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Dear readers,

Let's say we find life on Mars. Let's say we find life on Venus. Let's say we find life anywhere else in the solar system. It's epochal, right? It's a game-changer, right? We'd at last know that life can arise anywhere, that every one of the hundreds of billions of planets circling the hundreds of billions of stars in our galaxy—to say nothing of the hundreds of billions of other galaxies out there—could be home to biology. Right?

Well, not necessarily. The great hunt for extraterrestrial life has always centered on the planets in our own solar system, simply because those are the only ones we can physically access. But finding life on any of them may still not prove life arose on any of them. The fact is, life in our solar system may have arisen on just one world—and not necessarily Earth—and then moved around in microbial form, stowing away on asteroids and meteors.

The principle is known as "panspermia," and as Space.com reports this week, a new study submitted to Astrophysical Journal Letters makes the case more powerfully than ever, particularly in regards to Earthly microbes that may have found their way to Venus.

Venus was much in the news last week, when researchers reported they had found signs of a chemical indicator of life in the planet's atmosphere. That caused no end of excitement, but as Harvard University astronomers Amir Siraj and Abraham Loeb—the authors of the new paper—argue, we may be getting ahead of ourselves.

In the most common panspermia scenario, an asteroid collides with a life-harboring world, blasting debris back into space carrying microbes picked up during impact. Many forms of microscopic organisms could survive tens of thousands of years in a sort of suspended animation as they wander through space, waiting for chance and gravity to pull them toward another world, where they could crash land and thrive.

But there's a flaw in that model: the very collisions that pick up the microbes could also generate enough heat to destroy them. That's not to say that some organisms couldn't survive, but they would definitely have a hurdle to overcome. Siraj and Loeb propose a different scenario: what if the hypothetical asteroid doesn't collide with a living world, but simply grazes its atmosphere, collecting airborne microbes before continuing on into space?

Siraj and Loeb estimate that, over the past 3.7 billion years, at least 600,000 space rocks may have grazed our atmosphere, spiraled inward through the solar system, and got snatched up by Venus's gravity. Microbial stowaways would not have much likelihood of surviving if they made it to the inhospitably hot, high-pressure Venusian surface. But if the rock broke apart in the upper atmosphere where temperatures and pressure are far lower, the microbes might have found a comfortable home. Significantly, it is in Venus' atmosphere, not on its surface, that the authors of last week's study found their potential sign of life.

Such biological transfer need not be one-way. Rocks that grazed Venus's atmosphere have likely found their way to us too, and the same is true of a possible exchange of microbial emissaries between Earth and Mars. The implication: Martians, Earthlings, Venusians and any other life forms anywhere else in the cosmos might all be descendants of a single source from a single world. (None of that includes the idea of lithopanspermia, the theory that life in our solar system arrived aboard debris from another star system.)

"This potentially viable mechanism for transferring life between the two planets implies that if Venusian life exists, its origin may be fundamentally indistinguishable from that of terrestrial life, and a second genesis may be impossible to prove," the study authors wrote.

None of this means life couldn't arise independently in the different laboratories of different worlds all across the universe. What it does mean that our tiny, close-to-home sample group of eight planets, plus dwarf planets and a swirl of moons, is not enough to settle the question. Finding life on Venus or Mars or elsewhere in the solar system will indeed be a hinge-point in the history of science. But while it will answer some questions, it will raise still more.

—Jeffrey Kluger


IMAGE OF THE WEEK
NASA/JPL-Caltech/SwRI/MSSS; Image processing by: Gerald Eichstädt

Cyclones have never looked so beautiful. This cluster of storms is raging in Jupiter's north pole, and was captured in a false color rendering by NASA's Juno spacecraft. Each cyclone measures from 4,000 to 4,600 kilometers (2,500 to 2,900 mi.) across.


WHAT WE’RE READING

And speaking of space rocks...

...one just visited us. On Sept. 24, at 4:12 AM P.T., an asteroid the size of a school bus buzzed over the southeastern Pacific Ocean, according to NASA. The rock was small enough that even if it collided with the atmosphere it would have burned up long before reaching the ground. Still, it missed us by just 22,000 kilometers (13,000 miles), well below the 36,000-kilometer altitude at which geostationary satellites orbit. When an asteroid is looking up at a satellite, things have gotten a lot closer than we'd like them to be.

The big fear, of course, is of big rocks—140 meters (460 feet) across or more—which could cause real damage if they collide with the atmosphere. The bigger the asteroid, the greater the destruction—as the dinosaurs could tell you if they hadn't been, you know, wiped out. In 2005, Congress charged NASA with the task of detecting 90% of all asteroids in the 140-meter and larger category in the expectation that we will soon develop the technology to destroy or deflect inbound threats.

Cruise-ing to the space station

Never let it be said that Tom Cruise leaves the heavy lifting to his stuntmen. The 58-year-old star is famous for taking on even the most dangerous stunts himself, including climbing skyscraper walls and hanging off the side of an airplane. Now, Cruise, with the help of Elon Musk's Crew Dragon spacecraft, will be taking on his biggest stunt yet: flying to the International Space Station, in Oct. 2021, to shoot a film that doesn't yet have a title or storyline—but clearly does have some nifty location-shooting booked.

"NASA is excited to work with @TomCruise on a film aboard the @Space_Station!," tweeted NASA Administrator Jim Bridenstine about the trip. "We need popular media to inspire a new generation of engineers and scientists to make @NASA’s ambitious plans a reality."

But do we really? It might be skunk-at-the-picnic stuff to point out that whole generations of scientists and engineers have been inspired by NASA's many accomplishments without Hollywood needing to lend a hand. It might be wet-blanket naysaying to argue that the brutally difficult, dangerous business of flying in space is not elevated but rather diminished by turning it into a red-carpet spectacle when it is already spectacular enough. And it may really kill the buzz to point out that space has claimed the lives of too many people so far to make it remotely safe for joyriders and filmmakers to hop aboard for anything that isn't about doing the hard piloting and serious science that space travel is supposed to be about. Space is not a game. It's not a Hollywood junket. Hat tip to Tom Cruise for his courage. But, sorry, thumbs-down for his manifest folly.

You're sure about that moon mission?

You get a lot of things if you walk on the moon: fame, thrills, the chance to do good science and to go where only 12 human beings have trod before. But there's one other thing you'd get too: a big, crackling, potentially deadly dose of cosmic radiation. As a new study published in Science reports, astronauts on the lunar surface are exposed to 2.6 times the amount of radiation than those on the ISS. While that exposure might not be immediately dangerous, it raises the risk of long-term health consequences, especially cancer.

The new findings were the result of studies conducted by China's Chang'e 4 spacecraft, which is currently at work on the far side of the moon. Similar radiation studies were, surprisingly, not conducted by NASA's Apollo astronauts—at least in part because the imperative of getting to the moon in the Cold War atmosphere of the 1960s made the risks seem worth taking. What's more, none of the Apollo crews were on the surface for more than three days. Plans for future expeditions, however, involve longer-term stays.

Space junk problem gets worse

Not many people would immediately know what a "high concern potential conjunction is," except that the "high concern" part sounds like trouble. And it is. The little scrap of jargon is NASA-speak for what you get when a piece of space debris threatens to collide with the ISS. The station has faced such danger three times this year—most recently this week, when the crew sheltered near the Soyuz spacecraft for a quick getaway if needed while an uncrewed cargo ship attached to the station fired its engine to move the entire football-field sized structure out of the way.

The space junk passed a mile or so from the station and the all-clear was sounded—but only for now. Ever since humans started firing hardware into orbit in 1957, we have been bringing orbiting junk with us, creating a great river of debris made up of spent rocket stages, dead satellites, loose bolts and microscopic particles like paint chips and metal flecks. All of it—even the microscopic pieces, which are, after all, moving at 28,000 km/h (17,500 mph)—can damage functioning satellites and crewed spacecraft.

In the short term, NASA's Bridenstine wants Congress to fund better space junk tracking in order to help predict impacts. The longer-term answer is to develop methods to launch spacecraft and satellites that simply don't produce as much incidental rubbish.

Testing a space garden

There is nothing not to like about an upcoming flight of Blue Origin's New Shepard rocket. You can't not love the cargo: a microgravity lily pond. You can't not love what the lily pond will be growing: water lentils, which are more colloquially known as duckweed. And you can't not love the purpose of the brief, suborbital mission: testing ways to grow the crunchy, high-protein, antioxidant-rich crop in zero-g for future long-term space travelers.

The launch, originally scheduled for Sept. 24 but postponed to work out a technical glitch in the lily pond payload, will help researchers study how to grow crops hydroponically in zero-g, as a NASA release explains. That's a tricky business, because water hardly stays in one place in the absence of gravity. In order to overcome the problem, the new system uses shallow, closely-stacked growth trays, with water delivered through fine capillaries in the assembly and LED lights built in. When the crop is ready for harvest, a rotary sieve system separates the plants from the water and serves them up to the astronauts.

Since the very beginning of the space age, food technologists have tried to come up with options that are stable and easy to pack, don't shed too many crumbs and have a long shelf life. That doesn't always mean delicious, and it definitely doesn't leave a lot of room for fresh fruits and vegetables. That's why ISS crew members anxiously await fresh deliveries of apples, oranges and other produce that are generally gobbled up fast, leaving the crew to subsist on the pre-packaged stuff until the next shipment. Doing the actual farming in space will make the business of being off the Earth feel at least a little bit more like being on it.


THANKS FOR READING

TIME Space is written by Jeffrey Kluger, Editor at Large at TIME and the author of 10 books, including Apollo 13, Apollo 8 and two novels for young adults. Follow him at @jeffreykluger. It is edited by Alex Fitzpatrick.

We welcome any feedback at space@time.com.

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