Gregory Matloff’s contributions to interstellar studies need scant introduction, given their significance to solar-and beamed sail development for decades, and their visibility through books like The Starflight Handbook (1989) and Deep Space Probes (2005). A quick check of the bibliography online will demonstrate just how active Greg continues to be in analyzing the human future in space, as well as his newfound interest in the nature of consciousness (Star Light, Star Bright, 2016). The paper that follows grows out of Greg’s presentation at the 2016 iteration of the Tennessee Valley Interstellar Workshop, where he discussed ways to advance deep space exploration using near term technologies like Falcon Heavy, in conjunction with the solar sail capabilities he has so long championed. Read on for an examination of human factors beyond lunar orbit and a description of a useful near-term mission that could reach an object much closer than Mars relying on both chemical and sail...
A Prehistoric Close Pass
Given the vast distances of interstellar space, you wouldn’t think there would be much chance of stars colliding. But it’s conceivable that so-called ‘blue straggler’ stars are the remnants of just such an event. A large blue straggler contains far more hydrogen than smaller stars around it, and burns at higher temperatures, with a correspondingly shorter life. When you find a blue straggler inside an ancient globular cluster, it’s natural to ask: How did this star emerge? Packing stars as tightly as globular clusters must produce the occasional collision, and in fact astrophysicist Michael Shara (then at the American Museum of Natural History) has estimated there may be as many as several hundred collisions per hour somewhere in the universe. We would never be aware of most of these, but we could expect a collision every 10,000 years or so within one of the Milky Way’s globular clusters. In fact, the globular cluster NGC 6397 shows evidence for what may have been a three-star...
Mission to an Interstellar Asteroid
On the matter of interstellar visitors, bear in mind that our friend ‘Oumuamua, the subject of yesterday’s post, was discovered at the University of Hawaii’s Institute for Astronomy, using the Pan-STARRS telescope. The Panoramic Survey Telescope and Rapid Response System is located at Haleakala Observatory on Maui, where it has proven adept at finding new asteroids, comets and variable stars. Consider ‘Oumuamua a bonus, and according to a new paper from Greg Laughlin and Darryl Seligman (Yale University), a type of object we’ll be seeing again. Pan-STARRS may find objects like this every few years, but we’ll get a bigger payoff in terms of interstellar wanderers with the Large Synoptic Survey Telescope (LSST), now under construction at Cerro Pachón (Chile). Laughlin and Seligman think that this instrument will up the discovery rate as high as several per year, allowing us to see ‘Oumuamua in context, and also, perhaps, setting up the possibility of an intercept mission with a kinetic...
A Binary Origin for ‘Oumuamua?
The fleeting interstellar visitor we call 'Oumuamua is back in the news, an object whose fascination burns bright given its status as a visitor from another star system. Just what kind of system is the subject of a new letter just published in Monthly Notices of the Royal Astronomical Society, in which Alan Jackson and colleagues argue that the star-crossed wanderer is most likely the offspring of a binary stellar system, these being far more likely to eject rocky objects. Our first confirmed interstellar asteroid just grows in interest. Jackson (University of Toronto - Scarborough) is quoted in this news release from the Royal Astronomical Society as saying that the odds didn’t favor the first interstellar object detected in our system being an asteroid. Comets are more likely to be spotted, and our system is more efficient at ejecting comets than asteroids. But 'Oumuamua is what we got, and its eccentricity of 1.2 and 30 km/sec speed pegged its orbit as hyperbolic, clearly not...
A Changing Landscape at Ceres
Ceres turns out to be a livelier place than we might have imagined. Continuing analysis of data from the Dawn spacecraft is showing us an object where surface changes evidently caused by temperature variations induced by the dwarf planet's orbit are readily visible even in short time frames. Two new papers on the Dawn data are now out in Science Advances, suggesting variations in the amount of surface ice as well as newly exposed crustal material. Andrea Raponi (Institute of Astrophysics and Planetary Science, Rome) led a team that discovered changes at Juling Crater, demonstrating an increase in ice on the northern wall of the 20-kilometer wide crater between April and October of 2016. Calling this 'the first detection of change on the surface of Ceres,' Raponi went on to say: "The combination of Ceres moving closer to the sun in its orbit, along with seasonal change, triggers the release of water vapor from the subsurface, which then condenses on the cold crater wall. This causes...
Red Dwarfs: Their Impact on Biosignatures
We’re in the midst of a significant period defining the biosignatures life can produce and determining how we might identify them. Centauri Dreams regular Alex Tolley today looks at a paper offering a unique contribution to this effort. The work of Sarah Rugheimer and Lisa Kaltenegger, the paper looks at how exoplanet spectra change for different types of host star and different epochs of planetary evolution. As Alex points out, the effects are profound, especially given the fact that red dwarfs will be our testbed for biosignature detection as we probe planetary atmospheres during transits around nearby stars. How stellar class affects our analysis will affect our strategies especially as we probe early Earth atmosphere equivalents. What will we find, for example, at TRAPPIST-1? By Alex Tolley As the search for life on exoplanets ramps up, the question arises as to which types of stars represent the best targets. Based on distribution, M-Dwarfs are very attractive as they represent...
Maxing Out Kepler
What happens to a spacecraft at the end of its mission depends on where it's located. We sent Galileo into Jupiter on September 21, 2003 not so much to gather data but because the spacecraft had not been sterilized before launch. A crash into one of the Galilean moons could potentially have compromised our future searches for life there, but a plunge into Jupiter's atmosphere eliminated the problem. Cassini met a similar fate at Saturn, and in both cases, the need to keep a fuel reserve available for that final maneuver was paramount. Now we face a different kind of problem with Kepler, a doughty spacecraft that has more than lived up to its promise despite numerous setbacks, but one that is getting perilously low on fuel. With no nearby world to compromise, Kepler's challenge is to keep enough fuel in reserve to maximize its scientific potential before its thrusters fail, thus making it impossible for the spacecraft to be aimed at Earth for data transfer. In an Earth-trailing orbit...
Antimatter: The Heat Problem
My family has had a closer call with ALS than I would ever have wished for, so the news of Stephen Hawking's death stays with me as I write this morning. I want to finish up my thoughts on antimatter from the last few days, but I have to preface that by noting how stunning Hawking's non-scientific accomplishment was. In my family's case, the ALS diagnosis turned out to be mistaken, but there was no doubt about Hawking's affliction. How on Earth did he live so long with an illness that should have taken him mere years after it was identified? Hawking's name will, of course, continue to resonate in these pages -- he was simply too major a figure not to be a continuing part of our discussions. With that in mind, and in a ruminative mood anyway, let me turn back to the 1950s, as I did yesterday in our look at Eugen Sänger's attempt to create the design for an antimatter rocket. Because even as Sänger labored over the idea, one he had been pursuing since the 1930s, Les Shepherd was...
Stephen Hawking (1942-2018)
The Tau Zero Foundation expresses it deepest sympathies to the family, friends and colleagues of Stephen Hawking. His death is a loss to the the world, to our scientific communities, and to all who value courage in the face of extreme odds.
Harnessing Antimatter for Propulsion
Antimatter's staggering energy potential always catches the eye, as I mentioned in yesterday's post. The problem is how to harness it. Eugen Sänger's 'photon rocket' was an attempt to do just that, but the concept was flawed because when he was developing it early in the 1950s, the only form of antimatter known was the positron, the antimatter equivalent of the electron. The antiproton would not be confirmed until 1955. A Sänger photon rocket would rely on the annihilation of positrons and electrons, and therein lies a problem. Sänger wanted to jack up his rocket's exhaust velocity to the speed of light, creating a specific impulse of a mind-boggling 3 X 107 seconds. Specific impulse is a broad measure of engine efficiency, so that the higher the specific impulse, the more thrust for a given amount of propellant. Antimatter annihilation could create the exhaust velocity he needed by producing gamma rays, but positron/electron annihilation was essentially a gamma ray bomb, pumping out...
Antimatter in Motion
Antimatter will never lose its allure when we're talking about interstellar propulsion, even if the breakthroughs needed to harness it are legion. After all, a kilogram of antimatter, annihilating itself in contact with normal matter, yields roughly ten billion times the amount of energy released when a kilogram of TNT explodes. Per kilogram of fuel, we're talking about 1,000 times more energy than nuclear fission, and 100 times the energy available through nuclear fusion. Or we could put this into terms more suited for space. A single gram of antimatter, according to Frank Close's book Antimatter (Oxford, 2010), could through its annihilation produce as much energy as the fuel from the tanks of two dozen Space Shuttles. The catalog of energy comparisons could go on, each as marvelous as the last, but the reality is that antimatter is not only extremely difficult to produce in any quantity but even more challenging to store. Cram enough positrons or antiprotons into a magnetic bottle...
Lab Work on ‘Super-Earth’ Atmospheres
How we do laboratory work on exoplanet atmospheres is an interesting challenge. We’ve worked up models of the early Earth’s atmosphere and conducted well-known experiments on them. Still within our own system, we’ve looked at worlds like Mars and Titan and, with a good read on their atmospheric chemistry, can reproduce an atmosphere within the laboratory with a fair degree of accuracy. In the realm of exoplanets, we’re in the early stages of atmosphere characterization. We’re getting good results from transmission spectroscopy, which analyzes the light from a star as it filters through a planetary atmosphere during a transit. But thus far, the method has mostly been applied to gas giants. Getting down to the realm of rocky worlds is the next step, one that will be aided by space-based assets like the James Webb Space Telescope. Can lab work also help? Probing the Atmosphere of a ‘Super-Earth’ Worlds smaller than gas giants are plentiful. Indeed, ‘super-Earths’ are the most common...
Juno’s View of Jupiter’s Turbulent Poles
The imagery we're getting of Jupiter's polar regions is extraordinary. Juno's Jovian Infrared Auroral Mapper instrument (JIRAM) works at infrared wavelengths, showing us a vivid picture of a massive central cyclone at the north pole and eight additional cyclones around it. In the image below, we're looking at colors representing radiant heat, with yellow being thinner clouds at about -13 degrees Celsius, and dark red representing the thickest clouds, at about -118 degrees Celsius. JIRAM can probe down to 70 kilometers below the cloud tops. Image: This composite image, derived from data collected by the Jovian Infrared Auroral Mapper (JIRAM) instrument aboard NASA's Juno mission to Jupiter, shows the central cyclone at the planet's north pole and the eight cyclones that encircle it. Credit: NASA/JPL-Caltech/SwRI/ASI/INAF/JIRAM. This is hardly the orange, white and saffron belted world we are familiar with from telescope views of the lower latitudes. The scale of these storms is, as...
Extracting Exoplanet Topography from Transit Data
How do we go from seeing an exoplanet as a dip on a light curve or even a single pixel on an image to a richly textured world, with oceans, continents and, perhaps, life? We've got a long way to go in this effort, but we're already having success at studying exoplanet atmospheres, with the real prospect of delving into planets as small as the Earth around nearby red dwarfs in the near future. Atmospheric detection and analysis can help us in the search for biosignatures. But I was surprised when reading a recent paper to realize just how many proposals are out there to analyze planetary surfaces pending the development of next-generation technologies. Back in 2010, for example, I wrote about Tyler Robinson (University of Washington), who was working on how we might detect the glint of exo-oceans (see Light Off Distant Oceans for more on Robinson's work). And Robinson's ideas are joined by numerous other approaches. I won't go into detail on any of these, but l do want to illustrate...
A New Theory of Lunar Formation
Simon Lock and Sarah Stewart are intent upon revising our views on how the Moon was formed. Lock is a Harvard graduate student who last year, in company with Stewart (UC-Davis) presented interesting work on what the duo are calling a 'synestia,' which is the kind of 'structure' resulting from the collision of huge objects. Current thinking about the Moon is that it formed following the collision of a Mars-sized object with the Earth, two huge objects indeed. What Lock and Stewart asked is whether this formation scenario can produce the result we see today. What it calls for is the ejection of material that forms into a disk and, through processes of accretion, gradually becomes the Moon. The problem with it, says Lock, is that it's a very hard trick to pull off: "Getting enough mass into orbit in the canonical scenario is actually very difficult, and there's a very narrow range of collisions that might be able to do it. There's only a couple-of-degree window of impact angles and a...
Probing a ‘Hot Saturn’
When researchers talk about 'hot Saturns,' it's natural to imagine a ringed planet in a close orbit to its star, rings being Saturn's most prominent feature. But WASP-39b hardly fits this picture. Some 700 light years from Earth in the constellation Virgo, this is a tidally locked world that is 20 times closer to its star than the Earth is to the Sun. WASP-39 itself is a G-class star of about 90 percent of the Sun's mass. We have no evidence of planetary rings here, but we do see a planet whose temperature reaches 776 degrees Celsius, with a nightside not much cooler. What keeps this world from being called a 'hot Jupiter' is its low density coupled with a large radius, some 1.27 times that of Jupiter (its density is about 0.28 times that of Jupiter). 'Puffy' planets like this show density levels far more like Saturn, and they orbit close to their stars, accounting for their extended atmospheres. WASP-39b's atmosphere appears free of high-altitude clouds, allowing detailed study of...
A Plausible Path for Life on Enceladus
Cassini has shown us that the plumes of Enceladus are laden not just with ammonia and carbon dioxide but also traces of methane. Scientists at the University of Vienna (Austria) are not claiming this finding as evidence for life, but they have produced laboratory work showing that at least one kind of microbe could survive in conditions like those within the moon. Couple this with the presence of molecular hydrogen (H2), also found within the plumes, and the existence of microorganisms deep within Enceladus appears at least plausible. Some of the methane found in the Enceladus plumes may turn out to be produced by methanogens. The microorganism in question is Methanothermococcus okinawensis, which can be found around sea vents in the Okinawa Trough off Japan. In conditions like these, methanogenic archaea can sustain themselves by the chemical nutrients found around hydrothermal vents, a scenario that could likewise exist beneath the Enceladus ice. Simon Rittmann, working with...
Voyager at Pluto? Alternative Histories
With New Horizons in hibernation as it pushes on toward MU69, it's worth remembering how recently our knowledge of the Kuiper Belt has developed. Gerard Kuiper did not predict the belt's existence, though he did believe that small planets or comets should have formed in the region beyond the orbit of Neptune (he also thought they would have been cleared by gravitational interactions long ago). And I always like to mention Kenneth Edgeworth's work in a 1943 issue of the Journal of the British Astronomical Association, discussing the likelihood of small objects in the region. We could easily be calling the area the Edgeworth/Kuiper Belt, as I occasionally do in these pages. Which takes me back to the Voyager days. It wasn't until 1992 that astronomers discovered 15760 Albion, the first trans-Neptunian object detected after Pluto and Charon. Back in 1980, when controllers were deciding on adjustments to the trajectory of Voyager 1, Pluto was an option, as New Horizons PI Alan Stern has...
What We Are Trying to Find
What is it we are looking for when we probe nearby planetary systems? Certainly the search for life elsewhere compels us to find planets like our own around stars much like the Sun. But surely our goal isn't restricted to finding duplicate Earths, if indeed they exist. A larger goal would be to find life on planets unlike the Earth -- perhaps around stars much different from the Sun -- which would give us some idea how common living systems are in the galaxy. And beyond that? The ultimate goal is simply to find out what is out there. That takes in outcomes as different as widespread microbial life, perhaps leading to more complex forms, and barren worlds in which life never emerged. A galaxy filled with life vs. a galaxy in which life is rare offers us two striking outcomes. We ignore preconceptions to find out which is true. Flaring Red Stars Let's try to put Proxima Centauri's recent flare, discussed yesterday, in context. Events like this highlight our doubts about the viability...
Proxima Flare May Force Rethinking of Dust Belts
News of a major stellar flare from Proxima Centauri is interesting because flares like these are problematic for habitability. Moreover, this one may tell us something about the nature of the planetary system around this star, making us rethink previous evidence for dust belts there. But back to the habitability question. Can red dwarf stars sustain life in a habitable zone much closer to the primary than in our own Solar System, when they are subject to such violent outbursts? What we learn in a new paper from Meredith MacGregor and Alycia Weinberger (Carnegie Institution for Science) is that the flare at its peak on March 24, 2017 was 10 times brighter than the largest flares our G-class Sun produces at similar wavelengths (1.3 mm). Image: The brightness of Proxima Centauri as observed by ALMA over the two minutes of the event on March 24, 2017. The massive stellar flare is shown in red, with the smaller earlier flare in orange, and the enhanced emission surrounding the flare that...