Cassini ended its 13-year mission at Saturn on 15 September 2017 when it plunged into the gas giant's atmosphere, but the NASA/ESA Hubble Space Telescope is still keeping an eye on the ringed planet.
This is a composite image taken by Hubble on 6 June 2018 showing a fully-illuminated Saturn and its rings, along with six of its 62 known moons. The visible moons are (from left to right) Dione, Enceladus, Tethys, Janus, Epimetheus and Mimas (click here for an annotated version). Dione is the largest moon in the picture, with a diameter of 1123 km, compared to the smallest, oddly-shaped Epimetheus with a diameter around 116 km.
During Cassini’s mission, Enceladus was identified as one of the most intriguing moons, with the discovery of water vapour jets spewing from the surface implying the existence of a subsurface ocean. Icy moons with subsurface oceans could potentially offer the conditions to harbour life, and understanding their origins and properties are essential for furthering our knowledge of the Solar System. ESA's JUpiter ICy moons Explorer (Juice), due to launch in 2022, aims to continue this theme by studying Jupiter's ocean-bearing moons: Ganymede, Europa, and Callisto.
The Hubble image shown here was taken shortly before Saturn's opposition on 27 June, when the Sun, Earth and Saturn were aligned so that the Sun fully illuminated Saturn as seen from Earth. Saturn's closest approach to Earth occurs around the same time as opposition, which makes it appear brighter and larger and allows the planet to be imaged in greater detail.
In this image the planet’s rings are seen near their maximum tilt towards Earth. Towards the end of Cassini’s mission, the spacecraft made multiple dives through the gap between Saturn and its rings, gathering spectacular data in this previously unchartered territory.
The image also shows a hexagonal atmospheric feature around the north pole, with the remnants of a storm, seen as a string of bright clouds. The hexagon-shaped cloud phenomenon is a stable and persistent feature first seen by the Voyager 1 space probe when it flew past Saturn 1981. In a study published just last week, scientists using Cassini data collected between 2013 and 2017, as the planet approached northern summer, identified a hexagonal vortex above the cloud structure, showing there is still much to learn about the dynamics of Saturn’s atmosphere.
The Hubble observations making up this image were performed as part of the Outer Planet Atmospheres Legacy (OPAL) project, which uses Hubble to observe the outer planets to understand the dynamics and evolution of their complex atmospheres. This was the first time that Saturn was imaged as part of OPAL. This image was first published on 26 July.
ESA astronaut Alexander Gerst took this image of Hurricane Florence on 12 September 2018, 400 km high from the International Space Station. He commented:
"Watch out, America! Hurricane Florence is so enormous, we could only capture her with a super wide angle lens from the International Space Station, 400 km directly above the eye. Get prepared on the East Coast, this is a no-kidding nightmare coming for you."
The Copernicus Sentinel-1B satellite takes us over Semera in northeast Ethiopia. Semera is a new town with a population of just over 2600 and serves as the capital of the Afar region. The region spans an estimated 270 000 sq km, from close to the border with Eritrea towards the capital of Addis Ababa.
We can see the regional capital in the top right of this false-colour image, with the larger urban centre of Dubti just south of the town. Both are found in the Great Rift Valley, which lies between the Ethiopian Plateau and the Somalia Plateau.
The landscape of the Afar region is characterised by desert shrubland and volcanoes, particularly in the north. In this image we can see differences in altitude represented in the variations in colour. The left part of the image is dominated by yellow, signifying changes in vegetation found at higher altitudes. Two lakes, Hayk Lake and Hardibo Lake, are shown in the bottom left.
South of Dubti we can see the Awash River, which flows into the northern salt lakes rather than into the sea. Salt trade is typical of the area, whilst cotton is grown in the Awash River valley. Maize, beans, papaya and bananas are also cultivated in the Afar region. It is thought that 90% of the region’s population lead a pastoral life, rearing animals such as camels, sheep and donkeys.
Dallol, to the north of Semera in Ethiopia’s Danakil Depression, is frequently cited as one of the hottest inhabited places on Earth. Lying 125 m below sea level, with temperatures in the spectacular hydrothermal fields averaging 34.4 °C year-round, and the area receiving just 100–200 mm rainfall a year, conditions are thought to be amongst the most inhospitable in the world.
Sentinel-1B was launched in April 2016, carrying an advanced radar instrument to provide an all-weather, day-and-night supply of imagery of Earth’s surface. Along with Sentinel-1A, which was launched in April 2014, the mission benefits numerous services, including monitoring land-surface for motion risks and mapping to support crisis situations.
This image, which was captured on 5 April 2018, is also featured on the Earth from Space video programme.
The BepiColombo Mercury Transfer Module and Mercury Planetary Orbiter being prepared for chemical propulsion fueling.
The transfer module will use both ion propulsion and chemical propulsion, in combination with gravity assist flybys at Earth, Venus and Mercury to bring the two science orbiters close enough to Mercury to be gravitationally captured into its orbit. There, ESA’s Mercury Planetary Orbiter will use its small thrusters to deliver JAXA’s Mercury Magnetospheric Orbiter into its elliptical orbit around Mercury, before separating and descending to its own orbit closer to the planet.
This image of ESA astronaut Alexander Gerst was shared on his social media channels on 10 September 2018.
Alexander said "How do you weigh yourself in weightlessness? The answer is shaking. When we bounce ourselves at the end of a spring loaded rod, the time it takes for one bounce tells us our exact body mass."
ESA’s Industry Space Days, Europe's largest space business-to-business event, attracted a record 900 companies from 39 countries on 11–12 September.
About 1500 visitors attended the event at ESA's ESTEC technology centre in the Netherlands to showcase their products, services and technologies and find potential business partners.
An industry exhibition featuring 140 stands provided additional opportunities for European suppliers, especially SMEs, to present their products, projects, or their R&D to potential customers.
For further information, visit ESA's SME portal.
Between infrared and microwaves on the electromagnetic spectrum, terahertz waves can be used to survey galactic evolution and gather data on ozone depletion as well as in terrestrial airport body scanners.
More than 1 500 attendees and upwards of 850 European space companies participated in the two-day Industry Space Days, Europe’s leading conference on the business of space.
This year saw a special focus on the needs of small-medium enterprises. Also under discussion was the miniature satellites known as CubeSats, making space accessible to even the smallest companies, and fast evolving into a dynamic global market.
Attendees were also given guided tours of ESA’s suite of technical laboratories located at Noordwijk-based ESTEC in the Netherlands. These unique facilities are placed at the disposal of all European space companies as well as ESA missions.
To rewatch the two days of Industry Space Days main stage talks, go here.
Scene: the entrance of a cave, Riegelberg, Germany. An intrepid group of explorers carefully approach the opening, ready to seek out origins of life on this planet.
This scene is not out of a sci-fi film but from last week’s Pangaea field training course. Named after the ancient supercontinent, Pangaea equips future explorers with a better understanding of planetary geology and includes collecting and documenting interesting rock samples to assess the most likely places where to find traces of life on other planets.
Now in its third year, the 2018 campaign includes participants ESA astronaut Thomas Reiter, Roscosmos cosmonaut Sergei Kud-Sverchkov and ‘Spaceship EAC’ lead Aidan Cowley.
Lead by European planetary geologists, the crew attended lectures, worked with satellite imagery, and used robotic tools to analyse rock samples. They put knowledge into practice at the Ries crater in Germany, one of the best-preserved impact craters on Earth and the place to find extra-terrestrial minerals.
Around 15 million years ago, a one-kilometre-diameter asteroid hit Earth at 20 km/s releasing one trillion times the energy of the Hiroshima atomic bomb. The result is still visible in west Bavaria today: a 25 km-crater with a depth of roughly 200 metres.
At the Ries crater Pangaea participants find the best resemblance on Earth to a Moon crater. With eyes set on returning to our rocky satellite, practical knowledge of lunar formation is vital. Future astronauts must understand both the science and operations of lunar geology to make the right moves while on the Moon.
The structure in this image is made out of a megablock of limestone that was cracked open by the Ries impact event and is the ideal classroom for learning about cave formation. Tracing the origins of such rocky structures helps to tell the greater story of life on Earth and of detecting life on other planets.
This week the Pangaea course moves on to the Italian Dolomites to study layers that reveal a past characterised by an abundance of running water. The veins in the terrain are similar to those found on Mars and suggest sedimentary processes on the Red Planet.
Pangaea’s last stop will be the alien landscapes of Lanzarote, Spain, in November. This is one of the best areas on Earth to understand the geological interactions between volcanic activity and water – two key factors in the search for life.
Gravity is so much a part of our daily lives that it is all too easy to forget its awesome power — but on a galactic scale, its power becomes both strikingly clear and visually stunning.
This image was taken with the NASA/ESA Hubble Space Telescope’s Wide Field Camera 3 (WFC3) and shows an object named SDSS J1138+2754. It acts as a gravitational lens illustrates the true strength of gravity: A large mass — a galaxy cluster in this case — is creating such a strong gravitational field that it is bending the very fabric of its surroundings. This causes the billion-year-old light from galaxies sitting behind it to travel along distorted, curved paths, transforming the familiar shapes of spirals and ellipticals (visible in other parts of the image) into long, smudged arcs and scattered dashes.
Some distant galaxies even appear multiple times in this image. Since galaxies are wide objects, light from one side of the galaxy passes through the gravitational lens differently than light from the other side. When the galaxies’ light reaches Earth it can appear reflected, as seen with the galaxy on the lower left part of the lens, or distorted, as seen with the galaxy to the upper right.
This data were taken as part of a research project on star formation in the distant Universe, building on Hubble’s extensive legacy of deep-field images. Hubble observed 73 gravitationally-lensed galaxies for this project.
Something small and green recently flittered across our skies. On 10 September, comet 21P/Giacobini-Zinner made its closest approach to the Sun in 72 years — 151 million km from our star and just 58.6 million km away from Earth (about a third of the distance from here to the Sun).
Discovered in 1900, this small comet reappears every 6.6 years. At just two km in diameter, 21P’s cometary tail contains a stream of ‘cometary crumbs’, and as Earth moves through this stream of debris it creates the Draconid meteor shower which peaks every year around 8 October.
Comets are leftovers of the formation of the Solar System, and while they are typically less dense than asteroids they pass Earth at relatively higher speeds, meaning the impact energy of a comet’s nucleus is slightly larger than that of a similar-sized asteroid.
Although no comet is conclusively known to have impacted Earth, there are many proponents of the theory that a fragment of Comet Encke — a periodic comet that orbits the Sun every 3.3 years — resulted in one of the most well-known impact events in our planet’s history.
In 1930, the British astronomer F.J.W. Whipple suggested that the Tunguska event of 1908 — in which an explosion over Eastern Siberia Taiga flattened 2000 square km of forest — was in fact the result of a cometary impact.
No impact crater was ever found, and glowing skies were reported across Europe for several evenings after the event, both supporting the notion that a comet, composed of dust and volatiles — such as water ice and frozen gases — could have been completely vaporised as it smashed into Earth’s atmosphere leaving no obvious trace.
In order to better understand the risk that asteroids and comets pose to our planet, we need to better understand their orbit and composition. Missions such as Rosetta — the first spacecraft to orbit a comet’s nucleus — play a vital role in deepening our understanding of the objects in our Solar System that could pose some risk. ESA’s planned Hera mission to a binary asteroid to test asteroid deflection will be an important step in doing something about them.
This stunning image was taken on 9 September 2018 by Greg Ruppel, at his robotic observatory in Animas, New Mexico. For more of Greg’s images of Comet 21P/Giacobini-Zinner, and more, visit his website.
Week in images
10 - 14 September 2018