Universe Today

Look towards the Aquarius constellation in the early morning on May 6. Image credit: NASA. Click to enlarge.
The eta Aquarid meteor shower peaks on May 5th and 6th. The best time to look, no matter where you live, is during the hours before local sunrise on both days.

This is mainly a southern hemisphere shower, but northern observers can see it, too. In the United States, for example, observers far from city lights might see 5 to 10 meteors per hour. In Australia or South America, rates are better, between 15 and 60 meteors per hour.

This year (2005) the eta Aquarid meteors will be streaming from a point in the sky coincidentally close to Mars. The red planet, which is approaching Earth for a close encounter in October 2005, is already eye-catching.

Eta Aquarid meteors come from the most famous comet of all: Halley’s Comet. Our planet passes close to the orbit of Halley’s Comet twice a year. Although the comet itself is very far away [diagram] tiny pieces of Halley are still moving through the inner solar system. They’re leftovers from the comet’s many close encounters with the Sun. Each time Halley returns (every 76 years) solar heating evaporates about 6 meters of ice and rock from its nucleus! Debris particles called meteoroids, usually no bigger than grains of sand, gradually spread along the comet’s orbit forming an elongated stream of space dust. Earth passes through the debris stream once in May and again in October.

The eta Aquarids are named after a star in the constellation Aquarius. The star has nothing to do with the meteor shower except that the shower’s radiant happens to lie nearby. (The radiant of a meteor shower is a point in the sky from which the meteors appear to stream.) The eta Aquarid’s sister shower in October is called the Orionids, after the constellation Orion.

The eta Aquarid radiant never climbs very far above the horizon in the northern hemisphere. That’s why it is a better shower south of the equator. Most years northerners count about 10 eta Aquarid meteors per hour, while southerners see 3 to 6 times that many.

Northern sky watchers sometimes spot spectacular “Earth grazers,” while the active eta Aquarid radiant is low on the horizon. These are meteors that skim horizontally through the upper atmosphere. “Earth grazers” are typically slow and dramatic, streaking far across the sky. The best time to look for Earthgrazers is 2:00 to 2:30 a.m. local time.

Middle-latitude sky watchers in both hemispheres will see the eta Aquarid radiant rise over the eastern horizon at approximately 2:30 a.m. local time. Aquarius is a fairly dim constellation. The nearest bright star is 1st magnitude Fomalhaut in the constellation Piscis Austrini. Fomalhaut is a good finder star for sky watchers in the south, but it’s not much use to northerners because of its low altitude. In Sydney, Australia, for example, Fomalhaut will be visible at 4 a.m. at an elevation of +25 degrees, just above and westward of the shower’s radiant.

Experienced meteor watchers suggest the following viewing strategy: Dress warmly. Bring a reclining chair, or spread a thick blanket over a flat spot of ground. Lie down and look up somewhat toward the east. Meteors can appear in any part of the sky, although their trails will tend to point back toward the radiant.

Original Source: NASA Spaceweather

Image credit: NASA
Things seem to start simple then get more complex. Life is like that. And perhaps nowhere is this notion truer than when we investigate the origins of life. Did the earliest single cell life-forms coalesce from organic molecules here on Earth? Or is it possible that – like dandelions wafting spore above spring grass – cosmic winds carry living things from world to world later to take root and flourish? And if this is the case, how precisely does such a “dia-spora” occur?

450 years before the common era, Greek philosopher Anaxagoras of Ionia proposed that all living things sprung from certain ubiquitous “seeds of life”. Today’s notion of such “seeds” is far more sophisticated than anything Anaxagoras could possibly envision – limited as he was to simple observations of living things such as budding plant & flowering tree, crawling & buzzing insect, loping animal or walking human; not too mention natural phenomena like sound, wind, rainbows, earthquakes, eclipses, Sun, and Moon. Surprisingly modern in thought, Anaxagoras could only guess as to the details…

Some 2300 hundreds years later – during the 1830s – Swedish chemist J?ns Jackob Berzelius confirmed that carbon compounds were found in certain meteorites “fallen from the heavens”. Berzelius himself however, held that these carbonates were contaminates originating with the Earth itself – but his finding contributed to theories propounded by later thinkers including the physician H.E. Richter and physicist Lord Kelvin.

Panspermia received its first real treatment by Hermann von Helmholtz in 1879, but it was another Swedish chemist – 1903 Nobel Prize winning Svante Arrhenius – who popularized the concept of life originating from space in 1908. Perhaps surprisingly, that theory was based on the notion that radiation pressure from the Sun – and other stars – “blew” microbes about like tiny solar sails – and not as the result of finding carbon compounds in stony meteorite.

The theory that simple forms of life travel in ejecta from other worlds ? embedded in rock blasted from planetary surfaces by the impact of large objects – is the basis for “lithopanspermia”. There are numerous advantages to this hypothesis – simple, hardy forms of life are often found in mineral deposits on Earth in forbidding locales. Worlds – such as our own or Mars – are occasionally blasted by asteroids and comets large enough to hurl rock at speeds exceeding escape velocities. Mineral in rocks can shield microbes from shock and radiation (associated with impact craters) as well as hard radiation from the Sun as stony meteors move through space. The hardiest forms of life also have the ability to survive in a cold vacuum by going into stasis – reducing chemical interactions to zero while maintaining biological structure well enough to later thaw and multiply in more salubrious environs.

In fact several examples of such ejecta are now available on earth for scientific analysis. Stony meteors can include some very sophisticated forms of organic materials (carbonaceous chondrites have been found that include amino and carboxylic acids). Fossilized remnants from Mars in particular – though subject to various non-organic interpretations – are in the possession of institutions such as NASA. The theory and practice of “lithopanspermia” looks very promising – although such a theory can only explain where the simplest forms of life come from – and not how it originated to begin with.

In a paper entitled “Lithopanspermia in Star Forming Clusters” published April 29, 2005, cosmologists Fred C. Adams of the University of Michigan Center for Theoretical Physics and David Spergel of the Department of Astrophysical Sciences of Princeton University discuss the probability of carbonaceous chondrite distribution of microbial life within early star clusters. According to the duo, “the chances of biological material spreading from one system to another is greatly enhanced … due to the close proximity of the systems and low relative velocities.”

According to the authors, previous studies have looked into the likelihood that life-bearing rocks (typically exceeding 10 kgs in weight) play a role in the spread of life within isolated planetary systems and found “the odds of both meteroid and biological transfer are exceedingly low.” However “odds of transfer increase in more crowded environments” and “Since the time scale for planet formation and the time that young stars are expected to live in birth clusters are roughly comparable, about 10 – 30 million years, debris from planet formation has a good chance of being transferred from one solar system to another.”

Ultimately Fred and David conclude “young star clusters provide an efficient means of transferring rocky material from solar system to solar system. If any system in the birth aggregate supports life, then many other systems in the cluster can capture life bearing rocks.”

To arrive at this conclusion, the duo performed “a series of numerical calculations to estimate the distribution of ejection speeds for rocks” based on size and mass. They also considered the dynamics of early star forming groups and clusters. This was essential to help determine rock recapture rates by planets in neighboring systems. Finally they had to make certain assumptions about the frequency of life-encapsulated materials and the survivability of life-forms embedded within them. All this led up to a sense of “the expected number of successful lithopanspermia events per cluster.”

Based on methods used to arrive at this conclusion and thinking only in terms of present distances between solar systems, the duo estimated the probability that Earth has exported life to other systems. Over the age of life on Earth (some 4.0 Byr) Fred and David estimate that the Earth has ejected some 40 billion life-bearing stones. Of the estimated 10 bio-stones per annum, nearly 1 (0.9) will land on a planet suitable for further growth and proliferation.

Most cosmologists tend to address the “hard-science questions” of the origin of the Universe as a whole. Fred says that “exobiology is intrinsically interesting” to him and that he and “David were summer students together in New York in 1981” where they worked on “issues related to planetary atmospheres and climate, issues that are close to questions of exobiology.” Fred also says that he “spends a healthy fraction of research time on problems associated with star and planet formation.” Fred acknowledges David’s special role in thinking “up the idea of looking at panspermia in clusters; when we talked about it, it became clear that we had all the pieces of the puzzle. We just had to put them together.”

This interdisciplinary approach to cosmology and exobiology also led Fred and David to look at the question of lithopanspermia between clusters themselves. Again using methods developed to explore the proliferation of life within clusters, and later applied to the exportation of life from the Earth itself to other non-solar system planets, Fred and David were able to conclude that “a young cluster is more likely to capture life from outside than to give rise to life spontaneously.” And “Once seeded, the cluster provides an effective amplification mechanism to infect other members” within that cluster itself.

Ultimately however, Fred and David can not answer the question of where and under what conditions the first seeds of life took form. In fact, they are willing to admit that “if the spontaneous origin of life were sufficiently common, there would be no need for any panspermia mechanism to explain the presence of life.”

But according to Fred and David, once life gets a foothold somewhere, it manages to get around quite handily.

Written by Jeff Barbour