September 14, 2017

Exoplanet WASP-12b

Exoplanet WASP-12b

Astronomers have discovered that the well-studied exoplanet WASP-12b reflects almost no light, making it appear essentially pitch black. This discovery sheds new light on the atmospheric composition of the planet and also refutes previous hypotheses about WASP-12b’s atmosphere. The results are also in stark contrast to observations of another similarly sized exoplanet.

Using the Space Telescope Imaging Spectrograph (STIS) on the NASA/ESA Hubble Space Telescope, an international team led by astronomers at McGill University, Canada, and the University of Exeter, UK, have measured how much light the exoplanet WASP-12b reflects — its albedo — in order to learn more about the composition of its atmosphere.

The results were surprising, explains lead author Taylor Bell, a Master’s student in astronomy at McGill University who is affiliated with the Institute for Research on Exoplanets: “The measured albedo of WASP-12b is 0.064 at most. This is an extremely low value, making the planet darker than fresh asphalt!” This makes WASP-12b two times less reflective than our Moon which has an albedo of 0.12. Bell adds: “The low albedo shows we still have a lot to learn about WASP-12b and other similar exoplanets.”

WASP-12b orbits the Sun-like star WASP-12A, about 1400 light-years away, and since its discovery in 2008 it has become one of the best studied exoplanets. With a radius almost twice that of Jupiter and a year of just over one Earth day, WASP-12b is categorised as a hot Jupiter. Because it is so close to its parent star, the gravitational pull of the star has stretched WASP-12b into an egg shape and raised the surface temperature of its daylight side to 2600 degrees Celsius.

The high temperature is also the most likely explanation for WASP-12b’s low albedo. “There are other hot Jupiters that have been found to be remarkably black, but they are much cooler than WASP-12b. For those planets, it is suggested that things like clouds and alkali metals are the reason for the absorption of light, but those don’t work for WASP-12b because it is so incredibly hot," explains Bell.

The daylight side of WASP-12b is so hot that clouds cannot form and alkali metals are ionised. It is even hot enough to break up hydrogen molecules into atomic hydrogen which causes the atmosphere to act more like the atmosphere of a low-mass star than like a planetary atmosphere. This leads to the low albedo of the exoplanet.

To measure the albedo of WASP-12b the scientists observed the exoplanet in October 2016 during an eclipse, when the planet was near full phase and passed behind its host star for a time. This is the best method to determine the albedo of an exoplanet, as it involves directly measuring the amount of light being reflected. However, this technique requires a precision ten times greater than traditional transit observations. Using Hubble’s Space Telescope Imaging Spectrograph the scientists were able to measure the albedo of WASP-12b at several different wavelengths.

“After we measured the albedo we compared it to spectral models of previously suggested atmospheric models of WASP-12b”, explains Nikolay Nikolov (University of Exeter, UK), co-author of the study. “We found that the data match neither of the two currently proposed models.” The new data indicate that the WASP-12b atmosphere is composed of atomic hydrogen and helium.

WASP-12b is only the second planet to have spectrally resolved albedo measurements, the first being HD 189733b, another hot Jupiter. The data gathered by Bell and his team allowed them to determine whether the planet reflects more light towards the blue or the red end of the spectrum. While the results for HD 189733b suggest that the exoplanet has a deep blue colour, WASP-12b, on the other hand, is not reflecting light at any wavelength. WASP-12b does, however, emit light because of its high temperature, giving it a red hue similar to a hot glowing metal.

“The fact that the first two exoplanets with measured spectral albedo exhibit significant differences demonstrates the importance of these types of spectral observations and highlights the great diversity among hot Jupiters,” concludes Bell.

Image Credit: NASA, ESA, and G. Bacon (STScI)
Explanation from: https://www.spacetelescope.org/news/heic1714/

Spiral Galaxy NGC 6384

Spiral Galaxy NGC 6384

The NASA/ESA Hubble Space Telescope has produced this finely detailed image of the beautiful spiral galaxy NGC 6384. This galaxy lies in the constellation of Ophiuchus (The Serpent Bearer), not far from the centre of the Milky Way on the sky. The positioning of NGC 6384 means that we have to peer at it past many dazzling foreground Milky Way stars that are scattered across this image.

In 1971, one member of NGC 6384 stood out against these bright foreground stars when one of its stars exploded as a supernova. This was a Type Ia supernova, which occurs when a compact star that has ceased fusion in its core, called a white dwarf, increases its mass beyond a critical limit by gobbling up matter from a companion star. A runaway nuclear explosion then makes the star suddenly as bright as a whole galaxy.

While many stars have already come to the ends of their lives in NGC 6384, in the centre, star formation is being fuelled by the galaxy’s bar structure; astronomers think such galactic bars funnel gas inwards, where it accumulates to form new stars.

This picture was created from images take with the Wide Field Channel of Hubble’s Advanced Camera for Surveys. An image taken through a blue filter (F435W, coloured blue) was combined with an image taken through a near-infrared filter (F814W, coloured red). The total exposure times were 1050 s through each filter and the field of view is about 3 x 1.5 arcminutes.

Image Credit: ESA/Hubble & NASA
Explanation from: https://www.spacetelescope.org/images/potw1108a/

Star-Forming Region NGC 6729

Star-Forming Region NGC 6729

This image from ESO’s Very Large Telescope gives a close-up view of the dramatic effects new-born stars have on the gas and dust from which they formed. Although the stars themselves are not visible, material they have ejected is colliding with the surrounding gas and dust clouds and creating a surreal landscape of glowing arcs, blobs and streaks.

The star-forming region NGC 6729 is part of one of the closest stellar nurseries to the Earth and hence one of the best studied. This new image from ESO’s Very Large Telescope gives a close-up view of a section of this strange and fascinating region. The data were selected from the ESO archive by Sergey Stepanenko as part of the Hidden Treasures competition. Sergey’s picture of NGC 6729 was ranked third in the competition.

Stars form deep within molecular clouds and the earliest stages of their development cannot be seen in visible-light telescopes because of obscuration by dust. In this image there are very young stars at the upper left of the picture. Although they cannot be seen directly, the havoc that they have wreaked on their surroundings dominates the picture. High-speed jets of material that travel away from the baby stars at velocities as high as one million kilometres per hour are slamming into the surrounding gas and creating shock waves. These shocks cause the gas to shine and create the strangely coloured glowing arcs and blobs known as Herbig–Haro objects.

In this view the Herbig–Haro objects form two lines marking out the probable directions of ejected material. One stretches from the upper left to the lower centre, ending in the bright, circular group of glowing blobs and arcs at the lower centre. The other starts near the left upper edge of the picture and extends towards the centre right. The peculiar scimitar-shaped bright feature at the upper left is probably mostly due to starlight being reflected from dust and is not a Herbig–Haro object.

This enhanced-colour picture was created from images taken using the FORS1 instrument on ESO’s Very Large Telescope. Images were taken through two different filters that isolate the light coming from glowing hydrogen (shown as orange) and glowing ionised sulphur (shown as blue). The different colours in different parts of this violent star formation region reflect different conditions — for example where ionised sulphur is glowing brightly (blue features) the velocities of the colliding material are relatively low — and help astronomers to unravel what is going on in this dramatic scene.

Image Credit: ESO
Explanation from: https://www.eso.org/public/news/eso1109/

September 13, 2017

Alpha Centauri and Beta Centauri

Alpha Centauri and Beta Centauri

At the centre of this image of the Centaurus constellation are Alpha Centauri and Beta Centauri, two triple star systems. The brightest stars of both systems orbit near to each other, making them appear as one star. Alpha Centauri is the nearest "star" to Earth except for the Sun. This photograph of the Centaurus constellation was taken at ESO's La Silla Observatory.

Image Credit: ESO
Explanation from: https://www.eso.org/public/images/centaurus-ch17-bardon-cc/

Exoplanet WASP-19b

Exoplanet WASP-19b

Astronomers using ESO’s Very Large Telescope have detected titanium oxide in an exoplanet atmosphere for the first time. This discovery around the hot-Jupiter planet WASP-19b exploited the power of the FORS2 instrument. It provides unique information about the chemical composition and the temperature and pressure structure of the atmosphere of this unusual and very hot world.

A team of astronomers led by Elyar Sedaghati, an ESO fellow and recent graduate of TU Berlin, has examined the atmosphere of the exoplanet WASP-19b in greater detail than ever before. This remarkable planet has about the same mass as Jupiter, but is so close to its parent star that it completes an orbit in just 19 hours and its atmosphere is estimated to have a temperature of about 2000 degrees Celsius.

As WASP-19b passes in front of its parent star, some of the starlight passes through the planet’s atmosphere and leaves subtle fingerprints in the light that eventually reaches Earth. By using the FORS2 instrument on the Very Large Telescope the team was able to carefully analyse this light and deduce that the atmosphere contained small amounts of titanium oxide, water and traces of sodium, alongside a strongly scattering global haze.

“Detecting such molecules is, however, no simple feat,” explains Elyar Sedaghati, who spent 2 years as ESO student to work on this project. “Not only do we need data of exceptional quality, but we also need to perform a sophisticated analysis. We used an algorithm that explores many millions of spectra spanning a wide range of chemical compositions, temperatures, and cloud or haze properties in order to draw our conclusions.”

Titanium oxide is rarely seen on Earth. It is known to exist in the atmospheres of cool stars. In the atmospheres of hot planets like WASP-19b, it acts as a heat absorber. If present in large enough quantities, these molecules prevent heat from entering or escaping through the atmosphere, leading to a thermal inversion — the temperature is higher in the upper atmosphere and lower further down, the opposite of the normal situation. Ozone plays a similar role in Earth’s atmosphere, where it causes inversion in the stratosphere.

“The presence of titanium oxide in the atmosphere of WASP-19b can have substantial effects on the atmospheric temperature structure and circulation.” explains Ryan MacDonald, another team member and an astronomer at Cambridge University, United Kingdom. “To be able to examine exoplanets at this level of detail is promising and very exciting.” adds Nikku Madhusudhan from Cambridge University who oversaw the theoretical interpretation of the observations.

The astronomers collected observations of WASP-19b over a period of more than one year. By measuring the relative variations in the planet’s radius at different wavelengths of light that passed through the exoplanet’s atmosphere and comparing the observations to atmospheric models, they could extrapolate different properties, such as the chemical content, of the exoplanet’s atmosphere.

This new information about the presence of metal oxides like titanium oxide and other substances will allow much better modeling of exoplanet atmospheres. Looking to the future, once astronomers are able to observe atmospheres of possibly habitable planets, the improved models will give them a much better idea of how to interpret those observations.

“This important discovery is the outcome of a refurbishment of the FORS2 instrument that was done exactly for this purpose,” adds team member Henri Boffin, from ESO, who led the refurbishment project. “Since then, FORS2 has become the best instrument to perform this kind of study from the ground.”

Image Credit: ESO/M. Kornmesser
Explanation from: https://www.eso.org/public/news/eso1729/

Jupiter seen by NASA's Juno spacecraft

Jupiter seen by NASA's Juno spacecraft

This series of enhanced-color images shows Jupiter up close and personal, as NASA's Juno spacecraft performed its eighth flyby of the gas giant planet. The images were obtained by JunoCam.

From left to right, the sequence of images taken on September 1, 2017 from 3:03 p.m. to 3:11 p.m. PDT (6:03 p.m. to 6:11 p.m. EDT). At the times the images were taken, the spacecraft ranged from 7,545 to 14,234 miles (12,143 to 22,908 kilometers) from the tops of the clouds of the planet at a latitude range of -28.5406 to -44.4912 degrees.

Image Credit: NASA/JPL-Caltech/SwRI/MSSS/Gerald Eichstadt/Sean Doran
Explanation from: https://photojournal.jpl.nasa.gov/catalog/PIA21780

September 12, 2017

Earth and three hurricanes seen by Suomi NPP satellite

Earth and three hurricanes seen by Suomi NPP satellite

There was no shortage of storms brewing across the Atlantic basin in September 2017. On September 6, hurricanes Katia, Irma, and Jose lined up across the basin. The trio is visible in this image, captured that day by the Visible Infrared Imaging Radiometer Suite (VIIRS) on the Suomi NPP satellite. The image is a mosaic, assembled from images acquired throughout the day during several orbits of the satellite.

On September 6, Katia had strengthened over the southwestern Gulf of Mexico and was upgraded from tropical storm to hurricane status. The eye of Irma, a raging category 5 storm, passed north of Puerto Rico but still delivered strong winds and rain the Caribbean island. Meanwhile, Jose spun in the central Atlantic Ocean, and was also upgraded that day from a tropical storm to hurricane.

The bright strips are reflected sunlight, or “glint,” which show up over ocean areas in the middle of each orbit.

Image Credit: NASA Earth Observatory
Explanation from: https://earthobservatory.nasa.gov/NaturalHazards/view.php?id=90918

In search of exoplanets

In search of exoplanets

The Search for habitable Planets EClipsing ULtra-cOOl Stars (SPECULOOS) telescope will search for terrestrial exoplanets around nearby ultracool stars and brown dwarfs when it has first light in December 2017. SPECULOOS joins a fleet of exoplanet-searching telescopes, including the two TRAnsiting Planets and PlanetesImals Small Telescopes(TRAPPIST)— one at ESO’s La Silla Observatory in Chile and another at Ouka├»mden Observatory in Morocco.

Image Credit: H. Zodet/ESO
Explanation from: https://www.eso.org/public/images/upr-kh9a0928-cc/

X8.2 Solar Flare

X8.2 Solar Flare

The Sun emitted a significant solar flare, peaking at 12:06 p.m. EDT on September 10, 2017. NASA’s Solar Dynamics Observatory, which watches the Sun constantly, captured an image of the event. Solar flares are powerful bursts of radiation. Harmful radiation from a flare cannot pass through Earth's atmosphere to physically affect humans on the ground, however — when intense enough — they can disturb the atmosphere in the layer where GPS and communications signals travel.

This flare is classified as an X8.2-class flare. X-class denotes the most intense flares, while the number provides more information about its strength. An X2 is twice as intense as an X1, an X3 is three times as intense, etc.

This flare is the capstone on a series of flares from Active Region 2673, which was identified on August 29 and is currently rotating off the front of the Sun as part of our star’s normal rotation.

Image Credit: NASA/SDO/Goddard
Explanation from: https://www.nasa.gov/feature/goddard/2017/active-region-on-sun-continues-to-emit-solar-flares

September 11, 2017

Smoke over the United States seen by Suomi NPP satellite

Smoke over the United States seen by Suomi NPP satellite

With dozens of wildfires burning across the western United States and Canada, many North Americans have had the acrid taste of smoke in their mouths during the past few weeks. On September 5, 2017, the National Interagency Fire Center (NIFC) reported more than 80 large fires burning in nine western U.S. states. People living in large stretches of northern California, Oregon, Washington, Montana, and Idaho have been breathing what the U.S. government’s Air Now website rated as “hazardous” air.

The natural-color mosaic above was made from several scenes acquired on September 4, 2017, by the Visible Infrared Imaging Radiometer Suite (VIIRS) on the Suomi National Polar-orbiting Partnership (Suomi-NPP) satellite. The Ozone Mapper Profiler Suite (OMPS) on Suomi NPP also collected data on airborne aerosols as they were swept by winds from west to east across the continental United States (second image).

The OMPS map depicts relative aerosol concentrations, with lower concentrations appearing in yellow and higher concentrations appearing in dark orange-brown. Note that the sensor detects aerosols in high-altitude plumes more readily than lower plumes, so this map does not reflect air quality conditions at “nose height.” Rather it shows where large plumes of smoke were lofted several kilometers up into the atmosphere.

On September 5, roughly 7.8 million acres had burned in the United States since the beginning of 2017, according to NIFC. “While it is unlikely that this season will be record-breaking for modern fire record keeping in the western United States, it is above normal relative to the last decade—which has seen abundant fire activity,” said John Abatzoglou, a fire researcher at the University of Idaho. Unusually warm and dry conditions across a broad swath of the West has fueled the active fire season, noted Abatzoglou. A wet winter in some parts of the West also contributed by triggering the growth of more grass in the spring—grass that turns into fuel for fires in the summer.

Image Credit: NASA Earth Observatory
Explanation from: https://earthobservatory.nasa.gov/IOTD/view.php?id=90899

Saturn seen by Cassini spacecraft

Saturn seen by Cassini spacecraft

With this view, Cassini captured one of its last looks at Saturn and its main rings from a distance. The Saturn system has been Cassini's home for 13 years, but that journey is nearing its end.

Cassini has been orbiting Saturn for nearly a half of a Saturnian year but that journey is nearing its end. This extended stay has permitted observations of the long-term variability of the planet, moons, rings, and magnetosphere, observations not possible from short, fly-by style missions.

When the spacecraft arrived at Saturn in 2004, the planet's northern hemisphere, seen here at top, was in darkness, just beginning to emerge from winter. Now at journey's end, the entire north pole is bathed in the continuous sunlight of summer.

Images taken on October 28, 2016 with the wide angle camera using red, green and blue spectral filters were combined to create this color view. This view looks toward the sunlit side of the rings from about 25 degrees above the ringplane.

The view was acquired at a distance of approximately 870,000 miles (1.4 million kilometers) from Saturn. Image scale is 50 miles (80 kilometers) per pixel.

Image Credit: NASA/JPL-Caltech/Space Science Institute
Explanation from: https://photojournal.jpl.nasa.gov/catalog/PIA21345

Spiral Galaxy NGC 5398

Spiral Galaxy NGC 5398

This NASA/ESA Hubble Space Telescope picture shows NGC 5398, a barred spiral galaxy located about 55 million light-years away.

The galaxy is famous for containing an especially extensive HII region, a large cloud composed of ionised hydrogen (or HII, pronounced “H-two”, with H being the chemical symbol for hydrogen and the “II” indicating that the atoms have lost an electron to become ionised). NGC 5398’s cloud is named Tol 89 and sits at the lower left end of the galaxy’s central “bar” of stars, a structure that cuts through the galactic core and funnels material inwards to maintain the star formation occurring there.

Tol 86 is conspicuous in being the only large massive star forming complex in the entire galaxy, with an extension of roughly 5000 times 4000 light-years; it contains at least seven young and massive star clusters. The two brightest clumps within Tol 89, which astronomers have named simply “A” and “B”, appear to have undergone two bursts of star-forming activity — “starbursts” — roughly 4 million and less than 3 million years ago respectively. Tol 89-A is thought to contain a number of particularly bright and massive stars known as Wolf-Rayet stars, which are known for their high temperatures and extreme stellar winds.

Image Credit: ESA/Hubble & NASA
Explanation from: https://www.spacetelescope.org/images/potw1737a/