StarDate

To make a planet that’s comfortable for life, a lot of things have to fall into place. The planet has to orbit the right kind of star. It has to orbit at the right distance. It has to be made of the right materials. And the list goes on and on.

One factor may be whether a planet has plate tectonics, with slabs of its crust moving around and over each other. On Earth, the motions of the crust help regulate temperatures. Volcanoes belch carbon dioxide, which helps keep the air warm. But the plates also help bury carbon dioxide in Earth’s interior, keeping the air from getting too warm.

It may also help if a planet has a moon — especially one as big as Earth’s. Our moon helps keep Earth stable as it orbits the Sun. It also creates the tides, which are a big factor in sustaining life.

Another factor may be how close the planet’s birthplace was to a recently exploded supernova. The massive stars that become one type of supernova create a lot of heavy elements. Those elements are needed to make the rocky planets like Earth that are the most likely homes for life. When the star explodes, it blasts these elements into space. They “seed” nearby stellar nurseries, providing the ingredients for planets and life.

As astronomers discover more planets in other star systems, scientists are adding to the list of conditions. So we’re likely to find that many more things have to fall into place to make a planet comfortable.
 

Script by Damond Benningfield

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Astronomers have developed many ways to find planets in other star systems. The latest is with radio waves.

The first planet found that way was detected a couple of years ago by LOFAR, an array of radio telescopes in Europe. The planet orbits Gliese 1151, a star that’s 26 light-years away. The star is only a fraction the size and mass of the Sun, and its surface is thousands of degrees cooler than the Sun’s.

LOFAR picked up hints that something small was orbiting close to the star, but there was a wide range on the numbers. An instrument in the Canary Islands narrowed it down a bit. And another instrument zeroed in even more.

The Habitable-zone Planet Finder is attached to the Hobby-Eberly Telescope at McDonald Observatory. It’s designed to find planets orbiting small, faint stars. Its observations revealed that the planet at Gliese 1151 is about two and a half times the mass of Earth. It orbits the star once every couple of days.

It’s inside the star’s corona — a thin but hot outer atmosphere of charged particles. The planet interacts with the corona in a way that creates radio waves.

The discovery suggests that bigger radio telescopes in the future may be able to find many more planets — adding to the catalog of worlds beyond the solar system.

Gliese 1151 is in Ursa Major. As night falls, the star’s close to the lower left of the bowl of the Big Dipper. But it’s too faint to see without a telescope.
 

Script by Damond Benningfield

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It takes a village to discover and learn the details about a new planet. Consider TOI-532b. It was discovered using HPF — the Habitable-zone Planet Finder — an instrument attached to the Hobby-Eberly Telescope at McDonald Observatory. A dossier then was compiled by HPF, a space telescope known as TESS, and several smaller telescopes on the ground. It took dozens of astronomers at many organizations to make it work.

Astronomers have confirmed more than 5,000 planets in other star systems. There are several ways to find them, with different instruments and telescopes for each technique. It takes time and more instruments to fill in the details.

HPF participates in both sides of the work. It’s designed to find planets orbiting cool, faint stars. But it also follows up discoveries made by TESS. TOI-532 is one of many collaborations.

The system is about 440 light-years away. The star is cooler, smaller, and much fainter than the Sun. The planet, TOI-532b, is a half-dozen times the diameter of Earth, and more than 60 times Earth’s mass. That puts it in a special category, between Jupiter and Neptune, two giants of the solar system.

TOI-532 is in Orion, which is high in the southeast at dawn. The star is just above bright orange Betelgeuse, which marks the hunter’s shoulder.
 

Script by Damond Benningfield

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At first glance, the planet K2-18b sounds like just another set of numbers. It’s about 125 light-years from Earth. It orbits a cool, faint star about once a month. And it’s more than twice the diameter of Earth, and about nine times Earth’s mass.

Yet those numbers give scientists a profile of a remarkable world. It may be covered by liquid water, have a thick hydrogen atmosphere, and be at a comfortable distance from its star. That could make the planet a good place to hunt for life.

K2-18b is a possible example of a type of planet known as “hycean” — a combination of hydrogen and ocean. Such worlds are bigger and heavier than Earth, but smaller than Neptune, the solar system’s next-largest planet. Astronomers have discovered only a few candidate worlds, but a recent study says they could be quite common.

K2-18b resides in its star’s “habitable zone” — the region where temperatures are just right for water on the surface. Astronomers have even discovered water in its atmosphere.

But the combination of water and thick atmosphere could mean that such worlds could be “habitable” even if they were far outside that zone.

Scientists plan to study K2-18b and other candidates in detail. They’ll try to confirm the thickness and composition of the atmosphere. Eventually, they’ll look for “biomarkers” — combinations of compounds that, here on Earth, are produced by life.

More about exoplanets tomorrow.
 

Script by Damond Benningfield

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So far, the only place in the universe where we know there’s life is right here on Earth. But scientists are pondering the possibility of life elsewhere, from the moons of the solar system to planets in other star systems. They’ve even thought about life on “rogue” planets — worlds that roam through the galaxy in the darkness, far from any star.

A rogue planet probably started out orbiting a star. It was kicked away from the star by the gravity of other planets in the system. And astronomers have discovered several dozen possible rogues.

Without a star to warm it, such a world would quickly cool off. But the planet or an orbiting moon might provide enough heat for life to evolve and survive — perhaps for billions of years.

For one thing, a rocky world similar to Earth should have radioactive elements in its core. Heat from the decay of these elements could keep water below an icy crust from freezing — a global ocean that could be miles deep.

If the planet were born with a hydrogen-rich atmosphere, it might trap some of the internal heat, making the planet even warmer.

And if the planet kept one or more moons, they might generate heat through tides inside the solid planet. That heat could produce geysers of hot water carrying lots of minerals at the bottom of the global ocean. The combination of water, heat, and the right chemistry are the main ingredients needed for life — even on a world that’s far from the warmth of any sun.
 

Script by Damond Benningfield

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Tour books tell us that the best view of Prague comes from a 200-foot tower in the city’s Old Town. The tower has served many roles besides tourist attraction, though: weather station, clock, and astronomical observatory.

Klementinum tower was built in 1722. It’s part of a complex built beginning in the 1550s by Jesuit monks. They established a major university there. And while the university has moved on, the site is still home to the Czech Republic’s national library – considered one of the most beautiful in the world.

The tower became an observatory in 1751. It was founded by Joseph Stepling, a priest, mathematician, and astronomer. Three years earlier, he’d used a pair of eclipses to calculate the exact latitude and longitude of Prague. He acquired state-of-the art instruments for the observatory — many of which are on display today.

A few years later, observers began recording weather conditions — a practice that continues today. It’s one of the longest records of weather observations on the planet.

And in 1848, astronomers began keeping time for Prague. Sunlight entered the tower through a hole in the wall. The beam of light crossed a line inside the tower at noon. The astronomers then signaled the time to the rest of the city — first with flags, then with a cannon.

Klementinum tower was restored a few years ago. Today, it’s one of the top attractions in Prague — a spot that’s always offered a great view.
 

Script by Damond Benningfield

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The scorpion curves along the southern horizon as darkness falls on these late-summer evenings, with the bright orange star Antares at its heart.

Antares is one of the most impressive stars in the galaxy — a supergiant that’s destined to explode as a supernova. But a fainter star that stands close to its right is pretty impressive, too. Sigma Scorpii consists of four stars, at least one of which also will end its life with a giant bang.

Two of the four stars form a tight pair — their surfaces are separated by about half the distance from Earth to the Sun. They’re so close together that even the biggest telescopes see them as a single point of light. But instruments that break the light into its individual wavelengths measure two stars, not one.

Both stars are much bigger, brighter, and heavier than the Sun. Their details have proved a bit elusive, but the dominant member of the pair appears to be about 18 times as massive as the Sun and about eight times the Sun’s diameter. Its companion is smaller and lighter, but still a stunner.

The heavier star is almost certain to explode as a supernova sometime in the next few million years. The companion is likely to go as well, although it’s closer to the mass limit for a star to become a supernova. Above that limit, it goes boom. Below it, the star sheds its outer layers more gently, leaving its hot, dense core — a dead star known as a white dwarf.
 

Script by Damond Benningfield

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If you can escape the glare of the city the next few nights, the sky will present one of its most awe-inspiring sights: the glowing band of the Milky Way. It forms a beautiful arch in the eastern sky as darkness falls, and climbs directly overhead around midnight. And the Moon is out of the way for several nights.

That hazy band is the combined light of millions of stars in the disk of the Milky Way Galaxy. The stars are too faint to see as individuals, but when you add them all up it’s an impressive sight — and one that most Americans never get a chance to see. Street lamps, billboards, store signs, and even porchlights overpower the subtle Milky Way. It’s only from a dark location — someplace like a state or national park — that you can experience the Milky Way in its full glory.

The brightest patch of the Milky Way is above the “spout” of the teapot — an outline formed by the stars of Sagittarius. It’s low in the south at nightfall. That patch of sky marks the center of the galaxy, so we’re looking into a more densely packed region of stars.

The Milky Way then climbs to Cygnus, the swan, high in the east. It’s almost fully immersed in the glow. After that, it arcs down toward the northeast. It crosses W-shaped Cassiopeia, the queen, although it’s not nearly as prominent in that part of the sky. Still, if your sky is dark enough, it’s not hard to see — the seldom-seen spectacle of the Milky Way.
 

Script by Damond Benningfield

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Vega, in the constellation Lyra, stands high overhead at nightfall. Arcturus, in Boötes, is well up in the west. And Antares, the heart of the scorpion, is in the south-southwest.

Those stars are also known as Alpha Lyrae, Alpha Boötis, and Alpha Scorpii, indicating that each is the brightest member of its constellation. The names were devised by Johann Bayer, who was born 450 years ago.

Bayer was born in Germany in 1572, although the exact date is unknown. He was a lawyer, and became legal advisor to the Augsburg city council.

Bayer also was interested in astronomy. And in 1603, he published a star atlas. It was the first atlas to cover the entire night sky, including some southern constellations that had been plotted a few years earlier.

Bayer named the stars using a letter of the Greek alphabet followed by the constellation name. So a constellation’s brightest star was alpha, the second brightest was beta, and so on.

There were some exceptions, though — some stars were named based on their position. So while the star Dubhe is Alpha Ursae Majoris, it’s only the second-brightest star of Ursa Major. It marks the lip of the bowl of the Big Dipper, with the other Greek-letter stars tracing the dipper’s outline.

Bayer and a colleague created another atlas, published after Bayer died, that used names from Christianity. But it never caught on — leaving more than a thousand stars named with the Greek alphabet.
 

Script by Damond Benningfield

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Venus demonstrates that looks aren’t everything.

The planet is named for the Roman goddess of love and beauty — derived from the Greek goddess Aphrodite. And just seeing it in the sky explains why it got that name. It’s the brightest object in the night sky other than the Moon. Right now, it’s the “morning star” — a light so bright you might not believe it’s a planet.

Venus shines so brightly because it’s close to Earth and the Sun, and because it’s covered by an unbroken layer of clouds. As you dive into and below the clouds, though, the planet’s image begins to change.

The clouds themselves are made mostly of sulfuric acid — not exactly a beauty treatment. And as you drop below the clouds, the atmosphere gets dense, hot, and toxic. At the surface, the temperature is about 865 degrees Fahrenheit — hot enough to melt lead. And that’s the temperature around the entire planet, both day and night.

The atmosphere is made mainly of carbon dioxide — one reason that it’s so hot. As we know from experience here on Earth, CO2 traps heat, making the surface warmer.

And the pressure is about 95 times that at Earth’s surface — the equivalent of a depth of almost two-thirds of a mile in Earth’s oceans.

So deep down, Venus is no beauty.

Still, the planet is a treat to look at. Right now, it’s near the Moon in the dawn twilight. It will stand below the Moon tomorrow, and to the upper right of the Moon on Thursday.
 

Script by Damond Benningfield

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