A Mars Meteorite by Any Other Name

You remember that meteorite from Mars?  The one that purportedly had fossilized Martian microorganisms inside it? The controversy over that meteorite has never been fully settled.  And now, it’s not just one meteorite.  Now there are two of them.

That original meteorite was named ALH-84001. Names are important.  You can learn a lot simply by understanding where a name came from.  The name ALH-84001 tells us a bit about this particular meteorite’s history. It was found in the Allan Hills region of Antarctica (ALH) during a 1984 scientific expedition (84), and it was the first meteorite found by that expedition (001).

This new meteorite is named ALH-77005, so right there you know some important things about it.  It was found in the same region of Antarctica, a few years before ALH-84001. And like ALH-84001, ALH-77005 sat in storage for a while before anyone got around to examining it.  In fact, it sounds like ALH-77005 has been sitting in storage for a whole lot longer than ALH-84001 did.

When I first heard about ALH-77005 and the surprises that were found inside it, my initial reaction was enthusiastic.  Surely this would bolster the Martian fossil hypothesis for ALH-84001, I thought.  But after some of the research and having some time to think, I don’t think this new evidence actually changes anything.

It’s still possible that something happened to ALH-84001 once it landed here on Earth.  For example, maybe Earthly microorganisms somehow wormed their way inside the rock.  If so, the exact same thing may have happened to ALH-77005.  So have we found new evidence of life on Mars, or new evidence of life in Allan Hills?  There’s still no way to tell for sure.

But it does make you wonder: how many more meteorites are just sitting in storage, waiting to be opened up?

Sciency Words: Euphotic Zones

Sciency Words: (proper noun) a special series here on Planet Pailly focusing on the definitions and etymologies of science or science-related terms.  Today’s Sciency Word is:


Based on what Google ngrams has to tell me, it looks like “euphotic” and “euphotic zone” entered the English lexicon right at the start of the 20th Century, then really caught on circa 1940.

The word euphotic is a combination of Greek words and means something like “good lighting” or “well lit.”  In the field of marine biology, the euphotic zone refers to the topmost layer of the ocean, or any body of water, where there’s still enough sunlight for photosynthesis to occur.

My first encounter with this term was in this paper by astrophysicists Carl Sagan and Edwin Salpeter.  Sagan and Salpeter sort of co-opted this term from marine biologists and applied it to the layer of Jupiter’s atmosphere where—hypothetically speaking—Jupiterian life might exist.

I don’t see any reason why the term could not also by used for other planets as well.  There’s a euphotic zone just above the cloud tops of Venus.  The same could be said about Saturn or Uranus.  Or maybe if the ice is thin enough, we may find euphotic zones right beneath the surfaces of Europa or Enceladus.

Of course just because a planet has a euphotic zone, that doesn’t mean photosynthetic organisms are living there.  And also there are plenty of ecosystems here on Earth that do not depend on photosynthesis and that don’t exist anywhere near a euphotic zone.

Still, I’m very glad to have picked up this term.  The concept of euphotic zones can be very helpful in any discussion of where alien life may or may not be hiding.

Sciency Words A to Z: Noachian

Welcome to a special A to Z Challenge edition of Sciency Words!  Sciency Words is an ongoing series here on Planet Pailly about the definitions and etymologies of science or science-related terms.  In today’s post, N is for:


In the 1870’s, Italian astronomer Giovanni Schiaparelli began producing the most detailed and accurate maps of Mars anyone had ever seen.  Schiaparelli also assigned many of the names we still use today for Martian surface features today. One of those regions on Schiaparelli’s map got the name Noachis Terra—the Land of Noah.

In my opinion, no other name could have turned out to be more apt.  Schiaparelli got many of his names from the Bible, and I’m sure you remember the biblical story of Noah and the Great Flood.

Schiaparelli’s map of Mars.

Much like the geological history of Earth, Mars’s geological history is divided up into different periods.  Noachis Terra spawned the name for Mars’s Noachian Period, a time that roughly corresponds with the Archean Eon here on Earth—the time when the very first microbes were appearing on our planet.

So what was happening on Noachian Mars?  Based on the evidence presented in this textbook on Astrobiology, it wasn’t quite like the Great Flood in the Bible, but it was close!  Most if not all of Mars’s northern hemisphere was probably covered in water.  Circumstantial evidence of shorelines can be seen today.

And in the southern hemisphere, in regions like Noachis Terra, we see unambiguous evidence of ancient flowing water.  Craters show obvious signs of erosion.  There are dried up lakes and rivers, and those rivers appear to have been fed by tributaries, which tells us it used to rain on Mars.

And there’s more.  Many Noachian-aged minerals and rock formations are most easily explained if we assume there was water.  In some cases, water is the only possible explaination.  Our Mars rovers have found mudstone, clay minerals, sedimentary rock… iron and magnesium carbonate… hematite, jarosite, and more!  Some of these minerals would have required a hot and slightly acidic environment, like you might find in a hot spring or near a hydrothermal vent.

We shouldn’t jump to conclusions.  After all, there’s still so much we don’t yet know about Mars, and new discoveries are being made all the time.  But I’m going to go ahead and call a spade a spade here: Noachian Mars sounds an awful lot like Arcean Earth, and it’s easy to imagine that whatever was happening on Arcean Earth (by which I mean LIFE!!!) must’ve also been happening on Noachian Mars.

However, the Noachian Period did not last long—a mere 400 million years.  Earth and Mars have had very different geological histories since then.  After the Noachian, Mars rapidly lost its internal heat, its atmosphere, and its oceans.  By the time of Earth’s Cambrian explosion, when complex, multi-cellular organisms really “exploded” onto the scene, Mars had fully transformed into the barren, inhospitable world we know today.

Modern day Mars has been trying really hard to get our attention and convince us that it might still support life.

And maybe that’s true.  During the Noachian, life had a great opportunity to get started on Mars, and it’s possible that some isolated remnant of a Noachian ecosystem has persisted to this day.  But in my opinion, it’s far more likely that we’ll find fossils left over from the Noachian Period (assuming we haven’t found some already).

Next time on Sciency Words A to Z, did you know there’s a deadly chemical in the air you breathe?  It’s called oxygen.

Sciency Words A to Z: Hydrothermal Vents

Welcome to a special A to Z Challenge edition of Sciency Words!  Sciency Words is an ongoing series here on Planet Pailly about the definitions and etymologies of science or science-related terms.  In today’s post, H is for:


In his book All These Worlds Are Yours, Canadian astronomer Jon Willis recounts the story of how hydrothermal (hot water) vents were first discovered here on Earth.  It was 1977.  A scientific research vessel was towing a deep-sea probe along the ocean floor in the Pacific when the probe detected a temperature anomaly.

This was exactly what the crew of that research vessel was hoping to find: a sort of underwater volcano, right where two tectonic plates were moving apart.  But the real surprise came when that research team brought their deep-sea probe back to the surface and developed all its photographs.  They saw the hydrothermal vent they were expecting to see, but they also saw things living—yes, living!—all around it.

Marine microbiologist Holger Jannasch, who was part of a follow-up expedition in 1979, had this to say:

We were struck by the thought, and its fundamental implications, that here solar energy, which is so prevalent in running life on our planet, appears to be largely replaced by terrestrial energy—chemolithoautotrophic bacteria taking over the role of green plants.  This was a powerful new concept and, in my mind, one of the major biological discoveries of the 20th Century.

It’s become fashionable to suppose that, rather than the “warm little pond” that Charles Darwin once wrote about, perhaps life began its conquest of Earth in an environment like this: a place deep under water where heat and chemicals come spewing up out of the planet’s crust.

An Introduction to Astrobiology actually cites science fiction writer Arthur C. Clarke as the first to realize what all this might mean for life in our Solar System.  Specifically, Clarke thought of the icy moons of Jupiter.  In his 2001: A Space Odyssey novels, Clarke tells us of a hydrothermal vent on Europa—a “warm oasis” populated by plant-like, slug-like, and crab-like creatures.

The idea of life on Europa (or Saturn’s moon Enceladus) clustered around hydrothermal vents may have started out as science fiction, but it is now a possibility that astrobiologists take very seriously. But we’ll talk about that later this week.     

Next time on Sciency Words A to Z, what’s wrong with the I in SETI

Sciency Words A to Z: Earth Similarity Index

Welcome to a special A to Z Challenge edition of Sciency Words!  Sciency Words is an ongoing series here on Planet Pailly about the definitions and etymologies of science or science-related terms.  In today’s post, E is for:


From time to time, you might hear on the news that scientists have discovered a new Earth-like planet.  You’d think that would be huge news, but it’s rarely presented that way.  It’s more like a fluff story, the kind of thing news anchors can banter about before tossing to weather.  It’s enough to make you wonder what, exactly, the term Earth-like planet really means.

In 2011, this paper appeared in the journal Astrobiology.  The authors of that paper proposed a new system for quantifying how Earth-like another planet is.  They called their system the Earth Similarity Index or E.S.I.  The basic idea is you take four measurable properties—a planet’s mass, density, surface gravity (represented by escape velocity), and surface temperature—plug that information into an equation, and get a number between zero and one.

Numbers close to zero represent planets that are about as un-Earth-like as possible.  Numbers close to one represent planets that are almost exact matches for Earth. So in most cases, when people talk about Earth-like planets, what they mean are planets that scored highly on the E.S.I.

Unfortunately, because of the limits of current technology, a lot of guesswork has to go into our E.S.I. calculations.  Most of the time, we just can’t get the precise measurements we need.  Measuring a distant exoplanet’s surface temperature seems to be especially problematic.  But even if that weren’t the case, the E.S.I. still wouldn’t account for things like a planet’s atmosphere or the presence of liquid water, or many other key things that make Earth the planet that it is.

That same 2011 paper also proposes another system called the Potential Habitability Index or P.H.I.  Taken together, the E.S.I. and P.H.I. should give you a clear idea of just how Earth-like another planet really is.  A very clear idea.  But the stuff you have to measure for the P.H.I.—we’re not even close to being able to measure that stuff.  Not yet.

Someday in the future, as we continue to refine out observational techniques, maybe we’ll be able to put the E.S.I. and P.H.I. to good use.  Until then, any news you hear about newly discovered Earth-like planets is probably not as exciting as it sounds.  Unless, of course, this is the newscast you’re watching:

Next time on Sciency Words A to Z, nuclear physicist Enrico Fermi said it first: where is everybody?

Where Are the Earthlings?

Have you ever looked up at the night sky and wondered if maybe, somewhere out there, someone might be looking back at you?  Well, I’m here to tell you the answer to that question is yes.  Or at least there are aliens out there who are trying very hard to find us.  I even have video evidence to prove it!

For us Earthlings, it’s pretty obvious that there’s life on this planet.  How could you possibly miss it?  But for aliens observing Earth from a distance—perhaps a very great distance—the most obvious biosignatures are frustratingly difficult to detect.

In the early 1990’s, Carl Sagan wrote a famous paper about this problem.  One of NASA’s own space probes, which was heading out to Jupiter, briefly turned all its instruments back on Earth.  Based on that data alone, without any prior knowledge about this planet, you could probably figure out there’s life on Earth. Probably.

This more recent paper published in The Astrophysical Journal follows up on Sagan’s work.  Assuming the aliens are smart (a big assumption, based on what the video evidence shows us), they should be looking for a planet with both an oxidizing gas AND a reducing gas in its atmosphere.

Oxidizing and reducing agents should react with each other relatively quickly, removing each other from the planet’s atmosphere.  So in order to have those two things coexisting long term, some exotic process (like biological activity) must be constantly replenishing them.

A spectroscopic analysis of Earth’s atmosphere would reveal a whole lot of the chemicals in our air, but not all of them. Apparently some spectral signatures are so strong they cover up others, which I think is an important thing to know.  But oxygen (an oxidizing gas) should still be detectable in the visible light part of the spectrum, and methane (a reducing gas) should show up in visible and infrared.

But still, it sounds like difficult work, teasing the signatures of oxygen and methane out of all the other spectral signatures you’d get from Earth’s atmosphere.  This could be why the aliens are having such a hard time finding us, and also why we are having such a hard time finding them.

Where Are the Aliens?

I fell way behind on my science and space exploration research last year.  I now have a tall pile of to-be-read books and papers in my reading room.  But I’m now starting to catch up, beginning with this paper on the atmospheres of Earth-like planets.

As explained in this article from the Planetary Society, the goal of this paper is to start creating a guidebook for finding planets that might be home to alien life.  And based on what the paper says early on, it sounds like there are plenty of “habitable Earth-like planets” out there to be found!

If we’re looking only at red dwarf stars, which are the smallest and most common of stars, about 30% of them should have a habitable Earth-like planet orbiting them.  And between 5 and 20% of orange, yellow, and yellow-white dwarf stars should have habitable Earth-like planets too.  Our own Sun, by the way, is a yellow dwarf star.

Statistically speaking, this means we should find another Earth orbiting a red dwarf within only 2 parsecs of us.  And there should be another another Earth orbiting an orange, yellow, or yellow-white dwarf within 6 parsecs.  I feel like that’s surprisingly close, at least in the grand scheme of our universe.

Except when astronomers talk about Earth-like planets, what they’re actually describing does not necessarily sound much like Earth.  Any planet that’s about the same size and mass as Earth can be called Earth-like, and by that standard Venus is about as Earth-like as any planet can be, aside from Earth itself.

And when this paper talks about habitable Earth-like planets, I’m pretty sure all the authors mean are planets within the habitable zones of their parent stars.  But just because a planet orbits within a habitable zone does not mean that planet is truly habitable.  Again, look at Venus.

So when we do find a “habitable Earth-like planet” within 2 or 6 parsecs of us, how will we know we’re looking at another Earth and not another Venus?  That’s a tricky question.  Maybe it would help to think about the problem from a different perspective.  You see, while we humans are having a really difficult time finding alien life, the aliens may also be having a very difficult time finding us.

More on that in the next post!

Sciency Words: Karman Line

Sciency Words: (proper noun) a special series here on Planet Pailly focusing on the definitions and etymologies of science or science-related terms.  Today’s Sciency Word is:


If I may begin on a personal note, I spent most of 2018 essentially grounded by real life problems.  So for 2019, I’m dusting off the old imaginary spaceship, and I’m ready to launch myself back into outer space.  It seems I have a whole lot of space research I need to catch up on!  But first, where exactly is space?  How far away is it?

In the early 1960’s, Hungarian-American physicist Theodore von Kármán proposed an idea that has come to be known as the Karman line. Basically, the Karman line can be defined as the altitude where you need to stop thinking in terms of aerodynamics and start thinking in terms of orbital mechanics.

A traditional aircraft flying above the Karman line will no longer get enough lift to stay aloft, and a satellite or other space vehicle that dips below the Karman line will experience too much atmospheric drag to maintain its orbit.  Technically speaking, there are still more layers of Earth’s atmosphere above that line, but still this seems like a sensible enough place to define the beginning of outer space.

So how high up is the Karman line?  According to the Fédération Aéronautique Internationale (F.A.I.), which is sort of like the Guinness Book of World Records specifically for air and space flight, the Karman line is 100 km above sea level.  This is the value that seems to be most commonly accepted around the world, but it is not the value accepted by one noteworthy space agency: NASA.

According to NASA, space begins 50 miles above sea level. This 50 miles number is not merely a result of America’s famous disdain for the metric system.  As explained in this paper from Acta Astronautica, calculating the exact altitude where aircraft can no longer fly and satellites can no longer maintain their orbits has been a challenge for many decades; however, an estimate of 80 km (approximately 50 miles) may be closer to the real Karman line than the 100 km estimate set by the F.A.I.

A lot may depend on your spacecraft’s design, the parameters of your orbit, and solar activity, which causes Earth’s atmosphere to puff up slightly at times.  But to quote from that Acta Astronautica paper:

[…] elliptical orbits with perigees at 100 km can survive for long periods. In contrast, Earth satellites with perigees below 80 km are highly unlikely to complete their next orbit.

In other words, a satellite can safely dip below an altitude of 100 km, but if it gets as low as 80 km, that satellite is toast.

So when I climb back into my imaginary spaceship, how far up do I need to go to reach space?  50 miles?  100 km?  Or is there some other number I should be aiming for?

I’m still not sure.  But given the places I’m planning to go with my research in the coming year, maybe it doesn’t really matter.  Me and my imaginary spaceship will be flying well beyond the Karman line, wherever precisely that line is.