Blue Light Observations Indicate Water-Rich Atmosphere of Super-Earth

Artist's rendition of a transit of GJ 1214 b in blue light. The blue sphere represents the host star GJ 1214, and the black ball in front of it on the right is GJ 1214 b. (Credit: NAOJ)

Artist’s rendition of a transit of GJ 1214 b in blue light. The blue sphere represents the host star GJ 1214, and the black ball in front of it on the right is GJ 1214 b. (Credit: NAOJ)

A Japanese research team of astronomers and planetary scientists has used Subaru Telescope’s two optical cameras, Suprime-Cam and the Faint Object Camera and Spectrograph (FOCAS), with a blue transmission filter to observe planetary transits of super-Earth GJ 1214 b (Gilese 1214 b). The team investigated whether this planet has an atmosphere rich in water or hydrogen. The Subaru observations show that the sky of this planet does not show a strong Rayleigh scattering feature, which a cloudless hydrogen-dominated atmosphere would predict. When combined with the findings of previous observations in other colors, this new observational result implies that GJ 1214 b is likely to have a water-rich atmosphere….
… Read more at www.sciencedaily.com

Astronomers Image Lowest-mass Exoplanet Around a Sun-like Star

Using infrared data from the Subaru Telescope in Hawaii, an international team of astronomers has imaged a giant planet around the bright star GJ 504. Several times the mass of Jupiter and similar in size, the new world, dubbed GJ 504b, is the lowest-mass planet ever detected around a star like the sun using direct imaging techniques.

“If we could travel to this giant planet, we would see a world still glowing from the heat of its formation with a color reminiscent of a dark cherry blossom, a dull magenta,” said Michael McElwain, a member of the discovery team at NASA’s Goddard Space Flight Center in Greenbelt, Md. “Our near-infrared camera reveals that its color is much more blue than other imaged planets, which may indicate that its atmosphere has fewer clouds.”
GJ 504b orbits its star at nearly nine times the distance Jupiter orbits the sun, which poses a challenge to theoretical ideas of how giant planets form.

This composite combines Subaru images of GJ 504 using two near-infrared wavelengths (orange, 1.6 micrometers, taken in May 2011; blue, 1.2 micrometers, April 2012). Once processed to remove scattered starlight, the images reveal the orbiting planet, GJ 504b. Image Credit: NASA’s Goddard Space Flight Center/NOAJ

This composite combines Subaru images of GJ 504 using two near-infrared wavelengths (orange, 1.6 micrometers, taken in May 2011; blue, 1.2 micrometers, April 2012). Once processed to remove scattered starlight, the images reveal the orbiting planet, GJ 504b. Image Credit: NASA’s Goddard Space Flight Center/NOAJ

According to the most widely accepted picture, called the core-accretion model, Jupiter-like planets get their start in the gas-rich debris disk that surrounds a young star. A core produced by collisions among asteroids and comets provides a seed, and when this core reaches sufficient mass, its gravitational pull rapidly attracts gas from the disk to form the planet.
While this model works fine for planets out to where Neptune orbits, about 30 times Earth’s average distance from the sun (30 astronomical units, or AU), it’s more problematic for worlds located farther from their stars. GJ 504b lies at a projected distance of 43.5 AU from its star; the actual distance depends on how the system tips to our line of sight, which is not precisely known.
“This is among the hardest planets to explain in a traditional planet-formation framework,” explained team member Markus Janson, a Hubble postdoctoral fellow at Princeton University in New Jersey. “Its discovery implies that we need to seriously consider alternative formation theories, or perhaps to reassess some of the basic assumptions in the core-accretion theory.”
The research is part of the Strategic Explorations of Exoplanets and Disks with Subaru (SEEDS), a project to directly image extrasolar planets and protoplanetary disks around several hundred nearby stars using the Subaru Telescope on Mauna Kea, Hawaii. The five-year project began in 2009 and is led by Motohide Tamura at the National Astronomical Observatory of Japan (NAOJ).

This chart locates the fifth-magnitude star GJ 504, also known as 59 Virginis, which is visible to the unaided eye from suburban skies. Image Credit: NASA’s Goddard Space Flight Center

This chart locates the fifth-magnitude star GJ 504, also known as 59 Virginis, which is visible to the unaided eye from suburban skies. Image Credit: NASA’s Goddard Space Flight Center

While direct imaging is arguably the most important technique for observing planets around other stars, it is also the most challenging.
“Imaging provides information about the planet’s luminosity, temperature, atmosphere and orbit, but because planets are so faint and so close to their host stars, it’s like trying to take a picture of a firefly near a searchlight,” explained Masayuki Kuzuhara at the Tokyo Institute of Technology, who led the discovery team.
The SEEDS project images at near-infrared wavelengths with the help of the telescope’s novel adaptive optics system, which compensates for the smearing effects of Earth’s atmosphere, and two instruments: the High Contrast Instrument for the Subaru Next Generation Adaptive Optics and the InfraRed Camera and Spectrograph. The combination allows the team to push the boundary of direct imaging toward fainter planets.
A paper describing the results has been accepted for publication in The Astrophysical Journal and will appear in a future issue.
The researchers find that GJ 504b is about four times more massive than Jupiter and has an effective temperature of about 460 degrees Fahrenheit (237 Celsius).
It orbits the G0-type star GJ 504, which is slightly hotter than the sun and is faintly visible to the unaided eye in the constellation Virgo. The star lies 57 light-years away and the team estimates the systems is about 160 million years, based on methods that link the star’s color and rotation period to it age.
Young star systems are the most attractive targets for direct exoplanet imaging because their planets have not existed long enough to lose much of the heat from their formation, which enhances their infrared brightness.
“Our sun is about halfway through its energy-producing life, but GJ504 is only one-thirtieth its age,” added McElwain. “Studying these systems is a little like seeing our own planetary system in its youth.”

Read more at http://www.nasa.gov/content/goddard/astronomers-image-lowest-mass-exoplanet-around-a-sun-like-star/#.UgDv0dJ7Lbx

First Planet Discovered Orbiting a Brown Dwarf

Astronomers have long supposed that planets can form around brown dwarfs just as they do around ordinary stars. Now they’ve found the first example

Geometry of the lens system. The closed figures composed concave curves represent the caustic and the line with an arrow is the source trajectory. M1 and M2 represent the binary lens components, where M1 is the heavier one. Greyscale represents the lensing magnification where brighter tone denotes higher magnifications. All lengths are scaled by the Einstein radius corresponding to the total mass of the binary lens

Geometry of the lens system. The closed figures composed concave curves represent the caustic and the line with an arrow is the source trajectory. M1 and M2 represent the binary lens components, where M1 is the heavier one. Greyscale represents the lensing magnification where brighter tone denotes higher magnifications. All lengths are scaled by the Einstein radius corresponding to the total mass of the binary lens (http://arxiv.org/abs/1307.6335)

Astrophysical calculations show that any star that is smaller than about 1/10th of the mass of the sun cannot sustain hydrogen fusion reactions at its core. These failed stars never light up. Instead they wander the galaxy as warm, dark balls of hydrogen known as brown dwarfs.

Brown dwarfs probably form through the same process that lead to ordinary stars but merely on a smaller scale. If that’s correct, planets should also form in the protoplanetary disks of gas and dust around brown dwarfs. Indeed, astronomers have seen a number of protoplanetary disks of this type.

Until now, however, they’ve never seen a planet orbiting a brown dwarf. That’s not really surprising.

The standard methods for detecting planets look for the way a star wobbles as a planet orbits or at how its magnitude changes as a planet passes in front. But given that brown dwarfs are dim and difficult to see, these methods have yet to produce fruit.

All that changes today with the announcement by an international team of astronomers that they’ve discovered a planet orbiting a brown dwarf the first time. These guys have made their discovery using an entirely different method of detection called gravitational lensing. This occurs when one body passes in front of another and its gravity focuses light from the more distant object towards Earth. That works regardless of the brightnesses involved.

The brown dwarf in question is almost 6000 light years from Earth in the Fish Hook constellation. Astronomers first noticed an unusual change in its brightness in April 2012. Further investigation showed that this was indeed a lensing event.

These guys conclude that the brown dwarf is being orbited by a planet about twice the mass of Jupiter at a distance of just under one astronomical unit. The brown dwarf itself is about 10 times larger than its companion.

That’s the first time astronomers have found an object orbiting a brown dwarf that can be truly described as a planet. The technical definition of a planet is that it must have formed in the parent object’s protoplanetary disk.

Astronomers have seen other planet-sized objects orbiting brown dwarfs but only at distances of several tens of astronomical units. That’s too far to have been part of the protoplanetary disk. “Thus,…,they are not bona fide planets,” say the team.

So that’s a modest first for this team. It raises the question of what kind of conditions exist on such a planet and, of course, whether these could support life.

This planet almost certainly does not fall into that category but where there is one planet, there are almost certainly others. Astronomers can now have some fun speculating on the Goldilocks zones around brown dwarfs where conditions are just right for life and how to spot the interesting planets inside them.

Read more at http://www.technologyreview.com/view/517556/

A Warmer Planetary Haven Around Cool Stars …

… as Ice Warms Rather Than Cools

n a bit of cosmic irony, planets orbiting cooler stars may be more likely to remain ice-free than planets around hotter stars. This artist’s concept illustrates a planet orbiting a red dwarf star. (Credit: NASA)

n a bit of cosmic irony, planets orbiting cooler stars may be more likely to remain ice-free than planets around hotter stars. This artist’s concept illustrates a planet orbiting a red dwarf star. (Credit: NASA)

In a bit of cosmic irony, planets orbiting cooler stars may be more likely to remain ice-free than planets around hotter stars. This is due to the interaction of a star’s light with ice and snow on the planet’s surface.

Stars emit different types of light. Hotter stars emit high-energy visible and ultraviolet light, and cooler stars give off infrared and near-infrared light, which has a much lower energy.
It seems logical that the warmth of terrestrial or rocky planets should depend on the amount of light they get from their stars, all other things being equal. But new climate model research led by Aomawa Shields, a doctoral student in the University of Washington astronomy department, has added a surprising new twist to the story: Planets orbiting cool stars actually may be much warmer and less icy than their counterparts orbiting much hotter stars, even though they receive the same amount of light.
That’s because the ice absorbs much of the longer wavelength, near-infrared light predominantly emitted by these cooler stars. This is counter to what we experience on Earth, where ice and snow strongly reflect the visible light emitted by the Sun.
Around a cooler (M-dwarf) star, the more light the ice absorbs, the warmer the planet gets. The planet’s atmospheric greenhouse gases also absorb this near-infrared light, compounding the warming effect….
… Read more at http://www.sciencedaily.com/releases/2013/07/130719103151.htm

NASA’s Kepler Discovers its Smallest ‘Habitable Zone’ Planets to Date

elative sizes of Kepler habitable zone planets discovered as of April 18, 2013. Left to right: Kepler-22b, Kepler-69c, Kepler-62e, Kepler-62f, and Earth (except for Earth, these are artists' renditions). Image credit: NASA Ames/JPL-Caltech

Relative sizes of Kepler habitable zone planets discovered as of April 18, 2013. Left to right: Kepler-22b, Kepler-69c, Kepler-62e, Kepler-62f, and Earth (except for Earth, these are artists’ renditions). Image credit: NASA Ames/JPL-Caltech

NASA’s Kepler mission has discovered two new planetary systems that include three super-Earth-size planets in the “habitable zone,” the range of distance from a star where the surface temperature of an orbiting planet might be suitable for liquid water.

The Kepler-62 system has five planets; 62b, 62c, 62d, 62e and 62f. The Kepler-69 system has two planets; 69b and 69c. Kepler-62e, 62f and 69c are the super-Earth-sized planets.

Two of the newly discovered planets orbit a star smaller and cooler than the sun. Kepler-62f is only 40 percent larger than Earth, making it the exoplanet closest to the size of our planet known in the habitable zone of another star. Kepler-62f is likely to have a rocky composition. Kepler-62e, orbits on the inner edge of the habitable zone and is roughly 60 percent larger than Earth.

The third planet, Kepler-69c, is 70 percent larger than the size of Earth, and orbits in the habitable zone of a star similar to our sun. Astronomers are uncertain about the composition of Kepler-69c, but its orbit of 242 days around a sun-like star resembles that of our neighboring planet Venus.

Scientists do not know whether life could exist on the newfound planets, but their discovery signals we are another step closer to finding a world similar to Earth around a star like our sun….
…. Read more: http://www.nasa.gov/mission_pages/kepler/news/kepler-62-kepler-69.html

More planets could harbour life

Scientists should not exclude planets that reside in colder regions

By Jonathan Ball

New computer models suggest there could be many more habitable planets out there than previously thought.

Scientists have developed models to help them identify planets in far-away solar systems that are capable of supporting life.

Estimates of habitable planet numbers have been based on the likelihood of them having surface water.

But a new model allows scientists to identify planets with underground water kept liquid by planetary heat.

The research was presented at the British Science Festival in Aberdeen.

Water is fundamental for life as we know it.

Planets too close to their sun lose surface water to the atmosphere through evaporation.

Surface water on planets located in the more frigid distant reaches from their sun is locked away as ice.

The dogma was, for water to exist in its life-giving liquid form, a planet had to be the right distance from its sun – in the habitable zone.

As Sean McMahon, the PhD student from Aberdeen University who is carrying out the work explained: “It’s the idea of a range of distances from a star within which the surface of an Earth-like planet is not too hot or too cold for water to be liquid.

“So traditionally people have said that if a planet is in this Goldilocks zone – not too hot and not too cold – then it can have liquid water on its surface and be a habitable planet”

But researchers are starting to think that the Goldilocks theory is far too simple.

Planets can receive two sources of heat – heat direct from the star and heat generated deep inside the planet.

As you descend through the crust of the Earth, the temperature gets higher and higher. Even when the surface is frozen, water can exist below ground.

Immense quantities of water in fact – teeming with primitive life.

As Prof John Parnell, also from Aberdeen University said: “There is a significant habitat for microorganisms below the surface of the Earth, extending down several kilometres.

“And some workers believe that the bulk of life on Earth could even reside in this deep biosphere.”

So the Aberdeen team are developing models to predict which far-flung planets might harbour underground reservoirs of liquid water with the possibility of alien life.

Explaining their rationale, Mr McMahon said: “If you take into account the possibility of deep biospheres, then you have a problem reconciling that with the idea of a narrow habitable zone defined only by conditions at the surface.”

As you move away from the star the amount of heat a planet receives from the star decreases and the surface water freezes – but any water held deep inside will stay liquid if the internal heat is high enough – and that water could support life.

Even a planet so far from the star that it receives almost no solar heat could still maintain underground liquid water.

According to Mr McMahon, “There will be several times more [habitable] planets”.

Read more: www.bbc.co.uk