Category: Astronomy

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The International Space Station is big. About the size of American football field, it has an acre of solar panels, includes 358 cubic meters (12,626 cubic ft) of habitable volume, and there is enough reflective outer surface that in the right conditions, it can be seen from Earth during the day. But with the ISS, we’re just getting warmed up with building structures in space. There are some ideas out there for even larger structures — so called megastructures in space. Here are a few proposals for future space stations and structures that one day could be built in Earth orbit.

The top image is called an O’Neill cylinder, and is a space habitat proposed by physicist Gerard K. O’Neill. What started out as a design challenge for his students became structures O’Neill used in his book that promoted the idea of humans living in space, The High Frontier: Human Colonies in Space. An O’Neill cylinder consists of two very large, counter-rotating cylinders, each 5 miles (8 km) in diameter and 20 miles (32 km) long, that are connected at each end by a rod via a bearing system. The rotation provides artificial gravity on the inner surfaces while the central axis of the habitat would be a zero gravity region, where recreational facilities could be located.

To save the huge cost of rocketing the materials from Earth, this habitat could be built with materials launched from the moon with a mass driver.

After O’Neill proposed his structure, a later NASA/Ames study at Stanford University developed an alternate version, the Stanford torus. This is torus, or donut-shaped ring, 1.8 km in diameter. This structure would be capable of housing 10,000 to 140,000 permanent residents, similar to a suburb here on Earth.

The structure would rotate once per minute to provide between 0.9g and 1.0g of artificial gravity on the inside of the outer ring from centripetal acceleration. The interior of the torus would be used as living space, and is large enough that a “natural” environment can be simulated, including trees and other plants. Sunlight would be provided inside the structure with a system of mirrors.

A Bernal sphere is a another type of orbital space habitat intended as a long-term home for permanent residents. It was first proposed in 1929 by John Desmond Bernal, and is said to be one of the inspirations for Gerard O’Neill and his students. Bernal’s original proposal included a hollow spherical shell 1.6 km (1 mile) in diameter, filled with air for a target population of 20,000 to 30,000 people.

Bernal predicted that as the human race grew, their material and energy needs would outpace what planet Earth could provide. Orbiting colonies could harness the Sun’s energy and provide extra living space for a burgeoning population.

Rotating the sphere twice a minute would generate an artificial gravity aproximate to Earth’s. An advantage of the sphere is that it has the smallest surface area for a given internal volume, so minimizing the amount of radiation shielding required.

Our next Future Friday will take a look at megastructures at the planetary scale.

Source: Wiki

ESA’s XMM-Newton orbiting X-ray telescope has uncovered the first close-up of a white dwarf star that could explode into a type Ia supernova within a few million years. That’s relatively soon in cosmic time frames, and although this white dwarf that is orbiting its companion star HD 49798, is far enough away to pose no danger to Earth, it is close enough to become an extraordinarily spectacular celestial sight. Calculations suggest that it will blaze initially with the intensity of the full Moon and be so bright that it will be seen in the daytime sky with the naked eye. But don’t worry, it will be awhile!

Astronomers have been on the trail of this mysterious object since 1997, when they discovered that something was giving off X-rays near the bright star HD 49798. Now, thanks to XMM-Newton’s superior sensitivity, the mysterious object has been tracked along its orbit. The observation has shown it to be a white dwarf, the dead heart of a star, shining X-rays into space.

Sandro Mereghetti, INAF–IASF Milano, Italy, and collaborators also discovered that this is no ordinary white dwarf. They measured its mass and found it to be more than twice what they were expecting. Most white dwarfs pack 0.6 solar masses into an object the size of Earth.

This particular white dwarf contains at least double that mass but has a diameter just half that of Earth. It also rotates once every 13 seconds, the fastest of any known white dwarf.

The mass determination is reliable because the XMM-Newton tracking data allowed the astronomers to use the most robust method for ‘weighing’ a star, one that uses the gravitational physics devised by Isaac Newton in the 17th century. Most likely, the white dwarf has grown to its unusual mass by stealing gas from its companion star, a process known as accretion. At 1.3 solar masses, the white dwarf is now close to a dangerous limit.

When it grows larger than 1.4 solar masses, a white dwarf is thought either to explode or collapse to form an even more compact object called a neutron star. The explosion of a white dwarf is the leading explanation for ‘type Ia supernovae’, bright events that are used as standard beacons by astronomers to measure the expansion of the Universe. Until now, astronomers have not been able to find an accreting white dwarf in a binary system where the mass could be determined so accurately.

“This is the Rosetta stone of white dwarfs in binary systems. Our precise determination of the masses of the two stars is crucial. We can now study it further and try to reconstruct its past, so that we can calculate its future,” says Mereghetti.

So start telling your descendants to watch out for the spectacular show! (And hopefully no new hoax emails will be spawned about a supernova coming soon that will look as big as the full Moon to the naked eye a la the “Mars as big as the full Moon” hoax!)

Lead image caption: Illustration of the white dwarf and its companion HD49798. If it was possible to look at the system up-close, it would look something like this. Credits: Francesco Mereghetti, background image: NASA, ESA and T.M. Brown (STScI)

Source: ESA

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Think nothing ever happens on the Moon? New images from the Lunar Reconnaissance Orbiter Camera shows spectacular views of the famous Tsiolkovskiy Crater, and a close-up look reveals boulders that have rolled down the slopes of the crater. In the larger image, below, it is easy to see where the boulders came from by following their rolling, bouncing tracks. These are not small rocks by any means: the largest boulder in this image is about 40 meters wide – half as big as a soccer field! Seeing where the boulders originated from is a great clue to geologists reconstructing the local geology. What do they see here?

Tsiolkvoskiy Crater is 185 km in diameter, and is a great example of complex impact crater. It has a terraced rim, a central peak, and a floor flooded with mare basalts. Impact events release tremendous amounts of energy and result in very dynamic changes in the local landscape. Just after the initial impact, the central peak was uplifted from lower crustal rock, forming a giant mountain in the middle of the crater. That’s where the boulders rolled down the slopes, as pieces of the uplifted rock rolled down and accumulated at the base of the slope.

This is an easy way for explorers to find samples of the central peaks without having to climb the top. The Apollo 17 astronauts used this strategy as an easy way to sample nearby mountain tops without having to don any climbing gear!

Click the image for a larger “Zoomifiable” version.

The dark area in the lower right is the tip of enormous shadow cast by the central peak. Scroll north in the full image, and you will find the contact where the later-formed lavas pooled at the base of the peak. Even though the central peak formed before the mare, it has fewer craters due to its steep slope which tends to slump and slide erasing small craters. In this case, that’s an apparent violation of the rule that older surfaces have more craters!

Click here to see a zoomable look at Tsiolkovskiy Crater taken by the Apollo missions.

Source: LROC Journal

On September 4, 2009, Earth’s orbital motion will carry it through the same plane as Saturn’s rings. From our vantage point, the rings will disappear. Usually these ring plane crossings — which only happen about every 15 years — are great opportunities to observe Saturn’s moons. But this year’s ring plane crossing will be practically impossible to see, as Saturn will be very close to the sun, only 11 degrees away. So, disappointingly, we won’t see much. However, amateur astronomer Alan Friedman has given us a glimpse of what this event will look like, without the glare from the sun. Friedman has put together an animation of how the angle of Saturn’s rings have changed over the past six years. See the animation below. “It shows the changing plane of the ring system as viewed from my Buffalo backyard from 2004 to 2009,” said Friedman. “The final frame has been assembled from earlier 2009 observations to display how the planet will appear with its rings edge on.” Gorgeous!

But, Friedman says, our real view of Saturn should get much better and provide a real treat this autumn. “In the fall of 2009, Saturn will emerge from the glare of the sun in the early morning sky and provide Earth-bound astronomers with our first glimpse of its blue north pole in 14 years,” he said.

Enjoy perusing Friedman’s impressive gallery on his website.

And thanks, Alan, for sharing your six-year endeavor with Universe Today!

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As scientists attempt to learn more about how galaxies evolve, an open question has been whether collisions with our dwarf galactic neighbors will one day tear apart the disk of the Milky Way.

That grisly fate is unlikely, a new study now suggests.

While astronomers know that such collisions have probably occurred in the past, the new computer simulations show that instead of destroying a galaxy, these collisions “puff up” a galactic disk, particularly around the edges, and produce structures called stellar rings.

The finding solves two mysteries: the likely fate of the Milky Way at the hands of its satellite galaxies — the most massive of which are the Large and Small Magellanic Clouds — and the origin of its puffy edges, which astronomers have seen elsewhere in the universe and dubbed “flares.”

The mysterious dark matter that makes up most of the universe plays a role, the study found.

Astronomers believe that all galaxies are embedded within massive and extended halos of dark matter, and that most large galaxies lie at the intersections of filaments of dark matter, which form a kind of gigantic web in our universe. Smaller satellite galaxies flow along strands of the web, and get pulled into orbit around large galaxies such as our Milky Way.

Ohio State University astronomer Stelios Kazantzidis and his colleagues performed detailed computer simulations of galaxy formation to determine what would happen if a satellite galaxy — such as the Large Magellanic Cloud and its associated dark matter — collided with a spiral galaxy such as our own.

The researchers considered the impacts of many different smaller galaxies onto a larger, primary disk galaxy. They calculated the likely number of satellites and the orbital paths of those satellites, and then simulated what would happen during collision, including when the dark matter interacted gravitationally with the disk of the spiral galaxy.

The conclusion?  None of the disk galaxies were torn apart.  To the contrary, the primary galaxies gradually disintegrated the in-falling satellites, whose material ultimately became part of the larger galaxy.  The satellites passed through the galactic disk over and over, and on each pass, they would lose some of their mass, a process that would eventually destroy them completely.

Though the primary galaxy survived, it did form flared edges which closely resembled our galaxy’s flared appearance today.

Does that settle the question of the fate of the Milky Way?

Kazantzidis couldn’t offer a 100-percent guarantee.

“We can’t know for sure what’s going to happen to the Milky Way, but we can say that our findings apply to a broad class of galaxies similar to our own,” Kazantzidis said. “Our simulations showed that the satellite galaxy impacts don’t destroy spiral galaxies — they actually drive their evolution, by producing this flared shape and creating stellar rings — spectacular rings of stars that we’ve seen in many spiral galaxies in the universe.”

Source: Ohio State University