StarDate

Ghosts and demons roam the Halloween night. Vampires and zombies are there, too. So are black widows and Gorgons, witches and snakes and dragons – enough scary creatures to fill a galaxy of haunted houses. You’ll see some of them wandering the streets in search of treats. And if you look up, they’re all there in the stars.

As night falls, the star Algol is in the northeast, in Perseus the hero. Its name means “the demon star.” It represents Medusa, a monster who turned anyone who looked at her to stone. Her sisters – the other Gorgons – are represented by some fainter stars around Algol.

The constellation Cetus is low in the east and southeast. It represents a sea monster that was defeated by Perseus – using the head of Medusa.

The Witch Head Nebula climbs into view in late evening. It’s a cloud of gas and dust that’s being both illuminated and sculpted by Rigel, the brightest star of Orion. Through a telescope, it really does look like the profile of a witch.

Many “ghosts” float through the sky as well. They’re star clusters or the last gasps of dying stars – named for their ghostly appearance.

The vampires and zombies and black widows are all “dead” stars that are sucking the life from their companion stars. They’re all invisible – none of them is bright enough to see with the eye alone. But they’re sprinkled through the galaxy, haunting the skies of Halloween night – and every other night as well.

Script by Damond Benningfield

Several of the brightest stars in the night sky are really systems of at least two stars. But only one of those systems is known to contain six stars: Castor, the fainter “twin” of Gemini. It’s to the left of the gibbous Moon as they climb into good view late tonight, and to the upper left of Gemini’s brighter twin, Pollux.

Seen across 50 light-years of space, the light from all six stars blurs together to form a single point. But binoculars reveal two points, known as Castor A and Castor B. Castor A is the brighter of the two. Because of our viewing angle, the distance between the two pairs is getting bigger, so it’s easier to see them as separate points of light.

It turns out that A and B are both binaries – each of them consists of two stars. The stars in each pair are quite close together, so there’s no way to see them individually. Instead, their dual nature is revealed only by sensitive instruments.

One star in each pair is bigger, hotter, and brighter than the Sun. The other star in each pair is much smaller, cooler, and fainter than the Sun – a cosmic ember known as a red dwarf.

Castor’s third pair is Castor C. It’s a long way away from the other two. And both of its stars are red dwarfs, so the pair is quite faint – you need a telescope to pick it out. Even so, it helps make Castor the busiest bright star system in the night sky – three pairs of “twins” for the twins’ constellation.

Script by Damond Benningfield

The tiny moons of Mars are hard to explain. Scientists aren’t sure how they formed and how they wound up in their current orbits. But a Japanese mission that launched this month could settle the conundrum.

The mission is MMX – Mars Moons Exploration. It will scan both Phobos and Deimos – chunks of rock the size of a small city. And it will land on Phobos, gathering samples for return to Earth.

Both moons are dark, like a class of asteroids. In fact, astronomers long suspected they were captured asteroids. In this scenario, rocky “leftovers” from the birth of the planets flew close to Mars. The planet was surrounded by a cloud of gas and dust. As Phobos and Deimos passed through it, the cloud acted as a brake, slowing them enough for Mars to grab them.

But it’s not easy for a planet to capture an asteroid. And the orbits of the moons aren’t like those of the captured asteroids of the giant outer planets.

So scientists came up with another model: a giant impact. A massive space rock could have slammed into Mars, blasting out material that formed a ring around the equator. The debris coalesced to form several small moons. Phobos and Deimos are the only survivors.

In yet another scenario, Mars captured a single large asteroid. It was sheared apart by Martian gravity, creating a ring that gave birth to Phobos and Deimos.
MMX will arrive at Mars next year – a big step toward solving the mystery of the Martian moons.



Script by Damond Benningfield

In Gulliver’s Travels, which was published 300 years ago today, Jonathan Swift wrote that the people of Laputa had made an important discovery: “two lesser stars, or satellites, which revolve about Mars.” The fictional moons were small and close to the surface, orbiting the Red Planet in a matter of hours.

Earthly astronomers took a little longer to find the real moons – they weren’t discovered until 1877. They were named Phobos and Deimos – fear and panic – after attendants of the god of war.

Phobos is the larger moon. It’s lumpy, with an average diameter of about 14 miles. It orbits just 3700 miles from the surface of Mars. It rises in the west, then sets in the east less than four-and-a-half hours later.

Deimos is about eight miles in diameter. It’s about three times farther from Mars, so it takes about two-and-a-half days to cross the sky, from east to west. It’s shaped a bit like a potato with a big dimple on one side.

Several spacecraft have flown past the moons. But they’ve raised a lot of questions about them. Now, 300 years after Gulliver’s Travels, scientists may take a big step toward finding some answers. Japan launched the Mars Moons Exploration mission this month. The craft will study both moons from close range. And it will touch down on Phobos, hoovering up a few grams of pebbles and dust for return to Earth.

More about that tomorrow.

Script by Damond Benningfield

The Moon is crossing the constellation Taurus. Tonight, it’s quite close to the bull’s shoulder – the Pleiades star cluster. The bull’s bright eye, the star Aldebaran, is well below the Moon as they climb into view. It’ll be about the same distance to the right of the Moon tomorrow night.

A dead “starship” is headed in Aldebaran’s direction. It won’t get there for more than two million years. But just in case anyone finds it, it carries a message.

Pioneer 10 was launched in 1972. It was the first spacecraft to fly through the asteroid belt, and the first to explore Jupiter, the Sun’s largest planet. After that, it raced out of the solar system and into interstellar space. NASA last heard from it in early 2003. Today, it’s more than 13 billion miles away.

The “message” is a plaque that’s made of aluminum and coated with gold. It measures nine by six inches. It includes the outlines of a naked man and woman. They’re standing in front of an outline of Pioneer to indicate their size. It also includes a chart of the solar system that shows Pioneer’s home planet. Other diagrams help pinpoint Earth’s location in the galaxy.

No one expects Pioneer to ever be found. It won’t get all that close to Aldebaran, and the star’s only known planet isn’t a good home for life. After Aldebaran, Pioneer 10 will continue sailing through the cosmos – an extinct emissary from Planet Earth.

Script by Damond Benningfield