First Super-Earths Discovered Around Sun-like Stars

Astronomers say it’s a “neck-and-neck race” as to whether the first potentially habitable planets will be detected from the ground or from space, and today an international team of planet hunters announced they have discovered as many as six low-mass planets around two nearby Sun-like stars, using two ground-based observatories. This haul of planets includes two “super-Earths” with masses 5 and 7.5 times the mass of Earth.

The researchers, led by Steven Vogt of the University of California, Santa Cruz, and Paul Butler of the Carnegie Institution of Washington, said the two “super-Earths” are the first ones found around Sun-like stars. These planets have orbits close to their stars and so they would be too hot to support life or liquid water.

“These detections indicate that low-mass planets are quite common around nearby stars. The discovery of potentially habitable nearby worlds may be just a few years away,” said Vogt, a professor of astronomy and astrophysics at UCSC.

The team found the new planet systems by combining data gathered at the W. M. Keck Observatory in Hawaii and the Anglo-Australian Telescope (AAT) in New South Wales, Australia.

A comparison of the orbits of the planets of 61 Vir with the inner planets in our Solar System. All three planets discovered to date in this system would lie inside the orbit of Venus.
A comparison of the orbits of the planets of 61 Vir with the inner planets in our Solar System. All three planets discovered to date in this system would lie inside the orbit of Venus.

Three of the new planets orbit the bright star 61 Virginis, which can be seen with the naked eye under dark skies in the Spring constellation Virgo. Astronomers and astrobiologists have long been fascinated with this particular star, which is only 28 light-years away. Among hundreds of our nearest stellar neighbors, 61 Vir stands out as being the most nearly similar to the Sun in terms of age, mass, and other essential properties. Vogt and his collaborators have found that 61 Vir hosts at least three planets, with masses ranging from about 5 to 25 times the mass of Earth.

Click here to see an animation showing a simulation of the hot atmosphere of the 5.3 Earth-mass planet 61 Vir b as it circles around its star in a 4.2 day orbit. The imaginary observer sits in space above the planet, and sees the hot side (which always faces the star) rotate into and out of view.

Recently, a separate team of astronomers used NASA’s Spitzer Space Telescope to discover that 61 Vir also contains a thick ring of dust at a distance roughly twice as far from 61 Vir as Pluto is from our Sun. The dust is apparently created by collisions of comet-like bodies in the cold outer reaches of the system.

“Spitzer’s detection of cold dust orbiting 61 Vir indicates that there’s a real kinship between the Sun and 61 Vir,” said Eugenio Rivera, a postdoctoral researcher at UCSC. Rivera computed an extensive set of numerical simulations to find that a habitable Earth-like world could easily exist in the as-yet unexplored region between the newly discovered planets and the outer dust disk.

This image from a simulation of atmospheric flow shows temperature patterns on one of the newly discovered planets (61Virb), which is hot enough that it glows with its own thermal emission. A movie of the simulation is posted at the bottom of this story, showing global atmospheric flow for one full orbit of the planet around its star. Credit: J. Langton, Principia College.
This image from a simulation of atmospheric flow shows temperature patterns on one of the newly discovered planets (61Virb), which is hot enough that it glows with its own thermal emission. A movie of the simulation is posted at the bottom of this story, showing global atmospheric flow for one full orbit of the planet around its star. Credit: J. Langton, Principia College.

The second new system found by the team features a 7.5-Earth-mass planet orbiting HD 1461, another near-perfect twin of the Sun located 76 light-years away. At least one and possibly two additional planets also orbit the star. Lying in the constellation Cetus, HD 1461 can be seen with the naked eye in the early evening under good dark-sky conditions.

The 7.5-Earth-mass planet, assigned the name HD 1461b, has a mass nearly midway between the masses of Earth and Uranus. The researchers said they cannot tell yet if HD 1461b is a scaled-up version of Earth, composed largely of rock and iron, or whether, like Uranus and Neptune, it is composed mostly of water.

According to Butler, the new detections required state-of-the-art instruments and detection techniques. “The inner planet of the 61 Vir system is among the two or three lowest-amplitude planetary signals that have been identified with confidence,” he said. “We’ve found there is a tremendous advantage to be gained from combining data from the AAT and Keck telescopes, two world-class observatories, and it’s clear that we’ll have an excellent shot at identifying potentially habitable planets around the very nearest stars within just a few years.”

The 61 Vir and HD 1461 detections add to a slew of recent discoveries that have upended conventional thinking regarding planet detection. In the past year, it has become evident that planets orbiting the Sun’s nearest neighbors are extremely common. According to Butler, current indications are that fully one-half of nearby stars have a detectable planet with mass equal to or less than Neptune’s.

The Lick-Carnegie Exoplanet Survey Team led by Vogt and Butler uses radial velocity measurements from ground-based telescopes to detect the “wobble” induced in a star by the gravitational tug of an orbiting planet. The radial-velocity observations were complemented with precise brightness measurements acquired with robotic telescopes in Arizona by Gregory Henry of Tennessee State University.

“We don’t see any brightness variability in either star,” said Henry. “This assures us that the wobbles really are due to planets and not changing patterns of dark spots on the stars.”

Due to improvements in equipment and observing techniques, these ground-based methods are now capable of finding Earth-mass objects around nearby stars, according to team member Gregory Laughlin, professor of astronomy and astrophysics at UCSC.

“It’s come down to a neck-and-neck race as to whether the first potentially habitable planets will be detected from the ground or from space,” Laughlin said. “A few years ago, I’d have put my money on space-based detection methods, but now it really appears to be a toss-up. What is truly exciting about the current ground-based radial velocity detection method is that it is capable of locating the very closest potentially habitable planets.”

Lead image caption: 61 Virginis is one of only a handful of truly Sun-like stars that can be seen with the naked eye. Astronomers have discovered three low-mass planets orbiting the star. Credit: NASA’s Sky View

Papers:
A Super-Earth and two Neptunes Orbiting the Nearby Sun-like star 61 Virginis
A Super-Earth Orbiting the Nearby Sun-like Star HD 1461
A long-period planet orbiting a nearby Sun-like star

Source: UC Santa Cruz

Exoplanet Not Really There?

This artist’s concept shows the smallest star known to host a planet. Image credit: NASA/JPL-Caltech

In May 2009, astronomers were jubilant: finally, an extra solar planet had been found by using the method of astrometry. That’s great, except, they may not have found a planet after all. Researchers from JPL reported they found a Jupiter-like planet around a star smaller than our sun. But follow-up observations of the star VB10 are coming up empty. “The planet is not there,” said Jacob Bean from the Georg-August University in Gottingen, Germany, who used a different and more successful approach to look for exoplanets, radial velocity.

Astrometry measures the side-to-side motion of a star on the sky to see whether any unseen bodies might be orbiting it. Using this method is difficult and requires very precise measurements over long periods of time. Using astrometry to look for exoplanets has been around for 50 years, but it hadn’t bagged a verified exoplanet – until, astronomers thought, earlier this year. A team of researchers announced an exoplanet, six times more massive than Jupiter, orbiting a star about one-thirteenth the mass of the Sun, using a telescope at the Palomar Observatory in southern California (S. Pravdo and S. Shaklan Astrophys. J. 700, 623–632; 2009).

“This method is optimal for finding solar-system configurations like ours that might harbor other Earths,” astronomer Steven Pravdo of JPL said in May. “We found a Jupiter-like planet at around the same relative place as our Jupiter, only around a much smaller star. It’s possible this star also has inner rocky planets. And since more than seven out of 10 stars are small like this one, this could mean planets are more common than we thought.”

But using different methods, other astronomers aren’t finding anything.

“We would definitely have seen a significant amount of variation in our data if [the planet] was there,” said Bean, quoted in the online Nature News. Bean has submitted a paper to the Astrophysical Journal.

Radial velocity, which has found most of the extrasolar planets so far, looks for shifts in the lines of a star’s absorption spectrum to track its motion towards and away from Earth, which would be caused by the influence of a planet.

Pravdo says that Bean and his colleagues “may be correct, but there is hyperbole in their rejection of our candidate planet.” Bean’s paper, for instance, only rules out the presence of any planet that is at least three times more massive than Jupiter, says Pravdo, adding that the work “limits certain orbits for possible planets but not all planets.”

Astronomers expect astrometry to work much better above the distorting effects of the atmosphere. Two space missions in the works — the European Space Agency’s GAIA, due to launch in 2012, and NASA’s proposed SIM-lite (Space Interferometry Mission) will use the technique to search for planets as small as Earth around Sun-like stars. Astrometry potentially can yield the mass of a planet, whereas radial velocity only puts a lower limit on it.

Bean admits that astronomers might one day find a planet around VB10 if they scrutinize the star long and hard enough.

Source: Nature News

Exobiology

Exobiology (same thing as astrobiology) is about life in space (on other planets, and moons; in other solar systems): where it is, what it is, how it started, and how it evolved (all studied scientifically, of course). Because the origin of life right here on Earth, and its early evolution, is essentially unknown, and because of the distinct possibility of similiarities with the origin (and early evolution) of life elsewhere in the universe, exobiology includes research into abiogenesis (and early, and extreme, life on Earth).

Exobiology is very much a multi-disciplinary field, drawing on biology, chemistry, geology (and planetary science), physics, and astronomy.

Because we have a sample of just one – life on Earth – it is difficult to make anything but the most general decisions on what lines of exobiology research are likely to be productive (keep in mind that null results can, of course, be quite productive). Conservatively, looking for planets like Earth in orbit around stars like the Sun (in age as well as mass, metallicity, etc), and looking for clues for fossil life in planetary environments like those found today on Earth (e.g. early Mars) seem better options than investigating possible silicon-based life (to take just one example).

As the number of exosolar (or extrasolar) planetary systems known continues to grow, quickly, discovering the prevalence of Earth-mass planets, in goldilocks orbital zones, seems like a good idea … so today we have the Kepler mission and COROT.

As the early Mars becomes better understood – and the widespread distribution of liquid water then – so today we have plans for the Mars Science Laboratory and ExoMars (the discovery of methane in the Martian atmosphere certainly spurs such developments).

Less conservatively, the discovery of life around black smokers and sites like Lost City (not to mention entire ecosystems within crustal rocks … several km beneath the surface) sparked interest in the possibility of life in Europa, on Titan, even Enceladus (life – albeit rather simple life – we now know does not need to depend, ultimately, on the Sun’s (or another star’s) radiant energy … think chemolithoautotrophs).

Did you know that NASA has an exobiology branch? Check it out! Duke University’s Chemistry Department has an interesting Introduction to Exobiology you might find interesting too.

Universe Today stories on exobiology? Yep, lots; here’s a random selection: Martian Explorers Should Be Looking for Fossils, Did Life Arrive Before the Solar System Even Formed?, Extremophile Hunt Begins in Antarctica, Implications for Exobiologists , and New Targets to Search for Life on Europa.

Any Astronomy Cast episodes on exobiology? Yep … but it’s called Astrobiology.

Sources: NASA, ESA

Cool – Literally – Extrasolar Planet Imaged

Yet another planet outside of our Solar System has been directly imaged, bumping the list up past ten. Given that the first visible light image of an extrasolar planet was taken a little more than a year ago, the list is growing pretty fast. The newest one, planet GJ 758 B is also the coolest directly imaged planet, measuring 600 degrees Kelvin, and it orbits a star that is much like our own Sun. GJ 758 B has a mass of between 10-40 times that of Jupiter, making it either a really big planet or a small brown dwarf.

Unlike many of the other directly imaged planets, GJ 758 B resides in a system remarkably like our own Solar System – the star at the center is Sun-like, and the orbit of the planet is at least the same distance from its star as Neptune is from our own. Current observations put the distance at 29 astronomical units.

“The discovery of GJ 758 B, an extrasolar planet or brown dwarf orbiting a star that is similar to our own sun, gives us an insight into the diversity of substellar objects that may form around Solar-type stars,” said Dr. Joseph Carson, from the Max Planck Institute for Astronomy. “This in turn helps show how our own Solar system, and the environments that are conducive to life, are just one of many scenarios that may be the outcome of planet or brown dwarf formation around Sun-like stars.”

Another object, labeled “C?” in the image above, could potentially be another companion to the star. Further observations will be required to determine whether the object in fact orbits the star or is merely another star in the background of the image which is not part of the system.

The mass of the star still has yet to be exactly determined, thus the 10-40 Jupiter mass range. It is 600 degrees Kelvin, which corresponds to 326 Celsius and 620 Fahrenheit, about the hottest temperature that a conventional oven can reach. Though this may seem hot, it’s actually pretty cool for an extrasolar planet. Even though it is so far away from its Sun that, like Neptune, it receives very little warmth from the star it orbits, GJ 758 B is in a stage of formation where the contraction of the planet due to gravity is converted into heat.

A size comparison of the GJ 758 system and corresponding members of our own Solar System, with the Earth for reference. Image Credit: Credit: MPIA/C. Thalmann
A size comparison of the GJ 758 system and corresponding members of our own Solar System, with the Earth for reference. Image Credit: Credit: MPIA/C. Thalmann

Dr. Markus Janson from the University of Toronto, a co-author of the paper announcing the imaging, said, “This is also why the mass of the companion is not well known: The measured infrared brightness could come from a 700 million year old planet of 10 Jupiter masses just as well as from a 8700 million year old companion of 40 Jupiter masses.” The paper detailing the results will be published in Astrophysical Journal Letters, but is available here on Arxiv.

The planet was imaged using the Subaru Telescope’s new High Contrast Instrument for the Subaru next generation Adaptive Optics (HiCIAO) instrument, which utilizes the technology of adaptive optics to eliminate the interference of our atmosphere that blurs images in ground-based telescopes. The imaging of GJ 758 B is part of the commissioning run of the HiCIAO instrument, which plans to take a larger survey to detect extrasolar planets and circumstellar disks in the next five years.

Source: Max-Planck Institute for Astronomy

Shedding Light on the Sun’s “Lithium Mystery”

For decades, astronomers have known our Sun contains a low amount of lithium, while other solar-like stars actually have more. But they didn’t know why. By looking at stars similar to the Sun to study this anomaly, scientists have now discovered of a trend: the majority of stars hosting planets possess less than 1% of the amount of lithium shown by most of the other stars. “The explanation of this 60 year-long puzzle is for us rather simple,” said Garik Israelian, lead author on a paper appearing in this week’s edition of Nature. “The Sun lacks lithium because it has planets.”

This finding sheds light not only on the lack of lithium in our star, but also provides astronomers with a very efficient way of finding stars with planetary systems.

Isrealian and his team took a census of 500 stars, 70 of which are known to host planets, and in particular looked at Sun-like stars, almost a quarter of the whole sample. Using ESO’s HARPS spectrograph, a team of astronomers has found that Sun-like stars that host planets have destroyed their lithium much more efficiently than “planet-free” stars.

“For almost 10 years we have tried to find out what distinguishes stars with planetary systems from their barren cousins,” Israelian said. “We now have found that the amount of lithium in Sun-like stars depends on whether or not they have planets.”

These stars have been “very efficient at destroying the lithium they inherited at birth,” said team member Nuno Santos. “Using our unique, large sample, we can also prove that the reason for this lithium reduction is not related to any other property of the star, such as its age.”

Unlike most other elements lighter than iron, the light nuclei of lithium, beryllium and boron are not produced in significant amounts in stars. Instead, it is thought that lithium, composed of just three protons and four neutrons, was mainly produced just after the Big Bang, 13.7 billion years ago. Most stars will thus have the same amount of lithium, unless this element has been destroyed inside the star.

This result also provides the astronomers with a new, cost-effective way to search for planetary systems: by checking the amount of lithium present in a star astronomers can decide which stars are worthy of further significant observing efforts.

Now that a link between the presence of planets and curiously low levels of lithium has been established, the physical mechanism behind it has to be investigated. “There are several ways in which a planet can disturb the internal motions of matter in its host star, thereby rearrange the distribution of the various chemical elements and possibly cause the destruction of lithium,” said co-author Michael Mayor. ” It is now up to the theoreticians to figure out which one is the most likely to happen.”

Read the team’s paper.

Source: ESO

Multi-Planet System is Chaotic, Dusty

NASA’s Spitzer Space Telescope captured this infrared image of a giant halo of very fine dust around the young star HR 8799. Image credit: NASA/JPL-Caltech/Univ. of Ariz.

Just what is going on over at the star HR 8799? The place is a mess! But we can just blame it on the kids. Young, hyperactive planets circling the star are thought to be disturbing smaller comet-like bodies, causing them to collide and kick up a huge halo of dust. HR 8799 was in the news in November 2008, for being one of the first with imaged planets. Now, NASA’s Spitzer Space Telescope has taken a closer look at this planetary system and found it to be a very active, chaotic and dusty system. Ah, youth: our solar system was likely in a similar mess before our planets found their way to the stable orbits they circle in today.

The Spitzer team, led by Kate Su of the University of Arizona, Tucson, says the giant cloud of fine dust around the disk is very unusual. They say this dust must be coming from collisions among small bodies similar to the comets or icy bodies that make up today’s Kuiper Belt objects in our solar system. The gravity of the three large planets is throwing the smaller bodies off course, causing them to migrate around and collide with each other. Astronomers think the three planets might have yet to reach their final stable orbits, so more violence could be in store. The planets around HR 8799 are about 10 times the mass of Jupiter.

“The system is very chaotic and collisions are spraying up a huge cloud of fine dust,” said Su. “What’s exciting is that we have a direct link between a planetary disk and imaged planets. We’ve been studying disks for a long time, but this star and Fomalhaut are the only two examples of systems where we can study the relationships between the locations of planets and the disks.”

When our solar system was young, it went through similar planet migrations. Jupiter and Saturn moved around quite a bit, throwing comets around, sometimes into Earth. Some say the most extreme part of this phase, called the late heavy bombardment, explains how our planet got water. Wet, snowball-like comets are thought to have crashed into Earth, delivering life’s favorite liquid.

The Spitzer results were published in the Nov. 1 issue of Astrophysical Journal. The observations were made before Spitzer began its “warm” mission and used up its liquid coolant.

Source: JPL

No Earth-Sized Planet Hunting for Kepler Until 2011

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A glitch in the Kepler spacecraft’s electronics means the space telescope will not have the ability to spot an Earth-sized planet until 2011, according to principal investigator William Borucki. Noisy amplifiers are creating noise that compromises Kepler’s view, and the team will have to generate and upload a software fix for the spacecraft. “We’re not going to be able to find Earth-size planets in the habitable zone — or it’s going to be very difficult — until that work gets done,” said Borucki, who revealed the problem last week to the NASA Advisory Council.

The team knew about the problem before launch, as the noisy amplifiers were noticed during ground testing before the device was launched. “Everybody knew and worried about this,” says instrument scientist Doug Caldwell. But he said the team thought it was riskier to pry apart the telescope’s electronic guts than to deal with the problem after launch.

Kepler launched on March 6, 2009 and is designed to look for the slight dimming of light that occurs when a planet transits, or crosses in front of a star.

The problem was is caused by amplifiers that boost the signals from the charge-coupled devices that form the heart of the 0.95-metre telescope’s 95-million-pixel photometer, which detects the light emitted from the distant stars. Three of the amplifiers are creating noise, and even though the noise affects only a small portion of the data, Borucki says, but the team has to fix the software — it would be “too cumbersome” to remove the bad data manually — so that it accounts for the noise automatically.

The team is hoping to fix the issue by changing the way data from the telescope is processed, and looks to have everything in place by 2011.

Borucki pointed out that the team was probably going to have to wait at least three years to find an extrasolar Earth orbiting in the habitable zone anyway. Astronomers typically wait for at least three transits before they confirm a planet’s existence; for an Earth-sized planet orbiting at a distance similar to that between the Earth and the Sun, three transits would take three years. But Borucki said that the noise will hinder searches for a rarer scenario: Earth-sized planets that orbit more quickly around dimmer, cooler stars — where the habitable zone is closer in. These planets could transit every few months.

The delay for Kepler could mean ground-based observers could now have the upper hand in the race for the holy grail of planet hunting: finding an Earth-like planet.

Kepler and CoRoT (Convection, Rotation and Planetary Transits) both look for transiting planets while the ground-based telescopes use radial velocity, looking for tiny wobbles in the motion of the parent stars caused by the planets’ gravity. The journal Nature quoted astronomer Greg Laughlin from the University of California at Santa Cruz, saying that the delay for Kepler makes it “more likely that the first Earth-mass planet is going to go to the radial-velocity observers”.

Source: Nature

Organic Molecules Detected in Exoplanet Atmosphere

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The basic chemistry for life has been detected the atmosphere of a second hot gas planet, HD 209458b. Data from the Hubble and Spitzer Space Telescopes provided spectral observations that revealed molecules of carbon dioxide, methane and water vapor in the planet’s atmosphere. The Jupiter-sized planet – which occupies a tight, 3.5-day orbit around a sun-like star — is not habitable but it has the same chemistry that, if found around a rocky planet in the future, could indicate the presence of life. Astronomers are excited about the detection, as it shows the potential of being able to characterize planets where life could exist.

HD 209458b is in the constellation Pegasus.

“It’s the second planet outside our solar system in which water, methane and carbon dioxide have been found, which are potentially important for biological processes in habitable planets,” said researcher Mark Swain of JPL. “Detecting organic compounds in two exoplanets now raises the possibility that it will become commonplace to find planets with molecules that may be tied to life.”

Over a year ago, astronomers detected these same organic molecules in the atmosphere of another hot, giant planet, called HD 189733b, using the same two space telescopes. Astronomers can now begin comparing the chemistry and dynamics of these two planets, and search for similar measurements of other candidate exoplanets.

The detections were made through spectroscopy, which splits light into its components to reveal the distinctive spectral signatures of different chemicals. Data from Hubble’s near-infrared camera and multi-object spectrometer revealed the presence of the molecules, and data from Spitzer’s photometer and infrared spectrometer measured their amounts.

“This demonstrates that we can detect the molecules that matter for life processes,” said Swain. Astronomers can now begin comparing the two planetary atmospheres for differences and similarities. For example, the relative amounts of water and carbon dioxide in the two planets is similar, but HD 209458b shows a greater abundance of methane than HD 189733b. “The high methane abundance is telling us something,” said Swain. “It could mean there was something special about the formation of this planet.”

Rocky worlds are expected to be found by NASA’s Kepler mission, which launched earlier this year, but astronomers believe we are a decade or so away from being able to detect any chemical signs of life on such a body.

If and when such Earth-like planets are found in the future, “the detection of organic compounds will not necessarily mean there’s life on a planet, because there are other ways to generate such molecules,” Swain said. “If we detect organic chemicals on a rocky, Earth-like planet, we will want to understand enough about the planet to rule out non-life processes that could have led to those chemicals being there.”

“These objects are too far away to send probes to, so the only way we’re ever going to learn anything about them is to point telescopes at them. Spectroscopy provides a powerful tool to determine their chemistry and dynamics.”

For more information about exoplanets and NASA’s planet-finding program, check out PlanetQuest.

Source: Spitzer

HARPS Discovers 32 New Exoplanets

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Astronomers have found 32 new planets outside our solar system with the High Accuracy Radial Velocity Planet Searcher, better known as HARPS, the spectrograph for the European Southern Observatory’s (ESO) 3.6-metre telescope. The number of known exoplanets is now at 406, and HARPS itself has discovered more than 75 exoplanets in 30 different planetary systems. Included in this most recent batch are several low-mass planets – so-called “Super Earths” about the size of Neptune. The image above is an artist’s impression of a planet discovered that is 6 times the mass of Earth, which circles the low-mass host star, Gliese 667 C, at a distance equal to only 1/20th of the Earth-Sun distance. Two other planets were discovered previously around this star.

“HARPS is a unique, extremely high precision instrument that is ideal for discovering alien worlds,” said ESO astronomer Stéphane Udry. “We have now completed our initial five-year program, which has succeeded well beyond our expectations.”

No Earth-like planets were discovered in this group that was announced today at an exoplanet conference in Portugal.

HARPS has facilitated the discovery of 24 of the 28 planets known with masses below 21 Earth masses. As with the previously detected super-Earths, most of the new low-mass candidates reside in multi-planet systems, with up to five planets per system. This new group includes a total of 11 planets with masses between 5 and 21 times that of Earth – and 9 in multi-planet systems — and increases the number of known low-mass planets by 30%.

HARPS uses the radial velocity technique which measures the back-and-forward motions of stars by detecting small changes in a star’s radial velocity as it wobbles slightly from a gentle gravitational pull from an otherwise unseen planet. HARPS can detect changes in velocity as small as 3.5 km/hour, a steady walking pace.

Notable discoveries by HARPS during the past five years include the first super-Earth in 2004 (around µ Ara; ESO 22/04); in 2006, the trio of Neptunes around HD 69830 (ESO 18/06); in 2007, Gliese 581d, the first super Earth in the habitable zone of a small star (ESO 22/07); and in 2009, the lightest exoplanet so far detected around a normal star, Gliese 581e (ESO 15/09). More recently, they found a potentially lava-covered world, with density similar to that of the Earth’s (ESO 33/09).

“These observations have given astronomers a great insight into the diversity of planetary systems and help us understand how they can form,” says team member Nuno Santos.

Source: ESO

Exoplanet

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An exoplanet – or extrasolar planet – is a planet which orbits a star other than our own Sun.

After a bit of a false start – lasting many decades! – when a small number of detections of planets around other stars were reported but not confirmed, the first reliable, independently confirmed exoplanet was discovered – by Campbell, Walker, and Yang – in 1988 (though solid confirmation came only in 2003), around Gamma Cephei. Between 1988 and 2003, two planets were detected, and confirmed, orbiting a pulsar (which has the catchy name of PSR 1257+12) – in 1992 – and an exoplanet was discovered, and confirmed, around the ordinary (main sequence) star 51 Pegasi (in 1995). It was this discovery that started the modern exoplanet gold rush.

There are now nearly 400 exoplanets detected and confirmed (and a few more whose status is uncertain). The Extrasolar Planets Encyclopaedia is a website which keeps track of all announcements, confirmations, etc. It also has an excellent tutorial on the methods used to discover such planets.

The first multiple system – a star with more than one exoplanet – discovered was Upsilon Andromedae (this star is actually a binary, so the discovery was a first in two ways). The first planet was discovered in 1996, and the second (and third!) in 1999. In this case independent confirmation came quite quickly. Today more than 20 such multiple-planet systems are known.

Most exoplanets have been discovered by the radial velocity, or Doppler, method: the star’s apparent speed away from (or towards) us – as measured by sensitive spectrographs – varies in a regular way, due to the gravitational pull of the exoplanet (remember that two bodies in a stable gravitational system will orbit the center of mass). Almost all have been found by ground-based telescopes. This is likely to change in the next few years as dedicated space-based telescopes – such as NASA’s Kepler and the ESA’s COROT – continue to make new discoveries. As these use the transit method (detecting tiny changes in a star’s intensity, as an exoplanet goes between it and us), the Doppler method may soon lose its ‘most exoplanets discovered’ status.

There are literally dozens of Universe Today stories on exoplanets! Here are a few, covering many different aspects: Smallest Terrestrial Exoplanet Yet Detected, Astrometry Finds an Exoplanet, Exoplanet Has Oddball Orbit, New Technique Allows Astronomers to Discover Exoplanets in Old Hubble Images, Carbon Dioxide Detected on Exoplanet HD 189733 b, and Exoplanet Image Confirmed.

There’s also a great overview of this topic in the Astronomy Cast episode A Zoo of Extrasolar Planets, and the somewhat older episode Discovering Another Earth is excellent too.

Source: Wikipedia