Yesterday science and space news sites announced the first confirmed discovery of an amino acid on a comet. The revelation came from a new analysis of samples returned to Earth by NASA's Stardust spacecraft, which collected the samples from the tail of Comet Wild 2 in 2004.
This is news because amino acids are one of the building blocks of life. They form molecular proteins, which are an integral part of every living cell. The discovery suggests that amino acids may have been delivered to Earth via space, in a sense jump-starting the processes of organic chemistry that led to life here. Amino acids have already been found in meteorites collected on Earth. The simplest amino acid, called glycine, is the type recovered by Stardust. Glycine was also reportedly detected in interstellar space in 2002.
An interesting backdrop to this story is the steadily growing number of extrasolar planets detected by Earth-based and orbiting telescopes. Last November I posted 322 and Counting, which referenced the number of planets known at the time and also mentioned something called The Exoplanets Encyclopedia, a site that keeps tabs on the number of discoveries.
Here's a brief update: the resource's correct name is The Extrasolar Planets Encyclopaedia, and it's interactive catalog also tracks the number of planets by methods of detection, the number of known planetary systems, and the number of multiple planet systems.
So what are the current figures? The most recent totals (as of August 13) are 373 extrasolar planets, 316 planetary systems, and 39 multiple planet systems. Planetary systems include planets, but also other objects such as moons, asteroids, comets, and cosmic dust. Multuiple planet systems have more than one known planet in orbit around a star.
An obvious question comes to mind: Is it possible that some of those comets or grains of cosmic dust in planetary systems so far away contain glycine?
No one knows.
Meanwhile, it's important to remember the vast majority of known exoplanets are gas giants, also called hot Jupiters. Gas giants have masses similar to or greater than Jupiter but their orbits are much closer to their parent stars than Jupiter's is to the Sun. This explains their high number; gas giants exert more obvious gravitational effects on their stars than do smaller planets, and so they're relatively easier to find.
Detecting smaller, potentially Earth-like planets elsewhere in the Milky Way is the promise of NASA's Kepler spacecraft. Kepler was designed to find rocky worlds about the same size as Earth orbiting stars at distances where conditions are more favorable for maintaining liquid water -- in the so-called habitable zone. The idea, of course, is that where there is water, there may be life.
Since its successful launch and orbital insertion in March, engineers have been calibrating the craft's ultra-sensitive focal plane array and making sure all the software is running smoothly. An exciting confirmation that Kepler's systems are performing precisely as planned was announced less than two weeks ago.
On August 6, mission scientists reported Kepler test data revealed the atmosphere of a known gas giant called HAT-P-7b, some 1,000 light years from Earth. HAT-P-7b orbits its star every 2.2 days and its orbit is so close-in that the planet literally glows with heat. According to NASA's press release:
"The Kepler measurements show the transit from the previously detected HAT-P-7. However, these new measurements are so precise, they also show a smooth rise and fall of the light between transits caused by the changing phases of the planet, similar to those of our moon. This is a combination of both the light emitted from the planet and the light reflected off the planet. The smooth rise and fall of light is also punctuated by a small drop in light, called an occultation, exactly halfway between each transit. An occultation happens when a planet passes behind a star.
The new Kepler data can be used to study this hot Jupiter in unprecedented detail. The depth of the occultation and the shape and amplitude of the light curve show the planet has an atmosphere with a day-side temperature of about 4,310 degrees Fahrenheit. Little of this heat is carried to the cool night side. The occultation time compared to the main transit time shows the planet has a circular orbit. The discovery of light from this planet confirms the predictions by researchers and theoretical models that the emission would be detectable by Kepler."
In other words, the spacecraft's incredibly sensitive systems are up to the job of detecting Earth-sized planets. Kepler's steady gaze, focal plane array, and software will find them if they're out there.
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