StarDate

Earth and the solar system’s other rocky planets probably grew as smaller blobs of rock and metal slammed together, forming ever larger bodies. As they grew, gravity pulled heavier materials — iron and nickel — toward the middle, forming their cores. Lighter materials floated toward the top, forming the mantle and crust.

We can’t actually see the cores of these worlds. But a new NASA mission may be able to show us the next-best thing: the core of a possible protoplanet, one of the building blocks of planets.

Psyche will orbit an asteroid of the same name. The asteroid is a chunk of metal about 150 miles in diameter — the biggest metallic asteroid in the solar system. It could be the surviving core of a protoplanet. The little object’s outer layers could have been blasted away by collisions with other asteroids, leaving only its dense metallic core.

Observations by ground-based telescopes show that 90 percent of its surface is made of iron. The rest is made of various minerals. A close-up inspection of those minerals could confirm that Psyche is the leftover core of a protoplanet. On the other hand, it could show that the minerals came from impacts with other asteroids, telling us that Psyche never had a mantle or crust.

Either scenario will reveal more about how the inner planets formed and how they grew, and perhaps give us a hint of what their metallic cores look like.

We’ll talk about some other future missions of discovery tomorrow.

Script by Damond Benningfield

Two new NASA missions are solar-system time machines. They’ll visit relics from the early solar system, providing a glimpse into the materials and processes that gave birth to the planets.

Lucy will fly past seven asteroids — big chunks of rock, metal, and ice. One of them is in the asteroid belt, between the orbits of Earth and Mars. But the others share the orbit of Jupiter. Known as Trojans, they’re locked in place ahead of or behind the giant planet by the gravity of Jupiter and the Sun.

Jupiter itself probably moved around a bit when it was young. It slid much closer to the Sun, then back out again. The Trojans might have formed with Jupiter and followed its migrations. On the other hand, they might have been captured by Jupiter as it moved. Studying them may help explain when and where they formed.

In addition, the asteroids contain materials from the birth of the solar system. They probably haven’t changed much over the eons, so they preserve a record of conditions when the solar system was young.

The mission will take advantage of existing technologies. Two of its instruments will be based on those used on New Horizons, which flew past Pluto. And a third will be based on another asteroid mission, Osiris-Rex.

Lucy will launch in 2021, with arrival at Jupiter’s orbit six years later. By then, the second mission should be well on the way to its destination — the possible core of a would-be planet. More about that tomorrow.

Script by Damond Benningfield

Those of us in the United States will wake up to a new season tomorrow. Spring begins at 5:29 a.m. Central Daylight Time — the moment of the vernal equinox. It occurs when the Sun crosses Earth’s equator from south to north. It ushers in longer, warmer days here in the northern hemisphere, and shorter, cooler days in the southern hemisphere.

Over the course of a year, the Sun moves north and south across the sky. That’s only an apparent motion, though. The Sun itself isn’t moving. Instead, that motion is caused by Earth’s tilt on its axis.

As seen from the Sun, Earth doesn’t stand straight up and down. Instead, it slouches — by about 23 degrees. As Earth moves around the Sun, that causes the north and south poles to nod toward and away from the Sun. In June, the north pole aims toward the Sun. That brings longer days to the northern hemisphere. And in December, it’s the south pole that nods sunward, bringing less daylight to northern climes.

The equinoxes come halfway between these extremes. Neither pole dips sunward, so both hemispheres experience roughly equal amounts of daylight and darkness. In fact, that’s where the name “equinox” comes from — it means “equal nights.”

The equinoxes are also the only times of year when the Sun rises due east and sets due west. Unless you’re on the equator, it rises north or south of those points for the rest of the year.

So enjoy the first day of spring — the start of a new season under the Sun.

Script by Damond Benningfield

 

Many of the gods and goddesses of the ancient world weren’t very nice. They lied, they cheated, they stole, and they even killed. And many of these actions were aimed at their own families.

Consider the Greek god Kronos, who in Rome was known as Saturn. He was the father of an entire race of gods — the gods of Olympus. But to protect himself from his offspring, he swallowed them whole as soon as they were born — except for one.

According to the story, Kronos was the ruler of the gods known as the Titans. His parents had foretold that one of his children would defeat him. So each time his wife, Rhea, gave birth to a new baby, Kronos swallowed it.

Rhea wasn’t happy with that arrangement, though, so she tricked him. She hid her son Zeus in a cave. And — perhaps showing why you shouldn’t gobble your food — she gave Kronos a stone wrapped in a blanket.

When Zeus grew up, he drugged his father, forcing him to regurgitate his now-grown-up children. They ganged up and waged war against the Titans. They won, and imprisoned the Titans in a pit at the edge of the world. With Zeus as their leader, these brothers and sisters then ruled the world from Olympus.

The planet Saturn was named in honor of the god. And it’s in good view early tomorrow. It looks like a bright star to the lower left of the Moon at first light. And the bright star Antares is about the same distance to the lower right of the Moon.

Tomorrow: springtime.

Script by Damond Benningfield

The Sun’s two closest planets are staging a switcheroo this month. Mercury is climbing higher into the evening sky, while Venus is dropping out of the evening sky. And if you look at just the right time, you can see them standing almost side by side the next few evenings.

Mercury is the closest planet to the Sun. Since Earth is the third planet out, Mercury has a limited range of motion across our sky, so the little planet rarely climbs into really good view. At best, it’s visible for a little while before sunrise or after sunset, quite low above the horizon.

Mercury passed behind the Sun earlier this month. Now, it’s moving away from the Sun, so it’s climbing into the evening sky. In fact, this is its best evening appearance for the entire year. It’ll climb higher over the next few nights, making it easier to see.

Venus is the second planet from the Sun. It’s getting ready to cross between Earth and Sun, so it’s dropping lower in the sky each evening — ready to move into the morning sky in about a week.

For now, though, look for Venus quite low in the west beginning about 15 minutes after sunset. It’s the “evening star,” so if you have a clear horizon, you can’t miss it. Tonight, much fainter Mercury is close to its lower left, but you probably need binoculars to pluck it from the twilight glow. The two worlds will stand side by side tomorrow night, with Mercury climbing away from Venus — and into better view — on succeeding nights.

Script by Damond Benningfield

Given the chance, a star can easily become a cannibal — a bigger star can swallow a smaller one. The star that gets eaten can leave its mark on the surviving star, though. Among other things, it can trigger an eruption or change the way the star rotates.

An example of that just may be found in Betelgeuse, the bright orange shoulder of Orion. It’s high in the south-southwest as night falls, above the hunter’s three-star belt.

When Betelgeuse was young, it was probably a few dozen times the diameter of the Sun. As it aged, though, changes in its core caused its outer layers to puff outward. Today, it’s many hundreds of times the Sun’s diameter.

And as Betelgeuse expanded, it just might have swallowed a companion star. That’s the conclusion reached by University of Texas astronomer Craig Wheeler after a team of his students used a computer model to study how Betelgeuse spins on its axis.

Wheeler says its rotation rate is unusually fast for a star of its size. The computer model shows that the star would spin that fast if it swallowed a Sun-sized companion. As the star spiraled in, it transferred its orbital motion to Betelgeuse’s outer layers, making the star spin faster.

A shell of gas surrounds Betelgeuse. It could have been expelled from the star when it swallowed the companion. Judging from the size and motion of the shell, that would have happened about a hundred thousand years ago — when Betelgeuse might have become a cannibal.

Script by Damond Benningfield

Modern amateur telescopes reveal some amazing sights, from the colorful death throes of stars that are thousands of light-years away, to spiral galaxies millions of light-years away. Perhaps the most amazing sight of all, though, looks like an average star. But it’s really a maelstrom of gas around a supermassive black hole. It’s two and a half billion light-years from Earth, which means we see it as it looked two and a half billion years ago.

3C 273 is a quasar — one of the most powerful objects in the universe. It’s powered by a black hole that’s hundreds of millions of times as massive as the Sun. The black hole’s gravity pulls in gas, dust, and stars from the galaxy around it.

This material swirls around the black hole, forming a disk that’s about as wide as our solar system. Friction heats the material to millions of degrees, so it shines brighter than an entire galaxy of stars.

Magnetic fields direct some of the superhot gas in the disk into jets that shoot into space. The jets produce enormous amounts of radio waves. One of the jets aims at Earth, so we get a powerful blast of energy from it.

Astronomers have cataloged a couple of thousand quasars. Some are even more energetic than 3C 273. But they’re also farther away, so they don’t look as bright. That leaves 3C 273 as the most-distant object visible through most amateur telescopes. Right now, it’s in the east a couple of hours after night falls, well above the bright planet Jupiter.

Script by Damond Benningfield

 

The center of our home galaxy, the Milky Way, is pretty quiet. The supermassive black hole that lurks there isn't “feeding,” so it doesn't produce much energy.

That’s not the case for many other large galaxies, though. As many as a billion of them could be classified as active galaxies — their central black holes are generating enormous amounts of energy.

The black holes themselves aren’t actually producing the energy. Nothing comes out of a black hole, so it stays black. Instead, an active galaxy’s black hole — which is millions or billions of times the mass of the Sun — is pulling in big clouds of gas and dust, along with occasional stars.

As this material spirals toward the black hole, it forms a disk that’s heated to millions of degrees. At that temperature, the disk emits a lot of energy. Some of it is in the form of visible light, but much of it is in the ultraviolet and X-ray portions of the electromagnetic spectrum.

Some active galaxies also spew out long jets of gas that are moving at close to the speed of light. The jets produce radio waves, so the galaxy can shine brighter at radio wavelengths than any other form of energy; more about that tomorrow.

An active galaxy doesn’t stay active. Energy from the disk can blow away surrounding clouds of gas and dust. That deprives the black hole of food, so it shuts down. The black hole is still there, though, waiting to grab a passing star or gas cloud — once again turning its host into an active galaxy.

Script by Damond Benningfield

One of the most exotic bodies in the solar system is Io, one of the large moons of Jupiter. It’s covered by hundreds of active volcanoes — more than any other body in the solar system. Their molten rock and volcanic gases make Io look like a scarred apricot.

Io is so active because of a gravitational tug-of-war between Jupiter and its other large moons.

The same side of Io always faces Jupiter, just as the same side of our moon always faces Earth. But as Jupiter’s other moons move past Io, they tug at it, trying to turn it around. That creates tides in Io’s crust. While the highest tides in Earth’s oceans are about 50 feet high, the tides in Io’s solid surface are more than 300 feet high. All of that energy melts some of the rock in Io’s interior, which then pushes its way to the surface.

At the surface, the molten rock bubbles up through cracks in the crust, sometimes building broad volcanic mountains.

Some of the volcanoes produce giant plumes of ash and gas, including the most prominent volcano of them all, known as Pele — a red-and-black bull’s-eye that’s hundreds of miles across. And the plumes extend far into space, creating a fat “doughnut” of gas that encircles Jupiter.

Look for brilliant Jupiter rising below our Moon late this evening, with the bright star Spica close to the lower right of Jupiter. Through binoculars, Io and Jupiter’s three other big moons look like tiny stars arrayed near the giant planet.

Script by Damond Benningfield

A big light pollutes the sky tonight: the full Moon. Its glare blocks faint stars from view. But the Moon is so beautiful that it’s worth a little inconvenience — and besides, there’s not a thing we can do to change it.

But we can change other sources of light pollution — the glow of civilization. The International Dark Sky Association says that because of that glow, 99 percent of the American population lives under light-polluted skies. And new light fixtures have the potential to make the problem worse.

Many cities have been switching to LEDs for their streetlights. They last longer than older technologies, and they use less energy.

The problem, though, is that most LEDs produce a lot of blue light. A recent report by the American Medical Association says that blue light scatters inside the eye, clouding your vision. It can also interfere with sleeping patterns. And, in fact, some cities that installed LED lights have had complaints from the neighbors.

Blue light also scatters more in the sky; that’s why the daytime sky is blue. So blue light shining into the sky makes it harder to see the stars.

Fortunately, though, newer LEDs are available in warmer colors than older models. With less blue light, there are fewer problems for residents. Phoenix decided to install almost a hundred thousand of these fixtures, and a city in California replaced its blue LEDs with the warmer ones.

That makes it easier to sleep, drive — and enjoy a dark night sky.

Script by Damond Benningfield