Thursday, 26 July 2018

Oumuamua – Non-Gravitational Acceleration Observed but Probably not Alien Tech

Oumuamua – Non-Gravitational Acceleration Observed but Probably not Alien Tech

Observation of Non-Gravitational Acceleration

A recent paper in Nature has shown (Non-gravitational acceleration in the trajectory of 1I/2017 U1 (‘Oumuamua)), via a comprehensive analysis of multiple observations, that Oumuamua has deviated from a purely gravitational track, on its way through the solar system.  In other words, its trajectory has been influenced by some other push than the gravity of the major bodies of the solar system.  The effect is very small, so it took a lot of observational data to detect the anomalous motion.

In the graph below, Oumuamua’s non-gravitational component is shown, and can be compared to solar system bodies (it’s the black vertical line).  As you can see, it is within the range for solar system comets, in this respect, though rather far into the right tail of the distribution.  So, relative to “normal” solar system comets, its non-gravitational acceleration is actually quite large, even if it is small in an absolute sense.

Just as a reminder, Oumuamua appeared in our skies in 2017, and has been tracked with large ground-based telescopes as well as the Hubble Space Telescope.  Its velocity (26 km/second, which is more than the escape velocity from the solar system) and trajectory (highly hyperbolic eccentricity=1.3) indicate that it must have originated from outside of our solar system, probably from somewhere in the constellation Lyra.

Lyra contains the bright star Vega, which is easy to find, as it is one of the stars of the asterism The Summer Triangle.  It is also an interesting coincidence for SF fans that Vega is the star that was featured in the novel and movie “Contact”, as the home planet of the alien civilization that sent the instructions to build a wormhole device.

Some 177 ground-based and 30 space-based (Hubble) observations were analysed, to determine Oumuamua’s track through the solar system with great precision.  Various mathematical models were then produced, and compared to the actual data, using standard statistical techniques, such as Chi-square goodness-of-fit tests.

The analysis showed that the arc of the body’s path could not be explained by a solely gravitational model, even if the sun, eight planets, moon, Pluto and the 16 largest asteroid were included in the model.  Many of the observations deviated from prediction by 3 to 5 standard deviations (about 35 in all did so).  Furthermore, there appeared to be a clear trend to the offsets, so this was not likely due to random observational errors.

Below is a copy and paste graph from the paper, showing the model residuals, using a purely gravitational model (a) vs a model that also includes an extra push from some non-gravitational source (b).  The residuals are what is left over after subtracting the observational data points from the predictions of the model at the location that those observations were made (in declination and right ascension, which are sky coordinates somewhat similar to latitude and longitude).  Basically, a good model will tend to have low deviations from predictions, and the deviations will be randomly scattered throughout the dataset.  Using those criterial, one can see that model b gives a better fit with observational data.

The model with the extra push includes a term that provides a small positive impetus that varies with a 1/r**2 (or 1/r) term, with r being distance from the sun.  In other words, the push is stronger when the body is closer to the sun, and it seems to vary with something that falls off as one over R squared, as do radiation levels from the sun.

Off-Gassing Explanation of Non-Gravitational Acceleration

So, does this mean that Oumuamua is actually a spacecraft of some sort, under alien control?  Not too likely, according to the paper.  Their hypothesis is that Oumuamua is actually an extra-solar comet, rather than an extra-solar asteroid, and that the slight non-gravitational changes in the object’s track through our solar system are caused by off-gassing from the comet (primarily the sublimation of water ice, carbon dioxide ice or carbon monoxide ice).  The level of off-gassing will tend to fall off with distance from the sun, as it is the sun’s radiation that produces the off-gassing, and the strength of that falls off with distance, in a 1/R**2 manner.

Off-gassing and related dust basically creates the tail and/or halo of a comet.  By a simple application of Newton’s laws, you can see that this off-gassing will also provide a push to an object, much like a rocket does for a spacecraft (though obviously a much smaller effect).

Some nice closeup pictures of a comet off-gassing were taken by the ESA Rosetta probe, a few years ago.  Also shown, is an image of comet dust, as Rosetta made a close approach to Comet 67/P.

One problem with this hypothesis, is that earlier observations seemed to have ruled out the body being a comet.  There had been no optical signs of a coma, dust, nor spectroscopic evidence of gas emissions.  Basically, it looked like an inactive body, corresponding more to an asteroid than a comet, when compared to objects native to our solar system. 

On the other hand, a comet always seemed like a more likely explanation than an asteroid, as theory said that interstellar comets would be brighter, and therefore easier to detect than interstellar asteroids.  So there’s that.

So, why wasn’t the evidence of off-gassing and dust seen in earlier optical and spectroscopic measurements?  One possibility for the lack of dust is that Oumuamua has an atypical dust-grain size distribution, with fewer small dust particles than usual.  Solar radiation pressure would thereby not be able to create a significant dust halo, as large dust particles won’t be affected much by solar radiation pressure.  It is also possible that Oumuamua simply had a low dust to ice ratio, so there wasn’t much dust to create a dust halo.  Perhaps the long journey through interstellar space had produced this low dust-ice ratio, via a thin isolating mantle or the journey had changed the surface in some other relevant way.

Other Possible Explanations     

Some other physical models that might produce a non-gravitational acceleration were discussed.  For fun, I have included a Science Fiction possibility, which I have called SF response, where possible:

  • 1.     Solar Radiation Pressure, such as that which drives a light-sail spacecraft.  This was rejected on the basis that the object would have to have an unrealistically low density, three or four orders of magnitude lower than natural solar system objects.
  • SF response – what if actually was a solar sail?
  • 2.     Yarkovsky Effect.  This is another subtle effect, based on anisotropic thermal emission of photons from a rotating body.  As with solar radiation, this effect is far too small to produce the acceleration detected.
  • 3.     Friction or Drag.  Drag from collisions with small particles would tend to have a negative acceleration (slow Oumuamua down), whereas the observed acceleration was positive.
  • 4.     Single Impulsive Change in Velocity.  An example of this would be a collision with some other solar system body (or the firing of a retro rocket :)).  However, the observations seemed to indicate that the acceleration was constant and in a radial direction (away from the sun).
  •  SF response – what about the slow firing of a rocket, or other impulsive force (ion thruster?), perhaps energized by solar power, which would account for the 1 over R squared form of the acceleration?
  • 5.     Fragmented Object.  If the object was fragmented, with the center of mass following a different trajectory than the detected (brighter) part of the object, it could appear to be following a non-gravitational track, while its center of mass was actually following a gravitational track.  But no secondary object has been detected, and it would have to be very small to escape detection, which would mean it wouldn’t affect the apparent path enough to account for the observations.
  • SF response – How about a small, reflective craft that left the mother ship?
  • 6.     Odd Surface Brightness.  If one end of Oumuamua was very bright (and therefore detected) while the rest of the object was very dark, it could look as if Oumuamua was following a non-gravitational track.  But it would have to be extremely long and thin for that effect to account for the observational discrepancies.
  • SF Response - Oumuamua does appear to be very long and thin, more so than almost all natural bodies in our solar system (about 10 to 1).  However, it still seems to be far too small to account for the anomalies.
  • 7.     Strong Magnetic Field.  If Oumuamua had a very strong magnetic field, then interaction with the solar wind could change its motion.  But that effect would be orders of magnitude too small (about 10,000 times), even if the object was fairly highly magnetized, for a natural body.
  • SF Response - Interestingly enough, a ferromagnetic body (e.g. iron) has about 100,000 times more magnetic susceptibility than even the strongest magnetized rocks (according to my text of Applied Geophysics, by Telford et al).  So, how about an inactive spacecraft, perhaps built into a natural body?


So, it appears that the enigmatic interstellar visitor is best explained as a comet that was ejected from another solar system, somewhere in the vicinity of Vega.  But, its peculiar elongated shape, and now its non-gravitational motion, render it a fascinating object for speculation, whether scientific or science fiction.

Non-gravitational acceleration in the trajectory of 1I/2017 U1 (‘Oumuamua), Marco Micheli, et al, Nature 27 June 2018
Applied Geophysics, Telford et al

Now that you have read about a real interstellar interloper (natural or not), you should consider reading some Science Fiction.  How about a short story, also about interstellar interlopers.  It also features one possible scenario to explain why we haven’t met ET yet (as far as we know, anyway).  Only 99 cents on Amazon.

The Zoo Hypothesis or The News of the World: A Science Fiction Story

In the field known as Astrobiology, there is a research program called SETI, The Search for Extraterrestrial Intelligence.  At the heart of SETI, there is a mystery known as The Great Silence, or The Fermi Paradox, named after the famous physicist Enrico Fermi.  Essentially, he asked “If they exist, where are they?”.

Some quite cogent arguments maintain that if there was extraterrestrial intelligence, they should have visited the Earth by now. This story, a bit tongue in cheek, gives a fictional account of one explanation for The Great Silence, known as The Zoo Hypothesis.  Are we a protected species, in a Cosmic Zoo?  If so, how did this come about?  Read on, for one possible solution to The Fermi Paradox.

The short story is about 6300 words, or about half an hour at typical reading speeds.

Alternatively, consider another short invasion story, this one set in the Arctic.  Also 99 cents.

The Magnetic Anomaly

An attractive woman in a blue suit handed a dossier to an older man in a blue uniform.

“Give me a quick recap”, he said.

“A geophysical crew went into the Canadian north. There were some regrettable accidents among a few ex-military who had become geophysical contractors after their service in the forces. A young man and young woman went temporarily mad from the stress of seeing that. They imagined things, terrible things. But both are known to have vivid imaginations; we have childhood records to verify that. It was all very sad. That’s the official story.”

He raised an eyebrow. “And unofficially?”

“Unofficially,” she responded, “I think we just woke something up that had been asleep for a very long time.”

Thursday, 12 July 2018

Humanity Lights a Fire on Mars and the Implications for Life on Mars

Humanity Lights a Fire on Mars and the Implications for Life on Mars

The Fire on Mars and Kerogen

I was reading through the paper in Science recently, about the discovery of organic matter in Gale Crater on Mars, by the Curiosity Rover (Organic matter preserved in 3-billion-year-old mudstones at Gale crater), Mars, when I came across the following interesting passage:

Immediately preceding the 750°C peak set is a notable O2 release from sulfate  decomposition (3), with an increase in CO2 (Fig. 1E) suggesting that combustion limited to the most ignitable volatiles (12) occurred in parallel with pyrolysis. It is also possible that portions of the CO2 and CO (Fig. 2A) were derived from the decarboxylation (2, 3) and decarbonylation of larger organic compounds, which have been observed for Murchison macromolecular isolates (15). The same three peaks are present but less discernable in Confidence Hills data, where the 750°C O2 peak is lower, suggesting that combustion was less influential on hydrocarbon evolution (fig. S1 and S2).

So, we lit a fire on Mars.  I don’t recall any of the reports in the media noting this, or if they did, it was downplayed.  A bit of burying the lede, in my opinion.  After all, one of the first things human beings do, and probably always did, in any new land that they explore, is to start a fire.  So, this “Martian fire” strikes me as quite symbolic.  Sure, it was a fire confined to a glorified test tube, but still…

As the graph shows, there was a fairly sudden release of oxygen from the pyrolysis of the sample (i.e. heating of the instrument, via energy from a radioactive source on the probe), once the temperature reached about 700 C.  That was followed by CO2, which peaked a bit later in the experimental run.  So, it looks like a short, small blaze might have occurred. At any rate, a fairly rapid oxidation.

The idea behind the experiment was to sample a 3 billion year old Martian mudstone, located in the Gale Crater, then heat it up and test the resulting by-products, with a particular focus on whether and how much of the compounds detected were organic, in the sense of organic chemistry (i.e. carbon based molecules).

There was some precedent for believing that there would be organics – hints of this came from earlier work by Curiosity, as well as Martian meteorites that had fallen on  Earth.

At any rate, quite a rich soup of organic molecules were detected by the mass spectrometer.  Again, quoting the paper (note that the reference to Mojave and Confidence Hills are sites on Mars):

The diversity, composition, and temperatures of coevolving volatiles observed in the Mojave and Confidence Hills analyses above 500°C are consistent with the pyrolysis of geologically refractory organic macromolecules that are typically found in carbonaceous chondrites (14, 15), kerogens (17), and coals (18, 19).

Note that kerogen is a general term for a mixture of solid organics in sedimentary rocks on Earth (it is a coined word that translates from Greek as “wax birth”).  On Earth, kerogen is thought to be a by-product of living things, and can eventually turn into petroleum, natural gas or coal.  

That said, it is known that kerogen-like matter can come from non-living sources (e.g. it can be found in interstellar clouds and carbonaceous chondrite meteorites).  We obviously don’t know the source of the Martian material.  The paper notes that biological, geological or meteoritic sources are all possible.

The Connection to the Viking Experiments

The Viking lander experiments of the 1970’s showed tantalizing indications of life, in the Labelled Release results.  These tests “fed” a rich nutrient mixture to some Martian soil, and then looked for radioactive traced CO2 gas, that would be released by life forms in the soil, if they were metabolizing the nutrient mixture.  The experiments did show such a result, and they were consistent with results tested on Earth soils in which bacteria could be found.  However, the life explanation was mostly abandoned in favor of non-biological chemistry.

One of the main refutations of the “it’s life” interpretation of the Labelled Release experiment was that another Viking experiment that was designed to look for organic matter, failed to find any.  However as a 2016 paper by two of the Viking scientists states:

“Lack of biologically relevant organic molecules on the surface of Mars has also been considered a major detriment to extant life.  Recent reports of complex organics, possibly of biological importance, are encouraging, although analyses are ongoing and details are not yet available.”

The 2018 results from Curiosity certainly should bolster the case for Viking’s apparent discovery of life in the Labelled Release experiment. 

The Connection to Science Fiction

An interesting connection to Science Fiction comes from an old 1960’s movie called “Robinson Crusoe on Mars”.  In that movie, a stranded astronaut derives oxygen from heating oxygen-bearing rocks.  So, it is interesting that there is a bit to this idea, as far as we can tell from the Curiosity results.  Here’s a scene of the stranded astronaut filling his oxygen bottles (and, yes, he has a monkey).

The movie was filmed before much was known about Mars, even before the first NASA spacecraft did a flyby of the planet.  The movie was from 1964, and the first Mars probe flyby was in 1965.  It is a surprisingly good movie, for the most part, though the last part is a stretch.  It is well worth a viewing.


  • Organic matter preserved in 3-billion-year-old mudstones at Gale crater, Mars.  Buch and Patrice Coll, Joel A. Hurowitz, John P. Grotzinger, Sanjeev Gupta, Doug W. Ming, Dawn Y. Sumner, Cyril Szopa, Charles Malespin, Arnaud, Brad Sutter, Amy C. McAdam, Heather B. Franz, Daniel P. Glavin, Paul D. Archer Jr., Paul R. Mahaffy, Pamela G. Conrad, Jennifer L. Eigenbrode, Roger E. Summons, Andrew Steele, Caroline Freissinet, Maëva Millan, Rafael Navarro-González DOI: 10.1126/science.aas9185 Science 360 (6393), 1096-1101.
  • The Case for Extant Life on Mars and Its Possible Detection by the Viking Labeled Release Experiment.  Gilber V. Levin and Patricia Ann Straat
  • Wikipedia (Kerogen, Mariner 4 Mars Probe, Robinson Crusoe on Mars, Viking Probe)
  •  Google Images


And now that you have read about some real cutting-edge science, you should think about reading some Science Fiction (because all work and no play can make you a dull person, or so they say).  Here’s a novel that features a neutron star (and a pretty girl, who is also an engineer, among other characters).  The second book in the series features a lunar near-catastrophe and some science about Lagrange points:

The Witches' Stones, Book 1 - Rescue from the Planet of the Amartos

Young Earth woman and spaceship mechanic, Sarah Mackenzie, has unwittingly triggered a vast source of energy, the Witches' Stones, via her psychic abilities, of which she was unaware. She becomes the focal point of a desperate contest between the authoritarian galactic power, known as The Organization, and the democratic Earth-based galactic power, known as The Terran Confederation. The Organization wants to capture her, and utilize her powers to create a super-weapon; the Terra Confederation wants to prevent that at all costs. The mysterious psychic aliens, the Witches of Kordea also become involved, as they see her as a possible threat, or a possible ally, for the safety of their own world.

 A small but fast scout-ship, with its pilot and an agent of the Terra Confederation, Coryn Leigh, are sent to rescue her from a distant planet at the very edge of the galaxy, near space claimed by The Organization.  Battles, physical and mental, whirl around the young woman, as the agent and pilot strive at all costs to keep her from the clutches of the Organization.