Category Archives: Planetary Science

Life On Ocean Worlds

One of the great philosophical mysteries of our age is, in the words ascribed to Enrico Fermi (AKA, “the pope of physics”): “Where is Everybody?” [3]  (This is known as Fermi’s Paradox, though he didn’t originate it, nor is it really a ‘paradox’.  It’s still a Fermi-grade question, though.)

Humans have been watching the skies for millennia, and in the past century have looked ever wider and deeper into the universe, not to mention into physics and the biology. Everything we know indicates that there could very well be life and even technological civilizations everywhere in the vast universe.  But we have never seen evidence of life beyond Earth.

Where is everybody?

Coming up with answers to Fermi’s question is a great scientific parlor game.

In 2002, Stephen Webb describes 50 answers [2], and in his 2015 update he gives 75 (!) [3].  The “solutions” listed by Webb range from “they are already here”, through “they are so strange we don’t recognize that they are there”, as well as the possibility that life really is very, very rare.

Along the way, he points out many uncertainties in our estimates of how likely the development of life and “intelligent” life may be (e.g., we have only our own planet to extrapolate from), as well as unknowable hypotheses about the possible psychology or politics of putative non-human civilizations (e.g., just because we want to talk to everyone doesn’t mean anyone wants to talk to us).

There are also disturbing warnings that “civilizations” are likely to self-destruct before escaping their home planet, or, even worse, may be snuffed out in the nest by predators or catastrophes. (With this in mind, blasting our electromagnetic presence in all directions might not have been a healthy life style choice.)

Webb’s compendium of “solutions” is fun to read, but the game is hardly over.

At the 2017 Habitable Worlds workshop, S. Alan Stern proposes yet another solution to the Fermi Paradox: most life evolves in “interior water ocean worlds”, i.e., in oceans under thick ice covers [1].

most life, and most intelligent life in the universe inhabits interior water ocean worlds (WOWs) where their presence is cloaked by massive overlying burdens of rock or ice between their abode and the universe.

There are several such worlds in our own solar system, and at times in the past the Earth itself flirted with such conditions, covered over with a kilometer of ice.

Artist’s concept of Europa’s frozen surface. Credit: JPL-Caltech

Stern notes that these worlds appear to be highly conducive to the development of life.  The ice cap protects and stabilizes the ocean environment, providing a nest for fragile life to develop over long, evolutionary periods of time.  Thus, however likely life is to develop, ice worlds are prime candidates for successful evolution.

However, Stern also makes the interesting inference that life that evolved under a deep ice cap would have no direct view of the universe.  The protective shield overhead would also block out most evidence of other stars and planets. An emerging civilization under the ice would not know about the universe, at least until technology develops that detects (indirectly) the space above the ice.  Even then, intelligent beings might have difficulty imagining life that does not live under ice, so they might not think to look for signals from us or send signals we could detect.

Stern also argues that life adapted to an ice-covered ocean would find space travel difficult, at least compared to species adapted to the surface under a gaseous atmosphere. In addition to the technical challenge of penetrating many kilometers of rock hard ice, life-support would be necessary to support a dense, liquid environment.

He combines these arguments to answer the “Where is everybody?” question:  if much life develops in ice covered oceans, and any civilizations in such environments unlikely to know or care about the wider universe, then this explains why we haven’t heard from them.

This is an interesting idea to think about.  It is certainly useful to break out of the parochial idea that an Earthlike planet is the only or ideal locus for life or “civilization”.  In fact, we know that life on Earth has just barely survived at least five major extinction events, and an ice world might well be a safer crèche.

I’ll also note that his comment that life on such a planet “either cannot communicate or are simply not aware that other worlds exist” works both ways.  It is difficult for us to detect such inhabitants, and we haven’t be looking until recently.  In our own solar system, there are several ice worlds, but we still have no idea if they are inhabited or not.

On the other hand, several aspects of Stern’s argument are less convincing to me.

An ice-covered ocean world might be a favorable site for life to start, but it might also be a closed system that is quickly exhausted.  Experience on Earth certainly indicates that a closed “ark” will rapidly be overgrown, clogged, and die out.   It is likely that only some ice worlds will be sufficiently “active” or open enough for life to persist.  But who knows until we actually check.

I have to say that I find the arguments about the supposed psychology of native to ice worlds highly speculative, to say the least.  It is true that life on Earth can directly sense the solar system and wider universe, and there are plausible arguments that this knowledge has strongly influenced the development of what we call intelligence.  But it is very difficult to guess the implications of not having an open sky.

I also think that, should a technological civilization develop under an icecap, it will surely develop undertanding of the outside universe. They’ll surely learn about gravity, and when they learn to detect and manipulate electromagnetism, they’ll soon notice a lot of interesting stuff coming in through their icy roof.  For that matter, no matter how difficult space travel might be, wouldn’t they deploy robot explorers and harvesters on the outer side of the ice.  And from that perch, who would not look up and see other worlds?

In short, I’ll buy the idea that ice worlds are good places for life to develop, though they may not be great places to sustain life for billions of years.  But I reserve judgement on questions of how the lack of a sky might influence the development of “civilizations”.

In this article, Stern describes yet one more case for why there could be some extraterrestrial civilizations that we have not seen or heard.  But this clearly isn’t “the answer”. He joins the roster of all the dozens of other hypotheses (Indeed, Webb has a solution called “Cloudy Skies Are Common” ([3], p. 183), which probably subsumes Stern’s solution as a sub case.).

On the other hand, this thesis is yet more reason why icy ocean worlds are really interesting and really need to be explored..  There very well could be life under the ice, and we really should find out what we can.

We have several such worlds close at hand in our solar system that we could visit and actually see what is down under the ice. (EuropaEceladus!  Titan!)

Let’s go, already!

  1. S. Alan Stern, An Answer to Fermi’s Paradox in the Prevalence of Ocean Worlds?, in Habitable Worlds 2017: A System Science Workshop. 2017: Laramie, Wyoming.
  2. Stephen Webb, If the Universe Is Teeming with Aliens … WHERE IS EVERYBODY? Fifty Solutions to the Fermi Paradox and the Problem of Extraterrestrial Life, New York, Copernicus Books In Association With Praxis Pub, 2002.
  3. Stephen Webb, If the Universe Is Teeming with Aliens … WHERE IS EVERYBODY? Seventy-Five Solutions to the Fermi Paradox and the Problem of Extraterrestrial Life, New York, Springer, 2015.


Space Saturday

Revised Estimates on Methane Levels in The Atmosphere

As the Earth’s atmosphere and oceans warm up, theoretical models suggest that this is due to the effects of increased levels of various gasses, including CO2 and Methane (CH4).  But where are those gasses coming from, exactly?

In the case of Methane in the atmosphere, there are many sources, including human agriculture (livestock), fossil fuel use (oil, coal, gas), natural sources such as wetlands, as well as changes in chemical sinks that absorb Methane.  Uncertainties about the sources of Methane mean that projections of future growth are imprecise.

Global levels and isotopic composition of CH4 are measured by satellites, as are other atmospheric chemicals.  Satellites also measure vegetation growth on land and sea and large fires.  Wild fires release Methane and other gasses, so increases in the frequency or duration of fires is one possible source of increased Methane.

Puruseing an accurate assessment of this question, John R. Worden and colleagues report on efforts to improve the understanding of the total amount of biomass burning and the amount of Methane contributed [2], This is a complicated problem because fires are sporadic and irregular, and the effects are not necessarily easy to measure (e.g., to estimate how much and what kind of vegetation burned).

Their excellent study uses multiple data sources.

we combine bottom-up esti- mates of fire emissions, based on burnt area measurements, with the top-down CO emissions estimates…, based on the satellite concentration data” ([2], p. 2)

This is a very tricky bit of work, which has to take into consideration the details and error ranges of the different data sources it combines.

The overall results show that emissions from burning biomass were lower than previous estimates based on burned area. This brings the estimate into agreement with measures of atmospheric gasses. The finding that the atmospheric isotope studies accurately estimate emissions from burning biomass suggests that the increases in fossil fuel emissions from those same studies are accurate as well.

Overall, the study shows that the area of burned vegetation is not necessarily a good measure of the amount of emissions.  Combining multiple satellite datasets showed that the relationship is non-linear. This makes sense: all vegetation is not the same, nor are all fires equivalent.

It is also important to note that emissions from burning biomass are not themselves particularly large, and in fact are smaller than previous estimates.  The important thing is that this study makes the data from all sources more consistent with each other, increasing confidence in the accuracy of the data and the theoretical models.

Nice work.

  1. Adam Voiland. 2018. “What is Behind Rising Levels of Methane in the Atmosphere?” NASA Earrth Observatory, January 11.
  2. John R. Worden, A. Anthony Bloom, Sudhanshu Pandey, Zhe Jiang, Helen M. Worden, Thomas W. Walker, Sander Houweling, and Thomas Röckmann. 2017. “Reduced biomass burning emissions reconcile conflicting estimates of the post-2006 atmospheric methane budget.” Nature Communications 8 (1):2227. doi: 10.1038/s41467-017-02246-0


Space Saturday

Thirty Years of Space Archaeology

Over the sixty years of the Space Age, remote sensing from the air and space has developed into an amazing tool. Originally driven by military necessity, remote sensing from space has revolutionized Earth Science as well as planetary science in the whole solar system. There simply would be no arguments about climate change if not for terabytes of satellite data clearly and irrefutably showing world wide trends.

Airborne and satellite measurements have also begun to revolutionize archaeology. Remote sensing can see through jungle and sand, and cover thousands of kilometers with centimeter resolution. It not lonely helps find where to dig, it gives an essential bigger picture to understand what has been dug up.

For many modern archaeologists, remote sensing tools have become as valuable as carbon dating.

This summer Pola Lem discussed the history of space archaeology[1], Beginning with declassified images from spy satellites, imagery from the US Space Shuttle and now an ever growing fleet of Earth Observing satellites from many nations, archaeologists can explore areas of interest “from their desk” before rolling the dice on an expensive, dangerous, and time consuming excavation.

Lem recounts the 1985 observations of the Omani desert from the Space Shuttle. Based on historical guesswork, the radar imagery detected evidence to locate the ancient oasis and city of Ubar. This is the first recorded instances of space imagery being used specifically for archaeology.

Okay, let me get this straight: You want to use my spaceship to find your lost city?

Even more important is the development of LIDAR (light detection and ranging) deployed on aircraft and nowadays on UAVs. Lidar can generate extremely precise elevation maps which reveal buried structures or ancient landscapes. (Lidar is also one of the key technologies for intelligent and self-driving vehicles.) Lidar is especially useful for seeing through jungle foliage, and has led to discovery of vast new evidence about pre-Colombian Mesoamerica.

In a rather Karmic cycle, archaeology is threatened by the data they thrive upon. Space Archaeology was born from public release of declassified military secrets, and now many archaeologies try to keep their satellite imagery secret to protect the sites from looters. (This is unlikely to work for long—it is easy to get remote sensing data.) Archaeologists now seeks to use remote sensing to protect ancient sites from tourism and looting.

  1. Pola Lem, Peering through the Sands of Time: Searching for the Origins of Space Archaeology, in The Earth Observatory – Features. 2017, NASA.


Space Saturday

Cassini End of Mission

After twenty years in space (launched 10 years Bi, Before iPhone), traveling over a billion KM, and returning data for 13 years from more than a light-hour from Earth, the Cassini Spacecraft ended its mission this week.

The project has accomplished lots of amazing science, represented by 3,948 papers so far. There will surely be a few more—lets go for 5K papers!

The end was a planned dive into the atmosphere of Saturn, collecting a few more bits of data on the way down, and assuring the complete destruction of the spacecraft.

As has been explained before, the spacecraft needed to be vaporized to prevent even the slighted chance that it might contaminate the area with Earth microbes. Aside from not wanting to harm any life that might exist on the moons or dust, we also don’t want to accidentally leave something that a later spacecraft might find and not realize was inadvertently sent from Earth.

(Which, if you think about it is way, way cool. How many human endeavors have to worry about the possibility of contaminating alien ecosystems, even in principle?)

Hence, the final dive.

This montage of images, made from data obtained by Cassini’s visual and infrared mapping spectrometer, shows the location on Saturn where the NASA spacecraft entered Saturn’s atmosphere on Sept. 15, 2017. Credit NASA/JPL-Caltech/Space Science Institute

Cassini signed off permanently on September 15. Loss of Signal. End of Mission. Lots of accomplishments.


Space Saturday


Science makes you think, man. It makes you think big. And it makes you see yourself as tiny.

The Universe seems to be 98% Dark Matter and Energy—which we know nothing about.  Earth is teeming with life, 99% of it microscopic, and much of it unknown to humans [2]. The Earth is certainly several billion years old, and humans have been around only the last tick of that clock. Life has almost died out at least five times in those billions of years.

This month, Jochen Brocks and colleagues have published a rather fiddly study of biochemical traces in very old rocks [1]. The chemicals are left by squishy aquatic microlife that leaves little other fossil record.

Detecting these compounds is difficult because rocks are usually contaminated with younger chemicals (prominently including “anthropogenic petroleum products”) which swamp the faint older deposits. The researchers carefully screened out known contaminants, in order to measure the proportions of steranes and hopanes in the rocks. These are markers for eukaryotic cells, so the data indirectly indicate the predominance of bacteria in the environment.

They link these studies to current understanding of paleoclimate. They find evidence for a remarkable story. Roughly 700 million years ago was “Sturtian snowball glaciation”, an extreme ice age that froze the oceans all the way to the bottom. Before this period, eukarytes predominated, and they died back dramatically during the 100 million year ice age.

At the end of the Sturian, the abundance of bacteria increased, reaching modern abundance within a few tens of million years. Then something happened that enabled Algae to overcome the cyanobacteria, and eventually flood the world with oxygen and animals like us.

The researchers suggest that the glaciation and subsequent melting flooded the oceans with nutrients ground up by the ice cover, which eventually tipped the balance in favor of algae. They offer a possible scenario for this transition. At some point, algae evolved as a hybrid eukaryte engulfing a cyanobacteria, and thrived. This led to rapid evolution of animals that feed on algae.

If this scenario is correct then algae emerged and survived, but only came to dominate the oceans after a billion years. If so, then an episode of extreme global climate change probably led the rise of the biochemistry and ecology that we need to exist.

This study is very interesting, but far from conclusive. Even assuming the data is correct, it still isn’t clear whether the emergence of algae really triggered the evolution of animals, or how other factors were involved.[2].

Still, this is a reminder that the world we see is scarcely the only possible way things could work. It is also makes us realize just how much deep history is floating around in our own cells—we are descended from life that thrived on a radically alien Earth.

  1. Jochen J. Brocks, Amber J. M. Jarrett, Eva Sirantoine, Christian Hallmann, Yosuke Hoshino, and Tharika Liyanage, The rise of algae in Cryogenian oceans and the emergence of animals. Nature, advance online publication 08/16/online 2017.
  2. Friend, Tim, The Third Domain: The Untold Story of Archaea and the Future of Biotechnology, Washington, DC, Joseph Henry Press, 2007.
  3. Roland Pease, The algae that terraformed Earth, in BBC News – Science & Environment. 2017.


Grand Finale And A New Target

In the next weeks Cassini enters its final 5 orbits, swooping lower and lower, flying inside the rings of Saturn, until the final plunge on September 15, the “Grand Finale”.

At the same time, the New Horizons probe screamed past Pluto two years ago, but it has no brakes so it is still going out into the Kuiper Belt, which is cold, far away, and gigantic. The probe is still alive, though slumbering.   But with luck, it will wake up in 2019 and take some pix of Kuiper Belt object (KBO) 2014 MU69. This will be up close images 6 billion KM from home.

You can tell this is a long way out, because New Horizons is now half way between Pluto and the second stop on the itinerary.  This second leg is four years to complete.

This cunning plan got even more interesting this week, with reports from an occultation study in July that suggests that 2014 MU68 is not a ball. It may be an odd shaped blob or even two objects close together.

Whatever MUey-69 looks like, New Horizons may be able to get a good look.   Cool.

  1. Cassini Science Communications Team. The Grand Finale Toolkit 2017,
  2. Bill Keeter. New Horizons’ Next Target Just Got a Lot More Interesting. 2017,



Space Saturday

PS.  Yet more names for bands:

Final Five Orbits
Kuiper Belt & Braces
A Belt of Kuiper
The Grand Finale Toolkit

NASA Investigating Clockwork Rover Technology

NASA has the coolest projects!

With a long-term mission to visit and measure everywhere in the Solar System, NASA has not ticked off the easy stuff—Earth orbit, Moon, Mars, orbiting all the Planets.

There are plenty of places we really want to visit, but haven’t been able to. Cold places like the ice moons. And really hot places like the Sun  and the surface of Venus.

In the case of Venus,several spacecraft have orbited and are orbiting, and a handful of probes have reached the surface–just barely. The surface is hot, over 400 degrees C, and the pressure is a crushing 90 atmospheres. Most electronics simply don’t work at these temperatures. And it’s very cloudy, so solar power is minimal.  And so on.

In short, conventional engineering has little chance. To date, the record time to failure is 2 hours, set by a heroically insulated Vernera 13 probe in 1982. Building such extreme systems is hard and very expensive.

There is no way to make a rover to explore Venus. What’s to be done?

A NASA design group is exploring ways to build a rover that uses mechanical parts—clockwork—instead of electronics and computers. This is called “Automaton Rover for Extreme Environments (AREE)”.

When I saw their animation of some initial concepts, I immediately recognized that this is a Strandbeestand indeed they did invite Theo Jansen to JPL for some advice. (Evidently, Jansen’s advice was to get rid of the legs.)

Alternative locomotive ideas include wheels and tank treads.

But moving around is the least of the problems. How do you collect data?

In an interview with Evan Ackerman, they report several intriguing ideas under development.

First of all, mechanical calculation and number storage should be doable. And rough forms of obstacle avoidance are well known, too. (Toy cars navigate around furniture by bumping and backing up, no?.)

Image: Jonathan Sauder/NASA/JPL-Caltech Obstacle avoidance is another simple mechanical system that uses a bumper, reverse gearing, and a cam to back the rover up a bit after it hits something, and then reset the bumper and the gearing afterwards to continue on. During normal forward motion, power is transferred from the input shaft through the gears on the right hand side of the diagram and onto the output shaft. The remaining gears will spin but not transmit power. When the rover contacts an obstacle, the reverse gearing is engaged by the synchronizer, thus having the opposite effect. After the cam makes a full revolution it will push the bumper back to its forward position. A similar cam can be used to turn the wheels of the rover at the end of the reverse portion of the drive.

But if you had some data, how would you return data to Earth (i.e., to an orbital relay)? One possibility would be some kind of hard copy (e.g., etched into a metal disk), which is then lifted with a balloon and potentially pick up be a high altitude UAV. That sounds cool, but pretty iffy.

Another idea is to do semaphore code with radar reflectors. The orbiter beams radar and the rover reflects back on-off signals are certain wavelengths. This might have a bandwidth of a few bits per second (one way). That’s not much, but it’s a lot more than zero bps!   Pretty cool.

They are also trying to develop some kinds of sensors that will work under these conditions. This is difficult and it might be an area where small amounts of exotic high temperature electronics might be used.

This is such a cool design project!

I’m not sure how these ideas will pan out, but this work

is also important for changing the conversation on exploring Venus. Today, long duration in-situ mobile access on Venus has not been considered a realistic option. AREE demonstrates how such a system can be achieved today by cleverly utilizing current technology and enhanced by the technology of tomorrow.”

  1. Evan Ackerman, JPL’s Design for a Clockwork Rover to Explore Venus, in IEEE Spectrum – Automation. 2017.
  2. Jonathan Sauder. Automaton Rover for Extreme Environments (AREE). 2017,



Robot Wednesday