Life in the Universe "Extraordinary claims require extraordinary evidence." — attributed to Carl Sagan "It's important to keep an open mind, but not so far open that your brains fall out." — Jim Oberg Finding life in the Universe is really two separate problems: (1) Finding intelligent life. (2) Finding simple life. (1) Intelligent life in the Universe: Four spacecraft (Pioneer 10 and 11, and Voyager 1 and 2) have left the Solar System. All are bearing plaques, in case they are ever found. This is an unlikely way of making contact: the stars are so distant, it will take the spacecraft millions of years to get there. The Search for Extraterrestrial Intelligence (SETI) www.seti.org Astronomers are using radio telescopes to search for faint radio signals, as in the movie "Contact," starring Jodie Foster. Often discussions of SETI involve: The Drake Equation: (Frank Drake, UCSanta Cruz, 1961) N = R* x fp x ne x fl x fi x fc x L, where: N = the number of technologically advanced civilizations R* = the rate at which Sun-like stars form in the Galaxy fp = the fraction of these stars that have planetary systems ne = the average number of planets per such system that are Earth-like fl = the fraction of Earth-like planets on which life develops fi = the fraction of those life forms that are intelligent fc = the fraction of those intelligent species that develop the technology for interstellar communication (e.g., radio telescopes; possibly also lasers; other technologies) L = the average lifetime of such a technologically advanced civilization For the exam: Don't memorize these terms, but do understand what the equation means and what it does, as well as the following: What is a problem with the Drake equation? What is another problem with it? Describe these problems in a paragraph or so apiece. You may work in small groups, to help your imagination. Another problem with SETI: The Fermi Paradox: "Where is everybody?" (Enrico Fermi, 1950) We observe that: a) The Universe is very old, billions of years older than Earth. b) Sun-like stars are common (they make up 5% of stars). c) Planets appear to be common around Sun-like stars (although we still haven't found any Earth-like planets, but we can't, yet.) d) The commonest elements (hydrogen, carbon, nitrogen, oxygen) in life are also the commonest in the Universe (exception: helium, but it's chemically inert) e) Conditions hospitable for life appear to be common (e.g., water, complex organic substances, planets around Sun-like are common). f) In the one case we know, life on Earth developed very early in the history of the planet, seemingly as soon as Earth was capable of supporting life. g) We are intelligent, and are a relatively young species of life on Earth. We might summarize (2) through (7) and say that we might expect life and intelligence to be common throughout the Universe. When coupled with (1), we might expect most intelligent life in the Universe to be much older than us. SO: Where is everybody? Why do we not see them here? (2) Simple life in the Universe: – Life can survive in space: in November 1969, the Apollo 12 astronauts recovered some parts from Surveyor 3, a robot spacecraft that had landed on the Moon 30 months earlier. When the parts were examined, a colony of bacteria was found. These bacteria were freeze-dried and in deep hibernation, but upon placement in a nutrient-rich culture, they became active again (i.e., came back to life). Also, in 1995, two paleontologists found bacteria spores, 30 million years old, in a bee preserved in amber. They were able to culture these bacteria back to life, too! Life has the ability to travel across space: we need not wait for the starship Enterprise. • Life in a Martian meteorite (ALH 84001)? Claimed in 1996, but still inconclusive. All the evidence is indirect: no actual organisms that are alive now, and no remnants of life that couldn't possibly have been anything else, have been found. • The Viking 1 and 2 landers on Mars (in 1976) made chemical tests, which were inconclusive. The surface of Mars is hostile to life, because of solar ultraviolet radiation (since Mars has no ozone layer). But what about life underground? • Recent discovery: there is abundant life deep underground inside Earth, where the Sun never shines. • Deep-sea vents in Earth's oceans are very productive ecosystems. Some of the most primitive life forms on Earth are found there. Did life originate there? • Does this imply that Europa, Ganymede, and Callisto are likely places to find life? • Life on extrasolar planets: NASA's Terrestrial Planet Finder spacecraft (TPF) • Follow-up to TPF: get spectra of an extrasolar planet atmospheres, and search for oxygen (O2) or other out-of-equilibrium chemistry: sign of life? Why do we suspect life in the Universe is so common, anyway? • The Miller–Urey experiment (1952): Enclose some of the most primitive gases that exist, e.g. water vapor (H2O), ammonia (NH3), methane (CH4), and add electricity (or some other energy input). => It directly makes amino acids and proteins, the stuff of life! We would therefore expect any new planet to be knee-deep in protein, and indeed, we do see complex organic material (organic = containing carbon), everywhere we look. "Brown, organic, tarry gunk" is seemingly everywhere it can exist in space. - Carbonaceous asteroids (the most common type) and meteorites - Planetary rings (of Uranus and Neptune; Jupiter's are dust, Saturn's are ice) - Planetary satellite atmosphres: - Titan (the large satellite of Saturn) - Triton (the large satellite of Neptune) - Planetary atmospheres (Jupiter and Saturn have brown, yellow, red clouds) - Comets (the nucleus of Halley's comet was black, not white like a snowball) - Comet Shoemaker-Levy 9 collided with Jupiter in 1994, and made Earth-sized clouds of organic compounds in Jupiter's atmosphere! - Dark nebulae, the sites of star formation What any discussion of "life in the Universe" is almost certainly not about: Unidentified Flying Objects (UFOs), or "flying saucers." (a) Hoaxes are common. So far, the only evidence we have is someone's say-so. No clear, unambiguous physical evidence has ever been found. Typical physical evidence consists mainly of broken tree branches and disturbed soil. (b) False alarms: Venus, atmospheric phenomena, e.g. sundogs, haloes, glories, mirages. There are many unfamiliar phenomena in the sky. How many are truly unidentifiable, and not just unidentified? (c) An especially unlikely explanation is that conspiracies, particularly by the U.S. government, are keeping this evidence "secret." It is strange, then, that we daily see the government unable to keep secrets about even the most obvious things, e.g. certain embarrassing things about Bill Clinton, or atomic bomb designs. A finding of this magnitude couldn't be kept secret. It wouldn't be kept secret, either. No scientist, government, or journalist would hesitate at the chance for fame. Discuss: (a) What's wrong with the Drake equation? Why is it not useful science? (b) What are some possible solutions to the Fermi paradox? (c) Can you think of any questions to ask an extraterrestrial, the correct answer for which would clearly establish whether that person was an extraterrestrial, or not?