Living in the Universe

The Most Earth-like Planet Yet

Fourth Week of April 2007

This week saw major news in astrobiology: the discovery of the most Earth-like planet yet found. European astronomers have discovered a planet only five times the mass of the Earth, a place where liquid water can almost certainly exist on its surface. It’s not exactly a system like Earth. The Sun wouldn’t burn brightly there. It would hang close, large and blood-red in the sky, glowing faintly like a charcoal ember, and it would probably never set if you lived on the sunny side of the planet. If you could have a birthday party it would happen every thirteen days; that’s how fast this new planet circles its Sun-like star. But watch that cake. It would weigh a lot more than it would on Earth. You might be able to keep your current clothes, however. The temperature in this alien setting will be a lot like the Earth. It’s not too hot and not too cold, and that just right temperature is the reason astronomers think this planet could conceivably house life outside our solar system.

It’s as close to Earth-size as telescopes have yet found, and both elements make it the first potentially habitable planet beside the Earth or Mars. There’s a lot that’s not known about this planet, but as planets go, and in the galaxy we live in, it’s a neighbor. It’s only a hundred and twenty trillion miles away. That’s about twenty light years. The red dwarf star that this planet circles is one of the hundred stars closest to the Earth. It was discovered by a European team at La Silla in Chile, the European Southern Observatory, which has built a special instrument to look for Doppler shifts to detect planets.

What they found is the planet circling the red dwarf star Gliese 581. Red dwarfs are low energy, tiny stars that give off dim, red light and last longer than stars like our Sun. Until recently astronomers didn’t even consider these stars as possible hosts for planets that might sustain life. The discovery of this new planet is sure to fuel future studies of planets orbiting similar stars since eighty percent of the stars near the Earth are red dwarfs. This new planet is about five times heavier than the Earth. Surface gravity there would be sixty percent stronger than on the Earth.

The discoverers are not certain if it’s rocky like the Earth or a frozen ice ball with liquid water on or near the surface. If it’s rocky like the Earth, which is accord with the prevailing theory, it has a diameter one and a half times the size of our planet, but if it’s an ice ball it could be even bigger. Based purely on theory, Gliese 581C could and should have an atmosphere, but what’s in that atmosphere is a mystery. If it’s too thick or greenhouse heating occurs, the planet’s surface might be too hot for life. However, the research team believes that the average temperature is somewhere between thirty-two and a hundred degrees Fahrenheit, and that set off celebrations amongst astronomers, because until now every one of the two hundred and twenty planets astronomers have found outside the solar system have had the Goldilocks problem. They’ve been too hot, too cold, or just plain too big and gaseous like Jupiter in our solar system. This new planet seems just right.

Besides having the right temperature, the new planet is probably full of liquid water as hypothesized by Stephane Udry, the discovery team’s lead author and an astronomer from the University of Geneva, but that’s based solely on theory about how planets form and not on any direct evidence. Co-author Xavier Delfosse of Grenoble Observatory said, “Liquid water is critical to life as we know it.” Due to its temperature and relative proximity, this planet will most probably be a very important target of future space missions dedicated to the search for extraterrestrial life. Said Udry, “On the treasure map of the universe, one would be tempted to mark this planet with an X.” Other astronomers cautioned it’s a little too early to tell whether there’s water.

The new planet’s star system is only twenty and a half light years away, making it a very close companion to the Earth, but the star is so dim you can’t see it without a telescope, it’s somewhere in the constellation Libra which is currently low in the southeastern sky in the United States in the mid-evening. “Even so,” noted Steve Maran, the press officer for the American Astronomical Society, “we have no idea of how to get to these places in a human lifetime.” But the view if you could? The planet is fourteen times closer to the star it orbits than we are to the Sun. Udry has figures the red dwarf star would hang in the sky at a size twenty times larger than our Moon, and it’s likely, but still not known, that the planet doesn’t rotate so one side would always be sunlit and the other dark.

This is an exceptional discovery because it’s going to trigger searches for planets around the multitude of dim, red stars in our own galaxy. If habitable zones are extended to stars quite different from the Sun, much dimmer, much less luminous, then the number of potential habitable places in the galaxy could go up by a factor of ten, which is exciting news indeed for astrobiology.

Bookmark It

Hide Sites

Bring on the Nanobots!

Third Week of April 2007

Back in the mid-1970s a group of MIT undergraduates walked into the office of a mid-level NASA administrator. They managed to talk their way into a meeting with a pretty high level NASA official with a very weird idea. They wanted to send a set of robotic ants to the planet Mars. The ants would spill out of a lander and, connected by a neural net, would explore the surface, roaming over its terrain. These students excitedly explained how with a neural net and a lot of redundancy it didn’t matter if some of the ants fell into crevasses or their sensors failed to work. Overall, with hundreds or thousands of these little ants crawling over the surface a large amount of data would be contained and sent back to the spacecraft. It was a cheap and clever way of doing a mission.

I have a feeling they were laughed out of the office. Anyway, nothing came of it. At the time in the 1970s, computers were new, so the students were projecting towards a level of miniaturization and computer power that did not yet exist. However, now it does exist, and NASA is once again taking seriously the idea of using miniaturized probes rather than the large spacecraft we’re used to. These are called nanonauts. Engineers are now designing a new breed of planetary explorer. They’re tiny, shape shifting devices that can be carried on the wind like dust but can also communicate, fly in formation, and take scientific measurements. One name for them is smart dust and they may one day provide a unique method of studying locations interesting to astrobiology such as Mars and Venus.

This technology is already in use in various places. Geologists use smart motes or smart dust to go into volcanoes and places that are impossible for humans to reach. There is very strong evidence that security agencies are already using smart dust, perhaps even with tiny cameras onboard, to spy on us or for espionage purposes. It’s better not to think about that. Let’s just think about the scientific applications. Engineers at the University of Glasgow are designing some new nanobots, smart dust particles consisting of a computer chip about a millimeter in size surrounded by a polymer sheath that can be made to wrinkle or smooth out by applying a small voltage. Roughening the surface of the polymer means the drag on the smart dust particle increases, and it floats higher in the air. Conversely, smoothing out the surface causes the particle to sink. Simulations show that by switching between rough and smooth modes, the smart dust particles can gradually hop towards a target even in swirling winds. It’s a very clever idea.

Dr. John Barker from the University of Glasgow described applications of smart dust at the Royal Astronomical Society’s national meeting in Preston just a week ago. He said the concept of using smart dust swarms for planetary exploration has been talked about for some time, but this is the first time anyone has looked at how it could actually be achieved. Computer chips of the size and sophistication needed to make smart dust particles now exist, and scientists are looking through the range of polymers available to find one that matches a requirement for high deformation using minimum voltages.

Smart dust particles would use wireless networking to communicate with each other and form swarms. Dr. Barker explains, “We envisage that most of the particles can only talk to their nearest neighbors, but a few can communicate at much longer distances. In our simulations we’ve shown that to fly a swarm of fifty dust particles would organize them into a star formation, even in turbulent wind. The ability to fly in formation means the smart dust could form a phased array. Then it would be possible to process information between the distributed computer chips and collectively beam a signal back to an orbiting spacecraft.”

For the smart dust to be useful in planetary exploration, they would have to carry sensors. With current technology chemical sensors tend to be rather large for the sand grain-sized particles that would be carried in the thin Martian atmosphere. However, the atmosphere of Venus is much denser and could carry smart sensors up to a few centimeters in size. Dr. Barker says that scientific studies can be carried out on Venus using technology we have now, but with the speed of miniaturization, within ten years we should have chips that have components which are only a few nanometers across which means our smart particles would behave more like macromolecules diffusing through an atmosphere than dust grains. That means Mars is within reach too. This is a new and exciting way to do planetary exploration, and I’m sure we’ll be hearing more about it in the years to come.

Bookmark It

Hide Sites

Water and Foliage on Exoplanets

Second Week of April 2007

This week I want to talk about the two colors of extrasolar planets: blue and green. For blue, I’m speaking metaphorically or even poetically because the blue refers to water. Water is of course colorless and only appears blue in its liquid or solid form due to scattering, but blue and the water that implies life has always been sought in extrasolar planets. Over two hundred are known, and a few weeks ago for the first time water was identified in the atmosphere of one of them through a combination of previously published Hubble Space Telescope observations and new theoretical models.

Water is one of the most abundant molecules in the universe, so it’s not in fact surprising that it’s present in the atmosphere of extrasolar planets. But almost all of the two hundred plus planets known have been found by the Doppler method, and the Doppler method, whereby the planet reveals itself in its tug on the parent star and a periodic wobble of that star, gives very little information other than the mass of the planet. To learn more we need the very particular geometries of eclipsing solar planets. That is, we have to depend on the tiny fraction of the planets where the plane of the orbit happens to lie exactly along the line of sight to the Earth so that once every orbit the planet passes between us and its star, and once every orbit it passes on the far side of its star.

One of the extrasolar planets, a super-Jupiter with a very fast orbit and a very close massive planet, HD209458, displays such eclipses. Every three and a half days the planet passes in front of the star. During one of these observations, the Hubble Space Telescope measured spectra at optical and infrared wavelengths. When the planet passes in front of the star, its atmosphere blocks a different amount of the starlight at different wavelengths, and in particular absorption by water in the atmosphere makes the planet appear larger across a special part of the infrared spectrum compared to wavelengths in the visible spectrum. A careful analysis of this data and a comparison to new models by researchers at Lowell Observatory has produced evidence for water absorption in this planet, a hundred and fifty light years from the Earth.

It’s an exciting discovery but fair to say that it’s disputed by other astronomers. Theoretical modeling is important in the interpretation, and other theorists have produced conflicting results. This one is not yet nailed. What about the green of extrasolar planets? Well that’s the most exciting of all, the ability to detect microbial life and in particular vegetation, plants, on distant worlds. Research done at the Virtual Planetary Lab, a part of the California Institute of Technology’s NASA astrobiology initiative, has shown that if life exists on other planets, and it’s plant life, it may not be predominantly green. Scientists found that the predominant color of the foliage on Earth could be a range of other colors depending on the star that the planet orbits and the composition of the atmosphere.

Other planets may have foliage that’s yellow, orange, or red. It all depends on the color of the star. Determining the range of colors is important because scientists need to know what to look for when they begin gathering spectra of light from distant Earth clones. Lead author Nancy Kiang, a biometeorologist at NASA’s Goddard Institute of Space Studies and a visitor at the Spitzer Scientist Center, says, “The dominant color of photosynthesis could be yellow, or orange, or maybe red. I think it’s unlikely that anything will be blue, and of course green plants are also a possibility since that’s what we have here.” One of the most fun parts of this research is how interdisciplinary it is. These results could not be derived unless planetary scientists, atmospheric scientists, biologists, and others had pooled their expertise in modeling the possible spectra of light available to plants on Earth-like planets around other stars.

Vicki Meadows is the leader of this group, and she knows exactly how much expertise has to come to the table. “The study requires data about everything from the type of photons given off by a main-sequence star in a particular stage of its life, to the depth of water that an aqueous plant might prefer,” and, “a huge variety of information.” Meadows says, “No single astronomer or biologist or atmospheric scientist could have attacked this problem individually.” The researchers focused on the way plants use light for energy to produce sugar, which is pretty much the definition of photosynthesis because photosynthetic pigments must be adapted to the available light spectrum. The available light at a planet’s surface is a result both of the light from the parent star and filtering effects of the gas in the atmosphere.

For example, ozone on the Earth absorbs ultraviolet light, so not much of that reaches the Earth’s surface. Kiang said, “It turns out that the spectrum of the number of particles of light is what is important, and on Earth there are more particles in the red,” which, “could explain why plants [. . .] on Earth are mainly green.” On Earth, plants absorb the blue light because it is energetic and red light because its photons are plentiful. There is more than enough energy from the blue and red in sunlight, so plants do not really need more. Therefore, they reflect away relatively more green light, which is why they appear green to us. But on other worlds with other atmospheric compositions, things could be quite different, and so we’re starting to learn what the range of colors of planets with plant life might look like. That’s an exciting new advance in astrobiology.

Bookmark It

Hide Sites

Parsing the Microbial World

First Week of April 2007

One of the strong implications of life on Earth is its fantastic bacterial diversity and what that implies for the diversity of microbial life beyond the Earth. The range of organisms on Earth at the level of single-celled organisms is fantastic, and this is just one environment. There are many cosmic environments out there. Two reports released in the last week shed light on the microbial diversity of this planet which we believe is only just beginning to be explored.

One is based on a National Academy of Sciences study, and it’s about a field called metagenomics which is the field where the DNA of entire communities of microbes is studied simultaneously. According to this report this field presents, perhaps since the invention of the microscope, the greatest chance to revolutionize understanding of the microbial world. Microorganisms are essential to the Earth transforming key elements into energy, maintaining the energy and chemical balance in the atmosphere, providing plants and animals with nutrients, and performing other functions necessary for survival. There are billions of benign microbes in the human body for example that help digest food, break down toxins, and fight of disease-causing microbes. Microbes are used commercially for many purposes including antibiotics, getting rid of oil spills, enhancing crop production, and producing biofuels. Microbes are the most likely candidate for life on other planets, in the solar system and beyond, because they are the heartiest organisms on Earth and can survive our planet’s harshest and most unique environments.

Historically, microbiology focused on individual species of organisms that could be grown in the laboratory and examined under a microscope, but it turns out that most of the microbial diversity of the Earth is not studied because the organisms cannot be cultured in the lab. Most of the life supporting activities of the microbes are carried out by complex communities of microorganisms. Metagenomics will transform modern microbiology by giving scientists the tools to study communities of microbes, the vast majority of which are likely to be unknown species, and how they interact to perform such functions as balancing the atmosphere’s composition, fighting disease, supporting plant growth.

Metagenomic studies begin by extracting DNA from all of the microbes in a particular environment sample. There could be thousands or even millions of organisms in one sample. The extracted genetic material consists of millions of random fragments of DNA that can be cloned into a form capable of being maintained in laboratory bacteria. These bacteria are then used to create a library that includes the genomes of all the microbes found in a habitat. Although the genomes are fragmented, new DNA sequencing technology and powerful super- computers are now allowing scientists to make sense of this jigsaw puzzle. They can examine gene sequences with thousands of previously unknown organisms or induce bacteria to express proteins that can then be screened for capabilities that might help us with medicine and health. This is very exciting. The goal of these projects should be to characterize in great detail carefully chosen microbial communities and habitats worldwide according to the report.

These studies will unite scientists from different disciplines in their studies of a particular habitat. The large projects would be virtual centers collecting data from scientists working in many locations and probably will take a decade or more to work out. Craig Venter, one of the founders of the human genome project, has started on this work. In a ship he explores the oceans and trolls for new bacterial strains. Through a recent series of expeditions he found many strains previously unknown on Earth.

The second study comes from a report by the American Society of Microbiology. Until a decade ago scientists characterized microbes almost exclusively by their physical characteristics, how they looked, what they ate, and their byproducts, but with the advent of genomic sequencing techniques our understanding of the relationship between microorganisms has changed. In the light of this new knowledge, what exactly is the definition of a microbial species, and how should microbiologists be categorizing microorganisms? According to the report it’s clear that the current system of designating microbial species is functional but highly inadequate in many ways. It’s unclear whether this system should be replaced or renovated.

In the late 1800s, to make sense of the diversity of microbes, taxonomists developed a system of placing microorganisms into categories in which each organism was granted a genus and a species category. At the time the physical properties were the only means of describing microbes, so the system was based on measurable and observable characteristics. In the late twentieth century molecular biology discovered the genetic relationships between microbes, and some of the secrets of microbes that had yet to be cultured in the lab were revealed. Quoting from the report, “Much of this new knowledge was incorporated into species descriptions, but difficulties in classification persist and novel issues have arisen. Conflicts exist between phenotypic and phylogenic information. The means for classifying non-cultured microbes are limited under the current paradigm, and microbial species do not always demonstrate the phenotypic or genetic cohesiveness expected of them. For these reasons and others it has become clear that the species classification framework is not capable of fully portraying and organizing microbial diversity.”

The shorthand of this report is the genetic sequencing techniques are going to be the way we understand the microbial diversity of Earth, and if we could only get our hands on microbes from space the excitement of wondering about their genetic diversity would keep us busy for years.

Bookmark It

Hide Sites