Centauri Dreams
Imagining and Planning Interstellar Exploration
Destination Moon: A 70th Anniversary Appreciation
Al Jackson is back this morning with an essay examining another old friend, the 1950 film Destination Moon. Talk about fond memories! I first encountered the movie at a birthday party for a bunch of unruly 4th graders, finding the birthday boy absorbed in watching the spaceship Luna enroute to the Moon in an upstairs room while the party went on below. I stayed right there until his mother came up to scold him and bring us both back down to eat cake, dying to know what happened. Since then I’ve enjoyed the film numerous times, especially appreciating the Woody Woodpecker teaching sequence and the ingenious solution to the crew’s problems getting everyone back home. A veteran of the Apollo days and a science fiction fan with encyclopedic knowledge of the field, Dr. Jackson gives us a look at how the film was made and illuminates Robert Heinlein’s connections to the project. Time to pull out my DVD for another look.
by Albert A Jackson
I was two weeks away from age 7 in October 1947 when Chuck Yeager flew the Bell X-1 at Mach 1 over Rogers Dry Lake in California. That really seized my mind; I read what I could about rockets and jets. I built a StromBecker wooden model of the X-1. I finally got a spaceflight book in early 1951, when I was 10: Rockets, Jets, Guided Missiles and Space Ships, by Jack Coggins and Fletcher Pratt. Quite a treasure! I did not see a copy of Bonestell and Ley’s 1949 book Conquest of Space, which would have been a bit overwhelming when I was 10, until about 20 years later.
I remember seeing an article in LIFE magazine, (April 24th 1950), for a movie called Destination Moon [1]. Later there were ads for the film that really caught my eye. There was a movie about a rocket going to the Moon with people in spacesuits. There were even radio ads that I heard. Alas, I was 10 in the fall of 1950, and my family was 2 years away from taking me and brother and sister to downtown theaters. Destination Moon may have come to a neighborhood theater in the spring of 1951 but I did not see the film until the fall of that year at a kiddie matinee. The wait was worth it, for it was a moment of transport.
Origins
Destination Moon, or something like it, probably would have been made in the late 40s or early 50s; it pretty much owes its origin to Frau im Mond, the 1929 Fritz Lang film about a trip to the Moon. Willy Ley, who had worked as an uncredited technical adviser on that Fritz Lang film, came to know Lang well. (The technical adviser on Frau im Mond was Hermann Oberth, who Ley knew. Even though Oberth studied in Munich he was from a small town and hated Weimar Berlin. Ley had to shepherd him around and act as a liaison for Lang.) Lang moved to Los Angeles after the Nazis came to power. After the end of World War II, Robert Heinlein moved back to Los Angeles. During this time Willy Ley, who Heinlein knew, would come to LA to visit Lang.
With the end of World War II, Heinlein began to develop a close interest in rockets and atomic power. He made it a personal campaign at the end of 1945 and beginning of 1946 to get the Navy interested in rockets [2, 3]. The advent of the large rocket, the V2, was on Lang’s mind too; he talked to Ley about making another movie about a spaceship to the Moon. Ley put Lang in touch with Heinlein. Lang invited the Heinleins for dinner often in 1946 and 1947. During those years. Lang and Heinlein talked about a lot of things, Heinlein was reluctant to start writing young adult novels, but Lang convinced Heinlein it would be an excellent way to connect with an audience that had an appetite for space flight. So Heinlein wrote Rocket Ship Galileo, which turned out to be a commercial success. Finally, in March of 1948 [2, 3], Lang had Heinlein huddle with him over making a film. At first Heinlein suggested Rocket Ship Galileo, but he and Lang decided they needed a more adult narrative. During this time, Lang spent a lot of time trying to convince a studio to finance a film about a trip to the Moon. None would have it. Heinlein had earlier taken on a Hollywood agent, Lou Schor, because of the need to handle possible radio adaptations of his works. When Heinlein suggested that he and Lang use his Hollywood agent, Lang had a problem with this. This led, by mid-1948, to Heinlein and Lang parting ways, though they remained friends [2, 3].
Screenplay and George Pal
Heinlein now had a ‘Hollywood bug’, likely because he had just come out of a rough financial period. Lou Schor put him in touch with screen writer Alford (Rip) Van Ronkel [2, 3]. After a week of talking, Van Ronkel suggested Heinlein write a treatment of the story. Heinlein did this, and within a few weeks handed van Ronkel a 97 page story narrative called ‘Operation: Moon’ on July 21 1948 [3]. Heinlein may have had an extensive outline in hand from his work with Fritz Lang. Using his novel Rocket Ship Galileo, Heinlein took only the narrative about an atomic powered rocket, a trip to the Moon and a crew of four, now adults (the Nazis on the Moon in the novel were removed). Some of Heinlein’s “The Man Who Sold the Moon” also diffused into the treatment. Within a few weeks, van Ronkel wrote the first draft of the screenplay for the film. Shortly thereafter, Schor arranged for Van Ronkel to be at a cocktail party where he introduced him to George Pal; there he told Pal about the screenplay. At this time Pal wanted to move from his animated “Puppetoons” into full-up film features. Also, Pal’s home studio had lost its financing. Pal was intrigued and had Heinlein and Van Ronkel come to his office for a pitch meeting [2, 3]. They struck a deal; Pal took the project to Paramount, but that studio said no [4].
Heinlein and his wife Virginia moved to Colorado Springs in the fall of 1948. Pal was striking out when it came to finding a studio when the former head of RKO, Peter Rathvon, formed his own production company, Eagle-Lion, and showed interest. He made a deal with Pal for two films, although he considered Destination Moon too speculative, so arranged things so that if it had losses, Pal would make a ‘Christmas Film’ called “The Great Rupert” to cover Destination Moon‘s shortfall at the box office. It turned out the other way around! [2, 3]
It took until May of 1949 for Pal to swing this deal. In April 1949 Heinlein finally got paid for the screen story and the rights to Rocket Ship Galileo (even though very little of the novel was to be used). Heinlein also contracted to be the technical adviser (1) for the movie. He insisted that Chesley Bonestell be hired to work on the film [3]. Heinlein and Virginia moved, temporarily, back to LA. There, he worked with the production design crew and director Irving Pichel. He found Pichel to be bright, understanding and in agreement about the story. This was good because Rathvon convinced Pal to take on another screen writer, James O’Hanlon, who rewrote the script even to the point of making it a musical, or at least inserting a musical number! (2) Thankfully almost all of O’Hanlon’s revisions were torn up by Pichel. Shooting was delayed from summer of 1949 to November so that The Great Rupert could be completed, which Pichel also directed. Principal photography on Destination Moon began on the 14th of November, 1949, and ran until roughly the 16th of December.
Image: Robert Heinlein with director Irving Pichel
Heinlein and Bonestell worked out many designs for the film. The space ship, called Luna, was initially submitted by Bonestell, and was the Lunar ship (2) in Conquest of Space by Ley and Bonestell [6], except that Bonestell (maybe consulting with Heinlein) did away with the aft V2-like fins and modified the wings. (2) Art director Ernst Fegté changed the design, keeping the central ogive and moving the wings back, the wings and a strut became part of the ‘landing gear’.
Luna is a beautiful ship and is functional enough. Bonestell made a model of the landing site, the crater Harpalus, and then a 14 foot matte lunar surface painting for the set. Pal’s production crew spent 2 months building the on-set ‘surface’. Heinlein and Bonestell were appalled when they saw it! It looked like a dried lake bed, impossible on the Moon. Pal and cinematographer Lionel Lindon decided that on a relatively small set they needed to increase the depth of field , so the added ‘cracks’. Heinlein went along with this, but Bonestell was never happy with it. Luna’s cockpit had to be designed four times in a back and forth between Heinlein and Bonestell and production design. Amazingly the cockpit was a rotating set [10], quite a feat for 1949, on a budget, (roughly 18 years before Kubrick used one, in a spaceflight movie, Kubrick and Clarke’s 2001: A Space Odyssey).
Image: At left is the ship from Conquest of Space; at right is Bonestell’s design for Destination Moon.
The Movie
The movie starts in a block house with stock footage of a V2 launch. This is the only time we see a control room, one that looks pretty good, if simplified. Heinlein was in one when he went to a V2 launch at White Sands, New Mexico in 1946 [3]. There is a ‘motor’ failure, which is a bit kludgy since Dr. Charles Cargraves ‘engine’ is supposed to be a nuclear reactor. There is talk about sabotage but it’s all kind of vague. A technician, Joe Sweeney, is about to run outside but Cargraves (3) stops him.
General Thayer later visits Jim Barnes, owner of an aircraft company, and tells him he suspects the rocket was sabotaged. Thayer wants Barnes to help Cargraves. He also speculates that the next rocket Cargraves builds will have an improved engine powered by atomic energy and could travel to the Moon. Jim is skeptical, but Thayer convinces him that the combined resources of American industry could put a rocket on the Moon within a year.
We have now been introduced to the crew that goes to the Moon: John Archer as Jim Barnes, Warner Anderson as Dr. Charles Cargraves, Tom Powers as General Thayer and Dick Wesson as Joe Sweeney. Pal, as some references say, looked for a cast of actors who were unknown but is not clear why it was B-list wooden Indians (4)! It is not Z- level movie acting but certainly near low B level. Dick Wesson is the comic-relief, an old Hollywood cliché, and it seems Heinlein went along with this. Wesson’s character plays the part of an ‘everyman’ to whom some of the scientific facts can be explained.
At a formal gathering, Jim tries to interest a consortium of industrial leaders in the project, and he shows them a Woody Woodpecker cartoon that explains how space travel could become a scientific reality. Besides teaching some basic physics, the cartoon has mission detail never mentioned elsewhere in the film, namely that when Luna returns to Earth there is some areo-breaking and a landing by parachute [1], with fins down but no full retro rocket landing.
Image: Woody Woodpecker explains rocket flight, and recovery methods on Earth.
General Thayer tells the group it is vital to global security that America be the first country to reach the Moon, warning that a foreign power could use the Moon as a missile base and thus gain control of the earth. Shades of the cold war! The industrialists fall all over themselves to finance the project. No mention is made of just which foreign power he is talking about.
When Luna is finished, Cargraves receives word that the government has denied his request to test it at the construction site, citing concerns about radioactive fallout. (Actually as I will note later, and though Heinlein would not have known it, this would have been an extremely dangerous launch.) Growing public opposition to the project leads Jim to suspect they have been targeted by a subversive propaganda campaign, and he decides to launch the rocket without waiting for permission. The crew is Cargraves, Barnes, Thayer and replacement radio man Sweeney. There is a stressful launch. High-g tests were being done by the Aeronautical Systems Center in 1948. I don’t know if there were photographs of the effects — it was not hard to extrapolate that a 5 g launch would distort the face — but this was a bit overdone in the film, and I’m not sure why Heinlein decided on 5 gs. It is notable that there are no ground control scenes, though indirectly we see what looks like a control center. We see the initial liftoff but not even a portion of the ascent. That could have been due to budget constraints. Almost all the ascent is depicted inside the ‘cockpit’.
Image: Cockpit during ascent. Couches and control panels to the right in the rotating cockpit set.
Once they are in transit to the Moon, the men don magnetic boots, which allow them to walk around in the zero g environment. Zero g had been accounted for in Frau im Mond (though in that film it never appears on screen). Destination Moon seems to be the first ‘full up’ portrayal of freefall. Those magnetic boots were a bit clunky but served their purpose.
Image: Zero g in Destination Moon.
There is a failure of the radar antenna, forcing the crew to put on spacesuits and go outside the ship to repair it. The suits are derived from pressure suits Heinlein had seen at the labs at the Philadelphia Naval Shipyard where he worked in WWII. Science fiction writer L. Sprague de Camp, also there, had been involved with this. The suits have a remarkable resemblance to some from 1943 (2a). I also think this is a better airlock in a film about space flight because the one in Frau im Mond is kind of confusing. This airlock is nicely functional.
Cargraves, of all people, loses magnetic contact with the ship and goes adrift in space (it would have been hard to train for this zero-g extravehicular activity on the ground!). He has to be rescued. The outside point of view shots are very nicely done, with some good stop-motion work with miniatures, one of Pal’s specialties. Heinlein noted that the star background was the best they could do in 1949 [10], but it looks good enough.
The ship eventually approaches the Moon, and having to account for rough terrain, they do some translating (shades of Apollo 11!) before finally touching down, though they have used more propellant than expected. This sequence starts with a beautiful outside shot of Luna rotating to a tail-down attitude with the lunar surface below. Attitude control seems to be by ‘gyro’ alone, as it seems no one thought of attitude jets. An auto-pilot is mentioned several times and seems to be in command many times. I am pretty sure all these technicalities are due to Heinlein (2a).
Cargraves and Barnes emerge from the ship to climb down a long row of retractable ladder rungs; there is some good stop-motion work here. The duo claim the Moon in the name of the United States. “By the grace of God and in the name of the United States of America… I take possession of this planet on behalf of, and for the benefit of…all mankind.” The technicalities of just how one would enforce that claim are left hanging in the vacuum.
Image: On the Lunar surface with the ‘cracks’ Bonestell hated. The full sized bottom of Luna.
The crew members conduct scientific tests, with General Thayer discovering there may be deposits of uranium on the Moon. There is some 1/6th-g action in a traverse. I am not sure but this may have been the only low-g demonstration on the Moon in a movie until recent times. Some of this was done with suited midgets on wires using forced perspective on a small lunar landscape set.
Barnes communicates by radio with Dr. Hastings at ‘mission control’ back home (we never see ‘mission control’, or Hastings, the astrodynamics guy back on Earth). Hastings confirms that their difficulties during landing used up too much of their reaction mass. Not clear why it was Barnes talking with Hastings, since Cargraves would have had more technical knowledge.
The earlier extravehicular activity (EVA), during transit, was just a minor mishap; now have a real problem to solve. Hastings instructs them to lighten the ship, and the men strip off nearly 3,000 pounds by removing metal fixtures and discarding all non-essential equipment. When Hastings tells them they must eliminate another 110 pounds, Thayer, Cargraves and Branes each volunteer to stay behind. They are about to draw lots when Sweeney sneaks out of the ship. He urges the others to leave, but Jim devises a way for them to discard the radio and the last spacesuit, thus reaching their weight goal. The ship takes off successfully, and the four men joyfully begin their journey back to Earth. Those high-g couches must have smarted without their cushions! Unlike the Earth launch more of the ascent is shown, and it is not so ‘sparky’, with better exhaust effect. One supposes they got back without having to do an EVA! Earth recovery required only a very small reaction mass (5). (The shooting script, maybe added by O’Hanlon, had scenes of domestic life with Cargraves and his wife at home. These may have been shot and then cut for the final movie).
Image: Lunar descent and ascent in the film.
Luna and Technology
It is quite striking that the spaceship in Destination Moon is single stage to the Moon and back. Heinlein had used this in his ‘kind of Tom Swiftian’ novel Rocket Ship Galileo, and it was one of the few technologies he brought over to Destination Moon from that novel. If one listens carefully when General Thayer is talking to Barnes, he mentions two numbers: an exhaust velocity of 30,000 ft/sec and a thrust of 3,000,000 pounds [1]. Exhaust velocity of 30,000 ft. per second is 9144 meters per second. Heinlein would have known that to do a single stage to the Moon, the delta V budget is 15 to 16 km/sec. Playing with the rocket equation, if one picks a mass ratio of 5 and calculates the exhaust speed, one gets about 9000 m/sec. It also implies an Isp of about 1000. No ordinary chemical fuel has a specific impulse like that. A number of guys at Los Alamos had realized that Isp was attainable with atomic energy. The first mention of an atomic rocket motor, before 1945, may have been Stan Ulam. Many technical reports came in 1945-1948 [14, 15, 16, and 17].
Heinlein knew Robert Cornog, who was at Los Alamos and would have known the skinny on nuclear rocket propulsion. Cornog had probably seen reports by Theodore von Karman and Hsue-Shen Tsien (1945) [17]), as well as Robert Serber (1946) [14], and Cornog wrote a report of his own (1945) [15]. Shepherd and Cleaver were the first to describe nuclear rockets in the open literature in 1948 [16]. Heinlein knew Cornog well and helped him keep a clearance after the war. The same calculation by Willy Ley (early 1949 [6]) is, in a roundabout way, in Conquest of Space.
The reactor in Destination Moon is never described, but it is not the rather funky Thorium one in Rocket Ship Galileo. The word ‘reactor’ is never used; it is usually ‘pile’, and the reactor seems to be a solid core. The reaction mass in the Destination Moon propulsion system is water, which would be very easy and safe to handle. The problem is that one can’t get an Isp of 1000 using water with a solid core nuclear engine. One can — I doubt Heinlein knew this — do it with a liquid core nuclear reactor (5), attaining an Isp of 1000 seconds.
Piecing together clues from the dialog in the screenplay, Heinlein’s novelette and his article in Astounding [10], some people have figured out the size and mass of Luna (5). The ship is 150 ft tall, with a ‘wet’ mass of about 250 metric tons and a dry mass of about 50 metric tons. Luna is a very good extrapolation fix-up from Rocket Ship Galileo, and not a sort of ‘hobby’ ship as in the novel. It is more planned, and put together by a SpaceX-like company without government money.
One element in the film where the government was right — Heinlein would not have known this — is that a liquid core nuclear rocket (5) has a radioactive plume coming off the reactor system which would be a cloud of death. The system would have been extremely hazardous if used in the atmosphere. The order sent to the launch site, which Barnes ignores, was thus correct. Liquid core atomic rocket engines were not proposed until 1953.
Guidance, navigation and control goes under the heading ‘automatic pilot’ in the movie, since we don’t really know, as far as I can tell, what date the flight is made (it looks like 1950). Heinlein makes the extrapolation that the electronics for doing this exists in the story. Note that Werner von Braun worked up The Mars Project in 1948 with the same kind of vacuum tube GNC systems, with no details given.
There is the use of ‘gyro’ attitude control, common to other writers about space flight at the time. Reaction jet attitude control was known in the engineering community but didn’t seem to get into science fiction. Gyro control was a favorite of von Braun also.
When it came to spacesuits (2a), Heinlein had experience with the issue during WWII at the Aeronautical Materials Lab at the Philadelphia Naval Shipyard, where he was a supervisor. L Sprague de Camp was recruited by Heinlein and was studying high altitude pressure suits. The spacesuits in Destination Moon were based on these [24]. I can only recall one movie before Destination Moon, Frau im Mond, that had spacesuits, and they were not really needed there.
Image: Pressure suits in the film on the left; on the right, a design being tested in Philadelphia in 1945.
Summary
Destination Moon is the product mainly of Robert Heinlein (6), facilitated by producer George Pal and film director Irving Pichel. Heinlein, when talking about a possible film with Friz Lang, started a reformulation of Rocket Ship Galileo into a more mature narrative. The Nazis (6) are jettisoned, and his ‘treatment’ seems reflected in the novelette he wrote of the same name [13]. After things did not work out with Lang, he wrote a treatment of his conversations with Lang and incorporated some of ‘The Man who Sold the Moon” within it. The ‘screenplay’ is online. It is all dialog, with no scene headings, action or transitions, which is odd, but probably this is just one of several script forms for the movie.
It is not clear what Pal wanted in the screenplay, but he was committed to a sort of docudrama. That’s what made the film an almost Popular Mechanics movie, so to speak. Pichel seemed to go out of his way to give Pal what he wanted. There was outside interference — the owner and CEO at Eagle-Lion, Peter Rathvon, imposed screenwriter James O’Hanlon, who inserted goofy stuff like musical numbers! (7). Pichel threw away all of O’Hanlon’s ‘script-doctoring’; there seems no record of what Pal thought of this, but he sure did not discipline Pichel. (Nor do we know what Rathvon thought of the final film which he was so nervous about).
Heinlein and Ginny returned to LA for film production in June of 1949 and remained until February of 1950. It is not clear if Heinlein advised on any of the post-production work, which was not completed until April 1, 1950. The finished film, if one could see a pristine version, looks great in Technicolor. The budget of almost $600,000 was not generous but sufficient, with hard work, to produce good special effects and production design. Heinlein was paid for the option of Rocket Ship Galileo and paid a portion for the screenplay; also, he was hired as technical consultant. I could not find what he got paid but it was enough for him and Ginny to get a start on a house in Colorado Springs [3].
Heinlein and Ginny returned to Colorado Springs in February, 1950. Patterson states the advertising and promotion of the film had a budget of $1.2 million, which is twice as much as production cost [3]. (I also found a promotion budget of $500,000 for the film [19].) Heinlein did publicity work in LA before he left, even a TV interview show with Pal and Bonestell [20]. Magazine and radio ads were everywhere and created a buzz for the movie [2, 3].
The film premiered in New York on June 27th, 1950. It seems that John W. Campbell was there, but it is not clear if Willy Ley or any of the New York Futurians attended. Bosley Crowther’s review in the New York Times was favorable, finding the film a visual treat; he was not much taken with the narrative drama. Other film reviews of the time were favorable, seemingly because of its novelty. Destination Moon made $5 million on its first run, which is almost a 3-multiplier (or a 5-multiplier if the advertising budget was 500,000), very good by modern standards.
Alas, much of profit was eaten up by coverage of the losses from The Great Rupert. The film would have made more but Eagle-Lion ran into distribution problems due to distribution control by the major studios [19]. Eagle-Lion entered into litigation for several years. Neither Peter Rathvon nor James O’Hanlon’s reaction to the film seems to be on record anywhere. Patterson’s biography does not make clear when Heinlein saw the film. He had to wait two years to get royalties for the first run, a little over $4000, and four more years before he got a small final payment [3].
Destination Moon is a bit of a quirk in film history. The public interest in science and technology was impacted by World War II, the atomic bomb, ballistic missiles, supersonic flight, radar, and the Cold War. Hollywood in 1948 was still in a mode that considered spaceflight crazy Buck Roger’s stuff. It took an independent studio and maverick producer and a science fiction grand master to get the film made.
In a way, Destination Moon was a sort of culmination of John W Campbell’s ambition to move away from pulp SF to something more sophisticated. The film is about as far away from Brass Bras and Bug Eyed Monsters as one can get. Destination Moon‘s success did not usher in a great era of space flight movies. Its competitor in 1950, Rocket Ship X-M, was actually a more interesting story although with silly engineering physics and a pulp-fiction Mars story. Pal followed with a film based on the second rate SF novel When Worlds Collide, and we got the totally goofy, pulpish Flight to Mars in 1951.
There were some weak efforts after 1951. Heinlein had a possible TV series called The World Beyond, but the pilot was released as a poorly financed movie called Project Moon Base. Pal’s 1955 Conquest of Space was the last serious space flight movie of the 1950’s. Alas, even though technically pretty good, James O’Hanlon seemed to get his revenge with a sappy story for the film. Then followed a torrent of schlock SF, awful films most of which were not even up to bad pulp standards! (8)
Destination Moon is a unique film. It took 18 years before there was a film with the same factual rigor, and probably more — that was 2001: A Space Odyssey. Destination Moon was influential; I know it impacted my life. When I was 11, I had no idea who Robert Heinlein (9) was. A year later I was reading his young adult novels. Almost simultaneously, in 1952, the Colliers series on spaceflight came out, then the Disney TV series. I could not imagine, at the time, that I was headed toward participating in Apollo and the first lunar landing. Looking back I am still a bit amazed.
Notes
1. At one point Heinlein suggested a backup technical adviser, Jack Parsons. That was odd; Parsons only real knowledge was rocket propellants. At that time, there were three guys from CalTech who Parsons knew and they were young and significant experts in spaceflight: Frank Malina, Martin Summerfeld and Hsue-Shen Tsien. Apparently Heinlein met Tsien but not Malina or Sommerfeld. They were all in LA at the time. Malina was an SF fan and expert in the new field of spaceflight, but apparently Heinlein never met him.
Chesley Bonestell did some technical advising on the film.
It is not clear if Pal agreed with Rathvon’s interference. Pal had wanted a documentary-style film and he had it in hand. Adding O’Hanlon meant some money when to him.
Heinlein wrote Willy Ley asking technical questions. Ley was not happy about this. He wrote back an angry letter asking to be paid for consulting. At the time Ley was strapped for money; I also wonder if he was a bit upset that he had been a facilitator of the whole course of events, since Conquest of Space seemed to be an input to the movie too. Heinlein tried to smooth things over but Ley remained unhappy [5]. In the 1954 edition of Rockets, Missiles, and Space Travel, Ley has a footnote about Destination Moon, saying he liked the film and praising its technical information [7].
Heinlein also consulted astrophysicist Fred Zwicky at CalTech and Robert S Richardson, an astronomer at Palomar Observatory and an SF author. Richardson did some detailed astrodynamics for Heinlein for Destination Moon.
2. Luna shows up in at least one or two more films, but Bonestell’s modified Conquest of Space ship is copied an uncountable number of times in movies [8, 9]. It shows up next in the 1951 Flight to Mars, and in modified versions on Tom Corbett Space Cadet and other TV shows.
2a. The spacesuits were suggested by Heinlein [3]. Like Luna, they were copied in other movies and TV shows many times. Color coding on uniforms and other similar clothes was not new, but the film used it to good advantage and it enhanced the Technicolor. It’s interesting that years later Kubrick used the same suit colors in 2001: A Space Odyssey, with the commander in red and the 2nd in command in yellow, with blue suits for the other crew and green for the suit in the emergency entrance [8].
Werner von Braun had, in 1948, vacuum tube guidance, navigation and control technology in the mission design for his Mars Project.
3. Cargraves is the only character carried over from Rocket Ship Galileo. The name seems to be a play on the name of Sir William Congreve, a 19th century military solid rocket pioneer.
4. Pal was looking to keep the budget down. It is not clear why he picked these actors or if Pichel could have gotten better performances. Pichel as veteran actor could have doubled as a character himself. Across town, Lippert Pictures made a film to piggyback on Destination Moon‘s publicity campaign, Rocket Ship X-M, (where M is Moon). The screenplay by Dalton Trumbo is full of scientific howlers but the story is not as awful as the 1953 Cat Women of the Moon (or other Z movies of the 50s). On a budget of $94,000, Lippert hired good actors like John Emery and Noah Beery, Jr., as well as Lloyd Bridges and Hugh O’Brian. These guys sure would have been an improvement in Destination Moon even with the same dialog.
Heinlein found out about Rocket Ship X-M through a letter from L. Ron Hubbard. Hubbard claimed to be working on that film, though as far as can be determined, he had nothing to do with it [2,3]. How Pal’s film became known to Lippert is not known, although Heinlein had informed Forest J Ackerman about Destination Moon‘s greenlighting in May of 1949. Destination Moon seems to have become known to fans in the LA area in early 1949. It is odd that Lippert even put up $94,000 when all the majors were nervous about a movie Moon-trip story.
5. Winchell Chung at the web site Atomic Rockets has the best summary, with some massaged numbers to make the dynamics of Luna work better. I think he is the first to notice that using water as the reaction mass requires a liquid core nuclear reactor [18].
6. Heinlein in his prose was an accomplished storyteller and good at writing dialog. The novelette Destination Moon has better dialog, though not polished. The basic story feels guided by Heinlein’s hand but in a very strict narrative. He wanted a no-nonsense story line and that is what results.
In the novelette Destination Moon, ‘domes’ are found, supposedly Russian. I doubt this was in any version of the screenplay. Nazis on the Moon became a pop-idea that would not die. This is what the film Iron Sky (2012) was about.
7. Pal must have had a weak spot for this; in the 1955 film Conquest of Space, O’Hanlon inserted a televised musical number by Rosemary Clooney to the space station.
8. Ley finally got some money from Pal by selling him the rights to Conquest of Space, which had no film story in it [4]. Conquest of Space seems to have had no technical adviser, although director Byron Haskin is quoted as saying he talked to Werner von Braun a lot [21]. However, there is a picture of Pal, Bonestell, Ley and director Haskins around a large table with Ley expounding on technical issues.
The movie Conquest of Space, aside from the narrative, is an odd mix of von Braun, Ley and Bonestell’s popularization of space flight by way of the Collier’s series, von Braun’s The Mars Project and the book The Exploration of Mars. An April 1954 issue of Collier’s (the last issue of the spaceflight series) had a full realization of the 1948 von Braun Mars Project. Ley and Bonestell were pressuring von Braun to make a book of this. However, von Braun wanted to redesign the expedition, taking the Mars fleet down from 10 ships to 2. The movie Conquest of Space took it down to 1. Most of the rest of the design was from the Collier’s series: The space station, the spacesuits, the orbital ferries and the Mars ship. Somehow some retrorockets got added to the Mars ship; I doubt that was von Braun’s design.
I could not find a single reference that related what Wernher von Braun thought of Destination Moon.
Except for Destination Moon and Conquest of Space, I don’t think a single spaceflight movie in the 1950s had a technical adviser.
9. Reading several essays about Destination Moon it is strange how Heinlein’s involvement is either not mentioned or touched upon only briefly. The Moon flight film would have never been made if it had not been for Ley’s introduction to Lang, after Heinlein broke with Lang, and if Heinlein had not persisted with the story and screenplay in 1948.
10. Arthur C. Clarke had mentioned atomic propulsion in 1945 [22] and had written a novel, Prelude to Space in 1947 [23], which used a nuclear powered two stage vehicle.
References
1. Destination Moon, screen play by Rip Van Ronkel, Robert Heinlein and James O’Hanlon, from a novel by Mr. Heinlein; directed by Irving Pichel; produced by George Pal and released by Eagle-Lion. (Premiere: June 29 1950).
2. Patterson, William H., Jr. 2010. Robert A. Heinlein in Dialogue With His Century: 1907-1948 Learning Curve. An Authorized Biography, Volume I.
3. Patterson, William H., Jr. 2014. Robert A. Heinlein in Dialogue With His Century: 1948-1988 The Man Who Learned Better. An Authorized Biography, Volume II.
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5. Jared S. Buss, Willy Ley: Prophet of the Space Age. University Press of Florida, 2017.
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https://www.scripts.com/script/destination_Moon_6783
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Timing Titan’s Tidal Migration
Finding out that Titan is migrating away from Saturn should cause little surprise. Our own Moon moves away from the Earth at about 38 millimeters per year (even as Earth’s rotation slows ever so slightly, lengthening the day by 23 microseconds every year). Titan’s gravitational pull on Saturn causes frictional processes inside the giant world that ultimately impart energy to Titan, moving it away from its host in a similar way. The surprise attendant to a new paper on this phenomenon is the size of the movement, about 100 times greater than had been expected.
The paper explains the migration process like this:
Tidal friction within Saturn causes its moons to migrate outwards, driving them into orbital resonances that pump their eccentricities or inclinations, which in turn leads to tidal heating of the moons.
What we’re wrestling with here are the processes of energy dissipation in giant planets, which determine the timescale for their moons’ tidal migration. The theory advanced in this work may explain them.
The paper appears in Nature Astronomy, with Valéry Lainey (Paris Observatory) as lead author. Two teams of scientists used both astrometric and radiometric datasets, two different approaches into the same question, to measure Titan’s orbit over a ten year period. Astrometry produced measurements of Titan’s position in relation to background stars, tapping data from the Cassini orbiter. The radiometry work measured Cassini’s velocity as it was affected by the gravitational influence of Titan, revealed by analysis of the spacecraft’s radio transmissions during ten close flybys of the giant moon.
Usefully, the two datasets produced results in tight agreement. Co-author Jim Fuller (Caltech) proposed in 2016 that Titan’s migration rate would be considerably faster than predicted by standard tidal theories. Fuller’s idea was that Titan’s effect on Saturn, a gravitational squeeze at a particular frequency, would create strong oscillations, what the paper refers to as “inertial waves,” inside the planet. The process is a tidal forcing effect known as ‘resonance locking.’ Saturn’s oscillations, Fuller believed, would cause energy to be dissipated, allowing Titan to migrate outward at a faster rate only weakly sensitive to orbital distance.
The Cassini data from two different analyses confirm what Fuller has been saying. Indeed, whereas the prediction had earlier been that Titan would be migrating outward at 0.1 centimeters per year, the actual number is 11 centimeters per year. Resonance locking means that we can’t assume that moons like Titan form at the orbital distance at which we see them now. Instead, we see at Saturn a system that Fuller believes evolved far more dynamically.
Image: A giant of a moon appears before a giant of a planet undergoing seasonal changes in this natural color view of Titan and Saturn from NASA’s Cassini spacecraft. Titan, Saturn’s largest moon, measures 5,150 kilometers across and is larger than the planet Mercury. This mosaic combines six images — two each of red, green and blue spectral filters — to create this natural color view. The images were obtained with the Cassini spacecraft wide-angle camera on May 6, 2012, at a distance of approximately 778,000 kilometers)from Titan. Image scale is 29 miles (46 kilometers) per pixel on Titan. Credit: NASA/JPL-Caltech/Space Science Institute.
So we’re beginning to re-think how planets affect the orbits of their moons. These results suggest that Titan started out much closer to Saturn, with the system of moons expanding more quickly than earlier thought. Rather than assuming that outer moons like Titan migrated outward more slowly than inner moons, we learn that these outer moons can migrate at a similar rate. Migration turns out to be even more complex than first believed, with results at Saturn that have implications for how we study far more distant systems including exoplanets around host stars. Thus the paper’s conclusion:
Resonance locking could operate in other moon systems, such as the Jovian system, where it might drive the outward migration of Io/Europa/Ganymede and predicts a much smaller effective Q [the tidal quality factor] for Callisto if it is caught in a resonance lock. Resonance locking can also act in stellar binaries and exoplanetary systems, but it will not always dominate tidal dynamics, for instance, at very close separations when equilibrium tidal dissipation is more important, or when resonances are saturated by chaotic or non-linear effects. But resonance locking could be especially important at wider separations where equilibrium tidal dissipation is negligible (as it is for Titan’s migration), or in situations when a star or planet evolves on a relatively short timescale owing to a rapid evolutionary phase, accretion, magnetic braking or gravitational wave-driven inspiral.
The paper is Lainey et al., “Resonance locking in giant planets indicated by the rapid orbital expansion of Titan,” Nature Astronomy 8 June, 2020 (abstract).
KOI-456.04: Earth-like Orbit Highlights New Detection Tools
The planet candidate KOI-456.04 strikes me as significant not so much because of the similarity of its orbit with that of Earth (a 378 day orbital period around a star much like the Sun), but because of the methods used to identify its possible presence. Make no mistake, this is still very much a planet candidate, as co-authors René Heller and Michael Hippke are at pains to explain, noting that systematic measurement errors cannot be ruled out, though they estimate an 85 percent likelihood that it is there.
We don’t have many examples of small planets potentially in the habitable zone of a star like ours, and this is what has received the most media attention. So let’s look at this aspect of the story quickly, because I want to move past it. If this candidate is confirmed, it looks to be less than twice the radius of the Earth, receiving about 93 percent of Earth’s insolation from its star. Make assumptions about its atmosphere and you can arrive at a surface temperature averaging 5?, 10 degrees lower than Earth’s mean temperature.
Image: Most of the exoplanets from the Kepler mission are the size of Neptune and in relatively close orbits around their host stars, where temperatures on these planets would be far too hot for liquid surface water (third panel from above). Almost all of the Earth-sized planets known to have potentially Earth-like surface temperatures are in orbit around red dwarf stars, which do not emit visible light but infrared radiation instead (bottom panel). The Earth is in the right distance from the Sun to have surface temperatures required for the existence of liquid water. The newly discovered planet candidate KOI-456.04 and its star Kepler-160 (second panel from above) have similarities to Earth and Sun (top panel). MPS / René Heller.
But what I want to dwell on is the methodology used to study this system. Heller (Max Planck Institute for Solar System Research) and Hippke (Sonneberg Observatory, Germany) are joined here by colleagues at the University of Göttingen, UC-Santa Cruz and NASA Ames in a new look at archival data from Kepler on the star Kepler-160 in Lyra, which was observed by the mission between 2009 and 2013. The star is similar to the Sun in mass and radius and previously known to have two confirmed planets.
The new work analyzes transit timing variations in the orbital period of the planet Kepler-160c suggestive of a third planet. They find Kepler-160d, a third world that is disturbing the orbit of Kepler-160c. This is a planet without any transits that is thus only indirectly confirmed.
The intriguing candidate, potentially the fourth planet here, is KOI-456.04, which appears to be 1.9 Earth radii in an orbital period of 378 days. The Max Planck Institute for Solar System Research (MPS) happens to be building the PLATO Data Center, and the suggestion is that the PLATO mission, to be launched in 2026, will have the chance to confirm this interesting object of interest and study it in much greater detail.
Heller and Hippke have been developing their exoplanet detection pipeline in several recent papers, studying twelve detrending algorithms for stellar light curves in detail. ‘Detrending’ refers to eliminating noise within transit data to cull out evidence for a planet. The results pointed to a detrending algorithm available in the open source package called W?tan, used in combination with a transit search algorithm known as ‘transit least-squares’ as the most accurate choice. Heller and Hippke developed TLS specifically to look for smaller planets by modeling stellar limb darkening (see Dataset Mining Reveals New Planets for more on this).
What emerges is a more precise model of the brightness variations seen in a transit event, one that the duo believe improves upon the more established ‘box-like’ approximation known as the ‘box-fitting least square’ (BLS) algorithm. The latter is somewhat faster in computational terms, but the Wotan/TLS combination is in the authors’ view more sensitive. I talked to both Heller and Hippke about the new paper via email and asked Hippke about the advantages of their method. His response:
I… believe that W?tan+tls are the leading toolset in finding new transiting exoplanets. You gain about 10% sensitivity going from BLS to TLS. In other words, at the same false alarm rate (e.g., 1%) you get 10% more planets from TLS. Naturally these are at the small end of the size distribution (you find large planets as easily with BLS). Smaller planets are usually more interesting because rocky planets are believed to be < ~ 2 Earth radii.
The dominating noise source in transit observations is in many cases stellar variability, which is why Heller and Hippke tested a dozen detrending methods, all of which are available through W?tan (TLS is likewise an open source tool). According to Hippke, the W?tan methods are more important for more active stars — remember that M-dwarfs can be quite active in comparison to G-class stars like the Sun. Young stars just at the end of planet formation are likewise active, making them interesting targets for using the W?tan tools to achieve optimal detrending for exoplanet detection.
Heller told me that the team is 100% sure that Kepler-160d exists — this is the non-transiting world found through using transit timing variations of Kepler-160c. But what of the planet in the orbit roughly similar to that of the Earth around the Sun?
Our statistical analysis gives us 85% confidence that the signal belongs to a transiting planet. But 99% would be needed to call this a planet. In this case, this object would be called Kepler-160e. For now, it is not. So this object is transiting (I mean, if it is real in the first place), but we are less certain than for the non-transiting planet Kepler-160d that it actually exists. And so KOI-456.04 remains a candidate unless someone can show that it exists with more than 99% certainty.
Thus the tantalizing ‘world’ in the Earth-like orbit remains a Kepler Object of Interest (KOI), an object that cannot be currently validated or falsified, but one that will doubtless be on the target list for the PLATO exoplanet mission. The larger story is that the tools Heller and Hippke have deployed show the promise of pulling 10% more planets (and smaller ones at that) out of the raw data, which makes analysis of ongoing observations as well as reanalysis of older datasets more accurate. It will be fascinating to watch as the computational methods on display in this paper are applied to other known exoplanet systems, with their validity then put to the test by future space- and ground-based observatories.
The paper is Heller et al., “Transit least-squares survey. III. A 1.9 R? transit candidate in the habitable zone of Kepler-160 and a nontransiting planet characterized by transit-timing variations,” Astronomy & Astrophysics, Volume 638, id. A10 (June, 2020). Abstract/preprint.
Are Classic Habitable Zones Too Wide for Complex Life?
Selection is going to be a key issue for future ground- and space-based observatories. Given lengthy observing times for targets of high interest, we have to know how to cull from our exoplanet catalog those specific worlds that can tell us the most about life in the universe. Recently, Ramses Ramirez (Earth-Life Science Institute, Tokyo Institute of Technology) went to work on the question of habitable zones for complex life, which are narrower than the classic habitable zone defined by the potential for water on the surface. In today’s essay, Alex Tolley looks at Ramirez’ recent paper, which examines the question in relation to the solubility of gases in lipid membranes. What emerges in this work is a constrained habitable zone suited to complex life, with limits Alex explores. The model has interesting ramifications right here in the Solar System, but it also points the way toward constraining the list of planets upon which we’ll apply our emerging tools for atmospheric characterization.
By Alex Tolley
Daggerwrist on Darwin IV. Artist Wayne Douglas Barlowe. Source: Expedition.
Life on Earth, until its last three quarter-billion years, was almost entirely represented by unicellular organisms. As we explored in Detecting Early Life on Exoplanets, biosignatures for microbial life are likely to be far more prevalent than for worlds with complex life. While rocky worlds in the classic habitable zone (HZ) are still relatively few, academic PR departments trumpet every find as “Earth-like”, and a selection of these worlds will be targeted for biosignatures. However, as the number of these worlds increases, scientists will want to distinguish worlds that have a biosphere that can be characterized as more Earth-like, with verdant landscapes and megafauna in the seas and on land.
When the term “Earth-like” is used, the public thinks of a world that looks like Earth, with oceans, continents variously clothed in verdant landscapes, and perhaps most importantly of all, “charismatic megafauna”, the animals that you went to see at the zoo, or watched on David Attenborough’s excellent nature programs. A blue sea lapping on a muddy beach, despite teeming with microbes and other unicellular life, looks dead to the unpracticed eye, which means most of the human population. It is those human-scale animals like the daggerwrist pictured above from Barlowe’s “Expedition: Being an Account in Words and Artwork of the 2358 A.D. Voyage to Darwin IV” that excites the public.
If life is rare, then the classic HZ will have the least constraints, although most of those worlds will still have biospheres populated only with microbes, and fewer probably with unicellular plants and animals. If life is not rare, then there will be a desire to discover true Earth-like worlds with complex life, which may mean limiting the range of the HZ that will allow for such life to flourish.
The classic HZ range is defined by the possibility of liquid water remaining continuously on the surface, warmed by the star’s radiation and an atmosphere of sufficient pressure and with some greenhouse gases. This is because all Earth’s life requires liquid water and this has led to the mantra “Follow the water” for missions in the search for life. Inside the inner HZ limit, there will be a runaway greenhouse that eventually desiccates the planet, like Venus. Towards the outer edge, the atmosphere needs to be increasingly composed of greenhouse gases, particularly carbon dioxide (CO2) until a limit is reached.
For the solar system, the classic HZ lies at about 0.95 AU, inside Earth’s orbit, but excludes Venus, and extends to about 1.67 AU, outside of Mars’ orbit. It is this that offers the possibility of a second genesis and possibility of finding extant life in refuges and in the lithosphere beneath the now inhospitable Martian surface.
Complex, or multicellular, life on Earth emerged less than 1 billion years ago as photosynthesis reduced the CO2 in the atmosphere and replaced it with oxygen (O2). Except for a few recently discovered species, all multicellular life is aerobic and requires a rich O2 atmosphere. It is the much greater energy released by aerobic respiration compared to anaerobic respiration that allows for the energetic lifestyles of multicellular animal life (metazoa). At least for our planet, we believe that the conditions for complex life to survive are constrained; Earth has its own habitable zone limits that are narrower than the classic HZ. The question is, “What might those HZ limits be for complex life, and how does that translate for exoplanets around different stellar types?”
CO2 is one of the main greenhouse gases that extend the outer boundary of the HZ. Nitrogen (N2) also helps extend the outer edge of the HZ although it is not a greenhouse gas but a main constituent of the atmosphere. Are there limits to the pressures of these gases due to effects on complex life that limit the range of the possible HZ for multicellular life living on the planet’s surface?
A new paper by Dr. Ramses Ramirez attempts to answer that question by applying the relationship between the solubility of gases in lipid membranes and their anesthetic potency (see figure 1 below). This theory, a partial explanation for the still imperfectly understood mechanism of anesthesia, is that the solubility of gases in lipid membranes is correlated with their anesthetic potency. Anesthetists must monitor the use of these gases to maintain unconsciousness. Too little and the patient remains conscious of the pain during surgery, too much anesthetic, and the patient stops breathing and dies.
The anesthetic gases are to the bottom right of the chart in figure 1. Nitrous oxide (N2O) is less potent and still used in dentistry (as well as at “nitrous parties”). Less well known is that CO2 also acts as such a gas with solubility similar to N2O. Although physiologically CO2 initially increases breathing rate to flush it out of the lungs, at higher concentrations it then invokes respiratory, and later metabolic, acidosis, which sets in as CO2 dissolved in the blood serum eventually causes cessation of respiration and death. As can be seen in figure 1 below, N2 has low solubility in lipid membranes, 2 – 3 orders of magnitude lower than CO2, and concomitantly similar orders of magnitude lower anesthetic potency.
However, we are probably also familiar with the effects of high-pressure N2 as nitrogen narcosis that is experienced by divers breathing compressed air at depth. The argument is that both CO2 and N2 dissolving in the lipid membranes of cells will cause death if those gas concentrations reach the anesthetic level for complex life.
Figure 1: The Meyer-Overton correlation of oil/gas solubility versus anesthetic potential of inhaled gases. Figure recreated from published data. Source Ramirez [1].
Figure 1 above shows the relationship between gases and their anesthetic potential. CO2 solubility is similar to nitrous oxide, while N2 is far less potent and therefore apparently less of a constraint. Note that helium is at the upper end of the range and has low solubility and low anesthetic potency. This is why helium is used to replace N2 when deep diving in soft suits.
While the Meyer-Overton correlation is primarily for humans, it has been shown to apply across several different phyla as it is a physical, rather than physiologic effect. Determining the tolerance limits for CO2 and N2 provides a constraint that limits the HZ to a “Complex Life Habitable Zone (CLHZ).” Dr. Ramirez supports the general applicability of the lipid gas solubility to metazoa from prior experimental work, primarily on mammals, but also with other animals, to suggest that 0.1 bar (1/10th of surface atmospheric pressure or 1.4 psi) of CO2 might be a reasonable, conservative limit for complex life to tolerate CO2. N2 limits are primarily set by experiments for human divers. 2 bar of N2 seems to be the safe limit at which divers do not get narcosis. This is just 10 meters below the surface, a depth even beginner scuba divers can safely operate for short durations. Using upper limits for 0.1 bar CO2 and 2 bar N2, Dr. Ramirez finds that his radiative-convective model (RC) gives an estimated HZ for complex life (CLHZ) of 0.95 – 1.21 AU. Using an advanced energy balance model (EBM) that allows for different temperatures on the Earth’s surface, thus allowing for liquid water at the equator, but not at the poles, this CLHZ is extended from 0.95 – 1.31 AU.
The new outer range for this 2 bar N2 and 0.1 bar CO2 is 1.36 AU using the Energy Balance Model (EBM). This range is shown in figure 2 below not just for Earth, but for a range of main sequence star types. The relative decrease in the CLHZ compared to the HZ is greatest for cooler stars, the type we have most exoplanet examples in the HZ currently.
Figure 2. The Complex Life Habitable Zone (CLHZ) for A – M stars (2,600 – 9,000 K) compared to other definitions.The CLHZ is for a 0.1 bar, 2 bar N2 atmosphere which is compared to the classic HZ. While the inner edge of the HZ and CLHZ are the same at 0.95 AU, the outer edge of the CLHZ is now well inside the orbit of Mars. Image source: Ramirez.
Dr. Ramirez compares his results to a similar paper by Dr, Edward Schwieterman that looks at the same problem but through the lens of CO2 chemistry, with the note that carbon monoxide (CO), while not limiting the CLHZ, is toxic and could be limiting to the evolution of complex life [2]. (The CO is created by photolysis of CO2.) Schwieterman uses a 1D radiative-convective climate model for his calculations across a range of CO2 levels. Schwieterman does not investigate higher N2 pressures which results in his modeling having a narrower CLHZ than Dr. Ramirez’s most comparable modeling. However, the CO toxicity does not appear significant except for planets orbiting cool stars such as M dwarfs.
While both authors attempt to redefine the likely boundaries for the HZ of complex life based on Earth’s biological evolution, only Dr. Ramirez employs the possibility of increasing the N2 pressure to increase the outer limit.
To quote from the paper:
“The CLHZ is slightly wider at the higher N2 pressure because of increased N2-N2 collision induced absorption and a decrease in the outgoing infrared flux, which more than offset an increase in planetary albedo.”
Dr. Ramirez also states:
“I consider how our solar system’s HZ changes if we assume (for the moment) that complex life could evolve to breathe in a hypothetical 5-bar N2 atmosphere. For this sensitivity study, the RC model predicts that such worlds in our solar system can remain habitable at 1.24AU (SEFF = 0.65) whereas atmospheric collapse can be avoided as far as 1.36 AU (SEFF = 0.54) in the EBM (nearly 60% classical HZ width). I find that the additional N2 opacity is sufficient to counter the ice-albedo feedback, allowing for effective planetary heat transfer even at relatively far distances.”
Dr. Ramirez’s 0.1 bar constraint for CO2 should be put in context for life on Earth. CO2 is currently at about 0.04% (0.0056 psi) of the Earth’s atmosphere. Even during the Cambrian period when multicellular animals were rapidly diversifying into phyla, the atmospheric component of CO2 was never more than 1% and it fell fairly continuously during this period. The Great Permian Extinction which saw 90-95% of all complex life become extinct primarily by anoxia in the oceans, the CO2 levels were little more than 0.1% at their peak. [See “Climate Change and Mass Extinctions: Implications for Exoplanet Life”] and figure 3 below. For highly cognitive humans, NASA conservatively stipulated that the highest emergency level of CO2 in the Apollo Command and Lunar modules should be no more than 0.29 psi (0.02 bar) in an atmosphere of 5 psi O2 before cognitive skills become impaired [40]. The Centers for Disease Control and Prevention (CDC) guidelines for CO2 is that 0.04 bar CO2 is immediately dangerous [i].
It should also be noted that the analysis is limited to surface living, air-breathing animals. Bathypelagic organisms, such as oceanic fish may be adapted to tolerate far higher N2 pressures.
Figure 3. O2 and CO2 levels in the Phanerozoic. [3] While the Permian extinction is associated with a rise in CO2 levels to about 0.1%, and a decline in O2 levels from the Carboniferous, the CO2 levels were far higher at 1% at the start of the Cambrian and still high in the Devonian (the age of fishes).
But what about multicellular organisms other than animals? While Dr. Ramirez acknowledges that complex life includes plants and fungi, not just metazoa (animals), he is unable to address the possible range of CO2 and N2 pressures these complex life forms might be adapted to because there is next to no data on the effect high pressures and concentrations these gases have on plants or fungi, beyond incremental increases in CO2 to experiment on plant photosynthesis limits and productivity. Where we do have data is Earth’s history of complex life that indicates that relatively low levels of CO2 in the atmosphere due to volcanic emissions, and reduced plant life to draw down CO2 and replenish the O2 due to sulfur acid rains and ash-darkened skies, are sufficient to force most species, including plants, to extinction. We do not know what factor or combination of factors is important, nor whether it is primary factors such as anoxia, or n-th order factors that resulted in their final extinction.
Now that the inventory of exoplanets is rapidly increasing, it is certainly time that we start thinking more critically about what sort of life we are looking for and what that might mean for the range of the habitable zone that supports these different life forms. Rather than allowing the widest possible HZ that allows any atmospheric composition and pressure allowing liquid water, we could also be looking for possible constraints that appear required for the sort of surface, air-breathing complex life that will give rise to the charismatic fauna that we have on Earth. Dr. Ramirez has posited one interesting idea for terrestrial complex life that is based on respiration across a range of metazoans which then constrains the atmospheric gas composition and hence the HZ.
As Ramirez’ CLHZ has an outer limit well inside the orbit of Mars, this invites speculation that if Mars ever had any life during its earlier, wetter, period, it did not have complex life. If this model proves correct, while we may find subterranean microbial life on Mars, we will not find metazoan fossils, such as mollusk shells or vertebrate skeletons.
It should be borne in mind that life as a whole maintains Earth’s low CO2 levels to keep the surface temperature equitable for itself, maximizing biodiversity and biomass. While hotter (e.g. the Eocene maximum) and cooler (ice ages) periods upset that equitable temperature, life in concert with much slower geological processes act as a thermostat. It is also the case that biomass and diversity are greatest in the tropical forests and the lowest at the poles. It must have been relatively sparse during the “snowball Earth” period but recovered once the global ice sheets melted. Life has evolved on the Earth as it is, and has biochemistry that matches that requirement.
Today, that requirement is for an atmosphere that has a low CO2 level. On exoplanets, where much higher CO2 levels are needed to keep the planet warm, different biochemistries might develop, and this is a caveat that Ramirez considers for his analysis. However, without examples of such life, we are forced to use Earth’s life as our only model. In a half-billion or so years in the future, as the sun increases its luminosity, the required CO2 level to keep Earth cool enough will be below that needed by plants. A technological species might utilize technology like orbital sunshades or perhaps genetic engineering to maintain life on Earth.
The more important point is that we may be able to provide more granular characterizations of exoplanets. Rather than the binary in or out of the classic HZ for exoplanets and therefore potentially living or not, we can add granularity, such as inside the CLHZ and therefore capable of hosting complex life too. This conclusion does depend on exo-life following our terrestrial biology. If it doesn’t then we have to fall back to the more generous HZ calculations alone.
References
1. Ramirez, Ramses M. “A Complex Life Habitable Zone Based On Lipid Solubility Theory.” Scientific Reports, vol. 10, no. 1, 2020, doi:10.1038/s41598-020-64436-z.
2. Schwieterman, Edward W., et al. “A Limited Habitable Zone for Complex Life.” The Astrophysical Journal, vol. 878, no. 1, 2019, p. 19., doi:10.3847/1538-4357/ab1d52.
3. CO2 and O2 levels in the phanerozoic. Web accessed May 11, 2020. https://notrickszone.com/2018/05/28/2-new-papers-permian-mass-extinction-coincided-with-global-cooling-falling-sea-levels-and-low-co2/
4. Michel, E. L., et al, SP-368 Biomedical Results of Apollo – Chap. 5 Environmental Factors. Accessed from web, May 11th, 2020. https://history.nasa.gov/SP-368/s2ch5.htm
Exoplanet Hunting with CubeSats
55 Cancri e is a confirmed planet, and thus a departure from our topic of the last two days, which was the act of exoplanet confirmation as regards Proxima Centauri b and c, the latter still in need of further work before it can be considered confirmed. But 55 Cancri e has its uses in offering a tight orbit around a Sun-like star that can be detected using the transit method. That was just what was needed for ASTERIA (Arcsecond Space Telescope Enabling Research in Astrophysics), a technology demonstration mission involving a tiny CubeSat.
Sara Seager (MIT) has been at the heart of the investigation of CubeSats as exoplanet research platforms. I think the idea is brilliant. If we want to mount the most effective search of nearby Sun-like stars for Earth analogs, multiple telescopes must be in use. CubeSats are cheap. Why not launch a fleet of them, each with the task of monitoring a single star at a time. Launched in 2017, ASTERIA was the prototype, a nanosatellite equipped with precision pointing control and thermal stability of the sort needed to meet the tight tolerances of such observations.
Image: Left to right: Electrical Test Engineer Esha Murty and Integration and Test Lead Cody Colley prepare the ASTERIA spacecraft for mass-properties measurements in April 2017 prior to spacecraft delivery ahead of launch. ASTERIA was deployed from the International Space Station in November 2017. Credit: NASA/JPL-Caltech.
ASTERIA is a collaboration between the Jet Propulsion Laboratory and MIT, one in which MIT retains the lead in science operations while JPL handles overall project management. Seager is principal investigator on the project. Three mission extensions pushed the original 90 day prime mission into extensive prototype testing, which culminated in the CubeSat using its fine pointing control to detect 55 Cancri e’s transits. This is quite an achievement for the tiny satellite, given the need for a steady platform without movement or vibration as the star is examined.
And ponder this: 55 Cancri e blocks only 0.04% of the host star’s light. Mary Knapp is ASTERIA project scientist at MIT’s Haystack Observatory and lead author of the paper on this work, which will appear in the Astronomical Journal:
“We went after a hard target with a small telescope that was not even optimized to make science detections – and we got it, even if just barely. I think this paper validates the concept that motivated the ASTERIA mission: that small spacecraft can contribute something to astrophysics and astronomy.”
Image: The super-Earth exoplanet 55 Cancri e, depicted with its star in this artist’s concept, likely has an atmosphere thicker than Earth’s but with ingredients that could be similar to those of Earth’s atmosphere. Scientists say the planet may be entirely covered in lava. The planet is so close to its star that one face of the planet consistently faces the star, resulting in a dayside and a nightside. Credit: NASA/JPL-Caltech.
Yesterday we saw how data from three different sources were used to investigate Proxima Centauri c, strengthening the case for its existence but not yet confirming it. On its own, the ASTERIA data would be suggestive of a planet but not proof of it, but it was when comparing the CubeSat data with previous observations that it could be determined that the CubeSat had indeed seen the planet. As we develop CubeSat capabilities, we can use them to follow up on detections made by larger telescopes, focusing on one star and keeping our gaze fixed.
That’s especially useful for potential Earth analogs, where around G-class stars orbital times are long enough to require persistence if we are to see a transit. Thus it’s good news that Sara Seager has been awarded a NASA Astrophysics Science SmallSat Studies grant to develop a follow-on mission involving a constellation of satellites, each about twice the size of ASTERIA.
This excerpt from the paper describes the constellation concept:
ASTERIA was a successful technology demonstration of a future constellation of up to dozens of satellites, dubbed the ExoplanetSat Constellation. Each satellite would share ASTERIA’s precision pointing and thermal control capabilities, operate independently from the others, but may have different aperture sizes in order to reach down to fainter stars than ASTERIA’s current capability. The primary motivation is the fact that if there is a transiting Earth size planet in an Earth-like orbit about the nearest, brightest (V<7) Sun-like stars, we currently have no way to discover them; current missions saturate on these bright stars. The ultimate goal for the constellation is to monitor dozens of the brightest sun-like stars, searching for transiting Earth-size planets in Earth-like (i.e., up to one year) orbits.
The advantages of this ‘fleet’ approach are apparent. The paper continues:
Because the brightest sun-like stars are spread all across the sky, a single telescope will not do. Instead, each satellite would monitor a single sun-like star target of interest for as long as possible, before switching to another star, with targets only limited by the Sun, Earth and Moon constraints. To narrow down the approximately 3,000 target stars brighter than V=7, one would have to find a way to constrain the stellar inclinations and assume the planets orbit within about 10 degrees of the stars equatorial plane. This would reduce the number of target stars from about 3000 to about 300 (Beatty & Seager 2010), a much more tractable number of targets. The ExoplanetSat Constellation has a unique niche in context of existing and planned space transit surveys…, but is still in concept phase.
How to keep these spacecraft small? The use of CMOS detectors (complementary metal-oxide-semiconductor) working in visible light allowed ASTERIA to operate without a large cooling system, as would have been required by a CCD (charge-coupled device) to keep the instrument cold. We’ll follow MIT’s CubeSat work as the lessons learned from ASTERIA are drawn into the next design.
The paper is Knapp et al., “Demonstrating high-precision photometry with a CubeSat: ASTERIA observations of 55 Cancri e,” in process at the Astronomical Journal (preprint). Thanks to Centauri Dreams regular Andrew Tribick for the heads-up on this paper.
Confirmation of Proxima Centauri c?
Hard on the heels of the confirmation of Proxima Centauri b, we get news of Proxima c, which has now been analyzed in new work by Fritz Benedict (McDonald Observatory, University of Texas at Austin). Benedict has presented his findings at the ongoing virtual meeting of the American Astronomical Society, which ends today. The work follows up and lends weight to the discovery of Proxima c announced earlier this year by a team led by Mario Damasso of Italy’s National Institute for Astrophysics (INAF), which had used radial velocity methods to observe the star. We need further work, however, to say that Proxima c has been confirmed, as Dr. Benedict explained in an email this morning.
But first, let’s straighten out a question of identity. Yesterday, when discussing the confirmation of habitable zone world Proxima b, we talked about a second signal in data culled by the ESPRESSO spectrograph. If the second ESPRESSO signal does turn out to be a planet, it will be a third Proxima Centauri planet, not Proxima c. That signal does not rise to candidate planet status, nor does the ESPRESSO team claim it as such, but it suggests a minimum mass about a third of Earth’s at an orbital distance inside Proxima b in a five-day orbit.
Proxima c as studied by Benedict is a different world entirely. What the new work addresses is the Damasso finding of a planet in a 1,907-day orbit at a distance of 1.5 AU, well outside the star’s habitable zone. Seeing Damasso’s work, Benedict made the decision to re-examine data he had collected on Proxima Centauri using the Fine Guidance Sensors (FGS) on the Hubble Space Telescope. This is a classic case of tapping old data, as the Hubble work was done in the 1990s.
Image: Fritz Benedict, emeritus senior research scientist with the University of Texas at Austin’s McDonald Observatory. Credit: McDonald Observatory
And while Damasso used radial velocity methods (examining the star’s movements toward and away from Earth as influenced by planetary companions), the Hubble FGS, which were designed for pointing accuracy, allowed Benedict to use astrometry, the measurement of the positions and motions of stars. In the earlier study, Benedict worked with Barbara MacArthur, also at McDonald Observatory, to look for planets with orbital periods of 1,000 days or fewer, and found none. A re-investigation of the dataset looking for planets in longer orbital periods turned up the signal at 1,907 days.
Benedict then turned to images collected by INAF’s Raffaele Gratton using the SPHERE instrument on the Very Large Telescope in Chile, which showed what could be Proxima c at several points in its orbit. In An Image of Proxima c?, I ran a figure from the Gratton paper reproduced below, along with the paper’s caption.
Image: This is Figure 2 from the paper. The SPHERE images were acquired during four years through a survey called SHINE, and as the authors note, “We did not obtain a clear detection.” The figure caption in the paper reads like this: Fig. 2. Individual S/N maps for the five 2018 epochs. From left to right: Top row: MJD 58222, 58227, 58244; bottom row: 58257, 58288. The candidate counterpart of Proxima c is circled. Note the presence of some bright background sources not subtracted from the individual images. However, they move rapidly due to the large proper motion of Proxima, so that they are not as clear in the median image of Figure 1. The colour bar is the S/N. S/N detection is at S/N=2.2 (MJD 58222), 3.4 (MJD 58227), 5.9 (MJD 58244), 1.2 (MJD=58257), and 4.1 (MJD58288). Credit: Gratton et al.
What we now have on Proxima c, then, is the result of Hubble astrometry, radial velocity studies (Damasso et al.) and direct imaging (Gratton et al.), all of which allowed Benedict to refine the mass of the planet to about 7 times that of Earth. Older data serve us well.
“Basically, this is a story of how old data can be very useful when you get new information,” Benedict said. “It’s also a story of how hard it is to retire if you’re an astronomer, because this is fun stuff to do!”
Amen to that. Indeed, it’s hard to see how any astronomers specializing in planets around other stars could bring themselves to retire as we go ever deeper into what will surely be described as the ‘golden age’ of exoplanet studies.
When I contacted Dr. Benedict this morning, he told me that for now, his official statement on Proxima Centauri c is “A Preliminary Mass for Proxima Centauri C,” in Research Notes of the AAS Volume 4, Issue 4, id.46 (full text).
Because the individual detections from FGS, radial velocity and imaging, are all at the limit of detection, we should look toward more observations from SPHERE and future Gaia data on orbital perturbation at Proxima Centauri to serve as a further check for confirmation.
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