Mount Agung Volcano Eruption

Mount Agung, Bali, Indonesia

November 27, 2017

Image Credit: Firdia Lisnawati/AP

Saturn

After more than 13 years at Saturn, and with its fate sealed, NASA's Cassini spacecraft bid farewell to the Saturnian system by firing the shutters of its wide-angle camera and capturing this last, full mosaic of Saturn and its rings two days before the spacecraft's dramatic plunge into the planet's atmosphere.

During the observation, a total of 80 wide-angle images were acquired in just over two hours. This view is constructed from 42 of those wide-angle shots, taken using the red, green and blue spectral filters, combined and mosaicked together to create a natural-color view.

Six of Saturn's moons -- Enceladus, Epimetheus, Janus, Mimas, Pandora and Prometheus -- make a faint appearance in this image. (Numerous stars are also visible in the background.)

A second version of the mosaic is provided in which the planet and its rings have been brightened, with the fainter regions brightened by a greater amount. (The moons and stars have also been brightened by a factor of 15 in this version.)

The ice-covered moon Enceladus -- home to a global subsurface ocean that erupts into space -- can be seen at the 1 o'clock position. Directly below Enceladus, just outside the F ring (the thin, farthest ring from the planet seen in this image) lies the small moon Epimetheus. Following the F ring clock-wise from Epimetheus, the next moon seen is Janus. At about the 4:30 position and outward from the F ring is Mimas. Inward of Mimas and still at about the 4:30 position is the F-ring-disrupting moon, Pandora. Moving around to the 10 o'clock position, just inside of the F ring, is the moon Prometheus.

This view looks toward the sunlit side of the rings from about 15 degrees above the ring plane. Cassini was approximately 698,000 miles (1.1 million kilometers) from Saturn, on its final approach to the planet, when the images in this mosaic were taken. Image scale on Saturn is about 42 miles (67 kilometers) per pixel. The image scale on the moons varies from 37 to 50 miles (59 to 80 kilometers) pixel. The phase angle (the Sun-planet-spacecraft angle) is 138 degrees.

The Cassini spacecraft ended its mission on September 15, 2017.

Image Credit: NASA/JPL-Caltech/Space Science Institute
Explanation from: https://photojournal.jpl.nasa.gov/catalog/PIA17218

Exoplanet NGTS-1b

The Next Generation Transit Survey (NGTS) instrument at ESO’s Paranal Observatory in northern Chile has found its first exoplanet, a hot Jupiter orbiting an M-dwarf star now named NGTS-1. The planet, NGTS-1b, is only the third gas giant to have been observed transiting an M-dwarf star, following Kepler-45b and HATS-6b. NGTS-1b is the largest and most massive of these three, with a radius of 130% and a mass of 80% those of Jupiter.

The NGTS uses an array of twelve 20-centimetre telescopes to search for the tiny dips in the brightness of a star caused when a planet in orbit around it passes in front of it (“transits”) and blocks some of its light. Once NGTS-1b had been discovered its existence was confirmed by follow-up observations at ESO’s La Silla Observatory: photometric observations with EulerCam on the 1.2-metre Swiss Leonhard Euler Telescope; and spectroscopic investigations with the HARPS instrument on ESO’s 3.6-metre telescope.

Small planets are relatively common around M-dwarf stars, whereas gas giants like NGTS-1b appear to be rarer around M-dwarfs than they are around stars more like the Sun. This is consistent with current theories of planet formation, but observations of more M-dwarfs are needed before a clear understanding of the numbers of giant planets around them can be arrived at. The NGTS is specifically designed to provide better data on planets around M-dwarf stars, and since they account for around 75% of stars in the Milky Way, studying them will help astronomers to understand the majority population of planets in the Galaxy.

The future could be very exciting for this exoplanet system as it has the potential to be studied in greater detail by the suite of instruments on board the NASA/ESA/CSA James Webb Space Telescope (JWST) which is due to be launched in 2019.

Image Credit: University of Warwick/Mark Garlick
Explanation from: https://www.eso.org/public/announcements/ann17076/

Galaxy Cluster Abell 2537

This picturesque view from the NASA/ESA Hubble Space Telescope peers into the distant Universe to reveal a galaxy cluster called Abell 2537.

Galaxy clusters such as this one contain thousands of galaxies of all ages, shapes and sizes, together totalling a mass thousands of times greater than that of the Milky Way. These groupings of galaxies are colossal — they are the largest structures in the Universe to be held together by their own gravity.

Clusters are useful in probing mysterious cosmic phenomena like dark matter and dark energy, the latter of which is thought to define the geometry of the entire Universe. There is so much matter stuffed into a cluster like Abell 2537 that its gravity has visible effects on its surroundings. Abell 2537’s gravity warps the very structure of its environment (spacetime), causing light to travel along distorted paths through space. This phenomenon can produce a magnifying effect, allowing us to see objects that lie behind the cluster and are thus otherwise unobservable from Earth. Abell 2537 is a particularly efficient lens, as demonstrated by the stretched stripes and streaking arcs visible in the frame. These smeared shapes are in fact galaxies, their light heavily distorted by the gravitational field of Abell 2537.

This spectacular scene was captured by Hubble’s Advanced Camera for Surveys and Wide-Field Camera 3 as part of an observing programme called RELICS.

Image Credit: ESA/Hubble & NASA
Explanation from: https://www.spacetelescope.org/images/potw1748a/

Jupiter's Clouds

See Jovian clouds in striking shades of blue in this new view taken by NASA's Juno spacecraft.

The Juno spacecraft captured this image when the spacecraft was only 11,747 miles (18,906 kilometers) from the tops of Jupiter's clouds -- that's roughly as far as the distance between New York City and Perth, Australia. The color-enhanced image, which captures a cloud system in Jupiter's northern hemisphere, was taken on Oct. 24, 2017 at 10:24 a.m. PDT (1:24 p.m. EDT) when Juno was at a latitude of 57.57 degrees (nearly three-fifths of the way from Jupiter's equator to its north pole) and performing its ninth close flyby of the gas giant planet.

The spatial scale in this image is 7.75 miles/pixel (12.5 kilometers/pixel).

Because of the Juno-Jupiter-Sun angle when the spacecraft captured this image, the higher-altitude clouds can be seen casting shadows on their surroundings. The behavior is most easily observable in the whitest regions in the image, but also in a few isolated spots in both the bottom and right areas of the image.

Citizen scientists Gerald Eichstädt and Seán Doran processed this image using data from the JunoCam imager.

Image Credit: NASA/JPL-Caltech/SwRI/MSSS/Gerald Eichstadt/Sean Doran
Explanation from: https://photojournal.jpl.nasa.gov/catalog/PIA21972

Exoplanet WASP-18b

A NASA-led team has found evidence that the oversized planet WASP-18b is wrapped in a smothering stratosphere loaded with carbon monoxide and devoid of water. The findings come from a new analysis of observations made by the Hubble and Spitzer space telescopes.

The formation of a stratosphere layer in a planet’s atmosphere is attributed to “sunscreen”-like molecules, which absorb UV and visible radiation coming from the star and then release that energy as heat. The new study suggests that the “hot Jupiter” WASP-18b, a massive planet that orbits very close to its host star, has an unusual composition, and the formation of this world might have been quite different from that of Jupiter as well as gas giants in other planetary systems.

“The composition of WASP-18b defies all expectations,” said Kyle Sheppard of NASA’s Goddard Space Flight Center in Greenbelt, Maryland. “We don’t know of any other extrasolar planet where carbon monoxide so completely dominates the upper atmosphere.”

On Earth, ozone absorbs UV in the stratosphere, protecting our world from a lot of the Sun’s harmful radiation. For the handful of exoplanets with stratospheres, the absorber is typically thought to be a molecule such as titanium oxide, a close relative of titanium dioxide, used on Earth as a paint pigment and sunscreen ingredient.

The researchers looked at data collected for WASP-18b, located 325 light-years from Earth, as part of a survey to find exoplanets with stratospheres. The heavyweight planet, which has the mass of 10 Jupiters, has been observed repeatedly, allowing astronomers to accumulate a relatively large trove of data. This study analyzed five eclipses from archived Hubble data and two from Spitzer.

From the light emitted by the planet’s atmosphere at infrared wavelengths, beyond the visible region, it’s possible to identify the spectral fingerprints of water and some other important molecules. The analysis revealed WASP-18b’s peculiar fingerprint, which doesn’t resemble any exoplanet examined so far. To determine which molecules were most likely to match it, the team carried out extensive computer modeling.

“The only consistent explanation for the data is an overabundance of carbon monoxide and very little water vapor in the atmosphere of WASP-18b, in addition to the presence of a stratosphere,” said Nikku Madhusudhan a co-author of the study from the University of Cambridge. “This rare combination of factors opens a new window into our understanding of physicochemical processes in exoplanetary atmospheres.”

The findings indicate that WASP-18b has hot carbon monoxide in the stratosphere and cooler carbon monoxide in the layer of the atmosphere below, called the troposphere. The team determined this by detecting two types of carbon monoxide signatures, an absorption signature at a wavelength of about 1.6 micrometers and an emission signature at about 4.5 micrometers. This is the first time researchers have detected both types of fingerprints for a single type of molecule in an exoplanet’s atmosphere.

In theory, another possible fit for the observations is carbon dioxide, which has a similar fingerprint. The researchers ruled this out because if there were enough oxygen available to form carbon dioxide, the atmosphere also should have some water vapor.

To produce the spectral fingerprints seen by the team, the upper atmosphere of WASP-18b would have to be loaded with carbon monoxide. Compared to other hot Jupiters, this planet's atmosphere likely would contain 300 times more “metals,” or elements heavier than hydrogen and helium. This extremely high metallicity would indicate WASP-18b might have accumulated greater amounts of solid ices during its formation than Jupiter, suggesting it may not have formed the way other hot Jupiters did.

“The expected launch of the James Webb Space Telescope and other future space-based observatories will give us the opportunity to follow up with even more powerful instruments and to continue exploring the amazing array of exoplanets out there,” said Avi Mandell, an exoplanet scientist at Goddard.

Image Credit: NASA/GSFC
Explanation from: https://www.nasa.gov/feature/goddard/2017/wasp-18b-has-smothering-stratosphere-without-water