New Study Claims There are Four Exoplanets Around Nearest Sun-Like Star!

It has been an exciting time for the field of exoplanet studies lately! Last summer, researchers from the European Southern Observatory (ESO) announced the discovery of an Earth-like planet (Proxima b) located in the star system that is the nearest to our own. And just six months ago, an international team of astronomers announced the discovery of seven rocky planets orbiting the nearby star TRAPPIST-1.

But in what could be the most encouraging discovery for those hoping to find a habitable planet beyond Earth, an an international team of astronomers just announced the discovery of four exoplanet candidates in the tau Ceti system. Aside from being close to the Solar System – just 12 light-years away – this find is also encouraging because the planet candidates orbit a star very much like our own!

The study that details these findings – “Color difference makes a difference: four planet candidates around tau Ceti” – recently appeared online and has been accepted for publication in the Astrophysical Journal. Led by researchers from the Center for Astrophysics Research (CAR) at the University of Hertfordshire, the team analyzed tau Ceti using a noise-eliminating model to determine the presence of four Earth-like planets.

This illustration compares the four planets detected around the nearby star tau Ceti (top) and the inner planets of our solar system (bottom). Credit: Fabo Feng/CAR/Univ. of Hertfordshire

This discovery was made possible thanks to ongoing improvements in instrumentation, observation and data-sharing, which are allowing for surveys of ever-increasing sensitivity. As Steven Vogt, a professor of astronomy and astrophysics at UC Santa Cruz and a co-author on the paper, said in a UCSC press release:

“We are now finally crossing a threshold where, through very sophisticated modeling of large combined data sets from multiple independent observers, we can disentangle the noise due to stellar surface activity from the very tiny signals generated by the gravitational tugs from Earth-sized orbiting planets.”

This is the latest in a long-line of surveys of tau Ceti, which has been of interest to astronomers for decades. By 1988, several radial velocity measurements were conducted of the star system that ruled out the possibility of massive planets at Jupiter-like distances. In 2012, astronomers from UC Santa Barabara presented a study that indicated that tau Ceti might be orbited by five exoplanets, two of which were within the star’s habitable zone.

The team behind that study included several members who produced this latest study. At the time, lead author Mikko Tuomi (University of Hertfordshire, a co-author on the most recent one) was leading an effort to develop better data analysis techniques, and used this star as a benchmark case. As Tuomi explained, theses efforts allowed them to rule out two of the signals that has previously been identified as planets:

“We came up with an ingenious way of telling the difference between signals caused by planets and those caused by star’s activity. We realized that we could see how star’s activity differed at different wavelengths and use that information to separate this activity from signals of planets.”

Artist’s impression of the Tau Ceti system, based on data retrieved in 2012. Credit: J. Pinfield/Univ. of Hertfordshire

For the sake of this latest study – which was led by Fabo Feng, a member of the CAR – the team relied on data provided by the High Accuracy Radial velocity Planet Searcher (HARPS) spectrograph at the ESO’s La Silla Observatory in Chile, and the High Resolution Echelle Spectrometer (HIRES) instrument at the W. M. Keck Observatory in Mauna Kea, Hawaii.

From this, they were able to create a model that removed “wavelength dependent noise” from radial velocity measurements. After applying this model to surveys made of tau Ceti, they were able to obtain measurements that were sensitive enough to detect variations in the star’s movement as small as 30 cm per second. In the end, they concluded that tau Ceti has a system of no more than four exoplanets.

As Tuomi indicated, after several surveys and attempts to eliminate extraneous noise, astronomers may finally have a clear picture of how many planets tau Ceti has, and of what type. “[N]o matter how we look at the star, there seem to be at least four rocky planets orbiting it,” he said. “We are slowly learning to tell the difference between wobbles caused by planets and those caused by stellar active surface. This enabled us to essentially verify the existence of the two outer, potentially habitable planets in the system.”

They further estimate from their refined measurements that these planets have masses ranging from four Earth-masses (aka. “super-Earths”) to as low as 1.7 Earth masses, making them among the smallest planets ever detected around a nearby sun-like star. But most exciting of all is the fact that that two of these planets (tau Ceti e and f) are located within the star’s habitable zone.

Recent studies have shown that rocky planets orbiting red dwarf stars will be tidally-locked and subject to intense radiation, reducing their chances of being habitable. Credit: M. Weiss/CfA

The reason for this is because tau Ceti is a G-type (yellow dwarf) star, which makes it similar to our own Sun – about 0.78 times as massive and half as bright. In contrast, many recently discovered exoplanets – such as Proxima b and the seven planets of TRAPPIST-1 – all orbit M-type (red dwarf) stars. Compared to our Sun, these stars are variable and unstable, increasing their chances of stripping the atmospheres of their respective planets.

In addition, since red dwarfs are much dimmer than our Sun, a rocky planet would have to orbit very closely to them  in order to be within their habitable zones. At this kind of distance, the planet would likely be tidally-locked, meaning that one side would constantly be facing towards the sun. This too makes the odds of life emerging on any such planet pretty slim.

Because of this, astronomers have been looking forward to finding more exoplanets around stars that are closer in size, mass and luminosity to our own. But before anyone gets too excited, its important to note these worlds are Super-Earths – with up to four times the mass of Earth. This means that (depending on their density as well) any life that might emerge on these planets would be subject to significantly increased gravity.

In addition, a massive debris disc surrounds the star, which means that these outermost planets are probably subjected to intensive bombardment by asteroids and comets. This not doesn’t exactly bode well for potential life on these planets! Still, this study is very encouraging, and for a number of reasons. Beyond finding strong evidence of exoplanets around a Sun-like star, the measurements that led to their detection are the most sensitive to date.

Artist’s impression of how an infant earth might look. Credit: ESO.

At the rate that their methods are improving, researchers should be getting to the 10-centimeter-per-second limit in no time at all. This is the level of sensitively required for detecting Earth analogs – aka. the brass ring for exoplanet-hunters. As Feng indicated:

“Our detection of such weak wobbles is a milestone in the search for Earth analogs and the understanding of the Earth’s habitability through comparison with these analogs. We have introduced new methods to remove the noise in the data in order to reveal the weak planetary signals.”

Think of it! In no time at all, exoplanet-hunters could be finding a plethora of planets that are not only very close in size and mass to Earth, but also orbiting within their stars habitable zones. At that point, scientists are sure to dispense with decidedly vague terms like “potentially habitable” and “Earth-like” and begin using terms like “Earth-analog” confidently. No more ambiguity, just the firm conviction that Earth is not unique!

With an estimated 100 billion planets in our galaxy alone, we’re sure to find several Earths out here. One can only hope they have given rise to complex life like our own, and that they are in the mood to chat!

Further Reading: UCSC, arXiv

The Bright Spots on Ceres are Blinking

All right, maybe not blinking like a flashlight (or a beacon on the tippity-top of a communication tower—don’t even start that speculation up) but the now-famous “bright spots” on the dwarf planet Ceres have been observed to detectably increase and decrease in brightness, if ever-so-slightly.

And what’s particularly interesting is that these observations were made not by NASA’s Dawn spacecraft, currently in orbit around Ceres, but from a telescope right here on Earth.

Researchers using the High Accuracy Radial velocity Planet Searcher (HARPS) instrument on ESO’s 3.6-meter telescope at La Silla detected “unexpected” changes in the brightness of Ceres during observations in July and August of 2015. Variations in line with Ceres’ 9-hour rotational period—specifically a Doppler effect in spectral wavelength created by the motion of the bright spots toward or away from Earth—were expected, but other fluctuations in brightness were also detected.

“The result was a surprise,” said Antonino Lanza from the INAF–Catania Astrophysical Observatory, co-author of the study. “We did find the expected changes to the spectrum from the rotation of Ceres, but with considerable other variations from night to night.”

Watch a video below illustrating the rotation of Ceres and how reflected light from the bright spots within Occator crater are alternately blue- and red-shifted according to the motion relative to Earth.

First observed with Hubble in December 2003, Ceres’ curious bright spots were resolved by Dawn’s cameras to be a cluster of separate regions clustered inside the 60-mile (90-km) -wide Occator crater. Based on Dawn data they are composed of some type of highly-reflective materials like salt and ice, although the exact composition or method of formation isn’t yet known.

Since they are made of such volatile materials though, interaction with solar radiation is likely the cause of the observed daily brightening. As the deposits heat up during the course of the 4.5-hour Ceres daytime they may create hazes and plumes of reflective particles.

“It has been noted that the spots appear bright at dawn on Ceres while they seem to fade by dusk,” noted study lead author Paolo Molaro in the team’s paper. “That could mean that sunlight plays an important role, for instance by heating up ice just beneath the surface and causing it to blast off some kind of plume or other feature.”

Once day turns to night these hazes will re-freeze, depositing the particles back down to the surface—although never in exactly the same way. These slight differences in evaporation and condensation could explain the random variation in daily brightening observed with HARPS.

These findings have been published the journal Monthly Notices of the Royal Astronomical Society (full text on arXiv here.)

Source: ESO

Two Comet Groups Discovered Around Beta Pictoris

Between the years 2003 and 2011, the High Accuracy Radial velocity Planet Searcher – better known as HARPS – made more than a thousand observations of nearby star, Beta Pictoris. On board the ESO 3.6-metre telescope at the La Silla Observatory in Chile, the sensitive instrument normally combs the sky nightly in search of exoplanets, but lately it has contributed to another astounding discovery… exocomets!

Located about 63 light-years from the Sun, Beta Pictoris is a youthful star, estimated to be only around 20 million years old. Keeping it company in space is a vast disc of material. This swarm of gas and dust is the beginnings of an active planetary system and was likely created by the destruction of comets and collisions of rocky bodies like asteroids. Now a French team using HARPS has been able to create the most complete catalog of comets to date from this system. Researchers have found no less than five hundred comets belonging to Beta Pictoris and they divide in two unique branches of exocomets. Split into both old and new, these two active flows behave much like our own cometary groups… They have either made many trips around the parent star or are the product of a recent breakup of one or more objects.

Flavien Kiefer (IAP/CNRS/UPMC), lead author of the new study, sets the scene: “Beta Pictoris is a very exciting target! The detailed observations of its exocomets give us clues to help understand what processes occur in this kind of young planetary system.”

Beta Pictoris is located about 60 light-years away towards the constellation of Pictor (the Painter's Easel) and is one of the best-known examples of a star surrounded by a dusty debris disc. Earlier observations showed a warp of the disc, a secondary inclined disc and comets falling onto the star, all indirect, but tell-tale signs that strongly suggested the presence of a massive planet. Observations done with the NACO instrument on ESO’s Very Large Telescope in 2003, 2008 and 2009, have proven the presence of a planet around Beta Pictoris. It is located at a distance between 8 and 15 times the Earth-Sun separation — or Astronomical Units — which is about the distance Saturn is from the Sun. The planet has a mass of about nine Jupiter masses and the right mass and location to explain the observed warp in the inner parts of the disc. This image, based on data from the Digitized Sky Survey 2, shows a region of approximately 1.7 x 2.3 degrees around Beta Pictoris.  Credit: ESO/Sky Survey II
Beta Pictoris is located about 60 light-years away towards the constellation of Pictor (the Painter’s Easel) and is one of the best-known examples of a star surrounded by a dusty debris disc. Earlier observations showed a warp of the disc, a secondary inclined disc, and comets falling onto the star, all indirect, but tell-tale signs that strongly suggested the presence of a massive planet. Observations done with the NACO instrument on ESO’s Very Large Telescope in 2003, 2008, and 2009, have proven the presence of a planet around Beta Pictoris. It is located at a distance between 8 and 15 times the Earth-Sun separation — or Astronomical Units — which is about the distance Saturn is from the Sun. The planet has a mass of about nine Jupiter masses and the right mass and location to explain the observed warp in the inner parts of the disc. This image, based on data from the Digitized Sky Survey 2, shows a region of approximately 1.7 x 2.3 degrees around Beta Pictoris. Credit: ESO/Sky Survey II

Just like discovering planets through the transit method, astronomers believe exocomets can cause a disturbance in the amount of light we can see from a given star. When these icy travelers exhaust themselves, their gas and dust tails could absorb a portion of the star light passing through them. For nearly three decades scientists had been aware of minute changes in the light from Beta Pictoris, but attributing it to comets was next to impossible to prove. Their tiny light was simply overpowered by the light of the star and could not be imaged from Earth.

Enter HARPS…

Using more than a thousand observations taken by this sensitive equipment, astronomers chose a sample of 493 exocomets unrelated to each other, but sharing in the Beta Pictoris system. Of these, some were dutifully followed for hours at several different times. The size and speed of the gas clouds produced were carefully measured. Researchers were even able to document the orbital properties of some of these exocomets – the size and shape of their passage paths in relation to the parent star allowing scientists to infer their distances.

Knowing that comets exist around other stars is very exciting – and knowing that solar systems around other stars work much like our own is downright rewarding. Through this study, we’re able to take a unique look at what might be several hundreds of exocomets connected to a solitary exo-planet system. What the research has revealed is two distinct branches of the comet family tree. One of these is old comets – their orbit dictated by a single, massive planet. The other half of the family fork belongs to comets that might have arisen from the destruction of a larger object.

The older group behaves in a predictable manner. These exocomets have differing orbital patterns, and their gas and dust production is greatly reduced. If they follow the same rules as the ones in our solar system, it’s typical behavior for a comet which has exhausted its volatiles during multiple trips around the parent star and is also being controlled by the system’s massive planet. This is exciting because it confirms the planet’s presence and distance!

“Moreover, the orbits of these comets (eccentricity and orientation) are exactly as predicted for comets trapped in orbital resonance with a massive planet.” says the science team. “The properties of the comets of the first family show that this planet in resonance must be at about 700 million kilometres from the star – close to where the planet Beta Pictoris b was discovered.”

The second group also behaves in a predictable manner. These exocomets have nearly identical orbits and their emissions are active and radical. Observations of this cometary type tell us they more than likely originated from the destruction of a larger body and the rubble is caught in a orbit which allows the fragments to graze Beta Pictoris. According to the research team: “This makes them similar to the comets of the Kreutz family in the Solar System, or the fragments of Comet Shoemaker-Levy 9, which impacted Jupiter in July 1994.”

Flavien Kiefer concludes: “For the first time a statistical study has determined the physics and orbits for a large number of exocomets. This work provides a remarkable look at the mechanisms that were at work in the Solar System just after its formation 4.5 billion years ago.”

Original Story Source: “Two Families of Comets Found Around Nearby Star – Biggest census ever of exocomets around Beta Pictoris” – ESO Science News Release

Planets Plentiful Around Abundant Red Dwarf Stars, Study Says

Good news for planet-hunters: planets around red dwarf stars are more abundant than previously believed, according to new research. A new study — which detected eight new planets around these stars — says that “virtually” all red dwarfs have planets around them. Moreover, super-Earths (planets that are slightly larger than our own) are orbiting in the habitable zone of about 25% of red dwarfs nearby Earth.

“We are clearly probing a highly abundant population of low-mass planets, and can readily expect to find many more in the near future – even around the very closest stars to the Sun,” stated Mikko Tuomi, who is from the University of Hertfordshire’s centre for astrophysics research and lead author of the study.

The find is exciting for astronomers as red dwarf stars make up about 75% of the universe’s stars, the study authors stated.

The researchers looked at data from two planet-hunting surveys: HARPS (High Accuracy Radial Velocity Planet Searcher) and UVES (Ultraviolet and Visual Echelle Spectrograph), which are both at the European Southern Observatory in Chile. The two instruments measure the effect a planet has on its parent star, specifically by examining the gravitational “wobble” the planet’s orbit produces.

An artist's concept of a rocky world orbiting a red dwarf star. (Credit: NASA/D. Aguilar/Harvard-Smithsonian center for Astrophysics).
An artist’s concept of a rocky world orbiting a red dwarf star. (Credit: NASA/D. Aguilar/Harvard-Smithsonian center for Astrophysics).

Putting the information from both sets of data together, this amplified the planet “signals” and revealed eight planets around red dwarf stars, including three super-Earths in habitable zones. The researchers also applied a probability function to estimate how abundant planets are around this type of star.

The planets are between 15 and 80 light years away from Earth, and add to the 17 other planets found around low-mass dwarfs. Scientists also detected 10 weaker signals that could use more investigation, they said.

The study will be available shortly in the Monthly Notices of the Royal Astronomical Society and is available in preprint version at this link.

Source: University of Hertfordshire

HARPS Hauls in Over Fifty New Exoplanets

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Yesterday astronomers with the High Accuracy Radial velocity Planet Searcher or HARPS, announced a record-breaking discovery of more than fifty new exoplanets. This is the largest batch of confirmed extra solar planets ever announced at once. Another reason the discovery is noteworthy is that sixteen of the planets that were detected fall under the “super-Earth” classification, meaning the planets are thought to be rocky worlds less than ten times Earth’s mass.

The HARPS team, led by Michel Mayor from the University of Geneva, used the 3.6-metre telescope at ESO’s La Silla Observatory in Chile and claim their spectrograph instrument on the telescope is the most successful planet-finder to date. The team’s data suggests that about 40% of stars similar to our Sun have at least one planet less massive than Saturn.

The announcement of the big planetary haul was made at the Extreme Solar Systems II exoplanet conference taking place this week in Wyoming in the US.

How did Mayor and his team discover so many planets, and how are they certain of their findings?

The HARPS instrument uses a technique called “radial velocity”. Essentially, the instrument detects the slight movement of a star moving toward and away from observers on Earth. The changes in radial velocity shift the star’s light spectrum. When the star moves away from observers on Earth, the light is shifted to longer, redder wavelengths, called redshifting. When the star moves toward Earth, the opposite happens and the star’s light is blueshifted. Through various hardware and software upgrades over the years, HARPS is now so sensitive, it can detect radial velocities of about 1 meter per second and exoplanets less than twice the mass of Earth.

The radial velocity method of exoplanet detection that HARPS uses is different from say, the Kepler mission which uses the “transit” method to detect exoplanet candidates. The transit method, comparatively speaking, still uses the light from a distant star, but instead of measuring redshift or blue shift, Kepler instead looks for a dimming of the star’s light as exoplanets pass in front of their host star.

HARPS has been operating for the past eight years, using the radial velocity technique to discover over 150 new planets. HARPS has also detected a considerable portion of the known exoplanets less massive than Neptune (seventeen Earth masses). “The harvest of discoveries from HARPS has exceeded all expectations and includes an exceptionally rich population of super-Earths and Neptune-type planets hosted by stars very similar to our Sun. And even better — the new results show that the pace of discovery is accelerating,” said Mayor.

Image of the star HD 85512 using red and blue filters. The diffraction spikes are due to the telescope itself and are not caused by the star . Image Credit: ESO/Davide De Martin and Digitized Sky Survey 2.
One particular exoplanet Mayor and his team cited was HD85512b, estimated to be just over 3.5 times Earth’s mass. “The detection of HD 85512 b is far from the limit of HARPS and demonstrates the possibility of discovering other super-Earths in the habitable zones around stars similar to the Sun,” added Mayor. HD 85512b also happens to be situated on the edge of the “habitable zone” around its parent star – a zone where conditions could allow for water on the surface of a planet orbited in said zone.

Based on these latest findings, as well as previous HARPS discoveries, the team plans to install an exact copy of the HARPS instrumentation on the Telescopio Nazionale Galileo in the Canary Islands. The duplicate HARPS will allow scientists to survey stars in the northern sky.

“In the coming ten to twenty years we should have the first list of potentially habitable planets in the Sun’s neighborhood,” Mayor said. “Making such a list is essential before future experiments can search for possible spectroscopic signatures of life in the exoplanet atmospheres.”

The total tally of confirmed planets orbiting other stars stands at about 600, depending on who you ask. The Jet Propulsion Laboratory’s PlanetQuest website, shows 564 exoplanets while the Extrasolar Planets Encyclopedia, a database kept by astrobiologist Jean Schneider of the Paris-Meudon Observatory, lists 645 alien worlds. The discrepancy comes because PlanetQuest doesn’t add to their total until an exoplanet has been completely confirmed.

Source: ESO Press Release

Ray Sanders is a Sci-Fi geek, astronomer and space/science blogger. Visit his website Dear Astronomer and follow on Twitter (@DearAstronomer) or Google+ for more space musings.

HARPS Tunes In On Habitable Planet

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Using the High Accuracy Radial velocity Planet Searcher (HARPS), a team of scientists at University of Geneva, Switzerland, led by the Swiss astronomer Stephane Udry made a sound discovery… an Earth-like planet orbiting star HD 85512. Located about 36 light years away in the constellation of Vela, this extrasolar planet is one of the smallest to be documented in the “habitable zone” and could very well be a potential home to living organisms.

Circling its parent star every 54 days at about the quarter of the distance which Earth orbits the Sun, the newly discovered planet shows every sign of a temperate climate and a possibility of water. However, the rocky little world would need to exhibit some very cloudy skies to make the grade.

“We model rocky planets with H2O/CO2/N2 atmospheres, representative of geological active planets like Earth, to calculate the maximum Bond albedo as a function of irradiation and atmosphere composition and the edges of the HZ for HD 85512 b. These models represent rocky geological active planets and produce a dense CO2 atmosphere at the outer edge, an Earth-like atmosphere in the middle, and a dense H2O atmospheres at the inner edge of the HZ.” says the team. “The inner limit for the 50% cloud case corresponds to the “Venus water loss limit”, a limit that was empirically derived from Venus position in our Solar System (0.72 AU).”

But there’s always from one extreme to another when it comes to a planet being in just the right place. “The inner edge of the (Habitable zone) denotes the location where the entire water reservoir can be vaporized by runaway greenhouse conditions, followed by the photo-dissociation of water vapor and subsequent escape of free hydrogen into space. The outer boundary denotes the distance from the star where the maximum greenhouse effect fails to keep CO2 from condensing permanently, leading to runaway glaciation,” says the Kaltenegger/Udry/Pepe study.

While the whole scenario might not be exciting to some, the study is helping to lay a very solid foundation for evaluating current and future planet candidates for life supporting conditions. “A larger sample will improve our understanding of this field and promises to explore a very interesting parameter space that indicates the potential coexistence of extended H/He and H2O dominated atmospheres as well as rocky planet atmospheres in the same mass and temperature range.” says Kaltenegger. “HD 85512 b is, with Gl 581 d, the best candidate for exploring habitability to date, a planet on the edge of habitability.”

And one step closer to better understanding what’s out there…

For further reading: A Habitable Planet around HD 85512?.

More Help on the Way for Verifying ExoPlanets in Kepler’s Dataset

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With the Kepler spacecraft finding over 1,200 planetary candidates, the next step is verifying their actual status. That will be a big job, but help is on the way. In April 2012, a new spectrograph called HARPS-North will come online to help confirm and characterize Kepler’s planetary candidates. It will be mounted on the 3.6-meter Telescopio Nazionale Galileo (TNG) in the Canary Islands.

“The Kepler mission gives us the size of a planet, based on the amount of light it blocks when it passes in front of its star. Now we need to measure planetary masses, so that we can calculate the densities. That will allow us to distinguish rocky planets and water worlds from ones dominated by atmospheres of hydrogen and helium,” explained astronomer David Latham from the Harvard-Smithsonian Center for Astrophysics (CfA).


If the name HARPS (High-Accuracy Radial velocity Planet Searcher) is familiar, it is because this new instrument is a duplicate the successful design of an existing instrument in the Southern Hemisphere, the original HARPS spectrograph whichoperates on the 3.6-meter European Southern Observatory telescope at La Silla, Chile. At the TNG telescope, the new HARPS-North will be able to study the same region of the sky viewed by the Kepler spacecraft, within the northern constellations of Cygnus and Lyra.

The Harvard-Smithsonian CfA is part of an international collaboration building the new instrument.

Kepler main field of view. Credit: NASA/JPL - Caltech

Verifying a exoplanet can be tricky. In some circumstances, an eclipsing binary star can mimic the shallow dimming due to a planet crossing in front of its star. Ground-based measurements are needed to verify an orbiting world by spotting the gravitational wobbles it induces in its host star, in a method known as radial velocity.

A spectrograph operates by splitting the light from a star into its component wavelengths or colors, much like a prism. Chemical elements absorb light of specific colors, leaving dark lines in the star’s spectrum. Those lines shift position slightly due to the Doppler shift created by the gravitational tug of an orbiting planet on its star.

The new HARPS-North will be augmented by technology now under development, such as a laser comb for wavelength calibration, which will allow it to detect subtle radial-velocity signals.

“We have set up an enthusiastic collaboration among various institutions to build a northern copy of HARPS. We all expect HARPS-N to be as successful as its southern ‘brother,'” said HARPS-N principal investigator Francesco Pepe of the Astronomical Observatory of Geneva.

“HARPS-N will pursue the most interesting targets found by Kepler, at a level that no one else in the world can do,” said Dimitar Sasselov, Director of the Harvard Origins of Life Initiative. “HARPS-N will partner with Kepler to characterize worlds enough like Earth that they might be able to support life as we know it.”

Source: Harvard Smithsonian CfA

Scientists Predict Earth-Like Habitable Exoplanet Will Be Found in 2011

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Two astronomers have written a paper and say that the first Earth-like, habitable exoplanet will be announced in May of 2011. Do they have inside information, a crystal ball, or amazing powers of prediction? No, they base their projection on math and trends from the past 15 years of exoplanet discoveries. And if the discoveries continue at their present rate, the researchers say next year is the year of the long awaited holy grail of finding another Earth-like planet out in the cosmos.

Samuel Arbesman from Harvard Medical School in Boston and Gregory Laughlin at the University of California, Santa Cruz take a scientometric approach to their prediction. Scientometrics is the science of measuring and analyzing science, and is often done using bibliometrics which is a measurement of the impact of scientific publications. Arbesman and Laughlin said this type of work highlights the usefulness of predictive scientometric techniques to understand the pace of scientific discovery in many fields.

They use the properties of previously discovered exoplanets along with external estimates for the discovery of the first potentially habitable extrasolar planet.

In their paper they indicate that since astronomers have been discovering extrasolar planets at an increasing rate since 1995 and the discoveries follow a well understood pattern, it should be easy to predict when planet searchers will hit the jackpot.

The first exoplanets found were the massive Jupiter or larger-sized planets which were the easiest to find, and then as techniques improved over the past 15 years, astronomers have found smaller planets, some just a few times more massive than Earth.

A single realization of the habitability of extrasolar planets over time. H values for the extrasolar planets are plotted, with those of the upper envelope (maximum H for a given year of discovery) indicated in black. The black curve is the logistic best- t curve of the upper envelope, using a nonlinear model, where R = 28:78 and y = 2011:10. The horizontal grey line indicates the maximum value of H = 1, the presence of an Earth-like habitable planet. Credit: Arbesman and Laughlin

Arbesman and Laughlin took that rate of discovery, and they also needed to factor in all the variables for what we think will make a planet habitable: the surface temperature must allow liquid water to exist, so that life as we know it can appear, and that depends on the size of the star, how far the planet orbits from its star, and what type of surface the exoplanet has.

They conclude there is a 66 per cent probability of finding another Earth by 2013, a 75 per cent probability by 2020, and a 95 per cent probability by 2264, but the median date of discovery is in May 2011. And not just sometime in May, but “early May.”

In June 2010, the Kepler Telescope team revealed they had found 750 exoplanet candidates, and a fair number of those confirmed might be Earth-sized. They expect they can confirm and announce some of these candidates in February 2011. But Arbesman and Laughlin predict it might take longer. “Because of the limited time base line of the mission to date, the Kepler planet candidates to published in February 2011 may be too hot to support significant values for H (which is their habitability metric),” they wrote in their paper.

So, if their prediction comes true, that might mean another team, such as the HARPS, or Keck, or CoRoT, or other exoplanet-finding wizards might make the discovery.

“It must be noted that by publicizing our prediction, there is a concern that it will become accurate,” Arbesman and Laughlin write in their paper, “simply due to the well-studied Hawthorne Effect. However, due to the large number of observations and long periods of time required to confirm an extrasolar planet discovery, it is unlikely that our prediction at this time will appreciably affect the announcement of the discovery of an Earth-like planet. Therefore, it is reasonable to use the habitability metric curve as a rough prediction for when the first potentially habitable planet will be discovered, in this case, as early as May 2011, and likely by the end of 2013.”

It will be interesting to see how accurate their prediction turns out to be!

Read the paper: “A Scientometric Prediction of the Discovery of the First Potentially Habitable Planet with a Mass Similar to Earth.”

Additional Source: Technology Review Blog

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