Mars Is Pretty Clean. Her Job at NASA Is to Keep It That Way.
By KENNETH CHANG

At the National Aeronautics and Space Administration, Catharine A. Conley has a lofty job title: planetary protection officer.

That conjures to mind shades-wearing Will Smith and Tommy Lee Jones in the “Men in Black” movies. Indeed, on her first day on the job, nine years ago, she was presented with a pair of sunglasses.

But with no extraterrestrial invasions on the horizon, Dr. Conley’s job is not so much protecting Earth from aliens as protecting other planets from Earth.

Mars, in particular.

“If we’re going to look for life on Mars, it would be really kind of lame to bring Earth life and find that instead,” Dr. Conley said.

With the news last week that scientists had identified areas of flowing water on the Martian surface — some possibly reachable by NASA’s Curiosity rover — that concern has taken on new urgency.

Thousands, millions, sometimes many times more, bacteria travel across the solar system on spacecraft. Earth has been invading Mars since November 1971, when the Soviet Mars 2 lander crashed. Certainly life exists on Mars today — the microbes that have hitchhiked from Earth. Even in the harsh environs of Mars — cold, dry, bombarded by ultraviolet light — it takes many years for all of them to be killed off.

The concern is that some of them might not only survive but thrive.

Because of the residual microbes, NASA’s Opportunity and Curiosity rovers are prohibited from visiting what are known as “special regions” — places that Earth bacteria might happily call home. (InSight, NASA’s next Mars lander, to be launched in March, and the next rover, to be launched in 2020, will also not be sterilized. In considering landing sites for the 2020 rover, NASA has crossed off those in special regions.)

The thinking is that some Earth microbes have been jostled to the surface of the inhospitable parts of Mars, but they would remain dormant and not proliferate.

“So far, Mars is still pretty clean,” Dr. Conley said.

Areas treated as special regions include the periodic dark streaks known as recurrent slope lineae — R.S.L.s for short — spotted on the sides of craters, canyons and mountains. Scientists last week said they were generated by the percolating of liquid water, one of the essentials for life.

The caution brings up a Catch-22. NASA at present cannot explore the places with the greatest potential for life — one that could come into play for Curiosity, which is slowly climbing a mountain in Gale Crater.

Gale was selected as Curiosity’s destination in part because it was the “driest and least likely to have special regions,” Dr. Conley said. But some candidate R.S.L.s have been unexpectedly spotted from orbit on the mountain within a couple of miles of Curiosity’s planned path.

James L. Green, the director of NASA’s planetary science division, did not rule out that Curiosity might go to one of them.

If the streaks are confirmed as R.S.L.s, Dr. Green said, NASA might then evaluate how many Earth microbes are likely to survive on the outside of Curiosity. “That would tell us, if we can get approval from planetary protection, how close we could go,” Dr. Green said.

Dr. Conley would be the one to make that call. She said that at launch, there were probably 20,000 to 40,000 heat-resistant bacterial spores on Curiosity, and perhaps 100 or 1,000 times more microbes not counted. Many of them would have since perished in the vacuum of space. Intense ultraviolet radiation on the Martian surface would have killed many more — but not all, and some drop in the soil as Curiosity trundles by and performs its science work.

“We are still having ongoing discussions,” Dr. Conley said. “It depends on what the results of the calculations are.”

This is not just a fastidious whim of NASA, but an international agreement. The Outer Space Treaty of 1967 dictates that nations should take care when exploring other planets “to avoid their harmful contamination.”

The Committee on Space Research, part of the International Council of Science, develops planetary protection policies that Dr. Conley is responsible for carrying out. For most missions, like the Cassini orbiter at Saturn, the requirements are fairly simple — do not crash into a body where life might exist, and when done, dispose of the spacecraft. (Cassini will be sent on a death dive into Saturn, where heat and pressure will obliterate it and any remaining microbes.)

Similar care will be taken studying Europa, a moon of Jupiter, and Enceladus, a moon of Saturn, known to have oceans beneath the surface. But it will be many years before a lander sets down there. For now, the main concern is Mars.

“We’re treading new ground,” John M. Grunsfeld, NASA’s associate administrator for science, said of the discussions of Curiosity. “The issue of planetary protection has gone very much from one where we’re just trying to be careful to one that has very real, near-term consideration.”

With the two Viking landers in 1976 — NASA’s first and so far only attempts at detecting life on another planet — the agency took extraordinary precautions sterilizing the spacecraft, first cleaning it to fewer than 300 heat-resistant bacterial spores per square meter. Then it was packed up and baked for several days, reducing the number of spores by a factor of 10,000.

But most of the data from Viking pointed to Mars as a lifeless place. Since then, NASA has still cleaned its Mars spacecraft to the same standards — “better than a surgical suite,” Dr. Conley said — but skipped the baking step. Sterilization would add perhaps $100 million to the price of a mission.

Thus NASA has avoided the special regions, which include anywhere with water ice within a meter of the surface. (An exception was the Phoenix Mars lander, which dug into ice in the polar region. The arm — but only the arm — was sterilized to Viking standards.)

The salts known as perchlorates that lower the freezing temperature of water at the R.S.L.s, keeping it liquid, can be consumed by some Earth microbes. “The environment on Mars potentially is basically one giant dinner plate for Earth organisms,” Dr. Conley said.

The first Earth settlers could be one of the lowliest of plants. “I worry about lichen,” Dr. Conley said. “I worry about the stuff that grows on your roof. They basically eat rock and they breathe sunlight. And there’s rocks and sunlight on Mars.”

Dr. Conley inadvertently entered the planetary protection field because of the loss of the space shuttle Columbia, which was carrying an experiment of hers involving nematode worms when it disintegrated during re-entry in 2003. The experiment was recovered amid the wreckage, and the worms were still alive. “Multicellular animals, at least small ones, can survive uncontrolled atmospheric entry, so long as they don’t get too hot,” Dr. Conley said.

The insides of meteorites similarly stay cool when they streak through the atmosphere, and the findings support the idea that life could have traveled back and forth between Earth and Mars in rocks knocked to space by meteor impacts.

For some NASA critics, the concerns of planetary protection are just an expensive ball and chain that slow study of the solar system. Why the extreme caution now if one day in a few decades, astronauts, carrying a slew of Earth microbes, arrive to colonize Mars?

With a changing picture of present-day Mars that is not quite as desolate as once thought, “we actually do need to be careful,” Dr. Grunsfeld said, adding, “We do need to watch what we’re doing, because there could be life on Mars.”

「星際戰警」真實版 NASA派她保護火星

凱瑟琳．康利在美國太空總署（NASA）工作，有個很特別的職稱「行星保護官」，讓人想起電影「星際戰警」中，穿黑色西裝、戴墨鏡、保護地球不被外星人破壞的探員威爾史密斯與湯米李瓊斯。巧的是，九年前她到任的第一天，就有人送她一副墨鏡。

地球現在沒外星人侵襲，所以她的職責與其說是保護地球，不如說是保護其他行星不被地球人傷害，尤其是火星。康利說：「如果我們要在火星上尋找生命跡象，就不能先把地球上的生命帶過去，然後才發現火星生命是我們製造的。」

紐約時報報導，從1971年蘇聯「火星二號」登陸器在火星墜毀開始，地球上的微生物就一次次搭著太空船入侵火星，雖然火星地表寒冷、乾燥又有強烈紫外線照射，但經過多年後，仍有微生物倖存，不過行星保護專家認為，這些微生物會保持潛伏狀態，不會擴散。康利說：「到目前為止，火星還很乾淨。」

為免地球微生物汙染火星，NASA禁止火星探測器「好奇號」探索可能有水的「特區」，不過，火星的軌道衛星拍到，距離好奇號預定路徑不遠處疑似有會定期變黑的條紋區，科學家上周判斷這種區域有液態水。NASA行星科學主任葛林說，如果能確認那就是這種區域，NASA就要評估，好奇號外面可能有多少地球微生物，「這樣就能知道，如果行星保護官同意的話，好奇號能離這種區域多近」。

康利就是做這種決定的人之一。她說，好奇號發射時，大概有兩萬到四萬個抗熱細菌孢子，此外也許還有這個數量一百到一千倍的微生物沒算到，其中許多會在真空的外太空中死亡，火星上的紫外線也會殺死很多，但仍有一些會在好奇號滾動時掉入火星土壤中。

原文參照：
http://www.nytimes.com/2015/10/06/science/mars-catharine-conley-nasa-planetary-protection-officer.html

2015-10-07．聯合報．A13．國際．編譯李京倫