Interstellar studies toy with our expectations. Those of us who think about sending probes to other stars share the frustration of the long time-scales involved, not just in transit times but also in arriving at the technologies to make such missions happen. But the other half of interstellar studies, the observation and characterization of targets, is happening at a remarkable rate, with new instruments coming online and an entire class of extremely large telescopes in the pipeline. Exoplanet studies thrive. In between, upcoming events are encouraging. Having identified two interstellar objects – 1I/ʻOumuamua and comet 2I/Borisov – in our own Solar System, we will shortly be able to expand the number of such confirmed interlopers enormously. That puts us in position to build intercept missions to study and sample material from another stellar system in relatively short order. The Legacy Survey of Space and Time (LSST), being planned for the now under construction Vera C. Rubin...

Although I've written on a number of occasions about the project called Interstellar Probe, the effort to create what we might call a next-generation Voyager equipped to study space beyond the heliosphere, it's always been in terms of looking back toward the Solar System. What is the shape of the heliosphere once we see it from outside, and how does it interact with the local interstellar medium? The Voyagers have given us priceless clues, but they were never designed for this environment and in any case will soon exhaust their energies. Pontus Brandt (JHU/APL), who is project scientist for the Interstellar Probe effort, takes us beyond these heliosphere-centric ideas as he talks to Richard Stone in a fine article about the mission called The Long Shot that ran recently in Science. Because when you launch something moving faster than Solar System escape velocity, you just keep going, and while 1000 AU is often cited as a target for this mission, it's really only a milestone marker...

Between the Solar System and interstellar space is a boundary layer called the heliosheath. Or maybe I should define this boundary as being between the inner, planetary part of the Solar System and interstellar space. After all, we consider the Oort Cloud as part of our own system, yet it begins much further out. Both Voyagers have crossed the region where the Sun's heliosphere ends and interstellar space begins, while they won't reach the Oort, by some estimates, for another 300 years. The broader region is called the heliopause, a place where the outflowing solar wind of protons, electrons and alpha particles (two protons and two neutrons tightly bound) encounters what we can call the interstellar wind, itself pushing up against the heliosphere and confining the solar wind-dominated region to a bubble. We now learn that this boundary region has been mapped, showing interactions at the interface. A paper describing this feat has now appeared, with Dan Reisenfeld (Los Alamos National...

What are the long-lasting waves detected by Voyager 1? Our first working interstellar probe -- admittedly never designed for that task -- is operating beyond the heliosphere, which it exited back in 2012. A paper just published in Nature Astronomy explores what's going in interstellar space just beyond, but still affected by, the heliosphere's passage through the Local Interstellar Medium (LISM). We have a lot to learn out here, for even as we exit the heliosphere, the picture is complex. The so-called Local Bubble is a low-density region of hot plasma in the interstellar medium, the environment of radiation and matter -- gas and dust -- that exists between the stars. Within this 'bubble' exists the Local Interstellar Cloud (LIC), about 30 light years across, with a slightly higher hydrogen density flowing from the direction of Scorpius and Centaurus. The Sun seems to be within the LIC near its boundary with the G-cloud complex, where the Alpha Centauri stars reside. Image: Map of...

Studies of interstellar interloper ‘Oumuamua move at lightning pace, to judge from a recent exchange on hydrogen ice. A study by Greg Laughlin and Darryl Seligman (both at Yale) just published in June, has now met a response from Thiem Hoang (Korea University of Science and Technology, Daejeon) and Harvard’s Avi Loeb. The issue is significant because if, as Laughlin and Seligman argued, ‘Oumuamua were made of hydrogen ice, then the outgassing that drove its slight acceleration would not have been detectable. At least one mystery solved. Or was it? One reason the 0.2km radius object didn’t fit the description of a comet was that there was no explanation for its tiny change in velocity. Hoang and Loeb have examined the hydrogen ice concept and found it wanting. Says Hoang: "The proposal by Seligman and Laughlin appeared promising because it might explain the extreme elongated shape of ‘Oumuamua as well as the non-gravitational acceleration. However, their theory is based on an...

Memories play tricks on us all, but trying to recall where I saw a particular image of a laser lightsail is driving me to distraction. The image showed a huge sail at the end of its journey, docked to some sort of space platform, and what defined it were the tears and holes in the giant, shredded structure. It presupposed long passage through an interstellar medium packed with hazards, and although I assumed I would have seen it on the cover of some science fiction magazine, I spent an hour yesterday scanning covers on Phil Stephensen-Payne’s wonderful Galactic Central site, but all to no avail. The image must have run inside a magazine, then, but if so, I’m at a loss to identify it other than to say it would have appeared about twenty years ago. I had hoped to reproduce it this morning because our talk about starship shielding necessarily brought up the question of whether an enormous lightsail -- some of these are conceived as being hundreds of kilometers in diameter -- wouldn’t be...

Interesting new ideas about asteroid deflection are coming out of the University of Strathclyde (Glasgow), involving the use of lasers in coordinated satellite swarms to change an asteroid's trajectory. This is useful work in its own right, but I also want to mention it in terms of a broader topic we often return to: How to deal with the harmful effects of dust and interstellar gas on a fast-moving starship. That's a discussion that has played out many a time over the past eight years in these pages, but it's as lively a topic as ever, and one on which we're going to need a lot more information before true interstellar missions can take place. Lasers and the Asteroid But let's set the stage at Strathclyde for a moment. The idea here is to send small satellites capable of formation flying with the asteroid, all of them firing their lasers at close range. The university's Massimiliano Vasile, who is leading this work, says that the challenge of lasers in space is to combine high power,...

We've been looking at slowing down a starship, pondering ways the interstellar medium itself might be of use, and seeing how the stellar wind produced by the destination star could slow a magsail. A large solar sail could use stellar photons, but the advantage of the magsail is that it's going to be effective at a greater distance, and we can also consider other trajectory-bending effects like the Lorentz turning studied by Robert Forward and P.C. Norem. But if you take a look at the relevant papers on magsails and other uses of the medium, you'll find that they all assume the interstellar medium is more or less uniform. We know, of course, that it is not. For one thing, the Sun itself seems to be near the boundary of the Local Interstellar Cloud, and there are a number of such clouds within about 5 parsecs of the Solar System. In fact, we're not exactly sure whether the Sun is just outside the LIC or barely within it. In any case, as Ian Crawford has pointed out, Centauri A and B...

This morning I want to pick up on the 'problem of arrival' theme I began writing about on Friday, and we'll look at interstellar deceleration issues a good bit this week. But I can't let Monday start without reference to the Icarus results from Gran Sasso that finds neutrinos traveling at precisely the speed of light. All of this adds credence to the growing belief that the earlier Opera experiment was compromised by equipment problems. The news is all over the place (you might begin with this BBC account) and while we'll keep an eye on it, I don't plan to spend much time this week on neutrinos. We still have much to get done on the subject of slowing down. Magsails and Local Resources When you begin to unlock the deceleration issue, the options quickly multiply, and you find yourself looking into areas that weren't remotely the subject of your earlier research. As we saw on Friday, the concept of magnetic sails grew organically out of Robert Bussard's idea of an interstellar ramjet....

The beauty of having spacecraft that far outlive their expected lives is that they can corroborate and supplement data coming in from much newer missions. That's the case with our Voyager spacecraft as they continue their progress at system's edge. The Voyagers will be moving outside the heliopause in not so many years, and when they do, they will tell us much about the behavior of charged particles in the interstellar medium. This will bulk up incoming results from IBEX, the Interstellar Boundary Explorer spacecraft, as it studies the neutral particles that routinely penetrate the heliosphere. Our knowledge of true interstellar space is growing. It's at the heliopause that we see the boundary between the area defined by the solar wind flowing outward from the Sun and the interstellar medium that surrounds it. Racing outward at an average of 440 kilometers per second, the solar wind is pushing into a region of dust and ionized gas, inflating the bubble we know as the heliosphere. The...

When Voyager 2 was passing Neptune back in 1989, I stuck a video tape in the VCR and recorded the coverage -- two video tapes, actually, because I wasn't sure how much coverage there was going to be, and I didn't want to miss anything. That meant getting up in the middle of the night to change tapes, but I figured the loss of sleep was worth it. Going back to those tapes today, I'm still struck by the same sense of awe that both the Voyagers were simply going to continue, that although the media spoke as if their journeys were over after their encounters at Titan and Neptune respectively, they still had years of power left and would continue talking to us deep into the 21st Century. Image: Voyager 1 looks back to capture six planetary portraits. These six narrow-angle color images were made from the first ever "portrait" of the solar system taken by Voyager 1, which was more than 4 billion miles from Earth and about 32 degrees above the ecliptic. The spacecraft acquired a total of 60...

The recent debate between Jean Schneider (Paris Observatory) and Ian Crawford (University of London) is the sort of dialogue I'd like to see more of in public forums. When I began researching Centauri Dreams (the book) back in 2002, I was deeply surprised by the sheer energy flowing into interstellar flight research. True, it lacked focus and tended to be done by researchers in their spare time, as opposed to being funded by universities or government agencies, but I had not realized that the topic itself was under such serious investigation by so many scientists. All those fascinating concepts, from laser sails to fusion runways, were the catalyst for this site, where keeping an eye on the ongoing discussion is the order of the day. In an era of short-term thinking and instant gratification through one gadget or another, taking a longer look at the human enterprise and where it is going is an imperative. One way to do that is to consider whether our species has a future in deep...

We often think about interstellar probes only in the context of what they find at the end of their journeys -- astrobiologically interesting planets seem to be the whole story. But not so fast. As Ian Crawford (University of London) notes in a recent paper, there are quite a few fascinating -- and indeed critical -- things we need to learn about interstellar space itself, in this case what is known as the Local Interstellar Medium (LISM). Crawford, who has been analyzing these matters for the Project Icarus team, notes how much we've learned about the LISM since the Daedalus days. The new paper grows out of Crawford's presentation at the British Interplanetary Society symposium 'Project Daedalus - Three Decades On,' which was held last September in London. It reflects his thinking on interstellar probes in relation to planetary and stellar studies and astrobiology as well as the nature of the medium through which the probe will fly. But today I want to focus on the LISM because what...

When the Project Daedalus team went to work to design a starship back in the 1970s, they contemplated using the atmosphere of Jupiter as their source for helium-3, an isotope needed in vast quantity for Daedalus' fusion engines. More recently, though, attention has turned to the lunar surface as a possible source. Now the IBEX spacecraft, normally charged with studying the interactions between the heliosphere and what lies beyond, has been used to examine a useful recycling process as particles hit the Moon, pushed there by the Sun's 450 kilometer per second solar wind. A Glow of Energetic Neutral Atoms The process is straightforward -- lacking a magnetosphere, the Moon takes the full force of the solar wind, absorbing most of its particles into lunar dust. But the IBEX team, led by David McComas (Southwest Research Institute), has been able to show that about ten percent of the solar wind particles escape back to space in the form of energetic neutral atoms, or ENA's, detectable by...

I'm always sorry when a good conference like the Royal Astronomical Society's 2010 gathering ends, even if I'm attending it 'virtually' from the other side of an ocean. But virtuality has its advantages, as I'm reminded by several conference attendees who have struggled with Icelandic volcano ash when trying to book flights out of the UK. If I were with them in Glasgow, I'd praise my good fortune for extra time in Scotland and immediately take the train for Inverness, then on to Skye and the Inner Hebrides, where I've spent many good days and intend to spend many more. Volcanic ash or no, it was a lively conference with tantalizing results on planetary system residues in white dwarfs and retrograde exoplanet orbits, and a number of other issues that can be found in the conference program. I'll close our RAS coverage here with two items that deal with interstellar dust rather than the Earth-based dust and ash that closes airports. Red giants, the kind of star our Sun will eventually...

We've long known that the spaces between the stars are not empty, but are pervaded by a highly dilute mix of gas and dust. Now we're getting maps that show the presence of large cavities in this interstellar medium, created by supernova events as well as outflowing solar winds from clusters of hot, young stars. The Sun resides in the so-called Local Cavity, a low-density area of neutral gas that is about 80 parsecs in radius. The Local Cavity is, in turn, surrounded by a 'wall' of dense, neutral gas, with gaps in the wall -- 'interstellar tunnels' -- that are low-density pathways to surrounding cavities. We study the interstellar medium by looking at the light produced by stars and using absorption line spectroscopy to see how that light is affected by gases between us and the stars in question. Johannes Hartmann's classic study of the spectrum of Delta Orionis in 1904 was a huge advance, looking at absorption from the 'K' line of calcium and concluding that the gas was not present...

Last July at the Aosta conference Greg Matloff presented a paper on using near-Earth objects for transportation. It's an interesting concept (discussed here), one that takes advantage of the fact that there are a few such objects that pass close by the Earth and then go on to cross the orbit of Mars. Greg was able to show that it would be possible to exploit this trajectory to use the NEO as what Buzz Aldrin has called an 'orbital cycler,' hitching a ride at least one way and disembarking upon arrival. Reducing Starship Mass The idea is useful because space travel requires so much energy. Put all this in the interstellar context, as science fiction writer Karl Schroeder does in this interesting essay, and you realize that whether we're talking about beamed sails or antimatter or nuclear fusion, most of the mass of the vehicle is involved with accelerating and decelerating it. Schroeder pondered the question of using the cycler idea on an interstellar level. All you decelerate at...

We always cite the Mars rovers as examples of missions that perform far beyond their expected lifetimes, but the two Voyager spacecraft are reminding us once again that we have instrumentation at the edge of the Solar System that is still functioning after all these years. Both Voyagers are now in the heliosheath, the outermost layer of the magnetic bubble we call the heliosphere. With Voyager 1 crossing into the heliosheath in late 2004 and Voyager 2 in the summer of 2007, we get an estimate of the size of the heliosphere, a useful finding because it tells us something about what lies beyond. What's out there has been known for some time. Indeed, the interstellar medium (ISM) houses some ten percent of the visible matter in the Milky Way, mostly in the form of hydrogen gas. The ISM is patchy, enough so that astronomers have been able to isolate a Local Interstellar Cloud through which our Solar System is moving, a cloud flowing outward from the Scorpius-Centaurus Association, a...

One problem with journeys that are beyond today's technologies is that we forget, in our zeal to get a payload to the target, how little we know about the regions we'll pass through along the way. It's amazing how little we know, for example, about the heliosphere around the Solar System, yet any probe pushing into interstellar space will have to cross from the region of space under the Sun's influence into a zone where the interstellar medium flows around this 'bubble,' disturbing the solar wind and creating a secondary bubble, the heliosheath. We don't yet have a global view of what spacecraft will encounter in the heliosheath as the solar wind is heated and slowed by these interactions. Only recently have we gotten the Voyagers into these regions, and in any case these doughty vehicles can only produce single-point measurements. But we've got the IBEX (Interstellar Boundary Explorer) spacecraft making observations from near Earth, and now we learn that Cassini, our intrepid Saturn...