In the 1951 science fiction story “Pictures don’t lie,” by Katherine MacLean, an alien spaceship contacts the Earth and asks for permission to land. But when the visitors land, nobody sees them, nor do they see the welcoming committee. In fact, both earthlings and extra-terrestrial beings were searching on the wrong scale: the visitors were microscopic. A group of Brazilian researchers is discovering that this idea is closer to reality than it seems. They have shown that super-resistant bacteria would survive the trip through space, clinging to minute specks of dust.
This a pioneering conclusion in astrobiology, the area of science that in recent decades has been looking for evidence of life beyond Earth, for other habitable worlds, and trying to understand the conditions that are essential for the emergence of life. One of the best known astrobiology projects, SETI, (Search for Extraterrestrial Intelligence), is this year celebrating its fiftieth anniversary. The difference is that new technologies are now allowing us to extend the frontiers of knowledge. In Brazil, studies in this area should gain momentum over the coming months with the start of activities in the first national laboratory dedicated to astrobiology. In its installation phase in Valinhos, in São Paulo state, the new center will be coordinated by Eduardo Janot-Pacheco and linked to the Institute of Astronomy and Geophysics at the University of São Paulo (IAG-USP).
Astronomer Douglas Galante, the researcher at the IAG who is heading up the laboratory installation, has been showing how life can withstand even the most extreme cosmic phenomena, such as the explosion of supernovas and gamma rays. His work, alongside the experiments that biologist Ivan Paulino Lima carried out during his PhD research at the University of Rio de Janeiro (UFRJ), have contributed to the idea that living beings can travel through space. Both studied the bacterium, Deinococcus radiodurans, which distinguishes itself by being able to resist extremely high doses of radiation.
The species was discovered in the 1950’s, in the context of the American canned meat industry. Food was treated with radiation to eliminate contamination by bacteria, but it seemed impossible to put an end to them: Deinococcus radiodurans resisted sterilization. “If we’re exposed to gamma rays with an intensity of four Grays, we’ll be dead in a month,” says biophysicist, Claudia Lage, from UFRJ, Paulino Lima”‘s tutor for his PhD, “but Deinococcus radiodurans continues multiplying even when bombarded with 15,000 Grays.” In fact, the genetic material of bacteria becomes pulverized, but it only needs three hours without excessive radiation for the DNA to recompose perfectly and return to action; like the legendary phoenix that is reborn from the ashes.
Resistance to high levels of radiation, a vacuum, desiccation and temperature is what makes these bacteria ideal to test the possibility of living beings undertaking interplanetary travel without the protection of a spacecraft. Until now, international studies, which are also being carried out by the North American Space Agency (NASA), have been testing the possibility of life in space with bacteria that protect themselves by forming a shell, as if they were mummies (cysts). The difference is that Deinococcus enters dormancy, but does not form these cysts, and over the last few years Paulino Lima has been subjecting these bacteria to light beams that simulate the radiation that exists in solar rays in space, without the protection of an atmosphere.
Much of the work is being done at the National Synchrotron Light Laboratory (LNLS) in Campinas, in São Paulo state. According to results published in August in Planetary and Space Science, the research has shown that the only thing needed is protection from a speck of dust for the bacterium to survive conditions in space.
The dust is more important than it seems. It passes unscathed through physical barriers that would be impossible for larger bodies. When a large meteorite enters the atmosphere, for example, the friction is so intense that the rock heats up to temperatures that often pulverize it and are lethal to any bacteria. This problem does not exist with dust, whose microscopic size allows it to enter the atmosphere without any friction. And it is abundant, in part due to the comets that cross space with their bright tails. The tail of a comet emerges when it approaches the Sun; in fact i its surface is blown by solar winds. When it leaves for the frontiers of the universe, the comet leaves behind this dust and is slightly smaller because it has lost its outer layer; this layer is valuable for life: comets are full of amino acids, the organic molecules that go to make up proteins.
Theory in practice
“Around 10, 000 tons of dust from comets fall to Earth every year,” says Claudia. And the dust that reaches here is not, as far as she is concerned, the only evidence that the Earth is far from being an environment that is closed in upon itself, where nothing arrives and from which nothing leaves. Winds and typhoons suspend soil particles high up into the atmosphere, which is periodically swept by solar winds that carry the dust to other areas of space. “We”re polluting the universe,” she says.
In a period of research in the Diamond synchrotron, in England, Paulino Lima also showed that his favorite bacteria resist a simulated explosion of a supernova, a stellar phenomenon that releases large amounts of X-rays The study gained further strength with the highly unusual encounter between experimental and theoretical astrobiology. At this same time, Douglas Galante was plunging into theoretical calculations and simulations to discover how life reacts to extreme doses of the cosmic rays that are present in space and on young planets – in order to understand the origin of life and the evolution of biodiversity. Quite independently of the Rio group, for his simulations he had chosen precisely to use an organism that is difficult to kill: the Deinococcus radiodurans. In the Diamond synchrotron, the two young researchers worked together and showed that the theoretical and experimental data fit perfectly.
“I discovered that it’s not possible to kill all the life on a planet,” says Galante, who, besides the supernovas, made theoretical simulations of gamma-ray bursts, the events with the highest energy since the Big Bang. “The energy released in these events is immense, as if the entire mass of the sun was converted into energy within 10 seconds.” According to Galante, a gamma-ray burst is sufficient to sterilize all the exposed sides of planets up to a distance equivalent to the diameter of our galaxy: 30,000 parsecs or 99,000 light-years. But there will always be life protected in water, under the ground or simply on the face of heavenly bodies not affected by the gamma-rays.
Even so, these spatial events have long-lasting effects. In recent articles in Astrophysics and Space Science and the International Journal of Astrobiology, Galante showed that gamma-ray bursts alter the chemistry of the atmosphere and destroy the ozone layer, increasing the planet’s exposure to ultraviolet rays for several years, which causes damage to living beings. The simulations show what would happen if you eliminate almost all life on Earth, leaving only about 1 percent of the organisms. This, therefore, is important to other areas of science. “Extinction events are essential for the emergence of new species,” remembers the astronomer, speculating that perhaps these happenings are necessary for generating diversity. “Astrobiology studies the origin, evolution and destiny of life.”
In a partnership with the two scientists from UFRJ, he intends to keep on bombarding bacteria accustomed to extreme conditions in space with radiation, in experiments that replicate spatial situations. One of these bacteria was discovered this year by the group of Argentinian microbiologist, Maria Eugenia Farias, in a lake in the crater of a volcano in the Andes and will be tested in collaboration with the Brazilian team. These are bacteria that survive in different extreme conditions, even in extremely high salinity. It may be important for simulating the possibility of life on Mars, which is an extremely saline environment.
Much of the work is likely to be done in the laboratory in Valinhos, where there is already an IAG teaching observatory. In about six months, according to Galante, a simulation chamber should be operational that is more sophisticated than that of the LNLS, and capable of subjecting bacteria to a complete set of controlled parameters, such as temperature, radiation and pressure, in addition to simulating a protective atmosphere.
For Claudia and Paulino Lima, the results support the idea of panspermia, an hypothesis that believes that life may be spread right across the Universe. When the Earth emerged 4.5 billion years ago, the Universe was already 10 billion years old. When this planet was still very young on a geological timescale, 3.8 billion years ago, there was already microscopic life here, probably capable of using sunlight by means of chlorophyll and producing oxygen. This is what is revealed by the composition of rocks found in Greenland by researchers from England, the United States and Australia. Claudia sees these signs as evidence that life may have come from somewhere else. But there is little agreement on this view. Galante is cautious. “There are micro-organisms that are capable of withstanding the conditions of a journey through space, but it’s not known if that really happens.”
There is far more agreement on the view that, even if life itself did not come from outer space, pre-biotic molecules, the most elementary building blocks of genetic material, were already here soon after the Earth formed and they may have come from space. Many experts believe that the terrestrial conditions at the time were ideal for permitting chemical reactions and the emergence of life, perhaps from pre-biotic molecules that hitched a ride on a comet’s tail. Nuclear physicist, Enio da Silveira, from the Pontifical Catholic University of Rio de Janeiro (PUC-Rio), is trying to understand the formation of these chemical substances. “We’re studying inorganic molecules that are in comets, that are everywhere, and that were already in the solar system some 4 billion years ago,” he says. These are molecules such as water, methane, carbon monoxide, carbon dioxide and ammonia, in a solid state, which his group irradiates with ions emitted by a radioactive source, californium, which simulate a cosmic ray without the protection of an atmosphere.
This type of radiation is sufficient to produce a wide variety of molecules, which Silveira identifies and quantifies with the help of specialized techniques, such as mass and infrared spectrometry, which are capable of measuring the vibration that is characteristic of molecules. The longer he keeps up the bombardment the more molecules he sees emerging. The most important elements are carbon, nitrogen, oxygen and hydrogen, which together account for around 90 percent of the composition of organic molecules. By analyzing how these elements respond to radiation, he has been building up a database that should serve as a reference for astronomers to evaluate the age of a system, like a planet or an asteroid, for example, according to recent articles in the journals, Surface Science and Astronomy and Astrophysics.
The researcher from PUC noticed that carbon monoxide is important for the formation of organic molecules. “It’s a more generous source of carbon atoms, which manages to build the skeletons of large organic molecules.” Since comets have plenty of carbon monoxide and water – on which all biochemical reactions depend – the results indicate that it is likely that elementary life emerges under conditions that are different from those on the only planet where life has already been found.
What happens when these prebiotic molecules fall or are produced on Earth? With this question in mind, chemist Damas Zaia, from the State University of Londrina, in Parana, mixes molecules that may have existed following the formation of this planet, like the amino acid cysteine, with clay. This year in the journal, Amino Acids, he revealed that clay is a vehicle for forming biological molecules. “Cysteine reacts with iron compounds and so has a strong affinity for clay,” he says. Both in an acidic environment with pH of 3, as well as in an alkaline one, with pH of 8, which are characteristic of underwater volcanoes, he showed, with the help of analyses like infrared spectrometry, Mössbauer, EPR and X-rays, that cysteine molecules react with the substrate and give rise to cystine, a more complex molecule.
Finding living organisms in space is an arduous task and not only because they are microscopic. A spacecraft in full flight is going so fast that a collecting receptacle would cause friction strong enough to carbonize the sample, thereby killing and pulverizing any interplanetary bacteria. NASA has sent robotic probes to investigate, for example, the surface of Mars, but it has yet to find life. To make the search possible, Earth studies give researchers information about the expected signs of life beyond Earth, the so-called biosignatures, in addition to indicating where to look for them.
The planet announced at the end of September by American astronomers is one candidate. “It’s the first time that a rocky planet like Earth has been found in the middle of the habitable zone of its star,” comments Galante. But it is still not known if it has an atmosphere, water and the stability needed to generate life. And it has no day and night – one side is always dark and the other always light. For Galante, this might be a problem, especially for the emergence of complex life.
One of the explorers in search of habitable zones is astronomer Gustavo Porto de Mello, from UFRJ. Analyzing data from the best known zone in the solar system, up to 10 parsecs from the Sun, or 33 light-years away, he found 13 stars that might harbor habitable planets, based on criteria that include their composition, age and size and the radiation they receive, as described in 2006 in Astrobiology. Recent international studies have used less precise techniques to search for habitable zones and indicate a wider area. The results, however, coincide with the proposal by the Brazilian with respect to more promising stars. So far no planets have been detected, but the researcher argues that it is necessary to use them as the main target.
The search for habitable planets, which have suffered impacts from comets sufficient to supply water, but that are already stable, also keeps astronomer Jane Greaves, from the University of St. Andrews in Scotland busy. She was in Brazil for the Frontiers of Science symposium, held in upstate São Paulo with the support of FAPESP (see report). “The difficulty in finding planets in habitable zones is to make sure that it is a bio-signal,” she explains. “Methane can come out of volcanoes; oxygen and ozone may come from water molecules evaporating from oceans and broken up by radiation. It needs a lot of theoretical and experimental work, but the prospects for the next twenty years are very exciting.” Jane has identified a promising target 59 light-years away, but believes there should be another about 33 light-years away, according to an article this year in the Monthly Notices of the Royal Astronomical Society.
It is a distant horizon. To sweep these zones in the galaxy, it will be necessary to use interferometric telescopes, also part of a project that should be available in about 10 years time. In space, these instruments will be capable of cancelling out the light emitted by stars and detecting planets. Then, analyses with infrared would allow the wavelengths emitted by these planets to be measured at a distance in a search for signs of liquid water and other indications of life.
The presence of liquid water on the surface is the main paradigm in the search for life; besides enabling the formation of molecules containing carbon, it can be detected from afar. But there are other possibilities. Mars, for example, has no apparent liquid water, but it may have under the surface. In 2015 NASA plans to send a robot capable of drilling down a few meters and reaching the Martian subsurface. Another possibility is Europa, a moon of Jupiter. It is outside the area considered to be habitable, but appears to have water under a layer of ice. “We need to go back to Mars and to Europa,” says Porto de Mello, remembering that NASA has approved a robotic mission to Europa.
The astronomer from UFRJ is optimistic and will not be surprised if life is found on Europa or Mars. “It’ll be microbial life. Many things would have to happen for complex life to emerge,” he states. Anyone expecting little green men or slimy beasts full of teeth and tentacles, or even a higher intelligence like Steven Spielberg’s ET, may be frustrated. Aliens invisible to the naked eye, as imagined by Katherine MacLean 60 years ago, will surely be enough for the specialists to throw a big party.
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Paulino-Lima, I. G. et al. Laboratory simulation of interplanetary ultraviolet radiation (broad spectrum) and its effects on Deinococcus radiodurans. Planetary and Space Science. v. 58, p. 1.180-87. 2010.
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Porto de Mello, G. et al. Astrobiologically interesting stars within 10 parsecs of the Sun. Astrobiology. v. 6, n. 2, p. 308-31. 2006.