Living in the Universe

Lonely Stars and Planets

Fourth Week of September 2007

We imagine the skies that we see would be similar to the skies that other intelligent creatures around the galaxy might see, but that may not be the case. There may be very lonely skies and very lonely creatures out there in the galaxy. This past week, astronomers have found evidence that stars have formed in a long tail of gas that extends well outside its parent galaxy. The discovery suggests that orphan stars may be much more prevalent than previously thought.

The comet-like tail was discovered in the X-ray light with the NASA Chandra Observatory and in the optical light with the Southern Astrophysical Research Telescope in Chile. The feature extends for more than two hundred thousand light years and was created as gas was stripped from a galaxy called ESO137001 that is plunging towards the center of a giant cluster of galaxies. This is one of the longest tails that anyone has ever seen, and it’s a wake of creation, not destruction, because observations indicate that the gas in the tail has formed millions of stars. Because the large amounts of gas and dust needed to form stars are typically only found within galaxies, astronomers previously thought it was unlikely that stars could form outside a galaxy.

Team member Megan Donahue says, “This isn’t the first time stars have been seen to form between galaxies, but the number of stars forming here is unprecedented.” The evidence includes twenty-nine regions of ionized hydrogen glowing in optical light thought to be found nearby new stars. These regions are all downstream of the galaxy located in or near the tail. Two Chandra X-ray sources are seen near these regions, another indication of star formation activity. The researchers believe the orphan stars formed within the last ten million years which makes them very young stars. Mark Voit, another member of the team, says, “By our galactic standards, these stars are extremely lonely. If life were to form out there on a planet a few billion years from now, they would have incredibly dark skies.”

The gas that formed the stars was stripped out of its parent galaxy by pressure induced by the motion of the galaxy through the multi-million degree gas that pervades the intergalactic space. Eventually most of the gas will be scoured from the galaxy, depleting raw material for new stars and stopping star formation in the galaxy. This process may represent an important but short-lived stage in the transformation of a galaxy. Although apparently rare in the present-day universe, tails of gas and orphan stars may have been much more common billions of years ago when galaxies were younger.

This discovery leads to a speculation: what type of life might form, and what skies and vision of their galaxy might life have in other neighborhoods. Our Sun is an undistinguished star living in an unremarkable suburb of the Milky Way, but what if we were transported to a different part of the Milky Way and a different star? If we examine our expectations for life beyond Earth, we’re bounded not only by the history of our planet but also by our particular cosmic environment. So let’s do the visualization.

Our first stop isn’t far from home as the crow flies, eighteen hundred light years. We’re in Orion, a bustling region of star formation that traces a spiral arm of the Milky Way. Our journey through a wormhole dumps us near a hot, young star a hundred times brighter than the Sun. Cobwebs of gas drape the sky, and most stars look slightly red due to the gauze of dust. Four trapezium stars blaze brightly, and other massive stars litter the sky. There’s evidence of past supernovae and heavy elements have been ejected liberally. With so much material for planets, most stars have a dozen or more. On the other hand, many stars live less than a hundred million years, and those that live longer must contend with the violent death of their massive neighbors. Among the habitable planets there are many truncated biological experiments. The cosmic environment favors life with a fast evolutionary clock and life that develops below water and lives in rock.

Our next hop through the wormhole drops us near the urban center of the galaxy where the density of stars is a thousand times higher than near the Sun. The entire scene is lit brighter than a full moon sky on Earth, an unfamiliar sight. Where stars are crowded the tightest, the sky crackles with the high-energy radiation from the heart of darkness in the Milky Way galaxy, a supermassive black hole. A cool dwarf hangs like a blood orange over our heads. It has six planets on tight orbits, two of which are in the habitable zone. This seems like a promising environment for life. There’s a lot of iron and silicon for building planets and lots of carbon for life. Planets are drifting among the stars, ripped from their gravity moorings from stellar encounters. A few are shrouded in thick atmospheres and massive enough not to need external life support from a star. With a high density and many planets per star, the spread of life is guaranteed. Life-bearing rocks are routinely ejected from planet surfaces by impacts resulting in an inefficient but extensive shuttle system for life. The high degree of stellar concentration means the signaling time between intelligent civilizations, if they exist, is short. If there is an interstellar Internet anywhere in the galaxy, this is the place.

Our last jump takes us thirty thousand light years into the halo, and this is similar to the environment we started the story with. There’s dark matter here of course, like there is everywhere, but no gas or dust and very few stars. The two-armed spiral of our disk is laid out below like a Persian rug, blue light knots of star formation set into a sparkling yellow star field. The white dwarf nearby is hot, titanium white. Formed a long time ago with not much grist for planets, it has three the size of Mercury, and they’re all long dead. The nearest star is a hundred light years away. Biology is sprinkled lightly in the attic of the galaxy. It’s lonely here and a shame that such a gorgeous view is wasted.

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Immortal Bacteria

Third Week of September 2007

This week I want to talk about a story from a few weeks ago about the decay rate of bacterial DNA, indicating that the information coding molecule of biology has a half life for degrading due to radiation in the environment of about a million years. A team of researchers has talked about cells that are essentially immortal, in their words. If confirmed, immortal cells could prove the potential for life on Mars and Europa, one of Jupiter’s moons.

The cells come from Antarctica, home to the largest body of ice on Earth. Prior to about ten years ago, nobody thought that life could exist beneath the Antarctic life sheets, which can be more than two miles thick in places, because the conditions were believed to be too extreme. However, Brent Christner, assistant professor of biological sciences at LSU, spent a great deal of time in the world’s most hostile environment conducting research that proves otherwise. Christner’s discoveries of viable microbes in ancient ice cores in sub-glacial environments, coupled with the realization that large quantities of liquid water exist beneath the Antarctic ice sheet, have changed the way biologists view life in Antarctica. “More than a hundred and fifty lakes have been discovered underneath nearly two and a half miles of ice in Antarctica,” said Christner, “and most of these bodies of water have likely been covered by ice for at least fifteen million years.” The environmental conditions in the deep cold biosphere are unlike anything on the Earth’s surface, and this biome represents one of the most extreme habitats for life on the planet.

A time frame of up to one million years is required for microbes in the atmosphere to be transported through the sheet of ice and enter an Antarctic sub-glacial lake. Even though cells are preserved in the ice, the question of how the DNA in these organisms remains unscathed over such long periods of time remains. According to Christner there are two possible explanations for how these microbes could survive frozen for many millennia.

First, they may be dormant in the ice and possess very effective repair mechanisms that are initiated when the cells are introduced into a growth situation. He said that given enough time, dormant cells without active DNA repair mechanisms would eventually incur lethal levels of radiation induced damage from natural background sources in the ice. Alternatively, Christner suggests that the microbes might stay metabolically active while entrapped in the ice giving them the ability to repair damage as it occurs. If this is the case, these microbes may be essentially immortal when frozen, assuming a continuous energy supply is available. That’s an exciting prospect because we imagine there will be many cold environments out there in space on moons and planets.

Christner’s current laboratory research has shown that glacier microbes are capable of metabolic activity when frozen down to minus twenty degrees Celsius. Again, in his words “Our experiments have revealed the potential for microbes to metabolize under frozen conditions, but we lack the smoking gun which proves this occurs in nature. We’re taking what we learned in the lab at LSU and designing experiments which address this question in real Antarctic ice samples.” He and some students are heading down to the Antarctic in October, next month, and staying through January 2008 to continue the research.

Christner says, “The implication of our research is that large sheets of Antarctic which make up seventy percent of the planet’s fresh water resource may represent actual biomes, substantially expanding the known boundaries for life on Earth. Terrestrial glacier environments provide analogues to address questions relevant to the search for past or present microbial life in extraterrestrial ice on planets and moons in our Solar System. Based on everything we know about the tenacity of life in Earth’s deep cold biosphere, microbial life surviving and persisting in the ice on Mars or Europa is not that much of a stretch.” That’s exciting research; it lends extra motivation for a future return to Europa.

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Surviving the Sun’s Demise

Second Week of September 2007

Two related discoveries in the last few weeks talk about the possibility of Earth-like planets and in particular the fact that Earths can survive the death of their Sun, at least physically. It’s not clear if life or a biosphere would survive such an event. Chemical elements have been observed around a burned out star known as a white dwarf that give evidence that an Earth-like planet or several Earth-like planets once orbited it, indicating that worlds like our own may not be rare in the cosmos since most stars end their lives as white dwarfs.

The astronomers were at UCLA and the University of Kiel in Germany, and they studied a white dwarf called GD362 which is about a hundred and fifty light years away. They figured out that the composition of a huge asteroid must have been ripped apart by gravitational forces as it approached this star and found that the composition was similar to the Earth’s crust. It’s rich in iron and calcium and low in carbon just like a strong rock on the Earth is. The white dwarf is surrounded by dusty rings which were probably made of objects shredded as they ventured too close. It’s like a version of Saturn’s rings.

GD362 was once a star similar to the Sun, but after billions of years it exhausted its nuclear fuel and ballooned into a red giant; part of its death process expelled most of its outer material and then degenerated into a burned out remnant called a white dwarf. The fact that the asteroid that surrounded it and was ripped apart is similar to the makeup of the Earth as well as the Moon indicates that rocky planets like our own may have orbited the star eons ago. “The rocky asteroid that’s inferred by these observations had a diameter of about a hundred and twenty-five miles and may have been smashed by the white dwarf between a hundred thousand and a million years ago,” said the astronomers who did this research. While the white dwarf has a mass close to that of our Sun, it has collapsed now to the point where its diameter is about the size of the Earth.

Well, this evidence is a little indirect, but another discovery just in the last week is a better indication that the Earth might survive the Sun’s demise, which is going to happen in five billion years. Astronomers have found another planet, in this case a gas giant three times as massive as Jupiter. It orbits a hundred and fifty million miles from a faint star in Pegasus known as V391 Pegasi. It’s about forty-five hundred light years away, not very close at all. Before that star blew up as a red giant and lost half its mass, the planet must have been about as far from its star as the Earth is from the Sun, almost ninety million miles according to calculations by an international team of astronomers led by Roberto Silvotti of the Observatorio Astronomico de Capodimonte in Naples. Dr. Silvotti said the results show that the planet at the Earth’s distance can survive a red giant, and he said he hoped the discovery would prompt more searches. To quote him, “With some statistics and new detailed models we will be able to say something even more to the destiny of our Earth, which as we all know has more urgent problems by the way.” This from an email he wrote in the Nature magazine, showing that astronomers do sometimes care about things closer to home.

The star V391 Pegasi is about half as massive as the Sun, and it burns helium into carbon. It will eventually shrug off another shell of gas and settle into eternal death as a white dwarf. Meanwhile, the star’s pulsations cause it to brighten and dim every six minutes. After studying the star for seven years, Dr. Silvotti and his colleagues were able to find subtle modulations in the six-minute cycle, suggesting the star was being tugged to and fro over a three-year period by a massive planet. Essentially the observers were using the star as a clock as if it were a GPS satellite moving around the planet. This is a very clever technique for finding giant planets, but it’s not actually the first time it’s been used. The first time a pulsing star was found to have planets was the pulsar PSR1257+12 back in 1992 actually making those the first planets ever discovered beyond the solar system, but the Pegasus planet had to survive less lethal conditions, although it must have had a bumpy ride over its ten billion years of existence.

Alan Boss of the Carnegie Institute of Washington has said, “Stellar evolution can be a wild ride for a planet that’s trying to survive, especially inner planets like the Earth.” When our own Sun begins to graduate from a hydrogen-burning main sequence star to a red giant, two effects will compete. First, the Sun will blow off mass to conserve angular momentum, and the Earth will retreat to a more distant safer orbit, this not by any intention but happening just by the forces of gravity. At the same time, tidal forces between the Earth and the expanding star will drag the planet inward, or try to, where it could be engulfed. The latter is very difficult to compute. As a result, Earth’s fate is most uncertain because it’s at the borderline between being engulfed and surviving.

“A particularly dangerous time for the Earth,” said Dr. Silvotti, “would be the end of the red giant phase when the Sun’s helium ignites in an explosive flash.” In the case of V391 Pegasi, that explosion sent a large fraction of the mass of the star flying outward. So planets like the Earth could physically survive the death of their stars, but of course conditions in the lead up to that time would be intolerable and very difficult for life. However, as Dr. Silvotti pointed out, we do actually have slightly more proximate worries on the Earth.

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Developing a Better Space Skin

First Week of September 2007

It seems exciting to live the life of an astronaut, and to be in space, but there is something extremely clumsy and inelegant about the spacesuits they have to wear. Those of us who remember the Apollo astronauts sensed the euphoria of being on the Moon, but there were these people galumphing around slowly in their clumsy suits imagining the mission controllers cringing at the ease with which they could fall over and the fatal outcome of even a small puncture in the suit.

Astronauts have been lumbering around in the same heavy, energy-sapping suits for forty years. Well, Dava Newman, who’s a professor of aeronautics at MIT, wants to change all that. She and her team of researchers have just unveiled a promising new prototype called the BioSuit. It’s sleek. It’s white. It’s clingy, and its revolutionary design has the potential to make astronauts feel as agile as Spider-man. The new spacesuit is made of an elastic, skintight material, light enough to allow astronauts able to run, walk, or even climb mountains on a moon or a planet. These are acts that are physically impossible using the Tin Man design of NASA’s current spacesuit.

The form-fitting suit is not just a pretty photo-op. It keeps astronauts alive by creating what scientists call mechanical counter pressure, which balances the pull vacuum of space. The spacesuits today use gas pressurization. They essentially create a miniature Earth-like atmosphere inside the suit, which exerts appropriate force on the astronaut’s body. The system works, but many scientists consider it out of date because of the bulky equipment and life support that it requires. That weighs almost three hundred pounds.

Referring to current designs, Newman says “These suits are fine for space shuttles or stations but not for exploration.” In fact, estimates show that astronauts typically end up spending seventy to eighty percent of their energy just moving around in their suit. The new suit creates the same kind of pressurized environment simply by wrapping layers of specially padded nylon and spandex fiber tightly around the body. This method has been worked on by Newman for seven years. When the material is properly wrapped, it creates a mobile, skeleton-like shell that protects and supports the astronaut. When the new suit rolls out each one will be tailored to an individual astronaut like a snug wetsuit or a second skin.

There’s enough suit pressure to counter the vacuum of space, but to work the BioSuit needs to exert close to one third of the pressure exerted by the Earth’s atmosphere. So far the researchers haven’t been able to reach that level and they don’t know what the problem is, but they suspect it’s something to do with the suit’s pattern. Aside from its more appealing profile, Newman says the BioSuit will be safer for astronauts than the old suits. Currently when an astronaut’s suit is punctured, he or she simply has to go back to the base to undress or decompress. With the new suits, astronauts could slap a patch on over the tear.

The BioSuit also provides resistance that helps the body maintain muscle mass, and that’s important since astronauts lose about forty percent of their muscle mass during space travel. So if this suit doesn’t end up making it to Mars, researchers say it could be used by athletes in training. Newman still estimates that this new suit is about ten years away from being ready for prime time, but if astronauts ever want to take more than a few steps and explore on Mars or other moons, they will need these new suits.

This leads to an astrobiological thought. What if alien creatures of some advanced function and form could develop skins that were like a BioSuit? We usually think of planets or moons that don’t have much atmosphere or are near vacuum as being uninhabitable places, but we can imagine situations where under the surface they could exist. Think of the tiny Tardigrade, which has its own phylum. This creature has a separated, segmented body, eight legs, one gonad, and an exoskeleton called a tun. A skin is just one form of an exoskeleton, and a tun is a Tardigrade solution. But a BioSuit, if it could be developed by nature, would be even more impressive. What would habitable mean now? BioSuits will let humans exist on the surface of planets where they couldn’t normally live. Perhaps other advances creatures have used similar strategies.

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