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How far would we need to travel to leave our Galaxy?

It depends on whereabouts you want to get to; our vast Galaxy is thousands of light-years across, but for a decent vantage point you would need to travel much further.

Dr Alastair Gunn

Asked by: David Pollock, Cumbernauld

Our Galaxy, the Milky Way, is a disk of stars about 100,000 light-years across, and about 1,000 light-years thick. The Sun is situated about halfway from the centre and is near the middle of the disk in the vertical direction.

So, to leave our Galaxy, we would have to travel about 500 light-years vertically, or about 25,000 light-years away from the galactic centre. We’d need to go much further to escape the ‘halo’ of diffuse gas, old stars and globular clusters that surrounds the Milky Way’s stellar disk.

Finally, if we wanted to go far enough to see our entire Galaxy in all its glory, we’d need to travel about 48,000 light-years vertically. It’ll be a long time before we have the technology to do this, or even to send a telescope there, so for now we’ll just have to enjoy the incredible images we have of other spiral galaxies .

• Are there any stars between galaxies?
• How long does it take the Sun to orbit the galaxy?

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Is Interstellar Travel Really Possible?

Interstellar flight is a real pain in the neck.

Paul M. Sutter is an astrophysicist at The Ohio State University , host of Ask a Spaceman and Space Radio , and author of " Your Place in the Universe. " Sutter contributed this article to Space.com's Expert Voices: Op-Ed & Insights . 

Interstellar space travel . Fantasy of every five-year-old kid within us. Staple of science fiction serials. Boldly going where nobody has gone before in a really fantastic way. As we grow ever more advanced with our rockets and space probes, the question arises: could we ever hope to colonize the stars? Or, barring that far-flung dream, can we at least send space probes to alien planets, letting them tell us what they see?

The truth is that interstellar travel and exploration is technically possible . There's no law of physics that outright forbids it. But that doesn't necessarily make it easy, and it certainly doesn't mean we'll achieve it in our lifetimes, let alone this century. Interstellar space travel is a real pain in the neck. 

Related: Gallery: Visions of Interstellar Starship Travel

Voyage outward

If you're sufficiently patient, then we've already achieved interstellar exploration status. We have several spacecraft on escape trajectories, meaning they're leaving the solar system and they are never coming back. NASA's Pioneer missions, the Voyager missions , and most recently New Horizons have all started their long outward journeys. The Voyagers especially are now considered outside the solar system, as defined as the region where the solar wind emanating from the sun gives way to general galactic background particles and dust.

So, great; we have interstellar space probes currently in operation. Except the problem is that they're going nowhere really fast. Each one of these intrepid interstellar explorers is traveling at tens of thousands of miles per hour, which sounds pretty fast. They're not headed in the direction of any particular star, because their missions were designed to explore planets inside the solar system. But if any of these spacecraft were headed to our nearest neighbor, Proxima Centauri , just barely 4 light-years away, they would reach it in about 80,000 years.

I don't know about you, but I don't think NASA budgets for those kinds of timelines. Also, by the time these probes reach anywhere halfway interesting, their nuclear batteries will be long dead, and just be useless hunks of metal hurtling through the void. Which is a sort of success, if you think about it: It's not like our ancestors were able to accomplish such feats as tossing random junk between the stars, but it's probably also not exactly what you imagined interstellar space travel to be like.

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Related: Superfast Spacecraft Propulsion Concepts (Images)

Speed racer

To make interstellar spaceflight more reasonable, a probe has to go really fast. On the order of at least one-tenth the speed of light. At that speed, spacecraft could reach Proxima Centauri in a handful of decades, and send back pictures a few years later, well within a human lifetime. Is it really so unreasonable to ask that the same person who starts the mission gets to finish it?

Going these speeds requires a tremendous amount of energy. One option is to contain that energy onboard the spacecraft as fuel. But if that's the case, the extra fuel adds mass, which makes it even harder to propel it up to those speeds. There are designs and sketches for nuclear-powered spacecraft that try to accomplish just this, but unless we want to start building thousands upon thousands of nuclear bombs just to put inside a rocket, we need to come up with other ideas.

Perhaps one of the most promising ideas is to keep the energy source of the spacecraft fixed and somehow transport that energy to the spacecraft as it travels. One way to do this is with lasers. Radiation is good at transporting energy from one place to another, especially over the vast distances of space. The spacecraft can then capture this energy and propel itself forward.

This is the basic idea behind the Breakthrough Starshot project , which aims to design a spacecraft capable of reaching the nearest stars in a matter of decades. In the simplest outline of this project, a giant laser on the order of 100 gigawatts shoots at an Earth-orbiting spacecraft. That spacecraft has a large solar sail that is incredibly reflective. The laser bounces off of that sail, giving momentum to the spacecraft. The thing is, a 100-gigawatt laser only has the force of a heavy backpack. You didn't read that incorrectly. If we were to shoot this laser at the spacecraft for about 10 minutes, in order to reach one-tenth the speed of light, the spacecraft can weigh no more than a gram.

That's the mass of a paper clip.

Related: Breakthrough Starshot in Pictures: Laser-Sailing Nanocraft to Study Alien Planets

A spaceship for ants

This is where the rubber meets the interstellar road when it comes to making spacecraft travel the required speeds. The laser itself, at 100 gigawatts, is more powerful than any laser we've ever designed by many orders of magnitude. To give you a sense of scale, 100 gigawatts is the entire capacity of every single nuclear power plant operating in the United States combined.

And the spacecraft, which has to have a mass no more than a paper clip, must include a camera, computer, power source, circuitry, a shell, an antenna for communicating back home and the entire lightsail itself.  

That lightsail must be almost perfectly reflective. If it absorbs even a tiny fraction of that incoming laser radiation it will convert that energy to heat instead of momentum. At 100 gigawatts, that means straight-up melting, which is generally considered not good for spacecraft. 

Once accelerated to one-tenth the speed of light, the real journey begins. For 40 years, this little spacecraft will have to withstand the trials and travails of interstellar space. It will be impacted by dust grains at that enormous velocity. And while the dust is very tiny, at those speeds motes can do incredible damage. Cosmic rays, which are high-energy particles emitted by everything from the sun to distant supernova, can mess with the delicate circuitry inside. The spacecraft will be bombarded by these cosmic rays non-stop as soon as the journey begins.

Is Breakthrough Starshot possible? In principle, yes. Like I said above, there's no law of physics that prevents any of this from becoming reality. But that doesn't make it easy or even probable or plausible or even feasible using our current levels of technology (or reasonable projections into the near future of our technology). Can we really make a spacecraft that small and light? Can we really make a laser that powerful? Can a mission like this actually survive the challenges of deep space?

The answer isn't yes or no. The real question is this: are we willing to spend enough money to find out if it's possible?

• Building Sails for Tiny Interstellar Probes Will Be Tough — But Not Impossible
• 10 Exoplanets That Could Host Alien Life
• Interstellar Space Travel: 7 Futuristic Spacecraft to Explore the Cosmos

Learn more by listening to the episode "Is interstellar travel possible?" on the Ask A Spaceman podcast, available on iTunes and on the Web at http://www.askaspaceman.com . Thanks to @infirmus, Amber D., neo, and Alex V. for the questions that led to this piece! Ask your own question on Twitter using #AskASpaceman or by following Paul @PaulMattSutter and facebook.com/PaulMattSutter .  

Follow us on Twitter @Spacedotcom or Facebook . 

Join our Space Forums to keep talking space on the latest missions, night sky and more! And if you have a news tip, correction or comment, let us know at: [email protected].

Paul M. Sutter is an astrophysicist at SUNY Stony Brook and the Flatiron Institute in New York City. Paul received his PhD in Physics from the University of Illinois at Urbana-Champaign in 2011, and spent three years at the Paris Institute of Astrophysics, followed by a research fellowship in Trieste, Italy, His research focuses on many diverse topics, from the emptiest regions of the universe to the earliest moments of the Big Bang to the hunt for the first stars. As an "Agent to the Stars," Paul has passionately engaged the public in science outreach for several years. He is the host of the popular "Ask a Spaceman!" podcast, author of "Your Place in the Universe" and "How to Die in Space" and he frequently appears on TV — including on The Weather Channel, for which he serves as Official Space Specialist.

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Nasa’s webb telescope reveals links between galaxies near and far, nasa webb telescope team.

A new analysis of distant galaxies imaged by NASA’s James Webb Space Telescope shows that they are extremely young and share some remarkable similarities to “green peas,” a rare class of small galaxies in our cosmic backyard.

“With detailed chemical fingerprints of these early galaxies, we see that they include what might be the most primitive galaxy identified so far. At the same time, we can connect these galaxies from the dawn of the universe to similar ones nearby, which we can study in much greater detail,” said James Rhoads, an astrophysicist at NASA’s Goddard Space Flight Center in Greenbelt, Maryland, who presented the findings at the 241st meeting of the American Astronomical Society in Seattle.

A paper describing the results, led by Rhoads, was published Jan. 3 in The Astrophysical Journal Letters.  

Download high-resolution images from NASA’s Scientific Visualization Studio

Green pea galaxies were discovered and named in 2009 by volunteers taking part in Galaxy Zoo , a project where citizen scientists help classify galaxies in images, starting with those from the Sloan Digital Sky Survey . Peas stood out as small, round, unresolved dots with a distinctly green shade, a consequence of both the colors assigned to different filters in the survey’s composite images and a property of the galaxies themselves.

Green pea galaxy colors are unusual because a sizable fraction of their light comes from brightly glowing gas clouds. The gases emit light at specific wavelengths – unlike stars, which produce a rainbow-like spectrum of continuous color. Peas are also quite compact, typically only about 5,000 light-years across or about 5% the size of our Milky Way galaxy.

“Peas may be small, but their star-formation activity is unusually intense for their size, so they produce bright ultraviolet light,” said Keunho Kim, a postdoctoral researcher at the University of Cincinnati and a member of the analysis team. “Thanks to ultraviolet images of green peas from Hubble and ground-based research on early star-forming galaxies, it’s clear that they both share this property.”

In July 2022, NASA and its partners in the Webb mission released the deepest and sharpest infrared image of the distant universe yet seen , capturing thousands of galaxies in and behind a cluster known as SMACS 0723. The cluster’s mass makes it a gravitational lens, which both magnifies and distorts the appearance of background galaxies. Among the faintest galaxies behind the cluster were a trio of compact infrared objects that looked like they could be distant relatives of green peas. The most distant of these three galaxies was magnified by about 10 times, providing a significant assist from nature on top of the telescope’s unprecedented capabilities.

Webb did more than image the cluster – its Near-Infrared Spectrograph (NIRSpec) instrument also captured the spectra of selected galaxies in the scene. When Rhoads and his colleagues examined these measurements and corrected them for the wavelength stretch resulting from the expansion of space, they saw characteristic features emitted by oxygen, hydrogen, and neon line up in a stunning resemblance to those seen from nearby green peas.

Additionally, the Webb spectra made it possible to measure the amount of oxygen in these cosmic dawn galaxies for the first time.

As stars produce energy, they transmute lighter elements like hydrogen and helium into heavier ones. When stars explode or lose their outer layers at the ends of their lives, these heavier elements become incorporated into the gas that forms the next stellar generations, and the process continues. Over cosmic history, stars have steadily enriched the universe.

Two of the Webb galaxies contain oxygen at about 20% of the level in our Milky Way. They resemble typical green peas, which nevertheless make up less than 0.1% of the nearby galaxies observed by the Sloan survey. The third galaxy studied is even more unusual.

“We’re seeing these objects as they existed up to 13.1 billion years ago, when the universe was about 5% its current age,” said Goddard researcher Sangeeta Malhotra. “And we see that they are young galaxies in every sense – full of young stars and glowing gas that contains few chemical products recycled from earlier stars. Indeed, one of them contains just 2% the oxygen of a galaxy like our own and might be the most chemically primitive galaxy yet identified.”

NIRSpec was built for ESA ( European Space Agency ) by Airbus Industries. Its array of nearly half a million microshutters – tiny doors that can be opened or closed to admit or block light – allow it to capture spectra of up to 100 individual objects at a time. The microshutter array and detector subsystems were fabricated by NASA.

The James Webb Space Telescope, an international mission led by NASA with its partners ESA and CSA (Canadian Space Agency), is the world’s premier space science observatory. NASA Headquarters oversees the mission for the agency’s Science Mission Directorate. NASA’s Goddard Space Flight Center manages Webb for the agency and oversees work on the mission performed by the Space Telescope Science Institute, Northrop Grumman, and other mission partners. In addition to Goddard, several NASA centers contributed to the project, including the agency’s Johnson Space Center in Houston, Jet Propulsion Laboratory in Southern California, Marshall Space Flight Center in Huntsville, Alabama, Ames Research Center in California’s Silicon Valley, and others.

By  Francis Reddy NASA’s Goddard Space Flight Center , Greenbelt, Md.

Media Contacts: Laura Betz NASA’s Goddard Space Flight Center, Greenbelt, Md. (301) 286-9030

Claire Andreoli NASA’s Goddard Space Flight Center, Greenbelt, Md. (301) 286-1940

Scientists Have Calculated How Long It'll Take to Reach Distant Stars

Are we there yet?

• The researchers compared the predicted paths of four spacecraft to the paths of nearby stars, as measured by the Gaia space telescope, to see where and when they might overlap.
• According to their work , posted to the online pre-print server arXiv, it would take about 90,000 years for Pioneer 10 to swing within striking distance of a nearby star.

The intrepid Voyager 1 and 2 spacecrafts were launched in 1977, and despite having a roughly 12-year mission lifespan, are still hurtling through space and returning data to eager scientists on Earth. They’ve broken through barrier that protects our solar system and are now zipping through the interstellar medium along with Pioneer 10 and 11.

But how long might it take them, or another spacecraft, to actually reach another star system?

A team of scientists—Coryn Bailer-Jones of the Max Planck Institute for Astronomy in Switzerland and Davide Farnocchia of NASA’s Jet Propulsion Laboratory—have done the calculations. Essentially, the pair found a way to chart how long it would take a spacecraft to get from our humble solar system to the next system over, according to a paper uploaded to the pre-print server arXiv.

In the quest for answers, Farnocchia and Bailer-Jones turned to the European Space Agency’s Gaia space telescope for help. For more than five years, Gaia has been gathering data on billions of stars , charting their orbits and path through the cosmos.

Using this data and data about the projected paths of both the voyager spacecrafts as well as Pioneer 10 and 11, which are careening toward the outer reaches of the solar system, the researchers were able to create a timeline of when these crafts might reach distant star systems. For those eager to visit other worlds, brace for some bad news.

Should they continue their transit, the four spacecraft will come within striking distance of approximately 60 stars in the next million years. And in that same amount of time, they’ll get even closer—try two parsecs, the equivalent of 6.5 light years—to about 10 stars.

Who will have the best shot at reaching and exploring a distant star? Pioneer 10 will swing within .231 parsecs the star system HIP 117795 in the Cassiopeia constellation in approximately 90,000 years. And how long before one of these spacecrafts is hijacked by the orbit of one of these stars? It’ll be about 1,000,000,000,000,000,000,000 years.

You'll have some time to kill.

Jennifer Leman is a science journalist and senior features editor at Popular Mechanics, Runner's World, and Bicycling. A graduate of the Science Communication Program at UC Santa Cruz, her work has appeared in The Atlantic, Scientific American, Science News and Nature. Her favorite stories illuminate Earth's many wonders and hazards.

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Five things we’ve learned since Voyager 2 left the solar system

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One year ago, NASA’s Voyager 2 probe became just the second human-made object in history to exit the solar system and officially enter interstellar space . Voyager 2 was launched on August 20, 1977—16 days before its twin, Voyager 1, which exited the solar system’s northern hemisphere in 2012 . Voyager 2 was sent on a longer journey that allowed it to make encounters with Uranus and Neptune, and to this day it’s the only spacecraft to have visited these planets up close. It then made for the southern hemisphere of the heliosphere (the outermost region of the solar system, sometimes referred to as “the bubble”), straight for interstellar space.  

On November 5, 2018, Voyager 2 officially left the solar system as it crossed the heliopause, the boundary that marks the end of the heliosphere and the beginning of interstellar space. This happened 119 astronomical units from the sun (one AU is 93 million miles or 149.6 million kilometers, roughly the distance between the sun and Earth).

The spacecraft was able to analyse the makeup of solar winds, the composition and behavior of plasma particles, the interaction of cosmic rays, the structure and direction of magnetic fields, and other traits that define the edges of the solar system. Today, scientists published a bevy of papers in Nature Astronomy that detail the results of what Voyager 2 observed on its way out of the solar system. Here are the five biggest takeaways.

1. The bubble is leaking—both ways.

Voyager 2’s exit from the bubble was not without surprises. According to the data, the bubble was “very leaky,” says Stamatios Krimigis of Johns Hopkins University, the lead author of one of the new papers . Material from the solar bubble was discovered in interstellar space. 

Voyager 1 had actually found signs of a leaky bubble as well. In that instance, however, interstellar material was found streaming into the bubble––the opposite of what Voyager 2 discovered, says Edward Stone of Caltech, the lead author of a different paper . The new findings confirm that the leakiness of the heliopause, spotted in  two very different parts of the heliosphere, is not a rare characteristic of the bubble, although there is still no real explanation for what’s causing it.  

2. The boundary of the bubble is more uniform than we thought.

Before the Voyager missions, scientists predicted that the solar bubble just sort of dissolved into interstellar space as you ventured farther and farther from the sun. Voyager 2 seems to confirm that “in fact, there’s a very very sharp boundary there,” says Donald Gurnett of the University of Iowa, the lead author of this paper . Voyager 2’s plasma wave instrument ended up measuring plasma densities that were very much on par with what Voyager 1 detected. Because solar plasma is so hot (about 1 million °C), and interstellar plasma is incredibly cold (just 10,000 °C), the density of plasma jumps up by a factor between 20 and 50 as you cross the border. “That’s a characteristic of fluids, which oftentimes form very sharp boundaries,” says Gurnett. 

Krimigis was especially surprised that both Voyagers crossed the heliopause at the same relative distances (121 AU and 119 AU, respectively). Previous models heavily predicted that heightened solar activity during Voyager 1’s crossing in 2012 should have pushed the bubble’s boundary farther out. A period of low solar activity should have pulled the heliopause back a bit during Voyager 2’s crossing last year. The fact that both spacecraft left the solar system at pretty much the same distance, at two very different locations, is a source of confusion at the moment.

3. The makeup of the heliopause itself can vary by location.

Voyager 2 also made some observations that don’t square up with a sharp boundary—at least not what we’d expect. The biggest of these is the magnetic field measurements inside and outside the bubble. Astronomers expected the direction of the magnetic field would be very different between the two.  Yet when Voyager 2 crossed this thin surface, “there was essentially no change” in the direction of the field—something Voyager 1 observed as well, says Leonard Burlaga of NASA’s Goddard Space Flight Center, lead author for this paper . At the same time, the magnetic field observations on Voyager 2 suggest it found a thinner and simpler heliopause, filled with less energetic particles, than what Voyager 1 crossed. Again, all this data taken together raises more questions than it can answer.

4. The sun’s influence goes beyond the solar system.

The sun consistently spews out shock waves of plasma called coronal mass ejections (CMEs), which help shape the rest of the solar system. Turns out the sun’s impact goes beyond its own borders. The new Voyager 2 data, like the Voyager 1 data before it, shows how CMEs propagate past the heliopause and lower the amount of cosmic rays beyond the bubble. “This is somewhat similar to what you might find out in the galaxy,”  says Gurnett. Supernovae send shock waves out into the galaxy as well, stirring the interstellar medium, albeit at a much more intense scale than CMEs. “Even the formation of the solar system, most astronomers believe, was triggered by an interstellar shock wave from a supernova,” he says.

If we think about the potential for cosmic rays to promote biological mutations in life on Earth, these findings lend support to the idea that the sun could also have an influence on the evolution of living things on extraterrestrial worlds, in this planetary system and elsewhere. 

5. This was the Voyager program’s final major milestone. 

“When the two Voyagers were launched, the space age was only 20 years old,” says Stone. “It was hard to know at that time that anything could last 40 years.”

Still, the observations of the heliopause really are part of the last hurrah for both spacecraft. Each probe is powered by radioisotopic thermoelectric generators heated by plutonium-238. That material is undergoing natural decay. “We know that somehow, in another five years or so, we may not have enough power to have any scientific instruments on any longer,” says Stone. 

The two missions will continue to learn how the sun’s heliosphere interacts with the interstellar medium and give us clues about other star systems.“We believe every star has these features,” says Stone. “What we learn about this heliosphere will help us learn more about the astrospheres of other stars.” 

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January 13, 2016

What Will It Take for Humans to Colonize the Milky Way?

It's a common theme in science fiction, but migrating to planets beyond our solar system will be a lot more complicated and difficult than you might imagine

By Kim Stanley Robinson

The idea that humans will eventually travel to and inhabit other parts of our galaxy was well expressed by the early Russian rocket scientist Konstantin Tsiolkovsky, who wrote, “Earth is humanity’s cradle, but you’re not meant to stay in your cradle forever.” Since then the idea has been a staple of science fiction, and thus become part of a consensus image of humanity’s future. Going to the stars is often regarded as humanity’s destiny, even a measure of its success as a species. But in the century since this vision was proposed, things we have learned about the universe and ourselves combine to suggest that moving out into the galaxy may not be humanity’s destiny after all.

The problem that tends to underlie all the other problems with the idea is the sheer size of the universe, which was not known when people first imagined we would go to the stars. Tau Ceti, one of the closest stars to us at around 12 light-years away, is 100 billion times farther from Earth than our moon. A quantitative difference that large turns into a qualitative difference; we can’t simply send people over such immense distances in a spaceship, because a spaceship is too impoverished an environment to support humans for the time it would take, which is on the order of centuries. Instead of a spaceship, we would have to create some kind of space-traveling ark, big enough to support a community of humans and other plants and animals in a fully recycling ecological system.

On the other hand it would have to be small enough to accelerate to a fairly high speed, to shorten the voyagers’ time of exposure to cosmic radiation, and to breakdowns in the ark. Regarded from some angles bigger is better, but the bigger the ark is, the proportionally more fuel it would have to carry along to slow itself down on reaching its destination; this is a vicious circle that can’t be squared. For that reason and others, smaller is better, but smallness creates problems for resource metabolic flow and ecologic balance. Island biogeography suggests the kinds of problems that would result from this miniaturization, but a space ark’s isolation would be far more complete than that of any island on Earth. The design imperatives for bigness and smallness may cross each other, leaving any viable craft in a non-existent middle.

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The biological problems that could result from the radical miniaturization, simplification and isolation of an ark, no matter what size it is, now must include possible impacts on our microbiomes. We are not autonomous units; about eighty percent of the DNA in our bodies is not human DNA, but the DNA of a vast array of smaller creatures. That array of living beings has to function in a dynamic balance for us to be healthy, and the entire complex system co-evolved on this planet’s surface in a particular set of physical influences, including Earth’s gravity, magnetic field, chemical make-up, atmosphere, insolation, and bacterial load. Traveling to the stars means leaving all these influences, and trying to replace them artificially. What the viable parameters are on the replacements would be impossible to be sure of in advance, as the situation is too complex to model. Any starfaring ark would therefore be an experiment, its inhabitants lab animals. The first generation of the humans aboard might have volunteered to be experimental subjects, but their descendants would not have. These generations of descendants would be born into a set of rooms a trillion times smaller than Earth, with no chance of escape.

In this radically diminished enviroment, rules would have to be enforced to keep all aspects of the experiment functioning. Reproduction would not be a matter of free choice, as the population in the ark would have to maintain minimum and maximum numbers. Many jobs would be mandatory to keep the ark functioning, so work too would not be a matter of choices freely made. In the end, sharp constraints would force the social structure in the ark to enforce various norms and behaviors. The situation itself would require the establishment of something like a totalitarian state.

Of course sociology and psychology are harder fields to make predictions in, as humans are highly adaptable. But history has shown that people tend to react poorly in rigid states and social systems. Add to these social constraints permanent enclosure, exile from the planetary surface we evolved on, and the probability of health problems, and the possibility for psychological difficulties and mental illnesses seems quite high. Over several generations, it’s hard to imagine any such society staying stable.

Still, humans are adaptable, and ingenious. It’s conceivable that all the problems outlined so far might be solved, and that people enclosed in an ark might cross space successfully to a nearby planetary system. But if so, their problems will have just begun.

Any planetary body the voyagers try to inhabit will be either alive or dead. If there is indigenous life, the problems of living in contact with an alien biology could range from innocuous to fatal, but will surely require careful investigation. On the other hand, if the planetary body is inert, then the newcomers will have to terraform it using only local resources and the power they have brought with them. This means the process will have a slow start, and take on the order of centuries, during which time the ark, or its equivalent on the alien planet, would have to continue to function without failures.

It’s also quite possible the newcomers won’t be able to tell whether the planet is alive or dead, as is true for us now with Mars. They would still face one problem or the other, but would not know which one it was, a complication that could slow any choices or actions.

So, to conclude: an interstellar voyage would present one set of extremely difficult problems, and the arrival in another system, a different set of problems. All the problems together create not an outright impossibility, but a project of extreme difficulty, with very poor chances of success. The unavoidable uncertainties suggest that an ethical pursuit of the project would require many preconditions before it was undertaken. Among them are these: first, a demonstrably sustainable human civilization on Earth itself, the achievement of which would teach us many of the things we would need to know to construct a viable mesocosm in an ark; second, a great deal of practice in an ark obiting our sun, where we could make repairs and study practices in an ongoing feedback loop, until we had in effect built a successful proof of concept; third, extensive robotic explorations of nearby planetary systems, to see if any are suitable candidates for inhabitation.

Unless all these steps are taken, humans cannot successfully travel to and inhabit other star systems. The preparation itself is a multi-century project, and one that relies crucially on its first step succeeding, which is the creation of a sustainable long-term civilization on Earth. This achievement is the necessary, although not sufficient, precondition for any success in interstellar voyaging. If we don’t create sustainability on our own world, there is no Planet B.

Space: how far have we gone – and where are we going?

Billionaire entrepreneurs are trying to create rockets fit for human travel, while government agencies spend billions furthering their explorations. But we are still a long way off from making our way to the red planet

Who has travelled to space?

Space flight is now a venerable industry. Humanity’s first space explorer, Soviet cosmonaut Yuri Gagarin, orbited around the globe on 12 April 1961, more than half a century ago, when Britain remained a colonial power and people were still using halfpennies to buy their fish and chips.

Since then, more than 550 people have blasted themselves into the deep black abyss, although not all agree on how far up you need to go until you hit space, so there is no internationally accepted figure. Only a 10th of those have been women, in big part due to sexist policies by Nasa and Russia’s Roscosmos space agency.

Where have we been in space?

The Soviet Union pulled ahead with the first space walks, but US president John F Kennedy’s announcement that America would put a man on the moon by the end of the 1960s focused the space race squarely on that goal. Apollo 11 touched down on our dusty grey neighbour on 20 July 1969.

A total of 12 men walked on the moon over the next few years, all Americans, but no one has been back there since 1972. In fact, no one has left the outskirts of the Earth since then.

We imagine astronauts floating in free space or bouncing in moon craters, yet the majority of those lucky enough have instead spun around in low Earth’s orbit – between 99 and a few hundred miles high. That’s where the vast array of communications and navigation satellites live, speeding at thousands of miles an hour to avoid plummeting back to earth.

What do we do there?

Even though we did not go back to deep space, humans have begun to live and work outside the Earth’s atmosphere, often conducting experiments on themselves to determine the effects of weightlessness, or microgravity, on the human body.

By 1986, the Soviet Union had launched the Mir space station. When it eventually fell to Earth (thankfully unoccupied) and burned up, our current space outpost, the International Space Station (ISS), was launched. Since 2000, humans have been living in space constantly. There are three up there at the moment, speeding around the globe once every 90 minutes.

What happens to the body in space?

A lot, and until we properly understand how weightlessness affects humans, we won’t be able to send this era’s pioneers further afield to places such as Mars or wandering asteroids. Scott Kelly, a US former fighter pilot and long-time Nasa astronaut, spent a year bouncing around the cramped capsules of the ISS in an attempt to understand the long-term impact of space flight. He doesn’t hold the record for the most extended foray into the void – that is claimed by Gennady Padalka , who spent two and half years of his life up there on several missions – but the Kelly experiment had a natural advantage over others: he has a twin.

Comparing their bodies throughout, scientists were able to assess how bones, muscles and other parts of the body deteriorate in space. There is even a gym on the ISS where astronauts can keep their muscles – no longer needed to prop them up – from slowly wasting away. But they need to wear a harness to keep them from floating off the treadmill. One big issue is that eye problems develop, but Kelly found his body recovered fast on return. He and his twin seemed in similar shape – good news for future deep space missions.

Which countries have human space programmes?

Only three countries, China, Russia and the US, have human space programmes as it remains prohibitively expensive. However, they have provided lifts for space travellers from 40 countries, including a member of the Saudi royal family and even paying customers, such as South African millionaire Mark Shuttleworth, aged just 28.

How much does it cost to send them up?

Astronomical. The ISS is the most expensive machine ever constructed with a price tag at around $150bn (£115bn). Nasa’s space shuttle programme, which kicked off in the early 1970s by promising safe and affordable access to space, hoped to cost just a few tens of million dollars per launch. But as the shuttle was thrown in the scrapyard in 2011, the agency estimated the total cost at $209bn — nearly $1.6bn per flight.

Following the big fight over the shuttle, which looked fantastic but also restricted space adventuring to Earth’s orbit as well as costing a fortune, the US took a side seat in launches. Most astronauts are now sent by the Russian space agency, which sells round-trip rides on its Soyuz spacecraft for between $21m and $82m .

Is human space flight worth the cost?

Anyone involved in space travel will scoff at this, but it’s a good question, and space agencies often don’t communicate their achievements enough. Almost every sector of human progress has benefited from sending people into space. Just the act of attempting the feat forced scientists to invent new systems. The Apollo guidance computer was a predecessor to the microcomputer, now found in all smartphones. Clothes are more fire-resistant because of research on space fires . Remotely monitoring the health of astronauts has led to revolutionary systems for helping patients on Earth . Diseases behave and develop differently in microgravity, which assists scientists in finding cures.

Others say paying for human space flight pumps money into the economy, arguing that spin-off companies from space research and a growing commercial space industry generates seven to 14 times the cost of missions. And Nasa, the most significant global player, is not spending nearly as much as it used to. About $19bn is spent by the US government on its budget , roughly half a percent of all federal spending. During the early Apollo programme, that was between 4% and 5%.

How strong is space cooperation between countries?

The first space race was part of the chest-beating of the cold war, but since then human space exploration has been more about countries working together than against each other. The ISS is a massive collaboration between five space agencies (Nasa, Roscosmos, Japan’s Jaxa, the pan-European agency ESA and the Canadian Space Agency) and was assembled over a period of 13 years from 1998, slowly adding capsules like Lego.

A big exception to this is China, which has gone it alone with its space ambitions, never sending an astronaut to the ISS. In 2006, Beijing reportedly tested lasers against US imaging satellites in what appeared to be an attempt to blind or damage them, and US lawmakers later banned cooperation between Nasa and China’s state agency.

However, the future of any effective human space flight is certainly likely to be cooperative rather than antagonistic. Since 2011, national spaces agencies in 14 countries have attempted to coordinate their dreams into a single vision. The most recent plan, published in January this year , said they had agreed to “expand human presence into the solar system, with the surface of Mars as a common driving goal”.

We’re off to the red planet? Hurray!

Don’t start the countdown just yet. To get to Mars, most people in the human space flight community feel we need to first go back to the moon. “It’s the only logical step,” says Ian Crawford, professor of planetary science and astrobiology at Birkbeck, University of London. “I’m all in favour of sending people to Mars, but the technology, competence, the experience – I think it’s still out of reach”.

The moon has several advantages. It’s only three days away, rather than a several-month round trip to Mars, and has been touted as a location for a research station similar to the one in Antarctica. From their celestial laboratory, scientists could study the impact of radiation exposure and near-weightlessness on the body at a closer distance to Earth, but still within deep space, all while preparing for trips further afield.

So to the moon then?

Well. Not quite either. The Global Exploration Roadmap suggests first building a space station as an orbital base from which to send astronauts back and forth to the moon. This will look similar to the ISS except, instead of rushing around the Earth, it will orbit the moon.

Will we ever get to Mars?

It is a mammoth feat and it would be wise to expect serious delays. “Where we go in space is decided by a combination of what people would like to do and the reality of time and budgets,” says Henry Hertzfeld, director of the Space Policy Institute at George Washington University, Washington DC, and a former policy analyst at Nasa. “The idea of putting people on Mars has been around for a long time. If you read the policies, it is clearly a long-term vision without a date. But we probably are still lacking the technology to keep people for a long time in deep space.”

Who are the new contenders in human space flight?

The US and Russia have been giving way to new players. In 2003, China became the third country to put a person into orbit and India plans to follow in 2022. But the sector-changing impact is undoubtedly coming from the private space.

In what is being coined the “billionaire’s space race”, Elon Musk, founder of Telsa electric cars, Amazon CEO Jeff Bezos and Virgin boss Richard Branson all want to send private citizens to space. Their companies, SpaceX, Blue Origin and Virgin Galactic , are set on making human space travel cheaper.

They join a handful of commercial space flight companies that already work as contractors for national space agencies. Aerospace industry titans Boeing and Lockheed Martin send heavy launchers into space, but that costs at least $350m per launch – several times more expensive than SpaceX’s new $90m Falcon Heavy system.

SpaceX has around $10bn worth of launches already booked and saves costs through reusable spacecraft, where even the rocket boosters land themselves back on the ground and can be dusted off for reuse.

And while it is looking increasingly likely that the ISS will be defunded in the next decade, several private ventures are considering either taking over or rebuilding their own space stations.

What’s next?

As government agencies prioritise the moon, others are looking straight at Mars. Musk has said his life goal is to create a thriving Mars colony as a fail-safe for humanity in case of a catastrophic event on Earth, such as a nuclear war or Terminator-style artificial intelligence coup. For this, SpaceX is developing the Big Falcon Rocket (BFR), which he claims could send crewed flights to the red planet by mid-2020.

Musk says the BFR is partly inspired by Tintin’s rocket and will be the biggest ever made at close to 40 storeys high and capable of ferrying as many as 100 passengers per trip, depending on how much luggage they want to put in the hold.

As well as a healthy satellite launch business, SpaceX is raising money by selling tickets on the BFR for a trip, some would say a jolly, around the moon. Yusaku Maezawa , a Japanese fashion billionaire and art collector, is funding such a mission slated for 2023 and says he is going to invite artists with him for the week-long trip to re-engage the public in the wonder of our universe.

Further reading

An astronaut’s guide to life on Earth, Chris Hadfield

To space and back, Sally Ride

The Right Stuff, Tom Wolfe

The Martian, Andy Weir

Endurance: A year in space, a lifetime of discovery, Scott Kelly

• The briefing
• Richard Branson

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Welcome to ViewSpace

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Explore the Universe with Interactives and Videos

About ViewSpace

What is viewspace.

ViewSpace is a free, web-based collection of digital interactives and videos highlighting the latest developments in astronomy and Earth science.

ViewSpace gives you the opportunity to explore our planet, solar system, galaxy, and universe. Provided free with the support of NASA, ViewSpace is developed by a team of scientists, educators, and communication specialists who collaborate to ensure that content is accurate, up-to-date, engaging, relevant, and accessible to a wide audience.

Interactives

ViewSpace interactives allow you to explore objects and materials from different perspectives, discovering how we can combine information to better understand the universe.

Different forms of light: Explore visible and invisible wavelengths of light that help us understand features like the dusty brim of the Sombrero Galaxy roughly 30 million light-years away.

Hidden objects: Unveil invisible light to reveal hidden objects like the stars forming inside Mystic Mountain, a pillar of gas and dust 7,500 light-years from Earth.

ViewSpace videos tell the stories of the planets, stars, galaxies, and universe, giving viewers the opportunity to experience space and Earth as seen with satellites and telescopes.

Astronomy: Explore the sky with stories told through spectacular imagery from space telescopes.

Earth science: Gain new perspectives on our home planet based on data gathered by Earth-orbiting satellites.

ViewSpace is produced by the Office of Public Outreach at the Space Telescope Science Institute , in partnership with the NASA's Universe of Learning project and NASA's Earth Observing System, Hubble Space Telescope Project, and James Webb Space Telescope Project.

ViewSpace has been exhibited in museums, planetariums, and science centers across the country since 2000.

What Will You Explore?

The Latest Discoveries in Astronomy and Astrophysics

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In-depth Stories of How Science and the Universe Work

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Sample Images from ViewSpace

What objects and materials make up the universe, and how do we study the invisible as well as the visible?

Data from NASA’s Hubble Space Telescope and Chandra X-Ray Observatory are used to create a map of dark matter (blue) in galaxy cluster MACS J0717.5+3745.

What are galaxies; how do they vary; and how do they form, interact, and change over time?

The Penguin and the Egg (Arp 142) is a pair of galaxies that are being distorted by their mutual gravitational attraction.

How do the Sun, planets, moons, comets, and asteroids interact as a system?

Saturn’s moon Titan casts a shadow as it passes between the planet and the Sun.

How do telescopes help us better understand the objects and materials that light up the sky?

With telescopes, we can see details of the Milky Way, including glowing clouds of dust and gas like the Lobster Nebula.

How fast is the universe expanding and what does this tell us about its past and future?

Over time, space expands, stretching the wavelenghts of light and causing the distant galaxies seen in the Ultra Deep Field image from the Hubble Space Telescope to look redder than the closer galaxies.

How do we detect and study planets orbiting other stars?

Changes in the brightness of starlight, measured by NASA’s Spitzer Space Telescope, indicates the presence of a planet orbiting the star.

What happens to stars at the end of their lives, and how do stellar explosions affect the space around them?

Visible, infrared, and X-ray light from supernova remnant Cassiopeia A reveal remains of an exploded star.

How can we use interactions between light and matter to probe the deep universe?

The enormous mass of galaxy cluster Abell 370 bends the space around it, magnifying and distorting the light from more distant galaxies into arc-like streaks.

How are astronomers combining data from space and ground-based telescopes, particle detectors, and gravitational wave detectors to understand cosmic objects, processes, and events?

An artist’s illustration depicts the detection of neutrino particles and gamma rays emitted by a supermassive black hole at the center of a distant galaxy.

How and where do stars form, and how do they shape their surroundings?

Pillars of gas and dust in the Eagle Nebula are sculpted and illuminated by stellar winds and high-energy radiation of bright stars.

How can we use satellites to map, study, and monitor Earth’s land surface, oceans, and atmosphere?

An image captured by the Landsat 8 satellite in May 2018 shows active lava flows from Kilauea volcano in Hawaii.

What evidence supports our theories of how the universe formed and how it has evolved over time?

A map of the sky from the Planck Space Telescope highlights variations in the cosmic microwave background radiation—energy left over from the big bang some 13.8 billion years ago.

What tools and methods do scientists use to study Earth and space?

NASA’s Soil Moisture Active Passive satellite (SMAP) helps scientists monitor droughts, predict floods, and improve farm productivity.

Is Earth unique? Are we alone?

Observations from space telescopes have revealed thousands of exoplanets of different of sizes, compositions, temperatures, and atmospheres, including seven rocky Earth-sized planets of the TRAPPIST-1 system, 40 light-years from Earth (artist’s illustration).

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ViewSpace provides informal learning sites with engaging, accurate, relevant, and up-to-date astronomy and Earth science content. Access to ViewSpace is free, requiring only registration, a computer or Smart TV, and persistent internet access. ViewSpace content is self-updating and videos can be set to play automatically, requiring minimal staff effort to maintain.

Join hundreds of others in featuring ViewSpace as part of your exhibits.

Who Produces and Supports ViewSpace?

ViewSpace is produced by the Space Telescope Science Institute in Baltimore, Maryland, and is provided free of charge through financial support and subject matter expertise from the NASA’s Universe of Learning project, NASA’s Earth Observing System Project Science Office, NASA’s Hubble Space Telescope Project, and NASA’s James Webb Space Telescope Project.

Funded by NASA’s Science Mission Directorate, NASA’s Universe of Learning is an integrated astrophysics STEM learning and literacy project developed through a partnership between the Space Telescope Science Institute, Caltech/IPAC, NASA’s Jet Propulsion Laboratory, the Smithsonian Astrophysical Observatory, and Sonoma State University.

NASA’s Earth Observing System (EOS) is a coordinated series of satellites designed to observe Earth’s land, atmosphere, oceans, and biosphere. As part of the Earth Science Division of NASA’s Science Mission Directorate, the EOS Project Science Office (EOSPSO) is committed to sharing information with both researchers and the general public.

The Hubble Space Telescope and James Webb Space Telescope are two of NASA’s flagship missions designed to explore and advance our understanding of the universe. The missions’ communications programs are dedicated to sharing scientific advances and making the world’s astronomical information accessible to all.

How Long Would It Take to Cross the Milky Way at Light Speed?

The disk of our home galaxy – the Milky Way – is bigger than we previously thought. A new study shows it would take 200,000 years for a spaceship traveling at the speed of light to go across the entire galaxy.

Researchers made the find after analyzing the abundances of metals (heavy elements) in stars, also known as their metallicities. When looking beyond the previously assumed boundary of the Milky Way's disk, scientists were surprised to see stars with compositions resembling those of disk stars. [ Amazing Photos of Our Milky Way Galaxy ]

"We have shown that there is an appreciable fraction of stars with higher metallicity, characteristic of disc stars, further out than the previously assumed limit on the radius of the galaxy disc," study co-author Carlos Allende, a researcher at Astrophysics Institute of the Canary Islands (Instituto de Astrofisica de Canarias,  said in a statement . 

The new study estimates the size of the Milky Way's disk at 200,000 light-years across. Past studies have suggested the Milky Way is between  100,000 light-years  and  160,000 light-years across . (One light-year is the distance light travels in a year, about 6 trillion miles or 10 trillion kilometers.)

To put the find in perspective with the location of our own sun, astronomers said the newly found disk stars are about three times farther from the galaxy center than the sun. It's possible there could be even more disk stars about four times farther away, the team added in the statement. 

Researchers made the find after analyzing survey data from the Apache Point Observatory Galactic Evolution Experiment (APOGEE) and the Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST), which collect the spectra of stars. A star's spectrum is the breakdown of its light into different colors. By analyzing the pattern of colors, scientists learn what elements are present within the star.

It's not the first time scientists have revised a galaxy's parameters. A recent study of the Andromeda galaxy revealed that the celestial body  is actually about the same mass as the Milky Way , instead of larger. This affects predictions of the two galaxies' motions as they head for an inevitable crash in 4 billion years.

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The new study was published in the journal Astronomy & Astrophysics and led by Martin Lopez-Corredoira, a researcher at IAC.

Follow us  @Spacedotcom ,  Facebook  and  Google+ . Original article on  Space.com .

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Extra-galactic

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Extra-galactic was a term for objects situated, occurring, or originating outside the gravitational bounds of the galaxy .

• 2 Appearances
• 4 Notes and references
• 5 External links

History [ ]

The extra-galactic Yuuzhan Vong hailed from another galaxy.

Notable extra-galactic and alleged extra-galactic species included the Yuuzhan Vong and the Chazrach , [2] the Kwa , [3] the Nagai and Tofs (originating in Firefist ), [4] and the Silentium and Abominor droid species [5] which may have originated in the Yuuzhan Vong's home galaxy . The sentient ship (and its pilot) Luke and Leia encountered also originated in another galaxy. [6]

The InterGalactic Banking Clan had influence as far as the Rishi Maze and Firefist . [7]

The Sith Emperor Vitiate, when telling the Hero of Tython his plans for his galaxy-destroying ritual, said that there were other galaxies beyond theirs and that he would experience or ignore them as he wished. This implied that he, or the Sith Empire , had means of reaching these locations—assuming the galaxy-destroying ritual would not also consume the hyperspace disturbance at the edge of the galaxy . [1]

At some point during the height of the Galactic Empire , the Imperial Senate issued Intergalactic Passports to allow the owner to travel throughout the six known galaxies. [8] In addition, Arhul Hextrophon in a guest lecture for the Brionelle Memorial Military Academy speculated that Emperor Palpatine by the time of his resurrection and ruling of the Dark Empire may have planned to eventually engage in extra-galactic conquest due to his usage of World Devastators . [9]

Appearances [ ]

• Star Wars: The Old Republic (Mentioned only)
• Darth Plagueis (Mentioned only)
• Darth Plagueis audiobook (Mentioned only)
• † Star Wars: Republic: Infinity's End
• Young Jedi Knights: Shadow Academy
• † Star Wars: The New Jedi Order
• † Star Wars: Invasion
• Dark Nest I: The Joiner King
• Intergalactic Passport

Sources [ ]

• The Truce at Bakura Sourcebook
• Alien Encounters

• The New Essential Chronology
• The New Essential Guide to Droids
• The Complete Star Wars Encyclopedia
• The Essential Atlas
• The Essential Guide to Warfare
• The Essential Reader's Companion
• Star Wars: Edge of the Empire Core Rulebook
• Star Wars: Age of Rebellion Core Rulebook

Notes and references [ ]

• ↑ 1.0 1.1 Star Wars: The Old Republic
• ↑ Star Wars: The New Jedi Order
• ↑ The Official Star Wars Fact File 139 (DAT1, Dathomir )
• ↑ The Essential Atlas
• ↑ The New Essential Guide to Droids
• ↑ Star Wars (1977) 38
• ↑ The Essential Guide to Warfare
• ↑ Intergalactic Passport
• ↑ Dark Empire Sourcebook

External links [ ]

• Extragalactic battles
• Extragalactic conflicts
• 1 The Bad Batch Season 3
• 2 Edmon Rampart
• 3 Flash Strike