Three “Super-Earths” Found Orbiting One Star

Artist's impression of the trio of super earths. Image credit: ESO

“Does every single star harbor planets and, if yes, how many?” wonders planet hunter Michel Mayor. “We may not yet know the answer but we are making huge progress towards it.” Mayor and his team of European astronomers have found a star which is orbited by at least three planets. Using the High Accuracy Radial velocity Planet Searcher (HARPS) instrument at the ESO La Silla Observatory, they have found a triple system of super-Earths around the star HD 40307. This is the first system known to have at least three “super-Earth” sized planets.

Back in 1995, Mayor, along with Didier Queloz, made the first discovery of an extrasolar planet around 51 Pegasi, and since then more than 270 exoplanets have been found, mostly around sun-like stars.

Most of these planets are giants, such as Jupiter or Saturn, and current statistics show that about 1 out of 14 stars harbors this kind of planet.

“With the advent of much more precise instruments such as the HARPS spectrograph on ESO’s 3.6-m telescope at La Silla, we can now discover smaller planets, with masses between 2 and 10 times the Earth’s mass,” says Stéphane Udry, one of Mayor’s colleagues. Such planets are called super-Earths, as they are more massive than the Earth but less massive than Uranus and Neptune (about 15 Earth masses).

HD 40307 is slightly less massive than our Sun, and is located 42 light-years away towards the southern Doradus and Pictor constellations.

“We have made very precise measurements of the velocity of the star HD 40307 over the last five years, which clearly reveal the presence of three planets,” says Mayor.

The planets, having 4.2, 6.7, and 9.4 times the mass of the Earth, orbit the star with periods of 4.3, 9.6, and 20.4 days, respectively.

The group made the announcement at a conference about extrasolar planets being held in France. The same team also announced the discovery of two other planetary systems, also with the HARPS spectrograph. In one, a super-Earth (7.5 Earth masses) orbits the star HD 181433 in 9.5 days. This star also hosts a Jupiter-like planet with a period close to 3 years. The second system contains a 22 Earth-mass planet having a period of 4 days and a Saturn-like planet with a 3-year period as well.

“Clearly these planets are only the tip of the iceberg,” says Mayor. “The analysis of all the stars studied with HARPS shows that about one third of all solar-like stars have either super-Earth or Neptune-like planets with orbital periods shorter than 50 days.”

A planet in a tight, short-period orbit is indeed easier to find than one in a wide, long-period orbit.
“It is most probable that there are many other planets present: not only super-Earth and Neptune-like planets with longer periods, but also Earth-like planets that we cannot detect yet. Add to it the Jupiter-like planets already known, and you may well arrive at the conclusion that planets are ubiquitous,” concludes Udry.

Calculations from the sample of stars studied with HARPS implies that one solar-like star out of three harbors planets with masses below 30 Earth masses and an orbital period shorter than 50 days.

News Source: ESO press release

Re-use, Recycle and Share Your Spacecraft to Find Exoplanets

How do you get the most out of one spacecraft and find exoplanets in the process? Re-use, recycle and share. The spacecraft bus that brought the Deep Impact “impactor” to comet Tempel 1 in July of 2005 is still out in its heliocentric orbit and has been put to work double time where two new missions are sharing the same spacecraft. The combined operation is called EPOXI, which is a combo-acronym of the two separate missions. The Deep Impact Extended Investigation (DIXI) of comets will observe comet 103P/Hartley 2 during a close flyby in October 2010. But of current interest is the other half of the dynamic duo, called the Extrasolar Planet Observation and Characterization (EPOCh) which is observing stars already known to have transiting giant planets. Since the orbital plane of the giant planet has been identified, EPOCh is looking in that same plane for planets closer to Earth size. So far, 4 new planets have been found with this spacecraft, using the transit method. But EPOCh is also looking back at our home planet, using Earth as a baseline to be able to identify features on an exoplanet, such as continents and oceans.

The EPOXI team has focused most of its attention on the star GJ436. This red dwarf star which is 32 light-years from Earth has a Neptune-sized planet that transits in front of the star. Spitzer observations have shown its orbit to be oval shaped, or eccentric. “That virtually guarantees there is a second planet in this system,” said Drake Deming, Deputy Principal Investigator for EPOXI . “We have three weeks of data on this system. The habitable zone corresponds with where we believe this planet to be, and we hope to be below the Earth as far as the size.”

Earth observations will help to calibrate future observations of Earth-like exoplanets. EPOXI obtained a particularly interesting view of the Earth on May 29, when the Moon passed in front of the Earth as viewed from the spacecraft. This “transit” of the Moon is an event that may also be observed to occur for Earth-like exoplanets, and it may help us to deduce the nature of their surface features.

Deming and Deep Impact team leader Michael A’Hearn both said that sharing the spacecraft has gone smoothly. The EPOCh mission will continue until August 30 of this year, with the option of doing more planet searching if the team is able to preserve the margin of hydrazine fuel on board. “But,” said Deming, “when the hydrazine runs out we’re done for sure.”

Source: AAS press conference

Planet Discovered with Only 3 Times the Mass of the Earth

Most of the planets found to date have been massive and orbiting their parent stars at a fraction the orbit of Mercury – the hot jupiters. They’re interesting to astronomers, but the big goal is going to be finding Earth-mass planets orbiting other stars. To do this, astronomers are looking for less massive stars, where the effects of gravity from a smaller, Earth-sized planet will be easier to spot. Today, an international team of astronomers announced they have found a planet with only 3 times the mass of the Earth orbiting a tiny star that can barely support nuclear reactions.

The announcement of this new planet, known as MOA-2007-BLG-192Lb, was made at the 212th meeting of the American Astronomical Society held in St. Louis from June 1-5, 2008. Researchers from several universities, including the University of Notre Dame presented their findings.

The star is known as MOA-2007-BLG-192L, and it’s located about 3,000 light-years away. It’s probably not actually a star, with only 6% the mass of our own Sun. These objects are classified as brown dwarfs, because they don’t have enough mass to sustain nuclear reactions in the core. I say “probably” because the uncertainty of the observations might put it into the very low end of a hydrogen-burning star.

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.

This technique demonstrates the gravitational microlensing might be one of the best ways to find Earth-mass planets. In fact, the researchers think the technique will turn up the first one. Here’s David Bennett, from the University of Notre Dame: “I’ll hazard a prediction that the first extra-solar Earth-mass planet will be found by microlensing. But we’ll have to be very quick to beat the radial velocity programs and NASA’s Kepler mission, which will be launched in early 2009.”

Unfortunately, the lensing events can only happen one time. The foreground star will probably never be seen again since it was only revealed by the two stars lining up. Astronomers have to work fast to get all their data collected.

Original Source: University of Notre Dame News Release

Exoplanet Count Rises With New Discoveries

With several space- and ground-based telescopes, as well as dedicated space missions searching for exoplanets, or planets orbiting other stars, the count of new discoveries keeps rising. The current total now stands at 287 planets. The newest spacecraft dedicated to this search, the COROT Mission (Convection, Rotation and planetary Transits), announced the finding of two new exoplanets as well as an unknown celestial object. This discovery may be a “missing link” between stars and planets astronomers have been searching for.

The two new planets are gas giants of the hot Jupiter type, which orbit very close to their parent star and tend to have extensive atmospheres because heat from the nearby star gives them energy to expand. Most of the exoplanets found so far are the gas giant variety because of the limits of current technology.

In addition, an oddity dubbed “COROT-exo-3b” has raised particular interest among astronomers. It appears to be something between a brown dwarf, a sub-stellar object without nuclear fusion at its core but with some stellar characteristics, and a planet. Its radius is too small for it to be a super-planet.

If it is a star, it would be among the smallest ever detected. Follow-up observations from the ground have determined it to be at 20 Jupiter massses. This makes it twice as dense as the metal Platinum.

COROT has also detected extremely faint signals that, if confirmed, could indicate the existence of another exoplanet, as small as 1.7 times Earth’s radius.

This is an encouraging sign in the delicate and difficult search for small, rocky exoplanets that COROT has been designed for.

COROT launched in December 2006, with operations beginning in February of 2007. So far the mission has found four exoplanets. The mission started observations of its sixth star field at the beginning of May this year. During this observation phase, which will last 5 months, the spacecraft will simultaneously observe 12,000 stars.

More about COROT.

Original News Source: ESA

How to Detect Watery Worlds Around Other Stars

The Blue Marble. Image credit: NASA

If you want to know what a watery world might look like orbiting another star, just observe our own planet… from afar. The Blue Marble image of Earth, taken by the Apollo 17 astronauts on December 1972, shows how our planet is 70% water. Another world like ours, orbiting a distant star should be obvious – assuming you have a much more powerful telescope, and use the right techniques to analyze the light bouncing off the watery world.

Researchers from Penn State and the University of Hawaii have developed a technique that they think will help identify these watery worlds; potential homes for life around other stars. This technique is detailed in the most recent edition of the journal Icarus.

“We are looking for Earth-like planets in the habitable zone of their star, a band not too hot nor too cold for life to exist,” says Darren M. Williams, associate professor of physics and astronomy, Penn State Erie. “We also want to know if there is water on these planets.”

Here’s how you might tell the difference between a hellish planet like Venus, and a more comfortable watery world like Earth. A planet like Venus has a very dense atmosphere that scatters sunlight in all directions. From our vantage point, we would see the amount of light coming from the planet change depending on its position to its parent star. Just like Venus, we would see this extrasolar planet go through phases, changing in brightness in a very predictable way.

A watery world, like the Earth, would actually appear much darker when the whole disk is illuminated, since water is darker than dirt. But when the planet is in crescent, sunlight would glance off the surface of the water, and it would actually appear brighter.

The astronomers want to monitor the light curve of a distant planet as it spins on its axis and orbits its star. By watching the brightness of the light coming from the planet, they should be able to determine if it has a dense Venusian atmosphere, or is a better match for a watery world.

The equipment isn’t ready yet, but in the next 10 to 20 years, an observatory will probably be built with enough sensitivity to collect light from Earth-sized planets orbiting other stars. And this method should help determine if they’ll watery worlds, capable of supporting life.

Original Source: Penn State News Release

Another (Better) Opportunity to Send Your Name to Space

Kepler spacecraft. IMage credit: NASA

It’s a great idea, so all the missions might as well join in. Earlier today, Ian reported on how the Lunar Reconnaissance Orbiter mission is offering the chance for the public to ‘ride along’ to the moon by sending their names to be added to a computer chip which will be embedded on the spacecraft. Well, not to be outdone, the upcoming Kepler mission that will search for Earth-sized exoplanets is offering the same chance. But this is no sluff opportunity where you just fill in your name and you’re done: you’ve got to work a little and be creative! The Kepler folks would like you to also state in 100 words or less why you think the Kepler mission is important. I think that’s a great idea, and I’m going to add my name and statement right away. But there’s more reasons why I prefer the Kepler mission’s approach to sending your name to space:

Your name will be in an exciting Earth-trailing heliocentric orbit, going around the sun every 372.5 days.

This activity is done in association with the International Year of Astronomy 2009.

Your name will be on the spacecraft that will likely identify the first Earth-sized or smaller planet orbiting another star.

Your name will be launched on board a Delta II rocket.

Your name will be part of the mission that will determine the frequency of terrestrial and larger planets in or near the habitable zone of a wide variety of spectral types of stars.

Oh, the list goes on, but as you can see the Kepler mission will be THE mission to have your name be included.

So, here’s where you can add your name, as well as your statement of the importance of the Kepler mission. The deadline is November 1, 2008. And learn more about the mission here. Current plans are for a February 2009 launch for Kepler.

Original News Source: JPL press release

How Big Do Planets Get?

Artist's impression of Gliese 436 c

Question: How Big Can Planets Get?

Answer: Here in the Solar System, we have three kinds of planets: the inner terrestrial planets, the gas giants, and the ice planets. Sadly, Pluto is no longer a planet, so we won’t deal with that here. We know how big our planets are, but how big can planets actually get in other Solar Systems. What are the biggest possible planets?

Let’s start with terrestrial planets, like our Earth. We’ll set the size of the Earth and 1 Earth radius, and the mass as 1 Earth mass. We’ve seen that terrestrial planets can get smaller, with Mars and Mercury, and astronomers have detected larger terrestrial planets orbiting other stars.

The largest known rocky planet is thought to be Gliese 436 c. This is probably a rocky world with about 5 Earth masses and 1.5 times our planet’s radius. Amazingly, this planet is thought to be within its star’s habitable zone.

What’s the largest possible rocky planet? For this I put in an email to Dr. Sean Raymond, a post doctoral researcher at the Center for Astrophysics and Space Astronomy (CASA) at the University of Colorado. Here’s what he had to say:

“The largest “terrestrial” planet is generally considered the one before you get too thick of an atmosphere, which happens at about 5-10 Earth masses (something like 2 Earth radii). Those planets are more Earth-like than Neptune-like.”

Gas giants, of course, can come much larger. Jupiter is 317 times more massive than Earth, and 11 times larger. You could fit 1,400 Earths inside Jupiter.

Thebiggest planet in the Universe (at the time of this writing) is TrES-4, which is located 1,400 light years away in the constellation Hercules. The planet has been measured to be 1.4 times the size of Jupiter, but it only has 0.84 times Jupiter’s mass. With such a low density, the media was calling TrES-4 the puffy planet.

And once again, how large can they get? Again, here’s Dr. Raymond:

“In terms of gaseous planets, once they reach 15 Jupiter masses or so there is enough pressure in the core to ignite deuterium fusion, so those are considered “brown dwarfs” rather than planets.”

What is the biggest planet in the Solar System?

Why Haven’t Planets Been Detected Around Alpha Centauri?

Toliman
Artist impression of Alpha Centauri

Question: Why aren’t astronomers looking for planets around nearby stars like Alpha Centauri?
Answer: That’s a great question. Since Alpha Centauri is only a little over 4 light-years away, why aren’t astronomers studying it for planets, instead of the more distant stars.

Astronomers have included stars like Alpha Centauri in their search for extrasolar planets, they just haven’t found them yet. That’s because the techniques used to find extra solar planets require very large planets orbiting very close to their parent stars.

The first technique is called the radial velocity method. This is where the gravity of the planet yanks its parent star back and forth. The changes in the star’s velocity are measurable in the light that reaches the Earth.

The second technique looks for transits. This is where the planet passes in front of the parent star, dimming it slightly. By measuring the amount the light dims, astronomers are able to know if there’s a planet there, calculate its size and even determine what’s in its atmosphere.

A third technique detects microlensing events. A closer star focuses the light from a more distant star with its gravity. From Earth, we see a flare in brightness as the two stars line up perfectly. If the closer star has a planet orbiting it, that will change the light curve that astronomers detect, allowing them to calculate the size of the planet.

Most of the planets discovered to date are known as Hot Jupiters. These are planets much larger than Jupiter that orbit within the orbit of Mercury.

A team of astronomers led by Javiera Guedes from the University of California think that an Earth-sized planet should be detectable orbiting Alpha Centauri. They’re working to get a single dedicated telescope to watch the star, and work out if there are planets there. According to their calculations, it should only take about 5 years of intense observations by a dedicated telescope to work out the answer.

Using Laser Combs to Find Exoplanets

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We’ve run a couple of articles recently about new techniques to find Earth-like extra-solar planets. Here’s one more, but this new technique is really quite exciting. A new device, called a laser comb, uses femto-second (one millionth of one billionth of a second) pulses of laser light coupled with an atomic clock to provide a precise standard for measuring wavelengths of light. Also known as an “astro-comb,” these devices should give astronomers the ability to use the Doppler shift method with incredible precision to measure spectral lines of starlight up to 60 times greater than any current high-tech method, according to a new paper in the journal Nature.

Astronomers have been using the Doppler shift method to find exoplanets for the past 10 years. Current technology can measure spectral lines with a precision of 60 centimeters per second, which works good enough to find a planet 5 times the mass of Earth in a Mercury-like orbit around a Sun-like star. To find an Earth-mass planet in an Earth-like orbit, a precision of less than 5 cm per second is necessary, and the researchers believe they ultimately can achieve 1 cm per second precision.

The combs work by creating regular spikes of laser light that are evenly spaced in wavelength ”like the teeth of a comb” and can be projected onto a spectrograph.

One of the authors of the paper, Ronald Walsworth from the Harvard-Smithsonian Center for Astrophysics said the group should begin testing its prototype system in June 2008 at the Multi-Mirror Telescope (MMT) Observatory on Mount Hopkins in Arizona. And in 2009 the researchers plan to set up a planet-spotting system at the 4.2-metre William Herschel Telescope on La Palma, in the Canary Islands, in collaboration with the Geneva Observatory.

The inventors of the laser comb, John L. Hall and Theodor W. Hansch shared half of the 2005 Nobel Prize in Physics. This technology has previously been used in chemical sensing and telecommunications. If used with larger telescopes, researchers believe the astro comb could possibly make direct measurements of dark energy.

Original News Sources: Nature, and Nature News

New Search Technique May Lead to Discovery of Extra-solar Earth-Like Planets

The Holy Grail in the search for extra-solar planets would be to find an Earth-like world orbiting another star. A group of UK astronomers believe they have good chance of being the first to find such a planet with a revolutionary new camera called RISE. With RISE, scientists will search for extra-solar planets using a technique called “transit timing,” which may provide a short-cut to discovering Earth-like planets with existing technology.

The two primary techniques to find extra-solar planets are usually only sensitive to massive, gas giant planets in close orbit around their parent star, so-called “Hot Jupiters.” Firstly, planets can be found through their gravitational pull on the star they orbit – as the extra-solar planet moves the star wobbles back and forth, and by measuring this movement astronomers can deduce the presence of a planet. Secondly, the transit search technique looks for the changes in a star’s brightness as a planet passes in front of it.

But neither of these techniques is currently good enough to find small extra-solar planets similar to the Earth. With the new transit timing technique, the RISE camera will look for Earth-mass planets in orbit around stars already known to host Hot Jupiters.

Transit timing works on the principle that an isolated hot Jupiter planet orbiting its host will have a constant orbital period (i.e. its ‘year’ remains the same) and therefore it will block out the light from its parent star in a regular and predictable way. During the planet’s transit events, RISE can very accurately measure the rise and fall in the amount of light reaching the Earth from the parent star – the camera can be used to pinpoint the time of the centre of the event to within 10 seconds. RISE is a fast-read camera. It has a fixed “V+R” filter and reimaging optics giving a 7 x 7 acrminute field of view to maximize the number of comparison stars available. An e2V frame transfer detector is used to obtain a cycle time of less than 1 second.

Hot Jupiter planet.  Image Credit:  ESA

By observing and timing their transits, astronomers hope to detect small changes in the orbital periods of known hot Jupiters caused by the gravitational pull of other planets in the same system. In the right circumstances, even planets as small as the Earth could be found in this way.

“The potential of transit timing is the result of some very simple physics, where multi-planet systems will gravitationally kick one another around in their orbits – an effect often witnessed in our own Solar System,” said PhD student Neale Gibson of Queen’s University Belfast. “If Earth-mass planets are present in nearby orbits (which is predicted by current Hot-Jupiter formation theories) we will see their effect on the orbit of the larger transiting planets. RISE will allow us to observe and time the transits of extrasolar planets very accurately, which gives us the sensitivity required to detect the effect of even small Earth-mass planets.”

RISE was designed by astronomers at Queen’s University in collaboration with Liverpool John Moores University and is now installed on the 2 meter Liverpool Telescope on the Canary Island of La Palma. For more information about the RISE Camera, see Neale Gibson’s homepage.

Original News Source: NAM Press Release