This morning, the world witnessed the safe landing of the space shuttle Endeavour, after a 16-day mission to the International Space Station. For those of us inhabiting Earth’s more western time zones, we got to watch the landing last night, with no inconvenience, other than having to divert from the Colbert Report. While I did not travel to the Kennedy Space Center for the landing and recovery of the Planetary Society’s experiment known as Shuttle LIFE, my experience was infinitely better than it was the last time that I had an experiment on a shuttle, when I did go to the Cape to attend the landing.
This is because the last time for me was on February 1, 2003. I was waiting for the return of the Columbia, with friends and colleagues, Eran Schenker and Yael Barr, alongside the very runway where the Endeavour glided to a touch down this morning. Having developed the Planetary Society’s "GOBBSS" experiment –which came to be known as the "Peace Experiment", since we had recruited two students, one Israeli, the other Palestinian, to work together as co-investigators– I anticipated the post-flight analysis of the biological cultures from GOBBSS, and from two other experiments that Eran had developed dealing with probiotic microbes. But there was no sonic boom, no sign of the Columbia. The time to landing clock went into positive time, and we were directed to return to the bus that would take us back to the building where we had gathered earlier. Then we learned of the tragic fate of the seven people who had made up the Columbia’s crew, and we no longer cared about the experiments.
Like the Columbia mission, STS-107, this flight of the Endeavour, STS-134, was conceived as a mission of science. Shuttle-LIFE is only a tiny part of the Endeavour science payload; compared to cool-sounding devices like the alpha magnetic spectrometer, designed to detect anti-matter throughout the Cosmos, a few 10 microliter test tubes containing microorganisms must sound positively mundane. Why then did we book passage for our little bugs on the penultimate flight of NASA’s STS program?
To begin, the Planetary Society and all research groups who had flown experiments packaged by Instrumentation Technology Associates (ITA) for the STS-107 flight were offered a chance to fly new experiments on STS-134. The Shuttle-LIFE organisms flew inside an experiment module called CREST-1. LIFE stands for "Living Interplanetary Flight Experiment". This may sound strange, since the Endeavour, like all space shuttles, does not fly interplanetary missions. But Shuttle-LIFE is a precursor to another experiment –Phobos-LIFE. Conceived and developed earlier, Phobos-LIFE awaits launch at the end of this year to Phobos, one of the two tiny moons of Mars. The other is Deimos, Phobos’ twin brother in Greek mythology; both were children of Aphrodite by Aries, the war god, but Mars was his Roman name. When naming planets, we like using Greek gods by their Roman names, even in science fiction. That’s why Spock’s home is called Vulcan, and not Hephaestus.
Scheduled to be launched by the Russian Federal Space Agency (Roscosmos), a probe called "Grunt" will depart after the next launch window opens this December. It will be an unprecedented, 34-month voyage to Phobos and back to Earth. Sitting inside the probe is an 83-gram discoid canister, the LIFE biomodule. Like three identical biomodules that were loaded as experimental controls, the one in the Grunt probe contains 30 sample tubes housing ten biological species, most of them in triplicate, representing all three of Earth’s domains of life: Archaea, Bacteria, and Eukarya. Additionally, there is a sample of soil from the Negev desert in Israel whose mixed population of microorganisms will be studied by Russian microbiologists.
The purpose of Phobos-LIFE is to examine the effects of the space environment, particularly the radiation, on organisms traveling through interplanetary space for nearly three years. While many such experiments have been flown in low Earth orbit, very few have flown through interplanetary space. Those that have flown in interplanetary space have done so for relatively short periods.
Most of the meteoroids created from cometary impacts with the Martian crust that arrive on Earth as "Mars meteorites" take thousands or millions of years to make the voyage. A famous example is ALH84001, a Mars meteorite containing features that some scientists believe are fossils of ancient Martian microorganisms that were trapped inside the rock more than 3.5 billion years ago. A small piece of Martian crust that was ejected into space by an impact event about 16 million years ago, ALH84001 arrived on Earth, in Antarctica, only about 13,000 years ago. Between being ejected from Mars and landing in Antarctica, the rock was just floating about in space as a meteoroid. This is fairly typical of the forty or so meteorites that have been found and identified as being from Mars, but these represent only a tiny fraction of rocks and other Martian material that have traveled to Earth. Each year, about a ton of material ejected from Mars arrives on our planet. Most of it has taken a very long time to get here, but a small fraction of it, about one out of every ten million Mars rocks, has made the trip in only a year or so.
If any of such fast-transiting rocks carried microbes from Mars during the Solar System’s early years, it is plausible that they may have made it to Earth, before Earth had a chance to develop its own life. Since Mars is known to have cooled down earlier than Earth, it is not unreasonable to think that abiogenesis, the origin of life from non-living matter, could have occurred first on Mars, allowing Martian microbes to seed Earth, before Earth had a chance to develop its own life. In a sense, we might be Martians, or at least descendents of Martian immigrants.
Roughly the size of a basketball, the Grunt probe will serve as an artificial meteoroid of sorts, simulating –as best we can at this point– a 34-month voyage of microorganisms through interplanetary space. It is a model of the fast voyage scenario that occurs in that tiny fraction of ejected Martian material, but if seeding from Mars occurred this tiny fraction is the key.
It is important that the environment be interplanetary space, since a large component of the most high energy space radiation is blocked by the geomagnetosphere, thus protecting samples carried in spacecraft in low orbits, such as those flown by space shuttles and the international space station. If organisms from Earth can survive 34 months inside the artificial meteoroid, it is plausible that other organisms, including organisms that could have been living on Mars four billion years ago, could survive the trip too. We know that various microbes can survive the impact effects of a comet, a small asteroid, or a large meteorite, hitting the Martian crust and ejecting rocks into space. We also know that organisms a few centimeters inside a meteoroid would survive entry through Earth’s atmosphere. Therefore, survival of organisms in our artificial meteoroid would make more plausible the possibility that Earth’s biosphere could have developed from a seeding event.
As the year goes on, you will hear more about Phobos-LIFE, with its ten species, envoys from Earth’s biosphere. Mostly as practice for Phobos-LIFE, we’ve included five of the species in Shuttle-LIFE. So let’s talk about why they’re on the passenger list for Phobos LIFE in the first place.
Even in the downscaled version of the experiment that we’ve sent on the Endeavour flight, all three of Earth’s domains of life are represented. From the bacterial domain, there are two species. One is called Bacillus subtilis. It is a gold standard organism, both for space flight studies and for many studies on Earth. Like many types of bacteria, B. subtilis form spores when placed in an unfavorable environment in which the cells are dried out and denied nutrients. This ability helps the bacteria to survive for long periods, and also makes them quite resistant to radiation. B. subtilis has a long history of space biology missions, beginning in the days of Apollo, the space program, not the god of music and light. As one of the organisms flown in early experiments called Biostack 1 and Biostack 2, B. subtilis even has flown outside of the geomagnetosphere, in the Apollo 16 and Apollo 17 command modules. It also was exposed directly to the space environment for six years, though in low Earth orbit
The other bacterial species that flew in Shuttle LIFE is Deinococcus radiodurans. Unlike B. subtilis, D. radiodurans does not form spores, yet it is even more resistant to radiation. It is able to survive an acute radiation dose of 5,000 Grays (Gy). This is amazing, since an exposure of 10 Gy would kill the average human. This resistance to radiation, along with an unusual resistance to desiccation and starvation, is due to various genetic redundancies. Basically, you could chop up this organism’s DNA with radiation bursts, and it still works just fine, leading some to call D. radiodurans by a nickname, Conan the Bacterium.
If B. subtilis and D. radiodurans are capable of tolerating radiation exposures well above what is encountered during a voyage in a meteorite from Mars to Earth, it is not unreasonable to think that organisms native to Mars might also have evolved such capabilities long in the past. Mars has no global magnetic field that would reduce cosmic radiation exposure as Earth’s does. It seems to have had one in the past, but Earth’s atmosphere provides another radiation shield. The Martian atmosphere is much thinner, so more cosmic radiation gets in, and radiation also comes from radioactive substances in the crusts of both planets. Thus, Mars would have selected for organisms with good radiation survivability, and such organisms would have made good candidates for survival in a meteoroid traveling to Earth. As models for such theoretical Martians, B. subtilis and D. radiodurans were placed on the passenger list of Phobos-LIFE and Shuttle-LIFE too.
Members of the domain Archaea tend to be extremophiles, organisms that not only survive, but thrive, under conditions that we humans would consider to be extreme. Like bacteria, archaea are single-celled organisms lacking membrane-bound organelles, but here the similarity ends. One example, which is included both in Phobos- and Shuttle- LIFE, is Haloarcula marismortui. It is a salt lover, thriving in high saline environments. Indeed, it is native to the Dead Sea, as its name in Latin suggests. Studies of certain Mars meteorites have revealed high salt levels, while studies of Mars itself have suggested that large amounts of water have flowed on the surface. With an atmospheric pressure of only 7 millibars, to be in a liquid state and not evaporate, such bodies of Martian water would have to have been briny, like having Dead Seas and salty rivers all over the planet. Thus, if life exists there, it is not unreasonable to think that it may share certain characteristics with salt-loving microbes such as H. marismortui. That is why we are sending this organism a long journey through space and why we also included it in the experiment’s precursor, Shuttle-LIFE.
Discovered in 1986 in volcanically heated ocean sediments off the coast of Italy,Pyrococcus furiosus is a thermophile, a heat lover, thriving in temperatures from 70 to more than 100 degrees Celsius. We don’t think it’s analogous to anything living on Mars, which is a cold planet, but there is a tiny risk that somewhere in processing the payload, a mistake would cause the payload to overheat. While it is not thought that the reentry of the Grunt probe through Earth’s atmosphere will expose the payload to very high temperatures, in the unlikely event that the course of the capsule through the atmosphere is altered and it does get hotter inside than expected, P. furiosus will serve as a temperature control. If it is the only LIFE organism to survive, we’ll know that the demise of the other species in the biomodule cannot be attributed to the space environment. It too is included in Shuttle-LIFE
Finally, on both Shuttle and Phobos versions of the experiment we’ve included a member of the animal kingdom, which is part of the Eukaryotic domain. Tardigrades, also called water bears, are big compared with LIFE’s other passengers. The samples are a mixture of three tardigrade species. The body of each organism consists of four segments, each with two legs ending in claws. Like the archaea, they are extremophiles. Water bears can adapt to a wide range of temperatures from 150 degrees Celsius down to just a few degrees above absolute zero. They also are extremely tolerant to radiation. Who said that cockroaches would be the only animals to survive a nuclear war? Tardigrades would survive too, and they sure are a lot more lovable.
Images: 1) The diagram of the biomodule with parts labeled is from the Planetary Society, 2) Image mashup by David Warmflash, 3) Image from Did Life Come from Another World? by David Warmflash and Benjamin Weiss, Scientific American, 2005.
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