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Ask an Astrobiologist

Ask an Astrobiologist

David Morrison

Volume 22.2, Summer 2012

Question: What is the history behind Astrobiology? How was it founded and how does it differ from Exobiology?

Astrobiology is the study of the origin, evolution, distribution, and future of life in the universe. This interdisciplinary field encompasses the search for habitable environments in our solar system and habitable exoplanets outside our solar system, the study of prebiotic chemistry, laboratory and field research into the origins and early evolution of life on Earth, and studies of the potential for life to adapt to challenges on Earth and in outer space. Astrobiology ad­dresses the questions of whether life exists beyond Earth and how humans can detect it if it does.

Astrobiology grew out of a previous discipline called “exobiology,” and often the two terms are used interchangeably. Exo­biology, however, is somewhat narrower—it focuses on the search for life beyond Earth and the effects of extraterrestrial environments on living things. The transition to the term astrobiology at NASA in the mid-1990s was a response to several discoveries that suggested that the space exploration program might help provide answers to fundamental questions about the origin, distribution, and future of life on Earth as well as beyond. These events included the evidence that Mars rock ALH84001 might contain microbial fossils, the amazing life found deep in the ocean at hydrothermal vents, recognition that Jupiter’s moon Europa had a vast ocean of liquid water, and the discovery of the first planets orbiting other stars. Today astrobiology has become a major area of space research globally, although we have not yet found evidence of life on other worlds.

Question: How could we find life on other planets? Does life in the universe have to be rare because life requires very specific environments?

Never having found any life outside the Earth, we cannot answer the question of whether life is abundant or rare. However, recent research with the Kepler mission and other astronomical observations suggests that habitable planets are common, with Earth-sized planets within the habitable zone orbiting at least 1 percent of stars. Even if only one-tenth of these planets actually support life, there are still roughly a billion living planets in our galaxy alone. We have no reason to think that our own planet Earth is unique or even unusual among the rocky worlds orbiting distant stars. But until we have data, this is just speculation.

There are three ways that we might discover life on other worlds: (1) Within our solar system, where we have direct access through spacecraft missions. We are especially interested in Mars, Jupiter’s moon Europa, and Saturn’s moon Titan. It is possible to search directly for microbial life on these worlds. (2) If abundant microbial life exists on an Earth-like planet orbiting another star, it is likely to change the atmosphere in ways that can be detected using large telescopes. On Earth, life has contributed oxygen and methane to our atmosphere, both “biosignature gases” that can be detected remotely. (3) Finally, if an intelligent, technological civilization has developed on any planet, and if “they” choose to broadcast radio or optical signals, then perhaps these signals could be detected by SETI searches.

Question: Why is the U.S. government building bunkers to house the elite in case of a global disaster? Also I heard about two suns in China. Is one of them Nibiru?

These two questions both illustrate the Big Lie, which can happen when a story goes viral on the Internet. Both are old hoaxes that just won’t go away. The government bunker rumor has two sources. First is the well-known fact that the U.S. government built many deep air raid shelters during the early stages of the Cold War, including the underground complex at Greenbrier, West Vir­ginia, which was supposed to provide protection for the President and his staff, and the Cheyenne Mountain complex in Colorado, which is still used by the Strategic Air Com­mand. Second is an episode on bunkers in Jesse Ventura’s TV series Con­spiracy Theory. Unfortunately, many people don’t realize this is an entertainment show, not journalism—something that is given away by the title, since the phrase “conspiracy theory” implies an interpretation that is not based on facts. But even his episode about shelters is all innuendo; Ventura does not actually interview anyone who claims to have seen one of the phantom “government bunkers.”

The source of the “two suns in China” report is even less well understood by the public. If you watch the original news video with a friend who speaks Chinese, you will see that this is about a single photo, broadcast by a local TV station on a small island near Taiwan. It is based on a still picture (not a video), apparently rephotographed with a hand-held video camera. As far as I can tell, the “two suns” were not seen elsewhere in Taiwan, let alone across China. And obviously if this phenomenon were real, billions of people everywhere could have verified it just by looking up at the Sun.

Question: Is it true that the reason the far side of the Moon has more impact craters than the near side is because the Earth shields the near side from incoming comets and asteroids?

The Earth shield is not large enough to in­fluence crater densities. Just using simple straight-line geometry, you can calculate how much of the lunar sky is obscured by the Earth: about four square degrees out of 41,000 square degrees for the whole sky. Only one in ten thousand incoming projectiles would be intercepted by the Earth. The real reason there are more impact craters on the far side of the Moon is that the near side has a thinner crust that allowed volcanoes to erupt about three billion years ago, and these large lava flows have covered the craters that were formed early in the Moon’s history. It is likely that each side of the Moon has received equal numbers of impacts, but the resurfacing by lava results in fewer craters being visible on the near side than the far side.

Question: I’ve recently been hearing a lot about something called global/solar dimming. Are we headed for another ice age or will some horrid catastrophe be caused by the Sun?

Global dimming or solar dimming usually refers to the reduction in sunlight reaching the Earth’s surface due to atmospheric aerosols (smog). During the middle of the twentieth century, the increase in industrial smog partly compensated for the greater greenhouse effect by adding carbon dioxide into the atmosphere, thereby slowing the global warming that would have been expected. One effect of the environmental movement of the last third of the twentieth century was to clean up the emission of smog, which had the unintended effect of accelerating global warming from the greenhouse effect. The other effect that you mention, a decrease in solar energy output during time of low solar activity, is much smaller. The Sun’s energy output (which we measure with satellites built for that purpose) varies by less than one percent, as you might expect since the number of sunspots or flares at the surface can’t influence the rate of nuclear fusion in the core of the Sun. The Sun’s brightness cannot drop enough to counteract current global warming due to the greenhouse effect. There will be no more ice ages if humans keep polluting the atmosphere with more carbon dioxide and methane and other greenhouse gases.

Question: A recent spate of furious eruptions on the Sun hurled a huge amount of heat toward Earth, the biggest dose our planet has received in seven years. The solar storm of March 8–10, 2012, deposited twenty-six billion kilowatt-hours of energy in the upper atmosphere, enough energy to power every home in New York City for two years. Would this intense heating have any effect on the Earth’s climate?

Your question is an excellent example of how solar activity is being hyped as if it were a major threat to Earth. The Sun is the source of almost all of our energy, and Earth intercepts almost 200 trillion kilowatts from the Sun continuously in the form of light and infrared (heat) radiation. Thus in the three days (seventy-two hours) of March 8 through 10, we received about 1016 kilowatt-hours of ordinary sunlight. Compare this with 26 billion kilowatt-hours from the solar eruption. The energy from the eruption is less than that from sunlight by a factor of nearly a million, negligible compared to regular sunlight. Solar outbursts make no contribution to heating the Earth or to global warming. In the report you read, don’t you think it would have been more realistic if they had noted this fact rather than talk about the solar storm in comparison to the energy needed to light New York City?

David Morrison

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David Morrison is a long-time NASA senior scientist and Committee for Skeptical Inquiry fellow. He now divides his time between the SETI Institute and the NASA Lunar Science Institute. He hosts the "Ask an Astrobiologist" column at NASA's website.