Extrasolar Planets Archives

November 16, 2009December 24, 2015 by Nicholos Wethington

Second Exoplanet with Retrograde Orbit Discovered

The exoplanet HAT-P-7b has been observed to have a very curious orbit. It either has a highly tilted orbit – passing almost over the poles of its parent star, HAT-P-7 – or a retrograde orbit; that is, orbiting in the opposite direction of its parent star. Two teams of researchers, both using the Subaru Telescope in Japan, have published papers on the bizarre properties of this planet, the second exoplanet ever observed to have a retrograde orbit.

In our Solar System, the planets calmly rotate in the same direction as that of their parent star, in our case the Sun. This is called a prograde orbit, and the Earth has the most inclined orbit with regard to the equator of the Sun, of 7.15 degrees. The planet HAT-P-7b, however, has an orbit that is the opposite of the rotation of its parent star but in the same plane as the equator (effectively a 180 degree incline). This is called a retrograde orbit. It may also be the case that it is inclined to at least 86 degrees of the equator of its Sun, so as to have almost a polar orbit. The researchers have yet to determine the true rotation of the star HAT-P-7, and thus which scenario is true for the exoplanet.

“There is a large range of uncertainty because we have not measured the true angle between the orbit and the stellar equator. Instead we can only measure the angle that we see from our perspective on Earth,” said Winn in a MIT press release.

HAT-P-7b is about 1.4 times as wide and 1.8 times as massive as Jupiter, and lies approximately 1,000 light years from the Earth.

A Japanese collaboration led by Norio Narita of the National Astronomical Observatory of Japan, and a team led by MIT assistant professor of physics Joshua Winn both published papers detailing their studies of HAT-P-7b. These studies were published in the Publications of Astronomical Society of Japan Letters October 25, 2009 and the Astrophysical Journal Letters for October 1, 2009, respectively. The paper by the Japanese team is available for your perusal on Arxiv here.

Both research teams used the Subaru Telescope’s High Dispersion Spectrograph instrument to observe the star HAT-P-7. The spectrograph allowed the researchers to monitor the redshift or blueshift of light as the planet orbited the star. In planets with a prograde orbit, their transit in front of the star blocks the blue shifting of the light from the star first, then blocks the redshift of the light, making the star appear to move more that it actually is.

In the case of HAT-P-7b the effect was reversed – that is, the redshifted light appeared bluer, then the blueshifted light appeared redder, making it apparent that the orbit of the planet was not in the same direction of that of HAT-P-7. This effect is called the Rossiter-McLaughlin effect, illustrated below.

The Rossiter McLaughlin effect makes a star appear to have a greater radial velocity than it actually does because of a transiting planet. Image Credit: Nicholas Shanks, WikiMedia Commons

The odd orbit of HAT-P-7b could have been caused by a number of different factors, and theorists that model the formation of exoplanetary systems will not have to “go back to the drawing boards”. The general consensus is that planets form out of a large disk of material orbiting the star, and thus all orbit in the same direction as the disk out of which they formed.

Multiple planets could have formed in an unstable configuration around the star, and their proximity to each other could have caused a rather chaotic series of gravitational billiards to boot HAT-P-7b into its current orbit. Another explanation is the presence of a third object in the system, such as another massive planet or companion star, that is tilting the orbit of HAT-P-7b due to what’s known as the Kozai effect.

The announcement of the retrograde orbit of HAT-P-7b came only one day after the announcement on August 12th, 2009 that the planet WASP-17b orbits opposite its parent star. HAT-P-7b is also one of the first exoplanets to be studied by the Kepler mission, which studied the planet’s orbit over 10 days. Kepler will take further images of the star during its mission, and by observing the rotation of spots on the surface of the star, nail down the orbital direction, after which we’ll know whether HAT-P-7b is orbiting “backwards” or around the poles of the star.

Source: Subaru Telescope, MIT

November 11, 2009December 24, 2015 by Nancy Atkinson

Shedding Light on the Sun’s “Lithium Mystery”

Artist’s impression of a baby star still surrounded by a protoplanetary disc in which planets are forming. Credit: ESO

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

November 4, 2009December 24, 2015 by Nancy Atkinson

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

November 2, 2009December 24, 2015 by Nancy Atkinson

No Earth-Sized Planet Hunting for Kepler Until 2011

Artist concept of Kepler in space. Credit: NASA/JPL

[/caption]
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

October 20, 2009December 24, 2015 by Nancy Atkinson

Organic Molecules Detected in Exoplanet Atmosphere

Artist concept of exoplanet HD 209458b. Credit: NASA/JPL-Caltech/T. Pyle (SSC)

[/caption]

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

October 19, 2009December 24, 2015 by Nancy Atkinson

HARPS Discovers 32 New Exoplanets

A planet 6 times the mass of Earth orbits around the star Gliese 667 C, which belongs to a triple system. Credit: ESO

[/caption]

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

October 1, 2009December 24, 2015 by Nancy Atkinson

Rocky World COROT-7b Rains Rocks

The exoplanet Corot-7b is so close to its Sun-like host star that it must experience extreme conditions. Sister planet, CoRot-7c is seen in the distance. Credit: ESO

[/caption]
If any creature lives on COROT-7b, the recently confirmed rocky exoplanet, they might think the sky is falling. This planet is close enough to its star that its “day-face” is hot enough to melt rock, and according to models by scientists at Washington University in St. Louis, COROT-7b’s atmosphere is made up of the ingredients of rocks and when “a front moves in,” pebbles condense out of the air and rain into lakes of molten lava below. Yikes!

This unusual rocky world was the first planet found orbiting the star COROT-7, an orange dwarf in the constellation Monoceros, or the Unicorn. COROT-7b is less than twice the size of Earth and only five times its mass. But this place is nothing like Earth.

“The only atmosphere this object has is produced from vapor arising from hot molten silicates in a lava lake or lava ocean,” said Bruce Fegley Jr., Ph.D., professor at Wash U, who created models of COROT-7b along with research assistant Laura Schaefer. Their paper appears in the Oct. 1 issue of The Astrophysical Journal.

This star-facing side has a temperature of about 2600 degrees Kelvin (4220 degrees Fahrenheit). That’s infernally hot—hot enough to vaporize rocks. The global average temperature of Earth’s surface, in contrast, is only about 288 degrees Kelvin (59 degrees Fahrenheit).

The side in perpetual shadow, on the other hand, is positively chilly at 50 degrees Kelvin (-369 degrees Fahrenheit).

COROT detects small, transiting exoplanet. Credits: CNES

So, what might the planet’s atmosphere be like? To find out Schaefer and Fegley used thermochemical equilibrium calculations with a special computer program called MAGMA that was used to study high-temperature volcanism on Io, Jupiter’s innermost Galilean satellite.

Because the scientists didn’t know the exact composition of the planet, they ran the program with four different starting compositions. “We got essentially the same result in all four cases,” says Fegley.
Perhaps because they were cooked off, COROT-7b’s atmosphere has none of the volatile elements or compounds that make up Earth’s atmosphere, such as water, nitrogen and carbon dioxide.

“Sodium, potassium, silicon monoxide and then oxygen — either atomic or molecular oxygen — make up most of the atmosphere.” But there are also smaller amounts of the other elements found in silicate rock, such as magnesium, aluminum, calcium and iron.

Why is there oxygen on a dead planet, when it didn’t show up in Earth’s atmosphere until 2.4 billion years ago, when plants started to produce it?

“Oxygen is the most abundant element in rock,” says Fegley, “so when you vaporize rock what you end up doing is producing a lot of oxygen.”

The peculiar atmosphere has its own singular weather. “As you go higher the atmosphere gets cooler and eventually you get saturated with different types of ‘rock’ the way you get saturated with water in the atmosphere of Earth,” explains Fegley. “But instead of a water cloud forming and then raining water droplets, you get a ‘rock cloud’ forming and it starts raining out little pebbles of different types of rock.”

Even more strangely, the kind of rock condensing out of the cloud depends on the altitude. The atmosphere works the same way as fractionating columns, the tall knobby columns that make petrochemical plants recognizable from afar. In a fractionating column, crude oil is boiled and its components condense out on a series of trays, with the heaviest one (with the highest boiling point) sulking at the bottom, and the lightest (and most volatile) rising to the top.

Instead of condensing out hydrocarbons such as asphalt, petroleum jelly, kerosene and gasoline, the exoplanet’s atmosphere condenses out minerals such as enstatite, corundum, spinel, and wollastonite. In both cases the fractions fall out in order of boiling point.

The atmosphere of COROT-7b may not be breathable, but it is certainly amusing.

Source: Washington University

September 16, 2009December 24, 2015 by Nancy Atkinson

Smallest Expoplanet Yet Has Rocky Surface

[/caption]
More details are emerging on the extrasolar planet that was discovered by the CoRoT satellite back in February. New information about this planet make it first in many respects: It is the smallest known exoplanet, it is the closest exoplanet yet to its host star, which also makes it the fastest; it orbits its star at a speed of more than 750,000 kilometers per hour. Plus, data reveal the presence of twin sister planet, another so-called super-Earth called CoRot-7c in this alien solar system. Was Obi-wan wise to conceal it?

(Sorry, couldn’t resist the twin sister/Star Wars reference….)

“This is science at its thrilling and amazing best,” says Didier Queloz, leader of the team that made the observations. “We did everything we could to learn what the object discovered by the CoRoT satellite looks like and we found a unique system.”

Back in February, the team of astronomers weren’t sure if this was a rocky planet or a possibly a theoretical “ocean world.” In theory, such planets would initially be covered partially in ice and they would later drift towards their star, with the ice melting to cover it in liquid.

But the temperatures on this planet would mean whatever is on the surface of this planet is likely boiling, whether it be water or lava. The probable temperature on its “day-face” is above 2,000 degrees, but minus 200 degrees on its night face. Undoubtedly, this is an extreme environment.

The star TYC 4799-1733-1, now known as CoRot-7, and its satellites have been studied intensely since February with many telescopes on the ground. The system is located towards the constellation of Monoceros (the Unicorn) at a distance of about 500 light-years. Slightly smaller and cooler than our Sun, CoRoT-7 is also thought to be younger, with an age of about 1.5 billion years.

Every 20.4 hours, the planet eclipses a small fraction of the light of the star for a little over one hour by one part in 3,000. CoRoT-7b is only 2.5 million kilometres away from its host star, or 23 times closer than Mercury is to the Sun.

The initial set of measurements, however, could not provide the mass of the exoplanet. Such a result requires extremely precise measurements of the velocity of the star, which is pulled a tiny amount by the gravitational tug of the orbiting exoplanet. The problem with CoRoT 7b is that these tiny signals are blurred by stellar activity in the form of “starspots” (just like sunspots on our Sun), which are cooler regions on the surface of the star. Therefore, the main signal is linked to the rotation of the star, with makes one complete revolution in about 23 days.

To help look closely, astronomers used the High Accuracy Radial velocity Planet Searcher (HARPS) spectrograph attached to the ESO 3.6-metre telescope at the La Silla Observatory in Chile. This device is turning out to be one of the best planet hunters around.

“Even though HARPS is certainly unbeaten when it comes to detecting small exoplanets, the measurements of CoRoT-7b proved to be so demanding that we had to gather 70 hours of observations on the star,” said co-author François Bouchy.

HARPS delivered, allowing the astronomers to tease out the 20.4-hour signal in the data. This figure led them to infer that CoRoT-7b has a mass of about five Earth masses, placing it in rare company as one of the lightest exoplanets yet found.

“Since the planet’s orbit is aligned so that we see it crossing the face of its parent star – it is said to be transiting – we can actually measure, and not simply infer, the mass of the exoplanet, which is the smallest that has been precisely measured for an exoplanet,” says team member Claire Moutou. “Moreover, as we have both the radius and the mass, we can determine the density and get a better idea of the internal structure of this planet.”

The calculated density is close to Earth’s, suggesting that the planet’s composition is similarly rocky.

Could there be life there? Well, probably not as we know it.

“CoRoT-7b is so close [to its star] that the place may well look like Dante’s Inferno,” said Queloz. “Theoretical models suggest that the planet may have lava or boiling oceans on its surface. With such extreme conditions this planet is definitively not a place for life to develop,” says Queloz.

The sister planet, CoRoT-7c, circles its host star in 3 days and 17 hours and has a mass about eight times that of Earth, so it too is classified as a super-Earth. Unlike CoRoT-7b, this sister world does not pass in front of its star as seen from Earth, so astronomers cannot measure its radius and thus its density.

But as it stands now, CoRoT-7 is the first star known to have a planetary system made of two short period super-Earths.

Lead image caption: The exoplanet Corot-7b is so close to its Sun-like host star that it must experience extreme conditions. Sister planet, CoRot-7c is seen in the distance. Credit: ESO

Source: EurekAlert

August 18, 2009April 26, 2016 by Nancy Atkinson

Send a Tweet to our Alien Friends on Gliese 581 D

An artist’s impression of Gliese 581d, an exoplanet about 20.3 light-years away from Earth, in the constellation Libra. Credit: NASA

[/caption]

If you’ve ever wanted to communicate with aliens, here’s your chance. Cosmos Magazine is offering the chance to send a message to another planet, Gliese 581 d. This exoplanet is about 20.3 light-years from Earth, in the constellation Libra, and some have said if life is elsewhere in the Universe, this is the mostly likely place that we currently know about. It was first discovered in 2007, and astronomers say this planet is well within the habitable zone around its star, where liquid water oceans could exist. Cosmos is collecting short, 160 character messages to be transmitted out to the vicinity of Gliese 581 d with the Canberra Deep Space Communication Complex in Tidbinbilla, Australia. Cosmos says it will take about 20 years for the message to reach its destination, and admits there is no guarantee of a response. If interested, check out Cosmos’ “Hello From Earth” webpage. Hurry, as the deadline is 5pm Monday August 24, 2009 Sydney time (07:00 GMT Monday 24 August 2009).

This is Cosmos’ way of celebrating the IYA and National Science Week in Australia. However, we’ve had lively discussions here on before UT about if we are sending too much information out into the cosmos. What do you think?

August 12, 2009April 26, 2016 by Nancy Atkinson

Biggest Exoplanet Yet Orbits the Wrong Way

An artist's impression of a transiting exoplanet Credit:NASA/Hubble

[/caption]
Planet hunters from the UK have discovered the largest exoplanet yet, and its uniqueness doesn’t end there. Dubbed WASP-17, this extra large world is twice the size of Jupiter but is super-lightweight, “as dense as expanded polystyrene” one astronomer said. Plus it is going the wrong way around its home sun, making it the first exoplanet known to have a retrograde orbit. As a likely a victim of planetary billiards, astronomers say this unusual planet casts new light on how planetary systems form and evolve.

Astronomers say the planet must have flipped direction after a near miss with another huge “big brother” planet swung it around like a slingshot. “Newly formed solar systems can be violent places,” said graduate student David Anderson, of Keele University. “Our own moon is thought to have been created when a Mars-sized planet collided with the recently formed Earth and threw up a cloud of debris that turned into the moon. A near collision during the early, violent stage of this planetary system could well have caused a gravitational slingshot, flinging WASP-17 into its backwards orbit.”

An artist's impression of a transiting exoplanet. Credit: ESA C Carreau

Though it is only half the mass of Jupiter it is bloated to nearly twice Jupiter’s size.

Astronomers have long wondered why some extra-solar planets are far bigger than expected, and WASP-17 points to the explanation. Scattered into a highly elliptical, retrograde orbit, it would have been subjected to intense tides. Tidal compression and stretching would have heated the gas-giant planet to its current, hugely bloated extent. “This planet is only as dense as expanded polystyrene, seventy times less dense than the planet we’re standing on”, said Coel Hellier, also of Keele University.

WASP-17 is the 17th new exoplanet found by the Wide Area Search for Planets (WASP) consortium of UK universities. The WASP team detected the planet using an array of cameras that monitor hundreds of thousands of stars, searching for small dips in their light when a planet transits in front of them. Geneva Observatory then measured the mass of WASP-17, showing that it was the right mass to be a planet. The WASP-South camera array that led to the discovery of WASP-17 is hosted by the South African Astronomical Observatory.

Read the team’s paper here.

Source: STFC