Methane has been identified in the atmosphere of a planet orbiting another star, the first time that astronomers have found an organic compound on a planet outside of our own solar system. Earlier observations suggested that the planet also had water vapor in its atmosphere, and these new observations confirm that as well. This particular Jupiter-class planet is too close to its parent star, and thus too hot, for conditions there to be favorable for life, but the ability to analyze its atmosphere and detect methane there is still an exciting development. Someday the technique should prove useful for examining extrasolar planets that offer more potential as homes for extraterrestrial life.
The Pleiades star cluster is one of the better known open star clusters in the sky, and this time of year it’s high in the sky at mid-evening. If you happen to glance at it, keep in mind a new discovery: The famed Seven Sisters may harbor baby planets. In fact the cluster, about 400 light years away from us, contains a lot more than the seven most prominent stars. One of them, physically similar to our sun but only 100 million years old (just a puppy, in stellar terms), is surrounded by warm dust. Astronomers have concluded that the best explanation for the dust is that small rocky protoplanets around the star are colliding, with one recent collision spawning the dust that now surrounds the star. This is exciting evidence for brand new planetary bodies around this star. This and other evidence seem to indicate that terrestrial planets are probably common. Our own solar system went through a stage of colliding planetary embryos, and in fact the impact that formed the Earth’s moon might have thrown up a similar cloud of dust around our sun. This article from SpaceRef.com and this one from Science Daily have the details.
Another recent story about extrasolar planets described the system of planets around the star 55 Cancri. Four planets were already known to orbit the star, and a fifth was reported a couple of weeks ago. This makes 55 Cancri the biggest extrasolar planetary system known to date. Four gas giants orbit close to the star, with a large gap and then the fifth, newly discovered gas giant. Astronomers guess that the gap might in fact contain a smaller, rocky planet that we can’t see with current technology. The fifth planet is in the habitable zone for its star, and if there is a rocky body near it (another planet or a moon), it’s conceivable that conditions on it could be favorable for life. This article from Live Science has more information.
We have more information today than humans have ever had about what it’s like on other planets. As we learn about the past and present atmospheres and surface conditions on Mars and Venus, we also learn about the ways a planetary atmosphere can go haywire, producing conditions far different from the fine-tuned life-supporting system we thrive in here on Earth right now. This article from Seed Magazine describes what we know of Mars, Venus, and Saturn’s moon Titan, each lacking crucial components that might have made it a more hospitable place for life. Studying other planets can teach us about the complexities of planetary atmospheres, a vital subject with our own atmosphere undergoing a distinct human-generated change. And it also shows us how lucky we are:
“Venus became a desiccated oven, Mars a stale freezer. Comparative planetology teaches us that Earth is balanced between these fates. A stable, comfortable planetary climate, especially in the face of increasing industrial provocation, is not something one can take for granted.”
Even Earth’s climate has not always been equally comfortable for life. Paleontologist and astrobiologist Peter Ward’s Under a Green Sky: Global Warming, the Mass Extinctions of the Past, and What They Can Tell Us about Our Future describes what past climate catastrophes can tell us about our future. This review gave me the heebie-jeebies. Ward’s scenarios for possible futures are based not on models that project current atmospheric and climate conditions into the future, but on data from past occurrences of global warming, and they make for some disturbing reading. I hope we turn out to be a smart enough species to take heed and at least reduce the severity of the changes we’re making to our atmosphere.
Astronomers have discovered more than 200 extrasolar planets so far, and the discovery announced today by an international team of astronomers is one of the most exciting. The star Gliese 581, a red dwarf about 20.5 light-years away from Earth, was already known to have a Neptune-sized planet orbiting it. Further studies with a phenomenally sensitive spectrograph revealed the existence of two more planets orbiting Gliese 581, one of them somewhat bigger than Earth, likely rocky, and at just the right distance from the star for liquid water to be possible on its surface. Astronomers used the spectrograph to observe minute fluctuations in the star’s motion toward and away from us; these tiny wobbles are caused by the gravitational tug of its planets and are visible in the star’s spectrum as tiny red and blue shifts. The planet is much closer to its star than Earth is to the sun, and it orbits the star in about 13 days. The planet’s surface temperature is hospitable to life, even that close to the star, because the star is a good bit dimmer and cooler than the sun.
Liquid water is widely held to be the sine qua none for life, certainly life as we know it, so if this planet does in fact have water on its surface (which we don’t know yet), that would be an even more exciting development. Certainly this is a planet to watch.
In February the Spitzer Space Telescope was able to obtain the first-ever spectrum for an extrasolar planet, an amazing feat. According the current models for how the planet formed, it should have water, but the spectral data from Spitzer didn’t reveal any. However, newly released information based on an analysis of Hubble Space Telescope data does indicate that water is present, the first time we’ve been able to find water on an extrasolar planet. Now, it’s a so-called hot Jupiter, a gas giant orbiting very close to its parent star, so it’s far too hot to be bio-friendly. But still, this is an exciting advance in our knowledge about extrasolar planets. The analysis involved looking at the light from the parent star that filtered through the upper parts of the planet’s atmosphere when the planet passed in front of the star. The transparency of the planet’s atmosphere is different for different wavelengths, and the way it varies with wavelength depends on the chemical composition of the planet. By comparing the actual data to model atmospheres with a variety of plausible compositions, an astronomer at Lowell Observatory was able to determine that the best fit is to an atmosphere that contains water vapor. Spitzer might have missed the water because its spectral signature was obscured by high dust clouds. An alternative theory is that the planet has a fairly constant temperature throughout, which would affect Spitzer’s ability to detect water. In any event, the water does appear to be there. You can read more about it in this story from New Scientist.
For the first time, scientists have directly measured the light coming from planets orbiting another star. The planets are of a type called hot Jupiters–I love the way we have been able to detect so many extrasolar planets that we can cateorize them, by the way–which means they’re gas giants like Jupiter, but are very close to their respective stars. This story really surprised me, because I thought we were years away from having this kind of data for any extrasolar planets yet. Evidently the orbiting Spitzer infrared telescope was able to manage it by getting spectra for the star and the planet together and for just the star, and subtracting the latter from the former. Pretty cool stuff.
The interesting thing about looking at the light from these planets is that observing their spectra gives you information about the composition of their atmospheres, because of the way different elements and chemical compounds absorb light at specific wavelengths and thus provide something of a fingerprint that can be read from a spectrum. Someday astronomers want to be able to observe the spectra of Earth-like extrasolar planets and look for things that tell us about whether the planet might be hospitable to life (e.g., the presence of water) or whether there are any indicators that life might exist, e.g., oxygen (large quantities of oxygen in a planetary atmosphere would suggest the presence of life) or even chlorophyll. So getting these spectra for the hot Jupiters is a very important first step.
The results for these planets are surprising; there was no evidence for several compounds that astronomers expected to find, including water vapor. This article from Scientific American has more details.
The European Space Agency’s COROT spacecraft launched this morning on its mission to identify extrasolar planets. COROT will monitor stars for periodic dimmings that indicate the passage of a planet in front of the star; it will be able to detect rocky worlds several times bigger than Earth (later missions planned by ESA and NASA will be able to find Earth-sized planets in orbits that resemble Earth’s). The mission should notably expand the number of known extrasolar planets and increase the amount of data available to those who study and compare planetary systems. If all goes well, this could be an important step in the search for extraterrestrial life. You can read a news story about the launch and the mission on NASA’s Spaceflight.com page.
There’s been lots of cool extrasolar planet news lately, including some that has implications for whether or not complex life exists elsewhere in the cosmos.
The Hubble Space Telescope has discovered 16 possible new extrasolar planets off toward the center of our galaxy. The SWEEPS project (Sagittarius Window Eclipsing Extrasolar Planet Search) used the HST to repeatedly image a large star field and watch for minute dips in stellar brightness of the sort that would be caused by a planet crossing in front of its parent star and blocking part of its light. There’s a Washington Post article and you can also take a look at an image of the star field with most of the candidates’ stars identified.
Most of the 16 are planet candidates rather than confirmed planets; the way to confirm the discovery would be to measure a wobble in the star’s position caused by the planet tugging on it, but only two of the parent stars are close enough and bright enough for that technique to work. The follow-on to Hubble, the James Webb Space Telescope, will likely be able to make the observations that could confirm whether all of these are in fact extrasolar planets. But even now it looks pretty likely, and this discovery is another indicator of how many planets there are likely to be in the galaxy. As the number of possible planets goes up, the likelihood of finding one with conditions that would support complex life goes up too.
HST has also been involved in another piece of extrasolar planet news. Working with telescopes on the ground, HST has provided some details about the closest extrasolar planet known so far, one around Epsilon Eridani (about 10 1/2 light years away). The latest observations give a precise mass and the angle at which the planet’s orbit is tilted relative to our line of sight. The latter observation is particularly interesting because the angle matches that of a gas- and dust-filled disk around Epsilon Eridani, which is the first direct evidence we’ve got for the theory that planets form out of such disks. Here’s a news story that explains how the observations were made. It’s interesting that some of the ground-based observations came from the University of Pittsburgh’s Allegheny Observatory, which is just four miles north of downtown Pittsburgh and on the flight path of incoming planes bound for Pittsburgh’s airport. I flew into Pittsburgh once and looked down and spotted the little white dots north of the river; I hadn’t realized there was an observatory so close to the city, and I was happy to learn that it still has an active observing program. Astrometry, the precise measurement of stellar positions, does not rely on dark skies (at least not for nearby stars), and so astrometry observations continue. The observations of Epsilon Eridani involved measuring the tiny wobble in its position due to the gravitational pull of its planet.
Another satellite observatory, the infrared Spitzer Space Telescope, has measured temperature differences across the surface of an extrasolar planet, the first time we’ve been able to measure a property of an extrasolar planet that varies across the surface. The planet is a gas giant that orbits close to its star, apparently with one side permanently facing the star. The starward side shows a hot spot that makes a dramatic contrast with the other side of the planet. Here’s a news story with more info.