Category Archives: exoplanets

astronomy, exoplanets, gliese 581g

Finding a Habitable Planet

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Not Too Far Away

An artist's concept by Lynette Cook of the planet found around Gliese 581.

The news of a new planet only three times the size of Earth and orbiting in its star’s potentially habitable zone spurs on the great speculation that it’s only a matter of time before we find a planet with some sort of life on it.

The star is called Gliese 581, a red dwarf that lies only 20 light-years from Earth. The planet is called Gliese 581g. This discovery was the result of more than a decade of observations using the W. M. Keck Observatory in Hawai’i.

Finding a planet in a potentially habitable zone means that the planet lies in an orbit around the star that is just far enough away (but not too far away) that liquid water could exist on the planet’s surface.  That water hasn’t yet been found on the Gliese 581g, but the fact that it’s in the right place — the so-called “Goldilocks zone” is important.

Water is one of the prime ingredients for life, along with warmth and organic material.  If water is eventually found on the newly discovered planet, that would make it the most Earth-like exoplanet yet discovered and the first strong case for a potentially habitable one.  To astronomers, a “potentially habitable” planet is one that could sustain life, not necessarily one where humans would thrive.  Having habitable status depends  on more than just water and an atmosphere, but those two factors really raise the odds of the planet being hospitable to life.

So, how did astronomers find this planet?  The research is based on 11 years of observations of Gliese 581 using the HIRES spectrometer on the Keck I Telescope. That instrument lets astronomers make precise measurements of a star’s radial velocity (its motion along the line of sight from Earth). Changes in that radial velocity might indicate that something is tugging on the star, inducing slight changes in its motion in space.  The gravitational influence of an orbiting planet is one reason why we might see periodic changes in the radial velocity of a host star. Multiple planets induce complex wobbles in the star’s motion, and astronomers use sophisticated analyses to detect planets and determine their orbits and masses.

NO Intelligent Life.. or Any Life… Yet

As you might expect, some commentators and reporters in the media and Web-based React-O-Sphere are already breathlessly reporting the discovery of life on that planet.   It isn’t so.  Hasn’t been found. Yet.  The discovery is of a “potentially habitable planet” not an inhabited one. There’s a distinct difference when you stop to think about it.

But, that hasn’t stopped the React-O-Sphere from saying it.  It tells me that those commentators either didn’t read the press releases carefully or didn’t understand them.  This story is a great case for the value of reading comprehension on the part of the media and Web commentators.

For the straight scoop on what HAS been found, check out the link at the top, or go here or here.  That way you can get more of the story — straight from the sources who made the discovery.

european southern observatory, exoplanets, extrasolar planets, Kepler mission

One Star, Two Planets, Big News

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What Are They Like?

This artist’s concept illustrates the two Saturn-sized planets discovered by NASA’s Kepler mission. The star system is oriented edge-on, as seen by Kepler, such that both planets cross in front, or transit, their star, named Kepler-9. This is the first star system found to have multiple transiting planets. Credit: NASA/Ames/JPL-Caltech

It has been almost 20 years since the first extrasolar planets (worlds around other stars) were discovered.  Astronomers suspected they existed, but since tiny worlds can get lost in the glare of their stars’ light, we had to wait until we had the right kinds of instruments to observe distant worlds circling other stars. Today, the number of confirmed exoplanets lies at just under 500, and that number changes almost daily.

The latest news in planet-hunting circles is the discovery of two planets orbiting a star called Kepler-9.  The planets showed up in data taken by the Kepler mission, which is tasked to search for extrasolar planets in an area of the sky in the direction of the constellation Cygnus the Swan (which is high in the northern hemisphere sky these evenings).

Now, there have been lots of extrasolar planets discovered, but this is the first time two have been confirmed orbiting the same star. The planets, named Kepler-9b and Kepler-9c, have masses that are almost that of Saturn in our own solar system. Kepler-9b is the larger of the two and it orbits the star once every 19 days. The smaller Kepler-9c lies farther away and takes 38 days to make a trip around the star.

The Kepler spacecraft observed this system to tack down the precise length of each planet’s orbit around the parent star. This isn’t the only such system that the spacecraft has data for, but it’s the first to be confirmed — a big milestone for the team and the spacecraft.

The planets were discovered as the Kepler spacecraft’s camera measured tiny decreases in the star’s brightness–decreases that occur when a planet moves between us and the star. And yes, even something so small as a planet can have an effect on the star’s brightness, and Kepler is sensitive enough to detect those little dips in the star’s light.  In addition, the distance between each planet and the star can be calculated by measuring the time between successive dips as the planet orbits the star. Small changes in the regularity of these dips can help astronomers determine the masses of planets and detect other non-transiting planets in the system. In fact, the data seem to indicate that there may be at least one other planet in the system–a world about 1.5 times the Earth’s radius that follows a scorchingly short 1.6-day orbit around the star. Kepler scientists are still taking data to make sure that this is another planet and not an anomaly in the data.

The artist’s concept of the two confirmed planets show that these are gas giant-like worlds, so they’re not likely to be places where life is going to exist — at least life as we know it. And, if there IS another planet that’s closer to Earth-size? Well, it’s not likely to be a very hospitable place either. It’s likely a scorchingly hot place with little opportunity for life to take hold.

Kepler’s discovery is the second in a pair of exoplanet finds reported this week. The European Southern Observatory announced earlier that it has found a star that may have at least five planets orbiting around it. Astronomers used the HARPS spectrograph attached to the ESO’s 3.6-meter telescope in Chile to search for the existence of planets in the system. Unlike the Kepler mission, which checks for dips in light intensity of stars with planets in orbit around them, the HARPS insrtrument looks for stellar motions that indicate the existence of planets. The amount of motion tells them the mass of the planets that may exist, and helps them deduce the orbits of those distant worlds. The measurements correspond to planets with masses between 13 and 25 Earth masses. They appear to orbit  the star with periods ranging from about 6 to 600 days. These planets lie between 0.06 and 1.4 times the Earth–Sun distance from their central star. This is actually pretty well-populated system with five massive planets located within 1.4 AU.  By comparison, the Sun has only four planets — and small ones at that — in roughly the same space.

The science of planetary detection is a major growth area in astronomy. With Kepler’s ongoing mission and the ground-based work being done at places such as ESO, I think it’s only a matter of time before the community of worlds that we can detect will be well over a thousand. Now… if we could only find one with life on it!