Centauri Dreams
Imagining and Planning Interstellar Exploration
Planetary Collisions and their Consequences
What happens when worlds collide? The question recalls the novel by Philip Wylie and Edwin Balmer, which appeared as a serial in Blue Book magazine beginning in 1932 and concluded the following year. The book version of When Worlds Collide appeared in 1933, and the movie, directed by Rudolph Maté, came out in 1951 in a George Pal production. I would wager that most Centauri Dreams readers have seen it.
Let’s hope we never share such a fate, but it’s likely that collisions are commonplace in the late stages of planet formation, and many researchers believe that Earth’s Moon was the result of the collision of our planet with a Mars-sized planet about 4.5 billion years ago. Scientists at Durham University and the University of Glasgow have recently developed computer simulations tracking atmosphere loss during such collisions using the COSMA supercomputer, which is part of the DiRAC High-Performance Computing facility in Durham.
The work involves smoothed particle hydrodynamics (SPH) simulations to model giant impacts. The planets are modeled as digital ‘particles’ and run through a process of evolution under different conditions of gravity and pressure. This work appears to be the first time the erosion of thin atmospheres has been studied with full 3D, high-resolution simulations of giant impacts at various impact angles and speeds, injecting a range of atmospheric masses for the proto-Earth. The work takes advantage of a program called SWIFT to model hydrodynamics and gravity.
We can get a look at the results in a new paper in the Astrophysical Journal. The authors have created cross-section animations of the early stages of such collisions, modeling not only head-on strikes but grazing impacts like the one thought to have produced our Moon. They likewise model fast as well as slow giant impacts using 100 million particles. As you can see in the image below, these are color-coded for material as well as internal energy.
Image: Still image cross-section showing the impact (inset) and aftermath (main picture) of a 3D simulation of a giant planetary impact using 100 million particles, coloured by their internal energy, similar to their temperature. Credit: Dr Jacob Kegerreis, Durham University.
Jacob Kegerreis (Durham University) places the work in context:
“We know that planetary collisions can have a dramatic effect on a planet’s atmosphere, but this is the first time we’ve been able to study the wide varieties of these violent events in detail. In spite of the remarkably diverse consequences that can come from different impact angles and speeds, we’ve found a simple way to predict how much atmosphere would be lost. This lays the groundwork to be able to predict the atmospheric erosion from any giant impact, which would feed into models of planet formation as a whole. This in turn will help us to understand both the Earth’s history as a habitable planet and the evolution of exoplanets around other stars.”
We learn that the type of impact tells the tale in terms of how much atmosphere is lost. Higher-speed and/or head-on impacts create the greatest atmospheric loss, sometimes completely destroying not just the atmosphere but parts of the planet’s mantle layer beneath the crust. Earth’s likely grazing impact is the kind that disrupts but does not destroy the atmosphere. What actually happened on Earth during this period is not known, but the researchers believe our planet lost somewhere between 10 and 50 percent of the atmosphere.
Atmospheric survival is not assured in the early planet-forming environment, a time when planetary embryos collide after their accretion from a proto-planetary disk. To acquire an atmosphere, planets accrete gases from surrounding materials as well as from impacting volatiles, eventually outgassing volatiles from within. That means an infant rocky world must deal with not only the radiation pressure of its star but small and large impacts. In the case of Earth, we have Moon-formation scenarios but little information about the proto-Earth’s crust, ocean or atmosphere. Consider the evidence from early Solar System materials:
Focusing on the atmosphere, the Earth’s volatile abundances are remarkably different from those of chondrites (Halliday 2013), which act as a record of the condensable components of the early Solar System. Specifically, nitrogen and carbon are depleted compared with hydrogen, which could be explained by the loss of N2 and CO2 with an eroded atmosphere while retaining H2O in an ocean (Sakuraba et al. 2019). Unlike the abundances, the isotope ratios match those of primordial chondrites. Hydrodynamic escape – driven by XUV radiation from the star or heat from the planet below – preferentially removes lighter isotopes, while impacts remove bulk volumes of atmosphere. This suggests that impacts (not necessarily giant ones) are the primary loss mechanism, driving fractionation by removing more atmosphere than ocean while preserving isotope ratios…
Interestingly, there is at least one paper positing two occasions where Earth lost its atmosphere based on the relative abundances of helium and neon in mantle reservoirs of different ages. If giant impacts are relatively common, this would ensure that exoplanets in mass ranges between Earth and Neptune would show wide variation in atmospheric masses. Impacts, in other words, take precedence over irradiation and photoevaporation, according to the authors.
In Earth’s case, the ‘big whack’ that created the Moon may have been only part of the story:
…only around 10% of the atmosphere would have been lost from the immediate effects of the collision. This suggests that the canonical impact itself cannot single-handedly explain the discrepancies between the volatile abundances of the Earth and chondrites by eroding the early atmosphere, compared with alternative, more-violent Moon-forming scenarios. However, the caveat of ‘immediate’ erosion is important, because we have here only considered the direct, dynamical consequences of a giant impact.
The paper goes on to point to the thermal effects of such an impact, producing significant atmosphere erosion. Interestingly, the presence of an ocean can enhance atmosphere loss, creating the higher figure of 50 percent loss mentioned earlier. This work makes it clear how little we know about atmospheric loss, but it does produce a scaling law for total atmospheric erosion for a variety of scenarios involving Mars-sized impactors.
Promising targets for future study include: investigations of different impactor and target masses; extensions to both more massive and even thinner atmospheres; the inclusion of an atmosphere on the impactor as well as the target; and testing the dependence on the planets’ materials, internal structures, and rotation rates. This way, robust scaling laws could be built up to cover the full range of relevant scenarios in both our solar system and exoplanet systems for the loss and delivery of volatiles by giant impacts.
The paper is Kegerreis et al., “Atmospheric Erosion by Giant Impacts onto Terrestrial Planets,” Astrophysical Journal Vol. 897, No. 2 (15 July 2020). Abstract / preprint.
SPOCK: Modeling Orbital Scenarios around Other Stars
In addition to being a rather well-known character on television, SPOCK also stands for something else, a software model its creators label Stability of Planetary Orbital Configurations Klassifier. SPOCK is handy computer code indeed, determining the long-term stability of planetary configurations at a pace some 100,000 times faster than any previous method. Thus machine learning continues to set a fast pace in assisting our research into exoplanets.
At the heart of the process is the need to figure out how planetary systems are organized. After all, after the initial carnage of early impacts, migration and possible ejection from a stellar system, a planet generally settles into an orbital configuration that will keep it stable for billions of years. SPOCK is all about quickly screening out those configurations that might lead to collisions, which means working out the motions of multiple interacting planets over vast timeframes. To say this is computationally demanding is to greatly understate the problem.
Image: While astronomers have confidently detected three planets in the Kepler-431 system, little is known about the shapes of the planetary orbits. The left-hand image shows many superimposed orbits for each planet (yellow, red and blue) consistent with observations. Using machine learning methods, researchers removed all unstable configurations that would have resulted in planetary collisions and would not be observable today, leaving only the stable orbits (right-hand image). Using previous methods, this process would have taken more than a year of computing time. The new method instead takes just 14 minutes. Credit: D. Tamayo et al./Proceedings of the National Academy of Sciences 2020.
Thus we rule out dynamically unstable possibilities in, compared to older methods, the blink of an eye, a useful fact for making sense of planetary systems we can observe, and possibly giving us information about the composition of some of these worlds. Bear in mind that while we’ve discovered more than 4,000 planets around other stars, almost half of these occur in multi-planet systems, so understanding orbital architectures is vital.
The lead author on this work is Daniel Tamayo, a NASA Hubble Fellowship Program Sagan Fellow in astrophysics at Princeton. As you would expect, Tamayo and his co-authors relish the resonance of the acronym, as witness the note that closes their paper:
We make our ≈ 1.5-million CPU-hour training set publicly available (https://zenodo.org/record/3723292), and provide an open-source package, documentation and examples (https://github.com/dtamayo/spock) for efficient classification of planetary configurations that will live long and prosper.
A good choice, and an acronym with almost as much going for it as my absolute favorite of all time, TRAPPIST (Transiting Planets and Planetesimals Small Telescope), which contains within it not only a description of the twin telescopes but a nod to some of the world’s best beers (the robotic telescopes are operated from a control room in Liège, Belgium).
Thus we move from brute force calculations run on supercomputers to machine learning methods that quickly eliminate unstable orbital configurations, replacing tens of thousands of hours of computing time with the time it takes to quaff a Westmalle Tripel (well, maybe a Westmalle Dubbel). Configurations that would, over the course of a few million years, result in planetary collisions — the team calls these ‘fast instabilities’ — are identified.
The paper notes the relevance of the work to compact systems and the ongoing observations of TESS:
In the Kepler 431 system with three tightly packed, approximately Earth-sized planets,we constrained the free eccentricities of the inner and outer pair of planets to both be below 0.05 (84th percentile upper limits). Such limits are significantly stronger than can currently be achieved for small planets through either radial velocity or transit duration measurements, and within a factor of a few from transit timing variations (TTVs). Given that the TESS mission’s typical 30-day observing windows will provide few strong TTV constraints [Hadden et al., 2019], SPOCK computationally enables stability constrained characterization as a productive complementary method for extracting precise orbital parameters in compact multi-planet systems.
SPOCK can’t provide a solution to all questions of long-term stability, as Tamayo acknowledges, but by identifying fast instabilities in compact systems, where the issues are the most obvious, it can sharply reduce the options and allow astronomers to focus on likely solutions. Freeing up a significant amount of computer time for other uses is a collateral benefit.
The paper is Tamayo et al., “Predicting the long-term stability of compact multi-planet systems,” Proceedings of the National Academy of Sciences July 13, 2020 (preprint).
Two Unusual Brown Dwarfs
I track brown dwarfs closely because they have so much to teach us about the boundary between planet and star. I’m also intrigued by what might be found on a planet orbiting one of these objects, though life seems unlikely. Brown dwarfs begin losing their thermal energy after formation and continue cooling the rest of their lives, a period I’ve seen estimated at only about 10 million years. We know nothing about how long abiogenesis takes — not to mention how common it is — but the outlook for brown dwarf planets and astrobiology seems bleak.
It’s intriguing, though, that we’ve identified a number of brown dwarfs with planetary systems, including 2M1207b, MOA-2007-BLG-192Lb, and 2MASS J044144b, and in the latest news from the NEOWISE mission, we have two brown dwarfs that stand out for other reasons. What used to be the Wide-Field Infrared Survey Explorer would become a tool for the detection of near-Earth objects, but data from the earlier WISE incarnation is still turning up red and brown dwarfs. Along the way, the Backyard Worlds: Planet 9 project, armed with the talents of 150,000 citizen scientists, has more than proven its worth, but more on that in a moment.
Image: This artist’s concept shows a brown dwarf, a ball of gas not massive enough to power itself the way stars do. Despite their name, brown dwarfs would appear magenta or orange-red to the human eye if seen close up. Credit: William Pendrill (CC BY).
The brown dwarfs in question are notable because of their extreme lack of iron. In fact, a typical brown dwarf would have up to 30 times more iron and other metals than we find in either. Low levels of metallicity are something we would expect in ancient exoplanet systems, where supernovae spewing metals were scarce in nearby space, but the mechanisms involved remain problematic. Marc Kuchner is principal innvstigator for Backyard Worlds: Planet 9:
“A central question in the study of brown dwarfs and exoplanets is how much does planet formation depend on the presence of metals like iron and other elements formed by multiple earlier generations of stars. The fact that these brown dwarfs seem to have formed with such low metal abundances suggests that maybe we should be searching harder for ancient, metal-poor exoplanets, or exoplanets orbiting ancient, metal-poor stars.”
Adam Schneider (Arizona State) found one of the brown dwarfs, WISE 1810, back in 2016. Enter Backyard Worlds: Planet 9, which counts among its discoveries more than 1,600 brown dwarfs as well as the oldest known white dwarf, surrounded by a debris disk. Schneider was able to use WiseView, a tool created by Backyard Worlds citizen scientist Dan Caselden, to track the object’s motion, an indication of its relative proximity. The second brown dwarf is WISE 0414, this one discovered by a group of citizen scientists whose names deserve recognition: Paul Beaulieu, Sam Goodman, William Pendrill, Austin Rothermich, and Arttu Sainio.
Image: These images show the newly discovered brown dwarf WISE 1810 as seen with the WiseView tool. The object has an orange hue in these false-color images. In both images, a gray arrow on the left indicates the object’s position in 2010; the black arrow on the right indicates its position in 2016. Credit: Schneider et al. 2020.
The needed follow-up by astronomers using near-infrared spectroscopy confirmed that what the citizen scientists had found by working through hundreds of WISE images were indeed brown dwarfs. At the Jet Propulsion Laboratory, Federico Marocco and Eric Mamajek confirmed WISE 0414 using the Hale Telescope at Palomar Observatory in California. The unusual composition of both objects was apparent, as noted in the paper:
We find that the high proper motion objects WISEA 0414?5854 and WISEA 1810?1010 have exceptionally unusual spectroscopic and photometric properties that likely reflect significantly subsolar metallicities. The best-fitting models for these objects suggest very low metallicities ([Fe/H] ? ?1), though no single model provides a satisfactory fit across all wavelengths. Further astrometric and spectroscopic observations are warranted to better characterize these enigmatic systems.
What caught my eye in this paper is its discussion of what the authors call a “stellar-substellar transition phase.” Metal-poor brown dwarfs — and these are extreme examples — show higher rates of cooling than other dwarfs. Moreover, hydrogen fusion does not stop abruptly as we scale down from star to brown dwarf, but rather, can continue in an interesting way:
…covering a narrow range of masses and large range of effective temperatures over which “unstable fusion” can occur. The masses encompassed by this transition, and the range of temperatures it spans depend on the metallicity and age of the population, with a more pronounced spread expected for metal-poor halo subdwarfs.
Some seven objects meeting this description have previously been found. WISE 1810 and 0414 have the lowest masses and effective temperatures yet discovered in this grouping. The authors point out as well that using proper motion instead of colors to identify cold, low luminosity objects has its advantages, including detecting dwarfs with spectra as unusual as these.
The paper is Schneider et al, “WISEA J041451.67-585456.7 and WISEA J181006.18-101000.5: The First Extreme T-type Subdwarfs?” accepted at the Astrophysical Journal (preprint).
What Can SETI Scholars Learn from the Covid-19 Pandemic?
The pandemic has everyone’s attention, but it’s not too early to ask what lessons might be learned from public response to it. In particular, are there nuggets of insight here into what might occur with another sudden and startling event, the reception of a signal from another civilization? John Traphagan takes a look at the question in today’s essay. Dr. Traphagan is a social anthropologist and Professor of Religious Studies, in the Program in Human Dimensions of Organizations, and Mitsubishi Fellow at the University of Texas at Austin. He also holds a visiting professorship at Waseda University in Tokyo, as well as being a board member of SSoCIA, the Society for Social and Conceptual Issues in Astrobiology. His research focuses on the relationship between science and culture and falls into two streams: life in rural Japan and the culture and ethics of space exploration. John has published numerous scientific papers and several books, including Science, Culture, and the Search for Life on Other Worlds (Springer, 2016). His most recent book, Cosmopolitan Rurality, Depopulation, and Entrepreneurial Ecosystems in 21st Century Japan, was published in 2020 by Cambria Press. This essay is a shorter version of a more detailed paper that is slated to appear in JBIS.
by John W. Traphagan
For people interested in the potential outcome of contact with extraterrestrial life, whether intelligent or otherwise, the Covid-19 pandemic is a timely case-study that can help us think through some of the challenges first Contact with ETI or even simple life might present for humans, because it represents a potential existential threat to the entire population of our planet. And that threat has forced governments into actions with widespread social, political, and economic implications up to world-wide depression.
Like the emergence of Covid-19, first contact, in particular, has the potential to set in motion political machinations on the part of nation-states as national security interests are identified. If resources or information associated with contact are considered important to control by governments (see our earlier article On SETI, International Law, and Realpolitik in Centauri Dreams), then unexpected events which threaten global political and economic stability, regardless of the risks associated with contact itself may unfold. Indeed, this has been one of the outcomes of the Covid-19 pandemic in which there was early concern about the potential impact of policy responses to the pandemic and the associated collapse in oil prices. This could easily have led to political instability in already unstable areas of the world such as parts of the Middle East.
In general, successful human response to a pandemic (such as Covid-19) is based on a combination of credible action by governments, strong leadership from international organizations such as WHO, and responsible behavior by nation-states concerned with the well-being of their populations. The same factors apply to contact with extraterrestrial life. In the event of an encounter with life from another world, public safety and health (including mental health) depend on: 1) timely and credible actions by governments where contact is made; 2) clear direction and leadership from international organizations and the scientific community to coordinate a global response; and 3) responsible behavior on the part of governments naturally concerned with protecting parochial national interests.
In the case of non-intelligent extraterrestrial life, such as microbial life, the parallels with the Coronavirus pandemic are obvious, but are still complicated by the fact that we do not know how introduction of an alien microorganism into Earth’s ecosystem would affect life on Earth. But contact with any form of extraterrestrial life presents risks that have the potential to place our species in a position similar to what we are currently facing with Covid-19, which represents a global threat necessitating a global response.
So, what can we learn from the pandemic? There are at least four tactical points to take away from our current situation:
1. Differential values play a significant role in how governments respond to the pandemic, despite the fact that Covid-19 represents a global threat to human life.
2. Each nation-state is largely going it alone in assessing the level of threat and developing appropriate responses to the pandemic based on risk assessments.
3. There has been limited cooperation and some governments have withdrawn from the international political environment or even tried to thwart international organizations such as WHO.
4. Responses to government rules such as wearing masks in public have varied and in some cases been resisted.
The key point to take away from the Covid-19 pandemic for those interested in the potential risks and influences of contact with ETI is that different responses and policies are products of cultural, ideological, and political variations among and within nations of the world. Factors such as population density and socio-economic status also play a significant role in how the virus has spread and how governments and individuals have responded. And structural patterns of social and political life—such as the presence of systemic racism in the US—clearly shape how different people are affected by the pandemic. There is no reason to think contact with ETI would be different.
Culture matters. There are at least three strategic lessons we can draw from this observation:
• The world is unlikely to react as one. Even if it is determined that ETI poses an existential threat to humanity a well-coordinated and unified response to either physical or remote contact with ETI is unlikely, unless significant changes in human political behavior occur.
• Culture will drive state and sub-state response. Cultural variation evident in complex and conflicting value systems will influence nation-states and other groups as they interpret and respond to contact.
• Diversity of perspective, a significant advantage in assessing options, can be a hindrance to unified action. Diverse cultural, political, and economic characteristics that humans display and experience have the potential not only to provide multiple options in responding to contact, but may work against a successful response.
We should be concerned. In the face of potential existential threat, unified and coordinated action is central to successful results—thousands of years of experience with warfare have shown this clearly to be the case. Unless we prepare for the fact of diversity in human responses to contact, rather than being a source of strength and options when facing contact that diversity may work against a coordinated effort.
It would help for the SETI scientific community to move away from the often tacit assumption that humans live and operate within a single, unified (or monolithic) civilization to a concept of both our world and potential other worlds that expects diversity in cultures, interpretations, and likely responses to a contact scenario. Recognition of the potential for contact to stimulate increased conflict and disagreement among human groups—again as is evident in the Coronavirus pandemic—rather than to unify humanity in response to a real or perceived global threat, would represent a good starting point for thinking about protocols for contact.
Spin-Orbit Alignment: A Lesson from Beta Pictoris?
I hadn’t planned to write about the recent work out of the University of Exeter on Beta Pictoris, but yesterday’s article on KELT-9b dealt with planetary alignment, given that the planet shows marked spin-orbit misalignment. At Beta Pictoris, an international team of researchers led by Exeter’s Stefan Kraus has carried out measurements of the spin-orbit alignment of Beta Pictoris b, a gas giant orbiting a young star in an orbit about as distant as Saturn from the Sun. Here we have the first spin-orbit alignment measurement of a directly imaged planetary system.
How such alignments occur is clearly relevant to planet formation theories. There’s a bit of astronomy history here, for spin-orbit issues became significant for both Immanuel Kant (1724-1804) and Pierre-Simon Laplace (1749-1827), who looked at spin-orbit alignment in our own Solar System. It was apparent to both that the planets known to them orbited the Sun not only in alignment with each other but in alignment with the Sun’s axis as well. Hence the idea that the entire system formed from a rotating planetary disc, and a flattened one at that.
Other planetary systems may follow different paths of development, as Kraus notes:
“It was a major surprise when it was found that more than a third of all close-in exoplanets orbit their host star on orbits that are misaligned with respect to the stellar equator. A few exoplanets were even found to orbit in the opposite direction than the rotation direction of the star. These observations challenge the perception of planet formation as a neat and well-ordered process taking place in a geometrically thin and co-planar disc.”
Which is to say that close-in exoplanets can depart markedly from the apparent norm, making the study of these hot Jupiters significant for initial formation scenarios. Kraus and company went to work with the GRAVITY instrument at the Very Large Telescope Interferometer (VLTI) in Chile, exploiting the fact that a star’s spectral lines show a spatial displacement — an exceedingly small one, to be sure — caused by gas absorption in the star’s atmosphere. The team used this effect to determine the orientation of the star’s rotation axis.
Image: The new observations show that the stellar equator (right) is aligned with the orbital plane of the planet Beta Pictoris b (middle) and the plane of the extended disc of debris material that surrounds the system (left). Credit: ESO/A.M. Lagrange; ESO/A.M. Lagrange/SPHERE consortium.
At Beta Pictoris, some 63 light years from Earth, a displacement about 1/100th the apparent diameter of the star itself is used to demonstrate that planet and star are as well-aligned as our own Solar System. Thus the classic model of planet formation seems to apply, with implications for the hot Jupiters we see that demonstrate marked spin-orbit misalignment. From the paper (internal references removed for brevity):
Our finding of spin-orbit alignment for ? Pic b suggests that this planet formed in a coplanar disks without primordial misalignments. This is in contrast to theories that describe the occurence of obliquities as a natural by-product of the star formation process, for instance through turbulent motions in the star-forming cloud and fluid-dynamical effects during disk formation. In case our finding of a well-aligned system is representative for wide-separation planets, it would suggest that the population of Hot Jupiters on oblique orbits (found in RM survey at orbit separations between ? 0.02 and 0.3 au) are likely transferred to oblique orbits through dynamical processes post-formation. Possible mechanisms include planet-planet scattering, stellar flybys, or the Kozai-Lidov mechanism, where a wide companion orbiting a close binary on a highly inclined orbit can induce oscillations in inclination/eccentricity of the close pair.
Image: To derive the stellar rotation axis of Beta Pictoris the team used the unique high angular and high spectral resolution mode of VLTI/GRAVITY to measure shifts in the centroid position in the hydrogen Brackett-gamma absorption line on micro-arcsecond scales. In the blue-shifted part of the absorption line, the centroid of the emission is displaced to the North-East, which indicates that the South-Western hemisphere of the star is approaching the observer. Credit: Kraus et al. / University of Exeter.
Much depends on just how representative Beta Pictoris b really is of gas giants with wide separation from their star. The authors propose a new high-spectral resolution interferometric instrument at the VLTI to measure the spin-orbit alignment of hundreds of gas giants, dramatically increasing the data on long-period planets. Kraus is involved in a proposed VLTI
visitor instrument called BIFROST that could enable such an observing campaign. This, in turn, should stoke the discussion of planet formation and system evolution when it comes to architectures as extreme as the one we see at KELT-9.
The paper is Kraus et al., “Spin-Orbit Alignment of the ? Pictoris Planetary System,” Astrophysical Journal Letters, Vol. 897, No. 1 (29 June 2020). Abstract / Preprint.
Building the Psyche Asteroid Explorer
If all goes well (an often perilous assumption, as JWST so frequently reminds us), NASA’s Psyche mission to the intriguing asteroid of the same name will lift off in about two years. We’re now moving out of the design and planning stage into manufacturing the spacecraft hardware, this following a period of testing on the core engineering models that will deliver the spacecraft to its target in the main asteroid belt. The critical design review, a shakeout of the three science instruments and engineering subsystems, has just been passed with flying colors.
Principal investigator Lindy Elkins-Tanton (Arizona State University) calls the process “one of the most intense reviews a mission goes through in its entire life cycle.” True enough, as everything from telecommunications, power and propulsion must pass the test, not to mention the flight avionics and computing systems. We’re a long way past the digital blueprint stage, having followed it up with prototypes and engineering models of the science instruments and engineering subsystems, all performed before the flight hardware could be built.
“This is planning on steroids” said Elkins-Tanton. “And it includes trying to understand down to seven or eight levels of detail exactly how everything on the spacecraft has to work together to ensure we can measure our science, gather our data and send all the data back to Earth. The complexity is mind-boggling.”
So what’s next? Assembling and testing of the full spacecraft is to begin in February of 2021, with a deadline of April 2021 for each instrument to be delivered to the main clean room at the Jet Propulsion Laboratory. This is going to be a fascinating mission to watch from the technology standpoint, as it will involve a demonstration of the Deep Space Optical Communications system (DSOC), intended to improve communications performance by 10 to 100 times without corresponding increases in mass, volume or power.
We’re going to want to follow DSOC closely because of its deep space implications. The plan is to deploy advanced lasers in the near infrared, and a look through NASA materials on the project shows three technologies — a low-mass spacecraft pointing assembly; a flight laser transmitter; and a pair of photon-counting detector arrays — being integrated into the DSOC system, communicating with a ground-based receiver to enable efficient communications. All this by way of exploring a future that will one day demand high-definition imagery, live video feeds and real-time data transmission for long-duration missions to deep space.
So while it’s a demonstrator, DSOC is an important one, and the Psyche mission offers a test of the system’s ability to cull faint laser signals out of a noisy background. Beyond DSOC, engineers at Maxar Technologies in Palo Alto (CA) are building the main body of the spacecraft (the Solar Electric Propulsion Chassis), attaching propulsion tanks enroute to delivery early next year to JPL, followed not long after by the solar arrays critical to power the spacecraft’s systems.
The avionics subsystem is being built at JPL, where Psyche Project Manager Henry Stone notes:
“One of the things we pride ourselves on in these deep-space missions is the reliability of the hardware. The integrated system is so sophisticated that comprehensive testing is critical. You do robustness tests, stress tests, as much testing as you can – over and above. You want to expose and correct every problem and bug now. Because after launch, you cannot go fix the hardware.”
Imagine having a job where you can talk about your involvement in multiple deep space missions, the kind of thing that makes me wish for a quick rejuvenation and a new career doing exactly that at places like JPL. And then to watch the mission fly… Psyche is to launch in August of 2022, with a Mars gravity assist in May of 2023 and arrival at Psyche in 2026.
Image: This artist’s concept, updated as of June 2020, depicts NASA’s Psyche spacecraft. Set to launch in August 2022, the Psyche mission will explore a metal-rich asteroid of the same name that lies in the main asteroid belt between Mars and Jupiter. The spacecraft will arrive in early 2026 and orbit the asteroid for nearly two years to investigate its composition. Credit: NASA/JPL-Caltech/ASU/Peter Rubin.
What an interesting destination we’re dealing with. Psyche is made up mostly of iron and nickel, making it much like Earth’s core, so we may be looking at the stripped core of a differentiated planetesimal, unless the asteroid formed as a body rich in iron. If its mantle was stripped away, when did that occur, and how? Exactly how will this asteroid compare to known stony, icy objects we’ve visited? We can’t see planetary cores, but Psyche may give us a look into a planetesimal core from the era of collisions and accretion that produced the terrestrial planets.
The spacecraft will fly with a magnetometer to measure the asteroid’s magnetic field, along with a multispectral imager to collect images and data about the object’s composition and topography. Spectrometers will analyze the surface to determine its chemical abundances. The propulsion system is an electric hall thruster using xenon as the propellant. ATLO is next — Assembly, Test and Launch Operations — all beginning in February of next year. Love those NASA acronyms!
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