StarDate

When the solar system was young, Earth and the other worlds close to the Sun took a beating. They were pounded by giant asteroids and comets. The impacts gouged giant craters. On Earth, they blasted billions of tons of debris into the atmosphere — enough to block out the Sun. That could have had devastating effects on any life that was developing on our planet at the time.

A recent study says that those same types of impacts might have made the planet Mars more habitable, not less.

Today, Mars is cold and dry. And as far as we know, it’s lifeless as well. But it’s clear that the planet was much warmer and wetter in the distant past — making it more comfortable for life. Yet it’s difficult to see how Mars could have been more hospitable then, because the Sun was fainter, making Mars colder, not warmer.

A possible explanation comes from a recent study by scientists at the University of Colorado at Boulder. They used a supercomputer to simulate the global effects of impacts by comets and asteroids. They found that a collision could vaporize ice below the surface and spew it into the atmosphere. Each impact could have warmed and thickened the air for a million years or more. So a series of impacts could have kept the process going for a while — long enough to make Mars a comfortable abode for life.

And Mars is in good view tonight. It looks like a bright orange star below the Moon at nightfall, and to the lower left of the Moon as they set in early morning.

Script by Damond Benningfield

When the Van Vleck Observatory was dedicated 100 years ago tomorrow, it included just about everything astronomers and their students might need: a library, a lecture hall, a room for the observatory clocks, and two rooms for computers — young men and women who used pencil, paper, and a mechanical calculator to turn observations into data.

What it didn’t have was its telescope. The glass lens had been ordered from a German company, but when World War I began, the order couldn’t be fulfilled. So the observatory made do with a couple of older, smaller instruments until the 20-inch refractor was completed.

Tomorrow, astronomers and students from Van Vleck and elsewhere will gather on the campus of Wesleyan University in Middletown, Connecticut, to commemorate the observatory’s 100th anniversary.

The observatory is named for John Monroe Van Vleck, an astronomer and mathematician at Wesleyan in the 19th and 20th centuries. His family established a fund to pay for the new observatory. Van Vleck died in 1912, and Wesleyan hired Frederick Slocum, an up-and-comer from Yerkes Observatory, to complete and direct it. Slocum worked with the architect, Henry Bacon — best known for designing the Lincoln Memorial — to create a modern facility that was well adapted to the harsh northeastern climate.

Slocum dedicated the observatory to measuring the distances to the stars. That work and much more continues today — a century later.

Script by Damond Benningfield

For the stars of Spica, life is a never-ending give and take. The stars tug at each other and bombard each other with strong winds. And one of the stars may cause the other to vibrate like the string of a cello.

Spica is the leading light of the constellation Virgo. It stands close to the Moon as darkness falls tonight.

What we see as Spica is actually two heavy stars. One is about 11 times the mass of the Sun, while the other is about seven times the Sun’s mass. Each star is also much bigger than the Sun, and hundreds or thousands of times brighter.

The stars are so close together that they orbit each other in just four days. Since both stars are big and hot, they produce powerful “winds” of charged particles. The winds collide between the stars, producing X-rays. The combination of the winds and X-rays heats the side of each star that faces the other.

And the gravity of each star pulls more strongly at the side of the companion star that faces it. That distorts the stars, so each one is shaped more like an egg than a ball, with the small ends pointing toward each other.

A recent study found that gravity may have one more effect. The larger star pulses in and out. Astronomers have discovered at least three sets of pulsations — like notes played on three different strings of a musical instrument. One of those notes may be caused by the gravitational pull of the smaller star — plucking the strings of its bigger companion.

Script by Damond Benningfield

Astronomers are watching acts of birth and death in the stars: the possible birth of an Earth-sized planet in one system, and the destruction of a dwarf planet in another.

The act of creation is taking place in a system known as TW Hydra. The star itself is a little smaller and a good bit fainter than the Sun. And it’s just 10 million years old, compared to four-and-a-half billion years for the Sun.

A disk of gas and dust encircles the star. And an array of radio telescopes in Chile found several gaps in the disk. The gaps may have been swept clean by newly forming planets. One of the gaps is about the same distance from TW Hydra as Earth is from the Sun. So a rocky planet may be taking shape there — a planet as massive as Earth or heavier.

A much smaller planet in another system appears to be at the opposite end of the planetary lifecycle: It’s being torn apart.

The object appears to be about as big as Ceres, the largest member of the asteroid belt. It orbits a white dwarf — the small, dead core of a once-normal star.

Astronomers studied the system a couple of times last year. The first time, they saw the dwarf planet cross in front of the white dwarf. The second time, they saw evidence of several smaller chunks of material, with a cloud of debris around them. That suggests that the gravity of the white dwarf pulled the small planet apart. Eventually, the pieces may fall into the white dwarf — ending the life of a tiny planet.

Script by Damond Benningfield

The star Arcturus is a little bit heavier than our own star, the Sun. Yet that small difference has a big effect on the star’s evolution: Arcturus entered a final stage of life billions of years earlier than the Sun will.

Arcturus is one of the brightest stars in the night sky, and shines yellow-orange. Both of those characteristics are a result of its stage in life, which was triggered by its mass.

Mass is the key to how quickly a star consumes the hydrogen in its core. The gravity of a heavier star squeezes its core more tightly, making it hotter. That revs up the star’s nuclear engine, causing it to “burn” through the hydrogen more quickly than a less-massive star.

When the hydrogen is gone, the core shrinks and gets even hotter. That causes the star’s outer layers to expand and cool, making its surface look redder. In other words, the star becomes a red giant.

And that’s what’s happened with Arcturus. So even though it’s only about eight percent more massive than the Sun, it’s 25 times wider and a couple of hundred times brighter. And its surface is cooler, so it looks redder than the Sun.

Arcturus is about seven billion years old. That’s older than the Sun, but not as old as the Sun will be when it becomes a giant: It won’t reach that stage of life until it’s more than 10 billion years old.

Look for Arcturus high in the southern sky at nightfall, far to the upper left of the Moon — a puffy star that’s nearing the end of its life.

Script by Damond Benningfield

When a volcano erupts on Earth, its plume of ash can spread across thousands of miles. The strongest eruptions can blanket the entire planet, affecting the climate for months or years.

Eruptions on Jupiter’s moon Io are felt far beyond the moon itself. Some of their material escapes and forms a doughnut-shaped ring around Jupiter. That contributes to radiation belts that would be strong enough to kill an unprotected astronaut in hours.

Io is the most volcanically active body in the solar system. Hundreds of volcanoes dot its surface. They produce pools of lava that sizzle at more than 2,000 degrees Fahrenheit — much hotter than lava on Earth.

Some of the eruptions are so powerful that they shoot gas hundreds of miles high. Ultraviolet radiation from the Sun zaps some of this material, giving it an electric charge. Jupiter’s magnetic field then grabs the charged particles and sweeps them all the way around the giant planet, forming the ring.

This ring is so powerful that it can easily damage a spacecraft. So Jupiter missions use radiation-hardened components, and they avoid the ring as much as possible. And if people ever visit Jupiter, they’ll need good shielding to survive a plunge through Jupiter’s volcano-enhanced radiation belts.

And Jupiter is quite near our own Moon tonight. It looks like a brilliant star just to the right of the Moon. Through binoculars, Io and three other large moons look like tiny stars quite close to Jupiter.

Script by Damond Benningfield

A couple of bright companions flank the fat crescent Moon tonight. The brilliant planet Jupiter is to the upper left of the Moon, with the star Regulus about the same distance to the right of the Moon.

The Moon itself is approaching first quarter, when sunlight will illuminate half of the lunar hemisphere that faces Earth. So right now, the Moon is in its “waxing crescent” phase. The Sun lights up less than half of the visible Moon, but the fraction that’s in the light is getting bigger by the hour.

At first quarter, on Sunday morning, the Moon will be one-quarter of the way through its month-long cycle of phases. After first quarter, it’ll be in its “waxing gibbous” phase — more than half of the visible hemisphere will be in sunlight, with the fraction continuing to increase. The Moon will reach maximum illumination when it’s full, on June 20th.

After that, the cycle of phases will reverse. Less and less of the visible Moon will be in sunlight, so the Moon will be “waning.” First it’s waning gibbous, then it’s at last quarter, then it’s a waning crescent. The cycle comes to an end when the Moon is new — it passes between Earth and Sun, so it’s lost from view in the Sun’s glare. That’ll happen on the Fourth of July.

And a day or two after that, the Moon will pop into view as a thin crescent in the western evening sky — a waxing crescent that’s beginning the cycle all over again.

More about the Moon and Jupiter tomorrow.

Script by Damond Benningfield

The heart of the lion beats near the Moon this evening. Regulus, the bright heart of Leo, stands to the upper left of the Moon at nightfall. The Moon moves closer to Regulus before they set, after midnight.

Regulus is much bigger, brighter, and heavier than the Sun. And it spins about 15 times faster — more than 700,000 miles per hour at the equator.

Regulus whirls around so rapidly because it “stole” a lot of gas from a nearby companion star. As the hot gas poured in, Regulus twirled faster and faster. Today, it spins so fast that it bulges outward at the equator, so it looks like a severely squashed beachball.

If Regulus were to spin just 10 percent faster, it would rip itself apart. That’s unlikely to happen because it’s already pulled in all of the available gas from its companion. But some other stars are seen to spin much closer to that edge. Gas squirts away from such a star’s equator, forming a disk around it.

As the gas moves away from the star, it can condense to form tiny grains of dust. The dust absorbs some of the star’s light — especially blue light. That can make the star look much redder than it really is. In the 1800s, for example, astronomer John Russell Hind watched as one star changed from red to blue in a matter of weeks. The most likely explanation is that the star had spun off a shell of gas and dust, making it look red. The shell dissipated, though, allowing the star’s true color to shine through.

Script by Damond Benningfield

Modern America isn’t the first culture to expect a lot of flash from its stars. The astronomers of ages past, for example, linked the brightest stars in the night sky to make pictures. They depicted beasts, such as the lion; people, such as the strongman and the hunter; half-beast-half-people, such as the centaur; and even beastly people, such as vain Queen Cassiopeia.

But the astronomers neglected the faint stars between these patterns. In fact, many stars weren’t given a constellation home until just a few centuries ago.

An example is the stars of Leo Minor, the little lion. It’s in the west this evening, between Leo, the big lion, and the Big Dipper. It’s faint, so you need dark skies to find it.

The constellation was created more than three centuries ago by Johannes Hevelius. He included 18 stars in this new bit of celestial geography, but he didn’t give them names. Those were added later by other astronomers. But the list has a glaring omission.

In most constellations, the brightest star is designated with the Greek letter “alpha.” But Leo Minor has no alpha star at all. In fact, only one star has any Greek designation — Beta Leonis Minoris. And it’s not even the constellation’s brightest star. That honor belongs to 46 Leonis Minoris, which isn’t much to look at. It should have gotten the “alpha” name, but the first person to label the stars simply forgot. Then, as now, it seems, a star had to have some flash to get anyone to notice it.

Script by Damond Benningfield

The most-massive stars go out with massive explosions. But not all of these blasts are alike. Some make big booms, while others make humongous booms. And the biggest of all may shine trillions of times brighter than the Sun.

The death of a massive star is known as a supernova. It happens when the star can no longer produce enough radiation pressure in its core to counteract the inward pull of gravity. The core collapses. The star’s outer layers fall toward the core, then rebound with tremendous energy, blasting themselves into space.

But there appear to be several ways to make the blast even brighter. In one example, the core gets so hot that it generates electrons and their antimatter counterparts, positrons. These particles then ram together and annihilate each other in blazes of pure energy — enough to give the supernova’s brightness a big boost.

A recent study found that the brightest supernovae of all may be powered by powerful magnetic fields. When the core collapses, it forms a rapidly spinning neutron star. This ultra-dense ball is known as a magnetar because it produces a magnetic field a million billion times stronger than Earth’s. As the magnetar spins, it transfers energy from its own magnetic field to the expanding cloud of debris around it. That may make the supernova shine trillions of times brighter than the Sun — brighter, in fact, than an entire galaxy of normal stars — illuminating the mighty death of a mighty star.

Script by Damond Benningfield