StarDate

ET is quiet. Searches for radio signals from other worlds have come up empty. And while the search continues, astronomers are thinking up ways to broaden the hunt. They’re looking for “signatures” of intelligent life other than radio transmissions. And they’re pondering just how many civilizations that are as “talkative” as our own might be out there.

One new study, for example, will hunt for two kinds of “technosignatures.” One of them is industrial pollution in a planet’s atmosphere. Molecules like CFCs — compounds that’ve damaged Earth’s ozone layer — don’t occur naturally. So if they show up in a planet’s atmosphere, they must have been put there by a civilization.

The other signature is the “glow” of massive arrays of solar cells on a planet’s surface or in the space around it. Researchers will identify which wavelengths they need to scan to see that glow.

Another study found that talkative civilizations probably are pretty rare. The study considered some features of stars that are key to life. And it assumed that other civilizations would develop in about the same length of time as our own.

The study said there should be about three dozen civilizations in the galaxy that are at the same stage of development as our own. They would be emitting radio waves, just as we do. But they’d be so far away that current technology might not be able to hear them. So we’d need new ways to discover these distant civilizations.

Script by Damond Benningfield

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If anyone lives on the planet known as Trappist-1e, they should know their neighbors pretty well. There are six other confirmed planets in the system, and they’re all packed close together. As a result, they all pass within a few million miles of planet e. And two of them pass within about half a million miles — about twice as far as the Moon is from Earth. Since the planets are all bigger than the Moon, they’d be big presences in the sky.

The big question is whether anyone is there to enjoy the view. Scans for radio signals produced by a civilization there have come up empty. And our telescopes can’t see the planet clearly enough to know just what conditions are like. Even so, Trappist-1e is considered one of the best candidate worlds for life.

The planet is in the system’s “habitable zone.” That’s the distance from the star where conditions are most comfortable for life. And the planet is a lot like Earth. It could have a fairly thick atmosphere, and perhaps even big oceans.

Life would face some challenges, though. While the planet’s parent star is quite feeble, for example, it sometimes produces big outbursts of radiation that could damage the planet’s atmosphere.

But there’s plenty of time for life to take hold on Trappist-1e. The system is already a few billion years older than the Sun. And because the star is feeble, it will shine for trillions of years more — lighting up the busy skies of Trappist-1e.

Script by Damond Benningfield

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Trappist-1 is about as puny as a star can get. It’s less than 10 percent as massive as the Sun, and less than one-tenth of one percent as bright. Yet astronomers spend a lot of time studying it because it’s home to one of the most interesting planetary systems yet found.

The system consists of seven known planets. All of them are closer in than Mercury, the solar system’s innermost planet, is to the Sun. And five of them are about the same size and mass as Earth. And several of the planets could reside in the star’s habitable zone. That’s the distance from the star where temperatures are just right for liquid water — a key ingredient for life.

That doesn’t mean that those planets are habitable. Depending on the composition of their atmospheres, some of them could be hotter than Venus — hot enough to melt lead. And the outer planet could be an iceball.

What’s more, although the star is feeble, it sometimes produces giant outbursts of energy and charged particles. They could strip away a planet’s atmosphere or change its chemistry. Either one could render the planet unable to support life. Even so, one of the system’s planets is considered a reasonable home for life, and we’ll talk about that tomorrow.

Trappist-1 is in Aquarius, which is in the southeast at nightfall. It’s near the border with Pisces. But even though the star is only 40 light-years away, it’s far too faint to see without a big telescope.

Script by Damond Benningfield

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A beautiful trio highlights the eastern sky at dawn tomorrow. Two of its members are easy to see, while the third takes a little extra effort.

The bright members are the crescent Moon and Venus, the “morning star.” And the faint member is M44, the Beehive star cluster. It’s close above the Moon and Venus, but you’ll need binoculars to pick it out. Under dark skies, you might see a couple of dozen tiny stars packed close together — like bees buzzing around their hive.

Venus will continue its run as the morning star through the end of this year and into next year. For the next couple of months, it’ll stay at roughly the same height above the horizon at the same time before sunrise — roughly a third of the way up the sky.

But its location along the horizon will shift from due east to southeast — and for the same reason that the Sun and Moon slide along the horizon. As Earth circles around the Sun, our viewing angle to the Sun, Moon, and planets changes. That makes them “move” north and south across the sky. As a result, they rise and set in different directions at different times of year.

Venus is moving toward the Sun in our sky right now and will drop from sight in the Sun’s glare in January. It’ll pass behind the Sun in March. It will return to view around the first of May — this time in the evening sky — where it’ll spend the rest of the year.

Tomorrow: a star system that’s packed with planets.

Script by Damond Benningfield

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In the days before computerized precision, when someone wanted to create a constellation they simply linked up a few stars to make a picture. Some of those pictures are big and bold, such as the Great Square of Pegasus. It’s low in the east as night falls, and is tilted so that it looks more like a diamond than a square.

But as the science of astronomy became more precise, its practitioners needed something a little more organized. So they split the sky into 88 constellations, each with precisely defined borders. That gives each star and galaxy its own constellation to call home.

For the most part, these constellations incorporated the well-known star pictures. But in one case, a prominent star was moved from one constellation to another.

Alpheratz — a name that means “the horse’s shoulder” — is the brightest star of the Great Square. It’s at the left-hand point of the square during the evening hours. For millennia, it was also the brightest star in all of Pegasus.

But when astronomers approved the formal constellation borders in the 1930s, Alpheratz was given a new home. It’s just across the line in the adjoining constellation Andromeda. In fact, it’s tied for brightest-star honors in that constellation.

Yet when you look into the starry night sky, it’s hard to deny the star’s heritage. Alpheratz perfectly completes the Great Square of Pegasus — giving body to the flying horse.

Tomorrow: morning Moon, morning star.

Script by Damond Benningfield

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The giant planet Neptune probably has layers of hot “ice” — both the literal kind and the figurative kind: diamonds. They’re thousands of miles below the planet’s cloud tops, forged under extreme conditions.

Neptune is the fourth-largest planet in the solar system — almost four times the diameter of Earth. But it doesn’t have a solid surface. Instead, its deep atmosphere gives way to layers that are liquid, then solid.

The layers in the middle probably contain a lot of water. The region just below the atmosphere is liquid. At the bottom of that layer, though, temperatures and pressures are so high that the water molecules may break apart. Their oxygen atoms would form a rigid formation — like the framework of a building. But the electrically charged hydrogen atoms would flow through the framework. That flow might account for all or part of Neptune’s odd magnetic field.

And below that layer, conditions are even more extreme. They could squeeze carbon molecules so tightly that they’re transformed into diamonds. The diamonds would plummet deeper into Neptune, generating heat as they fall — producing more “hot ice” in this giant planet.

And Neptune is putting on its best showing of the year. The planet is lining up opposite the Sun, so it rises around sunset and is in view all night. It’s brightest for the year, too. Even so, you need a small telescope to see it, near the border between Aquarius and Pisces.

Script by Damond Benningfield

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Neptune is one of the forgotten giants of the solar system. It’s the fourth-largest planet — four times the diameter of Earth. But it’s so far away that it’s visible only with a telescope. And even through a telescope, it’s such a small target that it’s tough to study. It takes big telescopes and sensitive instruments to learn anything about it.

The planet is a little easier to study right now because it’s at opposition. That means it lines up opposite the Sun, so it’s closest to Earth for the entire year. It’s in the sky all night, too, near the border between Aquarius and Pisces.

Today, Neptune is almost three billion miles from the Sun. But when the solar system was born, it might have been much closer — perhaps just half as far as it is now.

Gravitational interactions with other bodies pushed it outward. At first, those interactions were with big iceballs left over from the birth of the planets. Such interplay changed the orbits of all the giant planets.

Later, interactions between the planets themselves altered their orbits even more. Neptune was given a swift “kick” by Jupiter, the largest planet. Before that kick, Neptune could have been the seventh planet from the Sun — inside the orbit of Uranus. But Jupiter pushed Neptune far beyond Uranus. Interactions with more small bodies then sculpted its orbit to the path it follows now — the edge of the realm of the planets.

We’ll have more about Neptune tomorrow.

Script by Damond Benningfield

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Cassiopeia is awash in star clusters. More than half a dozen clusters that are easy targets for binoculars huddle close to the letter “W” formed by some of the constellation’s brighter stars. And several fainter clusters are close by as well.

Clusters are common in Cassiopeia because the constellation lies along the glowing band of the Milky Way. When we look in that direction, we’re looking into some of the galaxy’s most densely populated regions.

One of the constellation’s busiest clusters is NGC 7789. At nightfall, it’s close to the right of Beta Cassiopeia, the star at the top right point of the W, which is in the northeast. Binoculars reveal a “haze” of stars, while a small telescope shows dozens of individual stars.

The cluster is also known as Caroline’s Rose. It’s named for its appearance — it resembles the petals of a rose — and for its discoverer, Caroline Herschel, who first saw it in 1783.

Caroline’s Rose isn’t as well understood as some of the other clusters in Cassiopeia. Even so, astronomers have put together a few details. It’s 6500 light-years away or farther, for example. It probably has somewhere between 600 and 1,000 stars, making it a fairly massive cluster. Most of the stars are packed in the cluster’s dense core, which spans about 30 light-years. And the stars are roughly a third the age of the Sun — a youthful stellar family in Cassiopeia.

Tomorrow: A giant planet moves around a bit.

Script by Damond Benningfield

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It’s not easy to measure the “weight” of a star that moves through space alone. You can’t just put it on a scale. Instead, astronomers try to determine its mass by measuring its temperature, its composition, how fast it spins, and more. And even then, they can change their minds as new observations become available. That applies even to some of the most intensely studied stars of all.

One example is Aldebaran, which marks the eye of Taurus, the bull. It appears near the Moon late tonight.

Aldebaran is one of the brightest stars in the night sky, so astronomers have been studying it for centuries. Until the last couple of years, most of their studies put its mass at about 1.7 times the mass of the Sun. But in 2018, a team of astronomers reported a new number: 1.16 times the mass of the Sun.

The team was studying a planet that orbits Aldebaran. The planet was discovered by measuring its gravitational pull on the star. The newer study measured not only that, but vibrations on the surface of Aldebaran. The vibrations are caused by sound waves that bounce around inside the star. The way they move can reveal the star’s mass.

If the newer mass is correct, it’s good news for life in the system. It means that Aldebaran would have been cooler and lived much longer than thought. So conditions on any moons around the heavy planet could have been fairly comfortable for a long time — giving life a chance to take hold.

Script by Damond Benningfield

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Ripples roll across the Milky Way Galaxy. They’re like the ripples on a pond after stones have been tossed into it. In the case of the Milky Way, the ripples were created by several impacts by a single “stone”: another galaxy.

The Sagittarius Dwarf Galaxy is only about one ten-thousandth as heavy as the Milky Way. But it’s plunged through the Milky Way’s disk three times — about five-and-a-half billion, two billion, and one billion years ago.

Each time it passed through, it created “waves” in the Milky Way. They ripple outward, pushing dust and gas in the Milky Way’s disk ahead of them. That triggers the birth of new stars.

Researchers looked at bouts of star formation in our part of the galaxy. They found three busy periods of starbirth. And all of them took place at about the same time the Sagittarius Dwarf was plunging through the Milky Way. That suggests that many of our stellar neighbors were born as a result of these passages. The researchers even speculated that one passage could have caused the birth of our own solar system.

Each pass through the Milky Way’s disk strips gas, dust, and stars from the dwarf galaxy. So it’s being consumed by the Milky Way.

The galaxy is in the constellation Sagittarius, which is due south at nightfall. It marks the center of the Milky Way. The dwarf galaxy is on the far side of the center, hidden behind clouds of gas and dust — regions that could be affected by future ripples.

Script by Damond Benningfield

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