Friday, February 3, 2012

Brave New Worlds

In 1584, the Catholic monk Giordano Bruno, who heroically declared that there were "countless suns and countless earths all rotating around their suns," was accused of heresy and burned at the stake.

The greatest scientists often chase after the mysterious, hidden truths of Nature with an obsessive dedication worthy of a star-struck lover--but, in this case, the pursuit of truth is their passion. As Albert Einstein once said, "Science can only be created by those who are thoroughly imbued with the aspiration toward truth and understanding."

Because of his heretical beliefs, Bruno gained the enmity of the Inquisition in Naples, and he was imprisoned for eight years and interrogated regularly. When, in the end, he heroically stood up for what he believed in and refused to recant, he was burned at the stake.

Giordano Bruno gave his life for what he believed was true, and we now know that he was right. As he once said: "Truth does not change because it is, or is not, believed by the majority of the people."

No bonfire lit by the ignorant and intolerant can ever lay ashes to the truth.

Less than twenty years ago, astronomer Dr. Geoffrey W. Marcy, now at the University of California at Berkeley, stood before an audience at a meeting of the American Astronomical Society in San Antonio, Texas. Dr. Marcy stunned his audience with the discovery of two brave new worlds--two extrasolar planets (or exoplanets) twirling around stars beyond our Sun. This proved to be only the tip of the iceberg--a very, very big iceberg. We now know of thousands of planets that circle stars other than our Sun and, based on this, we now suspect that there are billions of planets in our Galaxy alone--and there are billions and billions of galaxies dwelling in that relatively small portion of our Universe that we can observe.

Dr. Marcy and his team of planet-hunters went on to discover 70 of the first 100 exoplanets. The techniques employed by these trail-blazing astronomers eventually were used to find and characterize over 400 planets twirling around stars other than our own.

Planets seem to be as common as flecks of dust floating around in a dark attic. On February 2, 2011, astronomers from NASA's highly successful planet-hunting Kepler Mission shocked the world with the announcement of the existence of 1200 exoplanet "candidates". Mission leader Dr. William Borucki commented to the press that "The fact that we've found so many planet candidates in such a tiny fraction of the sky suggests that there are countless planets orbiting stars like our Sun in the Galaxy. Kepler can find only a small fraction of the planets around the stars it looks at because the orbits aren't aligned properly. If you account for those two factors, our results indicate there must be millions of planets orbiting the stars that surround our Sun." Of those 1,200 exoplanet candidates, Kepler scientists announced that about one-third were discovered frolicking in planetary systems hosting two or more planets--including one planetary system containing at least six planets.

The Kepler spacecraft is a U.S. space-borne observatory that is part of NASA's Kepler Mission. The primary goal of Kepler is to hunt down Earth-like worlds circling stars beyond our own Sun, dwelling in our Galaxy. The spacecraft, launched in March 2009, was named after the great 17th century German astronomer Johannes Kepler. The mission was specially designed to survey a small region of the Milky Way in order to hunt for dozens of Earth-like planets in or near the "habitable zone". Planets dwelling in the habitable zones of their stars enjoy comfortable temperatures that are not too hot, not too cold, but just right for water to exist in its life-friendly liquid state, which is necessary for the evolution of life as we know it. Kepler's goal is to determine how many of the billions and billions of stars in our Galaxy host such "Goldilocks" planets. It sports only one instrument--a photometer that keeps an unblinking eye on a small patch of sky in order to monitor the brightness of more than 145,000 main-sequence (hydrogen-burning) stars in a stationary field of view. This precious data is then dispatched back to Earth-bound astronomers, who then analyze it to detect the periodic dimming of a star's light that hints of an exoplanet transiting in front of the face of its parent star.

The recent discoveries of so many exoplanets has resulted in a revolutionary alteration in our scientific understanding. Our Solar System seemed to be unique in the cosmic scheme of things until 1994, when the discovery of the first exoplanets was announced. Now we know that our own Solar System, composed of our bedazzling golden Sun and its charming retinue of eight major planets, is only one of billions--there are other beautiful parent stars winking with incandescent light, encircled by their own families of planet-children that all possess their own special charms. We now know of planets that orbit binary stars--planets that circle two suns, just like the fictitious "Tatooine" of Star Wars. And we also know that there are planets that have no star at all, but float freely around the Galaxy like orphans bereft of their parent. We know of many weird and wonderful worlds that jitterbug around our Galaxy, dancing around their stars. We know of brave new worlds that were unimaginable less than a generation ago--a planet composed of diamond and a "miniature" planetary system where tiny planets circle a small ruby-red star! And we now know of planets that dwell in such comfortable orbits around their suns that they, like our own Earth, might host living creatures.

Planet-hunters are seeing planets everywhere! The recent avalanche of exoplanetary discoveries clearly shows us that our Universe churns out planets very easily--and that these abundant worlds are very diverse in their charming attributes.

If it is possible for a star to give birth to a planet, it will. Most of the planets that have been spotted by astronomers so far have been giants--similar in mass and size to Jupiter. The original Doppler shift (radial velocity) method, that was used by Dr. Marcy and his colleagues, hunts for the minute wobble induced by an orbiting planet on its star. This method favors the detection of giant planets (like Jupiter), hugging their stars in extremely close orbits--hence their name: "Hot Jupiters".

However, with more recent advances made in the extremely successful, trail-blazing radial velocity method, coupled with the successful launch of the Kepler Space Telescope, which utilizes the transit detection method (the passing of a planet in front of the face of its parent star, as seen from Earth), planetary systems composed of much smaller and lower-mass planetary children are now being spotted for the first time. We are now finding other Earth-sized planets--and some of them might very well be inhabited.

One of the most recent discoveries made by the prolific Kepler telescope shows two rocky, approximately Earth-sized planets twirling in tight orbits around a star very much like our own Sun, dubbed Kepler-20, which resides a mere 950 light-years away.

Both of these small planets huddle far too close to their parent star to have permitted the evolution of delicate living things. But the good news is that the duo represents the very first truly Earth-sized worlds confirmed by the Kepler team. Discovering habitable distant worlds--Earth-like planets dwelling at that precious Goldilocks distance from their stars--is the Holy Grail of the Kepler planet-hunters.

Dr. David Charbonneau, an astronomer at the Harvard-Smithsonian Center for Astrophysics (CfA) in Cambridge, Massachusetts, and a coauthor of the study announcing the discovery of the duo, noted to the press in January 2012, that "The hunt is on to find a... true Earth twin." The study was published online December 20, 2011 in the journal Nature.

One of the little planets, dubbed Kepler-20e, is a bit smaller than the planet Venus--0.87 times as wide as Earth--and zips around its parent star in a mere 6.1 Earth-days. The other, Kepler-20f, is 1.03 times as wide as our planet, and is also quite zippy, twirling around its star in a mere 19.6 Earth-days. It is thought that because both planets are so comparatively small, they are probably composed of the same rocky stuff that makes up our planet, as well as the three other terrestrial planets: Mercury, Venus, and Mars.

The architecture of the Kepler-20 system is bizarre. The planetary system is composed of three large planets (Kepler-20b, c, and d) and the Earth-sized duo. All five planets hug their parent star very tightly. In fact, all five of them are closer to their star than Mercury is to our Sun! Even weirder, the planetary system is not organized at all like our own Solar System. Our Solar System is very neatly divided, with four small rocky terrestrial planets orbiting relatively close to the Sun, and the four giant planets orbiting further away. Of the four large planets, Jupiter and Saturn are gas giants with immense gaseous atmospheres, and possibly no solid surface, while Uranus and Neptune are ice-giants, which have cores of icy-rocky stuff encased by heavy gaseous atmospheres--that are not as heavy as those possessed by the true gas giants. In our Solar System, the terrestrial planets and the giant planets are very neatly separated by the mostly rocky objects inhabiting the asteroid belt.

The Kepler-20 system is a lot messier than our familiar Solar System. Moving out from the star, the five worlds alternate in size, with the little twerps surrounded on either side by their larger sister-planets. Dr. Didier Queloz, an astronomer and planet-hunter at the Observatoire de Geneve in Switzerland, noted in the February 9, 2012 issue of Nature: "In contrast to the Solar System, where small rocky planets lie close to the Sun but the gas giants are far from it, these planets have no obvious hierarchical orbital location."

As Alice, lost in Wonderland said, things just keep getting "curioser and curioser." In about 5 billion years, our friendly, golden Sun will swell to monstrous size and turn blood-red. In this red-giant phase, the Sun's atmosphere will float out beyond Earth's orbit, and our Star will cannibalize most of its inner-planetary children--Mercury, Venus, and our Earth. It is thought that these three planets will be vaporized by the fiery heat of our Sun on steroids.

However, the recent discovery of a bizarre planetary system indicates that our beloved inner planets may not be so doomed. Dr. Stephane Charpinet and colleagues announced the weird discovery of an exoplanetary system that had possibly survived the cruel red fires of its own parent star, dubbed KIC 05807616. The findings, also derived from the Kepler Mission, were presented in the 22/29 December 2011 issue of Nature. Dr. Charpinet, of the Universite de Toulouse in France, and his team, reported what may be two tiny planets circling an elderly star--classified as a hot B subdwarf. Before KIC 05807616 had evolved into this very hot small blue star, it had been a star like our own Sun that had later swelled into a cannibalizing red giant. The two tiny planets twirl in orbits that hug this evolved little star--at distances that amount to less than one percent of the Earth-Sun separation. At these very close distances, both little planets would have been swallowed by their parent star in its red giant phase.

Yet, these little planets are there. How did they survive?

Dr. Charpinet and his colleagues believe that the little planets were born much farther away from their star, and that their orbits were eventually sucked inward during the star's expansion to its red giant phase, which ultimately swallowed the planets. In this scenario, the doomed duo would have originated as massive gas giants, like our Solar System's Jupiter and Saturn. However, their heavy gaseous atmospheres would have evaporated when the planets were swallowed by their parent star. All that now remains of the terrible feast are two barren cores of rock--the pathetic remnants of what once were two gigantic gaseous planets.

The prospect of planets being spotted alive and well in close orbit around an elderly star, long past its red giant phase, is certainly of great interest. Sun-like stars spend billions of years happily fusing hydrogen into helium before experiencing a sudden, violent growth spurt that marks their rite of passage into the red giant stage. The swelling of our Sun into this phase of its evolution will inevitably destroy any life that may still be dwelling on Earth. However, the existence of these little exoplanets circling an evolved star suggests the wonderful possibility that all inner planets are not necessarily devoured by their red-giant parent stars.

In February 2012, researchers, also at CfA, announced the discovery of an entirely new and strange exoplanet, composed not of rock or gas--but of water, very hot water!

The planet is "a waterworld enshrouded by a thick, steamy atmosphere," they said in a statement, after observing the weird world with NASA's venerable Hubble Space Telescope.

Astronomer Dr. Zachary Berta of CfA told the press on February 21, 2012 that "GJ1214b is like no planet we know of. A huge fraction of its mass is made up of water."

It is obvious, at this point, that astronomers are spotting planets here, there, and everywhere!

The discovery of a potentially habitable exoplanet was announced in February 2012. This Goldilocks planet circles a nearby star dubbed GJ667C. The planet, GJ667Cc twirls around in a triple star system a mere 22 light-years from Earth. It weighs at least 4.5 times as much as our planet, which makes it a so-called "super-Earth."

Furthermore, a recent survey using gravitational microlensing, whereby the light of a star is bent by a foreground object, resulting in its magnification, indicates that there are probably more planets than stars in the Milky Way--and that small planets like Earth are more common than gas giants like Jupiter and Saturn, and ice-giants like Uranus and Neptune! Gravitational microlensing permits the detection of small planets in wide orbits around their stars, in contrast to the Doppler technique. This finding was announced in January 2012 by Dr. Arnaud Cassan of the Paris Institute of Astrophysics, who led the research team.

The truth does not change whether it is believed or not. About 300,000,000 years ago, humanity's ancestral organisms commenced their momentous Great Crawl out of Earth's primeval waters to evolve into land-dwelling creatures. With the curiosity so characteristic of our adventurous species, we now take to flight, soaring high beyond Earth's clouds and into space--and with a lucky White Rabbit to guide us into our Cosmic Wonderland, we begin a new stage, from land-dwelling creatures to space-farers. And we seek in the wild wilderness of the Universe others who share it with us.

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