StarDate

A young star cluster that may be like a smaller version of the Pleiades moves low across the sky on late-autumn evenings. Despite that comparison, though, it hasn’t received a lot of attention.

In part, that’s because of its location. Blanco 1 is in the constellation Sculptor, which is quite low in the south at nightfall. Until recent decades, there weren’t a lot of research telescopes in the southern hemisphere, so the cluster was hard to study. And even today, astronomers are still trying to figure it out.

One thing they may have locked down is its distance. The Gaia spacecraft measured several of the cluster’s stars, and came up with a distance of about 750 light-years — a good bit closer than earlier estimates.

Astronomers are still working on Blanco 1’s population, though. The cluster appears to contain several hundred stars — roughly half as many as the Pleiades. It’s also home to several dozen “failed” stars, known as brown dwarfs.

The cluster’s age is uncertain as well. But it’s probably somewhere around a hundred million years.

When you put it all together, the cluster is like a smaller “twin” of the Pleiades, which is also known as the Seven Sisters — perhaps the most famous of all star clusters. Blanco 1 is about the same age as the Pleiades, and it contains about the same mixture of stars. The stars are more spread out, though. Combined with the cluster’s distance, that makes Blanco 1 a pale replica of its larger “twin.”

Script by Damond Benningfield

An American spacecraft is inching its way toward an asteroid. It’ll arrive on Monday, beginning an encounter that will continue for more than two years.

OSIRIS-REx will rendezvous with Bennu, an asteroid that’s about a third of a mile in diameter. Its a type of asteroid that probably hasn’t changed much since its formation. And it contains a lot of water and carbon, suggesting it also contains organic compounds — the basic building blocks of life. So Bennu could teach scientists about the materials and processes that give birth to planets — and perhaps about those that gave rise to life on Earth.

During its first month of operations, OSIRIS-REx will make several close passes by Bennu’s poles and equator. That will provide precise measurements of the asteroid’s mass and shape. After that, the craft will settle into orbit, beginning a long series of observations.

The mission’s highlight will come in July of 2020, when OSIRIS-REx is scheduled to scoop up a small sample from the surface. It’ll bring the sample to Earth three years later.

One of the reasons Bennu was selected is that it occasionally passes quite close to Earth, making it a relatively easy target. And there’s a small chance Bennu could actually hit Earth in the late 22nd century. So learning about its composition and structure could help future generations decide how to deflect this dangerous neighbor.

Tomorrow: a small “twin” for a famous star cluster.

Script by Damond Benningfield

A hyperactive comet is racing toward an especially close encounter with Earth next month. It’ll sweep past the beautiful Pleiades star cluster, and should be visible through binoculars. And one prediction says it could be bright enough to see with the unaided eye.

Comet 46/P Wirtanen isn’t all that big — less than a mile in diameter. But it’s described as “hyperactive.” That means it releases more gas and dust — especially water vapor — than expected for a comet of its size. The extra material makes it look brighter.

The comet orbits the Sun once every five and a half years. That wasn’t always the case, though. When it was discovered, in 1948, each orbit took more than a year longer. But close approaches to the planet Jupiter altered its orbit. They pushed the comet’s closest point to the Sun to just outside Earth’s orbit.

Wirtanen will pass closest to the Sun on December 12th, and to Earth just four days later. It’ll miss our planet by about seven million miles. That’s one of the closest approaches by any comet since 1950.

One comet expert estimates that it will reach naked-eye brightness. But others say it’ll remain too faint to see without some help. Either way, astronomers are keeping a close eye on this close comet.

They’re also keeping a close eye on an asteroid — not because it’s close to Earth, but because a spacecraft is closing in on it. More about that tomorrow.

Script by Damond Benningfield

When a comet is in deep space, it’s not really a comet at all. It’s still a ball of ice and rock, but it doesn’t have the key feature that makes it a comet: a tail. That’s because the word “comet” comes from an ancient phrase that means “long-haired star” — a reference to the beautiful tail.

Most of the objects that become comets spend most of their lives far from the Sun. In fact, some of them pass close to the Sun only once, then leave the solar system forever.

When a comet does approach the Sun, the Sun’s heat vaporizes some of the frozen water and gas at its surface. The vapor streams out into space. Radiation from the Sun zaps many of the molecules of water and other substances. That gives them an electric charge. So they’re easily blown away from the comet by the solar wind, which also has an electric charge. The tail aims directly away from the Sun.

A comet also has a second tail, made of dust. The dust flies into space along with the gases. The pressure of the Sun’s radiation pushes some of the dust away from the comet, forming the second tail. It’s usually much wider and brighter than the vapor tail.

The length of a comet’s tail depends on many factors, including how close the comet passes to the Sun. A typical tail might stretch a few hundred thousand miles or longer. And the longest tail ever recorded stretched about 350 million miles — a long streamer that made the comet a comet.

More tomorrow.

Script by Damond Benningfield

Heavy snow was falling over the Davis Mountains of West Texas. But the raw weather could do little to dampen the spirits of astronomers and visitors from across the country. Fifty years ago today, they dedicated McDonald Observatory’s 107-inch telescope. At the time, it was the third-largest telescope in the world.

The Observatory had started the quest to build a new telescope five years earlier. The University of Texas was looking to upgrade its astronomy program. It hired Harlan J. Smith to run the observatory and the new astronomy department.

One of Smith’s first goals was to build a big new telescope. And in a case of “timing is everything,” NASA needed help from telescopes on the ground to support its missions to the Moon and planets. So the space agency paid for the telescope and its instruments, while Texas paid for the dome to house it.

The telescope’s main mirror is almost nine feet across. It was made using a relatively new technique: Chunks of silica were melted together to produce a mirror that was stronger and tougher than conventional mirrors, and that didn’t “flex” as much under changing temperatures.

The telescope began its observations in 1969. Later, it was named for Harlan Smith. Today, the telescope remains as busy as ever, both as a research instrument and as a teaching tool for students. It could continue to produce world-class results — and astronomers — for many years to come.

Script by Damond Benningfield

The InSight spacecraft will take the most thrilling ride in the solar system tomorrow. It’ll hit the Martian atmosphere at about 14,000 miles per hour. And if everything works the way it’s supposed to, it’ll gently touch down on the surface just six minutes later.

InSight is scheduled to land on a smooth, featureless plain. It has cameras to view the landscape, and instruments to monitor the weather.

Its main mission, though, is to study the Martian interior. It’ll use a seismometer to record “marsquakes,” and a heat probe to measure temperatures below the surface. Those observations should tell us more about how Mars is put together.

To accomplish that goal, InSight first has to survive its tricky entry and landing.

The craft is sealed inside a capsule with a heat shield on its bottom. The shield will protect InSight from the fiery plunge through the atmosphere, and slow the craft down. When the shield’s work is done, it’ll fall away, and InSight will deploy a parachute and extend its landing legs. Next, the parachute and capsule will be jettisoned, and 12 small rocket engines will lower InSight to a gentle touchdown.

That sequence is scheduled to be monitored by a pair of cubesats — spacecraft that are about the size of a thick old-fashioned phone book. They’ll relay transmissions from the lander to Earth. After that, they’ll fly past Mars — leaving InSight to start studying the interior of the Red Planet.

Script by Damond Benningfield

Mars has some of the most spectacular scenery in the solar system. But the next Mars lander won’t see any of it. Instead, it’s scheduled to touch down in a wide, featureless plain near the equator.

That’s because the main mission for InSight, which will land on Monday, is to look deep into Mars. In fact, it’ll be the first Mars lander designed to the study the planet’s interior. For that, scientists simply want a landing site that’s safe and worry free.

Current models say Mars consists of the same layers as Earth: a core, a mantle, and a crust. The core is about 2200 miles wide — about half of the planet’s diameter. Like Earth’s core, it’s made mainly of nickle and iron. But unlike Earth’s core, it probably also has a lot of lighter elements — mainly sulfur.

The mantle once provided the molten rock that built the planet’s volcanoes. But the volcanoes all appear to be extinct or dormant, so the mantle may be more solid than Earth’s mantle. And it’s topped by a crust that averages about 30 miles thick.

InSight will use a pair of instruments to refine that model. One is a seismometer. It’ll listen for “marsquakes” and the impacts of space rocks. The way the shockwaves from these events travel through Mars can reveal its interior structure.

The other instrument is a heat probe that will drill down a dozen feet or so. It’ll measure the planet’s interior temperature — giving us a better look inside Mars.

More about InSight tomorrow.

Script by Damond Benningfield

Getting to Mars isn’t easy. In fact, about a quarter of all American missions to the Red Planet have failed. Two of them perished on launch. The other three made it to Mars, but failed during their arrival.

In 1993, for example, Mars Observer switched off its transmitter as it prepared to enter orbit just three days later. It was never heard from again. Its propellant tanks probably exploded when they were pressurized for the engine firing that would have placed the billion-dollar mission in orbit.

Six years later, Mars Climate Orbiter made it even closer to Mars before it failed. In fact, it passed too close to the planet. A math error caused it to plunge too deep into the outer atmosphere. The pressure ripped the craft apart.

And just a couple of months after that, Mars Polar Lander failed just seconds away from touchdown. Its computer thought the craft had already made contact, so it shut down the engines at an altitude of less than 150 feet. The lander crashed just moments later.

The last eight Mars missions have all made it safely. And NASA is hoping to make it nine in a row on Monday, when InSight is scheduled to touch down on Elysium Planitia. Because of some unique challenges, it will use a heavier heat shield than earlier missions, and a tougher parachute. If everything works as planned, InSight will spend a full Mars year studying the interior of a planet that’s hard to reach.

More about InSight tomorrow.

Script by Damond Benningfield

The only known planet of the star Aldebaran is a furnace. But that might not always have been the case. A recent study, in fact, says the planet could have spent billions of years in the zone that’s just right for life.

The difference is the result of changes in Aldebaran. Today, the star is nearing the end of its life, so it’s puffed up to giant proportions. That means its known planet receives so much energy that it’s far too hot for living organisms.

For billions of years, though, Aldebaran was much smaller and fainter than it is now — similar to the present-day Sun. The new study says that, under those conditions, the planet probably was in the habitable zone. That’s the distance from the star where temperatures are just right for liquid water, which is a key ingredient for life.

The planet, which was discovered by astronomers at McDonald Observatory, likely is a giant ball of gas much like Jupiter, the giant of our own solar system. Such worlds are considered unlikely homes for life. But if the planet has any moons, they could have been more comfortable — perhaps providing good conditions for life for billions of years.

And Aldebaran appears near our own moon the next couple of nights. The orange eye of Taurus, the bull, stands to the lower left of the Moon this evening. The Moon moves closer to it later on. And Aldebaran will stand even closer to the Moon tomorrow night.

Tomorrow: a dangerous approach.

Script by Damond Benningfield

Stars are more than just pretty sights that light up the night sky. They’re also chemical factories. Nuclear reactions in their cores create most of the chemical elements. In fact, their ancestors worked hard to create the elements that now make up our world, and even our bodies.

Some of the most common elements on Earth, such as oxygen, magnesium, and silicon, were made by stars that were much bigger and heavier than the Sun. When the stars exploded, their chemical brew was expelled into the galaxy.

But that’s not the case with all elements. One exception is manganese. Most of it comes not from big stars, but from little ones — stars that are smaller than Earth.

Manganese is slightly lighter than iron. It’s a metal that’s essential for making steel. And the human body needs it, too, although only in trace amounts; foods like oatmeal are the best sources.

Most of the manganese in the universe comes from small, dense stars known as white dwarfs. These stars are common. Indeed, the closest one is less than nine light-years away. It orbits the bright star Sirius, which climbs into view in the southeast in late evening at this time of year.

If a “normal” companion star dumps gas onto the white dwarf, it can become unstable and explode as a supernova. The explosion creates lots of iron, and also lots of manganese — so much that exploding white dwarfs were the source for most of the manganese that’s now on Earth.

Script by Ken Croswell