Fraser Cain, Author at Universe Today

March 26, 2012December 23, 2015 by Fraser Cain

Rare Rain on Titan; Once Every 1,000 Years

Lakes on Titan. Image credit: NASA/JPL/SSI

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Even though there are lakes and rivers of liquid hydrocarbons on the surface of Saturn’s moon Titan, the rains that feed them may come few and far between. According to data gathered by NASA’s Cassini mission, parts of Titan might not see rain for more than 1,000 years.

And according to Dr. Ralph Lorenz, from the John Hopkins Applied Physics Laboratory (JHUALP), a new mission to Titan is exactly what’s needed to get to the bottom of this.

Rain on Titan?! It sounds bizarre, but scientists have observed a complex cycle of liquid on Titan, with lakes and rivers, clouds, and the rain that must feed them. But on Titan, where surface temperatures plunge to -179C, we’re not talking about water. The whole hydrological cycle runs with methane: methane lakes, methane rivers, and methane rain.

And it appears that the rain on Titan can be extreme, with deep river channels that must have had enormous flows for brief periods. But this rain must also be rare. In all of its observations of Titan, Cassini only spotted two instances of darkened regions that might have indicated rainfall.

In a recent talk at the Lunar and Planetary Science Conference (LPSC), Dr. Lorenz presented his estimates of the Titan rainfall, and the need for a new mission that could study it.

Titan Mare Explorer. Image credit: NASA/JPL

Titan Mare Explorer (TiME)

Dr. Lorenz is one of the scientists involved with the proposed Titan Mare Explorer (TiME) mission; one of three shortlisted missions that might be turned into NASA Discovery missions.

If selected, TiME would travel to the Saturn system, descend through Titan’s thick atmosphere, and land in Ligeia Mara, a large lake on the surface of the moon. It would search for rainstorms on the descent – an extremely unlikely event – and then watch the skies for evidence of rainfall. It would be able to “hear” rain falling directly onto it, and in the liquid around it. TiME would also be equipped with instruments that would let it see cloud formation, rain shafts, and even methane rainbows.

Assuming the rain shafts are 10 km wide, and would be observable at distances of 20 km, the lander should be able to detect rainstorms within a 1200 km² area. According to Dr. Lorenz:

We might expect a 50% chance for a lander to be rained on directly in a 2500hr mission, but that its camera could observe nearby rainfall an expected ~5 times.

Once in 1,000 years?

While the weather system on Titan is similar to Earth, it probably has some significant differences, which Cassini observations have hinted at. Although there were possible storms seen in 2004, there was a huge gap until 2010. After the “storm”, the surface of Titan was changed with a large darkened area that could indicate saturation of liquid on the surface. These ponds seemed to dry up in future observations.

Estimates indicate that regions near Titan’s poles see rainfall for 10-100 hours every Titan year (30 Earth years). But the drier parts of the moon might not see more than a single rainfall every 1,000 years.

Source: USRA Presentation

March 15, 2012January 11, 2016 by Fraser Cain

Ride a Shuttle Booster to the Edge of Space and Back

We’ve posted space shuttle launch videos in the past, but this one is different. It’s a video captured from cameras on board the space shuttle’s booster engines as it blasts off. You go from launch to the point that the boosters separate from the orbiter and continue their journey back to splash down.

The video is great, and edited nicely, but the sound is amazing. It was remixed and edited by the good folks at Skywalker Sound as part of the upcoming DVD called Special Edition Ascent: Commemorating Space Shuttle.

Thanks to Michael Interbartolo for the tip.

March 13, 2012December 23, 2015 by Fraser Cain

Satellite Photo of Vancouver and the Fraser River

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I just had to post this satellite photograph of Vancouver with the sediment plume streaming out of the Fraser River. Not just because it’s beautiful, which it is, but also because so much of my life is tied together with that city and river.

I was born in Vancouver, and spent half my time there and half my time over on Vancouver Island which is on the left-hand side of this image. I currently live on Vancouver Island, but I have to commute to Vancouver quite a bit, which involves taking a ferry ride across the Straight of Georgia. When you take the route that carries you from Nanaimo (on the island) over to Tsawassen (the ferry terminal that juts out), you have to cross this plume.

Where you see the plume depends on the tides and the amount of material flowing out of the Fraser River, but it’s a stunning sight to see. It’s like the water has been separated into two different colors, with a very distinct dividing line between them.

You can see the line from a few kilometers away standing on the ferry deck, and then it approaches and widens, and then you cross it. The water switches from deep blue to muddy brown with almost no blending in between. Even the shape of the waves in the plume is different.

Anyway, cool image, thanks to NASA’s Earth Observatory.

March 13, 2012December 23, 2015 by Fraser Cain

Does The Sun Rotate?

A mosaic of 4 images taken of the Sun on Nov. 13, 2011. Credit: Leonard Mercer.

The rotation of the Sun is kind of hard to pin down. That’s because a day on the Sun depends on which part of the Sun you’re talking about. Confused yet? It kept astronomers puzzled for years too. Let’s look at how the rotation of the Sun changes.

A spot on the equator of the Sun takes 24.47 days to rotate around the Sun and return to the same position. Astronomers call this sidereal rotation period, which is different from the synodic period – the amount of time it takes for a spot on the Sun to rotate back to face the Earth. But the Sun’s rotation rate decreases as you approach the poles, so it can actually take 38 days for regions around the poles to rotate once.

The Sun’s rotation is seen by observing sunspots. All sunspots move across the face of the Sun. This motion is part of the general rotation of the Sun on its axis. Observations also indicate that the Sun does not rotate as a solid body, but it spins differentially. That means that it rotates faster at the equator of the Sun and slower at its poles. The gas giants Jupiter and Saturn also have differential rotation.

And so, astronomers have decided to measure the rotation rate of the Sun from an arbitrary position of 26° from the equator; approximately the point where we see most of the sunspots. At this point, it takes 25.38 days to rotate and return to the same spot in space.

Astronomers also know that the interior of the Sun rotated differently than the surface. The inner regions, the core and the radiative zone, rotate together like a solid body. And then the outer layers, the convective zone and photosphere, rotate at a different speed.

The Sun and the entire solar system orbits around the center of the Milky Way galaxy. The average velocity of the solar system is 828,000 km/hr. At that rate it will take about 230 million years to make one complete orbit around the galaxy. The Milky Way is a spiral galaxy. It is believed that it consists of a central bulge, 4 major arms, and several shorter arm segments. The Sun and the rest of our solar system is located near the Orion arm, between two major arms, Perseus and Sagittarius. The diameter of the Milky Way is about 100,000 light years and the Sun is located about 28,000 light-years from the Galactic Center. It has been suggested fairly recently that ours is actually a barred spiral galaxy. That means that instead of a bulge of gas and stars at the center, there is probably a bar of stars crossing the central bulge.

So when someone asks you what the rotation of the Sun is, ask them which part.

Here’s an article from Universe Today about the Sun’s magnetic field flip, and here’s an article about how there were no sunspots on the surface of the Sun.

Here’s more information on the topic from Windows on the Universe, and here’s an article from NASA.

We have recorded an episode of Astronomy Cast just about the Sun called The Sun, Spots and All.

March 13, 2012December 23, 2015 by Fraser Cain

Watch This 3D Printer Make a Microscopic Car

3D printing of a microscopic race car. Image credit: TU Vienna

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3D printers let you manufacture any 3-dimensional object out of plastic. You just download the design, fire up the old 3D printer, fill the hopper with plastic, and it’ll slowly print out the object. It sounds cool, and hackers are having a great time playing around with them, but it still doesn’t compare to the scale, quality and cost of traditional manufacturing. It’s still a toy for hackers… right?

As you know, technology has a way of creeping up and then dramatically changing everything. And once you watch this mind-bending video of an ultra-high-resolution 3D printer creating a tiny race car, I think you’ll agree with me that 3D printing technology is improving in leaps and bounds.

Researchers at the Vienna University of Technology recently demonstrated a new kind of 3D printer that can create objects orders of magnitude faster than previous devices, at much finer scales; just a few hundred nanometers wide.

Check out this amazing video of the new 3D printer technology quickly creating a microscopic model of a race car.

Their printer uses a liquid resin which is hardened at exactly the right spots by a focused laser beam (rule 1, everything cool is done with lasers). The lasers can be redirected by mirrors and can harden a line of this liquid resin just a few hundred nanometers wide, giving it a very high resolution.

But it’s also fast. In the past, 3D printers were clocked at millimetres per second. Well, this TU Vienna printer can harden a 5-meter line of resin in 1 second.

There were two discoveries that pushed this advance forward:

They improved the control mechanism of the mirrors so they’re in continuous motion, accelerating and decelerating at the precise times to get the high resolution printing.
They used photoactive molecules to harden the resin. When the laser light hits the resin, it induces a chain reaction that turns it from a liquid to a solid; only at the point of highest intensity.

What would you use a 3D printer like this for? If it’s this fast and accurate, the mind boggles with the possiblities. The researchers proposed medical applications, like building scaffolding for living cells to attach, allowing you to grow organs in the lab. But the imagination really breaks down trying to imagine the implications for this kind of technology.

Okay, now I want one.

Original source: TU Vienna, with a nod to SpaceRef.

March 13, 2012December 23, 2015 by Fraser Cain

Jupiter’s Jet Streams Get Thrown Off Course

Jupiter's jet streams. Image credit: NASA/JPL/SSI

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Both Earth and Jupiter have jet streams; fast-moving winds that circle the globe. On Jupiter, those jet streams are constrained to very specific bands of the planet, while they meander around the Earth. We can see huge variations of weather when Earth’s jet streams move around – like unusually cold weather in Florida.

These strange weather patterns can occur on Earth when the jet streams interact with another atmospheric phenomenon called Rossby waves. We have them here on Earth, and they were first identified on Jupiter about 20 years ago.

And now scientists have identified the signature of Rossby waves throwing the jet streams off course on Jupiter. During its flyby of Jupiter, NASA’s Cassini spacecraft captured these images of Jupiter’s atmosphere; 100 were stitched together into a time-lapse movie.

If you watch the movie, you’ll be able to see a series of small, dark, V-shaped “chevrons” forming along the side of the jet stream. Eventually the well-defined atmospheric band starts to ripple and distort because of these Rossby waves. This shows that the jet streams on Jupiter, like Earth, can be thrown off course by the Rossby waves.

Here’s a quote from the press release:

“A planet’s atmosphere is a lot like the string of an instrument,” says co-author Michael D. Allison of the NASA Goddard Institute for Space Studies in New York. “If you pluck the string, it can resonate at different frequencies, which we hear as different notes. In the same way, an atmosphere can resonate with different modes, which is why we find different kinds of waves.”

By studying these waves, scientists hope to be able to get an idea of what lies beneath Jupiter’s thick cloud layers; to understand the deeper atmospheric composition and structure.

Original source: NASA/JPL/SSI News Release

March 13, 2012December 23, 2015 by Fraser Cain

Who Discovered Mercury?

Mercury's limb. Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington

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Mercury is one of the 5 planets visible with the unaided eye. Even thousands of years ago, ancient astronomers knew that the 5 wanderers were different from the other stars in the sky. The 5 planets visible with the unaided eye are Mercury, Venus, Mars, Jupiter and Saturn. They gave them distinct names, and charted their positions with incredible accuracy. It’s impossible to say “when was Mercury discovered”, since that would have been before recorded history.

But when did astronomers realize that Mercury was a planet? That happened with Copernicus developed his model of a Sun-centered Solar System, published in 1543. With the Sun at the center of the Solar System, and not the Earth, it meant that both the Earth and Mercury were planets. This discovery was confirmed when Galileo first turned his telescope on the planets and realized they matched predictions made by Copernicus. Unfortunately, Galileo’s telescope wasn’t powerful enough to reveal a disk for Mercury, but it did show how Venus went through phases like the Moon.

This model was backed up by Galileo, who pointed his first rudimentary telescope at Mercury in the 17th century. Unfortunately his telescope wasn’t powerful enough to see Mercury go through phases like he saw with Venus.

Because it’s so small and close to the Sun, Mercury was difficult to observe with ground-based telescopes. More powerful telescopes only revealed a small grey disk; they didn’t have the resolution to display features on the planet’s surface, like craters or lava fields.

It wasn’t until the early 1960s when radio astronomers started bouncing signals off the surface of Mercury that more information was finally known about the planet. These signals revealed that Mercury’s day length is about 59 days. Even more detailed observations have been made with the Arecibo telescope, mapping surface features down to a resolution of 5 km.

The most detailed observations of Mercury have come from the exploration from spacecraft sent from Earth. NASA’s Mariner 10 spacecraft swept past Mercury in 1974, capturing images from an altitude of just 327 km. It eventually mapped about half of the planet in unprecedented detail, revealing that the planet looked very similar to the Earth’s moon, with many impact craters and ancient lava fields.

If you’re wondering who discovered the element mercury, nobody knows that either. The element has been known for thousands of years, and was used by the ancient Chinese. Liquid mercury was found in Egyptian tombs closed up almost 4,000 years ago.

We have written many articles about Mercury for Universe Today. Here’s an article about new mysteries unveiled on Mercury, and the possibility that Mercury could cause an interplanetary smash-up.

Want more information on Mercury? Here’s a link to NASA’s Solar System Exploration Guide, and here’s a link to NASA’s MESSENGER Mission Page.

We have also recorded a whole episode of Astronomy Cast that’s just about planet Mercury. Listen to it here, Episode 49: Mercury.

References:
NASA Cosmic Distance Scales
NASA Solar System Exploration: Mariner 10

March 13, 2012December 23, 2015 by Fraser Cain

Shock Diamonds

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I recently reported on Chinese plans to launch Shenzhou-9, and used a stock image of a Long March-2F rocket blasting off the launch pad. Nafin wanted to know what that diamond pattern trailing behind the rocket was, and ivan3man_at_large posted the answer: they’re called shock diamonds.

Shock diamonds? That term had somehow slipped past me, so I thought I’d dig into it some more.

Shock diamonds (alternatively known as “Mach disks”) occur when gas is exiting a nozzle at supersonic speeds, at a different pressure than the outside atmosphere. At sea level, the exhaust pressure might be lower than the thick atmosphere. And then at very high altitudes, the exhaust pressure might be higher than the thin atmosphere.

So these shock diamonds can appear just as a rocket is taking off, or at high altitude when it shifts into supersonic speed.

A classic example is the space shuttle blasting off, but another famous example is when Chuck Yeager’s X-1 rocket plane reached Mach 1.

Let’s take the example of a rocket blasting off. In this case, the exit pressure of the exhaust is lower than the outside atmosphere, and so you get a situation called “overexpansion”. The gas exits the rocket at a lower pressure, and fans outward from the exhaust nozzle in an “expansion fan”. But the outside atmosphere is higher pressure than the exhaust gas, and so compresses it inward. This difference in pressure forces the gas back together at a specific point – the first shock diamond.

(I’ll spare you all the complex fluid dynamics at this point.)

Then the gas compensates and expands again into a new expansion fan, and then it’s forced back together the same distance further along from the rocket at the next shock diamond, and so on and so on. Eventually atmospheric distortion and friction takes over, equalizing the pressure of the exhaust plume with the ambient atmosphere.

Shock diamonds behind the SR-71 Blackbird.

Shock diamonds were originally discovered by Ernst Mach, the famous Austrian scientist who did work on fluid dynamics.

One other interesting side note, shock diamonds aren’t just seen in rocket exhausts. They’ve also been seen blasting out of volcanoes and artillery guns

There are two great articles on Mach diamonds if you really want to understand them more deeply. Check out this article from Aerospace Web and this one from the Allstar Network.

March 13, 2012December 23, 2015 by Fraser Cain

Venus-Jupiter Conjunction, March 15th, 2012

The two conjunctions. Image credit: Stellarium

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In case you’re the only person on Earth who hasn’t heard about it yet, Venus and Jupiter will be in conjunction on March 15th, 2012, passing within 3° of each other. The two planets have been getting closer and closer in the sky for the last month, and now it’s time to see them side-by-side. Venus is the higher, brighter object, and Jupiter is the lower dimmer one.

Of course, Venus and Jupiter aren’t actually close to one another in the sky. They’re really separated by millions of kilometres. But from our perspective here on Earth, we see the two objects closely lined up. That’s a conjunction.

On March 15th, 2012 at 10:37 UTC, Venus and Jupiter reach 3° distance from one another. That’s approximately 6 times the width of the full Moon.

And in case you’re wondering, the conjunction will be visible from everywhere on Earth: from Australia to Canada, from Japan to Chile. The two planets will brighten in the West shortly after sunset. Since Venus and Jupiter are two of the brightest objects, they’ll be visible even in the most light polluted cities.

As a special bonus, the planet Mars is also high and bright in the sky, visible as that bright red “star” further to the East. Mars recently reached its closest point to Earth, known as opposition. Mars won’t be this close and bright for two more years.

Venus/Jupiter/Moon conjunction 2012 Image credit: Fraser Cain

The sky show will continue, and on March 25th, 2012, the New Moon will join the pair again to create a triple conjunction. Another great photo opportunity. Here’s our photo gallery of images Universe Today readers sent in during the last Moon/Venus/Jupiter conjunction.

Although 3° sounds close, they can actually get much closer. In October 26, 2015, for example, the two planets will only be 1° apart. But this is one of the best conjunctions we’ll see for a few years because the two planets are so high in the sky after the Sun sets.

We’d love to see your pictures of the conjunction. Please email them to [email protected], and we’ll post them in a few days.

March 12, 2012December 23, 2015 by Fraser Cain

Next Chinese Mission Might Include Some Women

Long March rocket launching the Shenzhou 5. Credit: Wikimedia

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Officials from the Chinese Space Agency announced today that they’ve completed crew selection for their next team of spacefarers – called taikonauts – and this time, the team includes some women.

The next major mission for China will be the first manned docking mission to the Tiangong-1 space station. This station was launched in September 2011, and was successfully docked with the unmanned Shenzhou-8 spacecraft back in November.

And so the next major step in the Chinese plans is for Shenzhou-9 to perform a manned docking with the station. Three taikonauts will be on board, and that crew might include some women – the first time the Chinese will have sent women to space.

This mission is already progressing nicely. The Shenzhou-9 spacecraft and its Long March-2F rocket have been completed. And if everything goes as planned, they’ll launch and perform the manned docking some time between June and August 2012.

The final composition of the Shenzhou-9 crew hasn’t been announced yet, so it might still be a few more years before the Chinese women finally get their chance to fly to space.

Original Source: Xinhua