Gaia finds candidates for interstellar ‘Oumuamua’s home

ESA - Gaia Mission patch.


25 September 2018

Using data from ESA’s Gaia stellar surveyor, astronomers have identified four stars that are possible places of origin of ‘Oumuamua, an interstellar object spotted during a brief visit to our Solar System in 2017.

The discovery last year sparked a large observational campaign: originally identified as the first known interstellar asteroid, the small body was later revealed to be a comet, as further observations showed it was not slowing down as fast as it should have under gravity alone. The most likely explanation of the tiny variations recorded in its trajectory was that they are caused by gasses emanating from its surface, making it more akin to a comet.

Artist impression of ‘Oumuamua

But where in the Milky Way did this cosmic traveller come from?

Comets are leftovers of the formation of planetary systems, and it is possible that ‘Oumuamua was ejected from its home star’s realm while planets were still taking shape there. To look for its home, astronomers had to trace back in time not only the trajectory of the interstellar comet, but also of a selection of stars that might have crossed paths with this object in the past few million years.

“Gaia is a powerful time machine for these types of studies, as it provides not only star positions but also their motions,” explains Timo Prusti, Gaia project scientist at ESA.

To this aim, a team of astronomers led by Coryn Bailer-Jones at the Max Planck Institute for Astronomy in Heidelberg, Germany, dived into the data from Gaia’s second release, which was made public in April.

The Gaia data contain positions, distance indicators and motions on the sky for more than a billion stars in our Galaxy; most importantly, the data set includes radial velocities – how fast they are moving towards or away from us – for a subset of seven million, enabling a full reconstruction of their trajectories. The team looked at these seven million stars, complemented with an extra 220 000 for which radial velocities are available from the astronomical literature.

As a result, Coryn and colleagues identified four stars whose orbits had come within a couple of light years of ‘Oumuamua in the near past, and with relative velocities low enough to be compatible with likely ejection mechanisms.

Gaia

All four are dwarf stars – with masses similar to or smaller than our Sun’s – and had their ‘close’ encounter with the interstellar comet between one and seven million years ago. However, none of them is known to either harbour planets or to be part of a binary stellar system; a giant planet or companion star would be the preferred mechanism to have ejected the small body.

While future observations of these four stars might shed new light on their properties and potential to be the home system of ‘Oumuamua, the astronomers are also looking forward to future releases of Gaia data. At least two are planned in the 2020s, which will include a much larger sample of radial velocities, enabling them to reconstruct and investigate the trajectories of many more stars.

“While it’s still early to pinpoint ‘Oumuamua’s home star, this result illustrates the power of Gaia to delve into the history of our Milky Way galaxy,” concludes Timo.

Notes for editors:

“Plausible home stars of the interstellar object ‘Oumuamua found in GaiaDR2” by C.A.L. Bailer-Jones et al is accepted in Astronomical Journal:  https://arxiv.org/abs/1809.09009

Related article:

Gaia’s second release: Gaia creates richest star map of our Galaxy – and beyond: https://orbiterchspacenews.blogspot.com/2018/04/gaia-creates-richest-star-map-of-our.html

Related links:

Gaia: http://www.esa.int/Our_Activities/Space_Science/Gaia

Gaia Data Release 2 Media Kit: http://sci.esa.int/gaia/60174-media-kit-for-gaia-data-release-2/

Gaia overview: http://www.esa.int/Our_Activities/Space_Science/Gaia/Gaia_overview

Images, Text, Credits: ESA/Hubble, NASA, ESO, M. Kornmesser.

Best regards, Orbiter.ch

SMOS offers new perspective on hurricanes

ESA - SMOS Mission logo.

25 September 2018

With recent stories in the news about the devastation brought by hurricanes and typhoons to the US and Asia, we are reminded of how important it is to predict the paths of these mighty storms and also learn more about how they develop. Many satellites have eyes on storms, but ESA’s SMOS mission can offer an entirely new perspective.

Tracking and forecasting hurricanes across the ocean brings obvious benefits to those at sea and to those who live in places where they make landfall. While forecasters have excellent tools to hand to make these predictions, ESA’s Soil Moisture and Ocean Salinity (SMOS) mission is now ready to add valuable information to help make these predictions even more accurate.

Typhoon Mangkhut

SMOS was built for scientific research, mainly into Earth’s water cycle. The satellite carries a novel microwave sensor to capture images of ‘brightness temperature’. These images correspond to radiation emitted from Earth’s surface, which are then used to collect information on soil moisture and ocean salinity.

Strong winds over oceans whip up waves and whitecaps, which in turn affect the microwave radiation from the surface. This means that although strong storms make it difficult to measure salinity, the changes in radiation can, however, be linked directly to the strength of the wind over the sea.

Typhoon Florence

The mission has a real advantage over satellites that carry optical images, which cannot see though the thick cloud of a hurricane, for example. Effectively, seeing through the storm, SMOS can deliver unique information on the speed of the wind near the sea surface at the base of the storm.

While scientists have known how SMOS can do this for a few years now, the mission is now being tested to see if it can supply this information for operational hurricane services.

Recently, SMOS has been used to image and track the wind under Hurricane Florence, Typhoon Mangkhut and Typhoon Jebi.

Typhoon Jebi

Buck Sampson from the US Naval Research Laboratory said, “ESA’s SMOS mission can give us really interesting new information for operational storm forecasting, which we hope to use along with our traditional sources of data.

“SMOS measurements can help us keep track of the structure of a dangerous storm. Combining SMOS data with that from its US counterpart SMAP mission, will give us more timely information which is essential for monitoring major storms.”

SMOS

Susanne Mecklenburg, ESA’s SMOS mission manager, added, “While SMOS is still delivering important information to further our scientific understanding of Earth, it will be really exciting to see it being used for practical applications once this testing phase finishes at the end of the year.

“Every year, hurricanes bring misery to many people around the world, so the hope is that SMOS will be useful to make better predictions, and ultimately help decision-makers with their damage mitigation strategies.”

Related links:

SMOS: http://www.esa.int/Our_Activities/Observing_the_Earth/SMOS

SMOS technical info & data: http://earth.esa.int/SMOS/

IFREMER: http://www.ifremer.fr/anglais/

NOAA: https://www.noaa.gov/

US Naval Research Laboratory: https://www.nrl.navy.mil/

Images, Text, Credits: ESA/Ifremer.

Greetings, Orbiter.ch

ESA choosing CubeSat companions for Hera asteroid mission

European Space Agency (ESA) logo.

25 September 2018

As the world marvels at the hopping mini-rovers deployed on asteroid Ryugu by Japan’s Hayabusa2, ESA is due to decide on the CubeSats planned for delivery to a binary asteroid system by its proposed Hera mission.

CubeSats are nanosatellites based on standardised 10 cm-sized units. This week an ESA evaluation board decides which two ‘6-unit’ CubeSat missions will ride with the next-decade Hera mission to the Didymos asteroid system. The CubeSats will be deployed around the smaller of the two bodies for eventual landing.

Hera and CubeSats

Landing in a low-gravity environment is a rare event – more akin to a docking than a traditional touchdown – so the Hera team has been following Hayabusa2’s deployment closely. Famously the Philae lander of ESA’s Rosetta mission bounced off the surface of Comet 67P/Churyumov–Gerasimenko during its 2014 landing, coming down in a shady spot that drained its solar arrays and limited its lifetime.

The MINERVA mini-lander accompanying Japan’s Hayabusa-1 to asteroid Itokawa was lost in space in 2005 when Itokawa’s gravity failed to bring it down. The two MINERVA-II mini-rovers deployed last week are designed to hop across Ryugu’s surface because traditional wheeled motion would cast them up into space again.

The MINERVA-II mini-rovers weigh in at about 1.1 kg each, compared to Philae’s 100 kg. Hayabusa2 is planned to deliver a larger 10kg Mascot lander on 3 October – built by the DLR German Aerospace Center, responsible for Philae, in cooperation with the French space agency CNES – which will similarly be able to hop. By comparison Hera’s 6-unit CubeSats will be intermediate in size, around 6 kg each.

Mini-rover hop

“The CubeSats we are selecting have a different operating concept, intended to fly close above their asteroid with their own propulsion systems,” explains ESA space scientist and Rosetta veteran Michael Küppers, today serving as Hera project scientist.

“At just 160 m across, the smaller component of the Didymos binary asteroid is too small to truly orbit around, but instead these CubeSats will fly Rosetta-like hyperbolic arcs, maintained by manoeuvres every few days, hopefully culminating in landings.

Hera is planned to be humankind’s first mission to a binary asteroid system, with multiple goals. As well as testing technologies in deep space and gathering bonus science, Hera would also be Europe’s contribution to an international planetary defence effort: it would survey the crater and other effects on the asteroid – plus its resulting orbital deviation – due to the collision of a NASA probe, called DART.

Hera surveying DART crater

‘It’s extremely helpful scientifically when asteroid missions get to touch the surface of their target,” comments CNRS Director of Research Patrick Michel of France’s Côte d'Azur Observatory. As well as serving as a co-investigator and interdisciplinary scientist on Hayabusa2’s science team he is also Hera’s lead scientist.

“With Hera this will already have been done by the DART impact: we’ll have a crater for which we have the initial conditions of its formation, offering us a documented impact experiment at actual asteroid scale. This will enable us to assess the effectiveness of asteroid deflection as a planetary defence technique and allow us to infer many things about collisions more generally and their fundamental role in all the stages of the history of the Solar System.

Hera networking with CubeSats

“In addition Hera’s CubeSats will give us additional close-up views and information, risking much closer approaches than their parent spacecraft before eventually landing.”

“The two proposals chosen to move to definition stage this week would be Europe’s first CubeSats to fly beyond Earth orbit,” explains Hera manager Ian Carnelli.

Hera mission

“CubeSats give an excellent opportunity for some Member States to oversee deep space missions for the first time. Hera’s CubeSats will let us investigate a novel intersatellite communications link technology and gather invaluable low gravity operational experience by flying very close to a small body, as well as crucial planetary defence findings and bonus science data.”

The two winning CubeSats will be announced later this week.

Related links:

ESA's Hera mission: http://www.esa.int/Our_Activities/Space_Engineering_Technology/Hera

ESA's comet chaser Rosetta: http://www.esa.int/Our_Activities/Space_Science/Rosetta

JAXA's Hayabusa2: http://www.hayabusa2.jaxa.jp/en/

Images, Animation, Video, Text, Credits: ESA/ScienceOffice.org/JAXA.

Best regards, Orbiter.ch

Spotlight on sea-level rise

ESA - European Space Agency patch.

25 September 2018

Scientists are gathering in the Azores this week to share findings on how satellite has revealed changes in the height of the sea, ice, inland bodies of water and more. Of concern to all is the fact that global sea level has not only been rising steadily over the last 25 years, but recently it is rising at a much fast rate.

The 25 Years of Progress in Radar Altimetry Symposium gives participants the opportunity to share information gained from this particular sort of satellite instrument.

Regional sea-level trends

Radar altimeters record the surface topography along the satellite’s ground track. They precisely measure the height of water, land and ice by timing the interval between the transmission and reception of very short radar pulses.

This is the only technology that can measure, systematically and globally, changes in the height of the ocean – and is therefore essential for monitoring sea-level rise.

The 25-year record of altimetry data allows scientists to determine trends. For example, between 1993 and 2018 the global ocean rose 3.2 mm every year, on average.

But, altimetry measurements also reveal that the over the last five years the global ocean has risen, on average, 4.8 mm a year.

Anny Cazenave from the Laboratoire d’Etudes en Géophysique et Océanographie Spatiales said, “Satellite altimeters are an essential tool for monitoring sea-level rise. We use reference missions such as the CNES–NASA series of Jason satellites along with other missions such as the Copernicus Sentinel-3 mission to gather a time series of data to understand how sea level is changing in the long term.

Satellite altimeters

“This information shows that sea level has been rising at an average rate of about 3 mm a year since these records began in 1993. However, recent re-analysis of our records has shown that sea-level rise is accelerating because of global warming.”

ESA’s Jérôme Benveniste added, “With many millions living in coastal communities around the world, sea-level rise is a major concern. The information we get from satellite altimeters is essential for understanding how fast our seas are rising so that decision-makers are equipped to take appropriate mitigating action.

“At this week’s symposium we are not only looking back over the last 25 years of satellite altimetry, but we are also looking to the future as we have the Copernicus Sentinel-6 mission in development and also a number of candidate satellite missions being studied.

“It is vital that we have satellite altimeters in the future to continue this long-term record of change.”

While trends and averages are important, it is equally important to understand regional differences. In some places the height of the sea is rising and in other places it is falling.

Causes of sea-level rise

There are a number of reasons for this. For example, when seawater warms it also expands, leading to a phenomenon called thermal expansion.

Although thermal expansion is the biggest cause of sea-level rise as a consequence of climate change, there are many local differences. These differences can be caused by events such as El Niño, for example.

Sea-level rise

Ice loss from the continental glaciers and from the polar ice sheets is also one of the most critical drivers of our rising seas. Ice loss from glaciers, Greenland and Antarctica accounts for about 45% of sea-level rise.

Another cause is discharge from waterbodies on land, but how much this contributes to sea-level rise is more uncertain.

As the symposium progresses, other scientific findings and discussions on the future will be discussed.

Observing the Earth: http://www.esa.int/Our_Activities/Observing_the_Earth

Earth System Science Data:

Global sea-level budget 1993–present: https://www.earth-syst-sci-data.net/10/1551/2018/essd-10-1551-2018.pdf

Related links

Climate Change Initiative – Sea Level: http://www.esa-sealevel-cci.org/

CNES: https://cnes.fr/en

CNES–Satellite Altimetry Data: https://www.aviso.altimetry.fr/en/home.html

Eumetsat: http://www.eumetsat.int/Home/index.htm

NASA: https://www.nasa.gov/

NOAA: https://www.noaa.gov/

Related missions:

Topex-Poseidon: https://sealevel.jpl.nasa.gov/missions/topex/

Jason-1 & Jason-2: https://jason.cnes.fr/en/JASON2/index.htm

Jason-3: https://sealevel.jpl.nasa.gov/missions/jason3/

ERS: http://www.esa.int/Our_Activities/Observing_the_Earth/ERS_overview

Envisat: http://www.esa.int/Our_Activities/Observing_the_Earth/Envisat

CryoSat: http://www.esa.int/Our_Activities/Observing_the_Earth/CryoSat

Sentinel-3: http://www.esa.int/Our_Activities/Observing_the_Earth/Copernicus/Sentinel-3

Images, Video, Text, Credits: ESA/CNES/LEGOS/CLS/EU Copernicus Marine Service/contains modified Copernicus Sentinel data (2018).

Greetings, Orbiter.ch

Partnership, Teamwork Enable Landmark Science Glovebox Launch to Space Station

ISS - International Space Station logo.

Sept. 24, 2018

As the Japan Aerospace Exploration Agency's H-IIB rocket carries NASA's Life Sciences Glovebox toward its berth on the International Space Station, hardware specialists at NASA's Marshall Space Flight Center in Huntsville, Alabama, and their partners around the world are eager to initiate new, high-value biological research in Earth orbit.

The JAXA H-IIB rocket, hauling the state-of-the-art microgravity research facility and other cargo via the H-II Transport Vehicle-7 (HTV-7), successfully lifted off at 1:52 p.m. EDT on Sept. 22 from Tanegashima Space Center in southern Japan.

"The teamwork and global partnership that delivered this hardware have been simply amazing," said Bobby Watkins, director of Marshall’s Human Exploration Development and Operations Office. "We can't wait to see it installed on the space station to enable more high-value biological and physical science experiments, with untold benefits on- and off-world."

Image above: NASA's new Life Sciences Glovebox undergoes testing at NASA's Marshall Space Flight Center in Huntsville, Alabama, prior to its Sept. 22 flight to the International Space Station. The research facility is 26 inches high, 35 inches wide and 24 inches deep, with a 15-cubic-foot workspace. It will enable researchers to conduct new experiments studying the effects of microgravity on the human body -- aiding deep space exploration missions into the solar system. Image Credits: NASA/Steve Moon.

Its launch, previously delayed by inclement weather and technical issues, marks a first for hauling bulky equipment to space. Roughly the size of a large fish tank, the Life Sciences Glovebox -- 26 inches high, 35 inches wide and 24 inches deep, with 15 cubic feet of available workspace -- is officially the largest flight hardware ever launched in a "soft-stowed" configuration in which the equipment is packed securely in protective foam.

The HTV-7 is expected to dock with the space station on Sept. 27. It will be installed on the Harmony module, where it will remain for several weeks. NASA TV coverage of the rendezvous is scheduled to begin at 6:30 a.m. EDT. Capture of the transport vehicle is scheduled for approximately 8 a.m. To learn more, visit: https://blogs.nasa.gov/spacestation

"The Life Sciences Glovebox is on its way to the space station to enable a host of biological and physiological studies, including new research into microgravity's long-term impact on the human body," said Yancy Young, project manager of the glovebox at Marshall. "This versatile facility not only will help us better protect human explorers on long voyages into deep space but it also could aid medical and scientific advances benefiting the whole world."

Boeing engineers at Marshall modified a refrigerator-freezer rack to house the core facility, even using state-of-the-art, 3D-printing technology to custom design key pieces of the rack to secure the unit in its protective foam clamshell. Soft-stowing offers an efficient, low-cost alternative to conventional, hard-mounted cargo stowage, said Chris Butler, payload integration manager for the glovebox at Marshall -- and could "open up new possibilities for other oversized flight hardware."

Image above: A joint team at NASA's Marshall Space Flight Center in Huntsville, Alabama -- including, from left, visiting Japan Aerospace Exploration Agency engineers Maki Abe, Kosuke Kudo and Yoshiaki Okui; Marshall flight systems test engineer Patrick Fulda; and Dona Smith, a Bastion Technologies contractor supporting Marshall's Safety and Mission Assurance Directorate -- conduct a fit check to ensure the glovebox is ready for its journey to the space station. Image Credits: NASA/Steve Moon.

The Life Sciences Glovebox will be transferred to a zero-gravity stowage rack in the station's Kibo module, where up to two crew members can conduct one or more experiments simultaneously, overseen in real-time by project researchers on Earth.

Originally built by JAXA and the Dutch firm Bradford Engineering, the glovebox was redesigned and upgraded in 2017. Engineers at Marshall contributed its secondary support structure and thermal control and power control systems and designed the facility's power supply, air filtration, lighting, video and data recording and real-time downlink capability.

NASA is now determining the roster of science investigations lined up to make use of the facility, beginning as early as late 2018. "We've already got more than a dozen glovebox experiments scheduled in 2019, with many more to follow," Butler said. "That's OK with all of us. We love to be busy."

Marshall manages the Life Sciences Glovebox for NASA and monitors space station science and communications from its Payload Operations Integration Center, supporting the ISS Research Integration Office at NASA's Johnson Space Center in Houston.

Learn more about scientific advances on the International Space Station at: http://www.nasa.gov/station/research

See more images of the Life Sciences Glovebox undergoing testing at Marshall: https://www.flickr.com/photos/nasamarshallphotos/albums/72157694215988074

Life Sciences Glovebox: https://www.nasa.gov/centers/marshall/news/news/2017/nasa-international-partners-ready-new-research-facility-for-space-station.html

NASA TV: https://www.nasa.gov/nasatv

H-II Transport Vehicle-7 (HTV-7): https://www.nasa.gov/mission_pages/station/structure/elements/htv.html

Japan Aerospace Exploration Agency (JAXA): http://global.jaxa.jp/

Space Station Research and Technology: https://www.nasa.gov/mission_pages/station/research/index.html

International Space Station (ISS): https://www.nasa.gov/mission_pages/station/main/index.html

Images (mentioned), Text, Credits: NASA/Lee Mohon/Marshall Space Flight Center/Janet Anderson.

Greetings, Orbiter.ch

Japan Delivery Due Thursday as Trio Preps Russian Spacecraft for Return

ISS - Expedition 56 Mission patch.

September 24, 2018

A Japanese cargo craft is orbiting Earth today and on its way to resupply the International Space Station. Meanwhile, the six Expedition 56 crew members are researching a variety of space phenomena as a trio prepares to return to Earth.

JAXA’s (Japan Aerospace Exploration Agency) resupply ship launched Saturday from Japan loaded with over five tons of new science and supplies destined for the crew. The H-II Transfer Vehicle-7 (HTV-7) is scheduled to arrive at the space station on Thursday. Flight Engineer Serena Auñón-Chancellor will be in the cupola backing up Commander Drew Feustel when he captures the HTV-7 with the Canadarm2 around 8 a.m. on Thursday.

Image above: Two docked Russian spacecraft are seen as the International Space Station orbited nearly 262 miles above New Zealand. Image Credit: NASA.

Included among the critical payloads packed inside the HTV-7 is the Life Sciences Glovebox. The new facility will enable research to advance human health on Earth and in space. HTV-7 is also delivering new lithium-ion batteries to upgrade power systems on the station’s truss structure. NASA TV begins its live coverage of the HTV-7 arrival and capture Thursday at 6:30 a.m.

Today’s science work aboard the orbital lab included looking at DNA and fluid physics. Auñón-Chancellor sequenced DNA extracted from microbial samples collected inside the station. Feustel activated gear for an experiment researching the atomization of liquids that could improve fuel efficiency on Earth and in space.

Image above: Flying over Austral Ocean, seen by EarthCam on ISS, speed: 27'570 Km/h, altitude: 422,36 Km, image captured by Roland Berga (on Earth in Switzerland) from International Space Station (ISS) using ISS-HD Live application with EarthCam's from ISS on September 24, 2018 at 20:45 UTC. Image Credits: Orbiter.ch Aerospace/Roland Berga.

Feustel later joined his Soyuz crewmates Oleg Artemyev of Roscosmos and Ricky Arnold of NASA and began preparations for their return to Earth Oct. 4. Artemyev will command the ride back to Earth inside the Soyuz MS-08 spacecraft flanked by the two astronauts. He and Feustel practiced on a computer their Soyuz descent back into Earth’s atmosphere. Arnold packed up crew provisions and other items inside the Russian spacecraft.

Related links:

Expedition 56: https://www.nasa.gov/mission_pages/station/expeditions/expedition56/index.html

Life Sciences Glovebox: https://cms.nasa.gov/feature/partnership-teamwork-enable-landmark-science-glovebox-launch-to-space-station

Sequenced DNA: https://www.nasa.gov/mission_pages/station/research/experiments/explorer/Investigation.html?#id=7687

Atomization of liquids: https://www.nasa.gov/mission_pages/station/research/experiments/explorer/Investigation.html?#id=282

NASA TV: https://www.nasa.gov/nasatv

Space Station Research and Technology: https://www.nasa.gov/mission_pages/station/research/index.html

International Space Station (ISS): https://www.nasa.gov/mission_pages/station/main/index.html

Images (mentioned), Text, Credits: NASA/Mark Garcia/Orbiter.ch Aerospace/Roland Berga.

Greetings, Orbiter.ch

Dust storms on Titan spotted by Cassini for the first time

ESA & NASA - Cassini-Huygens Mission to Saturn & Titan patch.

24 September 2018

Data from the international Cassini spacecraft that explored Saturn and its moons between 2004 and 2017 has revealed what appear to be giant dust storms in equatorial regions of Titan.

Dust storm on Titan

The discovery, described in a paper published in Nature Geoscience today, makes Titan the third body in the Solar System where dust storms have been observed – the other two are Earth and Mars. 

The observation is helping scientists to better understand the fascinating and dynamic environment of Saturn’s largest moon.

“Titan is a very active moon,” says Sebastien Rodriguez, an astronomer at the University Paris Diderot, France, and the lead author of the paper.

“We already know that about its geology and exotic hydrocarbon cycle. Now we can add another analogy with Earth and Mars: the active dust cycle.”

Complex organic molecules, which result from the atmospheric chemistry and, once large enough, eventually fall to the surface, can be raised from large dune fields around Titan’s equator.

Spotting dust storms on Titan

Titan is an intriguing world – in a way quite similar to Earth. In fact, it is the only moon of the Solar System with a substantial atmosphere and the only celestial body other than our planet where stable bodies of surface liquid are known to still exist.

There is one big difference though: while on Earth such rivers, lakes and seas are filled with water, on Titan it is primarily methane and ethane that flows through these liquid reservoirs. In this unique methane cycle, the hydrocarbon molecules evaporate, condense into clouds and rain back onto the ground.

The weather on Titan varies from season to season, just as it does on Earth. In particular around the equinox, the time when the Sun crosses Titan’s equator, massive clouds can form in tropical regions and cause powerful methane storms. Cassini observed such storms during several of its Titan flybys.

When Sébastien and his team first spotted three unusual equatorial brightenings in infrared images taken by Cassini around the moon’s 2009 northern equinox, they thought these might be exactly such methane clouds. A thorough investigation revealed they were something completely different, however.

“From what we know about cloud formation on Titan, we can say that such methane clouds in this area and in this time of the year are not physically possible,” says Sébastien.

“The convective methane clouds that can develop in this area and during this period of time would contain huge droplets and must be at a very high altitude, much higher than the 10 km that modelling tells us the new features are located.”

Dust storms on Titan

The researchers were also able to rule out that the features were actually on the surface in the form of frozen methane rain or icy lavas. Such surface spots would have a different chemical signature and remain visible for much longer, while the bright features in this study were only visible for 11 hours to five weeks.

Modelling also showed that the features must be atmospheric, but still close to the surface – most likely forming a very thin layer of tiny solid organic particles. Since they were located right over the dune fields around Titan’s equator, the only remaining explanation was that the spots were actually clouds of dust raised from the dunes.

Sébastien says that while this is the first ever observation of a dust storm on Titan, the finding is not surprising. 

“We believe that the Huygens probe, which landed on the surface of Titan in January 2005, raised a small amount of organic dust upon arrival due to its powerful aerodynamic wake,” says Sébastien.

“But what we spotted here with Cassini is at a much larger scale. The near-surface wind speeds required to raise such an amount of dust as we see in these dust storms would have to be very strong – about five times as strong as the average wind speeds estimated by the Huygens measurements near the surface and with climate models.”

Huygens landing on Titan

Huygens made only one direct measurement of the speed of the surface wind just before its landing on Titan, and at that time it was very low, less than 1 metre per second.

“For the moment, the only satisfactory explanation for these strong surface winds is that they might be related to the powerful gusts that may arise in front of the huge methane storms we observe in that area and season,” concludes Sébastien.

This phenomenon, called ‘haboob’, can also be observed on Earth with giant dust clouds preceding storms in arid areas.

The existence of such strong winds generating massive dust storms also implies that the underlying sand can be set in motion, too, and that the giant dunes covering Titan’s equatorial regions are still active and continually changing. 

The winds could be transporting the dust raised from the dunes across large distances, contributing to the global cycle of organic dust on Titan, and causing similar effects to those that can be observed on Earth and Mars.

Notes for editors:

“Observational evidence for active dust storms on Titan at equinox,” by S. Rodriguez et al. is published in Nature Geoscience: http://dx.doi.org/10.1038/s41561-018-0233-2

The results were obtained with Cassini’s Visual and Infrared Mapping Spectrometer.

The Cassini-Huygens mission is a cooperative project of NASA, ESA and the Italian Space Agency. http://sci.esa.it/cassini

Images, Animation, Video, Text, Credits: ESA/Markus Bauer/Nicolas Altobelli/University Paris Diderot/Sébastien Rodriguez/IPGP/Labex UnivEarthS/University Paris Diderot – C. Epitalon & S. Rodriguez et al. 2018/NASA/JPL-Caltech/University of Arizona/ESA/C. Carreau.

Best regards, Orbiter.ch