StarDate

For the scientists who study volcanoes, Venus would be the equivalent of Disneyworld. About 1600 volcanoes pockmark the planet’s surface. Most of them are extinct, but a few may still be active. And thousands of structures that are related to volcanoes dot the surface as well. They include formations that look like rings, pancakes, and even starbursts.

Perhaps the most intriguing formations are known as arachnoids. They consist of a series of concentric rings with dozens or hundreds of lines radiating away from them. That makes them look like giant spiders clinging to vast webs. Scientists have cataloged more than 250 of them.

How arachnoids form is a bit of a mystery. One study, though, says they most likely are created when blobs of molten rock bubble up from the planet’s mantle, which is the layer below the crust. As it pushes up it spreads outward, splitting the crust. That forms the rings, as well as cracks that radiate outward. Molten rock then fills the cracks, forming dikes that can be more than a hundred miles long.

Over time, the process may continue, forming even bigger features — rings and starbursts that may consume the Venusian spiderwebs.

And Venus is in great view right now. It’s low in the west at nightfall, and shines as the “evening star.” Tonight, the crescent Moon stands well to its upper left. And the fainter planet Mars stands beside the Moon, completing a beautiful alignment in the evening sky.

Script by Damond Benningfield

The Curiosity rover is climbing through time. As it climbs the central mountain peak in a wide crater on Mars, it sees rock layers that were deposited at different times in the planet’s history. The higher it goes, the more recent the rocks — hence, the rover is climbing through time.

That excursion is reinforcing the idea that early Mars was much warmer and wetter than it is today. In fact, conditions on the planet could have been fairly hospitable for life. Alas, there’s no hint of life itself in the rocks — only hints that if life existed, it could have been comfortable on the young planet.

Recently, for example, Curiosity found minerals containing boron. Here on Earth, such minerals form in a wet environment, in temperatures that are comfortable for life. The rover also found fairly high concentrations of clays and a mineral called hematite — both of which form in water.

Liquid water, energy, and the right chemistry are necessary ingredients for known life forms. And Curiosity is showing that all of those existed on Mars in the distant past — discoveries made by climbing through time on a Martian mountain.

And Mars forms the top point of a skinny triangle in the sky this evening. It’s well above the crescent Moon, and looks like a moderately bright orange star. The much brighter planet Venus, the brilliant “evening star,” stands closer to the upper right of the Moon.

We’ll have more about this evening trio tomorrow.

Script by Damond Benningfield

In late February of 1942, British anti-aircraft radar stations were bombarded with a “noise” that they couldn’t filter out. Fearing that Germany had found a new way to jam the radar, physicist and army officer Stanley Hey investigated. He discovered that the noise appeared only during the day, and that it tracked the Sun across the sky. He also found that a giant sunspot was moving across the Sun at the time.

Hey concluded that the noise came from the Sun itself — the first confirmed detection of solar radio waves. Thanks to wartime secrecy, though, Hey couldn’t share this discovery until after World War II.

Most of the time, the Sun is fairly quiet at radio wavelengths. It does produce some background radio waves, so it’s the brightest radio object in the sky — but only because it’s a big, close target.

The Sun produces more radio energy when more sunspots darken its surface. And it produces bursts of radio waves like this during solar flares and other outbursts. [SFX: sun audio]

Studying solar radio waves reveals details about the Sun itself, and especially about its atmosphere. The radio waves provide a 3-D view of what’s happening out to distances of millions of miles. They also reveal the magnetic field that permeates the atmosphere, and how the magnetic field may heat the outer atmosphere to millions of degrees — discoveries made possible by bursts of static on British radar 75 years ago.

Script by Damond Benningfield

Skywatchers in parts of South America and Africa are in for a treat today: a solar eclipse. Unfortunately, though, it’s not a total eclipse, but an annular one. That means a thin but bright ring of sunshine will outline the intervening Moon.

Solar eclipses occur when the new Moon passes directly between Earth and the Sun. When the alignment is just right, the Moon covers the entire solar disk, briefly turning day into an awe-inspiring twilight.

But the Moon follows a slightly elongated path around Earth. So if an eclipse occurs when the Moon is farthest from us, the Moon isn’t quite big enough to cover the entire Sun, leaving a ring of sunlight.

And that’s just what happens this morning across a narrow path that stretches from South America, across the Atlantic Ocean, and into southern Africa. The Moon will cover up to 98 percent of the Sun, leaving plenty of sunlight. Still, the sky will turn dusky, the air will get cooler, and beams of sunlight shining through leafy trees will project bright rings on the ground — good clues that something important is happening in the sky.

This is the first of two solar eclipses this year. The second takes place in August. It will slice across the width of the United States. Even better, it’s a total eclipse, so the Moon will cover the entire Sun. That will briefly expose the Sun’s hot but faint outer atmosphere, known as the corona — one of the most awe-inspiring of all astronomical sights.

More about the Sun tomorrow.

Script by Damond Benningfield

The giant planet Uranus hasn’t received a visit from Earth since 1986, when Voyager 2 gave us our only close-up view of the planet and its known moons. The spacecraft also found several new moons. And scientists recently have seen hints of two more satellites in the Voyager observations.

Uranus has 27 known moons. That’s a lot fewer than Jupiter and Saturn. Perhaps that’s because Uranus is smaller and less massive. Or perhaps it’s just harder to find moons because Uranus is farther away, and it’s farther from the Sun, so there’s less light to reveal its moons.

But scientists analyzing old Voyager data have found wavy patterns in two of the rings of Uranus. Each pattern may arise from the gravitational influence of a small, dark moon just beyond the ring. If the moons exist, they’re no more than a few miles across — smaller than any other Uranian moon yet seen.

Hubble Space Telescope may be able to find them. If not, though, a future mission to the planet may spot these elusive bodies — or else rule out their existence.

And with binoculars, the next few evenings offer a good chance to look for Uranus. Tonight, it stands close to the upper left of Mars, which itself is to the upper left of Venus, the “evening star.” Through binoculars, the solar system’s third-largest planet looks like a faint star, with perhaps a hint of blue-green. Mars and Uranus will stand almost side by side tomorrow night, with Mars above Uranus on Monday.

Script by Ken Croswell, Copyright 2016

Astronomers have kept a keen eye on Supernova 1987A since it first flashed in the night sky 30 years ago this week. It was the closest and brightest supernova in centuries — bright enough to see with the unaided eye, and to study in detail with telescopes.

They’ve watched the explosion fade away; a blast wave from the star ram into rings of material around the star; and atoms from the exploding star stick together to make solid particles.

The blast wave raced outward at millions of miles per hour. A few years after the explosion, it rammed into rings around the star — one around its equator, and two others above its poles.

Those rings probably formed after the star expelled a lot of material about 20,000 years before it exploded — perhaps as the result of a merger with another star. The supernova shockwave heated the rings, causing them to glow. As the shockwave continues to expand, it’s ripping the rings apart.

As the exploding material expands and cools, atoms are sticking together to form solid particles. How and where they form helps astronomers better understand the original star and its explosion. It also helps them understand how the particles get scattered through space.

Other supernovae are thought to have contributed many of the particles that make up our planet and our own bodies. So studying the particles around 1987A can provide new insights into the birth of our own solar system — continuing discoveries from a fascinating supernova.

Script by Damond Benningfield

Thirty years ago today, scientists caught the ghosts of an exploding star. The discovery helped confirm how the star died, and the kind of corpse it likely left behind.

Supernova 1987A was the brightest and closest supernova in centuries. It exploded in a small galaxy that’s about 165,000 light-years away.

Theory said the explosion took place when the star’s core could no longer produce energy from nuclear reactions. Without that radiation to push outward, the core collapsed. The star’s outer layers fell inward, then rebounded and blasted into space, forming the supernova.

The collapsing core was squeezed so tightly that electrons and protons were smashed together to form neutrons and neutrinos. The neutrons stayed in the core, forming a super-dense neutron star.

But the neutrinos raced outward. These ghostly particles almost never interact with other matter. The core’s collapse should have produced so many of them, though, that if even a tiny percentage interacted with the surrounding layers of gas, they’d help power the supernova. The rest would race into space unimpeded — including many aimed at Earth.

And on February 23rd, 1987, detectors on Earth caught a couple of dozen neutrinos from the supernova — a huge haul. A few hours later, the light from the blast reached Earth as well. The neutrinos matched what the theory predicted — helping to confirm what happens deep in the heart of a supernova.

More tomorrow.

Script by Damond Benningfield

 

Astronomers have been hunting a neutron star for 30 years. They know where it is, and they’re almost certain it’s there. Yet they still can’t see it, even with the most powerful telescopes on the ground and in space.

The neutron star would be the remnant of Supernova 1987A, an exploding star that was first seen 30 years ago this week. It’s in the Large Magellanic Cloud, a galaxy that’s about 165,000 light-years away.

At that range, 1987A is the closest supernova seen since the invention of the telescope. That’s allowed astronomers to study it in greater detail than any other supernova.

Their observations have shown that the exploding star was a blue supergiant. That would make it similar to Rigel, the brightest star of Orion, which is high in the south at nightfall, to the lower right of Orion’s three-star belt.

The star exploded when it could no longer produce nuclear reactions in its core. The core collapsed, and the star’s outer layers blasted into space, forming the supernova.

From the mass of the original star, astronomers expected the collapsed core to become a neutron star — a super-dense ball no bigger than a city, but about twice as heavy as the Sun. But despite a diligent search, they haven’t seen a thing. That could mean that the core collapsed even more, forming a black hole. Or it could mean that the neutron star is simply hidden from view — waiting for better observations to reveal its presence.

More about 1987A tomorrow.

Script by Damond Benningfield

It’s been half a century since astronomers discovered the first neutron star. During the intervening decades, they’ve pieced together the story of what neutron stars are and how they form. But some of the details are still unclear.

A space telescope that’s scheduled for launch to the International Space Station as early as next month should eliminate some of the mystery. In particular, it’ll reveal the sizes of neutron stars more precisely than ever before. That will help astronomers eliminate some models of how neutron stars are put together.

A neutron star is the crushed core of a star that was many times the mass of the Sun. When the core of such a star can no longer produce nuclear reactions, it collapses. That creates a ball that’s perhaps two or three times the mass of the Sun, but only about a dozen miles across. That makes it billions of times denser than normal matter.

NICER — the Neutron Star Interior Composition Explorer — will take a look at many known neutron stars, and discover many more. Its 56 X-ray detectors will measure how quickly the X-ray light from neutron stars changes, as well as the intensity of light across the X-ray spectrum.

Among other things, those readings will tell astronomers precisely how big the neutron stars are. That, in turn, will reveal precisely how dense they are. And that will tell astronomers much more about how these stellar corpses are put together.

We’ll talk about the birth of a neutron star tomorrow.

Script by Damond Benningfield

Orion, perhaps the most beautiful of all constellations, stands high in the south as night falls. It’s outlined by a rectangle of four bright stars, with a short diagonal line of three stars at its middle.

Within a few million years, though, all seven of those stars will disappear. Each star will explode, leaving behind a corpse that’s one of the most extreme objects in the universe: a neutron star.

A neutron star forms when a massive star can no longer produce energy in its core. Without radiation to counteract the pull of gravity, the core collapses to the size of a city, even though it’s a couple of times as massive as the Sun. Under that crushing gravitational grip, electrons and protons smash together to form a sea of neutrons, which give these odd stars their names.

The layers of gas around the core fall inward, then rebound, creating a titanic blast known as a supernova.

As the neutron star collapses, it spins much faster, like an ice skater pulling in her arms — up to hundreds of revolutions every second. As it spins, it emits a beam of energy into space. If we happen to line up along that beam, we see the star pulse on and off like a celestial lighthouse, making it a pulsar.

A neutron star may have a crust made of solid iron. But astronomers are still trying to model how neutron stars are put together and how matter deep inside their hearts behaves. A new space telescope will help with that effort. More about that tomorrow.

Script by Damond Benningfield