鈥淒OES epidemic disease come from space?鈥� In the relatively sober 1970s, this headline must have been even more alarming than it would be in our present era of fake news. Especially atop an article by famous astronomer Fred Hoyle and astrobiologist Chandra Wickramasinghe, arguing that infamous epidemics like the deadly Spanish flu of 1918-19 had been brought to Earth on interplanetary debris. Both authors were proponents of panspermia, the theory that life began elsewhere in the universe and came here aboard comets and meteorites. This belief arguably cost Hoyle a Nobel prize, although perhaps his notorious bluntness, verging on rudeness, may have been a factor too. The article, published in , ended with a plea to keep a 鈥渃ontinual microbiological vigil of the stratosphere鈥� to eliminate the havoc which will ensue from extraterrestrial invasions in the future鈥�.

By 1992, the declining frequency of Nobel prizes awarded to UK scientists was beginning to trouble us. In our 7 November edition, Ben Martin said this showed the nation鈥檚 shrinking status in world science, but conceded that one explanation for the worrying trend might be that 鈥済ifted scientists are being encouraged to apply their skills in industry鈥�.

So is research worthwhile only if it turns a profit? Fourteen years later, at least one sector of British science was doing just that. In our 4 November 2006 edition, we sang the praises of biotechnology: the jobs market was booming and half the country鈥檚 biotech companies had recently taken on extra staff. A map identified areas of the UK where research and development companies and institutions were gathered, with clusters not surprisingly found around Cambridge and Oxford.

The chair of biotechnology鈥檚 UK industry body almost certainly wasn鈥檛 being rude when he told us 鈥渢he UK is bloody good at it鈥�. But that鈥檚 not what they hand out Nobel prizes for.

Bacteria riding on an incoming meteorite may be able to survive the violent shockwave created when it crash-lands on a planet. Their cell walls have been seen to rapidly harden and relax after a sudden shock compression, enabling them to bounce back even after an extreme collision.

鈥淲hen you are exposing life to such extreme conditions, it is a surprise when they survive quite well,鈥� says at University College London

Microbes can withstand extreme environments on Earth, including the crushing pressure of the deep ocean or deep beneath the ground. This suggests that life forms could thrive on distant worlds in similar high-pressure environments.

But few people have studied what happens to microbes under dynamic 鈥渟hock compression鈥�, which is a very short-lived high-pressure environment.

To find out, Hazael and colleagues subjected a hardy, metal-eating microbe called Shewanella oneidensis to varying levels of sudden, extraordinarily high pressures. After each blast in increasingly high-pressure experiments, the team cultured the microbial survivors and found they fared better in a sudden high-pressure environment than in a long-lasting high-pressure condition.

Under pressure

To withstand these conditions, the microbes were adjusting the rigidity of their cell, says Hazael.

鈥淭hey don鈥檛 deform as you would expect, and they behave very rigidly, which protects the inner materials in the cell,鈥� says Hazael. 鈥淭hey adopt this glassy cellular behaviour, which allows them to maintain their integrity.鈥�

Bacteria could have small genetic mutations that would enable them to survive, says Hazael, or they might have been using certain chemicals or fats in a way that safeguarded their delicate interiors.

鈥淚t鈥檚 that very fast timescale that allows them to adopt these glassy responses. We鈥檝e held them at pressure for an hour, and they have a different response. We don鈥檛 get as many survivors,鈥� she says.

The rigid glass-like state is similar to what happens in a non-Newtonian fluid like oobleck, says , an astrobiologist at the University of South Florida in Tampa who studies extremophile bacteria. This mixture of flour and water hardens into a cohesive shape when thrown against a wall, but simply looks like wet flour when at rest.

However, he notes that the experiments were conducted at low temperatures, but the conditions that would cause a sudden shock compression would also cause extreme heating. It鈥檚 unclear how heat would have changed the microbes鈥� survival, he says.

鈥淚t does indicate that survival of bacteria would be possible on a meteorite or a comet,鈥� Herschy says. 鈥淚t actually shows life would be able to survive on a planet even if it was under bombardment.鈥�

Beating the blast

Hazael found that the microbes not only survived short blasts of pressure, but went on to reproduce in colonies. On Earth prior to and during the Late Heavy Bombardment 3.8 billion years ago, when the planet was hammered by meteorites, this type of bacteria could have not only survived but thrived.

This also means that bacteria might survive a spacecraft landing 鈥� or even crashing 鈥� on other planets. That would lend weight to the panspermia theory, in which comets or meteorites could potentially deliver life to otherwise sterile planets. It also means it is something to keep in mind for space agencies and private companies exploring the solar system and beyond.

鈥淓very time we explore a new environment, we find life is already there, so I鈥檓 never surprised when I find out these things,鈥� Herschy says. 鈥淎ny niche that becomes available, life finds a way to adapt to it.鈥�

Read more: 鈥�Follow the salt鈥� may be best strategy to find Martian microbes

More than flinging rocks

Three dice rolls

Primitive plants are the latest forms of Earth life to show they can survive in the harshness of space, and for many months. Cold-loving algae from the Arctic Circle have joined the space-travelling club, alongside bacteria, lichens and even simple animals called tardigrades.

of the algae after their return to Earth from the International Space Station lend some weight to the 鈥减补苍蝉辫别谤尘颈补鈥� theory, that comets and meteorites could potentially deliver life to otherwise sterile planets. The results also provide insights into the potential for human colonies on distant planets to grow crops brought from Earth.

The algae were a species of Sphaerocystis, codenamed CCCryo 101-99, and were returned to Earth in after spending 530 days on a panel outside the ISS. While space-borne, they withstood the vacuum, temperatures ranging from -20 掳C at night to 47.2 掳C during the day, plus perpetual ultraviolet radiation of a strength that would destroy most life on Earth if not filtered out by the atmosphere.

鈥淚鈥檓 sure that plants of many kinds have been on the ISS before, but on the inside, not the outside,鈥� says of the Fraunhofer Institute for Cell Therapy and Immunology in Potsdam, Germany, who organised the algae experiment. 鈥淎s far as I know, this is the first report of plants exposed on the surface of the space station.鈥�

Green and orange

It was Leya who discovered CCCryo 101-99 on Norway鈥檚 remote Svalbard peninsula. When dormant, these algae develop thick walls and become orange cysts rich in protective carotenoids, the substances that give carrots their colour.

But when seasonal rains arrive, they rapidly resume making chlorophyll and turn green again. 鈥淚f you give them water, the cysts germinate and revive,鈥� says Leya.

Leya chose CCCryo 101-99 for the space ordeal based on its ability to withstand extreme cold and drying out. To help the algae through, he dried them out beforehand and coaxed them into the dormant, cyst-like state where they simply ticked over, without reproducing, feeding or multiplying.

All samples were open to space but overlaid with a transparent filter to reduce the radiation exposure (pictured, top). All but one sample survived.

Preliminary results the institute released last week showed that within days of their return, all the algae bounced back to normal. 鈥淲ithin just two weeks they become green again,鈥� says Leya.

Team members at the Technical University in Berlin will now explore the extent of damage to the algal DNA, as this could give insights into the capacity of plants to survive and multiply away from Earth.

Leya stresses that if future missions to colonise other planets aim to grow crops, the seeds would need to be carefully protected in transit inside spaceships, unlike the algae just back from the ISS. Likewise, crops grown at the destination would need to be carefully shielded from environmental harms.

鈥淭hese algae had been desiccated before they went into space, and during their time on the ISS they were kept dormant, with no growth, no development and almost no metabolism,鈥� says Ren茅 Demets of the European Space Agency. 鈥淏ut the experiment shows that some terrestrial organisms are robust enough to cope with months of exposure to open space conditions without a space suit.鈥�

Leya also sent up photosynthesising microbes called cyanobacteria, specifically a species discovered in Antarctica, and found that it survived.

The work formed part of a bigger experiment called Biomex, led by Jean-Pierre Paul de Vera of the German Aerospace Centre in Berlin. It included mosses from the Alps, black microfungi from the Antarctic, desert lichens, and various bacteria.

Aside from a handful of astronauts, the only living beings to have seen an inhabited planet looming large in the sky come from science fiction.

But in other solar systems, a pair of planets could share a habitable zone 鈥� a region around a star with the right temperatures for liquid water. That proximity might help life to evolve, according to research at the meeting in Hawaii this week.

In our solar system, planets are spaced quite far apart, with Mars orbiting 50 per cent further from the sun than Earth does and Venus 30 per cent closer. But some exoplanet systems found by NASA鈥檚 Kepler satellite have planets with tightly packed orbits. In the , for example, an outer planet circles its star just 10 per cent further out than its only known inner neighbour does.

Those planets inspired of the University of Nevada, Las Vegas, working with of Harvard University, to simulate what would happen to planetary systems in which two worlds shared the habitable zone.

First, they looked at planets鈥� tilt, which on Earth determines the seasons. 鈥淚t would be much more difficult to grow corn in Iowa if Earth鈥檚 tilt were different than it is now,鈥� Steffen says. A close neighbour鈥檚 gravitational tides could conceivably make a planet鈥檚 tilt 鈥渇lop around鈥�, causing wild swings in climate.

But Steffen and Li鈥檚 simulations showed that this doesn鈥檛 happen for pairs of neighbouring habitable worlds that have no other planets in their systems. Nor would it happen if you replaced Earth in our solar system with two planets close to each other.

鈥淭he climate would be no worse in these systems than it would be in the solar system as we have it now,鈥� Steffen says.

Good neighbours

The pair also tested whether rocks ejected from one planet could make their way to another, potentially spreading life from world to world and back again. Earth has been hit by rocks from the moon, Mars and the asteroid Vesta, despite the looseness of our solar system.

Closely packed habitable planets would be able to exchange rocks even more easily, with a higher chance of spreading life, Steffen and Li found. Rocks kicked up in an impact would not have to travel far to reach another planet, so both the initial collision and the eventual crash-landing could happen at slower speeds, reducing the chances that microbes would be vaporised.

An ideal scenario for sharing life would be when a planet travels through a tight mass of rubble streaming out from a collision on the world next door, allowing spacefaring microbe life rafts to splash down over an entire hemisphere, says Steffen. Such an interchange could entangle evolution on both worlds by dropping in microorganisms that would adapt to their new environment. 鈥淵ou can imagine the biological family tree having roots and branches on both planets simultaneously,鈥� he says.

Steffen imagines an alternative history 鈥� one in which Earth itself had a close companion in the sky. 鈥淵ou could imagine if Galileo had looked at something like this through his telescope, you could communicate between these two planets for hundreds of years before you could ever have a space programme that could deliver a living person from one to the other,鈥� he says.

of Cornell University in Ithaca, New York, echoes the sentiment. 鈥淚 love the imagery,鈥� she says. 鈥淕alileo would have probably been even more motivated to go and find out what was going on with this planet.鈥�

Journal reference: , Astrophysical Journal, accepted

Panspermia would give rise to some lively stellar neighbourhoods (Image: NASA/JPL-Caltech)

Does life spread like an interstellar infection? If we spot it on clusters of planets, that might suggest it doesn鈥檛 stay put wherever it evolves.

The theory that life crosses space to reach new worlds, called panspermia, is hard to test. Life on Earth could have been seeded by just one microbe-laden rock, but there are too many rocks to check, even if we had a foolproof test for extraterrestrial life.

鈥淭hat鈥檚 not a very effective strategy of testing whether life came from outer space,鈥� says Henry Lin of Harvard University. He says the answer lies in mapping life across the galaxy.

Future probes like NASA鈥橲 James Webb Space Telescope will scrutinise the atmospheres of planets in other solar systems for possible signs of biological activity. If life spreads between planets, inhabited worlds should clump in space like colonies of bacteria on a Petri dish. Otherwise, Lin says, its signature would be seen on just a few, randomly scattered planets.

Radiating life

Lin argues that if we find 25 worlds with life on one side of the sky and 25 lifeless ones on the other, it might mean the sun sits on the edge of a panspermia bubble 鈥� a strong sign that life radiated outward. 鈥淲e would have smoking-gun evidence that panspermia actually happens,鈥� he says.

But panspermia would be harder to confirm from the bubble鈥檚 centre. If there are biosignatures all around as far as we can see, for example, we can鈥檛 draw conclusions one way or the other. And if we see only scattered life, Lin says, that could suggest either that panspermia doesn鈥檛 happen or that it proceeds so slowly as to be rare.

of the Massachusetts Institute of Technology, an expert on the hypothetical biosignatures the technique relies on, doubts Lin鈥檚 scenarios will come in handy any time soon. 鈥淚t would be great if there鈥檚 a time in which we have so many biosignatures that we see clumps throughout the galaxy. But I don鈥檛 know when that time will be,鈥� she says. 鈥淯ntil we find biosignatures we can鈥檛 actually proceed with any of this work.鈥�

Whether we manage to detect biosignatures or not, Lin thinks his work might have a second life in the distant future, if humans achieve interstellar travel. The spread of humans and other organisms riding our coat-tails would follow the same growth pattern, he says.

鈥淓ven if panspermia doesn鈥檛 happen, we might be the ones to bring it about. Maybe this paper will be useful a thousand years from now,鈥� he says.

Journal reference:

Fossils on the moon may be our best bet for discovering the origins of life in our solar system. New experiments suggest that if the precursors to life arrived on Earth encased in a comet or asteroid, the moon could have preserved a record of it, despite being covered in lava at the time.

The simplest forms of life appeared on Earth some 3.8 billion years ago, but scientists still have no idea how. Since that crucial time, Earth鈥檚 tectonic forces have destroyed almost all the rocks that might have kept records of the beginnings of life. 鈥淏oth geology and life are efficient recyclers and hinder preservation,鈥� says from Imperial College London.

Some think that rather than originating on Earth, life or its organic precursors could have been delivered on asteroids, comets or fragments from other planets. If so, similar rocks should also have hit the moon 鈥� which is in better shape to preserve them. 鈥淭he moon has been geologically quiet for billions of years,鈥� says of Imperial College London. Furthermore, previous studies have suggested that organic compounds flung to the moon from Earth could survive the crash landing.

But when life was emerging on Earth, the moon was covered in flows of lava. Sephton, Matthewman and their colleagues wondered: would that lava destroy the organic record on the moon?

Lava life preserver

In a series of experiments, they showed that far from destroying organic chemicals, the lava may have 鈥渟andwiched鈥� them and preserved them for billions of years.

The researchers put various organic compounds and signatures of life in fake moon dust and then heated it to as high as 700 掳C. Their results suggest that organic molecules would only need to be buried a few tens of centimetres below the surface of the rock they arrived in to survive the heat of the molten moon 鈥� even if the rock was covered with a layer of lava one-metre thick. And as long as the compounds endured the high temperatures, the lava would have protected them from solar wind, radiation and meteorite impacts.

That means that anything that hit Earth at the time life appeared here might be preserved on the moon. 鈥淓vidence of prebiotic evolution on asteroids and comets or the emergence of life on Earth and Mars could all be preserved,鈥� says Sephton. 鈥淚t is an ironic possibility that one of the best places to look for records of early life is our dry and lifeless Moon.鈥�

of the University of Kent in the UK, who ran the earlier study showing that Earth鈥檚 organics could survive the trip to the moon, calls the team鈥檚 work 鈥渃omprehensive and carefully done鈥�. He thinks that the moon is an underappreciated source of answers about the origins of life on Earth.

Journal reference: