President Ruth McDiarmid called the 2,217th meeting to order at 8:16 pm February 16, 2007 in the Powell Auditorium of the Cosmos Club. The recording secretary read the minutes of the 2,216th meeting and they were approved.
Ms. McDiarmid made announcements. She made a pitch for volunteers to help out the Society, by contributing effort, by financial contributions, and by bringing friends. She made the parking announcement.
Ms. McDiarmid then introduced the main speaker of the evening, Mr. William Newman of the University of California at Los Angeles. Mr. Newman spoke on Astrobiology.
“What is meant by astrobiology?” Mr. Newman began. It is the study of the emergence of life on this planet and on other planets and the search for habitable worlds.
Philosophically underpinning his talk, he gave this quotation: “Space is big, space is dark, it’s hard to find a place to park.” – Burma Shave. This was from science cartoonist Sidney Harris, not an actual Burma Shave ad.
Ten Presidential objectives guide the work of the Astrobiology Institute, which is a partnership among NASA and a group of universities including Mr. Newman’s, UCLA. The objectives are 1) Understand how life arose on Earth; 2) Determine the general principles governing the organization of matter into living systems; 3) Explore how life evolves on the molecular, organism, and ecosystem level; 4) Determine how the terrestrial biosphere has coevolved with the Earth; 5) Establish limits for life in environments that provide analogues for conditions on other worlds; 6) Determine what makes a planet habitable and how common these worlds are in the universe; 7) Determine the signature of life on other worlds; 8) Determine whether there is or was life elsewhere in our solar system; 9) Determine how ecosystems respond to environmental change on time-scales relevant to human life on Earth; and 10) Understand the response of terrestrial life to conditions in space or on other planets.
He discussed an abiding concern, anthropocentrism. In that connection, he pointed out that the temperature of earth is considerably lower than it was nearer its beginning, when life formed. Despite the anthropocentrism concern, they are looking for life that is carbon and water based. There are alternatives, silicon, for example, but carbon is ten times as common as silicon and is more capable of bonds, chains, and transformations.
Why water? Life needs a solvent, a medium where chemicals can mix and react.
They search for habitable planets, not inhabited ones. How would we see them? The sun is a billion times brighter than earth and the angle of separation is miniscule.
It’s tempting to look in our own solar system. Though Mars Rovers cost about $400 million each, that’s less than a stealth bomber, at $2.5 billion. But then, estimates for sending humans to Mars range from $300 to $400 billion. Mr. Newman says the problem is like real estate – location, location, location, and then how do we play it. He says we are not going to send humans to extrasolar planets. Mars, Venus, and Europa are the only places that seem likely to host life here.
Mars once had water and an atmosphere rich in carbon dioxide. It had an atmospheric pressure about 20% greater than Earth, although now its atmospheric pressure is about .8% of Earth’s.
The study of planets has been productive in surprising ways. The greenhouse effect was first discovered on Venus. Nuclear winter was first discovered on Mars.
Venus is hot enough to melt lead. Europa has ice and appears to have liquid water underneath the ice.
What about other solar systems? You need to find, first, the right kind of star. There are two kinds, stars like our sun, and stars not like our sun.
Like our sun, it should have a lifetime of many millions, preferably billions, of years. Our sun is about a 10 billion year star and it’s about half done. It has to generate just enough heat to warm planets to a narrow temperature range where the right chemistry happens, not hot enough to melt everything and warm enough not to freeze everything. It should have hydrogen and helium as primary components and a mix of elements like phosphorus, silicon, magnesium, aluminum, and other vital elements.
The hunt is handicapped by the numbers. There are 400 billion stars in our galaxy and there are 100’s of billions of galaxies.
Fortunately for the hunters, the lifetime of stars is highly related to mass. Large ones are very short-lived. Then, since small ones produce too little heat, the likely heat sources for life are stars about the size of our sun.
Most stars are of the first generation type, they have only helium and hydrogen. Our sun is a second generation and has the mix of elements presumably required for life.
Turning from stars to planets, Mr. Newman observed that before 1980, ours was the only known solar system. Now, there are more than 130 known, but many for technical reasons are not suitable.
Stars and planets condense by gravity out of giant clouds of dust. Gas pressure attempts to expand the cloud, mass pulls it in. When the cloud collapses it forms a core protostar and a disc of gas and dust. The disk breaks up to form planetesimals and ultimately planets.
Good planets are difficult to make. They can be too close, like Mercury, or two far, like Mars, from the star. Like Goldilocks’ amenities, they must be “just right.”
In other ways, also, they must be just right. If they are too big, they gather a massive hydrogen and helium envelope; if too small, their gravity is too weak to hold an atmosphere. Jupiter is too big, Mars may be too small.
Unfortunately, planets are dim. Earth is 109 fainter than the sun. Five methods have emerged in the search for planets. Only one, radial velocity, is in use. From the radial velocity, the mass of the planet can be estimated. The other methods will all require space based telescopes.
Radial velocity is determined by the Doppler shift of radiation from the star. As a planet rotates around a star, the star also rotates, or wobbles, in balance with the planet. Many planets rotate pretty fast, in a few days. Jupiter takes 11+ years. All the current measurements were designed to find proofs in principle that there are other planets out there, not to estimate their mass.
Finally, there is another question about extraterrestrial life? Would they want to be discovered? Would we?
It has been 50 years since Sputnik. We are past the bloom of enthusiasm about going to space. Where will we go now?
Mr. Newman says we are poised to discover another world like our own. In the final analysis, our search is determined by location, location, and location. Some of the great questions come down to sociology. Mr. Newman is not sure we know enough about human, let alone alien, sociology.
He invited questions.
One questioner asked if the speed of light and intergalactic distance limit the search to our galaxy. Even within our galaxy, Mr. Newman said, they are often looking backward in time. He quoted one theorist who observed that aliens, looking at us from a probable distance, would be seeing “I love Lucy.” The speed of space travel is useless in visiting other stars, even in the galaxy.
He was asked how many stars fit his criteria. With 400 billion stars in the galaxy, even if 1% of them might support life, that is a lot, he said.
He was asked if there is anything special about our solar system. Many orbits are elliptical, he responded; ours tend to be circular. Water, he said, is truly special. It is a polar molecule. The chemistry of water is truly rich compared to ammonia. That’s one of the reasons Mars is an immediate target. They now believe it had water, although they do not know how long it lasted there.
After the talk, Ms. McDiarmid presented Mr. Newman a plaque commemorating the occasion and invited everyone to stay for the social hour.
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Ronald O. Hietala
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