Stardate Radio Broadcast - McDonald Observatory
StarDate: September 20, 2013

Slowing Down

In the spring of 2012, a spinning stellar corpse suddenly slammed on the brakes. In an instant, its rotation rate slowed by about two millionths of a second. That may not sound like much until you consider this: the dead star was spinning once every seven seconds, and it weighs a half-million times more than the entire planet Earth. So slowing it down would take some pretty good brakes.

This object is a neutron star — the crushed core of a once-mighty star that exploded as a supernova. Despite its great heft, it’s only about a dozen miles in diameter.

Astronomers have watched the neutron star for years with X-ray telescopes in space. A couple of times, the star’s rotation rate has actually sped up — something that happens to quite a few neutron stars. But for the most part, it maintained a steady cycle, spinning about eight times a minute.

In April of last year, though, it produced a short but intense burst of X-rays. When astronomers looked at it afterwards, it had slowed down — something that no neutron star had ever been seen to do before.

The brake could have been the star’s interior. A neutron star consists of a solid crust, with a bizarre “fluid” beneath it. As the star spins, these two layers can rotate at different speeds. It’s possible that in this case, the fluid layer was spinning slower than the crust, and it “grabbed” the crust and slowed it down. That could have triggered the outburst of X-rays — and put the brakes on this tiny dead star.

Script by Damond Benningfield, Copyright 2013
StarDate: September 21, 2013

Journey’s End

After eight years and 35 looping orbits around Jupiter, the Galileo spacecraft was worn out. Its cameras had been destroyed by radiation, its tape recorder was cranky, and it was just about out of fuel. To eliminate any risk that it might crash into one of Jupiter’s icy moons and contaminate it with Earthly bacteria, engineers gave the craft one last command. They told it to slam into Jupiter, where it would burn up in the planet’s thick atmosphere. It did so on September 21st, 2003.

Galileo was a good-news/bad-news type of mission. Its launch was delayed, and its path to Jupiter lengthened, by the loss of space shuttle Challenger. The delays created mechanical problems that kept the craft’s main radio antenna from opening, severely limiting the amount of data it could transmit to Earth.

On the “good-news” side, Galileo became the first spacecraft to fly past an asteroid, and it discovered the first asteroid moon. And after it arrived at Jupiter, in 1995, it dropped a probe into the planet’s atmosphere.

After that, Galileo conducted extensive studies of Jupiter and its moons. It found evidence that oceans of liquid water are hidden beneath the icy crusts of three moons. It measured the composition of the Jovian clouds, and mapped the structure of the planet’s magnetic field.

Despite its problems, Galileo provided the most extensive view yet of the solar system’s largest planet — a mission of exploration that ended 10 years ago today.

Script by Damond Benningfield, Copyright 2013
StarDate: September 24, 2013

Dumbbell Nebula

For most of its life, a star like the Sun looks a bit drab — it’s a bright, glowing orb that doesn’t change much. At the very end, though, the star puts on a spectacular show. It expels its outer layers of gas into space, forming a colorful bubble that can be sculpted into many different shapes. The bubble can last for thousands of years before its gas dissipates and fades from sight.

One of the best-known examples stands high in the south as darkness falls, in Vulpecula, the fox.

The bubble is known by several names. The most evocative is the Dumbbell Nebula; seen through a telescope, it resembles a hand weight like you’d use at the gym.

The best measurements say the nebula is about 1360 light-years away, although that distance could be off by a couple of hundred light-years in either direction.

For most of its life, the star was like the Sun, steadily burning through the nuclear fuel in its core. Now, though, it can no longer sustain those nuclear reactions, so it’s shutting down.

In response, the star’s outer layers began streaming into space about 10,000 years ago. The gas left the star in waves and clumps, producing shells of gas with embedded “knots” that can be more massive than Earth.

Although the core is no longer producing nuclear reactions, it continues to shine because it’s extremely hot. Its energy causes the escaping outer layers to glow, setting the Dumbbell ablaze with color — a brilliant final act for a star.

Script by Damond Benningfield, Copyright 2013
StarDate: September 25, 2013

NGC 7052

Some galaxies are like cosmic works of art, with beautiful curves and splashes of color. Others aren’t so memorable — they look like fat, fuzzy footballs, with no features at all to set them apart. Yet these plain-looking agglomerations of stars can still be interesting — especially on the inside. Many of them — and perhaps all — contain supermassive black holes in their centers.

An example is NGC 7052. It’s almost 200 million light-years away in the constellation Vulpecula, the fox, which stands high in the south at nightfall.

NGC 7052 is one of those featureless footballs, known as an elliptical galaxy. It contains hundreds of billions of stars, but almost all of them are old and faint.

The galaxy’s center is a lot more interesting. A big doughnut-shaped cloud of dust surrounds a brilliant cluster of stars. And the stars surround a black hole that’s more than 300 million times as massive as the Sun.

The black hole itself is invisible — its gravity is so strong that not even light can escape from it. But several lines of evidence point to its existence.

For one thing, the galaxy’s core is a strong source of radio waves — the signature of matter ensnared by a strong magnetic field around a black hole. And the speed of stars and gas in the galaxy’s center show that they’re orbiting something small but extremely heavy: a black hole — an interesting feature in an otherwise dull galaxy.

More about Vulpecula tomorrow

Script by Damond Benningfield, Copyright 2013
StarDate: September 27, 2013

ER Vulpeculae

Although we sometimes think of the Sun as a typical star, stars like our own are actually pretty rare. Only about one in 25 stars has a similar color, temperature, and luminosity as the Sun. Yet the constellation Vulpecula, the fox, boasts a remarkable system that consists of two stars that are almost identical to the Sun.

ER Vulpeculae is bright enough to see through binoculars. But no telescope on Earth or in space is good enough to show you the two stars separately — they’re so close together that their light blurs into a single pinpoint. Their surfaces are separated by only about a million miles, and the two stars whirl around each other once every 17 hours.

The stars spin just as fast as they orbit each other. That’s because their mutual gravitational pull creates strong tides that force the same side of each star to face the other, just as terrestrial tides force one side of the Moon to face Earth. So each star makes one full turn on its axis every 17 hours — far faster than the Sun, which rotates only about once a month.

The rapid rotation strengthens the stars’ magnetic fields, producing enormous spots and flares on both stars of ER Vulpeculae. The intense activity provides insight into what our own planet may have confronted billions of years ago. That’s because when the Sun was young, it too spun fast — and likely hurled huge flares that may have helped or hindered the development of life here on Earth.

Script by Ken Croswell, Copyright 2013
StarDate: October 1, 2013

Uranus at Opposition

Hundreds of planets have been found in other star systems. They’re all so far away, though, that they’re seen as no more than squiggly lines on a computer screen. Yet astronomers are slowly starting to tease details out of some of those squiggles.

To understand how difficult the problem is, consider that there’s still a lot to learn about the planets of our own solar system, even though by astronomical standards they’re just next door.

One mystery, for example, is why the planet Uranus radiates so little energy into space.

The four outermost planets — Jupiter, Saturn, Uranus, and Neptune — are all giants. They’re so heavy that their gravity squeezes their interiors tightly, producing heat that radiates into space. In fact, three of the four worlds emit a good bit more energy than they receive from the Sun. The exception is Uranus, where the energy is roughly balanced — and scientists are trying to figure out why.

Another mystery is the planet’s climate. Uranus orbits the Sun on its side, with each pole receiving 42 years of sunlight followed by 42 years of darkness. Astronomers are watching to see how the planet’s climate changes with the seasons — one of the mysteries of a world in our own neighborhood.

And this is a good time to study Uranus because it’s closest to Earth, so it’s biggest and brightest for the year. Even so, you need binoculars to spot it. It’s low in the east as night falls, in a barren patch of sky.

More tomorrow.

Script by Damond Benningfield, Copyright 2013
StarDate: October 2, 2013

Uranus at Opposition II

As befits a giant planet, Uranus has a giant entourage of moons — at least 27. Yet the planet is so far away that its moons are tough to see. In fact, most of the moons weren’t discovered until the last three decades.

William Herschel discovered the first two in 1787 — not long after he discovered the planet itself. Herschel proposed naming them for characters from Shakespeare, and his colleagues agreed. So those first discoveries were named Titania and Oberon, for the queen of the fairies and her husband from “A Midsummer Night’s Dream.”

Not surprisingly, they’re the biggest of all the planet’s moons. Titania is a thousand miles in diameter, while Oberon is just a bit smaller.

William Lassell discovered the next two moons of Uranus — the third- and fourth-largest — in 1851. And Gerard Kuiper discovered the next one — the fifth-largest — at McDonald Observatory in 1948.

Since then, the moons have come in bunches. The Voyager 2 spacecraft revealed 10 new moons when it flew past the planet in 1986. The rest have been found since then, with Hubble Space Telescope, telescopes on the ground, and through further analysis of the Voyager observations — giving Uranus a mighty entourage.

Uranus itself is in view all night, near the border between Pisces and Cetus, and it’s brightest for the year, too. It’s so far away, though, that you need binoculars to see the planet — and a good telescope to see any of its moons.

Script by Damond Benningfield, Copyright 2013
StarDate: October 3, 2013


One of the greatest problems for astronomers is that they can’t go out and study their targets from close range — they’re just too far away. In fact, it’s hard to measure how far away the stars really are. And without knowing a star’s distance, you can’t know its size or true brightness — values that are critical to understanding how stars work.

The most accurate system for measuring stellar distances is parallax. In essence, you look at a given star when Earth is on opposite sides of the Sun. The change in position makes the star appear to shift a tiny amount compared to the background of more-distant stars. It’s like holding up your finger and looking at it with first one eye, then the other — it appears to move back and forth against the objects beyond it.

Even for the closest stars, though, the shift is tiny. And as you move deeper into space, it gets tinier still. Such angles are extremely difficult to measure — especially with ground-based telescopes, which must look through Earth’s blurring atmosphere.

So the best distances to date have come from space. Hubble Space Telescope has measured the distances to dozens of stars. And a couple of decades ago, a small European space telescope measured the distances to a hundred thousand stars with extreme precision, and a million more with slightly coarser precision.

But a new European mission should soon eclipse that record. It’ll measure the distances to more than a billion stars. More about that tomorrow.

Script by Damond Benningfield, Copyright 2013
StarDate: October 4, 2013

Gaia II

To the eye alone, the Milky Way is simply a hazy band of light — a glowing archway in a dark night sky. In fact, it vaults high overhead this evening, from southwest to northeast. But seen through a telescope, the Milky Way is a dazzling tapestry of individual stars — millions upon millions of them. They outline the disk of our home galaxy.

A new European space telescope will measure the distances to many of those stars with unprecedented accuracy. That effort will provide by far the best 3D map of our region of the galaxy. What’s more, the craft will measure each star’s temperature, brightness, and its motion through space. Astronomers will use that information to understand more about the evolution of the entire galaxy.

Gaia is scheduled for launch as early as this month. It’ll orbit the Sun about a million miles away from Earth, providing an unobstructed view of the heavens.

Over the next five years, it’ll look at a billion stars about 70 times each. That will allow the craft to compile a dossier on each of those stars, and measure each star’s distance with far greater accuracy than ever before — a thousandth of a percent for the closest stars.

Gaia also will discover new objects. Mission scientists expect it to find thousands of planets in other star systems, tens of thousands of the failed stars known as brown dwarfs, and hundreds of thousands of asteroids in our own solar system — all while compiling its map of our galactic home.

Script by Damond Benningfield, Copyright 2013
StarDate: October 5, 2013

Merging Stars

While our Sun travels through space alone, many stars have one or more companions. Alpha Centauri, our closest neighboring star system, consists of three stars. And Sirius, the brightest star in all the night sky, consists of two stars.

A recent study of young star clusters suggests that many single stars started as double stars that merged during the first million years of their lives.

This study modeled a newborn star cluster filled with leftover gas and dust from the birth of the stars. In this simulation, the double stars had orbital periods that matched what astronomers observe when they study real newborn double star systems.

But over time, the model found that many of the pairs that were born close together interacted with the cluster’s remaining gas and dust. That produced friction that caused the stars to spiral together and merge to form a single star. As a result, the star cluster ended up with fewer close-together binaries — which is exactly what astronomers observe when they look at older stars. Indeed, stars in the most common binaries are so far apart that they take about 200 years to orbit each other.

Could our Sun have been born as two separate stars that then merged into one? It’s possible, but the researchers say it’s unlikely. Small planets like Earth and Mars may not have been able to take shape around a close binary. So the fact that we’re here suggests that the Sun isn’t just alone today — it was born that way.

Script by Ken Croswell, Copyright 2013
StarDate: October 6, 2013

Draconid Meteors

The dragon breathes fire the next few nights. That’s because the Draconid meteor shower should be at its best tomorrow night. The best time to look is in the evening, after the sky gets good and dark.

The meteors are bits of debris from Comet Giacobini-Zinner, which orbits the Sun once every six-and-a-half years. Comets shed tiny grains of dust as they move through space. Over time, these grains spread out along the comet’s path. When Earth sweeps through this path, the grains plunge into the atmosphere and vaporize, creating the streaks of light known as meteors. In this case, the meteors appear to “rain” from the direction of Draco — hence the shower’s name.

Giacobini-Zinner probably entered our region of the solar system fairly recently, so its dusty debris is still clustered near the comet. So depending on how far we are from the comet, the number of meteors varies dramatically. In 1946, skywatchers in the southwestern U.S. recorded rates of up to 10,000 meteors an hour. And just two years ago, the shower reached several hundred meteors an hour.

We won’t see anything like that this year. But the shower is a bit unpredictable, so it’s still worth a look — especially since the Moon won’t be around to spoil the show.

To give the shower a try, find a dark but safe skywatching site away from city lights. The meteors are concentrated in the north, but they can appear just about anywhere in the sky — the fiery breath of the dragon.

Script by Damond Benningfield, Copyright 2013
StarDate: October 8, 2013

Juno at Earth

Earth is about to be robbed. A spacecraft that’s on its way to Jupiter will swing past Earth tomorrow. It’ll “steal” a bit of momentum from the home planet, giving it the final boost it needs to reach its destination.

Such a maneuver is known as a gravity assist, and it’s quite common. It makes it possible to reach the outer planets with less fuel, allowing a craft to use a smaller booster rocket, which cuts costs. It also makes it possible for a craft to maneuver between moons in a planetary system, allowing it to conduct far more close-range observations.

This encounter is with Juno, which was launched two years ago. It’ll swing about 300 miles above Earth’s surface, which will increase its speed by more than 16,000 miles per hour. Earth will actually slow down as a result of the encounter. But since our planet is about a million million billion times heavier than the spacecraft, we won’t notice a thing.

When Juno arrives at Jupiter in July of 2016, it’ll enter orbit around the planet’s poles — something that no craft has ever done before. That will allow it to probe Jupiter’s magnetic and gravitational fields in detail. From those readings, scientists will learn more about the planet’s structure. Current ideas say that Jupiter consists of a dense, rocky core surrounded by layers of hydrogen and helium. Juno’s observations should help confirm that picture — providing a look deep into the heart of the solar system’s largest planet.

Script by Damond Benningfield, Copyright 2013
StarDate: October 9, 2013

Mars on Earth

You don’t have to travel millions of miles to see Mars. Sometimes, a few thousand will do the trick. That’s because scientists have found several locations right here on Earth that offer some of the same conditions as the surface of Mars. Studying these spots can help scientists and engineers prepare for missions to Mars itself, and understand the results of those probes.

These “Mars-on-Earth” locations are known as Mars analogs.

Some of them are extremely cold, such as Devon Island in far northern Canada. Volunteers spend several weeks there during the Arctic summer to see what it would be like to live on Mars.

Other spots are extremely dry, such as the Atacama Desert in Chile. Much of the region receives only a few sprinkles of rainfall each year, with some parts getting none at all.

And still other spots offer unusual chemistry like that seen in some parts of Mars.

For example, a river in Spain, Rio Tinto, is highly acidic and contains high levels of iron and other metals. The river contains bacteria that derive energy from the chemicals in the water. And salty deposits in and around the river also contain unusual living organisms. Similar conditions prevailed several billion years ago in the region of Mars that’s being studied by the Opportunity rover. That suggests that life could have evolved on ancient Mars — and could still inhabit the planet today.

One of the best Mars analogs is Antarctica, and we’ll have more about that tomorrow.

Script by Damond Benningfield, Copyright 2013
StarDate: October 10, 2013

Heading for Mars

When spring arrives in the southern hemisphere of Mars, dark streaks begin inching down some steep slopes that are close to the equator. As spring turns to summer, the streaks grow longer and turn darker. And when the weather turns cold, the streaks vanish — only to form again when spring returns.

There are several possible explanations for the streaks. The most intriguing is that they’re trickles of water from snow or frost that mix with salts in the Martian soil. That makes them possible places for future landers to look for evidence of microscopic life.

Researchers have seen the streaks only in photos from Mars-orbiting satellites. Yet they’re learning more about the streaks by digging into similar features right here on Earth — in the valleys of Antarctica.

In satellite photos, the streaks in Antarctica look just like those on Mars. They form when ice just below the surface melts in the summer heat. It percolates to the surface and flows downhill, dampening the soil and making the streaks darker.

Later this month, a team from the University of Texas Institute for Geophysics will head for Antarctica to study the streaks found in the McMurdo Dry Valleys. In particular, the scientists will look at what happens when the salty water in the streaks freezes. The studies should help them better understand the streaks on Mars — and whether they’re good places to hunt for life on the Red Planet.

We’ll have more about Mars tomorrow.

Script by Damond Benningfield, Copyright 2013
StarDate: October 11, 2013

Icy Mars

At the surface, Mars is a desert world, its surface coated with a powdery orange sand that blows in the Martian winds. Dig just below the surface, though, and it’s a different story. Vast deposits of frozen water are found across much of the planet — perhaps more water than is found in the polar ice caps.

The Phoenix lander found almost pure water ice when it scraped just an inch or two below the surface. And radar aboard a Mars orbiter has found buried glaciers that may be hundreds of feet thick and cover hundreds of square miles.

The glaciers are in the middle latitudes of both the northern and southern hemispheres. Many of them are found hugging the sides of tall mesas, and they’re covered with a few feet of dirt. The radar observations show that the glaciers are almost pure ice, with little dirt or rocks mixed in.

The glaciers may have formed when Mars was tilted more severely than it is today. Water in the polar ice caps vaporized and moved toward the equator. The water condensed and fell to the ground as heavy snow, forming thick beds of ice. As the planet returned to a more gentle tilt, the ice was covered by blowing sand and dust — preserving vast glaciers beneath the Martian desert.

And Mars is in good view in the pre-dawn sky. It’s high in the east at first light, and looks like a fairly bright orange star. The true star Regulus, the leading light of Leo, is just below it, forming a beautiful duo with the “icy” Red Planet.

Script by Damond Benningfield, Copyright 2013

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