by Paul Gilster | Jul 8, 2019 | Missions |
I’m staying in Apollo mode this morning because after Friday’s piece about the Lunar Module Simulator, Al Jackson forwarded two further anecdotes about his work on it that mesh with the discussion. Al also reports that those interested in learning more about the LMS can go to the official Lunar Module familiarization manual, which is available here. I’ve also inserted some background on the LMS, with my comments in italics.
by Al Jackson
A couple of funny anecdotes about the Lunar Module Simulator.
It took some effort to get the LMS up and running … we could do a little simulation when it was first installed, but I had a very irregular schedule. I always worked at the LMS crew training 8 am to Noon, but for most of 1967, because the crew did not train after 5 pm, I came many the night with the Singer engineers to test the LMS, sometimes 6 to midnight, sometimes midnight to 7 am, and yeah I had to stick around for the 8 am to noon shift, and then go home and sleep.
There was a lot of weekend work too, it was 24-7-365 for about two years. (We did take Thanksgiving and Christmas off).
The most impressive glitch I remember was after Apollo 9 flew. Apollo 9 was Earth orbit only. We immediately then started doing lunar operations, especially ascents (I don’t think we had all the software and visuals for descent yet). All this was mostly digital to analog conversion. The equations of motion and the out-the-window visuals were being driven by a large bank of digital computers, most programmed in FORTRAN.
The reset point was the LM on the Lunar surface. So the set-up was that you looked out the LM cockpit window at a lunar surface (we had a better scene later), and when you hit the button to start the engine, the LM window showed the lunar surface slowly fade away and all went gray. The printout said our altitude was negative. We were sinking into the Moon!
So the guys fixed a Boolean in the software to keep us on the surface. Ok, then when one launched, that is turned on the ascent engine, we had engine on for 460 seconds. Ascent looked good, but look out the window and slowly the lunar surface came up and hit you in the face! The LM was doing a ballistic arc!
It took a day to figure it out. The solution was easy – looking at the code we saw that someone had forgotten to replace the central mass in the equations of motion, EOM. We were using the Earth’s mass, not the Moon’s!
A second anecdote. They finally installed the high fidelity Lunar Surface sim support, a model of the landing site made of plaster with a 6 degree of freedom TV camera rig, this video responding to the LMS EOM fed video to the cockpit windows. So, of course, the technicians glued a plastic bug to that model surface. When the crew made a landing, if facing the right way, a Godzilla sized bug appeared in the distance! The crews of course loved it, sim management not so much.
The Lunar Surface Sim
The Lunar Module Simulators in Houston and Cape Kennedy were produced by the Link Group of Singer General Precision Systems, under contract to Grumman Aircraft Engineering Corporation, with visual display units provided by Farrand Optical Company. From an article Al forwarded to me this morning titled “The Lunar Module Simulator,” by Malcolm Brown and John Waters, this description:
The Lunar Module Simulator was designed to train flight crews for the lunar landing mission. It is a complex consisting of an instructor-operator station, controlling computers, digital conversion electronics, external visual display equipment, and a fixed-base crew station. Actual flights are simulated,through computer control of spacecraft systems and mission elements which are modeled by real-time digital programs. Dynamic out-the-window scenes are provided through an infinity-optics display system during the simulated flights.
A five-ton system of lenses, mirrors and mounts made up the visual display system, which was attached to the LMS crew station. The heart of the simulator was a crew station that resembled in all details the actual spacecraft. Here is a photo Al sent showing the Mission Effects Projector. Another subsystem of the LMS visual suite, it used a film projection device for the early descent phase until switching to an optical unit that moved over a model of the Moon’s surface.:
Here’s the document’s description of this critical LMS component:
From approximately 8,000 feet almost to touchdown, the simulated views of the lunar surface are generated by the landing and ascent model, and are transmitted to the visual display system through high resolution television. The images are available to either forward window of the LMS crew station. The landing and ascent model, shown in Figure 18, consists of an optical probe located on a movable carriage and an overhead model of the lunar surface. This last is an accurate reproduction of one of the chosen lunar landing sites, constructed by the U.S. Army Topographical Command. Simulated sunlight on the lunar surface, which produces shadows used for visual evaluation of the landing site, comes from a special collimated light source.
Incidentally, in the incident with the bug that Al mentions above, this same document records that Armstrong, seeing what appeared to be a 200-foot tall horsefly in the distance after landing on the Moon, announced there would be no EVA, whereupon he was asked by the engineers simulating Mission Control why he would cancel, since large horseflies were common in Texas, where Armstrong lived. Neil’s response: He was not concerned as much about the 200-ft horsefly as he was about the 10,000 foot man who had placed it there.
Finally, Al sends along several LMS training reports. Here’s one I found particularly interesting, for obvious reasons.
by Paul Gilster | Jul 5, 2019 | Missions |
While compiling materials for a book on Apollo 11, Neil McAleer accumulated a number of historical items that he passed along to me (thanks, Neil!), and I’m thinking that with the 50th anniversary of the first landing on the Moon approaching, now is the right time to publish several of these. Centauri Dreams has always focused on deep space and interstellar issues, but Apollo still carries the fire, representative of all human exploration into territories unknown. In the piece that follows, Neil talked to Al Jackson, a well known figure on this site, who as astronaut trainer on the Lunar Module Simulator (LMS) worked with Neil Armstrong and Buzz Aldrin before Apollo 11 launched, along with other Apollo crews. McAleer finalized and synthesized the text, which I’ll follow with a piece Al wrote for Centauri Dreams back in 2012, as it fits with his reminiscences related to McAleer. I’ve also folded in some new material that Al sent me this morning.
by Al Jackson and Neil McAleer
In the fall of 2018, this writer began a correspondence with Al Jackson, a NASA Simulator Engineer and instructor for Neil Armstrong and Buzz Aldrin for the Apollo 11 mission.
“We instructors spent two and a half years with Neil and Buzz—almost every day for the first 6 months of 1969 [before the historic launch in July]. In those years we instructors spent almost that much time with the Apollo 9,10,12,13 crews and backup crews.
“When we were working with Neil and Buzz … Neil was indeed a very quiet man but he was not all that taciturn. He was easy going and approachable. The film First Man seemed to imply Neil was quite glum in private, but I never got that impression; even if there were times when he was, I never saw it. The movie even made it seem Neil was a bit morose in private, another aspect that I never detected from seeing him at work almost every day.
“It’s odd that we instructors on the Lunar Module Simulator worked with Neil and Buzz almost every day for those two and a half years, but we never socialized with them. We even traveled with them to MIT and TRW and only saw them at the technical briefings.”
Image: Al Jackson (facing the camera at the main console of the Lunar Module Simulator) performing a checkout of LMS systems with his colleagues. Credit: A. A. Jackson.
“One thing— we really saw more of Buzz than Neil. Buzz was, and still is, a Space Cadet! He put in extra time on manual rendezvous training; he was responsible for the neutral buoyancy facility; and he practiced EVA for Gemini so he had zero problems on Gemini 12. Buzz was more into spaceflight than any of the other astronauts.”
A Working Team
In one of my emails to Al Jackson, I asked his opinion on how Neil and Buzz worked together during the simulator training years:
“My observation is that during training both Neil and Buzz got along fine. Funny thing, Buzz would definitely express himself more than Neil, but those two were the quietest we ever had in the cockpit during Lunar Module simulations.
“One time they were in at 8 am and did not say a word to us or each other by 11 am. I remember someone suggested we go up to the cockpit and check to see if they had passed out!
“I know an odd story about Neil,” Al continued. “One day he was in the simulator, came out, and smoked a cigarette, looked at us and said, ‘That was my one cigarette for the year.’ He smiled and went back to the cockpit.”
In a reply to Al, I gave him my opinion that this comment was similar to Neil’s well-known quote about every living human on our planet having a finite number of heartbeats in their lives, and Neil didn’t want to waste any of them on basic exercise when he loved to fly so much. This writer considers these two comments as Neil’s personal nods to human mortality.
Another story came in another e-mail from Al Jackson in early 2019: “I was talking recently to the main Primary Guidance and Navigation System instructor on the Lunar Module Simulator, Bob Force (Force and I spent a lot of time together); he noted that the day after the LLTV [Lunar Landing Training Vehicle] crash [May 6, 1968], Armstrong came to the simulator.
“We asked how he was, and he said, ‘Oh just some stiffness’—That was all.”
Armstrong had cheated death by about 2 seconds because his parachute opened just before he landed.
“I talked to another instructor who I met early that day, and he said something like ‘have a hard time yesterday?’ Neil, who had bitten his tongue during ejection gave that guy a very hard look.”
Image: Astronaut Neil Armstrong flying LLRV-1 at Ellington AFB shortly before the crash (left) and ejecting from the vehicle just seconds before it crashed (right). Credit: NASA.
Buzz Aldrin’s Exit from Eagle to Join Neil on the Moon’s Surface
As I was researching information about Apollo 11’s EVA and walk on the moon, one of my major sources was to read portions of the official transcript of their EVA activities. Here something unusual emerged. Aldrin’s real exit from the Eagle needed his crewmate’s specific directions on orientation of his body as he went through the hatch—just like Aldrin assisted Neil exiting the Eagle from inside its cockpit.
ARMSTRONG: “Okay. Your PLSS [Portable Life Support System] is—looks like it’s clearing. The shoes are about to come over the sill. Okay, now drop your PLSS down. There you go . . . About an inch clearance on top of your PLSS. . . .
Okay, you’re right at the edge of the porch. . . . Looks good.
ALDRIN: Now I want to back up and partially close the hatch, making sure not to lock it on my way out. [My italics for emphasis!]
ARMSTRONG: “A particularly good thought.”
Neil was probably thinking about the time of their EVA simulation “dress rehearsal,” when the mock LM’s hatch turned out to be locked when Neil unsuccessfully tried to re-enter their mock Lunar Module during rehearsal. He had to file a report. The lesson was learned.
So the answer is that they were both very aware of the possible problem on the “real EVA” for Apollo 11, and the lockout experience in training was avoided.
[PG: Al also adds this note in a morning email about the ‘locked hatch’ situation.]
“That was probably the egress – ingress simulator, which was a full sized mock-up of the LM (though there was more than 1 of those). It was a pretty faithful mock-up. I remember the very first day I worked at the Manned Space Center in Houston, the day I mustered in, which was the first Monday of the last week in January 1966… after work I climbed up in that simulator looked out the windows and thought of Wernher von Braun and Robert Heinlein, the men who , with their writings, had gotten me there! I felt like a space cadet!”
Image: “When it was my turn to back out, I remember the check list said to reach back and carefully close the hatch, being careful not to lock it,” said Buzz Aldrin, Apollo 11’s lunar module pilot. He climbed down the ladder, looked around and described the sparse lunar landscape as “magnificent desolation.” Credit: NASA/Neil Armstrong.
On Apollos 11 and 12
And this is Al Jackson’s article from 2012, one I reproduce here for its insights into the Apollo program.
I spent almost 4 years in the presence of Neil Armstrong and Buzz Aldrin. I came to the Manned Spacecraft Center (MSC) in 1966, where I was placed as a crew training instructor. I had degrees in math and physics at that time. Seems engineers were pressed into real engineering work or had been siphoned off into the DOD. Spaceflight attracted a lot of physicists who could be put to work on all kinds of stuff.
I met Buzz first, I think as early as 1966. At MSC in those days I used to be in Bldg. 4 (my office) or Bldg. 5 (the simulation facility) in the evenings. Sometimes we worked a lot of second shift and I was unmarried at the time with a lot of time on my hands. Anyway Buzz would come to Bldg. 5 to practice in a ‘part task’ trainer doing manual rendezvous, something he had pioneered. So I kind of got to know Buzz, but I can’t remember much but small talk and later talk about the Abort Guidance System which was my subsystem.
When the Lunar Module Simulator (LMS) got into operation I started seeing Neil, but never talked to him much. Of all the Apollo crews Neil and Buzz were the most quiet. I do remember Neil from the trips to MIT and TRW, to go to briefings on the Primary Guidance and Navigation and the Abort Guidance System.
Image: Al Jackson (top left) and a NASA colleague testing the environmental system of the Lunar Module in 1968. Credit: Al Jackson.
I had seen Buzz do a little ‘chalk talking’ about technical stuff, but on the TRW trip Neil got up and gave a short seminar about rendezvous in orbit, some math stuff and all. He really knew his stuff. I remember being kind of surprised because I knew about Buzz’s doctorate in astronautics, but did not know Neil knew that much engineering physics.
The Apollo 11 crew were the backup crew for Apollo 8, except for Fred Haise — that crew too could have been first on the moon. I puzzle these days whether Deke Slayton and higher ups arranged that it would be Neil and Buzz or not. All the astronauts I worked with were very unusual and able men… but Neil and Buzz had more than the Right Stuff, they were kind of magicians of confidence. It would be years before the astronaut corps had anyone quite like them.
You know working Apollo, nearly 24 – 7 for five years, in those days we had our heads down in the trenches, so it is strange to think back, a lot of odd things and lore escaped my attention. I was never a diary keeper, but wish I had been. I do remember how seat-of-the-pants everything was. Everything became much more formalized in the Shuttle Era and I was glad I did not stay in crew training for all but 5 years of my tenure at JSC.
It was the Apollo 12 crew who were the most fun. Pete Conrad was the most free spirited man I ever met. He bubbled with enthusiasm and humor, a thinking man’s Evel Knievel. He was an ace pilot who kept us in stitches all the time. Conrad and Bean spent a lot of time in the LMS (I think Neil and Buzz spent the most) and we instructors really got tired of wearing our headsets , so when crews were in the LMS we would turn on the speakers we had on the console since the crew spent most of their time talking between themselves. When Conrad was in the cockpit we had to turn the speakers off, since we would unexpectedly have visitors come by.
The reason why: Conrad, an old Navy man, could string together some of the most creative blue language you would ever want to hear. The main guidance computer aboard both the Command Module and Lunar Module was called the Primary Guidance, Navigation and Control System (PGNCS), but the crews called it the PINGS. Conrad never called it that. I can’t repeat what he called it, but he never, in the simulator called it that. The instructors remembered the trouble Stafford and Cernan caused on Apollo 10 with their language, and we thought lord! Conrad is gonna make even Walter Cronkite explode in an oily cloud! Yet on Apollo 12 he never slipped once, that’s how bright a man he was.
A month or two before Apollo 11 Conrad and Bean were in the cockpit of the LMS and John Young was taking a turn at being the pilot in the CMS (Command Module Simulator). We were running an integrated sim. Young had learned that the CM would be named Columbia and the LM Eagle. Conrad being his usual individualistic self said that must have pleased Headquarters. (Of course Mission Control needed those names when the two vehicles were apart for comm reasons).
So Conrad could not resist. He told Bean and Young right then and there that they were going to name the CM and LM two names that I also can’t repeat. Bean and Young had a ball the rest of the sim giving those call signs, but that only lasted one day. Conrad, as you might suspect, never used the language in an insulting way or even to curse something — he was a very friendly and funny man. But it’s so second nature in the military to use language like that, and those Navy men, well, they never said “pardon my French!” Later the three Navy men (Conrad, Bean and Gordon) gave their spacecraft proper Navy names! Remember them?
[PG: I had to rack my brains on that one, but finally dredged up the command module’s name — Yankee Clipper. The LEM was Intrepid.]
Science Fiction and Apollo
[PG: Finally, this snip from another email Al sent me this morning, of interest to those of us who follow science fiction and its influence.]
“I have given interviews, by phone, to a few authors of recent Apollo 11 authors, I don’t know if it was Neil McAleer who asked me this question: ‘Did you meet any science fiction fans when you started at MSC in 1966.’ Somehow someone knew I had been in and still was (no longer in a strong way) in science fiction fandom. I said no. I did not meet any true blue fans in NASA till years later.
“About half the guys I worked with were avid SF readers, no surprise, but none had been in SF fandom.
“I did have one experience that Alan Andres, one of the authors of the new book Chasing The Moon, checked. In April of 1968 2001: A Space Odyssey had (I think) its 3rd USA premiere in Houston. I desperately wanted to see it opening night but was not able to wangle a ticket.
“I did see it the next night. The next week around the coffee pot in building 5 Buzz was there talking to the Apollo 11 backup crew Lovell, Anders, and Haise. They were asking him about the ending, I distinctly heard Aldrin telling them to read Clarke’s Childhood End. I was not surprised that Buzz was an SF reader. (Alan Andres told me that Buzz said he was tired from training that day and that he slept through most of the movie… still I think Buzz caught enough to know a good answer. I swear I heard this conversation in April of 1968. I am sure Buzz does not remember it).”
Image: A time like no other: Collins, Aldrin, Armstrong amidst an exultant crowd in August of 1969.
by Paul Gilster | Jul 3, 2019 | Astrobiology and SETI |
Remember ‘Nemesis’? The idea was that mass extinctions on Earth recur on a timescale of between 20 and 40 million years, and that this recurrence could be accounted for by the existence of a faint star in a highly elliptical orbit of the Sun. Put this object on a 26 million year orbit and it would, so the theory ran, destabilize Oort cloud comets, causing some to fall into the inner system at a rate matching the record of extinctions. Thus a cometary bombardment was to be expected on a regular basis, as were the mass extinctions that were its consequence.
No one has found Nemesis, though other theories about recurring mass extinctions are in play, including recent work from Lisa Randall and Matthew Reece that explores dark matter as the trigger, with the Sun periodically passing through a disk of the stuff. Of course, finding dark matter itself continues to be a problem. Moreover, the wide range in the proposed recurrences gives rise to the possibility that these events are not periodic at all but simply random.
Robert Zubrin now offers a paper arguing that random encounters between our Solar System and passing stars can account for the Oort Cloud disruptions leading to extinctions without the need for Nemesis. Appearing in the International Journal of Astrobiology, the paper weighs other discussions of periodicity and goes on to propose a model for calculating the frequency of these encounters. The model rides on the treatment of the galaxy as a gas, with stars as particles at a density of approximately 0.003 stars per cubic light year.
These stars, argues Zubrin, are clearly not in synchronized motion but have random velocities with respect to each other on the order of 10 kilometers per second. Much rides on the effective encounter distance — when do stars pass closely enough to disrupt the outer cometary shell? One encounter every 26 million years occurs in Zubrin’s calculations if the distance of effective encounter is taken to be 22,000 AU, which would send a passing star through the Sun’s Oort Cloud, while at the same time exposing the Sun to the cometary cloud around the passing star.
Image: The layout of the solar system, including the Oort Cloud, on a logarithmic scale. Credit: NASA.
We also have to take into account that the Sun is among the larger stars, the most common type of encounter being with far less massive M dwarfs. Zubrin assumes such stars have Oort Cloud analogs of their own, though we have as yet no observational evidence for this. He makes the case that comet bombardment of Earth will more likely occur from disrupted objects in the passing star’s Oort cloud than through objects native to the Sun’s Oort Cloud.
From the paper:
If the Sun were to travel through the alien star’s Oort Cloud at a range of 20,000 AU, it would probably be in the cloud for about that distance. Assuming a disruption range of 10 AU, it would sweep out a path with a volume of π(102) 20,000=6.3 million cubic AU. Assuming 4 Oort cloud objects per 1000 cubic AU, this implies that approximately 25,000 alien cloud objects could potentially be captured per pass, providing a significant chance of impact events to follow.
Indeed, disrupted Oort objects can in Zubrin’s calculations fall into their target stellar systems quickly, creating a cloud of short period comets and potential planet impacts while the other star is still relatively nearby. In the case where an M-dwarf passes through the Sun’s Oort Cloud while the Sun remains outside the smaller cloud of the dwarf, the dwarf star’s planetary system would be bombarded by objects from the Sun’s Oort Cloud while our own Solar System remained unaffected. By the calculations of this paper, while we might expect bombardments on the order of 30 million years or so in our system, our Oort Cloud would be delivering bombardments to a passing dwarf star every 7.5 million years.
Crucially, these events, transferring objects from one system to another, could happen fairly swiftly. If an object from an M-dwarf’s comet cloud were destabilized as it passed through our Solar System at a range of 10 AU, for example, it would have the possibility of reaching perihelion swiftly, in a matter of years. Note that Zubrin derives the figure of 10 AU for the distance a visiting star needs to come to an Oort Cloud object to turn it into a comet; i.e., the Sun can capture a visiting star’s Oort cloud objects if it passes within 10 AU of the object.
Here, then, is the hook for astrobiology:
If we estimate that each Oort Cloud object disrupted has an average mass of 1 billion tons, then an encounter [with a star] at 20,000 AU would appear to have the potential to import about 25 trillion tons of mass from another solar system into our own. Of course, only a tiny fraction if it would hit the Earth. But even so, the potential to transfer biological material is evident.
Most of these bombardments of our own system would occur from M-dwarf comet clouds, given the high percentage of M-dwarfs in the galaxy. The table below shows the distribution.
Table 1. Comparative responsibility of star types for cometary bombardment of our Solar System. Credit: Robert Zubrin.
We have the prospect, then, of material from one stellar system impacting a planet in the other, or at least, being captured in that system’s Oort cloud and stored until another encounter with a passing star causes it to be disrupted and fall inward. Notice that Zubrin is talking about microbes in the transferred material that would have to survive a journey far less than the multiple light years assumed necessary for interstellar panspermia, though they would have to survive Oort-like conditions, having traveled from their inner system to the comet cloud.
It may also be noted that with a typical time between incoming encounters of 25 million years, it is probable that our Solar System has had about 140 incoming-delivery encounters with other stars since life first appeared on Earth some 3.6 billion years ago… If each encounter with a dwarf star typically releases 1000 solar system Oort cloud objects, then our Solar System has been responsible for releasing some 140,000 objects into others over this period. But, as a large G star, the sun probably delivered at least three times as many bombardments on other stellar systems as it received.
Our star keeps orbiting galactic center somewhere in the range of every 225 to 250 million years. A lot of material could be exchanged in this way:
…while we have only travelled through the Oort clouds of other, mostly dwarf, stars 140 times, dwarf stars have probably travelled through our own Oort Cloud about 420 times. If only 10% of encounters actually result in the transfer of microbial life from the Earth to another solar system, then we have been responsible for seeding 42 other solar systems with life. If each of these were then to act as a similar microbial transmitter, the result would be billions of inhabited worlds seeded by Earth.
Here it’s interesting to speculate, as Zubrin goes on to do, about whether there is an optimal impact rate for the evolution of advanced life. More frequent impacts might actually be a useful evolutionary driver — the author notes that the biosphere recovered from the K-T impact within 5 million years, offering up mammals and birds that proved long-term survivors. But too frequent an impact rate would not allow sufficient recovery time. Thus it is conceivable that areas of the galaxy with perhaps double our population of stars might be those more likely to feature advanced species and civilizations.
So we have no ‘Nemesis’ to fall back on — a cometary impact of roughly 1 every 25 million years has no specific driver within our own system, but results from the movement of stars, a random motion as the Sun moves through the Milky Way. Harvesting objects from passing stars, most of them red dwarfs, we collect them on timescales of years or decades rather than millions of years, the result of their relatively close disruption. We wind up with a mechanism for exchanging materials with other stellar systems that could have implications for life.
A key question: Can life survive Oort-like conditions to allow such transfers? We’re also hampered by our lack of knowledge about the Oort Cloud itself and, indeed, the local interstellar medium beyond the Kuiper Belt. Zubrin draws his best estimates from the current peer-reviewed papers, as he must, but it’s clear that to tighten this kind of argument, we’re going to need data from future explorations of the Oort. In such ways does a speculative astrobiology sharpen its focus, within a process of scientific inquiry that is by necessity multi-generational.
The paper is Zubrin, “Exchange of material between solar systems by random stellar encounters,” published online by the International Journal of Astrobiology 18 June 2019 (abstract).
by Paul Gilster | Jul 2, 2019 | Astrobiology and SETI |
A paper called “The Natural History of ‘Oumuamua,” just out in Nature Astronomy, puts the emphasis on the word ‘natural.’ We know how much of a stir in the media the interstellar visitor has made given its peculiarities, and the hypothesis put forward by Harvard’s Avi Loeb that it could be a technological object. Now we have a group of 14 astronomers, European as well as American, who have assessed the available data from all angles.
This is a worthwhile effort, assembling a team at the International Space Science Institute (ISSI) in Bern, Switzerland that intends to meet once again later in the year. It considers the question of whether the extraterrestrial spacecraft hypothesis is supported by examination of all the peer-reviewed work that has thus far appeared. Matthew Knight (University of Maryland), working with Alan Fitzsimmons (Queen’s University Belfast) assembled the team. Knight believes that natural phenomena can explain ‘Oumuamua:
“We put together a strong team of experts in various different areas of work on ?Oumuamua. This cross-pollination led to the first comprehensive analysis and the best big-picture summary to date of what we know about the object. We tend to assume that the physical processes we observe here, close to home, are universal. And we haven’t yet seen anything like ?Oumuamua in our solar system. This thing is weird and admittedly hard to explain, but that doesn’t exclude other natural phenomena that could explain it.”
Image: This artist’s impression shows the first interstellar object discovered in the Solar System, ?Oumuamua. Observations made with the NASA/ESA Hubble Space Telescope, CFHT, and others, show that the object is moving faster than predicted while leaving the Solar System. The inset shows a color composite produced by combining 192 images obtained through three visible and two near-infrared filters totaling 1.6 hours of integration on October 27, 2017, at the Gemini South telescope. Credit: ESA/Hubble, NASA, ESO/M. Kornmesser, Gemini Observatory/AURA/NSF.
As we have no new observations of ‘Oumuamua, the paper produced by this team is an analysis of existing data, including a December 2017 paper on the object’s shape and spin co-authored by Knight. When the scientist calls the object ‘weird,’ he’s at least partially referring to its apparent acceleration along its trajectory, which suggests a comet even if astronomers could find no evidence of the kind of gaseous outflow that would propel even a small acceleration. We see no coma of ice, dust and gas, no evidence for gas jets, no cometary ‘tail.’
Karen Meech (University of Hawaii), who was lead author on the research paper that reported the discovery of ‘Oumuamua not long after it was identified at the Pan-STARRS observatory, had noted the object’s red color and elongated shape, apparent in changes in its reflectivity as it rotated. But on the matter of cometary behavior, Meech sees no need for anything beyond natural processes at work, saying “…while it is disappointing that we could not confirm the cometary activity with telescopic observations it is consistent with the fact that ?Oumuamua’s acceleration is very small and must therefore be due to the ejection of just a small amount of gas and dust.”
To see full text of the paper, see this link (thanks Alex Tolley for an alternate link!) On the specific question of alien technologies, the paper has this to say:
The key argument against the solar-sail hypothesis is ‘Oumuamua’s light-curve amplitude. For a solar sail to cause the observed non-gravitational acceleration, it needs to remain properly oriented towards the Sun. However, to yield the observed brightness variations, its orientation would need to be varying as viewed from Earth. Furthermore, since the actual dimensions of the solar sail would be >10:1, the orientation as viewed from Earth would need to be very nearly edge on, and remain so throughout the observations despite viewing geometry changes. It has not been shown that an orientation exists that can achieve all of these constraints imposed by the observational data. Furthermore, as discussed earlier, the shape of ‘Oumuamua’s light curve, with broad maxima and narrow minima, is consistent with an elongated ellipsoid.
We also find this on albedo:
The claim that ‘Oumuamua must be at least ten times ‘shinier’ than all Solar System asteroids to make the Spitzer Space Telescope data consistent with the ground-based observations is incorrect. The Spitzer observations are consistent with geometric albedos 0.01 ? pv ? 0.5…, with a most likely albedo of pv ~ 0.1. Comets have geometric albedos of pv = 0.02–0.07, carbonaceous and silicate asteroids have pv = 0.05–0.21, and the most reflective asteroids have pv ~ 0.5… Thus ‘Oumuamua’s measured reflectivity of about 0.1 is entirely consistent with normal Solar System small bodies.
And on the argument that the kinematics of the object are unusual:
While provocative, this argument is baseless. First, ‘Oumuamua’s trajectory is consistent with predictions for detectable inactive interstellar objects. Second, the measured number density cannot be claimed to be at odds with expectations because of our ignorance of the size distribution of interstellar objects.
‘Oumuamua is destined to remain enigmatic, for our dataset represents all that could be collected before the interstellar visitor had traveled beyond the view of our telescopes. With only a few weeks in play to observe the object, the ISSI astronomers acknowledge its rarity (“We have never seen anything like ?Oumuamua in our solar system,” says Knight) while finding its movement explicable through natural means. All report anticipating results from the Large Synoptic Survey Satellite (LSST), which comes online in 2022 and may give us more interstellar objects of the same kind, allowing a deeper and perhaps less controversial analysis.
“In the next 10 years, we expect to begin seeing more objects like ‘Oumuamua. The LSST will be leaps and bounds beyond any other survey we have in terms of capability to find small interstellar visitors,” says Knight. “We may start seeing a new object every year. That’s when we’ll start to know whether ‘Oumuamua is weird, or common. If we find 10-20 of these things and ‘Oumuamua still looks unusual, we’ll have to reexamine our explanations.”
The paper is Bannister et al. (The ‘Oumuamua ISSI Team), “The Natural History of ‘Oumuamua,” Nature Astronomy 19 July 1, 2019 (abstract). Knight’s 2017 paper is “On the Rotation Period and Shape of the Hyperbolic Asteroid 1I/’Oumuamua (2017 U1) from Its Lightcurve,” Astrophysical Journal Letters Vol. 851, No. 2 (12 December 2017). Abstract.
by Paul Gilster | Jul 1, 2019 | Exoplanetary Science |
The latest find from TESS, the Transiting Exoplanet Survey Satellite, is a reminder of how interesting, and useful, a planetary system can be even if we find no Earth-like worlds there. This seems obvious, but so much of the public attention to exoplanets has to do with finding a clone of our own world that we can forget the power of a ‘second Jupiter’ or, in this case, a ‘second Venus.’ For at L 98-59 we have not one but three planets that may fit this description.
One Venus, hellish as it is, would seem to be enough. But learning about planets with varying kinds of atmospheres that are in orbits that produce runaway greenhouse effects can help us place our own system’s evolution in context. To be sure, we don’t yet know what kind of atmospheres these planets have, or if they have atmospheres at all, but the encouraging thing is that tight orbits around relatively bright stars are what we need as we look toward future tools like the James Webb Space Telescope.
Astrophysicist Joshua Schlieder (NASA GSFC) is a co-author of the paper on this work, which was led by colleague Veselin Kostov:
“If we viewed the Sun from L 98-59, transits by Earth and Venus would lead us to think the planets are almost identical, but we know they’re not. We still have many questions about why Earth became habitable and Venus did not. If we can find and study similar examples around other stars, like L 98-59, we can potentially unlock some of those secrets.”
Image: The three planets discovered in the L98-59 system by NASA’s Transiting Exoplanet Survey Satellite (TESS) are compared to Mars and Earth in order of increasing size in this illustration. Credit: NASA’s Goddard Space Flight Center.
What we have at L 98-59 could conceivably become a primer in atmospheric transformation. The primary is an M-dwarf about a third the mass of the Sun, found 35 light years away in the constellation Volans. The planets include L 98-59b, about 80 percent the size of the Earth, and the smallest planet yet discovered by TESS. Here we have a 2.25 day orbit receiving 22 times the amount of insolation as the Earth. Moving outward, we find L 98-59c, about 1.4 times the size of Earth, in a 3.7 day orbit with 11 times the amount of energy Earth receives. The furthest planet found so far is L 98-59d, about 1.6 times Earth’s size, in a 7.5 day orbit with 4 times Earth’s radiant energy, possibly Venus-like or conceivably a hot Neptune.
This may not exhaust the possibilities, for there is the prospect of further discovery here, says GSFC’s Jonathan Brande, likewise a co-author of the paper:
“If you have more than one planet orbiting in a system, they can gravitationally interact with each other. TESS will observe L 98-59 in enough sectors that it may be able to detect planets with orbits around 100 days. But if we get really lucky, we might see the gravitational effects of undiscovered planets on the ones we currently know.”
The paper points out that these worlds are too small to retain atmospheres rich in hydrogen, so the focus will be on secondary atmospheres that are the result of volcanic activity, and infalling volatiles from the rest of the system via comets. The authors calculate that all three planets are in range for JWST to produce a transmission spectrum showing atmospheric features. The expected signal-to-noise ratio compares to another nearby red dwarf planet, GJ 1132b.
Understanding why Earth is habitable and Venus is not will depend upon our analysis of planets that have evolved through the greenhouse phase. In this regard, the L 98-59 planets stand out, particularly since other Venus analogs thus far discovered orbit fainter stars. From the paper:
The L 98-59 planets receive significantly more energy than the Earth receives from the Sun (a factor of between 4-22 more than Earth’s insolation) and fall into the region that Kane et al. (2014) dubbed the Venus Zone. This is a region where the atmosphere of a planet like Earth would likely have been forced into a runaway greenhouse, producing conditions similar to those found on Venus. The range of incident fluxes within the Venus Zone corresponds to insolations of between 1-25 times that received by the Earth. Planets in the Venus Zone that can be spectroscopically characterized will become increasingly important in the realm of comparative planetology that aims to characterize the conditions for planetary habitability. In that respect, and considering the potential for atmospheric characterization…, L 98-59 could become a benchmark system.
What we know of these worlds will be refined by future TESS observations, possibly uncovering other planets here and monitoring activity on the host star. The paper is Kostov et al., “The L 98-59 System: Three Transiting, Terrestrial-size Planets Orbiting a Nearby M Dwarf,” The Astronomical Journal Vol. 158, No. 1 (27 July 2019). Abstract / Preprint.
