Centauri Dreams
Imagining and Planning Interstellar Exploration
Towards Producing Food in Space: ESA’s MELiSSA and NASA’s VEGGIE
Before we can go to the stars we’ll need to build a robust infrastructure in our own Solar System. While most attention seems to be devoted to propulsion issues, I’m convinced that an equally critical question is how we can create and sustain closed-loop life support systems for such missions. Our point man on this is Ioannis Kokkinidis, who brings a rich background from his Master of Science in Agricultural Engineering (Agricultural University of Athens) and Mastère Spécialisé Systèmes d’informations localisées pour l’aménagement des territoires from AgroParisTech and AgroMontpellier, along with a PhD in Geospatial and Environmental Analysis from Virginia Tech. Here Dr. Kokkinidis discusses what has been done so far in the matter of growing foods in space, and takes us back to a mission that might have been, a manned flyby of Venus. As Ioannis notes, getting space foods up to the sumptuous standards of Greek cuisine will indeed be a challenge, but we’re at least making progress.
by Ioannis Kokkinidis
Introduction
A few years ago the Greek press was buzzing with a story about the European Space Agency asking two French caterers to create a meal for Mars based on nine foods: rice, onion, tomato, soybeans, potatoes, lettuce, spinach, wheat and spirulina. The news story was the first time I was exposed to the ESA’s MELiSSA project, which aims to produce food through an artificial ecology for solar system colonization, including space stations and spaceships. A somewhat related American project to grow food in microgravity is the VEGGIE project, which has recently made headlines by growing several plants which were consumed by astronauts on the International Space Station. The subject of this post is to describe two leading edge projects to produce food in a space environment. I am not and have never been affiliated with either of the projects, I have never met any of the people associated with either project nor is anyone asking me to publicize these projects. I am simply a learned amateur, albeit one with graduate degrees in agronomy who is fascinated by the projects and their potential.
MELiSSA
The Micro-Ecological Life Support System Alternative (MELiSSA) initiative is a European Space Agency project with almost 30 years of history behind it. Its origin lies in the flight of two tubes of nostoc algae in a recirculating system to space on the Chinese FSW-0 No 9 recoverable mission in 1987. In 1989 the MELiSSA Foundation was formed to create a closed loop artificial ecosystem for long spaceflights, based on aquatic ecosystems. MELiSSA aims to replace the current generation of mechanical Environment Control and Life Support Systems (ECLSS) with a new one based on biology, which will not only remove metabolic waste from the various streams (air, water) but also produce food in the process. The tool to accomplish this task is the MELiSSA cycle.
Fig 1: The MELiSSA cycle © ESA from http://www.melissafoundation.org/. The cycle has five compartments.
Compartment I: The liquefying compartment
This compartment gathers all the organic waste created in the spaceship and aims to convert it into ammonium, CO2, volatile fatty acids and minerals. For biosafety and efficiency reasons this compartment operates in thermophilic conditions (i.e. 55 C). The main biological functions involved are proteolysis, saccharolysis and cellulolysis. While saccharolysis is trivial, after all sugars are a main biological source of energy for most species, proteolysis and cellulolysis have proven more difficult to optimize, with proteolysis having an efficiency of 70% and cellulolysis of 44% in the cycle. Considering that despite billions in public and private investment in Europe and the United States to increase cellulolysis efficiency, cellulosic ethanol has not entered the market in meaningful quantities, these efficiency figures are pretty decent for the current state of technology.
Compartment II: The photoheterotrophic compartment
In this compartment volatile fatty acids, ammonium and minerals from component I are further broken down by Rhodospirillum rubrum bacteria into minerals and ammonium. The bacterium has proven very efficient in the process. For more, see this brief video.
Compartment III: The nitrifying component
This compartment has as feedstock urine from the crew, ammonium from compartment II and oxygen from compartment IV. It uses a mix of Nitrosomonas and Nitrobacter bacteria to oxidize ammonium into nitrates, which plants prefer as their nitrogen source
Compartment IV: The photoautotrophic compartment
This compartment is intended is to grow actual food and produce oxygen for the crew. It is divided into two parts: the algae compartment and the higher plant compartment.
- IVa: The algae compartment
In the current iteration of MELiSSA, the cyanobacterium Arthrospira platensis has been selected as the organism grown. This is one of two species (the other being Arthrospira maxima) that are known colloquially as spirulina. Several photobioreactors with this bacterium have been built and a predictive model has been created and validated experimentally.
- IVb: The higher plant component
This component is intended to provide both food and water for the crew. While several crops have been evaluated in the course of the project, 8 have been selected: wheat, tomato, potato, soybean, rice, spinach, onion and lettuce. Currently the status of this component is far less mature than the algae component, they are still compiling the biomass production rates, nutrient and mineral compositions of the plants based both on outside work and their own research.
Component V: The crew component
This is simply the crew component of the spaceship, composed of the astronauts and cosmonauts who consume the food, produce CO2, urine and other waste which is sent to the components of the cycle.
Status
Like all ESA programs, the intention of MELiSSA is not only to provide technology for space exploration but also for applications on earth. It has helped explored the concept of closed loop ecosystems, which are critical to colonize other bodies but also to help understand how earth ecosystems work. A pilot plant that uses rats as the trial crew (component V) has been running since 2009 at the School of Engineering of the Autonomous University of Barcelona. The greywater treatment plant of the Concordia station in Antarctica uses MELiSSA technology while a sensor for CO2 monitoring of sparkling wine has been commercialized. The BIOSTYR© bacterial support for wastewater treatment, commercialized by Veolia, has been derived from MELiSSA compartment III research. Andreas Mogensen conducted two MELiSSA related experiments during Expedition 44 to the ISS, consuming spirulina infused snack bars created by MELiSSA which he also shared with his fellow astronauts in the DEMES experiment, and keeping an eye on some micro-organisms and how they recycle our waste in space in the Bistro experiment.
The most recent news item associated with MELiSSA was the opening of a new facility called AlgoSolis to cultivate algae at an industrial scale in Saint-Nazaire in France. It seems that it is the intention of the project to construct a MELiSSA loop in the ISS or a future space station, though the concept still requires technological maturation. This is a very interesting project to follow in the future.
VEGGIE
The Vegetable Production System (VEGGIE) experiment is an experiment of NASA’s Human Exploration and Operations Mission Directorate to grow salad crops in the International Space Station run by the Kennedy Space Center and Orbital Technologies Corporation (ORBITEC) of Madison WI, a subsidiary of Sierra Nevada Corporation. It is not the first plant growth experiment in space, the Bulgarian/Russian SVET SG (Space Greenhouse) experiment grew various plants on a series of experiments aboard the Mir space station in the 1990’s, several of those in partnership with NASA. These however were biological experiments intended to study plant growth in microgravity; cosmonauts were not supposed to consume the plants though some have admitted to nipping bits. The Veggie experiment intends to grow fresh food for astronaut consumption on the ISS. So far the experiment has had three phases, named Veg-01, Veg-02 and Veg-03 and has been conducted during Expeditions 35/36, 39/40, 41/42, 43/44, 45/46, 47/48 and 49/50.
Overview
VEGGIE builds on heritage from the SVET SG experiment on Mir, the Biological Production System of Expedition 4 and the failed efforts of Expedition 2 astronaut Jim Voss and Expedition 6 astronaut Don Pettit to grow plants on old food bags (see http://www.orbitec.com/documents/Veggie-APH.pdf). It is made of a plant growth chamber which is made of modular planting pillows, an LED bank for lighting and a fan for humidity control. It weighs 7.2 kg and has external dimensions 53 by 40 cm (=0.212 m2) with a root mat of 0.16 m2 and a growth height of 45 cm. It provides lighting and nutrients, having a 2 l fluid reservoir, but depends on the ISS ECLSS for temperature and CO2. It draws 115 Watts of peak power, is able to support different day/night lengths for experiments and contains a data logger that records temperature, humidity and pCO2 (see http://spaceflight101.com/iss/veggie/). The plants grow on the planting pillows, containing the substrate, fertilizer and seeds, which are of single use and arrive in ready-to-activate form from earth. It is deployed in an EXpedite the PRocessing of Experiments to Space Station (EXPRESS) Rack.
Veggie hardware validation test (Veg-01)
Veg-01 had a variety of goals including a shakedown of the system to see if the experimental apparatus works in space. VEGGIE was delivered to the ISS by the SpaceX CRS-3 mission launched on April 18 2014. Expedition 39 flight engineers Steve Swanson and Rick Mastracchio installed it at the European Columbus module on May 7 2014 and activated it the next day. They used 6 planting pillows of ‘Outredgeous’ red romaine lettuce, having a substrate of two different sizes of arcillite (3 of one and 3 of the other), a calcined clay media used on baseball fields that included fertilizer. Two sizes were used so as to compare root zones between the two media, so as to determine water and root distribution for future investigations.
The pillows then received about 100 milliliters of water each to initiate plant growth. 24 hours after activation on the ISS an identical VEGGIE experiment was activated on the ground at KSC to serve as control (see also http://spaceflight101.com/iss/veggie/). Steve Swanson, who by that time had become the commander of Expedition 40, harvested VEGGIE on June 10, 33 days after planting. The next day the control experiment was harvested on the ground. Two plants on the ISS experiment were lost due to drought stress. The tops of the surviving lettuce were cut away from the plant pillows and swabbed for microbial samples. The pillows and bellows also were swabbed.
The plants, sample swabs and a couple of the plant pillows were packaged and placed in the ISS’ minus-eighty-degree freezer for storage. The crop, along with the pillows and sample swabs were returned from the ISS on the SpaceX CRS-4 mission which splashed down on October 25 2014. The lettuce was analyzed for microbes on the ground and found to be within safe limits, for that matter it had a lower microbial count than what is usual for lettuce on the market. A second crop was activated in early July 2015 by Commander Scott Kelly, who had arrived on the ISS on March 28 2015. Thirty three days later they were harvested in turn, having lost only one plant and on August 10 2015 expedition 44 astronauts wiped the lettuce leaves with citric acid-based, food safe sanitizing wipes before consuming them raw. See http://www.nasa.gov/mission_pages/station/research/news/meals_ready_to_eat.
Veg-02
There is conflicting information online whether Veg-02 is just the zinnia experiment (described below), if it also included the second lettuce experiment mentioned in the previous section or for that matter if there even was a Veg-02 experiment, rather than skipping the number and moving directly from Veg-01 to Veg-03. In any case what follows is a detailed description of the zinnia experiments compiled from available online sources.
The planting pillows with the ‘Profusion’ zinnia seeds for the Veg-02 experiment were carried to orbit along with the rest of the VEGGIE apparatus on the SpaceX CRS-3 resupply flight. These plants received quite a bit of attention from Commander Scott Kelly during his Year in Space mission; he took care of the plants and tweeted about them several times. On November 16 2015 astronaut Kjell Lindgren activated the experiment, which was the first flowering plant experiment grown on the ISS, 3 days after activation of the control experiment at KSC. The experiment was composed of a total of four plants and lighting was set on a photoperiod of 10 hours day and 14 hours night in order to stimulate flowering.
The plants started to grow [http://www.nasa.gov/image-feature/first-flower-grown-in-space-stations-veggie-facility] but two weeks into their growth period, NASA astronaut Kjell Lindgren noted that water was seeping out of some of the wicks – the white flaps that contain the seeds and stick out of the tops of the plant pillows. The water partially engulfed three of the plants. Within 10 days, scientists noted guttation on the leaves of some of the plants. Guttation is when internal pressure builds in the plants and forces excess water out of the tips of the leaves. It occurs when a plant is experiencing high humidity.
Additionally, the zinnia leaves had started to bend down and curl drastically. This condition, called epinasty, can indicate flooding in the roots. The anomalies all pointed to inhibited air flow in the plant growth facility that, when coupled with the excess water, could have the potential to cause major problems to the crop. Commander Kelly, who took over the experiment after Lindgren returned on Earth December 10, noted that the plants had grown a mold. On December 22nd, after late night consultations with the ground crew, he cut the two affected plants off and put them in cold storage for return to Earth. Then he increased the fan speed to reduce humidity. Scott Kelly, though, reported on Christmas Eve that the reverse problem was currently happening, the plants were getting too dry. Watering was scheduled for December 27, but despite the advice of the ground crew, he decided to take the initiative and water them on Christmas Eve. He then tweeted one of his most memorable tweets.
Our plants aren't looking too good. Would be a problem on Mars. I'm going to have to channel my inner Mark Watney. pic.twitter.com/m30bwCKA3w
— Scott Kelly (@StationCDRKelly) December 27, 2015
By January 8 the flowers were on the rebound, leading to another tweet.
Some of my space flowers are on the rebound! No longer looking sad! #YearInSpace pic.twitter.com/HJzXaTItIf
— Scott Kelly (@StationCDRKelly) January 8, 2016
while on January 12 they had begun to flower. The zinnia plants on the ground were harvested on February 11 while those in space on February 14, Valentine’s Day. See http://www.nasa.gov/mission_pages/station/research/news/flowers.
Veg-03
The aim of the Veg-03 experiment is to build on the success of the previous VEGGIE experiments by growing ‘Tokyo Bekana’ cabbage along with ‘Outredgeous’ lettuce as food crops. Plants are again to be grown in two different sizes of arcillite substrate with specialized fertilizer. Eighteen planting pillows (12 of cabbage, six of lettuce) were prepared at Kennedy Space Center on early April 2016, by gluing the seeds using guar gum to the Teflon and Kevlar envelopes [https://blogs.nasa.gov/kennedy/2015/06/18/future-lettuce-planting-the-seeds-for-veg-03/]. They were then packed in gas-impermeable bags and then into cargo transport bags so as to be shipped on the ISS with the SpaceX CRS-8 mission to the ISS [https://blogs.nasa.gov/kennedy/2016/04/08/veg-03-plant-pillows-readied-at-kennedy-space-center-for-trip-to-space-station/]. First lady Michelle Obama planted cabbage seeds from the same batch that were shipped to her from KSC at the White House vegetable garden on April 5th 2016. She was assisted in that task by NASA Deputy Administrator Dava Newman, astronaut Cady Coleman, Brad Carpenter, chief scientist for space life and physical sciences at NASA, Gioia Massa, NASA Veg-03 science team lead at Kennedy and kids from Bancroft Elementary School and Harriet Tubman Elementary School [http://www.nasa.gov/feature/nasa-s-veg-03-seeds-planted-in-first-lady-s-white-house-garden]. SpaceX CRS-8 launched on April 8 2016, was captured on April 10 and the experiment is awaiting activation. Future plans for VEGGIE include growing dwarf tomato seeds in 2018.
Overview
Despite its modest size VEGGIE is the largest plant growth chamber ever launched to space. So far over three growth periods it has produced only one lettuce crop that was consumed by the inhabitants of the ISS following a 33 day growth period. Alas I did not find a news item on whether it was actually all consumed in one or several meals. If we wished to scale the experiment to producing a significant fraction of the food consumed by the astronauts and cosmonauts in space, as is the purpose of the MELiSSA experiment, we have the issue that the ISS is simply not big enough, despite being the largest space station in history. The complete length of the ISS modules from one edge to the other is 51 m. Assuming a 4 m average module diameter this would mean an opening area of 200 m2.
Under intensive agriculture we would most likely need on Earth around 250 m2 per inhabitant per year, though this needs to be validated in space conditions. But the ISS is three dimensional; we could say fit throughout the ISS modules enough VEGGIE modules to have sufficient growth area in the volume provided, if there were enough EXPRESS racks. Other issues would still need to be resolved. If a single 0.212 m2 VEGGIE module consumes 115 W of peak power, then 250 m2 of VEGGIE modules should consume 135,6 kW of power. The ISS power system produces, according to Wikipedia, between 84 and 120 kW of power on each orbit. Furthermore 1000+ Veggie modules would require quite a bit of astronaut attention and time that might not be available: Scott Kelly was aware of the rot issue in the zinnia experiment on the single Veggie module he was tending at least two days before he intervened, but he had to delay his intervention due to an unplanned spacewalk. Growing food in space requires very significant amounts of space and human resources, which is why so far space food has been grown, prepared and sent to space from Earth.
Cooking in Space
After growing food in space we would most likely need to cook it. While Veggie is intended to grow only raw food, MELiSSA intends to produce raw materials for balanced, cooked, or at least somewhat prepared, meals. This raises the issue of cooking in space, especially under microgravity conditions, which is still in a rather primitive form. Expedition 18 astronaut Sandra Magnus has produced a slideshow and an article of her cooking efforts in space. I admit that I am showing my cultural bias as a Greek here but with the exception of putting onions and garlic with olive oil at the Russian food warmers for several cycles, the rest of her cooking would not qualify as cooking in my book but rather as recombination of already partially prepared foods. Then again I have to admit that not everyone’s baseline for cooking is their grandmother spending two or three hours preparing lunch in the kitchen followed by a couple of hours of baking in the oven to cook it.
Moving from having raw produce to fully prepared cooked food requires several steps that have yet to be demonstrated in space. Let us assume that we have grown wheat and we wish to create a taco shell, a foodstuff quite popular with ISS astronauts and cosmonauts. We would need to separate and shell the wheat grains from the rest of the plant. Then we would need to mill the grains into flour which is a critical step in more ways than one: we depend on modern mills to separate several pathogens from the seeds and protect us from, say, ergotism. Then we would need to turn the flour into dough in microgravity, which is not very conductive to mixing materials that are in different phases. Next we would shape the dough and put it into an oven for cooking, which most likely would have to look like a toaster oven so as to avoid having the shaped dough wander inside the oven along with the convection currents. Then hopefully we would have a taco to fill with what we desire. As we can see we still need to prove that several of these steps can be achieved under microgravity conditions.
Growing space food in perspective
One of the offshoots of the space race was the Apollo Applications Program (AAP), an effort to use the hardware developed during the Apollo program in other uses. It eventually studied three major applications: the Orbital Workshop, a permanent Lunar Base and a Manned Venus Flyby. A central concept of the AAP was the Wet Workshop: The upper stage of either a Saturn IB or a Saturn V (the S-IVB stage) would be launched to space, fire its engines to reach the appropriate trajectory, then the remaining fuel and oxidizer would be vented and the astronauts would move into the tanks after sealing them behind them using tools launched with them placed at the location where the Lunar Module would be during Apollo lunar missions.
In the end only the Orbital Workshop was launched in the form of Skylab, which was a Dry Workshop: It was launched already preconfigured as a habitat from Earth. Skylab can be seen as a prototype for the Manned Venus Flyby spaceship, which after all has been called “Skylab to Venus”. It is unfortunate that in the 5 decades since, very few spaceship plans can claim to have reached the level of maturity that Manned Venus Flyby reached with the launch of Skylab. Only the Soviet Mars Train, released a few years before the collapse of that country, can also claim to be based on space tested systems, more specifically the Mir Space Station and the Russian segment of the ISS which was based on Mir/Mars Train designs. While some of the NASA Mars plans have talked about the use of Destiny derived modules, so far only the Manned Venus Flyby has had a plausible plan using existing hardware in production at the time of its planning. For a review of Mars plans see http://history.nasa.gov/monograph21.pdf.
Skylab holds to this day the record for food weight and portions packed in a single launch. Skylab, like the first generation Salyut stations, lacked the ability to receive unmanned resupply missions and while some food was carried along with the crews, most of the food consumed aboard was carried to space during the launch of the Space Station. More specifically, Skylab was launched with approximately 2500 lbs of food packages and another approximate 350 lbs were launched along with the astronauts, mostly with Skylab 4. I use imperial units in this section because that was what NASA used at the time in the documentation.
The workshop included 5 freezers each weighing about 60 lbs (without the food inside them), 22 unrefrigerated food assemblies at 90 lbs each and 3 overage containers at 30 lbs each (see http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19760011703.pdf). Adding all these numbers up totals 2850 lbs of food and 2370 lbs for the containers, and a system total of 5220 lbs. Considering that the total weight of Skylab without the Apollo CSM at launch was 150,350 lbs, the mass fraction of the food system was 3.5% of total weight, including the food that was later launched. Food without the support equipment was 1.9% of total Skylab weight. Originally Skylab food was packed for 140 days of operation; in the end the three manned missions lasted 171 days and they kept a 10 day contingency margin of food for the last flight in case weather delayed the return of the last crew. My understanding is that when Skylab 4 landed only the contingency food was left on board the station.
The Manned Venus Flyby spacecraft was to last for 400 days. The planners allotted 1800 lbs for the food for the 3 astronauts, a figure that does not include the weight of its containers. Furthermore, the thrown weight of the whole MVF assembly stack was 106,775 lbs of which 37,710 was for the Environmental Support Module and 34,600 for the S-IVB stage and the Instrument Unit [https://www.devin.com/cruft/19790072165_1979072165.pdf]. This would give a food fraction of 1.7%, as opposed to Skylab’s 1.9%.
Now on Skylab the Orbital Workshop weighed 62,500 lbs, IU 4,600 lbs with a total weight (including the 22,200 lbs Apollo Telescope Mount but not the Apollo CSM carrying the astronauts) of 150,300 lbs. If for 181 days of food supplies Skylab need 2850 lbs of just food, for 400 days of supplies they would need 6300 lbs. While it is true that when MVF was studied we had little idea how much food astronauts and cosmonauts needed in space, the differences in mass between the MVF plans and what was their equivalent weight on Skylab offer a cautionary tale on planning without having built any actual equipment. It is rather difficult to find figures online on how much weighs the food that each ISS astronaut or cosmonaut consumes every year, but my understanding is that since the 1970’s actually food weight consumed is more or less the same but packing material weight has significantly decreased.
My foray into the Apollo/Skylab era is intended to show just how small a fraction of spaceship weight is taken by the food system. I have not performed this sort of analysis with later spaceship plans, assuming they were ever that detailed, but even for a two year trip in space (say to Jupiter) food weight should not be a showstopper. Growing food would still be beneficial for psychological reasons and to supply vitamins in a more pleasant form than pills. For long term interstellar travel, when we surpass a trip length of a decade, which is generally the maximum that canned foods survive, growing food will become critical. The projects mentioned in this post will probably be among the ancestors of the systems and their designed used on these starships.
Looking for Life Around Red Giant Stars
I suppose the most famous fictional depiction of the Sun as it swells to red giant stage is in H. G. Wells’ The Time Machine, in a passage where the time traveler takes his device by greater and greater jumps into the remote future. This is heady stuff:
I moved on a hundred years, and there was the same red sun–a little larger, a little duller–the same dying sea, the same chill air, and the same crowd of earthy crustacea creeping in and out among the green weed and the red rocks. And in the westward sky, I saw a curved pale line like a vast new moon.
‘So I travelled, stopping ever and again, in great strides of a thousand years or more, drawn on by the mystery of the earth’s fate, watching with a strange fascination the sun grow larger and duller in the westward sky, and the life of the old earth ebb away. At last, more than thirty million years hence, the huge red-hot dome of the sun had come to obscure nearly a tenth part of the darkling heavens.
Wells would have had no real idea of the chronology here, but we now know that in several billion years, the Sun will become a red giant, with effects upon our own planet’s habitability showing up long before that. Because the inner planets will be consumed when this happens, and Earth itself rendered a rocky hellscape, it’s easy to assume that life in our Solar System will come to an end. But Ramses Ramirez and Lisa Kaltenegger (Carl Sagan Institute at Cornell University) beg to disagree. Their new paper paints the possibilities of post red-giant habitable zones.
Just where is the habitable zone located in the later stages of a star’s evolution? To find out, the researchers have computed the luminosities of stars as they move off the main sequence, expanding through the Red Giant Branch and Asymptotic Giant Branch. They work with a grid of stars ranging all the way from A5 down to M1, with calculations starting at the beginning of the red giant phase. Here the stellar luminosities increase in stars of the Sun’s mass and greater, decreasing after the helium flash before again increasing along the Asymptotic Giant Branch.
For stars that are less massive, stellar winds during the Red Giant Branch phase reduce their masses sharply, enough to prevent them undergoing the Asymptotic Giant Branch phase. The fascination here — and this paper should provide scenarios for more than a few science fiction writers — is watching what happens to the habitable zone given high stellar winds, atmospheric erosion and an expanding central star. We might take our own Solar System as a starting point, since while life on Earth would be devastated, prospects further out begin to open up.
Image: Normal yellow stars, like our Sun, become red giants after several billion years. When they do, the planetary habitable zone changes, as analyzed in a new paper by Lisa Kaltenegger and Ramses Ramirez. Credit: Wendy Kenigsburg / Carl Sagan Institute.
Consider this: Over 99.9 percent of the water in the Solar System is found beyond the so-called ‘snowline,’ meaning that the outer system could offer the potential of biological evolution. As Ramirez and Kaltenegger calculate post-main sequence habitable zone distances for the stars on their grid, they show that a planet at Jupiter’s distance could remain in the newly warmed, much more distant habitable zone of a G-class star for hundreds of millions of years. We don’t know how long it takes life to evolve, but this may be long enough for the process to start, given that life on Earth is now thought to have begun about 3.8 billion years ago, and perhaps even earlier.
But here is a key point: Evolution in a post-main sequence phase may not be necessary. One possibility is that life could have started in an early habitable environment, perhaps before the star ever reached the main sequence. Moving below the surface as conditions changed, it could emerge once again after the star goes into its red giant phase. Another possibility: Life could evolve below the surface on a world outside the traditional habitable zone, only emerging once the post-main sequence phase begins. Let’s look more closely at this issue, as it has implications for the detection of life in other solar systems:
In our own Solar System, if life exists in the subsurface ocean of icy exo-moons like Europa or Enceladus, this life may be exposed during our Sun’s red giant branch phase (RGB), during which the post-MS HZ will move outward to Jupiter’s orbit, allowing atmospheric biosignatures to potentially become remotely detectable at those orbital distances. For planets or moons as small as Europa, such atmospheric signatures would be short-lived due to the low gravity. But for super-Europa analogues or other habitable former icy planets such atmospheric signatures could build up. Higher disk densities around massive stars may translate into more massive objects than in our Kuiper belt region (~ 3 times the terrestrial planets; Gladman et al., 2001). Such planets may be present around current post-main-sequence stars.
In a 2014 paper, Ramirez and Kaltenegger looked at habitable zone boundaries in stars that had not yet reached the main sequence, considering the possibilities for the detection of biomarkers, which obviously affect how we choose the stars we target for observation. Now we’re moving into the later stages of a star’s evolution, finding that habitable zone limits evolve throughout this period thanks to changing luminosity and stellar energy distribution. The notion of a habitable zone expands to include multiple periods and places in a star’s long development.
We learn that the orbital distance of the post-main sequence habitable zone changes over time for all the stellar types studied. Our Sun, for example, shows initial post-MS habitable zone limits of 1.3 and 3.3 AU respectively, but these expand outward to 46 and 123 AU by the end of the Red Giant Branch phase, covering a timespan of about 850 million years. During the Asymptotic Giant Branch phase, the habitable zone edges move from 5 and 13 AU to 39 and 110 AU, during a timespan of some 160 million years.
The coolest stellar type the authors consider is an M1 dwarf, which can sustain a planet in a post-main sequence habitable zone for about 9 billion years (assuming metallicity levels like our Sun). A planet orbiting an A5 star, the hottest the researchers consider, can only remain in the post-MS habitable zone for tens of millions of years. A planet around a post-MS Sun may have up to 500 million years. These numbers assume an unchanging orbital radius, though the authors note that as the star loses mass, orbits move outward, thus increasing time in the HZ.
Image: The?distance?of?the?habitable?zone?as?a?small?red?star?ages.?Credit:?Ramses?Ramirez.
It’s interesting to consider that cool K stars and the even cooler M1 stars under discussion here would not yet have had time to reach the post-MS phase, but they’re a useful part of the model as we try to expand our notions of astrobiological detectability. In our own system, icy moons that might currently have life beneath their surfaces are not massive enough to maintain a dense atmosphere once they are heated. But more massive moons or Earth-mass planets could well be found at equivalent distances in other solar systems. The paper thus calculates how long Earth-mass bodies would retain their atmospheres at the location of Mars, Jupiter, Saturn and the Kuiper Belt in our own Solar System. Let me turn to the paper on this point:
Planetary atmospheric erosion during the post-main-sequence is mainly due to high stellar winds produced by the stellar mass loss, which can erode planetary atmospheres. Super-Moons to super-Earths’ atmospheres can survive the RGB and AGB phase of their host star – except for planets on close-in orbits. Even super-moons survive at a Kuiper-belt equivalent distance for all grid stars to the end of the AGB phase.
So while it’s natural enough to look for life around stars comparable to the Sun in type and age, this work argues that we should widen our parameters, considering that we have a ‘red giant habitable zone’ that can last for long enough to allow life to emerge. In terms of life’s future in the universe, it’s remarkable that a small red star of M1 class could sustain a habitable zone for up to 9 billion years in a phase of its life when we would expect life to be destroyed. In this Cornell University news release, Ramirez refers to a planetary system’s ‘second wind,’ a fascinating metaphor indeed as we model the future evolution of living worlds.
The paper is Ramirez and Kaltenegger, “Habitable Zones of Post-Main Sequence Stars,” Astrophysical Journal Vol. 823, No. 1 (16 May 2016). Abstract / preprint.
Moons of the Outer Dwarf Planets
Yesterday’s post on the dwarf planet 2007 OR10 brought comments asking why an object this large hasn’t yet been named. Actually it has been, but only briefly. It was Meg Schwamb, then a graduate student of Caltech’s Michael Brown, who discovered 2007 OR10, and Brown quickly gave it the nickname Snow White — as the seventh dwarf Brown’s team had discovered, the name seemed made to order. What derailed the nickname was the realization that 2007 OR10 is not white but red, and as we saw yesterday, one of the darkest known Kuiper Belt objects.
Schwamb herself was quoted in this JPL news release on the matter:
“The names of Pluto-sized bodies each tell a story about the characteristics of their respective objects. In the past, we haven’t known enough about 2007 OR10 to give it a name that would do it justice. I think we’re coming to a point where we can give 2007 OR10 its rightful name.”
We’ll see just what that rightful name is. Remember, too, that 2007 OR10 is now known to be just larger than Makemake, making it about a third smaller than Pluto. As to Makemake itself, a dwarf planet named after a creation deity of the Rapa Nui people of Easter Island, we learned in late April that it has a small, dark moon about 160 kilometers across. That one is designated S/2015 (136472) 1 but is referred to informally as MK 2. The moon is going to be useful as astronomers study the density of Makemake, just as Charon helped us understand Pluto.
Image: This Hubble Space Telescope image reveals the first moon ever discovered around the dwarf planet Makemake. The tiny moon, located just above Makemake in this image, is barely visible because it is almost lost in the glare of the very bright dwarf planet. The moon, nicknamed MK 2, is roughly 160 kilometers wide and orbits about 21,000 kilometers from Makemake. Makemake is 1,300 times brighter than its moon and is also much larger, at 1400 kilometers across. Credit: NASA, ESA, A. Parker and M. Buie (Southwest Research Institute), W. Grundy (Lowell Observatory), and K. Noll (NASA GSFC).
On to Haumea
These are good times for those of us interested in small worlds at the edge of the Solar System, especially when you factor in the continuing dataflow from New Horizons. And now we have new analysis of the dwarf planet I would most like to get an orbiter around, the ever intriguing Haumea. Its unusual shape — Haumea is a flattened ellipsoid with its longest axis about 2000 kilometers across — is likely the result of an ancient collision. It’s also highly reflective, with a surface evidently covered with crystalline water ice (cryovolcanism?).
Rotating every 3.9 hours, which is faster than any other large object in the system, Haumea was discovered to have a dark spot on its otherwise bright surface in 2009, an area evidently richer in minerals and organic compounds than surrounding areas. The dwarf planet also has two moons, known as Hi?iaka (the outer satellite) and Namaka (the inner), and is evidently the parent body of a family of icy fragments with similar albedo now orbiting the Sun. Just how the moons formed and what we can learn about the composition of Haumea itself make this an intriguing object for those trying to piece together the early history of the outer system.
Both Pluto and Haumea have multiple moons, while Eris and Makemake have a single moon each. But what Haumea seems to lack in comparison to Pluto are small icy moons like Pluto’s Nix, Hydra, Kerberos and Styx. In a new paper, Luke Burkhart (Harvard-Smithsonian CfA) and colleagues look at Haumea via Hubble data taken in July of 2010, in a search for additional moons that came up dry. The work sets strong limits on the size and location of any possible undiscovered moons, with implications for the formation of the satellite system.
From the paper:
As the properties of the dwarf planet satellite systems differ significantly, it was not anticipated that Pluto’s small satellites would necessarily find counterparts around Haumea, though it seems that Makemake may have a satellite of similar size (Parker et al. 2016). Our null result affirms that, for the time being, Pluto is the only known KBO with a retinue of small satellites, though such could have been detected or nearly detected around all four dwarf planets. This implies that the satellite systems may result from somewhat different formation pathways, although all the dwarf planet satellites are probably connected with a collisional formation. Pluto’s small satellite system may be connected with Charon since, from a dynamical perspective, the other dwarf planet satellites are more like small moons compared to the near-equal-sized Pluto-Charon binary.
Darin Raggozine (Florida Institute of Technology) says that despite some similarities, the satellite systems we’ve observed around the outer dwarf planets must have had different formation processes. Both Pluto and Haumea have planetary scientists searching for answers. “There is no self-consistent formation hypothesis for either set of satellites,” adds Raggozine in this FIT news release.
We also learn that moons the size of Pluto’s Nix and Hydra would have been detected if present at Makemake, and in fact would be near the detection threshold even for distant Eris. The paper notes that improving these detection limits would take extensive observations, a task perhaps suited to the James Webb Space Telescope. What we do know is that no satellites larger than about 8 kilometers in radius are found between 10,000 and 350,000 kilometers of Haumea. This is the region which, around Pluto, contains Charon and the four smaller satellites.
Image: A comparison of the four icy dwarf planets and their moons, with all objects to scale. These large bodies in the outer Solar System share many similarities, but one difference is that only Pluto has a collection of tiny moons (shown near the center). Research from Luke Burkhart at Yale University, Darin Ragozzine at Florida Institute of Technology and Michael Brown at Caltech found that Haumea, a dwarf planet on the edge of our Solar System, doesn’t have the same kind of moons as its well-known cousin Pluto. Credit: D. Ragozzine (FIT)/NASA/JHU/SwRI.
The paper is Burkhart et al., “A Deep Search for Additional Satellites around the Dwarf Planet Haumea” (preprint).
New Work on Dwarf Planet 2007 OR10
Although we always think of Kepler — and its successor mission K2 — as an exoplanet observatory, the spacecraft has also been put to work on objects much closer to home. Enter 2007 OR10, a dwarf planet that is currently about twice as distant from the Sun as Pluto. The Kepler instrument is, of course, fine-tuned for spotting the minute variations in light caused when a planet passes in front of a distant star. But that makes it an excellent tool for studying 2007 OR10, whose dim light and red color have proved difficult to parse by other instruments.
Kepler, though, is not alone in this work. What we see is a useful collaboration between it and the European Space Agency’s Herschel Space Observatory. Using archival data from the latter, researchers have been able to measure both the fraction of starlight absorbed and later re-radiated as heat (via Herschel) as well as the fraction of starlight reflected from 2007 OR10 via Kepler. K2, sensitive to minute changes in brightness, was able to show that the object is one of the slowest rotating objects in the Solar System, taking about 45 hours to complete a revolution.
Image: The orbit of 2007 OR10 compared to the orbit of Eris, Pluto, and the outer planets. Credit: kheider [GPL (http://www.gnu.org/licenses/gpl.html)], via Wikimedia Commons.
Coupled with the Herschel data in the infrared, we’ve now established a more accurate measurement of 2007 OR10’s diameter than Herschel could provide on its own. The dwarf planet has a diameter of 1535 kilometers, some 250 kilometers greater than previously thought. That makes the surface darker as well, given that the same amount of light is being reflected by a larger object. The paper on this work discusses what this implies about the surface:
The red color of 2007 OR10 is likely to be due to the [retention] of methane, as it was proposed by Brown, Burgasser & Fraser (2011). In Fig. 1 in Brown, Burgasser & Fraser (2011), 2007 OR10 is nearly placed on the retention lines of CH4, CO and N2. The larger diameter derived in our paper places this dwarf planet further inside the volatile retaining domain, making the explanation of the observed spectrum more feasible.
The newly determined larger size of the dwarf planet, then, makes it more likely that the object can retain these volatile ices than if it had been smaller. The size, in fact, makes 2007 OR10 the third largest dwarf planet known after Pluto and Eris, just ahead of Makemake.
Image: New K2 results peg 2007 OR10 as the largest unnamed body in our solar system and the third largest of the current roster of about half a dozen dwarf planets. The dwarf planet Haumea has an oblong shape that is wider on its long axis than 2007 OR10, but its overall volume is smaller. Credits: Konkoly Observatory/András Pál, Hungarian Astronomical Association/Iván Éder, NASA/JHUAPL/SwRI.
This isn’t the first time K2 has been involved with objects within the Solar System. Its previous targets have included the objects (278361) 2007 JJ43, 2002 GV31 and Neptune’s moon Nereid. Now, at 2007 OR10, we’re seeing variations in rotational brightness that are intriguing for their suggestion of variations in surface albedo. Here I can’t help recalling New Horizons and the way we went from faint indications of surface features during the long approach, to the close-up clarification of numerous kinds of terrain. How long will it be before we can repeat that feat with another outer system object like this one?
The paper is Pál et al., “Large size and slow rotation of the trans-Neptunian object (225088) 2007 OR10 discovered from Herschel and K2 observations,” Astronomical Journal Vol. 151, No. 5 (2016). Abstract / preprint.
Extraterrestrial First Contact in Space Protocols
As we move into the outer Solar System and beyond, the possibility exists that we may encounter an extraterrestrial species engaged in similar exploration. How we approach first contact has been a theme of science fiction for many years (Murray Leinster’s 1945 story ‘First Contact’ is a classic treatment). In the essay below, Ken Wisian looks at how we can develop contact protocols to handle such a situation. A Major General in the US Air Force (now retired) with combat experience in Iraq, Afghanistan and the Balkans, Ken brings a perspective seasoned by command and a deep knowledge of military history to issues of confrontation and outcomes, building on our current rules of engagement to ask how we will manage an encounter with another civilization, one whose consequences would be momentous for our species.
By Ken Wisian Ph.D
Galactic Ventures LLC, Austin, Texas
Abstract
How do two ships approach each other in a first contact setting? When it happens it will be a pivotal moment for human history. The slightest mistake or misperceived intention could cascade into violence. Therefore even future deep space robotic probes, let alone a true interstellar ship whether crewed by humans or AI, should incorporate courses of action for this possibility,
The development of first contact protocols is obviously rife with unknowns since we only have a one-planet historical data set build on; nevertheless we must proceed. The bulk of the thinking on first contact so far has focused on a remote contact via electromagnetic signal exchange (SETI) or finding non-sentient microbiota (aka Apollo post-mission quarantine), but what if we stumble upon another intelligence in space? Admittedly, this may not be the most likely course of action, but as we start to move deeper into space it is an increasing possibility. Through centuries of trial and error, protocols have been developed for military ship and aircraft encounters on Earth. These earth protocols provide as good a basis as we have for building extraterrestrial first contact protocols.
This paper will review human rules of encounter currently used and build a set of simple rules for a ship-to-ship encounter in space based on the assumption that there is no effective communication prior to or during the encounter.
1. Introduction
How do you approach a totally unknown entity in such a way as to not provoke a hostile reaction? This is not as easy a question as it might first appear. We are loaded with human-cultural preconceptions that are frequently subconscious. An example; smiling in humans is universally regarded as a friendly gesture, but in some primates and most species on earth (with a face that is) showing your teeth is a dominance/aggressive/threat gesture. And this difference here on earth exists between closely related species – who is to say how divergent the interpretation of gestures might be between species that evolved in different star systems? Another example is the white flag. Most industrialized states recognize it as a sign of surrender, some also would recognize its use to request parley, but it is far from universal in time or across cultures even today on earth. Thus nothing can be taken for granted and substantial on-the-spot sound judgement will be required.
Why worry about the vanishingly small chance of an unanticipated first contact? Risk management both in the military and civilian world considers not just the probability of an event, it also considers the potential consequences. In the case of a first contact, the odds of such an event are nearly vanishingly small, but they are cancelled out (and then some) by the off-the-chart potential impact of an encounter unintentionally entering an instantaneous, violent escalation spiral. Thus it is critically important that humans think through first contact in space before it happens.
Science fiction (SF) deals frequently with first contact scenarios. The volume of material is immense – far too much to even briefly review here. SF has explored, often quite well and with great “outside the box” thinking probably every conceivable scenario. So while there are no specific SF references here, the body of SF work informs all aspects of this paper.
We have a limited knowledge base from which to start and extrapolate general rules for first encounters, namely one technological species – homo-sapiens. This situation presents a danger that we must guard against as best we can; anthropomorphic bias. Given that potential bias, we will none the less start by looking at what humans do in the closest analog we currently have for first encounters; the meeting of unknown, neutral or potentially hostile ships and or aircraft. Through trial and (often fatal) error there are now well-defined rules of conduct for these situations (up to the level of international law).
The human-human contact experience is perhaps our best foundation upon which to build a set principles and protocols for a potential encounter in space. The envisioned scenario; two ships meeting in space rest on several assumptions.
Assumptions:
1. No effective telecommunication. There may be attempts to communicate via electromagnetic or other means, but understanding has not been achieved, thus we are without effective communication – “comm-out”.
2. Neither side is overtly hostile, but both are guardedly cautious.
3. At least one of the ships involved has “reasonable” maneuvering capability.
a. This will most likely be an “endpoint” encounter, in a solar system. An encounter in transit in deep interstellar space would likely mean neither ship has the ability to stop and/or maneuver in order to match vectors and effect a rendezvous.
Not a scenario assumption, but an important point is that these protocols apply just as well to Artificial Intelligence (AI) crewed ships as they do to human crewed ships. Also, ships is taken to include space stations or other similar outposts. Even probes without true AI can incorporate complex, branched Courses Of Action (COAs) for dealing with encounters. For instance, detection of radiation anywhere in a wide range of EM frequencies that does not correlate with known astronomical sources would be a target to slew all sensors to and report on. At that point, depending on level of sophistication, you enter COAs for determining artificiality etc.
Image: Confronting the unknown. A still from Steven Spielberg’s Close Encounters of the Third Kind. Credit: EMI Films / Columbia Pictures.
2. Current human protocols
There are internationally accepted protocols for encounters between ships and correspondingly between aircraft. Some are based on international law and custom (Law of the Seas), some are rules by governing bodies (International Civil Aviation Organization). Similar laws and rules exist also within the boundaries of individual countries. Regardless of origin, they follow broadly similar, mostly common sense (at least to us nowadays) paths based on centuries of experience. Underlying much of this is an unwritten intent to minimize potential misunderstanding that could lead to violence. This point is critical for our purposes. It is difficult enough to minimize misunderstanding and escalation within our own species, it could be significantly more difficult to do the same when civilizations from different stars meet.
Much of the law and customs for ships at sea pertain to piracy or the right of a country to inspect a ship to ensure that it is conducting legal business (particularly in territorial waters). Even here though reasonable cause is required for more than a cursory inspection. The rules governing intercept of aircraft are more slanted towards the need to immediately protect a country from devastating attack that can result from a craft moving at or above supersonic speed and thus can lead much more quickly to lethal action.
In all air and sea cases there is a hierarchy of communication means used to establish meaningful dialog between ships from straightforward radio communication to flag and light signals up to and including weapons fire – the shot across the bow, so yes, even gunfire can be a form of communication. With aircraft there are no flags, but brief maneuvers (such as rocking wings) can be used for communication.
For ships at sea, there are rules for avoiding collision such as pass to the right (starboard). There is also a rule that the most maneuverable ship has primary responsibility to avoid collision. For example a functional ship at sea that comes upon a ship adrift, unable to maneuver, besides having a responsibility to help, is responsible to maneuver so to avoid collision. Correspondingly, the less maneuverable ship is obligated to maintain constant speed and heading or come to a stop. For aircraft meeting aircraft there is a similar most maneuverable has primary responsibility to avoid collision rule, so for instance a powered aircraft has responsibility to avoid a hot air balloon.
For military aircraft or ships meeting other military ships or aircraft there are additional guidelines that are critical for avoiding escalation. First is to avoid collision courses or aggressive maneuvers such as those designed to put one in a (better) shooting position. Right along with that are restrictions on pointing guns or (and this gets tricky) putting support systems such as radars into modes such as target track that are standard preparatories to firing weapons. Radar modes have become particularly problematic as technology has advanced; many weapon system no longer require a distinctive target tracking mode in order to shoot. Furthermore electromagnetic jamming during an intercept is a potentially hostile act. These rules unfortunately are not universally followed and not following them has resulted in very serious international incidents to the present day.
3. Excursion into past human civilizational first contacts
The past record of human civilization first contacts is a well-trodden area of history and will only briefly be covered as it pertains to extraterrestrial scenarios – the longer term consequences such as disease transfer and cultural domination will not be addressed. Less commonly studied though are the details and consequences of the actual first contact. The bottom line is that first encounters have often, though not always turned violent and in such cases the side with a major technological advantage usually wins. Commonly Western Europeans with well advanced gunpowder technology encountering stone or bronze/iron age technologies have won most violent encounters, but have sometimes been overcome bu numbers. The question of why encounters have turned violent and the cause is much more ambiguous – some encounters have been peaceful, but in many cases territoriality and xenophobia have been prompt causes for violence. Who can say for sure that any species encountered may not have these traits (even more markedly than humans)? Perhaps more disturbing, there are human cultures that consider war/killing a necessary prerequisite to full citizen status. Fortunately none of these cultures are dominant on earth today, but what if such a culture achieved an interstellar civilization?
4. Towards a protocol
The above review of human encounter situations and history gives us a good starting point for thinking about alien ship to ship encounters. First a few general principles to go with the assumptions already laid down at the beginning. These principles are distilled from the human contact procedures above which in turn are built upon millennia of experience.
Contact principles
- 1. Be predictable
- 2. Avoid any appearance of hostile intent
- 3. Attempt communication
These seem straightforward, but #2 has many subtleties and #3 is a very complex subject which is beyond the scope or this paper or the expertise of the author.
The principles are in priority order; communicating is far less important than the closely related ideas of being predictable and not showing hostile intent. These principles are broadly applicable in human experience. For example besides applying at the level of international affairs, these are also appropriate at the level of individuals for an encounter with law enforcement around the world, driving a car, or encountering strangers on the street.
What has not been stated before is the underlying motivation for these principles and that is to avoid putting the other party into a position where they have to make a snap judgement about your intent. In human interactions between two wary parties ambiguity of intent is almost always interpreted in the most hostile way (unless the parties have a considerable experience base, which in a first contact they will not, that allows them to presume accidental ambiguity versus hostility). It is also important to note that for the foreseeable future, considering that we have only just become a spacefaring species, we are most likely to be the less technologically advanced of the two encountering civilizations and thus it becomes particularly important that we not precipitate any escalation that we are very likely to lose.
Image: David Bowman (Keir Dullea) and a famous monolith, from Stanley Kubrick’s 2001: A Space Odyssey. Credit: Metro-Goldwyn-Mayer.
First, be predictable. Being predictable is taken to mean with respect to maneuvering primarily. If it is possible to determine that one ship has a decided maneuver advantage on the other, then rendezvous can be attempted with the ships adopting the convention of the most maneuverable ship takes primary responsibility for a safe rendezvous. In these cases gradual, deliberately slow maneuvers would be employed even if there is capability to rapidly affect course changes. With regards to maneuvers there are multiple COAs available. The simplest is to make no changes to what you are doing; if “coasting” – continue, if drive engines are engaged, continue at current setting. Alternatively, you might want to stop engines (this is not the same as stopping in space, which is probably not a practical thing to do (for that matter what frame of reference would you use to determine “stop”)). Regardless unless there is an overriding need (discussed shortly), maintain heading (in three dimensional terms – maintain vector).
What if one ship is approaching an orbital situation – remember that an encounter will most likely be at the endpoint of an interstellar journey. In such a case, in order to avoid catastrophe it might be necessary to start or continue maneuvers to achieve a safe, stable orbit, but this brings with it a slightly elevated risk misunderstanding. In this situation we would be forced to rely on the other parties’ ability to perceive the obvious need to conduct maneuvers. Note the potential for unintended consequences; for a ship that would need to “flip” end-to-end in order to reverse its engines and thrust, you would not want to “sweep” your thrust vector across the other ship and therefore place them in a position of having to decide if you are about to use you most destructive weapon (main drive) on them.
Secondly, avoid any appearance of hostile intent. This is a much more problematic issue than being predictable. The main problem with avoiding appearance of hostile intent is the perception problem. In any encounter between entities that do not share a common culture, there can be serious misinterpretations of intent and meaning, as exemplified by the smile and white flag examples earlier.
If a ship is equipped with weapons you would obviously not want to point them at the other ship. If practical stowing or deactivating them is good, but this then poses another question: would you want to have weapons that require time to activate completely deactivated, thus costing valuable time to spin up if things go bad?
Besides weapons, other non-destructive systems are used by the military; jammers and expendable decoys for example. These would obviously not want to be triggered (but what might be the difference between jamming and a high-powered attempt at communication?).
“But we are peaceful and will not be going armed into space” you say. Any conceivable ship will have technology/systems that are dual-use. The main drive of any self-powered interstellar ship will obviously be extremely high energy and could be used as a weapon of great range and destructive power, thus even a peaceful braking maneuver (with the drive off) that sweeps the business end of the drive towards the other ship, could prompt a swift reaction. Other systems that must be accounted for include communication systems; radios or lasers strong enough to communicate across interstellar distances could be very destructive at short range. So what is one to think when you see a high power laser move to point at you? Perhaps part of a communication protocol would be to only use low-power omnidirectional radio until good understanding is established. Shielding to protect ship and crew from radiation and or collisions has obvious military application – do you reduce its power, turn it off, or leave it in normal on mode? Can you? What if there is an active collision prevention system that destroys or pushes objects out of the way – that has major weapon potential. Is it safe to turn it off?
Tertiary considerations. Avoid looking like you are hiding (aircraft that turn off transponders are usually considered to have hostile or at least illegal intent). Turn on lights and anything else that makes you easily visible (but will this in turn blind any of the other ships sensors?). In your turn you will obviously use every sensor available to learn about the other ship, but passive sensors are probably best until goodwill is firmly established – an active radar scan may look like targeting to another party (just as targeting and search modes of radars are often indistinguishable in modern aircraft). A decoy, a probe, or a vessel containing materials to allow for communication and understanding, might be indistinguishable from a bomb, when launched from a ship.
Lastly, at what range do these actions need to start? As early as practical, probably at detection of the other ship. Your need to be predictable starts when they can see you and that is probably at least at the point when you can see them, if not much earlier.
5. Conclusion
What can be determined from the above discussion is that there are vast unknowns in any potential extraterrestrial encounter in space where effective communication is not established in advance. In these circumstances there are good principles to follow – be predictable, display no hostile intent, and attempt to establish communication, but the specific actions involve many gray areas where judgement, assumptions, or just plain hope, will be the guide. For any ship making an interstellar journey the scenarios must be “gamed” extensively in advance, but any COAs or checklist for an encounter should only be a guide/starting point. Flexibility, sound judgement and quick learning will be very important in these circumstances. The number one goal is to not put the other party in the position of having to make an instantaneous judgement about your intent.
The Surface Gravity Plateau
What’s a movie director supposed to do about gravity? In The Martian, we see Matt Damon moving about on Mars with a gait more or less similar to what he would use on Earth, despite Mars’ 0.38g. Harrison Ford changes worlds but never strides in The Force Awakens. About the gravitational challenges of 1953’s Cat Women of the Moon, the less said the better. Even so, we can chalk all these problems up to the fact that both top directors and their B-film counterparts are forced to film at the bottom of a gravity well, so a certain suspension of disbelief is at least understandable.
But assuming that gravity invariably increases as planets get bigger can be misleading, as Fernando J. Ballesteros (Universitat de València) and Bartolo Luque (Universidad Politécnica de Madrid) demonstrate in a new paper in Astrobiology. We learn that some larger worlds in our own Solar System have gravity not all that different from the Earth. In fact, the surface gravities for Venus, Uranus, Neptune and Saturn weigh in at 0.91g, 0.9g, 1.14g and 1.06g respectively, although these worlds are 0.82, 14, 17 and 95 times Earth’s mass.
Image: Walking on the planet Takodana looks more or less like walking on Earth in The Force Awakens, although the bar scene there is more interesting. Credit: Disney/Lucasfilm/Bad Robot Productions.
How do we go about making these deductions? Usefully, we have plentiful planets to work with as a result of the Kepler mission, and the fact that Kepler works with transits is likewise helpful. A transit light curve can show us how much starlight is blocked by the planet, which provides an estimate of the planet’s size, assuming we have a pretty good idea of the central star’s size.
Radial velocity measurements can then be brought to bear, a technique that supplements the transit method by adding a lower boundary to the planet’s mass. Remember that this measurement depends upon the viewing angle, as we can’t always know the orientation of a given planet’s orbit; i.e., in straight radial velocity studies, we won’t know whether we’re looking at a solar system edge-on, or from directly above (the measurement is M x sin(i), with i corresponding to the viewing angle. With transiting planets, though, we have a better read on the viewing angle because we see the planet transit across its star.
With an idea about the size of a world and a sound estimate of its mass, we can work out the planet’s surface gravity (gs = GM/R2). Ballesteros and Luque plot the surface gravity vs. mass for a range of exoplanets, folding in data from our own Solar System, where measurements are, obviously, far more precise. Three ‘regimes’ emerge from this work:
- Rocky worlds with masses lower than Earth’s ME;
- A ‘transition zone’ including super-Earths, Neptunes, and some Solar System planets, with masses from one to hundreds of Earth masses;
- Gas giants, with masses above hundreds of Earth masses.
And it’s in the transition zone that things get interesting. Let me quote from the paper:
In the first regime, planetary radius grows with mass as R ~ M¼; therefore surface gravity grows as gs ~ M½ (faster than what would be expected for incompressible bodies, gs ~ M?). On the other hand, for gas worlds, planetary radius remains roughly constant (i.e., gas giants with very different masses have similar sizes due to electron degeneracy), so surface gravity grows linearly with mass, gs ~ M. But in the transition zone, we find some sort of plateau where planetary radius has the fastest growth, as R ~ M½, which thereby yields a constant surface gravity roughly similar to that of Earth.
Hence the similarity in surface gravity between Venus, Uranus, Neptune, Saturn and the Earth, a non-intuitive result given the differences between these planets in structure and composition. As the number of confirmed exoplanets grows — and we saw the largest single addition to the catalog ever yesterday — we are able to understand that having five worlds with roughly the same surface gravity is a general trend. Fitting these findings in with planet formation models will be a challenge that should ultimately improve our understanding of the processes at work.
The accretion process and the competition for materials during planetary formation impose severe constraints on feasible planets. Current models of population synthesis (Mordasini et al., 2015) are designed to take this into account and can address many of the observed features. However, such models fail to explain this plateau and predict instead a noticeable increasing trend in surface gravities in this region.
Hence the value of our steadily increasing exoplanet catalog as we contrast real planetary systems with the theories we apply to their formation. Thus, as Ballesteros and Luque note, watching Harrison Ford walking on the planet Takodana as if he were taking a stroll down Hollywood Boulevard is not a simple moviemaker concession to Earth’s gravity. In this case, what we’re learning about surface gravity makes such strolls plausible.
The paper is Ballesteros and Luque, “Walking on Exoplanets: Is Star Wars Right?” Astrobiology Vol. 16, No. 5 (2016). Abstract. Preprint on arXiv.
Follow with RSS or E-Mail
