a flatbed truck across the US for a nearly two week trip back to Kennedy where it will arrive just in time for the Christmas holidays.

NASA Administrator Charles Bolden briefs the media about the ‘Big Deal’ goals of the first Orion deep space crew module during prelaunch meeting backdropped by Orion and Delta 4 Heavy Booster at Space Launch Complex 37 (SLC-37) at Cape Canaveral Air Force Station in Florida prior to launch on Dec. 5, 2014. Credit: Ken Kremer - kenkremer.com — NASA Administrator Charles Bolden briefs the media about the “Big Deal” goals of the first Orion deep space crew module during prelaunch meeting backdropped by Orion and Delta 4 Heavy Booster at Space Launch Complex 37 (SLC-37) at Cape Canaveral Air Force Station in Florida prior to launch on Dec. 5, 2014. Credit: Ken Kremer – kenkremer.com

Technicians at KSC will examine every nook and cranny of Orion and will dissemble it for up close inspection and lessons learned.

NASA’s first Orion spacecraft blasts off at 7:05 a.m. atop United Launch Alliance Delta 4 Heavy Booster at Space Launch Complex 37 (SLC-37) at Cape Canaveral Air Force Station in Florida on Dec. 5, 2014. Launch pad remote camera view. Credit: Ken Kremer - kenkremer.com — NASA’s first Orion spacecraft blasts off at 7:05 a.m. atop United Launch Alliance Delta 4 Heavy Booster at Space Launch Complex 37 (SLC-37) at Cape Canaveral Air Force Station in Florida on Dec. 5, 2014. Launch pad remote camera view. Credit: Ken Kremer – kenkremer.com

Stay tuned here for Ken’s continuing Earth and planetary science and human spaceflight news.

Ken Kremer

Prelaunch night view of NASA’s first Orion spacecraft bolted atop triple barreled United Launch Alliance Delta 4 Heavy Booster at Space Launch Complex 37 (SLC-37) at Cape Canaveral Air Force Station in Florida. Credit: Ken Kremer - kenkremer.com — Prelaunch night view of NASA’s first Orion spacecraft bolted atop triple barreled United Launch Alliance Delta 4 Heavy Booster at Space Launch Complex 37 (SLC-37) at Cape Canaveral Air Force Station in Florida. Credit: Ken Kremer – kenkremer.com

December 12, 2014December 23, 2015 by Elizabeth Howell

New Map Shows ‘Marsquakes’ Shook Wet Valles Marineris Sand, NASA Says

A color mosaic of Candor Chasma (part of Mars' Valles Marineris) based on data from Voyager 1 and Voyager 2. Credit: NASA

Mars today is a planet that appears to be mostly shaped by wind, but that wasn’t always the case. A new map adds information to the hypothesis that “marsquakes” affected at least a part of the planet’s vast canyon, Valles Marineris, while the area contained spring-filled lakes.

When the damp sand got shaken up, it deposited itself in hills. NASA says the new map, based on observations from the Mars Reconnaissance Orbiter (which you can see below), adds credence to the theory that it was water that made these deposits.

“The conditions under which sedimentary deposits in it formed have been an open issue for decades,” NASA wrote in a press release. “Possibilities proposed have included accumulation in lakebeds, volcanic eruptions under glaciers within the canyons, and accumulation of wind-blown sand and dust.”

The map you see below was created by the U.S. Geological Survey, which has more extensive information on the findings at this website. The observations also produced a suite of research in recent years, such as this 2009 paper led by Scott Murchie at the Johns Hopkins University Applied Research Laboratory.

Part of a map of Candor Chasma (part of Mars' Valles Marineris) based on observations from the Mars Reconnaissance Orbiter. Green is knobby terrain, pink is lobate deposits (ridged material) and blue "stair-stepped morphology" of hills and mesas. Credit: U.S. Geological Survey — Part of a map of Candor Chasma (part of Mars’ Valles Marineris) based on observations from the Mars Reconnaissance Orbiter. Green is knobby terrain, pink is lobate deposits (ridged material) and blue “stair-stepped morphology” of hills and mesas. Credit: U.S. Geological Survey

December 12, 2014December 23, 2015 by Elizabeth Howell

Freak Fast Winds Created Titan’s Massive, Mysterious Dunes

Titan's surface is almost completely hidden from view by its thick orange "smog" (NASA/JPL-Caltech/SSI. Composite by J. Major)

Titan is Saturn’s largest moon and is constantly surprising scientists as the Cassini spacecraft probes under its thick atmosphere. Take its dunes, for example, which are huge and pointed the wrong way.

Why are they pointing opposite to the prevailing east-west winds? It happens during two rare wind reversals during a single Saturn year (30 Earth years), investigators suggest.

Investigators repurposed an old NASA wind tunnel to simulate how Titan is at the surface, watching how the wind affects sand grains. (They aren’t sure what kind of sand is on Titan, so they tried 23 different kinds to best simulate what they think it is, which is small hydrocarbon particles that are about 1/3 the density of what you find on Earth.)

After two years of work with the model — not to mention six years of refurbishing the tunnel — the team determined that the wind must blow 50% faster than believed to get the sand moving.

Dunes on Titan seen in Cassini's radar (top) that are similar to Namibian sand dunes on Earth. The features that appear to be clouds in the top picture are actually topographic features. Credit: NASA — Dunes on Titan seen in Cassini’s radar (top) that are similar to Namibian sand dunes on Earth. The features that appear to be clouds in the top picture are actually topographic features. Credit: NASA

“It was surprising that Titan had particles the size of grains of sand—we still don’t understand their source—and that it had winds strong enough to move them,” stated Devon Burr, an associate professor at the University of Tennessee Knoxville’s earth and planetary science department, who led the research. “Before seeing the images, we thought that the winds were likely too light to accomplish this movement.”

The winds reverse when the Sun moves over the equator, affecting Titan’s dense atmosphere. And the effects are powerful indeed, creating dunes that are hundreds of yards (or meters) high and stretch across hundreds of miles (or kilometers).

To accomplish this, the winds would need to blow no slower than 3.2 miles per hour (1.4 meters per second), which sounds slow until you consider how dense Titan’s atmosphere is — about 12 times thicker surface pressure than what you would find on Earth. More information on the research is available in the journal Nature.

Sources: Arizona State University and the University of Tennessee, Knoxville.

December 12, 2014December 23, 2015 by Nancy Atkinson

Giveaway: Another Chance to Win the 2015 Year In Space Wall Calendar!

Still looking for the perfect holiday gift? The 2015 edition of Steve Cariddi’s wonderful Year in Space Wall Calendar is now available to order, and thanks to Steve, Universe Today has 5 copies to give away!

This is a gorgeous wall calendar that has over 120 beautiful photos of space, and is larger, more lavishly illustrated, and packed with more information than any other space-themed wall calendar. It’s a huge 16 in. x 22 in. when hanging up!

You can read our full review of the 2015 calendar here.

To be entered into our giveaway drawing, just put your email address into the box at the bottom of this article (where it says “Enter the Giveaway”) before Wednesday, December 17, 2014.

If this is the first time you’re registering for a giveaway from Universe Today, you’ll receive a confirmation email immediately where you’ll need to click a link to be entered into the drawing. For those who have registered previously, you’ll receive an email later where you can enter this drawing.

These calendars normally sell for $17.95, but Universe Today readers can buy the calendar for only $13.95 or less (using the “Internet” discount), and get free U.S. shipping and discounted international shipping. There are also volume discounts. Check out all the details here.

There’s also the 136-Page Desk Calendar at a similar discounts.

You can preview the entire calendar at the Year in Space Calendar website.

It’s published in cooperation with The Planetary Society, with an introduction by Bill Nye. Our thanks to Steve Cariddi for providing this giveaway opportunity for our readers!