StarDate Online

Asteroid Thruster

damonddb — Thu, 02 Sep 2010 05:00:00 +0000

It doesn't take a Ph.D. to understand the warming and cooling cycle of day and night. During the day, the Sun warms the surface, with temperatures reaching their peak in late afternoon. Some of that heat radiates back into space at night, so temperatures are lowest around dawn.

For some of the smallest bodies in the solar system, that cycle can have a profound effect: It can push them around a little bit, changing their orbits around the Sun. And that makes their orbits tough to predict more than a few decades into the future.

Tens of thousands of asteroids orbit the Sun. Thousands of them range from perhaps a hundred yards to a few miles in diameter. And many of those objects come close to Earth's orbit. If one of the big space rocks were to hit us, it could cause a regional or even global catastrophe.

So astronomers are finding and tracking these objects to see if any are on potential collision courses.

But the predictions break down more than a few decades in advance, largely because of that cycle of day and night. As the asteroid rotates, it radiates heat into space, creating a tiny bit of thrust. Over time, it adds up. A few years ago, for example, astronomers determined that an asteroid that weighs millions of tons had been displaced by about 10 miles in just 12 years. But without a lot more information about the asteroid, it's impossible to predict how that "thrust" will affect its orbit -- even with a Ph.D.

Hanging On

damonddb — Wed, 01 Sep 2010 05:00:00 +0000

The old adage "what goes up, must come down" works fine here on Earth. But there are tens of thousands of worlds in the solar system where that's not the case. Throw a baseball into the sky, and it'll just keep going.

These worlds are the asteroids -- chunks of rock and metal left over from the birth of the planets. Even though thousands of them are the size of mountains, their surface gravity is incredibly weak. Toss a ball gently into the sky and it could escape the asteroid and float away.

That sounds like fun, but it'll be hard for asteroid explorers to deal with -- even a normal-sized step could propel them into space.

That's not just an academic problem. Earlier this year, President Barack Obama scrapped NASA's plans to send astronauts back to the Moon, and instead instructed the agency to plan an expedition to a Near-Earth Asteroid -- one that passes within a few million miles of Earth's orbit around the Sun. Astronauts will need a way to anchor themselves to the surface to keep from drifting off into space.

Once they reach an asteroid, the explorers will drill into the surface for samples that haven't been changed by impacts and solar radiation -- samples that might not have changed since the birth of the solar system. The samples could help scientists fill in some of the gaps in our knowledge of how Earth and the other planets were born.

More about asteroids tomorrow.

Spacewatch

damonddb — Tue, 31 Aug 2010 05:00:00 +0000

A month from now, a space rock that could be as big as a basketball arena will sweep about a million and a half miles from Earth. There's no danger of it hitting us, but it's worth keeping an eye on because it periodically passes even closer to us. It's probably big enough to do some pretty good damage if it hit.

The small asteroid was discovered with a telescope in Australia that scans the sky for objects that could one day threaten our planet. Several other telescopes in the United States and elsewhere do the same thing.

And they're doing the job pretty well. Astronomers have cataloged about 7,000 N-E-Os -- Near Earth Objects -- mostly asteroids with orbits that come close to Earth's. About one in six is classified as "potentially hazardous" -- their orbits come really close to Earth's.

Most NEOs are small, like the one that'll pass us at the end of September. But a few are big enough to cause damage on a global scale. And that's why it's so important to find and track them. With enough observations, astronomers can plot an asteroid's orbit decades into the future, telling us if it's on a collision course. Enough warning should give us time to nudge the asteroid off course just enough to miss us.

The job isn't done yet, though -- hundreds or even thousands more NEOs await discovery. So telescopes around the world will continue to watch the skies for dangerous invaders.

We'll have more about asteroids tomorrow.

Sierra Madera

damonddb — Mon, 30 Aug 2010 05:00:00 +0000

US highway 385 south of Fort Stockton, Texas, is pretty lonely. You can drive for miles without seeing another human being, and just about everything that lives there bites, pokes, or stings. But the drive offers one thing you won't find anywhere else in the country: hills formed by an ancient cosmic collision.

The hills are known as Sierra Madera. They're at the center of an impact crater that formed perhaps a hundred million years ago, when a space rock as big as a football field slammed into Earth. It gouged a crater about eight miles across. The crust at the center of the crater rebounded, creating the hills.

Wind and rain have worn away much of the crater's rim, so today only a few ridges remain. The central hills have eroded, too, but they still rise up to 800 feet above the surrounding landscape.

The hills helped geologists identify the crater. Similar hills are often created by the motions of Earth's crust, which deform layers of rock far below the surface. When scientists drilled around Sierra Madera, though, they found that the underlying rock layers were undisturbed. What's more, some of the rocks at the surface had been subjected to a powerful shock wave. So 50 years ago, geologists proposed that Sierra Madera was created by a cosmic impact. It's one of the few impact craters in the United States, the only one with central mountain peaks -- and the only one you can drive through.

More about cosmic impacts tomorrow.

Nova Cygni 1975

damonddb — Sun, 29 Aug 2010 05:00:00 +0000

Cygnus, the swan, glides high across the sky tonight. It's high in the east at nightfall, with its brightest star, Deneb, marking its tail.

35 years ago tonight, the swan's tail grew even more impressive. That's because a star not far from Deneb in our sky staged a powerful eruption. It briefly grew more than two million times brighter than before -- bright enough to rival Deneb.

It's known as Nova Cygni 1975. It was the result of an act of stellar thievery that had been going on for millennia.

The eruption took place in a binary system -- two stars locked in a mutual orbit. One star is a white dwarf -- the small, dense corpse of a star that was once like the Sun. The other is a red dwarf -- a faint stellar ember.

The white dwarf's gravity pulled gas from its companion. An extremely powerful magnetic field funneled the gas onto the white dwarf's poles. From there, it spread out to form a superhot "skin" around the white dwarf. When it got hot enough, it triggered an explosion that blasted the gas into space. For a while, the nova shone almost as bright as Deneb. Within about a week, though, it had faded from sight.

The blast was so strong that it changed the white dwarf's rotation speed. Before the blast, the system was synchronized so that the same side of one star always faced the same side of the other star, just as the same side of the Moon always faces Earth. But the explosion threw them out of sync -- by about four minutes.

Barnard's Menagerie

damonddb — Sat, 28 Aug 2010 05:00:00 +0000

Few astronomers have a star named after them. Fewer still have an entire galaxy named for them. But one astronomer has both: Edward Emerson Barnard.

Although he was born in Tennessee just before the Civil War, Barnard did most of his astronomical work at Lick Observatory in California, and then at Yerkes Observatory in Wisconsin.

In 1916, Barnard compared a new photographic plate of the constellation Ophiuchus with an old one. He discovered that one star had shifted position from the old plate to the new. That shift indicated that the star is moving across the sky in a hurry, which means that it must be quite close -- just six light-years away. That makes it the second-closest star system to our own, after Alpha Centauri.

Now named Barnard's Star, it's a red dwarf -- a stellar ember that produces far less light than the Sun does. That's why it wasn't discovered until the twentieth century.

South of Ophiuchus is the constellation Sagittarius, which houses Barnard's galaxy. Just as Barnard's Star is one of our nearest stellar neighbors, so Barnard's Galaxy is one of our nearest galactic neighbors. It belongs to the Local Group -- a small cluster of galaxies that includes our own Milky Way. It's an irregular galaxy -- an oddly shaped galaxy with lots of gas and dust, which are spawning new stars.

Barnard's Star -- and Galaxy -- both honor one of the greatest observers astronomy has ever known: Edward Emerson Barnard.

More Moon and Jupiter

damonddb — Fri, 27 Aug 2010 05:00:00 +0000

It's been almost four decades since the last Americans walked on the Moon, and it could be decades more before anyone follows in their footsteps. But like good scouts, scientists and engineers are staying prepared. Among other things, they're testing equipment and techniques in environments that are as Moon-like as possible.

An example is a project called Desert RATS, which is scheduled to get underway this week in Arizona. In years past, the project has tested a lunar rover, plus an ungainly vehicle that could walk across especially rough or steep landscapes.

Desert RATS is one of a long list of expeditions to sites that are like the Moon, Mars, or other space environments. In the last few months, for example, astronauts spent two weeks underwater to test techniques for spacewalks. A little later, another expedition was testing ways to live and work on Mars on a remote Canadian island.

One of the highlights of Desert RATS has been testing a new lunar rover. It has a pressurized cockpit that allows the two-person crew to live and work in shirtsleeves for days at a time. And when crewmembers want to get a closer look at something, they can slide into spacesuits that are attached to the back of the rover.

With a hot set of wheels to whisk them around, all astronauts need now is a ride to the Moon -- which is in good view tonight, by the way. It rises not long after darkness falls, with the brilliant planet Jupiter to its right.

Puffy Planet

damonddb — Thu, 26 Aug 2010 05:38:34 +0000

Featured on

Thursday, August 26, 2010

An artist's concept shows the atmosphere of a planet known as HD209458b boiling away into space, as seen from a hypothetical moon. The planet and star are so close together that winds and radiation from the star are stripping away the planet's atmosphere. The star's energy and the planet's own magnetic field are also causing the planet to puff up like a big balloon. [NASA/ESA/G. Bacon (STScI)]

HD209458b Planet

Moon and Jupiter

damonddb — Thu, 26 Aug 2010 05:00:00 +0000

The biggest planet in the solar system puts in a big-time showing tonight. It rises not long after darkness falls, a little below the Moon. Jupiter looks like a brilliant star, so you won't have any trouble picking it out.

Jupiter is big enough to hold more than a thousand Earths. In fact, it's just about as big as a planet should get. Astronomers have discovered many planets in other star systems that are heavier than Jupiter, but that doesn't mean they're bigger. Their extra mass increases their gravity, which keeps them from getting wider.

But at least one planet defies the size limit. And one team of astronomers says it knows why.

The planet is HD209458b. It periodically passes in front of its star, blocking a bit of the star's light. How much the light dims, and how long the dimming lasts, reveals the planet's size -- about 30 percent wider than Jupiter.

The planet orbits close to its parent star, so it's quite hot. That puffs up its outer atmosphere a bit, but not nearly enough.

But a team from Caltech says the heat puffs up the star in another way. The combination of heat and strong winds gives an electrical charge to the upper layers of the atmosphere. A powerful magnetic field captures some of the charge and conducts it deep into the planet's interior. That heats up not just the outside, but the inside as well -- inflating HD209458b like a giant balloon.

More about Jupiter and the Moon tomorrow.

Building Solar Systems III

damonddb — Wed, 25 Aug 2010 05:00:00 +0000

The little guys often get pushed around by the big guys. In the case of a planet, the "pushing" can have a big effect on the quality of life. In fact, it can determine whether a planet can sustain life at all.

For a planet to sustain life as we know it, it must reside in a region known as the habitable zone. It's the distance from the parent star where temperatures are just right for liquid water.

In young solar systems, it's hard for an Earth-like planet to find that zone -- especially if it has larger siblings that follow elongated orbits. As a bigger planet orbits the star, its gravity pushes and pulls on the Earth-like planet -- perhaps shoving the planet into an elongated orbit of its own.

As a result, the planet may spend part of its time inside the habitable zone, and part of its time outside. If the planet snuggles too close to its star, it gets too hot -- the water on its surface boils off. And if the planet moves too far from the star, it gets too cold, so water freezes. Either way, it's difficult or even impossible for life to arise.

And that may be what's going on in many of the planetary systems that astronomers have discovered. Many of these systems have giant planets in stretched-out orbits. No Earth-like planets have yet been found in these systems. But if such worlds exist, the pushing around they get from the giant planets may make it tough for them to support life.

More about giant planets tomorrow.