A future interstellar probe mission aims to travel beyond the heliosphere to the local interstellar medium to understand where our home came from and where it is going. Credit: John Hopkins Applied Physics Laboratory.
The edge of the Solar System is defined by the heliosphere and its heliopause. The heliopause marks the region where the interstellar medium stops the outgoing solar wind. But only two spacecraft, Voyager 1 and Voyager 2, have ever travelled to the heliopause. As a result, scientists are uncertain about the heliopause’s extent and its other properties.
Some scientists are keen to learn more about this region and are developing a mission concept to explore it.
Artist's rendition of the upcoming NASA Solar Cruiser mission due to launch in February 2025, an example of the type of solar sail being developed for this most recent study. (Credit: NASA)
A recent study submitted to Acta Astronautica explores the potential for using aerographite solar sails for traveling to Mars and interstellar space, which could dramatically reduce both the time and fuel required for such missions. This study comes while ongoing research into the use of solar sails is being conducted by a plethora of organizations along with the successful LightSail2 mission by The Planetary Society, and holds the potential to develop faster and more efficient propulsion systems for long-term space missions.
An updated model suggests the shape of the Sun’s bubble of influence, the heliosphere (seen in yellow), may be a deflated croissant shape, rather than the long-tailed comet shape suggested by other research.
Credits: Opher, et al
At first glance, it looks like something from an alien autopsy. A strange organ cut from a xenomorph’s thorax, under the flickering lights of an operating room in a top secret government facility, with venous tendrils dangling down to the floor, dripping viscous slime. (X-Com anyone?)
An artist concept depicting one of NASA's twin Voyager spacecraft, humanity's farthest and longest-lived spacecraft.
Voyager 2 just lost contact with Earth while Voyager 1 is still reporting back. Credit: NASA/JPL-Caltech
Only two of humanity’s spacecraft have left the Solar System: NASA’s Voyager 1 and Voyager 2. Voyager 1 left the heliosphere behind in 2012, while Voyager 2 did the same on Nov. 5th, 2018. Now Voyager 2 has been in interstellar space for one year, and five new papers are presenting the scientific results from that one year.
Earth's Greatest Hits: the Golden Record attached to the Voyager 1 and 2 spacecraft. Credit: NASA/JPL.
Forty years ago, the Voyager 1 and 2 missions began their journey from Earth to become the farthest-reaching missions in history. In the course of their missions, the two probes spent the next two decades sailing past the gas giants of Jupiter and Saturn. And while Voyager 1 then ventured into the outer Solar System, Voyager 2 swung by Uranus and Neptune, becoming the first and only probe in history to explore these worlds.
This summer, the probes will be marking the fortieth anniversary of their launch – on September 5th and August 20th, respectively. Despite having traveled for so long and reaching such considerable distances from Earth, the probes are still in contact with NASA and sending back valuable data. So in addition to being the most distant missions from Earth, they are the longest-running mission in history.
In addition to their distance and longevity, the Voyager spacecraft have also set numerous other records for robotic space missions. For example, in 2012, the Voyager 1 probe became the first and only spacecraft to have entered interstellar space. Voyage 2, meanwhile, is the only probe that has explored all four of the Solar System’s gas/ice giants – Jupiter, Saturn, Uranus and Neptune.
The launch of the Voyager 2 probe, which took place on August 20th, 1977. Credit: NASA
Their discoveries also include the first active volcanoes beyond Earth – on Jupiter’s moon Io – the first evidence of a possible subsurface ocean on Europa, the dense atmosphere around Titan (the only body beyond Earth with a dense, nitrogen-rich atmosphere), the craggy surface of Uranus’ “Frankenstein Moon” Miranda, and the ice plume geysers of Neptune’s largest moon, Triton.
These accomplishments have had immeasurable benefits for planetary science, astronomy and space exploration. They’ve also paved the way for future missions, such as the Galileo and Juno probes, the Cassini-Huygens mission, and the New Horizons spacecraft. As Thomas Zurbuchen, the associate administrator for NASA’s Science Mission Directorate (SMD), said in a recent press statement:
“I believe that few missions can ever match the achievements of the Voyager spacecraft during their four decades of exploration. They have educated us to the unknown wonders of the universe and truly inspired humanity to continue to explore our solar system and beyond.”
But what is perhaps most memorable about the Voyager missions is the special cargo they carry. Each spacecraft carries what is known as the Golden Record, a collection of sounds, pictures and messages that tell of Earth, human history and culture. These records were intended to serve as a sort of time capsule and/or message to any civilizations that retrieved them, should they ever be recovered.
Each of the two Voyager spacecraft launched in 1977 carry a 12-inch gold-plated phonograph record with images and sounds from Earth. Credit: NASA
As noted, both ships are still in contact with NASA and sending back mission data. The Voyager 1 probe, as of the writing of this article, is about 20.9 billion km (13 billion mi; 140 AU) from Earth. As it travels northward out of the plane of the planets and into interstellar space, the probe continues to send back information about cosmic rays – which are about four times as abundant in interstellar space than around Earth.
From this, researchers have learned that the heliosphere – the region that contains the Solar System’s planets and solar wind – acts as a sort of radiation shield. Much in the say that Earth’s magnetic field protects us from solar wind (which would otherwise strip away our atmosphere), the heliopause protects the Solar planets from atomic nuclei that travel at close to the speed of light.
Voyager 2, meanwhile, is currently about 17.7 billion km (11 billion mi; 114.3 AU) from Earth. It is traveling south out of the plane of the planets, and is expected to enter interstellar space in a few years. And much like Voyager 1, it is also studying how the heliosphere interacts with the surroundings interstellar medium, using a suite of instruments that measure charged particles, magnetic fields, radio waves and solar wind plasma.
Once Voyager 2 crosses into interstellar space, both probes will be able to sample the medium from two different locations simultaneously. This is expected to tell us much about the magnetic environment that encapsulates our system, and will perhaps teach us more about the history and formation of the Solar System. On top of that, it will let us know what kinds of hazards a possible interstellar mission will have to contend with.
Illustration showing how NASA’s Hubble Space Telescope is looking along the paths of NASA’s Voyager 1 and 2 spacecraft as they journey through the solar system and into interstellar space. Credit: NASA/ESA/Z. Levy (STScI)
The fact that the two probes are still active after all this time is nothing short of amazing. As Edward Stone – the David Morrisroe Professor of Physics at Caltech, the former VP and Director of NASA’s Jet Propulsion Laboratory, and the Voyager project scientist – said:
“None of us knew, when we launched 40 years ago, that anything would still be working, and continuing on this pioneering journey. The most exciting thing they find in the next five years is likely to be something that we didn’t know was out there to be discovered.”
Keeping the probes going has also been a challenge since the amount of power they generate decreases at a rate of about four watts per year. This has required that engineers learn how to operate the twin spacecraft with ever-decreasing amounts of power, which has forced them to consult documents that are decades old in order to understand the probes’ software and command functions.
Luckily, it has also given former NASA engineers who worked on the Voyager probes the opportunity to offer their experience and expertise. At present, the team that is operating the spacecraft estimate that the probes will run out of power by 2030. However, they will continue to drift along their trajectories long after they do so, traveling at a speed of 48,280 km per hour (30,000 mph) and covering a single AU every 126 days.
The Voyager 1 spacecraft has started to transverse what JPL has dubbed as a “cosmic purgatory” between our solar system – and interstellar space. Credit: NASA/JPL
At this rate, they will be within spitting distance of the nearest star in about 40,000 years, and will have completed an orbit of the Milky Way within 225 million years. So its entirely possible that someday, the Golden Records will find their way to a species capable of understanding what they represent. Then again, they might find their way back to Earth someday, informing our distant, distant relatives about life in the 20th century.
And if the craft avoid any catastrophic collisions and can survive in the interstellar medium of space, it is likely that they will continue to be emissaries for humanity long after humanity is dead. It’s good to leave something behind!
Artist's concept of Antimatter propulsion system. Credit: NASA/MFSC
When it comes to the future of space exploration, one of the biggest questions is, “how and when will we travel to the nearest star?” And while space agencies have been pondering this question and coming up with proposals for decades, none of them have advanced beyond the theory stage. For the most part, their efforts has been focused on possible missions to Mars and the outer Solar System.
But there are some people, like Dr. Gerald Jackson, who are working towards making an interstellar mission possible in the near future. He and his research team, which have been funded by NASA in the past, are looking to create an antimatter engine that will be capable of reaching (or exceeding) 5% the speed of light. Towards this end, they have launched a Kickstarter campaign to fund their efforts.
As advanced propulsion concepts go, antimatter has quite a lot going for it. As propulsion goes, it has the highest specific energy of any known method, 100 times more than fission/fusion reactions, and 10 billion times more than chemical propellants. It is also the most fuel-efficient, requiring mere milligrams of antimatter to produce the same amount of energy as tons of chemical fuel.
Typically, this theoretical concept relies on the collision between hydrogen and antihydrogen (which have the same mass but opposite charge) to generate thrust. This process unleashes energy and a shower of particles (pions and muons), which can be channeled by a magnetic nozzle to generate thrust.
And while laboratories like CERN have been producing antimatter, and research is being conducted on large-scale storage, no propulsion systems exist that could turn antimatter into thrust. Dr. Jackson, a graduate of Cornell University, is hoping to change that. Before entering the private sector, Jackson worked as an accelerator physicist at the Fermi National Accelerator Laboratory for 14 years.
In 2002, he co-founded a limited-liability company (HBar Technologies) for the sake of developing commercial markets for antimatter. In 2002, NASA’s Institute for Advanced Concepts (NIAC) awarded Dr. Jackson and his company $75,000 to develop a mission concept that could traverse 250 AUs of space within 10 years time, and with a fuel supply of 10 kg.
These specifications essentially called for the creation of an antimatter rocket that could travel as far as the heliopause within a decade’s time. The result was a propulsion concept that relied on a beam that would fire focused antiprotons onto a sail to generate propulsion. This sail would measure 5 meters in diameter and be composed of a carbon backing on one side and uranium foil on the other (measuring 15 and 296 microns thick, respectively).
Illustration of the solar system and its nearby galactic neighborhood on a logarithmic scale extending (from < 1 to) 1 million AU. Credit: NASA/JPL
When a pulse of antiprotons is annihilated against a small section of the uranium side, the resulting fission causes momentum. As Dr. Jackson explained to Universe Today via email:
“Note that antiprotons have a negative electrical charge, similar to an electron. When the antiprotons enter the sail, they displace an electron orbiting an uranium nucleus. Because antiprotons and electrons do not share any quantum numbers, the antiproton immediately cascades down into the atomic ground state, causing a high probability of interaction between the antiproton and either a proton or neutron within the nucleus.
“On average, a fission event results in the creation of two daughter nuclei of roughly equal mass. These daughters travel in opposite directions with a kinetic energy of 1 MeV per proton or neutron. Because the daughters are charged, the one travelling further into the sail is absorbed and transfers is forward momentum. The other daughter flies into space with an exhaust velocity of 4.6% of lightspeed. This selective transfer of momentum is thrust.”
Unfortunately, due to the budget environment of the time, the NIAC was forced to cancel its funding after a second round had been granted. Because of this, Dr. Jackson and his colleagues are now seeking public support so that they may finish their work on the experimental sail and prepare it for exposure to an antiproton beam.
Diagram showing Hbar’s concept for a antimatter-driven propulsion system. Credit: antimatterdrive.org
Much like Project Starshot (whom they acknowledge on their campaign page), Jackson and his team are looking to produce an interstellar mission proposal that does not involve shortcuts (i.e. warp drive, wormholes, star gates, etc.). Starshot, as you may recall, calls for a wafer craft and a laser-driven lightsail that would be capable of reaching speeds of up to 20% the speed of light, thus making the journey to Alpha Centauri in 20 years.
In the same vein, a antiproton-driven sail that could reach speeds of 5% the speed of light or more would be capable of making it to Alpha Centauri (or Proxima Centauri) in about 90 years time. All the while, the science behind it would remain within the realm of established physics, being consistent with Newton’s Laws of Motion and Einstein’s Theory of Special Relativity.
“The revolutionary aspect of the antimatter-driven sail is that the antimatter is not the fuel, but rather the spark plug that initiates fission reactions,” said Jackson. “Because the fission reactions can produce thrust without heavy shielding or other structures, the mass of the propulsion system can be comparable to the mass of the instrument package.”
Project Starshot, an initiative sponsored by the Breakthrough Foundation, is another concept for making humanity’s first interstellar voyage. Credit: breakthroughinitiatives.org
To see their project through, Jackson and his colleagues are hoping to raise $200,000. Should they prove successful, they hope to mount follow-up campaigns to finance a series of validation experiments, storage demonstrations, and mission details. In the end, their goal is nothing less than making antimatter propulsion a reality, which they hope will one day lead interstellar mission.
“We expect that these campaigns will provide the data needed to convince people to fund full scale antimatter production and an actual mission to a nearby solar system,” Jackson added. “The goal of those early interstellar missions is to provide information about these other solar systems, such as whether they are habitable or inhabited. If the latter, we will want to study or interact with those life forms in follow-on missions. If habitable and not inhabited, we need sufficient information to assure the success of a manned migratory mission.”
As of the penning of this article, Jackson and his colleagues have raised $672 of their $200,000 goal. However, the campaign launched only a few days ago and will remain open for another 25 days. For those interesting in following their progress, or have an interest in donating to their cause, check out the links below.
After almost 35 years traveling at over 35,000 mph, the venerable (and still operational!) Voyager 1 spacecraft is truly breaking through to the other side, crossing the outermost boundaries of our solar system into interstellar space — over 11 billion miles from home.
Data received from Voyager 1 — a trip that currently takes the information 16 hours and 38 minutes to make — reveal steadily increasing levels of cosmic radiation, indicating that the spacecraft is leaving the relatively protected bubble of the Sun’s influence and venturing into the wild and wooly space beyond.
“The laws of physics say that someday Voyager will become the first human-made object to enter interstellar space, but we still do not know exactly when that someday will be,” said Ed Stone, Voyager project scientist at the California Institute of Technology in Pasadena. “The latest data indicate that we are clearly in a new region where things are changing more quickly. It is very exciting. We are approaching the solar system’s frontier.”
The data making the 16-hour-38 minute, 11.1-billion-mile (17.8-billion-kilometer), journey from Voyager 1 to antennas of NASA’s Deep Space Network on Earth detail the number of charged particles measured by the two High Energy telescopes aboard the 34-year-old spacecraft. These energetic particles were generated when stars in our cosmic neighborhood went supernova.
“From January 2009 to January 2012, there had been a gradual increase of about 25 percent in the amount of galactic cosmic rays Voyager was encountering,” said Stone. “More recently, we have seen very rapid escalation in that part of the energy spectrum. Beginning on May 7, the cosmic ray hits have increased five percent in a week and nine percent in a month.”
This marked increase is one of a triad of data sets which need to make significant swings of the needle to indicate a new era in space exploration. The second important measure from the spacecraft’s two telescopes is the intensity of energetic particles generated inside the heliosphere, the bubble of charged particles the sun blows around itself. While there has been a slow decline in the measurements of these energetic particles, they have not dropped off precipitously, which could be expected when Voyager breaks through the solar boundary.
“When the Voyagers launched in 1977, the space age was all of 20 years old. Many of us on the team dreamed of reaching interstellar space, but we really had no way of knowing how long a journey it would be — or if these two vehicles that we invested so much time and energy in would operate long enough to reach it.”
Addition: Check out the accompanying video from Science@NASA below:
Top image: Artist’s concept showing NASA’s two Voyager spacecraft exploring a turbulent region of space known as the heliosheath, the outer shell of the bubble of charged particles around our sun. Credit: NASA/JPL-Caltech. Secondary image: Artist’s concept of NASA’s Voyager spacecraft. Credit: NASA/JPL-Caltech.
Artist's interpretation depicting the new view of the heliosphere. The heliosheath is filled with “magnetic bubbles” (shown in the red pattern) that fill out the region ahead of the heliopause. In this new view, the heliopause is not a continuous shield that separates the solar domain from the interstellar medium, but a porous membrane with fingers and indentations. Credit: NASA/Goddard Space Flight Center/CI Lab
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The barrier at the edge of our Solar System may not be the smooth shield that scientists once thought. The venerable Voyager spacecraft have detected a huge, turbulent sea of magnetic bubbles in the heliosheath — the interface between the heliosphere and interstellar space — similar to an actively bubbling Jacuzzi tub. At a briefing today, scientists said the finding is significant as “we now will have to change our view of how the Sun interacts with the Solar System,” said Arik Posner, Voyager program scientist at NASA Headquarters. But it also means that the “force field” that surrounds the entire Solar System may be letting in more harmful cosmic rays and energetic particles than previously thought.
Over 30 years into their mission, the Voyagers are still monitoring their environment and sending back data. In 2007, scientists noticed that Voyager 1 recorded dramatic dips and rises in the amount of electrons it encountered as it traveled through the heliosphere, the barrier that surrounds the entire Solar System and is created by the Sun’s magnetic field. Voyager 2 made similar observations of these charged particles in 2008.
Computer simulation of the magnetic reconnection in the heliosheath, which look like bubbles, or sausages. Credit: NASA/J.F. Drake, M. Swisdak, M. Opher
Using a new computer model to analyze the data, scientists found the Sun’s distant magnetic field is likely made up of bubbles approximately 100 million miles (160 million kilometers) wide — “like long sausages,” said Merav Opher at the briefing, an astronomer at Boston University who is the lead author of a paper published in the Astrophysical Journal.
And the bubbles are moving around, with oscillations of plus or minus 10 to 20 km. “It is very bubbly as far as we can tell,” Jim Drake from the University of Maryland said at the press conference. “The entire thing is bubbly, like where the jets come out from a Jacuzzi.”
Opher said the bubbles, while not visible from Earth, cover a large portion of the sky at about 38 degrees latitude and as the solar winds “bumps” up against the heliopause, the bubbles fill up the entire region next to the heliopause.
Like Earth, our Sun has a magnetic field with a north pole and a south pole. The field lines are stretched outward, and as the sun rotates, the solar wind twists them into a spiral as they are carried outward.
The bubbles are created when magnetic field lines reorganize. The new model suggests the field lines are broken up into self-contained structures disconnected from the solar magnetic field.
These magnetic bubbles should act as electron traps, so the spacecraft would experience higher than normal electron bombardment as they traveled through the bubbles.
But the implications of this new finding, said Opher, is also that the heliosheath is very different from what scientists expected. She prefaced by saying that any earlier ideas about the region was only conjecture since no spacecraft has been there before. “We thought heliopause would be a smooth surface and shield us from intergalactic cosmic rays,” she said. “It is not a shield but more like a membrane that is a sea of bubbles.”
One argument would say the bubbles would seem to be a very porous shield, allowing lots of cosmic rays through the gaps. But another view would be that cosmic rays could get trapped inside the bubbles, making the bubbling froth a very good shield indeed.
However, the scientists are still working on figuring out exactly what these bubbles are. The Voyagers’ instruments, while still working fine, are being tested in this new region of space. “The magnetic instruments on Voyager were designed to measure magnetic fields, but they are right at very edge of what the instruments are capable of sensing,” said Drake. “The magnetic field is very weak. While trying to find out what these magnetic bubbles are, we haven’t reached that moment where we say, ‘yes, that is it.’ We’d like to be able to pin it down much better.”
This video from NASA’s Goddard Spaceflight Center helps to visually explain the new findings:
You can follow Universe Today senior editor Nancy Atkinson on Twitter: @Nancy_A. Follow Universe Today for the latest space and astronomy news on Twitter @universetoday and on Facebook.
