Contaminare extraterestră

 One of the Viking landers being prepared for dry heat sterilization.
One of the Viking landers being prepared for dry heat sterilization.

Contaminarea extraterestră (engleză back-contamination) este o introducere de organisme ipotetice microbiene extraterestre în biosfera Pământului, de exemplu cu ocazia reîntoarcerii misiunilor spațiale. Se presupune că un astfel de contact ar fi perturbator sau cel puțin ar putea avea consecințe puțin controlabile de către ființele umane. Amenințarea contaminării extraterestre cu organisme microbiene originare de pe Lună (ipotetice) a fost principalul motiv pentru adoptarea procedurilor de carantină în cadrul programului Apollo, până la finalizarea lui Apollo 14. Astronauții și mostrele lunare aduse pe Pământ au trebuit să stea în carantină la întoarcerea pe Terra în clădirea numită Lunar Receiving Laboratory (LRL).
Această contaminare la înapoierea pe Pământ poate fi ușor înțeleasă greșit. Probabilitatea ca o ființă umană sau orice alt animal să dobândească literalmente un virus extraterestru este efectiv zero, pentru că virusurile au gazde specifice. Totuși, microbii extratereștri, dacă ar exista, ar putea acționa patogenic asupra noastră: sporii ar putea utiliza un organism ca gazdă, în timp ce ingestia de bacterii în orice formă ar putea produce substanțe chimice toxice. Când ființele umane ingeră alimente contaminate, de exemplu, aceste alimente nu aduc în organism vreun virus capabil de a produce gripa, dar cu toate astea experiența ar putea fi letală – din cauza compușilor toxici rezultanți.
În plus, există posibilitatea ca un microb extraterestru ipotetic să metabolizeze agresiv unele resurse ale Pământului sau să modifice condițiile atmosferice sau ale circuitului apei.[necesită citare]


Back contamination is the introduction of extraterrestrial organisms and other forms of contamination into Earth’s biosphere, it also covers infection of humans and human habitats in space and on other celestial bodies by extraterrestrial organisms, if such exist.
The main focus is on microbial life and on potentially invasive species. Non biological forms of contamination have also been considered including e.g. contamination of sensitive deposits (such as lunar polar ice deposits) of scientific interest by rocket exhausts. In the case of back contamination, multicellular life is thought unlikely but not been ruled out, and in case of forward contamination, then again, forward contamination by multicellular life (e.g. lichens) becomes a consideration if you have human missions though unlikely for robotic missions.
Current space missions are governed by the Outer Space Treaty and the COSPAR guidelines for planetary protection. Forward contamination is prevented primarily by sterilizing the spacecraft. In the case of backward contamination, however, the aim of the mission is to return biological material to Earth if such exists, and sterilization of the samples would make them of much less interest. So back contamination would be prevented mainly by containment, and breaking the chain of contact between the planet and Earth. It would also require quarantine procedures for the materials and for anyone who comes into contact with them.

Since the Moon is now generally considered to be free from life, the most likely source of contamination is from Mars either during a Mars sample return or as a result of colonization of Mars.
There are no immediate plans for a Mars sample return, but it remains a high priority for NASA and the ESA, because of its great potential biological interest. The European Space Foundation report cites many advantages of a Mars sample return. In particular, it would permit extensive analysis with any of the equipment available on Earth, without the size and weight constraints for instruments sent to Mars on rovers. These analyses could also be carried out without the communication delays for experiments carried out on Martian rovers. It would also make it possible to repeat experiments in multiple laboratories with different instruments to confirm key results.[38]
Carl Sagan was first to raise and publicise back contamination issues that might follow from a Mars sample return. In Cosmic Connection (1973) he writes:

Precisely because Mars is an environment of great potential biological interest, it is possible that on Mars there are pathogens, organisms which, if transported to the terrestrial environment, might do enormous biological damage.[39]

He makes the analogy of the plot twist in The War of the Worlds, by H.G. Wells, where Earth pathogens made the Martian invaders of Earth sick and then they die. Perhaps, he suggests, the same could happen to us on Earth if we return samples containing micro-organisms from Mars. On the one hand, he points out, this possibility seems unlikely because of the lack of contact between the two planets and because pathogens adapt to their host. But on the other hand, the lack of contact also means that we would have never evolved any defences against any pathogens.

Also, pathogens when they adapt to a host normally evolve to be less rather than more lethal. Also, some pathogens such as Legionnaire’s disease attack humans using essentially the same mechanism they use to infect other microbes (in this case amoeba) so a disease of microbes on Mars could become a pathogen of animals on Earth.
Ledeberg wrote [40]

“Whether a microorganism from Mars exists and could attack us is more conjectural. If so, it might be a zoonosis to beat all others. On the one hand, how could microbes from Mars be pathogenic for hosts on Earth when so many subtle adaptations are needed for any new organisms to come into a host and cause disease? On the other hand, microorganisms make little besides proteins and carbohydrates, and the human or other mammalian immune systems typically respond to peptides or carbohydrates produced by invading pathogens. Thus, although the hypothetical parasite from Mars is not adapted to live in a host from Earth, our immune systems are not equipped to cope with totally alien parasites: a conceptual impasse”

This possibility has been confirmed in all the later studies, as the worst-case scenario. Other possibilities have also been raised such as micro-organisms that have harmful effects on crops, or that disrupt natural cycles, and pathogens that infect other micro-organisms.[41][42][43][44][45]
As a result, the possibility of new human pathogens, or environmental disruption due to back contamination is considered to be of extremely low probability but can’t yet be ruled out completely.
Later in Cosmos (1980) Carl Sagan wrote:

Perhaps Martian samples can be safely returned to Earth. But I would want to be very sure before considering a returned-sample mission.[46]

The PPO and NASA and ESA view is similar to this. The findings were that with present day technology, Martian samples can be safely returned to Earth provided the right precautions are taken.

The risks of environmental disruption resulting from the inadvertent contamination of Earth with putative martian microbes are still considered to be low. But since the risk cannot be demonstrated to be zero, due care and caution must be exercised in handling any martian materials returned to Earth.


Pathogenic Effects
Understanding of pathogenesis and the nature of biological epidemics has expanded significantly in recent years.2,3 However, the potential for large-scale pathogenic effects arising from the release of small quantities of pristine martian samples is still regarded as being very low. Significant changes have been made in requirements for containing both known pathogens and novel, or unknown, biological materials, and there have been major improvements in containment design, laboratory practices, and operational oversight.4,5,6 Numerous reports for planning a Mars sample return mission have acknowledged that biocontainment requirements and planetary protection controls will be integrated as essential elements for handling and testing returned samples.7,8,9,10
As reviewed in Chapter 3, extreme environments on Earth have not yet yielded any examples of life forms that are pathogenic in humans. However, it is worth noting in this context that interesting evolutionary connections between alpha proteobacteria and human pathogens have recently been demonstrated for natural hydrothermal environments on Earth,11 suggesting that evolutionary distances between nonpathogenic and pathogenic organisms may be quite small in some instances. It follows that, since the potential risks of pathogenesis cannot be reduced to zero,12 a conservative approach to planetary protection will be essential, with rigorous requirements for sample containment and testing protocols.

Ecological Effects
New discoveries in environmental microbiology continue to expand understanding of the taxonomic and metabolic diversity of the microbial world, yet much remains unknown.13 It is worth noting, however, that extreme environments on Earth have not yet yielded any examples of life forms that are disruptive to ecosystem functions. The risks of environmental disruption resulting from the inadvertent contamination of Earth with putative martian microbes are still considered to be low. But since the risk cannot be demonstrated to be zero, due care and caution must be exercised in handling any martian materials returned to Earth. The demand for a conservative approach to both containment and test protocols remains appropriate.

Toxicity and Other Potential Effects
Although negative effects from nonreplicating biological materials (e.g., toxins and other metabolic by-products) are possible, they are unlikely to be responsible for large-scale pathogenic effects.14 Nonetheless, they are important as potential biohazards that must be considered when designing protection for the workers who will handle returned martian materials. Operationally, the committee anticipates that existing regulatory frameworks (e.g., that of the Occupational Safety and Health Administration and the Centers for Disease Control and Prevention), coupled with rigorous laboratory biosafety controls, will be incorporated into future discussions of handling and testing protocols and other operations used in the analysis of returned martian materials.

Dissenting views on back contamination issues
The International Committee Against Mars Sample Return[61] maintains that it is not possible to return samples to Earth safely at this stage. Their main reason for saying this is the novelty of the containment procedures required combined with the possibility of human error and mission design mistakes, either during the return flight or after return of the samples. They urge more in situ studies on Mars first, and preliminary biohazard testing in space before the samples are returned to Earth.
At the other extreme, Robert Zubrin (Mars surface colonization advocate and director of the Mars Society) maintains that the risk of back contamination has no scientific validity. He supports this using an argument based on the possibility of transfer of life from Earth to Mars on meteorites.[62][63]

Rosetta Finds Out Much About a Comet, Even With a Wayward Lander

A November image of Comet 67P/Churyumov-Gerasimenko shows faint jets of gas and dust. Credit European Space Agency
A November image of Comet 67P/Churyumov-Gerasimenko shows faint jets of gas and dust. Credit European Space Agency
Rosetta a descoperit mai multe despre o cometă, chiar și cu Lander-ul Wayward.

A November image of Comet 67P/Churyumov-Gerasimenko shows faint jets of gas and dust. Credit European Space Agency[/caption]Photographs and data from the European Space Agency’s Rosetta spacecraft have provided an unprecedented close-up examination of a comet, but there is one thing that has not shown up yet: the small lander that bounded to the surface in November.

Scientists working on the mission described their initial observations of Comet 67P/Churyumov-Gerasimenko in seven articles published Thursday in the journal Science. “This sets the baseline for the rest of the mission,” said Matt Taylor, the project scientist.

Rosetta arrived at the comet in August after a trip of 10 years and four billion miles. For the first time, scientists are having an extended look at a comet as the spacecraft accompanies it for at least a year as it swings around the sun. As the comet heats up, it will spew greater amounts of gas and dust.

In November, a washing-machine-size lander named Philae made it to the surface, but systems designed to anchor it failed, and the lander bounced, ending far from the intended site in a position that greatly reduced the amount of sunlight hitting its solar panels. Instruments on the lander operated for two days until the batteries drained.

A large fracture running across the comet. Credit Eureopean Space Agency
A large fracture running across the comet. Credit European Space Agency

In mid-December, the orbiter’s high-resolution camera took pictures of the spot where the scientists think the lander ended up, but the scientists were not able to find it — a few pixels in a four-million-pixel image.

Holger Sierks, the principal investigator for Rosetta’s main camera, said that Philae, which photographed its surroundings and performed various measurements after landing, was still expected to awake in the spring when increasing sunlight recharged the batteries. Even if Philae does not wake up, Rosetta should be able to spot it after the comet has made its closest approach to the sun, in August.

The high-resolution camera has taken photographs with a resolution as fine as two and a half feet per pixel. The comet, just two and a half miles wide with a two-lobe shape that resembles a rubber duck toy, has a remarkably wide variety of terrain. That includes smooth dust-covered regions, fields of boulders, steep cliffs and large depressions that may have been blown out by underground melting of carbon dioxide. The variety is surprising because many think the comet is, by and large, made of the same material throughout. Scientists are not sure if the shape comes from two smaller comets that bumped and stuck together or one large comet that eroded in an unusual manner.

On the surface of Comet 67P, there are even what look like ripples of sand dunes like those seen on Earth and Mars. That appears befuddling, as a comet has no atmosphere — and so no wind — and only a wisp of gravity.

“You have to ask yourself, is that possible?” said Nicolas Thomas, a professor of experimental physics at the University of Bern in Switzerland and lead author of one of the papers. Dr. Thomas said that back-of-the-envelope calculations indicated that it might be plausible, with the jets of gas acting as wind and the particles held together through intermolecular attraction known as the van der Waals force instead of gravity. “You can convince yourself you can make them move,” Dr. Thomas said. “It’s plausible, at least at the moment.”

A large fracture running across the comet. Credit Eureopean Space Agency
A large fracture running across the comet. Credit European Space Agency

The scientists split the surface into 19 regions based on terrain, naming them after Egyptian gods. Rosetta is named after an inscribed rock, found in Egypt, that proved crucial in deciphering ancient hieroglyphics.

In another region, along the comet’s “neck,” is a cliff about 3,000 feet high with fractures hundreds of feet long. The scientists cannot agree on what they are seeing, whether the lines reflect layering in the material making up the comet or cracks caused by the heating and cooling of the material as it passes in and out of sunshine.

In the smooth regions, there are circular structures. “Which look very, very bizarre,” Dr. Thomas said. “To be frank, we don’t know how those things were created. We have no clue.”

There is also a long crack, about a yard wide and several hundred yards long, that runs around the neck. Dr. Thomas said it was unclear whether the comet was about to snap in two.

The jets of gas currently emanate from the neck area, a region named Hapi. That, too, seems counterintuitive because the neck is often in shade and cooler. But Dr. Sierks said the area was still warm enough and gravity was weaker there, allowing particles to escape more easily.

The scientists previously described some of the most significant findings reported in the Science papers — that the water on the comet does not resemble that found on Earth, probably ruling out comets as the source of the Earth’s oceans, and that a diverse stew of molecules streaming off the surface includes those found in the odors of rotten eggs and urine.

Notă: A version of this article appears in print on January 23, 2015, on page A6 of the New York edition with the headline: Close-Up of Comet Fails to Pinpoint Stray Lander. Order Reprints| Today’s Paper|Subscribe

Ciuriumov-Gherasimenko, oficial denumită 67P/Ciuriumov-Gherasimenko, este o cometă cu o perioadă orbitală curentă de 6,45 ani și o perioadă de rotație de aprox. 12,7 ore[2]. Cometa va ajunge la periheliu (cea mai scurtă distanță de Soare) la 13 august 2015. Cometa este numită după descoperitorii ei, Klim Ciuriumov și Svetlana Gherasimenko, primii care au observat-o pe plăci fotografice în 1969.

Această cometă a fost descoperită de astronomul Klim Ivanovici Ciuriumov în timp ce examina o placă fotografică a cometei 32P/Comas Solà / 32P/Comas Solá, luată la 11 septembrie 1969 de astronoma Svetlana Ivanovna Gherasimenko la Institutul de Astrofizică de la Alma-Ata, acum Almatî, fostă capitală a Kazahstanului.
El a găsit imaginea unui obiect pe marginea plăcii fotografice și a presupus că era vorba de cometa 32P/Comas Solà.
La Kiev, plăcile au fost minuțios inspectate și, la 22 octombrie, s-a descoperit că obiectul nu putea fi cometa Comas Solà, întrucât poziția sa diferea cu mai mult de 1,8° de poziția așteptată.
O examinare mai atentă a scos în evidență o slabă imagine a cometei Comas Solà în poziția corectă, ceea ce a dovedit că obiectul identificat de Ciuriumov era o cometă care nu fusese încă descoperită.

Orbita cometei 67P/Ciuriumov-Gherasimenko are o istorie destul de interesantă.
Când cometa se apropie de unul din giganții gazoși, Jupiter sau Saturn, orbita sa este deseori modificată.
S-a putut calcula, pentru această cometă, că, înainte de 1840, ar fi fost aproape imposibil să fie observată, distanța sa la periheliu fiind de circa 4 ua. Din cauza gravitației exercitate de Jupiter, orbita cometei s-a modificat, iar distanța la periheliu s-a redus la 3 ua.
Mai târziu, în 1959, o altă apropiere de Jupiter a modificat, din nou, orbita cometei, distanța la periheliu ajungând la valoarea actuală, 1,28 ua.

Misiunea Rosetta
Ciuriumov-Gerasimenko este destinația misiunii Rosetta a Agenției Spațiale Europene, lansată la 2 martie 2004. Rosetta a intrat pe orbită în jurul cometei pe 6 august 2014[3], după care o va studia și va identifica un loc de coborâre și de așezare pe solul nucleului cometei potrivit pentru sonda (engleză lander) Philae, programate pentru data de 10 noiembrie 2014.
Potrivit Agenției Spațiale Europene, s-a hotărât ca așezarea sondei Philae pe solul cometei să aibă loc miercuri, 12 noiembrie 2014, în jurul orelor 17:35 (ora României), într-o regiune cu diametrul de circa 1 kilometru.[4]
La 12 noiembrie 2014, minilaboratorul „Philae” s-a desprins de pe „Rosetta” și s-a așezat pe cometa 67P/Ciuriumov-Gherasimenko, exact în locul stabilit.[5] La asolizare au apărut probleme. Unele din experimentele planificate nu vor mai putea avea loc.[6]

Caracteristici fizice
Clișeele luate de Telescopul Spațial Hubble în martie 2003[7] au permis să se estimeze diametrul obiectului la circa 4 kilometri. În iulie 2014, noi imagini luate de Rosetta au scos în evidență faptul că nucleul lui „Ciuri” este un binar de contact, cu o talie globală de 4 km pe 3,5 km. [8]
Cometa se rotește în jurul ei însăși în 12,4 ore.[9]
Temperatura solului nucleului cometei este de -90°C.