StarDate

The Apennine Mountains are the tallest on the Moon. They top out at almost three miles above the surrounding plains. And for Apollo 15 astronauts Dave Scott and Jim Irwin, who landed at the base of the Apennines 50 years ago today, they offered quite a view.

SCOTT: Oh, look at the mountains today, Jim, when they’re all sunlit — isn’t that beautiful? IRWIN: It really is. SCOTT: By golly, that’s just super. It’s, you know, unreal!

The mountains represented some of the Moon’s earliest crust. And another nearby landmark — a canyon known as Hadley Rille — contained evidence of fairly recent volcanic activity.

Scott and Irwin bagged about 170 pounds of rocks and dirt. And they covered a lot of ground — about 17 miles — in the first lunar rover.

SCOTT: This is really a rockin’, rollin’ ride, isn’t it? I’ve never been on a ride like this before. Oh, boy. I’m glad they’ve got this great suspension system on this thing.

Scott and Irwin spent three days on the Moon. Then they rejoined crewmate Al Worden, who’d been operating a set of Moon-watching cameras from orbit. During the trip home, Worden took the first “walk” in deep space to retrieve the film.

Before they left orbit, though, the astronauts achieved one more “first”: They ejected a small satellite to observe the environment around the Moon.

APOLLO 15: 3, 2, 1, launch. ... Tallyho!

It operated for several weeks — extending the work of Apollo 15.
 

Script by Damond Benningfield

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The crew of Apollo 15 had a spectacular view. The astronauts landed at the edge of a deep canyon, near the base of some of the tallest mountains on the Moon. For scientists, the site offered a chance to study several eras of lunar geology.

Dave Scott, Jim Irwin, and Al Worden headed for the Moon on July 26th, 1971.

LAUNCH CONTROL: 4, 3, 2, 1, all engines running. Launch commit. Liftoff! We have liftoff ...

They entered lunar orbit 50 years ago today, aboard their command module, Endeavour.

APOLLO 15: Hello, Houston, the Endeavour is on station with cargo, and what a fantastic sight. CAPCOM: Beautiful news! Romantic, isn’t it?

The next day, Scott and Irwin boarded the lunar module, Falcon, and headed for the surface.

FALCON: Eight feet, minus one. Contact! Man! Okay, Houston, Falcon is on the plain at Hadley. CAPCOM: Roger roger, Falcon.

The site was ringed by the Apennine Mountains, which are almost three miles high. They formed when an asteroid slammed into the Moon four billion years ago. Shockwaves piled up layers of rock. So geologists hoped the base of the mountains might offer samples of the Moon’s early crust. The site also offered details on the impact.

Falcon landed at the edge of Hadley Rille, a canyon a mile wide and a quarter of a mile deep. It probably formed when a lava tube collapsed. So it offered a chance to study recent volcanic activity — at one of the most spectacular sites on the Moon.

More tomorrow.
 

Script by Damond Benningfield

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Our closest neighbor star is a bare cosmic ember. It’s much lighter and smaller than the Sun, and less than one ten-thousandth as bright. Yet the star produces giant explosions that are much more powerful than anything ever seen from the Sun. An outburst two years ago, in fact, was the brightest from any star at some wavelengths.

Proxima Centauri is just four-and-quarter light-years away, but it’s too faint to see without a telescope.

The star is put together a little differently from the Sun. A conveyor-belt effect carries hot gas from the core to the surface, where it cools and falls back toward the core. This motion generates a powerful magnetic field. As the star spins, the lines of magnetic force get tangled. When they cross, they snap, producing massive eruptions.

Proxima has produced many such outbursts over the years. But one in May of 2019 beat them all. Astronomers recorded a flare that lasted just seven seconds. At visible wavelengths, though, it was a hundred times brighter than any flare seen from the Sun. And it was even brighter in X-rays and ultraviolet light — the brightest ever seen from any star.

Two planets orbit Proxima Centauri. One of them is at a comfortable distance from the star for life. But getting zapped by such powerful radiation is dangerous. So if anything lives on the planet, it most likely would have to be quite different from life on Earth to survive such powerful outbursts.
 

Script by Damond Benningfield

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Our planet appears to be in one of the safest neighborhoods in the Milky Way Galaxy. We’re away from the regions where deadly exploding stars are most common.

That’s the finding of a study released this year. Researchers in Italy looked at the number of supernovas and gamma-ray bursts over the entire history of the galaxy.

A supernova is the death of a star. It fills its region of space with radiation and particles. They can sterilize nearby planets, and be harmful at distances of dozens of light-years. A gamma-ray burst is also an exploding star. But it emits powerful beams from its poles that can zap life thousands of light-years away.

The researchers found that early on, the safest region of the Milky Way was its rim, far beyond Earth. There were fewer exploding stars out there. Earth’s region, about halfway out to the edge, was a little more dangerous.

Over time, though, the “safe” zone moved inward. And over the last half-billion years, we’ve been at the outer edge of that zone. There have been more supernovas closer to the center, and more gamma-ray bursts out on the rim.

In the future, the number of exploding stars in our neighborhood should keep going down — making it even safer.

The Milky Way arches across the eastern evening sky now. The center of the galaxy is in the south, above the “spout” of the teapot formed by the stars of Sagittarius. That’s the galaxy’s danger zone — a neighborhood to avoid.
 

Script by Damond Benningfield

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Monster black holes were forming when the universe was young — just a few percent of its current age. And that’s a problem. Most ideas of how supermassive black holes form can’t explain such a rapid birth. But a new idea says the black holes could have had some help: the gravitational pull of dark matter.

Supermassive black holes are millions or billions of times as massive as the Sun. They inhabit the cores of most large galaxies, including our own. And they’ve been seen in galaxies that were forming as little as 800 million years after the Big Bang — 13 billion years ago.

One idea says that such monster black holes formed from the collapse of giant clouds of gas and dust. Another says that smaller black holes merged to form the supermassive ones. But neither process could form a giant black hole quickly enough to match what astronomers see.

The new idea says these early galaxies formed around clouds of dark matter. Dark matter produces no energy, but we see its gravitational pull on the “normal” matter around it. If there was enough dark matter, it could pull in huge amounts of normal matter in a short time. The combined matter then would collapse to form a supermassive black hole.

According to this idea, supermassive black holes would form quickly — even before their home galaxies could fully take shape. So the dark monsters at the hearts of galaxies could have formed under the influence of dark matter.
 

Script by Damond Benningfield

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The Moon shines big and bright tonight. It climbs into good view by about 11 p.m., and is well up in the southwest at first light tomorrow. And it has a big and bright companion: the planet Jupiter. It looks like a brilliant star to the upper left of the Moon as they rise, and to the right of the Moon at dawn.

By that time, the Moon will be about two and a half days past full. So for American skywatchers, the Sun will light up about 93 or 94 percent of the lunar disk.

You might think that means the Moon will be 93 or 94 percent as bright as the full Moon. And your eyes might seem to agree — since the Moon looks almost full, it must be almost as bright.

This is one of those times that you can’t trust your lying eyes, though. The pre-dawn Moon will be only half as bright as a full Moon. By comparison, when the Sun lights up half of the disk, it’s only one-sixth as bright as a full Moon.

One reason is that the lunar surface reflects sunlight most efficiently when the Moon lines up opposite the Sun — when it’s full.

The main reason, though, is that when the Moon is full, we don’t see many shadows — the central portion of the disk is in direct sunlight. At other times, though, the Sun is at a lower angle. Mountains, the rims of craters, and even big boulders cast shadows that make the surface appear darker. And the farther the Moon is from full, the longer the shadows — and the darker the Moon looks in our sky.
 

Script by Damond Benningfield

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Jupiter and Saturn are the largest planets in the solar system. Jupiter is about 11 times the diameter of Earth, while Saturn is almost 10 times Earth’s diameter. Despite their size, though, they spin faster than any other planets — 10 hours for Jupiter, a bit longer for Saturn. That’s compared to 24 hours for Earth.

You might wonder why these giants turn so fast. But scientists wonder why they aren’t faster. They should have spun a lot faster when they were born, but they slowed down.

A study a couple of years ago proposed a solution.

Jupiter and Saturn grew so big by gobbling up huge amounts of gas from a disk around the newborn Sun. As the gas fell onto the planets, it caused them to spin faster. Eventually, they should have been spun once every few hours — so fast that they were about to break apart.

But some of the gas was directed back outward, forming a disk around each planet. The planets’ magnetic fields grabbed onto the gas. That acted like a brake, slowing each planet to a much slower rate than we see today. Their own gravity quickly caused the planets to shrink, which made them spin faster — the same way a skater spins faster by pulling in its arms. That set up the rates we see today — fast or slow.

Jupiter and Saturn form a wide triangle with the Moon tonight. As they climb into view in late evening, bright Jupiter is to the left of the Moon, with fainter Saturn to the upper right.
 

Script by Damond Benningfield

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The Moon and Titan, the largest moon of Saturn, have something in common: The best places to get wet are at the poles. The Moon has lots of water ice. And Titan has actual liquid — lakes and seas filled not with water, but with hydrocarbons.

On the Moon, the ice is mixed with dirt at the bottoms of deep craters. Sunlight never hits the crater floors, so the ice remains frozen. A recent study suggested there’s more than a billion tons of ice around the poles, with most of it near the south pole.

Because of that, most lunar exploration over the coming years will be targeted at the south pole. Robotic landers will sniff out and study the ice. And human explorers may use the ice for water, oxygen, and rocket fuel.

On Titan, most of the wet stuff is near the north pole — about 95 percent. The largest body of liquid, the Kraken Sea, holds more than all the Great Lakes combined.

Differences in climate and landscape account for some of the imbalance between the poles. But one study says the major difference is that the southern landscape is more porous. The liquid ethane and methane can drain away to lower latitudes, where they evaporate — leaving the south pole much drier than the north.

And Saturn appears close to our Moon the next couple of nights. Tonight, it’s to the left of the Moon as they climb into good view by 10 o’clock, and above the Moon at first light. The giant planet looks like a bright star.
 

Script by Damond Benningfield

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The galaxy IC 10 is small but busy. It’s only a few thousand light-years across — a small fraction of the size of the Milky Way. But pound for pound, it’s giving birth to more stars than the Milky Way is. Many of those stars are big, bright, and heavy. At the ends of their short lives, they’ll explode. The cores of some of those stars will collapse to form black holes.

One system in the galaxy consists of a current black hole and a future one. IC 10 X-1 was the first source of X-rays discovered in the galaxy. The X-rays come from a “wind” of hot gas from the bright star, plus a disk of hot gas around the black hole.

Early observations indicated the black hole was about 15 times the mass of the Sun, with its companion about 25 times the Sun’s mass. But more recent work has found the masses a little tougher to pin down.

The companion appears to be heavy enough to explode as a supernova, leaving behind a second black hole. The blast may send the star and the current black hole racing away from each other. If they stick together, though, in a few billion years they’ll merge — forming an especially heavy black hole.

IC 10 is in Cassiopeia, which is low in the northeast in early evening and overhead at first light. IC 10 is near the top right point of the “W” that outlines the queen. The galaxy is a couple of million light-years away — quite close as galaxies go. But it’s so faint that you need a telescope to see it.
 

Script by Damond Benningfield

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[Double booms] MISSION CONTROL: Piercing the pre-dawn skies, the space shuttle announces its arrival at the launch site with its signature sound of twin sonic booms, having gone subsonic for the last time.

The space shuttle program rolled to a halt 10 years ago today. Atlantis completed the 135th shuttle mission, 30 years after the first.

The shuttle had been intended to replace almost all of America’s rockets. NASA promised to launch up to a flight a week. But shuttles were harder to maintain than expected. So launches were separated by months, not days.

Still, the shuttle was a remarkable machine. Its crews launched and repaired satellites, including Hubble Space Telescope. They conducted experiments. And they built most of the International Space Station.

But after the shuttle Columbia was destroyed during re-entry in 2003, NASA decided to ground the fleet after the space station was done.

For the final flight, Atlantis carried up spare parts and scientific equipment. Then it headed home. AUDIO: three bells. ISS: Atlantis departing the International Space Station for the last time.

It landed at Kennedy Space Center on July 21st, 2011.

MISSION CONTROL: Nose-gear touchdown. ... Having fired the imagination of a generation, a ship like no other, its place in history secured, the space shuttle pulls into port for the last time—its voyage at an end.
 

Script by Damond Benningfield

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