Centauri Dreams

Imagining and Planning Interstellar Exploration

A Necessary Break

It’s time to write a post I’ve been dreading to write for several years now. Some of my readers already know that my wife has been ill with Alzheimer’s for eleven years, and I’ve kept her at home and have been her caregiver all the way. We are now in the final stages, it appears, and her story is about to end. I will need to give her all my caring and attention through this process, as I’m sure you’ll understand. And while I have no intention of shutting down Centauri Dreams, I do have to pause now to devote everything I have to her. Please bear with me and with a bit of time and healing, I will be active once again.

Recalibrating ‘Hot Jupiter’ Migration

What catches your eye in this description of an exoplanetary system? Start with a ‘hot Jupiter,’ with a radius 0.87 times that of our Jupiter and an orbit of 7.1 days. This is WASP-132b, confirmed in 2016, and first discovered through the labors of the Wide-Angle Search for Planets program. Subsequent confirmation came through the CORALIE spectrograph installed on the Euler telescope at the European Southern Observatory’s La Silla site. This world orbits a K-class star 403 light years out in Lupus.

The CORALIE measurements gave hints of another giant planet in a long period orbit. The system came still further into focus in 2021, when observations from TESS (Transiting Exoplanet Survey Satellite) showed a transiting super-Earth with a diameter of 1.8 Earth radii in a tight orbit of 1.01 days. The mass of the planet, as measured by the HARPS spectrograph at La Silla, is six times that of Earth. So we have both a hot-Jupiter and a super-Earth hugging the star, along with an outer gas giant.

Image: The WASP-132 system was known to harbour WASP-132b, here in the foreground, a hot Jupiter planet orbiting around a K-type star in 7.1 days. New data confirms the system has more planets, including an inner super-Earth, here seen transiting in front of the orange host-star. Visible as a pale blue dot near the top right corner is also the giant planet WASP-132d discovered in the outskirts of the system. © Thibaut Roger – Université de Genève.

While the European Space Agency’s Gaia satellite continues to take astrometrical data on WASP-132, follow-up work has shown the super-Earth to have a density similar to Earth’s and a composition of metals and silicates fairly similar to our planet (remember, we have both radius and mass measurements to work with because of the multiple datasets from different detection methods). Meanwhile, the problem here should be apparent.

Ravit Helled (University of Zurich) and a co-author of the study offers this:

‘‘The combination of a Hot Jupiter, an inner Super-Earth and an outer giant planet in the same system provides important constraints on theories of planet formation and in particular their migration processes. WASP-132 demonstrates the diversity and complexity of multi-planetary systems, underlining the need for very long-term, high-precision observations.’’

All true, of course, but it doesn’t get across how unusual this finding is. For hot Jupiters as thus far observed have been relatively isolated from planets further out in their systems. That makes sense because the model for their formation involves migration, with the giant worlds forming far enough out from the star to feed off plentiful gas and dust in the protoplanetary disk, and then moving inward as the system takes form. Woe to inner planets, whose fate might include ejection from the system entirely.

WASP-132 shouldn’t have the system architecture it does given this theory of migration, meaning we have to re-examine the nature of migration, or ponder ways to achieve a planet of this size in a tight stellar orbit that leave migration behind altogether. The hot Jupiter here leads François Bouchy (University of Geneva), a co-author of the study, to say this:

“The WASP-132 system is a remarkable laboratory for studying the formation and evolution of multi-planetary systems. The discovery of a Hot Jupiter alongside an inner Super-Earth and a distant giant planet calls into question our understanding of the formation and evolution of these systems.”

To my knowledge, WASP-132 is the second example of a planetary system in this configuration. WASP-47 takes precedence in terms of discovery, having been first analyzed by the WASP team in 2012 (discovery of the hot Jupiter) and then expanded through work with K2 data in 2015. WASP-47, a G-class star in Aquarius some 880 light years away, hosts a super-Earth inside the hot Jupiter’s orbit, a hot Neptune outside its orbit, and an outer gas giant (‘warm Saturn’) within the habitable zone. The discovery paper of the smaller worlds at WASP-47 is worth quoting:

The continued existence of the companions in this system indicates that HEM [high eccentricity migration] ] cannot serve as the sole formation mechanism for hot Jupiters. HEM would likely have disrupted the orbits of the smaller planets. It is quite possible that there is more than one potential formation mechanism for hot Jupiters. Additionally, recent observations have identified an additional Jupiter-mass planet in a 571-day orbit (called WASP-47c; Neveu-VanMalle et al. 2015) in this system, making this the first hot Jupiter with both close-in companions and an external perturber. Future dynamical work will place limits on the architecture of this system.

The paper is Thibaut et al., ”Discovery of a cold giant planet and mass measurement of a hot super-Earth in the multi-planetary system WASP-132′,” Astronomy and Astrophysics Vol. 693 (15 January 2025), A144 (full text). On WASP-132, see Becker at al., “WASP-47: A Hot Jupiter System With Two Additional Planets Discovered by K2,” Astrophysical Journal Letters Vol. 812, No. 2 (12 October 2015), L18 (full text).

Planet Population around Orange Dwarfs

Last Friday’s post on K-dwarfs as home to what researchers have taken to calling ‘superhabitable’ worlds has caught the eye of Dave Moore, a long-time Centauri Dreams correspondent and author. Readers will recall his deep dives into habitability concepts in such essays as The “Habitability” of Worlds and Super Earths/Hycean Worlds, not to mention his work on SETI (see If Loud Aliens Explain Human Earliness, Quiet Aliens Are Also Rare). Dave sent this in as a comment but I asked him to post it at the top because it so directly addresses the topic of habitability prospects around K-dwarfs, based on a quick survey of known planetary systems. It’s a back of the envelope overview, but one that implies habitable planets around stars like these may be more difficult to find than we think.

by Dave Moore

To see whether K dwarfs made a good target for habitable planets, I decided to look into the prevalence and type of planets around K dwarfs and got carried away looking at the specs for 500 systems of dwarfs between 0.6 mass of the sun and 0.88.

Some points:

i) This was a quick and dirty survey.

ii) Our sampling of planets is horribly skewed towards the massive and close, but that being said, we can tell if certain types of planets are not in a system. For instance Jupiter and Neptune sized planets at approximately 1 au show up, so if a system doesn’t show them after a thorough examination, it won’t have them.

iii) I had trouble finding a planet list that was configurable to my needs. I finally settled on the Exoplanets Data Explorer configured in reverse order of stellar mass. This list is not as comprehensive as the Exosolar Planetary Encyclopedia.

iv) I concocted a rough table of the inner and outer HZ for the various classes of K dwarfs. Their HZs vary considerably. A K8 star’s HZ is between 0.26 au and 0.38 au while a K0’s HZ is between 0.72 au and 1.04 au. This means that you can have two planets orbiting at the same distance around a star and one I will classify as outside the HZ and the other inside the HZ.

v) Planets below 9 Earth mass I classified as Super-Earth/Sub-Neptune. Planets between 9 Earth masses and 30 are classified as Neptunes. Planets over that size are classified as Jupiters.

Image: An array of planets that could support life are shown in this artist’s impression. How many such worlds orbit K-dwarf stars, and are any of them likely to be ‘superhabitable’? Credit: NASA, ESA and G. Bacon (STScI).

What did I find:

By far the most common type are hot Super-Earths/Sub-Neptunes (SE/SNs). These are planets between 3 EM (Earth mass) and 6 EM. It is amazing the consistency of size these planets have. They are mostly in close (sub 10 day) orbits. There also appears to be a subtype of sub 2EM planets in very tight orbits (some quoted in hours) and given some of these were in multi-planet systems of SE/SNs, I would say these were SE/SNs, which have been evaporated down to their cores.

I also found 7 in the HZ and 2 outside the HZ.

I found 52 hot Jupiters and what I classified as 43 elliptical orbit Jupiters. These were Jupiter-sized planets in elliptical orbits under 3 au.

There were also 10 Jupiter classification planets in circular orbits under 3 au. and 3 outside that limit in what could be thought of as a rough analog of our system.

There were also 46 hot Neptunes and 14 in circular orbits further out, only one outside the habitable zone.

Trends:

At the lower mass end of the scale, K dwarf systems start off looking very much like M dwarfs except that everything, even those in multi-planet systems, is inside the habitable zone.

As you work your way up the mass scale, there is a slight increase in the average mass of the SE/SNs with 7-8 EM planets becoming more prevalent. More and more Jupiters appear, and Neptune-sized planets appear and become much more frequent. Also, you get the occasional monster system of tightly packed Jupiters and Neptunes like 55 Cancri.

An interesting development begins at about the mid mass range. You start getting SE/SNs in nice circular longer period orbits but still inside the HZ (28 in 20-100d orbits.)

Conclusions:

If we look at the TRAPPIST-1 system around an M-dwarf, its high percentage of volatiles (20% water/ice) implies that there is a lot of migration in from the outer system. If a planet has migrated in from outside the snow line, then there’s a good chance that even if it’s in the habitable zone, it will be a deep ocean planet.

Signs of migration are not hard to find. Turning back to the K-dwarfs, if we look at the Jupiters, only three show signs of little migration (analogs of our system). Ten migrated in smoothly but sit at a distance likely to have disrupted a habitable planet. Forty-three are in elliptical orbits, which are considered signs of planet-planet scattering.

Hot Jupiters can be accounted for by either extreme scattering or migration. As to inward migration, Martin Fogg did a series of papers showing that as Jupiter mass planets march inwards they scatter protoplanets, but these can reform behind the giant, and so Earth-like planets may occur outside of the hot Jupiter.

Neptunes in longer period circular orbits and the longer period SE/SNs all point to migration. These last groups are intriguing as they point to a stable system with the possibility of smaller planets further out. I would include the 7 planets in the habitable zone in this group. But if these planets all migrated inwards they may well be ocean planets.

K dwarfs have an interesting variety of systems, so they’d be useful to study, but I don’t see them as the major source of Earth analogs—at least not until we learn more.

Superhabitability around K-class Stars

We think of Earth as our standard for habitability, and thus the goal of finding an ‘Earth 2.0’ is to identify living worlds like ours orbiting similar Sun-like stars. But maybe Earth isn’t the best standard. Are there ways planets can be more habitable than our own, and if so where would we find them? That’s the tantalizing question posed in a paper by Iva Vilović (Technische Universität Berlin), René Heller (Max-Planck-Institut für Sonnensystemforschung) and colleagues in Germany and India. Heller has previously worked this issue in a significant paper with John Armstrong (citation below); see as well The Best of All Possible Worlds, which ran here in 2020.

The term for the kind of world we are looking for is ‘superhabitable,’ and the aim of this study is to extend the discussion of K-class stars as hosts by modeling the atmospheres we may find on planets there. While much attention has focused on M-class red dwarfs, the high degree of flare activity coupled with long pre-main sequence lifetimes makes K-class stars the more attractive choice, although less susceptible to near-term evaluation, as the paper shows in its sections on observability. It’s intriguing, for example, to realize that K-class stars are expected to live significantly longer than the Sun, as much as 100 billion years, and because they are cooler and less luminous than G-class stars, their habitable zone planets produce more frequent transits.

Image: This infographic compares the characteristics of three classes of stars in our galaxy: Sunlike stars are classified as G-stars; stars less massive and cooler than our Sun are K-dwarfs; and even fainter and cooler stars are the reddish M-dwarfs. The graphic compares the stars in terms of several important variables. The habitable zones, potentially capable of hosting life-bearing planets, are wider for hotter stars. The longevity for red dwarf M-stars can exceed 100 billion years. K-dwarf ages can range from 50 to 100 billion years. And, our Sun only lasts for 10 billion years. The relative amount of harmful radiation (to life as we know it) that stars emit can be 80 to 500 times more intense for M-dwarfs relative to our Sun, but only 5 to 25 times more intense for the orange K-dwarfs. Red dwarfs make up the bulk of the Milky Way’s population, about 73%. Sunlike stars are merely 8% of the population, and K-dwarfs are at 13%. When these four variables are balanced, the most suitable stars for potentially hosting advanced life forms are K-dwarfs. Image credit: NASA, ESA, and Z. Levy (STScI).

Let’s dig into this a little further. The contrast in brightness between star and planet is enhanced around K-dwarfs, and spectroscopic studies are aided by lower levels of stellar activity, which also enhances the habitability of planets. While an M-dwarf may be in a pre-Main Sequence phase for up to a billion years, K stars take about a tenth of this. They emit lower levels of X-rays than G-type stars and are also more abundant, making up about 13 percent of the galactic population as opposed to 8% for G-stars. With luminosity as low as one-tenth of a star like the Sun, they offer better conditions for direct imaging and their planets are far enough from the host to avoid tidal lock.

So we have an interesting area for investigation, as earlier studies have shown that photosynthesis works well under simulated K-dwarf radiation conditions. The authors go so far as to call these ‘Goldilocks stars’ for life-bearing planets, and there are about 1,000 such stars within 100 light years of the Sun, Thus modeling superhabitable atmospheres to support future observations stands as a valuable contribution.

The authors model these atmospheres by drawing on Earth’s own history as well as astrophysical parameters, finding that a superhabitable planet would be somewhat more massive than Earth so as to retain a thicker atmosphere to support a more extensive biosphere. Plate tectonics and a strong magnetic field are assumed, as are elevated oxygen levels that would “enable more extensive metabolic networks and support larger organisms.” Surface temperatures are some 5 degrees C warmer than present day Earth and increased atmospheric humidity supports the ecosystem.

The paper continues:

In terms of the atmospheric composition, key organisms and biological sources affecting Earth’s biosphere and their atmospheric signatures are considered. A superhabitable atmosphere would have increased levels of methane (CH4) and nitrous oxide (N2O) due to heightened production by methanogenic microbes, as well as denitrifying bacteria and fungi, respectively (Averill and Tiedje 1982, Wen et al. 2017). Furthermore, it would have decreased levels of molecular hydrogen (H2) due to higher enzyme consumption (Lane et al. 2010, Greening and Boyd 2020). Lastly…molecular oxygen (O2) levels could increase from present-day 21% by volume on Earth to 25% to reflect a thriving photosynthetic biosphere (Schirrmeister et al. 2015).

Given these factors, the authors deploy simulations using three different modeling tools (Atmos, POSEIDON and PandExo, the latter two to examine observability of transiting planets). Using Atmos, they simulate three pairs of superhabitable planets in differing locations in K-dwarf habitable zones, varying stellar radii and masses and star age. They focused on organisms and biological sources that had influenced Earth’s biosphere, including O2, H2, CH4, N2O and CO2 at a variety of surface temperatures.

The results offer what the authors consider the first simulated data on superhabitable atmospheres and assessments of the observability of such life. What stands out here is the optimum positioning of a superhabitable world around its star. Note this:

We find that planets positioned at the midpoint between the inner edge and center of the habitable zone, where they receive 80% of Earth’s solar flux, are more conducive to life. This contrasts with previous suggestions that planets at the center of the habitable zone—where our study shows they receive about 60% of Earth’s solar flux—are the most favorable for life (Heller and Armstrong 2014). Planets at the midpoint between the center and the inner edge need less CO2 for temperate climates and are more observable due to their warmer atmospheric temperatures and larger atmospheric scale heights. We conclude that a superhabitable planet orbiting a 4300K star with 80% of the solar flux offers the best balance of observability and habitability.

Image: An artist’s concept of a planet orbiting in the habitable zone of a K-type star. Image credit: NASA Ames/JPL-Caltech/Tim Pyle.

Observability presents a major challenge. Using the James Webb Space Telescope, a biosignature detection at 30 parsecs requires 150 transits (43 years of observation time) as compared to 1700 transaits (1699 years) for an Earth-like planet around a G-class star. That would be a mark in favor of K-stars but it also underlines the fact that studies of that length are impractical even with the anticipated Habitable Worlds Observatory. The JWST is working wonders, but clearly we are talking about next-generation telescopes – or the generation after that – when it comes to biosignature detection on potential superhabitable planets.

So what we have is encouraging in terms of the chances for life around K-class stars but a clear notice that observing the biosignatures of these planets is going to be a much harder task than doing the same for nearby M-class dwarfs, where extremely close habitable zones also give us a much larger number of transits over time.

The paper is Vilović et al., “Superhabitable Planets Around Mid-Type K Dwarf Stars Enhance Simulated JWST Observability and Surface Habitability,” accepted at Astronomical Notes and now available as a preprint. The earlier Heller and Armstrong paper is “Superhabitable Worlds,” Astrobiology Vol. 14, No. 1 (2014). Abstract. Another key text is Schulze-Makuch, Heller & Guinan, “In Search for a Planet Better than Earth: Top Contenders for a Superhabitable World,” Astrobiology 18 September 2020 (full text), which looks at candidates. Cuntz & Guinan, “About Exobiology: The Case for Dwarf K Stars,” Astrophysical Journal Vol. 827, No. 1 10 August 2016 (full text) should also be in your quiver.

A ‘Manhole Cover’ Beyond the Solar System?

Let’s start the year with a look back in time to 1957, a time when nuclear bombs were being tested underground for the first time at the Nevada test site some 105 kilometers northwest of Las Vegas. If this seems an unusual place to launch a discussion on interstellar matters, consider the story of an object that some argue became the fastest manmade artifact in history, an object moving so fast that it would have passed the orbit of Pluto four years after ‘launch,’ in the days of Yuri Gagarin and Project Mercury.

I’m bringing it up because the tale of the nuclear test known as Plumbob Pascal B is again active on the Internet, and it’s a rousing tale. Operation Plumbob involved a series of 29 nuclear tests that fed the development of missile warheads both intercontinental and intermediate. The history of such underground nuclear testing would make for an interesting book and indeed it has, in the form of Caging the Dragon (Defense Nuclear Agency, 1995), by one James Carothers.

But let’s narrow our focus to the nuclear devices known as Pascal A and B, the former used used in the first nuclear test below ground. This would have been the first such test in history, as the Soviet Union did not begin its underground program until 1961.

Image: The scene following the detonation of Ranier, an underground nuclear test similar to Pascal B. Credit: Plane Encyclopedia.

The key player here was Robert Brownlee (Los Alamos National Laboratory), who supervised the detonation of Pascal A and duly noted the fact that the yield was much greater than anticipated, so that a column of flame shot into the sky. The blast was not remotely contained. Pascal B was partially an attempt to fix that problem by lowering a 900-kilogram, 4-inch thick iron lid over the borehole. It seemed sensible to at least some at the time, but Brownlee himself evidently did not believe it would work to contain the blast, as indeed it did not.

The detonation of Pascal B caused the blast, like its predecessor, to climb straight up the borehole and escape. The interesting part is that the lid was never found. The only camera footage of the event caught the iron plate in only one frame, and that fact seems to be the source of the current interest. For Brownlee, extrapolating from the speed of the filming (one frame per millisecond) attempted a calculation on the speed of the object. He wound up with something on the order of six times Earth’s escape velocity, which would be 241,920 kilometers per hour, or 67.2 kilometers per second.

That’s an interesting figure! Voyager 1 is moving at about 17.1 kilometers per second and is more or less the yardstick for our thinking about where we are today in achieving deep space velocities. So what is commonly being described as a ‘manhole cover,’ which is pretty much what this object was, is conceivably the fastest moving object humans have ever produced.

Brownlee, recalling these events in 2002, described the iron cap as requiring a lot of ‘man-handlng’ to get it into place. And he goes on to say this:

For Pascal B, my calculations were designed to calculate the time and specifics of the shock wave as it reached the cap. I used yields both expected and exaggerated in my calculations, but significant ones. When I described my results to Bill Ogle [deputy division leader on the project], the conversation went something like this.

Ogle: “What time does the shock arrive at the top of the pipe?”
RRB: “Thirty one milliseconds.”
Ogle: “And what happens?”
RRB: “The shock reflects back down the hole, but the pressures and temperatures are such that the welded cap is bound to come off the hole.”
Ogle: “How fast does it go?”
RRB: “My calculations are irrelevant on this point. They are only valid in speaking of the shock reflection.”
Ogle: “How fast did it go?”
RRB: “Those numbers are meaningless. I have only a vacuum above the cap. No air, no gravity, no real material strengths in the iron cap. Effectively the cap is just loose, traveling through meaningless space.”
Ogle: And how fast is it going?”

This last question was more of a shout. Bill liked to have a direct answer to each one of his questions.

RRB: “Six times the escape velocity from the earth.”

Image: Los Alamos’ Robert Brownlee (1924-2018). Credit: American Astronomical Society.

According to Brownlee, the answer delighted Ogle, who had never heard of a velocity given in terms of escape velocity from the Earth. Brownlee himself notes that because the object was only caught in one camera frame, there was no direct velocity measurement. He could only summarize the situation by saying that the ‘manhole cover’ was “going like a bat!” But he also notes that neither he nor Ogle believed that the cap would actually have made it into space. And the story doesn’t end just yet.

As passed along by my ever-reliable buddy Al Jackson (Centauri Dreams readers will know of Al as astronaut trainer on the Lunar Module Simulator during the Apollo era, and as the author of numerous papers on interstellar propulsion), I point to a set of calculations by one R. Finden titled “The Fastest Object Ever: The Manhole Cover,” evidently sent in response to an article in a magazine called Business Insider in 2016. The note appeared originally on a Reddit thread. Finden notes that his or her work should be considered as a rough estimate because “flight at a mach number upwards of 200 has not been studied and may never be.” Good point.

Finden’s calculations show that the cover would have reached temperatures five times its melting point before it could ever escape the atmosphere. And then this:

If the steel plate were magical and did not burn in the atmosphere, it would have escaped the upper stratosphere (50km) at 53 km/s just 934ms from launch. This not only means it would have made it to space, but it would have eventually escaped our solar system (depending on the time of day at launch). What likely happened was the plate was initially launched parallel to the ground and rotated with oscillation into the upright position, and by that time the drag from the first second of flight decreased its speed enough to prevent it from entering the upper stratosphere.

Conclusion: No manhole cover in space. It’s worth recalling, the Finden note adds, that the Chelyabinsk meteor was moving at only one-third the speed and had 13,900 times the weight of the flying cover, and even this mass was unable to survive Earth’s atmosphere. I dislike this result, as the idea of an object ‘launched’ in 1961 escaping the Solar System while we were still trying to get to the Moon is utterly delightful. And because R Finden’s math skills are well beyond my pay grade, I can’t reach a definitive conclusion about the result. So maybe we can still dream of flying manhole covers even if the odds seem long indeed.

Interstellar Reprise: Voyager to a Star

As I write, Voyager 1 is almost 166 AU from the Sun, moving at 17 kilometers per second. With its Voyager 2 counterpart, the mission represents the first spacecraft to operate in interstellar space, continuing to send data with the help of skilled juggling of onboard systems not deemed essential. Despite communications glitches, the mission continues, and it seems a good time to reprise a piece I wrote on the future of these doughty explorers back in 2015. Is there still time to do something new with the two probes once the demise of their plutonium power sources makes further communications impossible? The idea is hardly mine, and goes back to the Sagan era, as the article below explains. It’s also a notion that is purely symbolic, and for those immune to symbolism (the more practical-minded among us) it may seem trivial. But those with a poet’s eye may see the value of an act that can offer a futuristic finish to a mission that passed all expectations and will inspire generations yet unborn.

After Voyager 2 flew past Neptune in 1989, much of the world assumed that the story was over, for there were no further planetary encounters possible. But science was not through with the Voyagers then, and it is not through with the Voyagers now. In one sense, they have become a testbed for showing us how long a spacecraft can continue to operate. In a richer sense, they illustrate how an adaptive and curious species can offer future generations the gift of ‘deep time,’ taking its instruments forward into multi-generational missions of interstellar scope.

Now approximately 24 billion kilometers from Earth, Voyager 1, which took a much different trajectory than its counterpart by leaving the ecliptic due to its encounter with Saturn’s moon Titan, is 166 times as far from the Sun as the Earth (166 AU). Round trip radio time is over 46 hours. The craft has left the heliosphere, a ‘bubble’ that is puffed up and shaped by the stream of particles from the Sun called the ‘solar wind.’ Voyager 1 has become our first interstellar spacecraft, and it will keep transmitting until about 2025, perhaps longer. Voyager 2, its twin, is currently 138 AU out — 20.7 billion kilometers from the Sun — with a round-trip radio time of 38 hours.

Throughout history we have filled in the dark places in our knowledge with the products of our imagination, gradually ceding these visions to reality as expeditions crossed oceans and new lands came into view. The Greek historian Plutarch comments that “geographers… crowd into the edges of their maps parts of the world which they do not know about, adding notes in the margin to the effect, that beyond this lies nothing but sandy deserts full of wild beasts, unapproachable bogs, Scythian ice, or a frozen sea…” But deserts get crossed, first by individuals, then by caravans, and frozen seas yield to the explorer with dog-sled and ice-axe.

Voyager and the Long Result

Space is stuffed with our imaginings, and despite our telescopes, what we find as we explore continues to surprise us. Voyager showed us unexpected live volcanoes on Jupiter’s moon Io and the billiard ball-smooth surface of Europa, one that seems to conceal an internal ocean. We saw an icy Enceladus, now known to spew geysers, and a smog-shrouded Titan. We found ice volcanoes on Neptune’s moon Triton and a Uranian moon — Miranda — with a geologically tortured surface and a cliff that is the highest known in the Solar System.

But the Voyagers are likewise an encounter with time. The issue raises its head because we are still communicating with spacecraft launched almost forty years ago. I doubt many would have placed a wager on the survival of electronics and internal mechanisms to this point, but these are the very issues raised by our explorations, for we still have trouble pushing any payload up to speeds equalling Voyager 1’s 17.1 kilometers per second. To explore the outer Solar System, and indeed to travel beyond it, is to create journeys measured in decades. With the Voyagers as an example, we may one day learn to harden and upgrade our craft for millennial journeys.

New Horizons took nine years to reach Pluto and its large moon Charon. To reach another star? An unthinkable 70,000 years-plus at Voyager 1 speeds, which is why the propulsion problem looms large as we think about dedicated missions beyond the Solar System. If light itself takes over 23 hours to reach Voyager 1, the nearest star, Proxima Centauri, is a numbing 4.2 light years away. To travel at even a paltry one percent of lightspeed, far beyond our capabilities today, would mean a journey to Proxima Centauri lasting well over four centuries.

What is possible near-term? Ralph McNutt, a veteran aerospace designer at the Johns Hopkins Applied Physics Laboratory, has proposed systems that could take a probe to 1000 AU in less than fifty years, giving us the chance to study the Oort Cloud of comets at what may be its inner edge. Now imagine that system ramped up ten times faster, perhaps boosted by a close pass by the Sun and a coordinated shove from a next-generation engine. Now we can anticipate a probe that could reach the Alpha Centauri stars in about 1400 years. Time begins to curl back on itself — we are talking trip times as great as the distance between the fall of Rome and today.

The interesting star Epsilon Eridani, some 10.5 light years out, would be within our reach in something over three thousand years. Go back that far in human history and you would see Sumerian ziggurats whose star maps faced the sky, as our ancestors confronted the unknown with imagined constellations and traced their destinies through star-based prognostications. The human impulse to explain seems universal, as is the pushing back of frontiers. And if these travel times seem preposterous, they’re worth dwelling on, because they help us see where we are with space technology today, and where we’ll need to be to reach the stars.

A certain humility settles in. While we work to improve propulsion systems, ever mindful that breakthroughs can happen in ways that no one expects, we also have to look at the practicalities of long-haul spaceflight. Both Voyagers have become early test cases in how long a spacecraft can last. They also force us to consider how things last in our own civilization. We have buildings on Earth — the Hagia Sophia in Constantinople, the Pantheon in Rome — that have been maintained for longer than the above Alpha Centauri flight time. A so-called ‘generation ship,’ with crew living and dying aboard the craft, may one day make the journey.

Engagement with deep time is not solely a matter of technology. In the world of business and commerce, our planet boasts abundant examples of companies that have been handed down for centuries within the same family. Construction firm Kongo Gumi, for example, was founded in Osaka in 578, and ended business activity only in 2007, being operated at the end by the 40th generation of the family involved. The Buddhist Shitennoji Temple and many other well known buildings in Japanese history owe much to this ancient firm.

The Japanese experience is instructive. Hoshi Ryokan is an innkeeping company founded in Komatsu in 718 and now operated by the family’s 46th generation. If you’re ever in Komatsu, you can go to a hotel that has been doing business on the site ever since. Nor do we have to stay in Japan. Fonderia Pontificia Marinelli has been making bells in Agnore, Italy since the year 1000, while the firm of Richard de Bas, founded in 1326, continues to make paper in Amvert d’Auvergne, providing its products for the likes of Braque and Picasso.

Making Missions that Last

We have long-term thinking in our genes, as the planners of the Pyramids must have assumed. The Long Now Foundation, which studies issues relating to trans-generational thinking and the long-term survival of artifacts, has pointed out that computer code has its own kind of longevity. Enduring like the Sphinx, deeply planted software tools like the Unix kernel may well be operational a thousand years from now. Jon Lomberg and the team behind the One Earth Message — an attempt to transmit a kind of digital ‘Golden Record’ to the New Horizons spacecraft as a catalog of the human condition — estimate that the encoded data will survive at least one hundred thousand years, and perhaps up to a million if given sufficient redundancy.

‘Deep time’ takes us well beyond quarterly stock reports, and even beyond generational boundaries, an odd place to be for a culture that thrives on the slickly fashionable. It’s energizing to know that there is a superstructure that persists. The Voyagers are uniquely capable of keeping this fact in front of us because we see them defying the odds and surviving. Stamatios “Tom” Krimigis (JHU/APL) is on record as saying of the Voyager mission “I suspect it’s going to outlast me.”

Krimigis is one of the principal investigators on the Voyager mission and the only remaining original member of the instrument team. His work involves instruments that can measure the flow of charged particles. Such instruments — low-energy charged particle (LECP) detectors — report on the flow of ions, electrons and other charged particles from the solar wind, but because they demanded a 360-degree view, they posed a problem. Voyager had to keep its antenna pointed at the Earth at all times, so the spacecraft couldn’t turn. This meant that the tools needed included an electric motor and a swivel mechanism that could swing back and forth for decades without seizing up in the cold vacuum of space.

The solution was offered by a California company called Schaeffer Magnetics. Krimigis’ team tested the contractor’s four-pound motor, ball bearings and dry lubricant. The company ran the motorized system through half a million ‘steps’ without failure. The instruments are still working, still detecting a particle flow that is evidently a mix of solar and interstellar particles, one that is moving in a flow perpendicular to the spacecraft’s direction of travel, so that it appears we’re just over the edge into interstellar space, a place where the medium is roiled and frothy, like ocean currents meeting each other and rebounding.

One Last Burn

Although the spacecraft are expected to keep transmitting for several more years, we’ll continue to see both Voyagers suffering from power issues. But there is a way to keep them alive, if not in equipment then as a part of our lore and our philosophy. They will take about 30,000 years to reach the outer edge of the Oort Cloud (the inner edge, according to current estimates, is maybe 300 years away). Add another 10,000 years and Voyager 1 passes some 100,000 AU past the red dwarf Gliese 445, which happens to be moving toward the Sun and will, by this remote date, be one of the closest stars to the Solar System. As to Voyager 2, it will pass 111,000 AU from Ross 248 in roughly the same time-frame, at which point the red dwarf will actually be the closest star to the Sun.

Carl Sagan and the team working on the Voyager Golden Record wondered whether something could be done about the fact that neither Voyager was headed for another Solar System. Is it possible that toward the end of the Voyagers’ active lifetimes (somewhere in the 2020s), we could set up a trajectory change that would eventually lead Voyager as close as possible to one of these stars? Enough hydrazine is available on each craft that, just before we lose radio contact with them forever, we could give them a final, tank-emptying burn. Tens of thousands of years later, the ancient craft, blind, mute but still more or less intact, would drift in the general vicinity of a star whose inhabitants, if any, might find them and wonder.

A trajectory change would increase only infinitesimally the faint chance that one of these spacecraft would someday be intercepted by another civilization, and neither could return data. But there is something grand in symbolic gestures, magic in the idea that these venerable machines might one day be warmed, however faintly, by the light of another sun. Our spacecraft are our emissaries and the manifestations of our dreams. How we conceive of them through the information they carry helps us gain perspective on ourselves, and shapes the context of our future explorations. Giving the Voyagers one last, hard shove toward a star would speak volumes about our values as a questioning species determined to confront the unknown.

Charter

In Centauri Dreams, Paul Gilster looks at peer-reviewed research on deep space exploration, with an eye toward interstellar possibilities. For many years this site coordinated its efforts with the Tau Zero Foundation. It now serves as an independent forum for deep space news and ideas. In the logo above, the leftmost star is Alpha Centauri, a triple system closer than any other star, and a primary target for early interstellar probes. To its right is Beta Centauri (not a part of the Alpha Centauri system), with Beta, Gamma, Delta and Epsilon Crucis, stars in the Southern Cross, visible at the far right (image courtesy of Marco Lorenzi).

Now Reading

Recent Posts

On Comments

If you'd like to submit a comment for possible publication on Centauri Dreams, I will be glad to consider it. The primary criterion is that comments contribute meaningfully to the debate. Among other criteria for selection: Comments must be on topic, directly related to the post in question, must use appropriate language, and must not be abusive to others. Civility counts. In addition, a valid email address is required for a comment to be considered. Centauri Dreams is emphatically not a soapbox for political or religious views submitted by individuals or organizations. A long form of the policy can be viewed on the Administrative page. The short form is this: If your comment is not on topic and respectful to others, I'm probably not going to run it.

Follow with RSS or E-Mail

RSS
Follow by Email

Follow by E-Mail

Get new posts by email:

Advanced Propulsion Research

Beginning and End

Archives