Artist's rendering of the Giant Magellan Telescope and support facilities at Las Campanas Observatory, Chile, high in the Andes Mountains. Photo by Todd Mason/Mason Productions
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Astronomy organizations in the United States, Australia and Korea have signed on to build the largest ground-based telescope in the world – unless another team gets there first. The Giant Magellan Telescope, or GMT, will have the resolving power of a single 24.5-meter (80-foot) primary mirror, which will make it three times more powerful than any of the Earth’s existing ground-based optical telescopes. Its domestic partners include the Carnegie Institution for Science, Harvard University, the Smithsonian Institution, Texas A & M University, the University of Arizona, and the University of Texas at Austin. Although the telescope has been in the works since 2003, the formal collaboration was announced Friday.
Charles Alcock, director of the Harvard-Smithsonian Center for Astrophysics, said the Giant Magellan Telescope is being designed to build on the legacy of a rash of smaller telescopes from the 1990s in California, Hawaii and Arizona. The existing telescopes have mirrors in the range of six to 10 meters (18 to 32 feet), and – while they’re making great headway in the nearby universe – they’re only able to make out the largest planets around other stars and the most luminous distant galaxies.
With a much larger primary mirror, the GMT will be able to detect much smaller and fainter objects in the sky, opening a window to the most distant, and therefore the oldest, stars and galaxies. Formed within the first billion years of the Big Bang, such objects reveal tantalizing insight into the universe’s infancy.
Earlier this year, a different consortium including the California Institute of Technology and the University of California, with Canadian and Japanese institutions, unveiled its own next-generation concept: the Thirty Meter Telescope. Whereas the GMT’s 24.5-meter primary mirror will come from a collection of eight smaller mirrors, the TMT will combine 492 segments to achieve the power of a single 30-meter (98-foot) mirror design.
In addition, the European Extremely Large Telescope is in the concept stage.
In terms of science, Alcock acknowledged that the two telescopes with US participation are headed toward redundancy. The main differences, he said, are in the engineering arena.
“They’ll probably both work,” he said. But Alcock thinks the GMT is most exciting from a technological point of view. Each of the GMT’s seven 8.4-meter primary segments will weigh 20 tons, and the telescope enclosure has a height of about 200 feet. The GMT partners aim to complete their detailed design within two years.
The TMT’s segmented concept builds on technology pioneered at the W.M. Keck Observatory in Hawaii, a past project of the Cal-Tech and University of California partnership.
Construction on the GMT is expected to begin in 2012 and completed in 2019, at Las Campanas Observatory in the Andes Mountains of Chile. The total cost is projected to be $700 million, with $130 million raised so far.
Artists concept of the Thirty Meter Telescope Observatory. Credit: TMT
Construction on the TMT could begin as early as 2011 with an estimated completion date of 2018. The telescope could go to Hawaii or Chile, and final site selection will be announced this summer. The total cost is estimated to be as high as $1 billion, with $300 million raised at last count.
Alcock said the next generation of telescopes is crucial for forward progress in 21st Century astronomy.
“The goal is to start discovering and characterizing planets that might harbor life,” he said. “It’s very clear that we’re going to need the next generation of telescopes to do that.”
And far from being a competition, the real race is to contribute to science, said Charles Blue, a TMT spokesman.
“All next generation observatories would really like to be up and running as soon as possible to meet the scientific demand,” he said.
In the shorter term, long distance space studies will get help from the James Webb Space Telescope, designed to replace the Hubble Space Telescope when it launches in 2013. And the Atacama Large Millimeter Array (ALMA), a large interferometer being completed in Chile, could join the fore by 2012.
COROT-exo-7b, bottom left dot shadows in front of his central star (artist's impression). Aufgrund der großen Nähe zu seiner Sonne vermuten Forscher Temperaturen von über 1000 Grad Celsius auf dem extrasolaren Planeten. Because of its proximity to large solar researchers suspect temperatures over 1000 degrees Celsius on the extrasolar planets. Bild: Klaudia Einhorn. Image: Klaudia Einhorn.
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The CoRoT satellite has found the smallest terrestrial exoplanet yet, — with a diameter just under twice that of Earth — complete with a rocky surface you could walk on and possibly even oceans to sail across. However, if you traveled there, you might want to bring some protection, as the temperature of this planet is likely very high. CoRoT-Exo-7b is located very close to its parent star, orbiting once every 20 hours. Astronomers estimate temperatures on the planet could be between 1000 and 1500°C and it possibly could be covered in lava or water vapor. This latest exoplanet was detected as it transited in front of its parent star, dimming the light from the star just enough to be noticeable.
The parent star lies about 140 parsecs from Earth, located about half way between the star Sirius in Canis Major and Betelgeuse, the red giant star in Orion.
The internal structure of CoRoT-exo-7b particularly puzzles scientists; they are unsure whether it is an ‘ocean planet’, a kind of planet whose existence has never been proved so far. In theory, such planets would initially be covered partially in ice and they would later drift towards their star, with the ice melting to cover it in liquid. COROT detects small, transiting exoplanet. Credits: CNES
“This discovery is a very important step on the road to understanding the formation and evolution of our planet,” said Malcolm Fridlund, ESA’s CoRoT Project Scientist. “For the first time, we have unambiguously detected a planet that is ‘rocky’ in the same sense as our own Earth. We now have to understand this object further to put it into context, and continue our search for smaller, more Earth-like objects with COROT,” he added.
About 330 exoplanets have been discovered so far, most of which are gas giants likeJupiter and Neptune. The density of COROT-Exo-7b is still under investigation: it may be rocky like Earth and covered in liquid lava. It may also belong to a class of planets that are thought to be made up of water and rock in almost equal amounts. Given the high temperatures measured, the planet would be a very hot and humid place.
“Finding such a small planet was not a complete surprise”, said Daniel Rouan, researcher at the Observatoire de Paris Lesia, who coordinates the project with Alain Léger, from Institut d’Astrophysique Spatiale (Paris, France). “CoRoT-Exo-7b belongs to a class of objects whose existence had been predicted for some time. COROT was designed precisely in the hope of discovering some of these objects,” he added.
Small terrestrial planets are difficult to detect, and so very few exoplanets found so far have a mass comparable to Earth, Venus, Mars, and Mercury. Most of the methods used to find planets are indirect and sensitive to the mass of the planet. The CoRoT spacecraft can directly measure the size of a planet’s surface, which is an advantage. In addition, its location in space allows for longer periods of uninterrupted observation than from ground.
Astronomers say this discovery is significant because recent measurements have indicated the existence of planets of small masses but their size remained undetermined until now. CoRoT (Convection Rotation and Transits) was launched in December 2006 and consists of a 27 cm-diameter telescope designed to detect tiny changes the brightness of nearby stars. The mission’s main objectives are to search for exoplanets and to study stellar interiors.
The planet HD80606b glows orange from its own heat in this computer-generated image. A massive storm has formed in response to the pulse of heat delivered during the planet's close swing past its star. The blue crescent is reflected light from the star. Image by D. Kasen, J. Langton, and G. Laughlin (UCSC).
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As mentioned in a previous article today about global warming, we on Earth worry about our planet’s atmosphere rising by a few degrees on average over the next century. But imagine living on a planet where temperatures could rise 700 degrees in just a few hours! A distant planet known as HD80606b, is a gas giant orbiting a star 200 light-years from Earth. It’s extremely eccentric orbit around the star takes it from a relatively comfortable distance in an Earth-like habitable zone to the blazing hot regions much closer than Mercury is to our Sun. Infrared sensors aboard NASA’s Spitzer Space Telescope measured the planet’s temperature as it swooped close to the star, observing a planetary heat wave that rose from 800 to 1,500 degrees Kelvin (980 to 2,240 degrees Fahrenheit) in just six hours. Wow!
And for those readers who like to complain about artist impressions images, the image here is a novel type of “photorealistic” image, created by a new computer program that calculates the radiative transfer processes in astrophysics.
“We can’t get a direct image of the planet, but we can deduce what it would look like if you were there. The ability to go beyond an artist’s interpretation and do realistic simulations of what you would actually see is very exciting,” said Gregory Laughlin, professor of astronomy and astrophysics at UCSC. Laughlin is lead author of a new report on the findings published this week in Nature.
“This is the first time that we’ve detected weather changes in real time on a planet outside our solar system,” said Laughlin “The results are very exciting because they give us important clues to the atmospheric properties of the planet.”
Spitzer observed the planet for 30 hours before, during, and just after its closest approach to the star. The planet passed behind the star (an event called a secondary eclipse) just before the moment of its closest approach. This was a lucky break for Laughlin and his colleagues, who had not known that would happen when they planned the observation. The secondary eclipse allowed them to get accurate measurements from just the star and thereby determine exact temperatures for the planet.
HD80606b has an estimated mass of about four times that of Jupiter and completes its orbit in about 111 days. At its closest approach to the star it experiences radiation about 800 times stronger than when it is most distant.
At the closest point, the sunlight beating down on the planet is 825 times stronger than the irradiation it receives at its farthest point from the star. “If you could float above the clouds of this planet, you’d see its sun growing larger and larger at faster and faster rates, increasing in brightness by almost a factor of 1,000,” Laughlin said.
“Even after finding nearly 200 planets, the diversity and oddness of these new worlds continues to amaze and confound me,” says Paul Butler of the Carnegie Institution for Science’s Department of Terrestrial Magnetism. Butler made the precision velocity measurements of the host star that allowed the planet’s orbit to be calculated. Butler’s work has uncovered about half of the known extra-solar planets.
Daniel Kasen, a Hubble postdoctoral fellow at UCSC, was able to generate the image with the new program. “It calculates the color and intensity of light coming from the glowing planet, and also how starlight would reflect off the surface of the planet,” Kasen said.
The resulting image shows a thin blue crescent of reflected starlight framing the night side of the planet, which glows cherry red from its own heat, like coals in a fire. “These images are far more realistic than anything that’s been done before for extrasolar planets,” Laughlin said.
The planet is expected to pass in front of its star when viewed from Earth on February, and the team will be watching again.
This artist's conception reveals the newly discovered Super-Neptune planet orbiting a star 120 light years away from Earth. Normally blue in color, its red hue is caused by the illumination from the nearby Red Dwarf star. Credit: David A. Aguilar (CfA)
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Another extrasolar planet has been found, this time a Neptune-sized world orbiting a star 120 light-years from Earth. It was found by a network of automated telescopes set up to search for other worlds, known as “HATNet,” which is operated by the Center in Arizona and Hawaii. This latest extrasolar world, called HAT-P-11b is the 11th planet found by HATNet, and the smallest yet discovered by any projects that are searching using the transit method. As a planet passes directly in front of (transits) its parent star, it blocks a small amount of light coming from the star. In this case, the planet blocked about 0.4 percent of the star’s light. This discovery puts the current extrasolar count at 335.
Transit detections are particularly useful because the amount of dimming tells the astronomers how big the planet must be. By combining transit data with measurements of the star’s “wobble” (radial velocity) made by large telescopes like Keck, astronomers can determine the mass of the planet.
While Neptune has a diameter 3.8 times that of Earth and a mass 17 times Earth’s, HAT-P-11b is 4.7 times the size of Earth and has 25 Earth masses.
A number of Neptune-like planets have been found recently by radial velocity searches, but HAT-P-11b is only the second Neptune-like planet found to transit its star, thus permitting the precise determination of its mass and radius.
The new-found world orbits very close to its star, revolving once every 4.88 days. As a result, it is baked to a temperature of around 1100 degrees F. The star itself is about three-fourths the size of our Sun and somewhat cooler.
There are signs of a second planet in the HAT-P-11 system, but more radial velocity data are needed to confirm that and determine its properties.
Another team has located one other transiting super-Neptune, known as GJ436b, around a different star. It was discovered by a radial velocity search and later found to have transits.
“Having two such objects to compare helps astronomers to test theories of planetary structure and formation,” said Harvard astronomer Gaspar Bakos, who led the discovery team.
HAT-P-11 is in the constellation Cygnus, which puts in it the field of view of NASA’s upcoming Kepler spacecraft. Kepler will search for extrasolar planets using the same transit technique pioneered by ground-based telescopes. This mission potentially could detect the first Earth-like world orbiting a distant star. “In addition, however, we expect Kepler to measure the detailed properties of HAT-P-11 with the extraordinary precision possible only from space,” said Robert Noyes, another member of the discovery team.
Artist's concept of the current mission configuration. Credit: JPL
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Two of the hottest and most engaging topics in space and astronomy these days are 1.) exoplanets – planets orbiting other stars – and 2.) dark matter—that unknown stuff that seemingly makes up a considerable portion of our universe. There’s a spacecraft currently in development that could help answer our questions about whether there really are other Earth-like planets out there, as well as provide clues to the nature of dark matter. The spacecraft is called SIM – the Space Interferometry Mission. “We’ll be looking for other Earths around other stars,” said Stephen Edberg, System Scientist for the mission, “and by making accurate mass measurements of galaxies, we should be able to measure dark matter, as well.”
The concept for this mission has been around for awhile, and the concept has changed over time, with the telescope going through different incarnations. Currently, the mission is being called SIM Lite, as the spacecraft itself has gotten smaller, however the mirrors for the interferometer have gotten bigger.
While interferometry at radio wavelengths has been done for over 50 years, optical interferometry has only matured recently. Optical interferometry combines the light of multiple telescopes to perform as a single, much larger telescope. SIM Lite will have two visible-wavelength stellar interferometer sensors – as well as other advanced detectors, that will work together to create an extremely sensitive telescope, orbiting outside of Earth’s atmosphere.
“These are instruments that can measure positions in the sky to almost unbelievable accuracy,” said Edberg. “Envision Buzz Aldrin standing on the moon. Pretend he’s holding a nickel between thumb and forefinger. SIM can measure the thickness of that nickel as seen by someone standing on the surface of the Earth. That is one micro arc second, a very tiny fraction of the sky.” Watch a video depicting this — (Quicktime needed)
Having the ability to make measurements like that with SIM, it will be possible to infer the presence of planets within about 30 light-years from Earth, and those planets can be as small and low mass as Earth. As of now, the SIM team anticipates studying between 65 and 100 stars over a five year mission, looking for Earth analogs, planets roughly the same mass as Earth orbiting their stars in the habitable zone, where liquid water could exist.
So, for example, SIM Lite would be able to detect a habitable planet around the star 40 Eridani A, 16 light-years away, known to fans of the “Star Trek” television series as the location of Mr. Spock’s home planet, Vulcan. See a movie depicting this possible detection — (QuickTime needed).
SIM will not detect a planet directly, but by detecting the motion it causes in the parent star. “That’s a difficult task, there’s no question,” said Edberg, “but it gets complicated, based on what we see with our own solar system and what we’ve seen in other planetary systems. We know there are other systems out there that have more than one planet. Multiple planets can confound the measurements.”
But SIM should be able to detect the different sized planets orbiting other stars. SIM Lite recently passed a double blind study conducted by four separate teams who confirmed that SIM’s technology will allow the detection of Earth-mass planets among multiple-planet systems, by having the ability to measure the mass of different sized planets, to as low as Earth-mass.
“With a few exceptions all the planets we know about were detected using a method called radial velocity,” said Edberg, “where we look at the periodic motion of the star coming toward us and moving away from us on a regular basis. But when you make measurements like that, when you have no other information, you don’t know the orientation of the planets’ orbit with respect to the star, or the mass of either the star or the planet.”
With the hottest stars, radial velocity can’t be used to look for planets. But SIM Lite will be able to look at stars clear across the diagram from the coolest to the hottest stars.
“It’s a big question mark in the other planets we know about now – I believe we know only about 10% of the masses of extrasolar planets,” said Edberg.
A second planet search program, called the “broad survey,” will probe roughly 2,000 stars in our galaxy to determine the prevalence planets the size of Neptune and larger. Graphic illustrating the mass and quantity of planets SIM Lite could potentially detect. Number of terrestrial planets assumes 40% of mission time divided evenly between 1-Earth mass and 2-Earth mass surveys. Credit: JPL
SIM will also be used to measure the sizes of stars, as well as distances of stars, and be able to do so several hundred times more accurately than previously possible. SIM Lite will also measure the motion of nearby galaxies, in most cases, for the first time. These measurements will help provide the first total mass measurements of individual galaxies. All of this will enable scientists to estimate the distribution of dark matter in our own galaxy and the universe.
“Dark matter is known for its gravitational affects,” said Edberg. “It doesn’t seem to interact with normal matter as we know it. To get more clues on it, we want to know where it is.”
SIM will measure on two different scales. One is within the Milky Way Galaxy, making measurements of stars and globular clusters, and making measurements of stars that have been torn out of smaller galaxies that orbit the Milky Way.
“We can do mass model of our galaxy and find out where that mass is, including what has to be a lot of dark matter,” said Edberg. “When we make measurements of how our galaxy rotates, you find that it rotates like a solid. Instead of being Keplerian, where you think of Mercury going around the sun faster than Pluto, from all the way inside the galaxy as close as we can measure to the center, out to beyond the sun’s distance, the Milky Way rotates like it’s a solid body. It’s not a solid body, but that means it must have a density that is constant all the way through and that means there is far more matter than we can see.”
“Another thing we’d like to know is the concentration of dark matter in cluster of galaxies,” Edberg continued. “The Milky Way is part of the Local Group of galaxies, and SIM has the capability to measure stars within the individual galaxies, which in turn can be modeled to tell us where the dark matter is within the Local Group. This is cutting edge. This is one of the big mysteries right now in astrophysics and cosmology.”
Extra solar planets and dark energy may seem like two completely different things for one spacecraft to be looking for, but Edberg said this is an example of how everything is tied together.
“To get planet masses we need to know the masses of the parent stars,” he said. “SIM will make measurements of stars, particularly binary stars, and determine the masses of stars for a wide variety of star types, and be able to estimate the sizes of the planets that are causing the reflex motion. To make the measurements, and because stars with planets are going to be scattered around the sky, we need to have a grid of stars that are the fixed points to give us latitude and longitude, so to speak. If you know exactly where St. Louis and Los Angeles are, then it’s much easier to triangulate where things between them are. We need to do this all around the sky, and to do that we tie that down to the stars, and SIM can do that. These are fundamental questions that we don’t know the answers to, but SIM will help us find the answers.”
So, SIM Lite will be searching from within our neighborhood to the edge of the universe.
What’s the status of this future spacecraft?
“We’re on hold right now,” said Edberg. “We recently passed the double blind test to show that SIM can find Earth-like planets in systems that have multiple planets. SIM is also undergoing a decadal review to make the case that the astronomical science community needs to have a mission like SIM to strengthen the foundations enormously.”
Technical work is being done to prepare to build the actual instruments, but due to budgetary reasons, NASA has not set a launch date. “We think we could be ready to launch by 2015 once we get the go-ahead from NASA,” said Edberg, “and the go ahead depends on the decadal review, and the reports should be out in about a year.”
SIM Lite would provide an entirely new measurement capability in astronomy. Its findings would likely stand firmly on their own, while complimenting the capabilities of our current, as well as other planned future space observatories.
For more information about SIM check out the mission website.
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In June of 2008, astronomers announced the finding of one of the smallest exoplanets yet around a normal star other than the Sun. The planet – believed to be a rocky exo-world — was found through a microlensing event, and was estimated to be 3.3 times the size of Earth, orbiting a brown dwarf star. But new analysis suggests the star may be larger than first thought, making the planet smaller than the original estimates. Astronomers say the exoplanet, called MOA-2007-BLG-192-L b could weigh just 1.4 Earths – less than half the original estimate. Observations over the next few months should be able to test the prediction.
Most known “exoplanets” are huge gas giants, hundreds of times Earth’s mass, and are discovered by detecting the wobble they induce in their parent stars.
But researchers found the planet and star using the gravitational microlensing technique. This is where two stars line up perfectly from our point of view here on Earth. As the two stars begin to line up, the foreground star acts as a lens to magnify and distort the light from the more distant star. By watching how this brightening happens, astronomers can learn a tremendous amount about the nature of both the foreground and background star.
In this case, there was an additional gravitational distortion from the planet orbiting the foreground star MOA-2007-BLG-192L, which astronomers were able to tease out in their data.
However, analyzing these events takes time, because there are so many variables to take into account, including the sizes of planet and star, their separation, and the distance from Earth.
Initially, the team believed that this host star was a brown dwarf – an object too small to sustain nuclear fusion, as normal stars do. That suggested MOA-2007-BLG-192-L b weighed 3.3 Earths.
But more recent observations suggest the parent star is actually heavier than first thought – a type of star called a red dwarf, team member Jean-Philippe Beaulieu of the Paris Astrophysical Institute reported last week at a meeting of the Royal Astronomical Society in London.
That suggests the planet weighs just 1.4 Earths. In size terms, that makes it a near twin of our own planet, closer in mass than any known planet except Venus.
“The result is important because this is the lowest-mass planet yet detected, and is extremely close to the mass of the Earth,” said Scott Gaudi of Ohio State University in Columbus. “Obviously, finding a true Earth-mass planet is one of the biggest goals of searches for exoplanets. We are very close to that goal now.” Very Large Telescope Facility. Credit: ESO
The team will attempt to get more data on the parent star in April or May using the Very Large Telescope in northern Chile.
If their analysis is confirmed, it is an unclear whether the tiny planet could host any life. Because its host is a very dim red dwarf, the planet is likely to be frozen – even though it orbits at about the same distance as Venus from our Sun.
However, if the planet boasts a thick, insulating hydrogen atmosphere, it could sustain a habitable surface temperature, capable of supporting life of some kind.
TrES-3b is a gas giant like Jupiter, but with an orbit much closer to its star than Mercury is to our Sun.Credit: Leiden Observatory.
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For the first time, astronomers have measured light emitted from extrasolar planets around sun-like stars using ground-based telescopes. The observations were obtained simultaneously and independently by two separate teams for two different planets. Incredibly, they were also able to determine properties of the exoplanets’ atmospheres as well. Measuring the light emitted from a planet at different wavelengths reveals the planet’s spectrum, which can be used to determine the planet’s day-side temperature. In addition, this spectrum can reveal many physical processes in the planet’s atmosphere, such as the presence of molecules like water, carbon monoxide and methane, and the redistribution of heat around the planet. “This first direct detection of light emitted by another planet, using existing telescopes on the ground, is a major milestone in the study of planets beyond our own Solar System,” said Professor Gary Davis, Director of the United Kingdom Infrared Telescope (UKIRT). “This is a very exciting scientific discovery.”
The measurements of the first planet, TrES-3b, were conducted by a team of Astronomers from the University of Leiden, using the William Herschel Telescope (WHT) on La Palma (Canary Islands, Spain) and the United Kingdom Infrared Telescope on Mauna Kea in Hawai`i. TrES-3b is in a very tight orbit around its host star, TrES-3, transiting the stellar disk once per 31 hours. For comparison, Mercury orbits the sun once every 88 days. TrES-3b is just a little larger than Jupiter, yet orbits around its parent star much closer than Mercury does, making it a “hot jupiter.”
UKIRT observations caught the planet transiting in front of the star, from which the size of the planet has been worked out extremely precisely. The WHT observations also show the moment the planet moves behind the star, and allow the strength of the planet light to be measured. Astronomers have been trying to observe this effect from the ground for many years, and this is the first success.
Ernst de Mooij, leader of the research team, said, “While a few such observations have been conducted previously from space, they involved measurements at long wavelengths, where the contrast in brightness between the planet and the star is much higher. These are not only the first ground-based observations of this kind, they are also the first to be conducted in the near-infrared, at wavelengths of 2 micron for this planet, where it emits most of its radiation.” This image shows a comparison between the sizes of the orbits of TrES-3b and Mercury around the primary star. Note that while the orbits are to scale, the sizes of the planets and the star are not.
The researchers determined the temperature of TrES-3b to be a slightly over 2000 Kelvin. “Since we know how much energy it should receive by the type of its host star, this gives us insights into the thermal structure of the planet’s atmosphere,” added Dr. Ignas Snellen, “which is consistent with the prediction that this planet should have a so-called ‘inversion layer.’ It is absolutely amazing that we can now really probe the properties of such a distant world”.
An atmospheric inversion layer is a layer of air where the normal change of temperature with altitude reverses. Current theory says that there are two types of “hot jupiters,” one with an inversion layer, and one without. One theory is that the presence of an inversion layer would depend on the amount of light the planet receives from its star. If the inversion layer could be confirmed, for example by measurements at other wavelengths, these observations would fit in perfectly with this theory.
A second team has made a ground-based detection of a different extrasolar planet, OGLE-TR-56b,using the Southern Observatory’s Very Large Telescope. This planet is about 5,000 light-years away, located towards the center of the galaxy. The planet is quite hot; its atmosphere is more than 4,400 degrees Fahrenheit (2,400 degrees Celsius). This is one of the hottest extrasolar planets detected.
The researchers say both landmark observations will open up a new window for studying exoplanets and their atmospheres using ground-based telescopes, and show great promise for using future extremely large telescopes which will have much higher sensitivity than the telescopes used today.
Earth scenes and corresponding spectra reconstructed for two observer’s positions. Credit: Arnold, et al.
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What if another civilization had telescopes and spacecraft better than ours? Would Earth be detectable from another planet a few light-years away? Likewise, what will it take for us to detect life on an Earth-like planet within a similar distance? It’s interesting to consider those questions, and now, there is data to help answer them. In December 1990, when the Galileo spacecraft flew by Earth in its circuitous journey to Jupiter, scientists pointed some of the instruments at Earth just to see how the old home planet looked from space. Since we knew life could definitely be found on Earth, this exercise helped create some criteria that if found elsewhere, would point to the existence of life there as well. But what if Earth’s climate was different from what it is now? Would that signature still be detectable? And could potential biomarkers from extra solar planets holding climates much colder or warmer than ours be obvious? A group of researchers in France input some various criteria garnered from different epochs in Earth’s history to test out this hypothesis. What did they find?
One of the most telling of the criteria from the Galileo flyby revealing life on Earth was what is called the vegetation red edge –a sharp increase in the reflectance of light at a wavelength of around 700 nanometers. This is the result of chlorophyll absorbing visible light but reflecting near infrared strongly. The Galileo probe found strong for this evidence on Earth in 1990.
Luc Arnold and his team at the Saint-Michel-l’Observatoire in France wanted to determine some different parameters where plant life similar to Earth’s would still be detectable via the vegetative red edge on an Earth-like planet orbiting a star several light years away. Earth from space.
At that distance the planet would be a non-resolvable (in visible light) point-like dot, so the first question to consider is whether the red edge would be visible at different angles. The planet is likely to be rotating, and for example, on Earth, the continents that have the most vegetation are mainly in the northern hemisphere. If that hemisphere wasn’t leading the view, would a bio-signature still be detectable? They also wanted to allow for the different seasons, where a hemisphere in winter would be less likely to have vegetative biomarkers than one in summer, and potential heavy cloud cover.
They also input different climate criteria from the last Quaternary climate extremes, using climate simulations have been made by general circulation models. They used data from the present time and compared that to an ice age, The Last Glacial Maximum (LGM) which occurred about 21,000 years ago. Temperatures globally were on the order of 4 degrees C colder than today, and ice sheets covered most of the northern hemisphere. Then, they used a warmer time, during the Holocene epoch 6,000 years ago, when the Earth’s northern hemisphere was about 0.5 degrees C warmer than today. The sea level was rising and the Sahara Desert contained more vegetation.
Surprisingly, the researchers found even during winter in an ice age, the vegetation red signal would not be significantly reduced, compared to today’s climate and even the warmer climate.
So if another Earth is out there, the vegetaion red edge should allow us to find that Earth-like planet. But we need better telescopes and spacecraft to find it.
The best hope on the horizon is the Terrestrial Planet Finder. ESA has a similar instrument in the works called Darwin.
The teams behind these instruments say they could spot Earth-like planets orbiting stars at distances of up to 30 light years with an exposure measured in a couple of hours.
Arnold’s team says that spotting the signs of life on such a planet would be much harder. The vegetation red edge might only be seen with an exposure of 18 weeks with a telescope like the Terrestrial Planet Finder’s. An 18 week exposure of a planet orbiting another star would be an almost impossible task.
So when might we eventually see vegetation on another planet? The Terrestrial Planet Finder (TPF) looks unlikely to be launched before 2025 and even then might not have the power to do the job.
More ambitious telescopes later in the century, such as a formation of 150 3-meter mirrors would collect enough photons in 30 minutes to freeze the rotation of the planet and produce an image with at least 300 pixels of resolution, and up to thousands depending on array geometry. “At this level of spatial resolution, it will be possible to identify clouds, oceans and continents, either barren or perhaps (hopefully) conquered by vegetation,” the researchers write.
Exoplanet collision in BD+20 301. Possibly an Earth-like rocky exoplanet was involved? (Lynette Cook)
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In September, it was announced the Chandra X-ray Observatory had spotted something very odd about BD+20 307. The binary system appeared to have a dusty disk surrounding it, indicative of a young, planet-forming system a fraction of the age of the Solar System. However, it was well known that the binary was actually several billion years old. It turns out that this disk was created by a rare planetary event; a cataclysmic planetary collision.
On Wednesday, at the AAS conference in Long Beach, I attended the “Extrasolar Planets” session to listen in on more results from Hubble about the exciting exoplanet discoveries in November… however, for me, the most captivating talk was about the strange, dusty old binary and the future detective work to be carried out to track down a planet killer…
The talks by astrophysicists working with the optical Hubble data were superb, showing off some of the science behind last years spate of direct observations of exoplanets, particularly the massive planet orbiting the star Fomalhaut, shaping a scattered disk of dust. However, there was no further news to report, apart from some cool numerical models the scientists will be using to characterize Fomalhaut b and a very interesting talk about the predicted lifetimes of exoplanets undergoing tidal stresses (which, unfortunately, I missed the first five minutes of as I got lost in the Long Beach Convention Center).
The one presentation that did pique my interest was Ben Zuckerman’s review of the progress being made in the study of BD+20 307. A few months ago, this piece of research caused a huge amount of interest as it provided the first piece of evidence of a huge, rocky planetary collision in the star system 300 light years away. Naturally, many news sources ran with article titles like: Is this what the Solar System would look like after Earth was hit by another planetary body? As Zuckerman pointed out, the fact that the group used an artist impression of a colliding Earth-like body (plus land masses and oceans, as pictured top) was no accident. BD+20 307 is certainly at an age when oceans might have formed and life–as Zuckerman morbidly conjectured–may have thrived. Not for any longer…
Usually when we observe dust around a star, we can assume that it is a planet-forming star system that is fairly young. Conversely, as I found out to great depth in the conference, very old white dwarf systems can reveal a lot about their past planetary population when their dusty contaminants are studied. However, the dust contained in the BD+20 307 system is a puzzle. Astronomers had discovered a system, of comparable age to ours with a large amount of warm dust (T~500K). A system of that age will have long since expelled (via stellar wind pressure) or accreted any left-over dust from the planet-forming stages. Therefore, the only remaining explanation is that a rocky body collided with another, ejecting a huge amount of micron-sized warm dust particles.
So is this what the Solar System would look like after Earth is shattered by another planet? Possibly.
Zuckerman then pushed into some work being done to understand how the planetary collision could have happened in the first place. After all, the planets in our Solar System have settled into long-term stable orbits, any planet in BD+20 307 will have the same qualities. There were some questions as to whether the binary stars may have contributed to destabilizing the system, but Zuckerman quickly argued against this idea as the binary has such a tight orbit (with an orbital period of only 3.5 days), the destroyed planet will have found a stable orbit far from any gravitational variations.
So what could have caused the carnage in BD+20 307? We know that massive planetary bodies exert a huge gravitational pull on their host star and other planets in a system (i.e. Jupiter in the case of our Solar System), occasionally bullying (and sometimes capturing) them along the way. A small nudge in the wrong direction and planets could be knocked from their orbits, set on a collision course. So, much effort is now being put into a search for a third, faint star in BD+20 307. Perhaps it could be orbiting far away from the dancing binary, occasionally swinging past the planetary bodies, setting up the huge collision event.
This certainly seems reasonable, as 70% of binary star systems are found to have a third star. However, Zuckerman’s team have yet to find the “killer” third star and he appears confident that after careful analysis that there is no other stellar body within a 20 AU radius of the binary pair. Next, he intends to study the “wobble” of the centre of mass of the BD+20 307 binary to see if there is any gravitational anomaly as the mysterious “third star” tugs at the pair.
Artist illustration of a super Earth around Gliese 581
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We stand on the edge of the next phase of planetary discovery. Hundreds of massive, Jupiter-like planets have been discovered, but now astronomers are turning up smaller, more familiar planets. Planets the mass of Earth are out of reach today, but a new class of super Earth planets are now being discovered, and more will be turned up with the next generation of ground and space-based telescopes. Perhaps the most interesting research will be in the atmospheres of these planets.
Super Earths can have up to 10 times the mass of the Earth, but with a solid surface and liquid water they could very well be habitable. A recent presentation by Eliza Miller-Ricci from Harvard University at the 213th meeting of the American Astronomical Society discussed the kinds of atmospheres astronomers might see as these super Earths start turning up. Although interesting scientifically – geologic outgassing, evidence of plate tectonics, and the thickness or thinness of the atmosphere, the most interesting question will be: can super Earth planets support life?
To have life as we understand it, super Earth planets (like regular Earth planets) will need to have liquid water on their surface, and the requires a certain temperature range – the parent star’s habitable zone. As we see in our own Solar System, the atmosphere of a planet helps regulate its temperature; Venus has a thick atmosphere and it’s hot enough to melt lead, while Earth has a nice temperature to allow liquid water to form on its surface. Mars has a thin atmosphere and it’s really cold. It’s not just the thickness of the atmosphere that matters, it’s also what’s in it: carbon dioxide, water, etc.
High mass planets like Jupiter are mostly formed from hydrogen. Low mass terrestrial planets like Earth can’t hold onto their hydrogen and it escapes into space during the planet’s early history. But these super Earths might be able to hold onto their hydrogen. Instead of a low-hydrogen atmosphere like Earth, they might have an atmosphere with large quantities of water. And water is a powerful greenhouse gas – trace amounts of water vapor in Earth’s atmosphere account for 60% of our greenhouse effect, keeping the planet warm and habitable.
I asked Miller-Ricci about what impact large quantities of hydrogen will have on the atmosphere of a super Earth planet. We have water here on Earth, but very little in the atmosphere. Water vapor is a powerful greenhouse gas and would help define the temperature of the planet. “The amount of hydrogen in the atmosphere of a super Earth planet would significantly affect its habitable zone. This is a really important question, it’s what we’re looking at next.”
Current missions can detect super Earths using the transit method, where the planet dims light from its parent star as it passes in front. By subtracting the chemical signature when the planet passes behind the star, astronomers can determine its atmosphere.
Finding super Earths is at the limit of current telescopes, but more powerful instruments are launching soon. NASA’s Kepler mission, launching in April 2009, will turn up even more super Earths than have already been found. But the next generation of space telescopes, like NASA’s James Webb Space Telescope will allow astronomers to image these planet’s atmospheres directly.
