Kepler takes to the heavens to look for other Earths

By Matt Ford

Just seconds before 10:50pm Friday night on the east coast, a Delta II rocket carried NASA's tenth item in its "discovery" series, the Kepler Mission, into the night sky. The Kepler Mission has a singular focus: to search for other Earths. In pursuit of this goal, it is going to spend at least three and a half years, and possibly up to six, searching a single patch of the heavens for other planets that exist in the habitable zone of stars in the Milky Way.

In 1960, at the Green Bank meeting in Green Bank, West Virginia, a group of astronomers, physicists, biologists, and other scientists gather and established SETI as a scientific endeavor. At this meeting, Prof. Frank Drake put forth what is now termed the "Drake equation":

It attempts to ascertain the average number of civilizations that we may have the ability to contact in the Milky Way at any given time. In the equation, R* is the rate of star formation, f_p is the fraction that contain planets, n_e is the number of habitable planets, f_l is the fraction that develops life, f_i is the fraction that develops intelligent life, f_c is the number of civilizations scientifically advanced enough to contact us, and L is the length of time that civilization lasts. Using Drake's 1960 values, he calculated that there would be 10 civilizations, on average, that we may be capable of communicating with.

The equation draws a great deal of criticism from those who claim the values for some of the terms are at best arbitrary and unknowable. Over the past 49 years, we have gotten a much better idea as to the rate of star formation in the Milky Way (R*), and in the past decade we are starting to get a handle on the number of exosolar planets that exist (f_p). The Kepler Mission hopes to indirectly answer what fraction of stars have rocky, earth-sized planets that exist in the habitable zone about a star (n_e)—the region of space near a star where liquid water exist as a stable phase.

So far, 342 exosolar planets have been detected by a variety of indirect—and a few direct—measurements. The vast majority of the exosolar planets found have been gas giants orbiting close to their stars. Known as hot Jupiters, these are planets that have a low probability of supporting life. The Kepler Mission will use a single piece of observational equipment—a highly advanced photometer—to look for Earth-like exosolar planets transiting their host star.

A transit is the name given to a planet passing in between us and its host star; such an event would be observed as a slight change in the output of the star. For an Earth-sized planet transiting a Sun-sized star, the change in the star's output would be less than 84 parts per million, and there would be less than a one percent chance of the transit even being viewable from Earth. Kepler's photometer is so sensitive that it will be capable of detecting a 20 parts-per-million change in stellar output in a star that is 250 times fainter than any that can be seen with the naked eye.

To rule out false positives, an object will need to make at least three transits with a consistent period and change in brightness. In order to maximize the chances of seeing such a rare event, the Kepler Mission will only look at a single area of the sky. For the next three and a half years, Kepler will look towards the constellations Cygnus and Lyra and stare at the over 100,000 stars in that region. The spacecraft's orbit will not be about the Earth itself, rather it will be placed into an Earth-trailing heliocentric orbit, which will allow for a very stable pointing attitude.

While in this orbit, different classes of planets will be discovered within different time frames. The first to be spotted will be the hot Jupiters, gas giants orbiting close to their host stars within a period of only a few days. Once about a year's worth of data is collected, Mercury-like planets—those with an orbit of a few months—will be able to be picked out. For planets like Earth, which require a full year to orbit a star, it will take the full three years of mission time to be able to conclusively identify these objects. As one mission scientist quipped, they are not looking for ET, but they may find ET's home.

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Cannibalistic Jupiter ate its early moons

by Marcus Chown

Jupiter now has only four large moons, but in the early days of the solar system it may have had 20 or more (Image: JPL / NASA)

THE four giant "Galilean" moons orbiting Jupiter are the last survivors of at least five generations of moons that once circled the gas giant.

"All the other moons - and there could have been 20 or more - were devoured by the planet in the early days of the solar system," says Robin Canup of the Southwest Research Institute in Boulder, Colorado.

The four Galilean moons have played a key role in the history of science - their discovery by Galileo 400 years ago provided irrefutable evidence that not all bodies orbited the Earth. But until recently, nobody had suspected that Jupiter had once had many more moons.

Astronomers have long been aware of a mystery thrown up by simulations of the way Jupiter and its moons formed, says Canup. These models indicate that the mass of the debris disc around Jupiter, from which the moons formed, was several tens of a per cent of the mass of giant planet. And yet only 2 per cent is enough to make the moons we see today.

Now Canup and her colleague William Ward believe they know why. The extra mass can be explained if other moons formed while the debris disc was still present (www.arxiv.org/abs/0812.4995). "A key process is therefore the interaction between the growing moons and the disc material still flowing in from the solar system," says Canup. This interaction would have caused the early moons to spiral in towards Jupiter and eventually be "eaten".

This would explain the discrepancy in the earlier simulations, says Canup: as one set of moons was swallowed, a new set immediately began to form. "There could have been five generations of moons," she says. "The current Galilean moons formed just as the inflow of material into the disc from the solar system choked off, so they escaped the fate of their unfortunate predecessors."

According to Canup and Ward, in each generation the total mass of the moons was the same, but the number of moons could have varied. "We think something similar happened around Saturn, where the last generation contained one giant moon - Titan," says Canup.

This could have implications for the solar system as a whole. Rocky planets may take as long as 10 million years to aggregate, chunk by chunk. The process continues long after the debris disc around the sun has blown away, so these planets would not have been at risk of spiralling inwards.

In contrast, the gaseous cores of gas giants like Saturn and Jupiter condense out of the solar debris disc very quickly via gas shrinkage. This means they would have had time to interact with the debris disc. John Papaloizou of the University of Cambridge says it is entirely conceivable that the sun may have swallowed numerous gas cores before the current stable configuration of the solar system emerged.

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U.N. report: Forestry can create 10 million jobs

By Katy Byron

(CNN) -- The United Nations is urging countries to invest in green jobs working with "sustainable forest management" to address the growing problem of unemployment worldwide.

A deforested area appears in a rain forest in Brazil's Para state in October.

At least 10 million such jobs could be created, the U.N. Food and Agriculture Organization will say in a report to be released this week.

The report does not mention any countries but is aimed at "mainly regions with substantial rural unemployment and degraded land areas," said C.T.S. Nair, chief economist in the U.N. Forestry Department and one of the authors of the report.

While all countries could benefit from investing in these green jobs, Nair said, Asia and Africa -- and to some extent Latin America -- could benefit the most. India, China and almost all countries in Africa stand to benefit, he added.

The United Nations said it already is seeing indications that some countries -- such as the United States, India and South Korea -- are interested and taking action to invest in sustainable forest management by making it part of their economic stimulus plans.

Sustainable forestry aims to prevent depletion of forests by managing them and making sure their use does not interfere with natural benefits or the local environment.

For example, in forests where wood is being removed, the United Nations is suggesting that people be hired to monitor and manage how much wood is taken out to ensure the forest does not become depleted and can grow back fully. Managers also would make sure the wood harvest wouldn't affect biodiversity and the water supply.

The report will be discussed and analyzed next week at the U.N. Committee on Forestry meeting in Rome, Italy. The Food and Agriculture Organization has designated next week as World Forest Week.

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