Astronomy

What is the word for space that is in the solar system, but outside the heliopause?

What is the word for space that is in the solar system, but outside the heliopause?


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Wikipedia says the definition of interplanetary space is

the region dominated by the interplanetary medium, which extends out to the heliopause where the influence of the galactic environment starts to dominate over the magnetic field and particle flux from the Sun

While it defines the solar system as the region in which the sun is the primary gravitational influence

The Sun's gravitational field is estimated to dominate the gravitational forces of surrounding stars out to about two light years (125,000 AU).

So, if the region outside the heliopause but inside the solar system isn't interplanetary space, then what is it?


There doesn't seem to be such a word. Interstellar space within the Solar System is still just interstellar space.

There doesn't seem to be a demand for the word you're looking for either. We distinguish space by its contents; the space within the heliosphere is called the interplanetary medium (it contains solar plasma, dust, etc.), while the interstellar medium comprises sparse gaseous molecules from the Local Fluff and (if you go far enough) the rest of the Local Bubble.

Whereas there are about 10 oxygen molecules per cubic centimeter in the interplanetary medium, there is only 1 oxygen molecule per cubic centimeter in the interstellar medium. Seeing that there is no clear boundary for the Milky Way (nor is there any single definition for a boundary for galaxies), the intergalactic medium just vaguely describes the medium within galaxy filaments; here, the space is so rarified that there is only 1 oxygen molecule per cubic meter.


The Sun's Hill Sphere may be the term you're looking for. Or perhaps "within the Oort Cloud diameter" would do it for you. According to Wikipedia, the outer gravitational zero velocity distance (Hill Sphere) isn't known - it's thought to lie between 50,000 AU and 200,000 AU - or up to over 3 light years.


NASA Detects “Hum” Coming From Beyond Solar System

Almost a decade ago, NASA’s Voyager 1 spacecraft left the outer edge of our Solar System to enter interstellar space.

It marked the first time a spacecraft had ever done so, a culmination of almost 35 years of traveling through space.

Now, researchers are digging through all the fascinating data from it that’s making its way back to Earth — and they’ve found something strange: a background “hum” beyond the edge of our solar system.

“We’re detecting the faint, persistent hum of interstellar gas,” Stella Koch Ocker, Cornell doctoral student in astronomy and lead author of a new paper published in Nature Astronomy, said in a statement. “It’s very faint and monotone, because it is in a narrow frequency bandwidth.”

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As Voyager 1 traveled from the heliopause, the boundary between our solar system and interstellar space, into the interstellar medium, its scientific instruments detected a constant stream of plasma waves.

The insight could allow us to gain a better understanding of the shape of the heliosphere, the protective bubble around the Solar System, and how it’s influenced by this constant buffeting of interstellar gas.

Voyager 1’s Plasma Wave System detected a shift in the gases once it crossed the heliopause. Between bouts of strong solar eruptions caused by the Sun, there was this continuous “hum,” a signature sound of interstellar gases.

“The interstellar medium is like a quiet or gentle rain,” said senior author James Cordes, from the George Feldstein Professor of Astronomy, in the statement. “In the case of a solar outburst, it’s like detecting a lightning burst in a thunderstorm and then it’s back to a gentle rain.”

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“We’ve never had a chance to evaluate [the density of interstellar space],” Shami Chatterjee, co-author and Cornell researcher, said. “Now we know we don’t need a fortuitous event related to the sun to measure interstellar plasma.”

Despite Voyager 1 being 14 billion miles away, in other words, scientists are still able to get tantalizing glances of what space is like outside of our own home star system.


'A quiet or gentle rain'

Voyager 1 has traveled farther from Earth than any other spacecraft in history. It's one of only two human-made objects that have ever crossed into interstellar space — the other i sits counterpart, Voyager 2, which left the solar system in 2018.

NASA launched the twin Voyagers in 1977 to swing around Jupiter and Saturn over the course of a 5-year mission. The spacecraft taught astronomers about the composition of Saturn's rings and the existence of volcanoes on Jupiter's moon, Io. Then Voyager 2 went on to visit Uranus and Neptune, while Voyager 1 continued on toward the edge of our solar system.

To truly reach interstellar space, both Voyager probes had to cross the heliopause — the outer boundary of the stream of charged particles shot out by the sun. This solar wind, as the stream is known, extends beyond our solar system, but at the heliopause, it encounters pressure from the wind in interstellar space and gets turned back toward the sun.

Research suggests the sun's influence can sometimes extend beyond the heliopause, though. Occasionally, the sun spits out billions of tons of charged particles from its atmosphere in the form of solar flares. These eruptions can cause violent disturbances in interstellar gas. Voyager 1 has detected such shockwaves before.

But the farther into the heliopause Voyager 1 goes, the less the sun's energy should ooze into the interstellar medium and push or pull on the gas therein.

According to NASA, there will come a point in Voyager 1's travels when solar particles no longer influence its measurements. Once the probe gets there, "it will sense the stirrings from sources deeper in the cosmos," the agency said.

Indeed, the humming outlined in the new study seems unrelated to what the sun is doing — unlike those erratic shockwaves, this is a constant vibration in the interstellar medium, which suggests a different source of energy that astronomers might not know about yet.

"The interstellar medium is like a quiet or gentle rain," James Cordes, a Cornell astronomer and another study co-author, said in the release. "In the case of a solar outburst, it's like detecting a lightning burst in a thunderstorm and then it's back to a gentle rain."

Listening for the hum of that gentle rain could help researchers better understand how dense the space between stars is — and whether that density changes — as Voyager 1 gets farther and farther from Earth. It could also reveal clues about how and where the most stellar nurseries are, since stars form in high-density interstellar clouds.


Studying Waves has its Ups and Downs

The far-flung pilgrim to the stars has now spent eight years exploring the void between the stars. Slowly, astronomers and astrophysicists are forming new ideas about this region of space from the findings of the two Voyager spacecraft.

“The Voyager 1 Plasma Wave System has given point estimates of the plasma density spanning about 30 au of interstellar space, revealing a large-scale density gradient and turbulence outside of the heliopause,” researchers wrote in the journal Nature Astronomy.

After crossing into interstellar space, the Plasma Wave System instrument onboard Voyager 1 recorded changes in the interstellar medium caused by the influence of our distant star.

Even now, however, this NASA spacecraft is still close enough to the heliosphere that most of the “waves” in the ocean felt by the spacecraft are the result of solar effects. However, as the spacecraft moves further from the Sun, effects from other stars will become more prominent.

“We have some ideas about how far Voyager will need to get to start seeing more pure interstellar waters, so to speak. But we’re not entirely sure when we’ll reach that point,” Ocker explains.

This new study (likely) represents the first continuous measurement of interstellar material. Researchers suggest low-level disturbances in the plasma waves may be greater than expected, allowing study of these perturbations over a long period for the first time.

Earlier studies relied on waiting until the Sun happened to be influencing these outer boundaries of the Solar System, providing an opportunity to see ripples in the interstellar medium.

“V’Ger must evolve. It’s knowledge has reached the limits of this universe and it must evolve. What it requires of it’s god, doctor, is the answer to it’s question, ‘is there nothing more?’” — Commander Spock, Star Trek: The Motion Picture

Researchers found this lone, faint signal — a plasma wave emission, like a single note which changes over time — recorded by Voyager over years. By measuring the change in pitch, it was possible to map out the density of the interstellar medium through which Voyager 1 passed.

They found the density of the interstellar medium around Voyager 1 rose 4000% between 2013 and 2014, reaching current readings in 2015.

“Regardless of what the sun is doing, Voyager is sending back detail. The craft is saying, ‘Here’s the density I’m swimming through right now. And here it is now. And here it is now. And here it is now.’ Voyager is quite distant and will be doing this continuously,” Cornell research scientist Shami Chatterjee describes.

Astronomers hope this discovery will help them learn more about how the interstellar medium interacts with the heliosphere — the protective layer of charged particles at the edge of our family of planets which protects our solar system from galactic cosmic rays.

If, by any strange coincidence, an alien intelligence were to encounter either Voyager in the distant future (in a weird-please-don’t-make-this-sequel twist on Star Trek: The Motion Picture), they would find a message in a bottle. Attached to each of the spacecraft are golden records, featuring the sights and sounds of Earth. This message to the stars was the brainchild of famed astronomer Carl Sagan.

The Voyager spacecraft continue to make advances in science more than 40 years after beginning their marathon missions to interstellar space.

James Maynard is the founder and publisher of The Cosmic Companion. He is a New England native turned desert rat in Tucson, where he lives with his lovely wife, Nicole, and Max the Cat.

D id you like this article? Join us onThe Cosmic Companion Network for our podcast, weekly video series, informative newsletter, news briefings on Amazon Alexa and more!


NASA Voyager 2 Could Be Nearing Interstellar Space

NASA's Voyager 2 probe, currently on a journey toward interstellar space, has detected an increase in cosmic rays that originate outside our solar system.

NASA's Voyager 2 probe, currently on a journey toward interstellar space, has detected an increase in cosmic rays that originate outside our solar system. Launched in 1977, Voyager 2 is a little less than 11 billion miles (about 17.7 billion kilometers) from Earth, or more than 118 times the distance from Earth to the Sun.

Since 2007 the probe has been traveling through the outermost layer of the heliosphere -- the vast bubble around the Sun and the planets dominated by solar material and magnetic fields. Voyager scientists have been watching for the spacecraft to reach the outer boundary of the heliosphere, known as the heliopause. Once Voyager 2 exits the heliosphere, it will become the second human-made object, after Voyager 1, to enter interstellar space.

Since late August, the Cosmic Ray Subsystem instrument on Voyager 2 has measured about a 5 percent increase in the rate of cosmic rays hitting the spacecraft compared to early August. The probe's Low-Energy Charged Particle instrument has detected a similar increase in higher-energy cosmic rays.

Cosmic rays are fast-moving particles that originate outside the solar system. Some of these cosmic rays are blocked by the heliosphere, so mission planners expect that Voyager 2 will measure an increase in the rate of cosmic rays as it approaches and crosses the boundary of the heliosphere.

In May 2012, Voyager 1 experienced an increase in the rate of cosmic rays similar to what Voyager 2 is now detecting. That was about three months before Voyager 1 crossed the heliopause and entered interstellar space.

However, Voyager team members note that the increase in cosmic rays is not a definitive sign that the probe is about to cross the heliopause. Voyager 2 is in a different location in the heliosheath -- the outer region of the heliosphere -- than Voyager 1 had been, and possible differences in these locations means Voyager 2 may experience a different exit timeline than Voyager 1.

The fact that Voyager 2 may be approaching the heliopause six years after Voyager 1 is also relevant, because the heliopause moves inward and outward during the Sun's 11-year activity cycle. Solar activity refers to emissions from the Sun, including solar flares and eruptions of material called coronal mass ejections. During the 11-year solar cycle, the Sun reaches both a maximum and a minimum level of activity.

"We're seeing a change in the environment around Voyager 2, there's no doubt about that," said Voyager Project Scientist Ed Stone, based at Caltech in Pasadena. "We're going to learn a lot in the coming months, but we still don't know when we'll reach the heliopause. We're not there yet -- that's one thing I can say with confidence."

The Voyager spacecraft were built by NASA's Jet Propulsion Laboratory in Pasadena, California, which continues to operate both. JPL is a division of Caltech. The Voyager missions are a part of the NASA Heliophysics System Observatory, managed by the Heliophysics Division of the Science Mission Directorate in Washington.


Voyager 1 Reaches Interstellar Space. But Has It Left the Solar System? Wellllll…

Yesterday, NASA announced with some fanfare that after 36 years in space, the probe Voyager 1 has entered interstellar space.

I have two things to say here, and I want to be careful. First, this is an amazing event, and well worth celebrating. Second, a lot of people are saying Voyager 1 has left the solar system, and that’s not really accurate.

More Bad Astronomy

First things first. What scientists discovered is that in mid-to-late 2012, Voyager entered a new region of space. This all has to do with the solar wind, a stream of subatomic particles blown outward by the Sun. This wind expands outward, and far beyond the orbit of Neptune it encounters the particles that exist between the stars. It pushes those aside, and loses momentum as it does so. At some point, the pressure from the wind is no longer strong enough to expand against the pressure of those external particles, and it slows to a stop. This region is called the heliopause. For years, we’ve known that Voyager is in the fuzzy volume of space where the heliopause lies, but it’s been maddeningly difficult to know if it had punched through.

Diagram showing the positions of Voyager 1 (upper left) and Voyager 2 (middle left). The inner blue region is the expanding solar wind, the lighter blue the interaction of the solar wind and interstellar material. Note that Voyager 1 is outside both regions. Credit: NASA/JPL-Caltech

The Sun then gave us a gift: a coronal mass ejection. These vast explosions of material sweep outward, and one went off in March 2012. After more than a year of travel, this blast reached the heliopause. When it did so, it interacted with the material there, causing it to vibrate. This type of interaction is detectable by Voyager, and when scientists analyzed the data, they realized the density of the material was far higher than expected. This is just what would happen if Voyager had in fact flown through the heliopause.

So. It looks like, after traveling 19 billion kilometers (12 billion miles), one of our spacecraft has entered what can reasonably be considered interstellar space.

But does this mean it has left the solar system? Well, no. That might seem odd, since I just said it’s in interstellar space, but that’s only when you look at the Sun’s influence on the particles out there.

However, there’s more to our solar system’s far-flung suburbs than errant electrons and protons. Even out there, over 120 times farther from the Sun than the Earth’s orbit, there are more substantive objects: huge, frozen chunks of ice that are essentially giant comets. The Sun is surrounded by trillions of these iceballs, a countless swarm of them called the Oort Cloud. They take thousands of years to orbit the Sun even once, but enthralled to its gravity they are.

This makes them bona fide solar system objects, and that’s why we can’t really say Voyager 1 has left the solar system. There’s still more solar system beyond it!

It’s like walking outside the front door of your house and saying you’ve left your property. While you’ve left your house, there’s still the yard all around you. You have a ways to go yet.

I make this point because the claim that Voyager has left the solar system has been made before. Many times. Many, many times. The latest was in March of this year, when some scientists announced they had detected a change in the environment Voyager was in, marking the boundary to interstellar space. That announcement was quickly contradicted by the Voyager team at JPL, including Voyager team leader Ed Stone. Full disclosure and mea culpa: I said at the time that Voyager had left the solar system, but then quickly backed off that claim when the Voyager team chimed in.

However, with these new results, Stone has given his blessing. So while Voyager still has a ways to go (many thousands of years, actually) before it actually leaves what we can think of as our solar system, I think it’s fair to say it’s now in interstellar space.

And this is an astonishing achievement for humanity. It was inevitable we knew this would happen even before Voyager (and its twin Voyager 2) was even launched, in 1977. But still, after all these years, and so much terribly empty space traveled, this point has now been reached. Humanity is now an interstellar species.

I think the words I wrote back in March, premature as they were, finally can ring even more truly today:


Boundary Between The Heliosphere And Interstellar Space Has Been Mapped For The First Time

Part of the heliosphere and the heliopause that surrounds it. The boundaries have been mapped for the first time, although the true extent trailing behind has yet to be confirmed. Image Credit: NASA/IBEX/Adler Planetarium

By Stephen Luntz

The area around the Sun where the solar wind exerts its force is known as the heliosphere, but the name is misleading. We've known for a long time its shape isn't spherical, but it took longer to make it reveal its true form to us. Now, however, the heliosphere's boundary has been mapped for the first time, offering insight into the forces that sculpt our bubble from the outside.

As the solar wind pushes outwards from the Sun it gradually loses strength, eventually becoming unable to overcome even the weak winds of interstellar space. The location where this happens is called the heliopause, and the area inside is known as the heliosphere.

Both Voyager spacecraft have crossed the heliopause, beaming back its location in the directions they left the Solar System. However, sending probes on enough extra-system missions to create a detailed map would be slow and prohibitively expensive. A faster method has been described in the Astrophysical Journal.

"Just as bats send out sonar pulses in every direction and use the return signal to create a mental map of their surroundings, we used the Sun's solar wind, which goes out in all directions, to create a map of the heliosphere," Dr Dan Reisenfeld of Los Alamos National Laboratory said in a statement.

Sonar of course relies on a return signal. In this case, it's hydrogen and oxygen atoms known as energetic neutral atoms (ENAs) produced by collisions between particles in the solar and interstellar winds. As its name suggests, NASA's Interstellar Boundary Explorer (IBEX) satellite was designed with one capacity in mind: to detect ENAS and identify the direction from which they come.

IBEX checks each seven by seven piece of the sky every six months. Variations in Solar activity produce an uneven solar wind, which is in turn reflected in the number of ENAs that IBEX detects. It takes two to six years for a peak to reach the heliopause and the ENAs produced to travel back to IBEX's location in an orbit that dips in and out of Earth's magnetosphere. The longer the delay, the further the heliopause must be in the direction the ENAs are coming from.

The primary reason the heliosphere is not, in fact, spherical is that the Sun is moving through the galaxy, and therefore through the interstellar medium. It's 110–120 Astronomical Units (AU) to the heliopause in the direction the Sun is traveling, and at least 350 AU behind. The trailing distance could be greater, however, since IBEX isn't sensitive enough to detect a more distant heliopause. External influences, such as inconsistencies in the interstellar medium, play a subsidiary role, for example producing a ribbon of high ENAs.

The true shape of the heliosphere has been a matter of discussion in astronomical circles for some time, with many attempts to model it. One paper combined less complete IBEX data with information from the Cassini and New Horizons space probes to propose the heliosphere resembles a “deflated croissant”.

The heliosphere may seem distant, but that doesn't mean it can't affect us. It serves as a bubble in which the Earth, and other planets, are shielded from the high-energy radiation between the stars, like a vastly larger version of our own ionosphere.


A long time coming

“We certainly didn’t know that a spacecraft could live long enough to leave the bubble and enter interstellar space,” said Edward Stone, a project scientist for the Voyager mission at a press conference to announce the findings.

“We had no good quantitative idea of how big this bubble is that the sun creates around it,” he said.

The ‘bubble’ refers to the boundary that the sun creates around it and it’s attendant planets. Solar wind emitted by the sun interacts with wind coming in from interstellar space, creating a heliosphere that stretches beyond the planets’ orbits. The heliosphere also protects Earth and the rest of the solar system from potentially damaging cosmic rays coming in from elsewhere in the galaxy.

Dan Reisenfeld, a research scientist at Los Alamos National Laboratory, who was not involved in the research, says astronomers took bets on when they were going to make it through.

“Voyager’s fame came from its exploration of the planets,” Reisenfeld tells Inverse. “Then it went quiet for years because it’s just traveling through the depths of space beyond the planets.”

Voyager 2’s crossing was particularly exciting because it had a working plasma instrument onboard. Voyager 1’s instrument, unfortunately, was damaged in the 1980’s. The tool is essential in determining the transition from the sun’s hot plasma within the heliosphere to the colder and denser material that exists beyond that boundary.

Because they took place at different locations, and at different points of the sun’s magnetic cycle, the data collected by the two spacecraft are quite different. Voyager 2 revealed a much smoother, thinner heliosphere boundary, with a stronger magnetic field, than did Voyager 1, for example.

The second set of data also gave a better idea of the shape of the heliosphere.

“When Voyager 2 crossed the heliopause, it showed us that our heliosphere is not perfectly round but that it’s asymmetric,” Reisenfeld says.


NASA's Voyager 2 Probe Enters Interstellar Space

For the second time in history, a human-made object has reached the space between the stars.

For the second time in history, a human-made object has reached the space between the stars. NASA's Voyager 2 probe now has exited the heliosphere - the protective bubble of particles and magnetic fields created by the Sun.

Members of NASA's Voyager team will discuss the findings at a news conference at 11 a.m. EST (8 a.m. PST) today at the meeting of the American Geophysical Union (AGU) in Washington. The news conference will stream live on the agency's website.

Comparing data from different instruments aboard the trailblazing spacecraft, mission scientists determined the probe crossed the outer edge of the heliosphere on Nov. 5. This boundary, called the heliopause, is where the tenuous, hot solar wind meets the cold, dense interstellar medium. Its twin, Voyager 1, crossed this boundary in 2012, but Voyager 2 carries a working instrument that will provide first-of-its-kind observations of the nature of this gateway into interstellar space.

Voyager 2 now is slightly more than 11 billion miles (18 billion kilometers) from Earth. Mission operators still can communicate with Voyager 2 as it enters this new phase of its journey, but information - moving at the speed of light - takes about 16.5 hours to travel from the spacecraft to Earth. By comparison, light traveling from the Sun takes about eight minutes to reach Earth.


Artist's concept of Voyager 2 with 9 facts listed around it. Image Credit: NASA
Larger view

The most compelling evidence of Voyager 2's exit from the heliosphere came from its onboard Plasma Science Experiment (PLS), an instrument that stopped working on Voyager 1 in 1980, long before that probe crossed the heliopause. Until recently, the space surrounding Voyager 2 was filled predominantly with plasma flowing out from our Sun. This outflow, called the solar wind, creates a bubble - the heliosphere - that envelopes the planets in our solar system. The PLS uses the electrical current of the plasma to detect the speed, density, temperature, pressure and flux of the solar wind. The PLS aboard Voyager 2 observed a steep decline in the speed of the solar wind particles on Nov. 5. Since that date, the plasma instrument has observed no solar wind flow in the environment around Voyager 2, which makes mission scientists confident the probe has left the heliosphere.


At the end of 2018, the cosmic ray subsystem aboard NASA's Voyager 2 spacecraft provided evidence that Voyager 2 had left the heliosphere. There were steep drops in the rate of heliospheric particles that hit the instrument's radiation detector, and significant increases in the rate of cosmic rays. Image Credit: NASA/JPL-Caltech/GSFC
Larger view

"Working on Voyager makes me feel like an explorer, because everything we're seeing is new," said John Richardson, principal investigator for the PLS instrument and a principal research scientist at the Massachusetts Institute of Technology in Cambridge. "Even though Voyager 1 crossed the heliopause in 2012, it did so at a different place and a different time, and without the PLS data. So we're still seeing things that no one has seen before."

In addition to the plasma data, Voyager's science team members have seen evidence from three other onboard instruments - the cosmic ray subsystem, the low energy charged particle instrument and the magnetometer - that is consistent with the conclusion that Voyager 2 has crossed the heliopause. Voyager's team members are eager to continue to study the data from these other onboard instruments to get a clearer picture of the environment through which Voyager 2 is traveling.

"There is still a lot to learn about the region of interstellar space immediately beyond the heliopause," said Ed Stone, Voyager project scientist based at Caltech in Pasadena, California.

Together, the two Voyagers provide a detailed glimpse of how our heliosphere interacts with the constant interstellar wind flowing from beyond. Their observations complement data from NASA's Interstellar Boundary Explorer (IBEX), a mission that is remotely sensing that boundary. NASA also is preparing an additional mission - the upcoming Interstellar Mapping and Acceleration Probe (IMAP), due to launch in 2024 - to capitalize on the Voyagers' observations.

"Voyager has a very special place for us in our heliophysics fleet," said Nicola Fox, director of the Heliophysics Division at NASA Headquarters. "Our studies start at the Sun and extend out to everything the solar wind touches. To have the Voyagers sending back information about the edge of the Sun's influence gives us an unprecedented glimpse of truly uncharted territory."

While the probes have left the heliosphere, Voyager 1 and Voyager 2 have not yet left the solar system, and won't be leaving anytime soon. The boundary of the solar system is considered to be beyond the outer edge of the Oort Cloud, a collection of small objects that are still under the influence of the Sun's gravity. The width of the Oort Cloud is not known precisely, but it is estimated to begin at about 1,000 astronomical units (AU) from the Sun and to extend to about 100,000 AU. One AU is the distance from the Sun to Earth. It will take about 300 years for Voyager 2 to reach the inner edge of the Oort Cloud and possibly 30,000 years to fly beyond it.

The Voyager probes are powered using heat from the decay of radioactive material, contained in a device called a radioisotope thermal generator (RTG). The power output of the RTGs diminishes by about four watts per year, which means that various parts of the Voyagers, including the cameras on both spacecraft, have been turned off over time to manage power.

"I think we're all happy and relieved that the Voyager probes have both operated long enough to make it past this milestone," said Suzanne Dodd, Voyager project manager at NASA's Jet Propulsion Laboratory (JPL) in Pasadena, California. "This is what we've all been waiting for. Now we're looking forward to what we'll be able to learn from having both probes outside the heliopause."

Voyager 2 launched in 1977, 16 days before Voyager 1, and both have traveled well beyond their original destinations. The spacecraft were built to last five years and conduct close-up studies of Jupiter and Saturn. However, as the mission continued, additional flybys of the two outermost giant planets, Uranus and Neptune, proved possible. As the spacecraft flew across the solar system, remote-control reprogramming was used to endow the Voyagers with greater capabilities than they possessed when they left Earth. Their two-planet mission became a four-planet mission. Their five-year lifespans have stretched to 41 years, making Voyager 2 NASA's longest running mission.

The Voyager story has impacted not only generations of current and future scientists and engineers, but also Earth's culture, including film, art and music. Each spacecraft carries a Golden Record of Earth sounds, pictures and messages. Since the spacecraft could last billions of years, these circular time capsules could one day be the only traces of human civilization.

Voyager's mission controllers communicate with the probes using NASA's Deep Space Network (DSN), a global system for communicating with interplanetary spacecraft. The DSN consists of three clusters of antennas inGoldstone, California Madrid, Spain and Canberra, Australia.

The Voyager Interstellar Mission is a part of NASA's Heliophysics System Observatory, sponsored by the Heliophysics Division of NASA's Science Mission Directorate in Washington. JPL built and operates the twin Voyager spacecraft. NASA's DSN, managed by JPL, is an international network of antennas that supports interplanetary spacecraft missions and radio and radar astronomy observations for the exploration of the solar system and the universe. The network also supports selected Earth-orbiting missions. The Commonwealth Scientific and Industrial Research Organisation, Australia's national science agency, operates both the Canberra Deep Space Communication Complex, part of the DSN, and the Parkes Observatory, which NASA has been using to downlink data from Voyager 2 since Nov. 8.

For more information about the Voyager mission, visit:

More information about NASA's Heliophysics missions is available online at:


Does our heliosphere reach Alpha Centauri?

We don’t know much about this edge of our solar system - this is largely because it takes a very long time to get that far out, and we haven’t sent that many spacecraft out there. That said, Voyager 1 and Voyager 2 were sent out with the hopes of studying the heliopause, and what it means to leave our solar system.

Voyager 1 has recently been in the process of leaving the heliopause, but it turns out that leaving the solar system is not as straightforward as we had guessed! Originally we had thought that Voyager would leave, like escaping from a bubble - quickly. Instead we’ve had about 3 or 4 false alarms, where one of our expected symptoms of leaving has appeared, but not all of them. So if you remember a few “Voyager Has Left The Solar System” headlines, that’s not your memory playing tricks on you - there have been more than one occasion where we’ve though it had, and then worked out that it hadn’t.

In any case, it seems that the heliopause is somewhere around 121 AU from the sun, which works out to 0.0019 light years. (That’s two thousandth’s of a light year.) The nearest star, Alpha Centauri, is over 4 light years away literal orders of magnitude further.

The solar system doesn’t actually end at the heliopause, though. Outside the heliopause is the Oort Cloud, which is a sphere of small-ish lumps of ice surrounding our solar system, and is the source of all of (or most of) our comets. The Oort cloud is huge - it starts somewhere around several thousand AU away from the sun, and continues for a few tens of thousands of AU. It’s possible it extends as far as 3 light years away from our sun. Even that won’t get near Alpha Centauri - there’s another entire light year of space left between them.

Something here unclear? Have your own question? Feel free to ask! Or submit your questions via the sidebar, Facebook, twitter, or Google+.


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SAGAN, CARL
Carl Sagan (1934-1996) was an American astronomer who discovered that the surface of Venus was extraordinarily hot and noxious (contrary to previous models of a mild Venusian surface). Sagan also showed that the universe has many organic (carbon-based) chemicals and that life is likely to exist throughout the cosmos. He was a great popularizer of astronomy, was involved in many NASA flights and SETI, and also pioneered the field of exobiology.

SANDAGE, ALLAN R.
Allan Rex Sandage (1926-) is an astronomer who, in the 1950's, measured the rate of the expansion of the Universe, Hubble's constant (H), which he calculated to be 50 km/sec/mpc. From this, Sandage estimated of the age of the Universe (T) to be 19.2 billion years [T = 2/3 x (1/H) ]. These calculations have changed through the years and now, H=


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