The Extreme Tardigrade

Most extremophiles are bacteria, living in places like the deep-sea hydrothermal vents, sulfuric hot pools, oxygenless layers in the ocean, and other environments that are deadly to every other form of life. But there are a few extremophile animals, such as the tardigrade.

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Impressed yet? These invertebrates are some of my favorite living animals, and are a fascinating study in how evolution works. We still barely understand extremophiles of this sort, and there's a lot more research to be done. If you are interested in learning more, there are some resources below the break.

Scientific Unknowns: What is Life Redux

Image Credit: JFantasy via Wikimedia Commons

Almost three years ago now, I wrote a post about the difficulty of defining life. Now this has come back into the news and I thought I would add my two cents.

This all started when Edward Trifonov, a biologist at the University of Haifa Isreal, proposed a three word definition of life. To quote from the article by Carl Zimmer on Txchnologist...

Trifanov analyzed the linguistic structure of 150 definitions of life, grouping similar words into categories. He found that he could sum up what they all have in common in three words. Life, Trifonov declares, is simply self-reproduction with variations.

In his article, Zimmer does acknowledge that there is a considerable amount of criticism but he mostly focuses on what this definition might be missing, metabolism, information and so on. I was interested, though, when I read a critical piece by Sean Carroll asking if reproduction should even be a part of our definition. He says...

...the idea of reproduction looms large in many people’s definitions of life. But I don’t think it really belongs. If you built an organism from scratch, that was as complicated and organic and lifelike as any living thing currently walking this Earth, except that it had no reproductive capacity, it would be silly to exclude it from “life” just because it was non-reproducing. Even worse, I realized that I myself wouldn’t even qualify as alive under Trifonov’s definition, since I don’t have kids and don’t plan on having any.

3 Legged dog on the right
Photo Credit: Jon Hurd via Wikimedia Commons

It is a really interesting question. We could define dogs in part as having four legs, but does that mean if a dog loses one leg it is no longer a dog? If we created a cell in the lab that is identical to a natural cell in every way except it can't reproduce is it alive? To give another example, I think it is easy to imagine a robot that can copy itself but that we would still not want to call alive.  My personal thought, is that reproduction is a necessary component for any type of life that will survive for long stretches of time. That doesn't mean reproduction is what makes something alive.

So what is life? I certainly don't have an answer. Right now we have a sample size of one*. Until we find life somewhere else in the universe, I wouldn't expect any real agreement on this deceptively simple question.

*After all, every living thing we have found on the Earth shares a common ancestor.

Scientific Unknowns: Life on Titan?

Sunlight reflecting of one of the lakes of Titan
Image Courtesy: NASA/JPL/University of Arizona/DLR

Of all the places we look for life in the solar system, there is one that has captured my imagination more than any other. Maybe it is because of this obscure moons weirdness, or the possibly of an entirely new biology. Either way I could not discuss life in the solar system and leave it out. So what plausibly and evidence is there for life on Saturn's largest moon? The answer may surprise you.

Here on Earth all life requires water. Water makes a great solvent. This simply means a large variety of different molecules can be taken up by the water. Suspended in liquid water, those molecules can move around to do the things of life. This works great here on Earth and water may even be a good solvent for possible life on Europa. Titan however, is a balmy -290 ^oF, putting water out of the picture. Luckily Titan is covered with another liquid that may be able to fill the same role as water, liquid methane. I need be clear in saying that we have no idea if life can form in liquid methane. Maybe it forms easier in methane than it does in water. While there are some good reasons to think water may be the liquid of choice, we simply don't know. This is what make Titan such an interesting world to explore.

An infrared image of Titan showing Titan's Northern Lakes
Image Courtesy: NASA/JPL/Space Science Institute

So now we have a feel for the plausibility of life on Titan, but what about the evidence? Often in science you test a hypothesis by building a model that produces predictions. Then you test those predictions to see if the model reflects reality. In 2005 a team of astrobiologists published a paper making some suggestions about what we might expect to see if some sort of methanogenic life were enjoying the orange haze of Titan. In 2010 data from the Cassini Huygens probe matched those predictions. So what does that mean? Well it means that this model deserves strong consideration. That said, we should not be quick to accept any claim of alien life. There are a huge multitude of processes not involving life that can change the chemistry of an atmosphere. This evidence is a exciting starting point, but it is not proof.
So when it comes to Titan, even more so than Mars or Europa, I can only say we have no clue if there is any life present. Titan is a moon we have only recently gotten a good look at. Astronomy has a history of dismissing early speculations of life with future observations. Will that pattern hold true on Titan? We need more scientists and more spacecraft to find the answer. Right now I can only say that I don't know, but that I am extremely excited to see the discoveries made as we hunt down the solution.

Scientific Unknowns: Life on Europa

Europa as seen by the Galileo Spacecraft. 

Credit NASA/JPL/DLR

When we think of aliens we often think of a place similar to Earth. We think of creatures with similar body plans and similar needs. But what about the possibility of creatures that have never seen the Sun? This is the kind of life that could be hiding on Europa, Jupiter's fourth largest moon.

There are two sides to every claim, plausibility and evidence. Some claims, like many new medical drugs, start with a high plausibility but the evidence never bears them out. Others, such as quantum mechanics, start with low plausibility but the evidence becomes overwhelming until they are accepted. Right now, to my knowledge, there is no evidence of life on Europa. What makes it exciting, however, is how plausible it is that life could exist there.

Europa's entire surface is covered with ice. Located almost a half billion miles from the Sun, there is nowhere near enough heat from the sun to melt Europa's ice covered surface. Still many, if not most, scientists agree that there is likely a ocean under that ice. As Europa orbits around Jupiter, it is squeezed and stretched. This is what creates the cracks you see on the surface. This also heats Europa's core in the much the same way playing with Silly Putty will warm it up over time, creating a layer of liquid water. There is a lot of debate between scientists on how thick this ocean is. Right now, it seems likely that the ice is tens of kilometers thick with an ocean that is between 25 to 100 kilometers thick. So the question is could anything survive in the ocean?

A cutaway view showing Europa's interior. Notice the
inner rocky core surrounded by liquid water and capped
 off an outer layer of ice.
Credit: NASA/JPL

If there is any life in Europa's ocean, it have had to have formed and survive with no sunlight. The ice above this ocean is just too thick to allow in enough sunlight for any organism to use that as a source of energy. So scientists have looked to the Earth for creatures that can survive without the Sun. Probably the most similar environment to Europa here on Earth is the ocean under the Antarctic ice. When scientists have drilled into the ice there we have found life. In fact scientists have found entire colonies of organisms called black smokers that live in some of the harshest conditions on the Earth. These organisms live off of hydrothermal vents at the very bottom of the oceans where there is no light at all. Some scientists have even speculated that this is where life on Earth originated in the first place. These unique adaptations of life here on the Earth make it reasonable to think similar creatures could survive on Europa.

A hydrothermal vent on the
Mid-Atlantic Ridge. Credit NOAA

So when it comes to life on Europa we have a really good story. We have solid reasons to think the ocean is there and that life could possibly survive in that ocean. What we are missing is the evidence. A detailed study of Europa is high on NASA's priority list, but without the proper funding it could easily still be more than a decade away. At this point, we don't have the evidence to say if life exists on this icy moon or not. I hope in my lifetime a spacecraft arrives at Europa and drills through that ice. What we find in that ocean could change how we think about ourselves and the universe we live in.

Alien Update

I want to quickly revisit the alien meteorite from last week. Here are some good links to take a look at if you are curious.

I was wondering what NASA was going to say about this. Here is their official statement. If this research really carried some weight, I would expect NASA to be publicizing it to no end. Instead, they are distancing themselves.

This is the best review of the science in the paper I have seen so far. They also a fairly good job of reviewing the journal itself.

I know I linked to Bad Astronomy before but I am going to do it again. He does a nice job laying out the criticisms made other places in a very understandable way.

After reading all of the follow-up here and other places, my original opinion still holds. The science here is just not nearly enough to prove the claim being made.

Aliens Exist: Proof Pending

Last week I mentioned how I wanted to do some posts talking about the possibility of life in the solar system. Well, apparently that is going to be a waste of time, since this Saturday Yahoo News released an article reading in its first line "Aliens exist, and we have proof." Fox News was no better with their first line "We are not alone in the universe -- and alien life forms may have a lot more in common with life on Earth than we had previously thought." How much did we think we have in common with alien life forms before? Anyway, both articles discuss a paper done by NASA astrobiologist Dr. Richard Hoover who claim that he has found evidence for fossil alien bacteria in a meteorite. With a news story like this spreading across the Internet, I couldn't help but do some digging.

First, I went looking around my usual astronomy news sites. As of Sunday evening, I couldn't find a thing mentioning it. This is really peculiar and made me that much more skeptical. The one article I could find was on Bad Astronomy by Phil Plait. It is a good review of the paper and makes several of the same points that came to mind for me. Still, the vast under-reporting of this breakthrough in the specialized media is a point I think is worth mentioning. If you ever see something in the mainstream media, look to see what the people who deal with that subject on a regular basis have to say. While not always true, I have found that breakthroughs tend to go from the specialized media to the mainstream; nonsense tends to flow the opposite way.

With no luck in the space news, it was time to go to the paper itself. The largest problem this paper faces is in that pesky relationship between claim and evidence. If you are going to claim extraterrestrial life, you need a mountain of evidence to back you up. Dr. Hoover works hard in the paper to rule out any earth-based contamination. He is quoted in the journal press release with the following.

"What is both exciting and extraordinary is although many of the bacteria resemble and can be associated with generic species on Earth, there are others which are completely alien. Neither I nor other experts who have seen the evidence have any idea what these creatures might be."

It could be true that no one who has studied the rock has been able to identify the bacteria inside. This does not mean however, that they are necessarily alien. In the paper itself, he tries to use the specific chemistry to the meteorite and the "fossils" to rule out abiotic causes and earthly contamination. I do not have the technical knowledge to delve into these details, so it will be interesting to see what the editors of paper said when those are released.

In the end, I think this paper falls short. I want to see how the scientific community responds over the next few days and what, if anything, comes of this. That is part of what makes science so interesting. Now the paper is published and the real critique can start. For now I remain unconvinced but eagerly await to hear what story will come from this.

Scientific Unknowns: Life on Mars

The question of how much life there is in the universe is one of the most fundamental questions in astronomy, and possibly all of science. While we are just now on the brink of finding Earth-like planets around other stars, the possibility of life existing on planets very different from our own still remains. While scientists have dismissed the old notions of grand civilizations on Venus and Mars, there is tantalizing evidence of microbial life throughout the Solar System. This is a first in a series of posts I will do over the next few weeks looking at some of the top contenders.

Of all the places we look for life in our solar system, none seems to have the mystique of Mars. The search for life on Mars has deep historical roots. Percival Lowell infamously reported his evidence for a grand civilization on Mars with a grand irrigation network. This and other stories firmly set Mars as the home of extraterrestrials in science fiction. While scientists are no longer searching little green men on the surface, microbes on the red planet have become hot topic of debate. Mars surface is bathed in radiation that would likely prevent anything from living on its surface. Liquid water also can no longer exist on the surface of Mars. These both come from the fact Mars lacks the thick atmosphere and magnetic field we have on the Earth. So planetary scientists are now searching for microbes under the surface of mars. For those scientists there are three main lines of evidence.

1. Recently, there has been a growing consensus that a few billion years ago, Mars had at least a some running water on its surface. The Earth appears to have developed life fairly quickly once the oceans formed. The thinking goes that if Mars had conditions similar to that of the early Earth, it is reasonable to assume that it would have developed life in a similar way. Mars has changed so much over the last few billion years to become the dry and harsh world it is today, that it is not surprising that we don't see the abundance of life we now have on the Earth. This idea gives hope that possibly some microbial life was able to take hold on Mars during the planet's youth and maybe still be surviving under the surface.

2. If life ever existed on Mars, we could maybe find evidence of it the same way we find evidence of past life on the Earth: fossils. It is well accepted that large impacts from meteorites on the surface of Mars can lob chunks of the Red Planet into space. The Sun can then pull those into the more inner part of the solar system where they collide with the Earth. What is controversial is a claim made by a group of scientists in 1996 that one such Martian meteorite contained a fossilized bacteria. If true, this would be sure evidence of at the very least past life on Mars. After 15 years of research however, the scientific community is still far from a consensus.

In science, extraordinary claims require extraordinary evidence. Life on Mars is certainly an extraordinary claim. Unfortunately, the evidence has yet to match. Without going into extreme technical detail, the core issue is whether or not the meteorite in question, Martian meteorite ALH84001, could have plausibly formed without life. Scientists look at a multitude of characteristics, mostly based around the various minerals including their isotopes, distribution, and texture. I think it is safe to say that our current results have been inconclusive. There are scientists with strong points on either side. In the end, the evidence is just not there to make a solid decision.

3. The final hint of life on Mars is methane. This is something I touched on briefly in the past and the basic story is this. The chemistry of Mars atmosphere is such that methane breaks down over time. We have found large quantities of methane in Mars atmosphere, so we know it must be replenished by some ongoing process. At this point all we have is the observation of the methane itself, and speculation about what is causing it. The reason people get excited is because one of the ways methane is produced here on Earth is by bacteria. Scientists, however, are also quick to point out that we know of geologic processes that can produce methane in the quantities we seen on Mars. Again, this line of evidence seems tantalizing, but non-conclusive.

So, what is the final story for Mars? I have to say that, while there is good reason to continue looking for microbes under the surface, we can't say we know they will be there. Either we will see exciting geology or revolutionary biology. Regardless, Mars continues to be a place worth exploring with mysteries lurking just beneath the surface.

Have Scientists Found a Second Earth?

Ever since we stared finding exoplanets (planets orbiting a start other than our sun) back in 1992, the hunt has been on to find a Earth-like planet. Of course, the planets we found first were not the small rocky worlds like our own, but massive gaseous Jupiter-sized objects that are very close to their stars, appropriately called hot Jupiters. Over time, we got better at the techniques and have become able to find smaller and smaller planets farther and farther from their host stars. Now, have we finally found that long sought-after 'second Earth'?

So our first question is simply, what did they find? To really understand this situation, you need to understand the star this planet is orbiting. This is not a medium-large yellow star like our sun, but a much smaller red dwarf. Red dwarfs have about 1/3 of the mass of the sun and a luminosity of about 1.3% of our sun. This means a planet has to be much closer to the star then the Earth to our Sun to have any chance for life to survive.

That brings us to the planet Gliese 581g (such a creative name). Because of the method used to discover this planet, we know it has a minimum mass of about three times that of Earth, and it is unlikely that it is much larger than that. It is also the right distance away from the star to be in what's called the "habitable zone". This is the zone where a planet could potentially have liquid water on its surface. So far, so good.

Now is when things get tricky. There is still much astronomers don't know when it comes to rocky planets, and planets in general for that matter. Gliese 581g is large enough to hold on to an atmosphere, but atmospheres are tricky things to understand. Atmospheres are also hugely important for life. Mars and Venus can both be said to be in the habitable zone of our Sun, but because of Venus's overabundant atmosphere, and Mars' lack thereof, they are both devoid of life. To make things more complicated, Gliese 581g is probably tidally locked with its host star. This means that one side of the planet is in perpetual day while the other side never sees the sun.

Science rarely, if ever, gives us cut-and-dry answers. Does Gliese 581 harbor life, or would life even have a chance there? We can't be sure. What makes this discovery truly exciting, though, is the speed at which it happened. We have only been finding exoplanets for less than two decades and, of that time, our technology has only become sensitive enough to find small planets much more recently. We have really only begun to survey our neighbor stars in the galaxy and already we have found a planet that is a decent candidate to support life. If this trend continues, there could be millions of such worlds in our own galaxy alone. Think of the prospects if even just a small percentage of those worlds ever developed life.

I think it's time to kick up the planet hunt one more notch.