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Does Humanity's Destiny Lie in Interstellar Space Travel? (Op-Ed)

Donald Goldsmith   |   January 27, 2015 01:14am ET

An artist's interpretation of utilizing a wormhole to travel through space, Thorne kick-started a serious discussion among scientists about whether or wormhole travel is possible. Credit: NASA View full size image

Donald Goldsmith is a freelance science writer and co-author (with Neil deGrasse Tyson) of "Origins: Fourteen Billion Years of Cosmic Evolution." Goldsmith contributed this article to Space.com's Expert Voices: Op-Ed & Insights.

Imagine a time when humans, having spent decades exploring the solar system through landings on Venus and Mars; passages by the largest asteroids; close-up surveys of Jupiter and its giant moons; repeated loops through Saturn's system of rings and satellites; detailed photography of Uranus, Neptune and Pluto; and even landing on a comet, finally create a coherent plan to travel through interstellar space to reach the nearest stars and their planets.

That time has almost arrived. Once NASA's Dawn spacecraft arrives at the asteroid Ceres in March of this year , and the space agency's New Horizons spacecraft flies by Pluto in July, humans will have completed the solar system exploration described above. They will have done so, of course, by creating complex and highly capable spacecraft that not only secure high-resolution images of the objects they encounter, but also roll across planetary surfaces to measure local conditions in a dozen different ways, including spectroscopic and chemical analysis of the composition and history of each object. 

Will humans ever replace robotic explorers?

To many of us, the success of our automated spacecraft heralds the long-awaited moments when humans finally land on Mars, Ganymede (Jupiter's largest moon) or Titan (Saturn's largest moon), eventually to establish self-sustaining colonies that might provide a continuing opportunity to maintain our existence if our home planet were to become uninhabitable. The interplay between our logical wishes to deepen our knowledge of the solar system and our gut-level desires for personal encounters with new situations — always present though not always acknowledged — has governed humans' ever-shifting plans to explore our nearby cosmic environment for half a century. 

Just about everyone welcomes new information about the solar system, but what many really — really — want is for humanity to plant its boots on new soil, as Earth-bound explorers have done for many centuries. Lonely humans in space speak directly to our emotions, but pioneering spacecraft far less so. (Even an apparent exception, such as the hero of the movie "WALL-E," connects with us through its seeming humanity, a fact that won't surprise anyone who reflects for a moment on how storytelling works.)

Some facts remain evident: Human exploration of space is dangerous and expensive, requiring the provision of food and water, recycling of wastes, significant amounts of energy to run those systems, protection against harsh radiation and a return journey (or not, depending on volunteers' propensities). In comparison, automated spacecraft have only modest energy requirements, and can last for decades or more. As time passes, this comparison progressively favors machines, since they (thanks to humans!) become ever more competent, while our bodies evolve at a much slower pace. 

As the brilliant physicist Freeman Dyson explains in the new podcast available at RawScience.tv, "Instruments have gotten enormously … humans are really out of it. If you want to go to space, that's for fun, not for science … This is not understood by the people in charge [of planning for future exploration missions]." 

To be sure, when we dream of the far future, we can easily envision (thanks, in part, to many science-fiction stories and films) beings that combine today's human bodies with advanced technology to produce a human-machine hybrid far more capable of long journeys and survival in strange situations than individuals are today. 

Humanity's destiny in space

Dyson's argument in favor of machines counts for little among those who insist — who know — that our destiny lies in the presence of humans, not our mechanistic surrogates, in space. For many of us, this knowledge runs more deeply than argument can reach. A glance at the history of the United States' space program reminds us of the many times, during the 40-plus years since the last lunar landing, that NASA has attempted to produce a reasonable plan to send humans beyond low-Earth orbit — only to have the expense of such projects, combined with the lack of a clear focus for astronaut activity, lead to their abandonment. Because the manned lunar program basically served as a counterpunch to Soviet efforts in space, once NASA and the United States achieved their initial goal of landing on the moon, they proved unable of following a coherent plan for future space exploration by humans.

What do these ambitions tell us about the future of interstellar exploration? Even before we consider human versus automated journeys, we should note that any answers to this question begin with a number: 1 million. The stars nearest to the sun lie at distances approximately 1 million times the distance to Mars at its closest approach to Earth. This ratio implies that travel to the stars at speeds our best spacecraft are capable of will take hundreds of thousands of years, and this, in turn, implies that any interstellar exploration will require either a civilization that knows how to plan for the long haul, or the ability to make spacecraft that can travel much faster — perhaps 10,000 times more rapidly — than what we have now. (I'll save the discussion of "wormholes" like those seen in the movies "Contact" and "Interstellar " for later.)

On the fast track, or slow and steady?

Consider spacecraft that could carry astronauts through space at speeds approaching the speed of light, conferring two great advantages on the crew. Most obviously, the journey requires less time — only a few years to reach the nearest stars, and only a couple of decades to span the distances to the closest thousand stars. In addition, time slows down at near-light velocities — by a factor of 10, for example, for those who travel at 99.5 percent the speed of light. At that velocity, an astronaut who makes an interstellar journey covering 50 light years in each direction would age by only 10 years, but would return to an Earth where everyone has aged by 100 years. (Those who suspect that Einstein's theory of relativity creates a "twin paradox" — that the traveler and those who stay behind should each see time slow down by a factor of 10 — can find an excellent explanation of the apparent paradox in David Mermin's book "Space and Time in Special Relativity" (Waveland, 1989).) 

But how can we hope to move through space at close to the speed of light? More than 50 years ago, Dyson — who, even then, created intriguing and controversial ideas at the Institute for Advanced Study in Princeton, New Jersey — proposed that nuclear explosions could accelerate a spacecraft to ever-higher speeds. The "Project Orion" study, directed by Ted Taylor, though largely Dyson's brainchild, envisioned that a series of nuclear explosions would strike a "pusher plate" attached to the rear of a spacecraft, eventually accelerating the spacecraft to any desired velocity. 

The concept remains theoretically feasible, though one can easily see that the expense would be enormous. As Dyson recalls in the RawScience podcast, by using the power of nuclear explosions, the Orion spacecraft could provide "both fast acceleration and fast travel, which nothing else could do … In principle, the idea was good," Dyson said, but "it had one fatal flaw: The bombs are highly radioactive … As soon as you had the test-ban treaty … Orion was dead." 

Even if we manage to accelerate a spacecraft to velocities close to the speed of light (10,000 times faster than our fastest space probes), any spacecraft moving at near-light velocities encounters a significant problem. The same special-relativity rules that allow a traveler to return to Earth much younger than her twin brother who stayed home also imply that collisions with space debris — even tiny dust particles — inevitably pose great dangers. [Photos: Step-by-Step Guide to NASA's EFT-1 Orion Spacecraft Test Flight ]

When the spacecraft encounters dust and pebbles, the objects' near-light velocities, relative to the craft, enormously elevate their effective masses. An impactor's increase in mass, together with the tremendous collision speeds, call for enormous amounts of shielding to protect anyone inside the spacecraft. Hence, any plans to travel through the Milky Way at near-light speeds must embrace not only a truly massive propulsion system, but also enough shielding to protect the humans inside the craft.

Thinking in centuries

Nevertheless, Dyson's Orion concept remains, in many ways, the gold standard for visions of interstellar travel. In the recent podcast, Dyson noted that the name "Orion" has been passed on to NASA's most recent spacecraft design not for an interstellar vehicle, but for a far more modest craft to take astronauts to other worlds in the solar system. Dyson also identified the most basic requirement for interstellar spaceflight: a society capable of long-term planning and execution. "If you want to have a program for moving out into the universe, you have to think in centuries, not in decades." 

That necessity for a long-term vision poses a serious barrier to interstellar journeys in a society that has great difficulty planning for even the next five years. 

If we are prepared to think in centuries, as Dyson recommends, we should ask the key technological question: What prospects exist for interstellar space travel at comparatively low velocities? In the decades since this question first seriously arose, theorists have provided plenty of answers, which build on the success of our current interplanetary space probes. If you want to probe deeply into them, the coordinated websites of the Tau Zero Foundation and Centauri Dreams offer useful information on this topic. And if you want to examine a representative plan for interstellar travel, I recommend the PowerPoint presentation created by Steve Kilston, an astronomer who spent much of his career at Ball Aerospace (and with whom I have been friends since our undergraduate days). Kilston's "Plausible Path to the Stars" envisions the creation — in approximately 500 years — of a cylindrical spaceship that will carry a million inhabitants, will rotate in order to simulate Earth's gravity, will travel at 0.2 percent of the speed of light, and could reach the few dozen nearest stars in 10,000 years' time.

In other words, Kilston's "Plausible Path," like any other low-velocity journey, requires that generations upon generations of spacefarers pass their entire lives short of their goal. Today, this plan would attract few volunteers. But if human society came to feel sure of its long-term viability, so that our time horizon stretched beyond the current limits of (at most) our grandchildren's lifetimes, the situation would become quite different. Perhaps the wisest aspect of Kilston's plan lies in its final prelaunch phase: a 100-year cruise through the solar system to demonstrate the full feasibility of the spacecraft and the willingness of its crew to pass their lives in space.

Thus, a practical, technologically reasonable plan to explore our cosmic environment rests simply upon achieving a society in which a 100-year journey, and a few thousand years of travel time, seem both logical and desirable. To see how far we now stand from this goal, we may merely compare a film based on Kilston's "Plausible Path" with a movie like "Avatar" or "Interstellar." In today's world, almost no one is interested in moving from a situation in which months of spacecraft travel is far too long to one that tolerates multi-thousand-year journeys. Instead, we must hope for a better tomorrow.

If you're a topical expert — researcher, business leader, author or innovator — and would like to contribute an op-ed piece, email us here.

Credit: SPACE.com

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The wormhole option

If we don't want to wait, what about taking the "Interstellar" route and using a wormhole to pass near-instantaneously from here to there? Kip Thorne, a physicist at the California Institute of Technology who's an expert on the subject — and whose screenplay inspired "Interstellar" — has written a book to accompany the film: "The Science of Interstellar" (W.W. Norton and Company, 2014). In the book, Thorne demonstrates that humans cannot rule out wormhole travel, but there is no guarantee that this method actually works, or that it could allow safe conduct through the voids of space. 

Physicists have recently suggested that the Milky Way could contain — or even be! — a giant wormhole. On the other hand, an argument against wormhole travel, or at least against its easy operation, lies in the fact that no creatures of a more advanced civilization appear to be popping out of wormholes in our solar system. A similar argument can be made against time travel, at least in the backward direction, since we have yet to encounter beings from the future who have decided to visit our present.

To be frank, concepts of interstellar travel have progressed only modestly since Dyson envisioned the Orion project decades ago. Yes, layers of refinement have been added: "Slow" versus "fast" spaceflight has been debated and scored, experience has now given some indications of how well humans can survive long periods in space, and theoretical physics has provided some tantalizing possibilities that might make such journeys much easier than they now appear. But the big picture has not changed: First, we must figure out how to live successfully for the long term on Earth, and then we can go to the stars

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LA CONQUISTA DEL ESPACIO

NASA Probe Snaps Amazing New Views of Dwarf Planet Ceres 

A spacecraft closing in on the dwarf planet Ceres in the solar system's asteroid belt has captured tantalizing new views of the huge space rock, revealing hints of craters and other structures on the surface of this mysterious body.

NASA's Dawn spacecraft snapped the new images of Ceres, which is the largest object in the asteroid belt between the orbits of Mars and Jupiter, on Jan. 13. Scientists unveiled the images on Monday (Jan. 19).

Dawn is rapidly approaching Ceres and is due to arrive in orbit around the dwarf planet on March 6. The images are still blurry, and are primarily for navigation purposes for Dawn, but they show hints of craters on Ceres' surface, including a mysterious white spot near the upper left, which may be light reflecting off of a crater. The photos are an early taste of the much more detailed view of Ceres that Dawn will bring in 2015. [Photos: Dwarf Planet Ceres Revealed]

"The [Dawn] team is very excited to examine the surface of Ceres in never-before-seen detail," Chris Russell, principal investigator for the Dawn mission, said in a statement from NASA's Jet Propulsion Laboratory in Pasadena, California. "We look forward to the surprises this mysterious world may bring."

A zoomed-in view of the dwarf planet Ceres, seen from a distance of 238,000 miles (383,000 kilometers) by the Dawn spacecraft on Jan. 13, 2015. The image hints at the presence of craters and other features on Ceres' surface.
Credit: NASA/JPL-Caltech/UCLA/MPS/DLR/IDA/PSI

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The dwarf planet Ceres is about the size of Texas, with an average width of 590 miles (950 kilometers). It is the largest object in the asteroid belt but the smallest known dwarf planet in the solar system.  

The Dawn spacecraft will be the first spacecraft to study Ceres — or any dwarf planet — up close. By the end of January, Dawn will obtain higher-resolution images of Ceres than the Hubble Space Telescope, NASA said in the statement. The new images from Dawn were taken at a distance of 238,000 miles (383,000 km) and are three times sharper than a batch taken in December, which were used primarily to calibrate the spacecraft's instruments.

The dwarf planet Ceres, seen from a distance of 238,000 miles (383,000 kilometers) on Jan. 13, 2015, by the Dawn spacecraft.
Credit: NASA/JPL-Caltech/UCLA/MPS/DLR/IDA

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Ceres was discovered in 1801 by Sicilian astronomer Giuseppe Piazzi and was initially considered a planet. But when scientists later discovered that Ceres was just one of many objects in the asteroid belt, it was reclassified as an asteroid. In 2006, Ceres' classification changed once again — this time, to dwarf planet (in order to gain full planet status, Ceres would need to gravitationally clear its neighborhood of debris). Today, Ceres enjoys joint classification as both an asteroid and a dwarf planet.

Earlier this year, scientists announced the discovery of water on Ceres, in the form of vapor plumes that erupt into the sky. The plumes may come from volcano-like ice geysers. The vapor gives Ceres a bit of an atmosphere, and scientists wonder if there may also be liquid oceans beneath the surface.

ARTÍCULOS CIENTÍFICOS

What causes the aurora borealis or northern lights?

People at high northern latitudes sometimes experience an ethereal display of colored lights shimmering across the night sky – the aurora borealis or northern lights. What causes them?

Aurora just west of Saskatoon, by Colin Chatfield. He said, “We were just about to leave as the Aurora was just a dull band, then it came alive for about an hour or so. This was taken at 2:02am today [January 27, 2015] … It is not very visible, but I caught Comet Lovejoy at centre left of this photo.”

Those who live at or visit high latitudes might at times experience colored lights shimmering across the night sky. Some Inuit believed that the spirits of their ancestors could be seen dancing in the flickering aurora. In Norse mythology, the aurora was a fire bridge to the sky built by the gods. This ethereal display – the aurora borealis or aurora australis, the northern or southern lights – is beautiful. What causes these lights to appear?

Our sun is 93 million miles away. But its effects extend far beyond its visible surface. Great storms on the sun send gusts of charged solar particles hurtling across space. If Earth is in the path of the particle stream, our planet’s magnetic field and atmosphere react.

When the charged particles from the sun strike atoms and molecules in Earth’s atmosphere, theyexcite those atoms, causing them to light up.

What does it mean for an atom to be excited? Atoms consist of a central nucleus and a surrounding cloud of electrons encircling the nucleus in an orbit. When charged particles from the sun strike atoms in Earth’s atmosphere, electrons move to higher-energy orbits, further away from the nucleus. Then when an electron moves back to a lower-energy orbit, it releases a particle of light or photon.

What happens in an aurora is similar to what happens in the neon lights we see on many business signs. Electricity is used to excite the atoms in the neon gas within the glass tubes of a neon sign. That’s why these signs give off their brilliant colors. The aurora works on the same principle – but at a far more vast scale.

When charged particles from the sun strike air molecules in Earth's magnetic field, they cause those molecules' atoms to become excited. The molecules give off light as they calm down. Image Credit: NASA

The aurora often appears as curtains of lights, but they can also be arcs or spirals, often following lines of force in Earth’s magnetic field. Most are green in color but sometimes you’ll see a hint of pink, and strong displays might also have red, violet and white colors. The lights typically are seen in the far north – the nations bordering the Arctic Ocean – Canada and Alaska, Scandinavian countries, Iceland, Greenland and Russia. But strong displays of the lights can extend down into more southerly latitudes in the United States. And of course, the lights have a counterpart at Earth’s south polar regions.

The colors in the aurora were also a source of mystery throughout human history. But science says that different gases in Earth’s atmosphere give off different colors when they are excited. Oxygen gives off the green color of the aurora, for example. Nitrogen causes blue or red colors.

So today the mystery of the aurora is not so mysterious as it used to be. Yet people still travel thousands of miles to see the brilliant natural light shows in Earth’s atmosphere. And even though we know the scientific reason for the aurora, the dazzling natural light show can still fire our imaginations to visualize fire bridges, gods or dancing ghosts.

“This photo was captured a couple of hours ago in Nordreisa, Norway. I was dressed in my very best winter clothes and I can easily admit that I was freezing most of the time anyways, 22 below (-7.6 fahrenheit) kinda has that effect.” January, 2015. © 2015 Tor-Ivar Næss

Aurora in Vesterlålen, Norway, January 2015 by Stig Hansen

Mike Taylor in Maine caught this photo in September, 2014. More about Mike and this photo.

Photo © 2014 Tor-Ivar Næss

Aurora borealis over Norway’s Steinvikholmen Castle on April 3, 2014 by Hallvor Hobbyfotograf Lillebo.View larger. | Photo credit: Hallvor Hobbyfotograf Lillebo

Reisafjorden, Norway bathing in auroras on January 2, 2014. When charged particles from the sun strike atoms in Earth’s atmosphere, they cause electrons in the atoms to move to a higher-energy state. When the electrons drop back to a lower energy state, they release a photon: light. This process creates the beautiful aurora, or northern lights. Image copyright 2014 Tor-Ivar Næss. Via WaitForIt on Facebook.

View larger. | Mike Taylor calls this photo Moonlight Aurora II. He captured it on February 19, 2014. Visit Taylor Photography

View larger. | Aurora over Mt. Hood in Oregon as captured by Ben Coffman Photography during the night of May 31-June 1, 2013. Visit Ben’s photography page on G+ or visit Ben on Facebook.

Aurora on January 1, 2014 by Geir-Inge Bushmann. The lights typically are seen in the far north – the nations bordering the Arctic Ocean – Canada and Alaska, Scandinavian countries, Iceland, Greenland and Russia. See more photos from Geir-Inge Bushmann

View larger. | Aurora seen by EarthSky Facebook friend Colin Chatfield in Saskatchewan, Canada on May 19, 2012.

View larger. | Spectacular aurora, or northern lights, seen by EarthSky Facebook friend Colin Chatfield in Saskatchewan, Canada on October 24, 2011.

Bottom line: When charged particles from the sun strike atoms in Earth’s atmosphere, they cause electrons in the atoms to move to a higher-energy state. When the electrons drop back to a lower energy state, they release a photon: light. This process creates the beautiful aurora, or northern lights.

ASTRONOMÍA

Artículo Científico

¿Qué son los Quasars? Esos objetos tan distantes y tan luminosos.

Fuente:  Tweeter  

Astronomers solve 20-year-old quasar mystery

New works suggests most observed quasar phenomena depend on two things: how efficiently a central black hole is being fed and the astronomer’s viewing orientation.This is an artist’s concept of a quasar: a supermasive black hole at the center of a faraway galaxy. Image via European Southern Observatory

Discovered in the early 1960s, quasars are highly luminous objects shining over vast intergalactic distances. Until the early 1980s, the nature of quasars was controversial, but now most astronomers agree a quasar is a supermassive black hole in the center of a distant massive galaxy. The black hole rapidly accretes (accumulates) matter toward its center to create a quasar’s powerful luminosity. Still, mysteries about quasars have remained, and now two scientists say they’ve solved a quasar mystery that astronomers have been puzzling over for 20 years. These scientists say that most observed quasar phenomena can be unified with two simple quantities: how efficiently the central black hole is being fed and the viewing orientation of the astronomer. The journal Nature published this work on September 11, 2014.

The study comes from the Carnegie Observatories‘ Hubble Fellow Yue Shen – who describes himself as a “quasarologist” – and Luis Ho of the Kavli Institute for Astronomy and Astrophysics (KIAA) at Peking University. They note that:Quasars are rapidly accreting supermassive black holes at the centers of massive galaxies. They display a broad range of properties across all wavelengths, reflecting the diversity in the physical conditions of the regions close to the central engine [black hole]. These properties, however, are not random, but form well-defined trends.

These “well-defined trends” are sometimes referred to as the “main sequence” of quasars. The trends were discovered more than 20 years ago, but the mystery since then has been: what causes these trends? That is the question answered by Shen and Ho.

To answer the question, they developed and conducted statistical tests on the largest and most-homogeneous sample to date of over 20,000 quasars from the Sloan Digital Sky Survey. In this way, they were able to demonstrate that one particular property – called the Eddington ratio – is the driving force behind the main sequence of quasars.The Eddington ratio describes the efficiency of matter fueling a quasar’s central black hole. That fueling process is essentially a competition between the gravitational force pulling matter inward and the luminosity driving radiation outward. This push and pull between gravity and luminosity has long been suspected to be the primary driver behind the so-called main sequence, and Shen and Ho say their work confirms this hypothesis.

They also found that the orientation of an astronomer’s line-of-sight when looking down into the black hole’s inner region plays a key role. In this inner region of the hole, fast-moving gas produces quasar spectra with broad emission lines. Knowing that the astronomer’s orientation with respect to the quasar is key to understanding quasar spectra will help astronomers improve their measurements of black hole masses for quasars, Shen and Ho say.

Shen said:Our findings have profound implications for quasar research. This simple unification scheme presents a pathway to better understand how supermassive black holes accrete matter and interplay with their environments.

Ho added:And better black hole mass measurements will benefit a variety of applications in understanding the cosmic growth of supermassive black holes and their place in galaxy formation.

Bottom line: The Carnegie Observatories’ Yue Shen and Luis Ho of the Kavli Institute for Astronomy and Astrophysics at Peking University conducted extensive statistical tests of over 20,000 quasars from the Sloan Digital Sky Survey. They now say most observed quasar phenomena depend on two simple quantities: how efficiently a central black hole is being fed and the astronomer’s viewing orientation.

FÍSICA

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